Rethinking of the intraparticle diffusion adsorption kinetics model: Interpretation, solving methods and applications

Industrial dye absorption and elimination from aqueous solutions through bio-composite construction of an organic framework encased in food-grade algae and alginate: Adsorption isotherm, kinetics, thermodynamics, and optimization by Box-Behnken design

A potential bio-adsorbent material for removing Rhodamine B (RB) from aqueous solution is Ru-MOF@FGA/CA beads. The adsorption capability of the material is probably enhanced by the use of a natural substance made of food-grade algae (FGA) and calcium alginate (CA), which has been cross-linked and loaded with ruthenium metal-organic frameworks (Ru-MOF). The Ru-MOF@FGA/CA beads were analyzed by XPS, PXRD, FT-IR, and SEM. The nitrogen adsorption-desorption isotherm analysis of the Ru-MOF@FGA/CA beads before and after the adsorption of RB revealed that had a surface area of 682 m2/g, a pore size of 2.92 nm, and a pore volume of 1.62 cc/g, that decreased after adsorption as the surface area reduced to 468.62 m2/g, while the pore volume reduced to 0.76 cc/g. indicating that the RB molecules occupied the available space within the pores of the material. The decrease in both surface area and pore volume specifies that the Ru-MOF@FGA/CA beads' pores were able to effectively adsorb the RB molecules. The adsorption of RB against the Ru-MOF@FGA/CA beads is affected by pH, adsorbent dose, starting RB concentration, and salinity. Controlling these factors can enhance the adsorption capability and effectiveness of the beads for RB removal. With an adsorption energy of 22.6 kJ/mol, the adsorption of RB onto the Ru-MOF@FGA/CA beads was determined to be a chemisorption process, demonstrating a strong bond among the adsorbent and the adsorbate. The pseudo-second-order kinetics and Langmuir isotherms were used to suit the adsorption process. Because the adsorption procedure was endothermic, it increased as the temperature increased. By using this information, the adsorption conditions may be improved, and the beads' ability to absorb RB can be increased. Up to six reuses of the Ru-MOF@FGA/CA beads are possible without affecting their chemical makeup and maintaining analogous PXRD and FT-IR data after each reuse. The adsorption process can be optimized through the application of the Box-Behnken design (BBD) approach and may entail H-bonding, electrostatic forces, n-π stacking, and pore filling. The exceptional stability of the beads makes them useful for creating long-lasting and efficient adsorbents that remove contaminants from water.

The adsorption-desorption behavior of chlorothalonil in the cuticles of apple and red jujube

The distribution fate of chlorothalonil (CHT) in the environment (soil and water) and fruits is controlled by the capacity of cuticles to adsorb and desorb CHT, which directly affects the safety of both the environment and fruits. Batch experiments were conducted to reveal the adsorption-desorption behaviors of CHT in the cuticles of apple and red jujube. The adsorption kinetics showed that both physisorption and chemisorption occurred during the adsorption process. Furthermore, the isothermal adsorption of CHT in the fruit cuticles followed the Freundlich model. The thermodynamic parameters (ΔG ≤ -26.16 kJ/mol, ΔH ≥ 31.05 kJ/mol, ΔS ≥ 0.20 kJ/(mol K) showed that the whole CHT adsorption process was spontaneous, and the hydrophobic interaction was predominant. The CHT adsorption capacity of the apple cuticle was higher than that of the red jujube cuticle, potentially due to the significantly higher alkanes content of apples than that of red jujubes. An appropriate ionic strength (0.01 moL/L) could induce a higher adsorption capacity. In addition, the desorption kinetics were shown to conform to a Quasi-first-order model, meaning that not all the adsorbed CHT could be easily desorbed. The desorption ratios in apple and red jujube cuticles were 41.38% and 35.64%, respectively. The results of Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy further confirmed that CHT could be adsorbed and retained in the fruit cuticles. Investigating the adsorption-desorption behavior of CHT in the apple and red jujube cuticles allowed to determine the ratio of its final distribution in the fruits and environment, providing a theoretical basis to evaluate the risk of residue pesticide.

Adsorption and recovery of phosphate using sodium carbonate as co-precipitant synthesized La&Zr dual-metal modified material: Adsorption mechanism and practical application

Adsorption methods offer efficient recovery of phosphorus from water bodies. Modification adsorption materials combining lanthanum (La) and zirconium (Zr) dual-metal immobilized via co-precipitation method have been widely applied in the adsorption and recovery of phosphate. Meanwhile, sodium carbonate (Na2CO3) is gradually replacing sodium hydroxide (NaOH) as the mainstream co-precipitant for immobilizing metals into supporting matrices due to its excellent performance and environmental friendliness. However, the adsorption mechanisms of materials synthesized with different co-precipitants and the synergistic effects between dual-metal components are not well understood, which is not conducive to the further optimization of dual-metal adsorption materials. In this study, anion exchange resin was utilized as the supporting matrices, and La&Zr dual-metal-modified materials, La&Zr-CO32- and La&Zr-OH-, were prepared using Na2CO3 and NaOH as co-precipitants, respectively. The results indicate that La&Zr-CO32- exhibits superior performance in phosphate adsorption and recovery, with adsorption capacity and recovery efficiency reaching 36.28 mg/g and 82.59%, respectively. Additionally, this material demonstrates strong stability in reuse, phosphate selectivity, and a wide pH applicability range. La&Zr-CO32- achieves phosphate adsorption through surface electrostatic affinity, ligand exchange, and intraspherical complexation, whereas La&Zr-OH- primarily relies on electrostatic adsorption on the surface and interior of the material. Synergistic effects between La and Zr result in enhanced adsorption performance of the dual-metal material compared to individual metals. Specifically, phosphate adsorption is predominantly governed by La, while the presence of Zr further enhances ligand exchange between lattice oxygen and metals. Simultaneously, Zr doping enhances the phosphate recovery capacity and reusability of the materials. Continuous flow adsorption results from actual water bodies demonstrate that La&Zr-CO32- is more suitable for the removal and recovery of phosphate in water treatment engineering. This study provides a theoretical basis and technical support for the adsorption and recovery of phosphate using dual-metal-modified materials.

Synergistic adsorption of methylene blue using ternary composite of phosphoric acid geopolymer, calcium alginate, and sodium lauryl sulfate

The removal of dyes from the aquatic ecosystem is necessary being a major threat to life. For enhanced remediation of methylene blue (MB) dye, a new ternary biopolymer-geopolymer-surfactant composite adsorbent is synthesized by combining phosphoric acid geopolymer (PAGP), calcium alginate (Alg), and sodium lauryl sulfate (SLS). During the synthesis of the composites, PAGP and SLS were mixed with the alginate matrix, producing porous hybrid beads. The PAGP-SLS-alginate (PSA) beads prepared were characterized using different analytical tools, i.e., scanning electron microscopy (SEM), Fourier transform infrared spectrophotometry (FTIR), X-ray diffractometry (XRD), surface area and porosimetery (SAP), and thermogravimetric analysis (TGA). To ascertain the ideal conditions for the adsorption process, a batch reactor procedure was used to investigate the effects of several parameters on MB adsorption, including pH (2, 4, 6, 8, 10), PSA adsorbent dosage (0.06-0.12 g), MB concentration (50-500 mg/L), contact time (15 to 300 min), and temperature (25, 35, and 45 °C). The SEM investigation indicated that ~ 1860 μm-sized PSA beads with 6-8 μm voids are generated. Based on XRD, FTIR, and SAP examinations, the material is amorphous, having numerous functional groups and an average pore size of 6.42 nm. Variation of pH has a little effect on the adsorption process, and the pH of 7.44 was found to be the pHpzc of the PSA beads. According to the findings of the batch study, equilibrium adsorption was obtained in 270-300 min, showing that the adsorption process was moderately slow-moving and effective. The dye adsorption linearly increased with initial dye concentration over concentration range of 50-500 mg/L and reciprocally decreased with rise in temperature. 0.06 g adsorbent dose, 25 °C, pH10, and 270 min were found to be the better conditions for adsorption experiments. Langmuir isotherm fitted well compared to Freundlich, Temkin, and Dubinin-Radushkevich (DR) isotherm models on the experimental data, and the maximum adsorption capacity(qmax) calculated was 1666.6 mg. g-1. Pseudo-second-order (PSO) kinetics model and multi steps (two) intra particle diffusion (IPD) model fitted well on the adsorption kinetics data. The system's entropy, Gibbs free energy, and change in enthalpy were measured and found to be -109.171 J. mol-1. K-1, - 8.198 to - 6.014 kJ. mol-1, and - 40.747 kJ. mol-1. Thermodynamics study revealed that adsorption process is exothermic, energetically favorable and resulting in the decrease in randomness. Chemisorption is found to be the dominant mechanism as confirmed by pH effect, Langmuir isotherm, PSO kinetics, IPD model, and thermodynamics parameters. PSA beads were successfully regenerated using ethanol in a course of 120 min and re-used for five times. To sum up, the PSA adsorbent's impressive adsorption capability of 1666.66 mg/g highlights its potential as a successful solution for methylene blue removal. The results of this study add to the expanding corpus of information on sophisticated adsorption materials and demonstrate PSA's potential for real-world uses in wastewater treatment and environmental clean-up.

Endogenous iron-enriched biochar derived from steel mill wastewater sludge for tetracycline removal: Heavy metals stabilization, adsorption performance and mechanism

Steel mill wastewater sludge, as an iron-enriched solid waste, was expected to be converted into iron-enriched biochar with acceptable environmental risk by pyrolysis. The purpose of our study was to evaluate the chemical speciation transformation of heavy metals in biochar under various pyrolysis temperatures and its reutilization for tetracycline (TC) removal. The experimental data indicated that pyrolysis temperature was a key factor affecting the heavy metals speciation and bioavailability in biochar, and biochar with pyrolysis temperature at 450 °C was the most feasible for reutilization without potential risk. The endogenous iron-enriched biochar (FSB450) showed highly efficient adsorption towards TC, and its maximum adsorption capacity could reach 240.38 mg g-1, which should be attributed to its excellent mesoporous structure, abundant functional groups and endogenous iron cycling. The endogenous iron was converted to a stable iron oxide crystalline phase (Fe3O4 and MgFe2O4) by pyrolysis, which underwent a valence transition to form a coordination complex with TC by electron shuttling in the FSB450 matrix. The study provides a win-win approach for resource utilization of steel wastewater sludge and treatment of antibiotic contamination in wastewater.

Adsorption dynamics of Cd2+(aq) on microwave-synthetized pristine biochar from cocoa pod husk: Green, experimental, and DFT approaches

Biochar obtained via microwave-assisted pyrolysis (MAP) at 720 W and 15 min from cocoa pod husk (CPH) is an efficient adsorbent of Cd2+(aq). Biochar of residual biomass of CPH (BCCPH) possesses favorable physicochemical and morphological properties, featuring a modest surface area yet a suitable porous structure. Adsorption, predominantly governed by physisorption, is influenced by the oxygen-containing active sites (-COOR, -C(R)O, and -CH2OR; R = H, alkyl). CdCO3 formation occurs during adsorption. Experimental data were well-fitted into various kinetic models for a broad understanding of the sorption process. Langmuir model indicates a maximum adsorption capacity of 14.694 mg/g. The thermodynamic study confirms the spontaneous and endothermic sorption. Studies at the molecular level have revealed that the Cd2+ ion tends to bind to surface aromatic carbon atoms. This sustainable approach produces BCCPH via MAP as a solution for waste transformation into water-cleaning materials.

Removal of Bisphenol S (BPS) by Adsorption on Activated Carbons Commercialized in Brazil

This study assessed three powdered activated carbons (BETM, COCO, and SIAL) commercialized in Brazil at the bench scale in agitated reactors, analyzing their kinetic behavior and adsorptive capacity for BPS and BPA in ultrapure water. BETM exhibited the highest adsorption capacities (Q0max) for BPS and BPA at 260.62 and 264.64 mg/g, respectively, followed by SIAL, with a Q0max of 248.25 mg/g for BPS and for 231.20 mg/g BPA, and COCO, with a Q0max of 136.51 mg/g for BPS and 150.03 mg/g for BPA. The Langmuir isotherm model can describe the processes well. A pseudo-second-order model can describe the adsorption kinetics, and SIAL carbon had the highest rate constants (7.45 × 10-3 mg/g/min for BPS and 2.84 × 10-3 mg/g/min for BPA). The Weber-Morris intraparticle diffusion model suggests intraparticle diffusion as the rate-limiting step of all adsorption processes. Boyd's model confirmed more than the mechanism actuating in the bisphenol adsorption. The results suggest that adsorbents with basic surfaces, high specific surface areas, and high mesopore volumes tend to remove BPS and BPA efficiently. Therefore, activated carbons can effectively complement the existing treatment in Brazilian water treatment plants (WTPs).

Crosslinked Polydiallyldimethylammonium Chloride Adsorbent for the Selective Separation of Rhenium Ions from Pregnant Leach Solutions

The depletion of valuable mineral reserves has rendered effluents generated from mining and industrial processing activities a promising resource for the production of precious elements. The synthesis and improvement of new adsorbents to extract valuable compounds from industrial wastes and pregnant leach solutions, besides increasing wealth, can play a significant role in reducing environmental concerns. In this work, a new and low-cost adsorbent for the selective extraction of rhenium (perrhenate ions, ReO4-) was synthesized by the free-radical polymerization (FRP) of a diallyl dimethylammonium chloride monomer (quaternary amine) in the presence of a crosslinker. Various methods were employed to characterize the polymeric adsorbent. The results revealed that the designed polymeric adsorbent had a high surface area and pores with nano-metric dimensions and a pore volume of 6.4 × 10-3 cm3/g. Four environments-single, binary, multicomponent, and real solutions-were applied to evaluate the adsorbent's performance in the selective separation of Re. Additionally, these environments were used to understand the behavior of molybdenum ions, the primary competitors of perrhenate ions in the ion exchange process. In competitive conditions, using variations in qe,mix/qe, an antagonism phenomenon (qe,mix/qe < 1) occurred due to the inhibitory effect of surface-adsorbed molybdenum ions on the binding of the perrhenate ions. However, across all conditions, the separation values for Re were higher than those for the other studied elements (Mo, Cu, Fe).

Immobilization of polypyrrole on waste face masks using a novel in-situ-surface polymerization method: removal of Cr(VI) from electroplating wastewater

In this work, polypyrrole (PPy) was synthesized on the surface of waste surgical face masks (SFM) with a novel environmentally-friendly in-situ-surface polymerization approach and used as an adsorbent for removing hexavalent chromium (Cr(VI)). In this method, the SFM surface was activated using KMnO4, resulting in the immobilization of porous MnO2, on which pyrrole can be polymerized efficiently. The novelty of this method is the presence of the oxidant on the surface before the polymerization step, which results in a better surface modification with polypyrrole. This method provides adsorbents with higher adsorption capacity compared to the conventional polymerization method with ammonium persulfate (APS). The adsorbent prepared at the mass ratios of 1.0 and 2.0; respectively, for KMnO4/SFM and pyrrole/SFM showed the highest performance. The adsorbent characterization revealed the successful polymerization of pyrrole on the surface of SFM. Reusability of the KMnO4 and pyrrole solutions were successful with remarkable results, showing the advantage of this technique compared to the conventional polymerization method with APS. The effect of different factors on the adsorption process was investigated. The removal rate was around 98% under the optimum conditions (pH, 2; adsorbent dosage, 3 g L-1; contact time, 60 min). The equilibrium data were well fitted by Langmuir isotherm (R2 =  0.9999). Kinetic investigations revealed that the adsorption process fitted well with the pseudo-second-order model. The adsorbent was regenerated for up to five cycles. One of the most important advantages of the proposed method compared to other methods is the reduction of wastewater during the synthesis process.

Adsorption of Pb, Cu, and Ni Ions on Activated Carbon Prepared from Oak Cupules: Kinetics and Thermodynamics Studies

Agricultural residue-activated carbon and biochar, inexpensive and environmentally friendly adsorbent materials, have recently received significant research attention. This study investigated the potential use of oak cupules in activated carbon form to remove widespread heavy metals (Pb2+, Cu2+, and Ni2+) from wastewater. The oak-activated carbon was prepared from oak cupules and activated with phosphoric acid. Oak-activated carbon was characterized using FTIR, BET analysis, energy-dispersive X-ray spectrometry (EDS), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The Freundlich, Langmuir, and Temkin isotherm models were used to assess the equilibrium data. The impact of various parameters, including pH effect, temperature, adsorbent dose, and contact time, was estimated. The Freundlich model was the most agreeable with Pb2+ adsorption by oak-based activated carbon, and Langmuir was more compatible with Cu2+ and Ni2+. Under optimum conditions, the average maximum removal was 63% Pb2+, 60% Cu2+, and 54% Ni2+ when every ion was alone in the aqueous solution. The removal was enhanced to 98% Pb2+, 72% Cu2+, and 60% Ni2+ when found as a mixture. The thermodynamic model revealed that the adsorption of ions by oak-based activated carbon is endothermic. The pseudo-second-order kinetic best describes the adsorption mechanism in this study; it verifies chemical sorption as the rate-limiting step in adsorption mechanisms. The oak-activated carbon was effective in removing Pb2+, Cu2+, and Ni2+ from wastewater and aqueous solutions.

Tailoring Physicochemical Properties of V2O5 Nanostructures: Influence of Solvent Type in Sol-Gel Synthesis

The influence of different solvents, including aqueous and nonaqueous types, on the physicochemical properties of V2O5 nanostructures was thoroughly investigated. Various characterization techniques, such as XRD, XPS, FTIR, Raman spectroscopy, UV-vis DRS, SEM, TEM, and BET, were employed to analyze the obtained materials. Additionally, the adsorption properties of the synthesized V2O5 nanostructures for methylene blue were examined, and kinetic parameters of adsorption were calculated. The results demonstrate that the morphology of the obtained crystals can be finely controlled by manipulating water concentration in the solution, showcasing its profound impact on both the structural characteristics and adsorption properties of the nanostructures. Furthermore, the structural changes of the resulting V2O5 material induced by solvents show strong impacts on its photocatalytic properties, making it a promising photocatalyst.

Facile synthesis of a magnetic molecularly-imprinted polymer adsorbent for solid-phase extraction of diclofenac from water

Numerous pollutants endanger the safety and purity of water, making water pollution a major worldwide concern. The health of people and aquatic ecosystems are at risk from these contaminants, which include hazardous microbes, industrial waste, and agricultural runoff. Fortunately, there appears to be a viable option to address this problem with adsorptive water treatment techniques. The present study presents a magnetic adsorbent (MMIP) based on molecularly imprinted polyaniline and magnetite nanoparticles for the solid-phase extraction of diclofenac, an anti-inflammatory medication, from industrial wastewater. The adsorbent nanomaterial was characterized using dynamic light scattering, zeta potential measurement, vibrating sample magnetometry, X-ray diffraction, and scanning electron microscopy. The MMIP demonstrated a particle size of 86.3 nm and an adsorption capacity of 139.7 mg g-1 at 600 mg L-1 of diclofenac and after a 200 min incubation period. The highest %removal was attained at pH range of 3-7. The adsorption process follows the pseudo-second order kinetic model. In addition, it was found that the adsorption process is enthalpy-driven and may occur via hydrogen bonding and/or van der Waals interactions.

Efficient Selective Adsorption of Rubidium and Cesium from Practical Brine Using a Metal-Organic Framework-Based Magnetic Adsorbent

Rubidium (Rb) and cesium (Cs) have important applications in highly technical fields. Salt lakes contain huge reserves of Rb and Cs with industrial significance, which can be utilized after extraction. In this study, a composite magnetic adsorbent (Fe3O4@ZIF-8@AMP, AMP = ammonium phosphomolybdate) was prepared and its adsorption properties for Rb+ and Cs+ were studied in simulated and practical brine. The structure of the adsorbent was characterized by SEM, XRD, N2 adsorption-desorption, FT-IR, and vibrating sample magnetometer (VSM). The adsorbent had good adsorption affinity for Rb+ and Cs+. The Langmuir model and pseudo-second-order dynamics described the adsorbing isotherm and kinetic dates, respectively. The adsorption capacity and adsorption rate of Fe3O4@ZIF-8@AMP were increased by 1.86- and 2.5-fold compared with those of powdered crystal AMP, owing to the large specific surface area and high dispersibility of the adsorbent in the solution. The adsorbent was rapidly separated from the solution within 17 s using an applied magnetic field owing to the good magnetic properties. The composite adsorbent selectively adsorbed Rb+ and Cs+ from the practical brine even in the presence of a large number of coexisting ions. The promising adsorbent can be used to extract Rb+ and Cs+ from aqueous solutions.

Biofilm hydrogel derived from physical crosslinking (self-assembly) of xanthan gum and chitosan for removing Cd2+, Ni2+, and Cu2+ from aqueous solution

This study aimed to fabricate a series of biodegradable hydrogel films by gelating/physically crosslinking a blend of xanthan gum (XG) and chitosan (CS) in various combinations using a facile, green, and low cost solution casting technique. The adsorption of Cd2+, Cu2+ and Ni2+ by the XG/CS biofilm in aqueous solution was studied in batch experiments to determine how the pH of the solution, contact time, dosage of adsorbent, initial metal ion concentration and ionic strength affect its adsorption. A highly pH-dependent adsorption process was observed for three metal ions. A maximum amount of Cd2+, Ni2+, and Cu2+ ions was adsorbable with 50 mg of the adsorbent at pH 6.0 for an initial metal concentration of 50 mg.L-1. An empirical pseudo-second-order model seems to fit the kinetic experimental data reasonably well. It was found that the Langmuir model correlated better with equilibrium isotherm when compared with the Freundlich model. For Cd2+, Ni2+, and Cu2+ ions at 25 °C, the maximum monolayer adsorption capacity was 152.33, 144.79, and 139.71 mg.g-1, respectively. Furthermore, the biofilm was capable of regenerating, allowing metal ions to adsorb and desorb for five consecutive cycles. Therefore, the developed biodegradable film offers the potential for remediation of specified metal ions.

A self-assembling hydrogel nanocomposite based on xanthan gum modified with SiO2 NPs and HPAM for improved adsorption of crystal violet cationic dye from aqueous solution

This paper presents the rational design and novel synthesis of multifunctional nanocomposite hydrogel derived from xanthan gum (XG) modified with silica nanoparticles and partially hydrolyzed polyacrylamide (HPAM) via H-bonding interactions (self-assembly) through the "green" gelation process in water. Different techniques have been employed to characterize HPAM/SiO2@XG, including FT-IR, FE-SEM, XRD, TEM, BET, and TG/DTG as well as swelling kinetics. Crystal violet (CV)'s adsorption performance was investigated using batch experiments by varying various variables involving adsorbent composition, pH, adsorbent quantity, contact time, CV concentration, ionic strength, and temperature. A well-fitting Langmuir isotherm was found for the adsorption data at 30 °C and pH 7.0, yielding 342.19 mg CV/g as the equilibrium state's maximum adsorption (qm). CV adsorption data agreed better with the pseudo-second-order model than other kinetic models. Furthermore, the HPAM/SiO2@XG nanocomposite hydrogel showed a significant increase in adsorption capacity over the SiO2@XG hydrogel precursor. According to thermodynamic analysis, CV adsorbs to HPAM/XG@SiO2 spontaneously and exothermically. Our results showed that the nanocomposite hydrogel's functional groups interact with CV predominantly through electrostatic interactions, coupled with H-bonding. Nanocomposite hydrogel has been regenerated using a five-cycle adsorption-desorption process, and the efficiency of CV removal has remained a satisfactory level of removal efficiency (94.5 % to 71.5 %).

Phosphination of amino-modified mesoporous silica for the selective separation of strontium

Radioactive strontium (90Sr) is considered as one of the most dangerous radionuclides due to its high biochemical toxicity. For the efficient and selective separation of Sr from acidic environments, a novel functional adsorbent CEPA@SBA-15-APTES was prepared in this work through the phosphorylation of amino-modified mesoporous silica with organic content of approximately 20 wt%. CEPA@SBA-15-APTES was characterized by TEM, SEM, EDS, TG-DSC, BET, FTIR, and XPS techniques, revealing its characteristics of an ordered hexagonal lattice-like structure and rich functional groups. The experimental results demonstrated that the adsorbent exhibited good adsorption capacity for Sr over a wide acidity range (i.e., from 10-10 M to 4 M HNO3). The adsorption equilibriums of Sr by CEPA@SBA-15-APTES in 10-6 M and 3 M HNO3 solutions were reached within 30 and 5 min, respectively, and the adsorption capacities at 318 K were 112.6 and 71.8 mg/g, respectively. Furthermore, by combining the experimental and characterization results, we found that the adsorption mechanism consisted of ion exchange between Sr(II) and H+ (in P-OH) in the 10-6 M HNO3 solution and coordination between the Sr(II) and oxygen-containing (CO and P = O) functional groups in the 3 M HNO3 solution.

A novel monolayer adsorption kinetic model based on adsorbates "infect" adsorbents inspired by epidemiological model

Adsorption is a unit operation process with broad applications in environmental, pharmaceutical, and chemical fields, with its most significance in environmental fields for water and wastewater treatment. Adsorption involves continuous/batch modes with fixed/dispersed adsorbents, leading to diverse systems. The adsorption kinetic models provide essential insights for effectively designing these systems. However, many adsorption models are semi-empirical/empirical, making it challenging to identify the adsorption mechanisms. Additionally, a consistent method for modelling the adsorption kinetics of different processes would be helpful for the comparison and analysis of various adsorption systems, but no such unified model is available. In epidemiological modeling, populations are often categorized into susceptible, infected, and removed individuals, simplifying disease transmission dynamics without considering individual-level movement intricacies. Likewise, we have employed a similar approach within adsorption systems, classifying adsorbates into absorbable, adsorbed, and removed (to the effluent) segments, thus developing the Monolayer-Absorbable-Adsorbed-Removed (MPQR) kinetics model. This model is applicable to continuous/batch adsorption systems, regardless of whether fixed or dispersed adsorbents are employed. The model was validated using experimental data across water/wastewater treatment, drug separation/purification, metal recovery, and desalination. The results showed that our model successfully fitted the kinetic data from various adsorption systems. It outperformed commonly used models for continuous/batch adsorption. The model allowed us to directly compare the parameters among various adsorption processes. The solving method based on Excel was provided and can be used by the researchers. Our model offers a versatile and unified approach to model adsorption kinetics, enabling the analysis and design of various adsorption systems.

Sulfuric acid-assisted ball milling for the preparation of Si-O-enriched straw biochar: removal efficiency of rhodamine B and adsorption mechanism

Traditional pyrolysis biochar has been widely employed to treat dye wastewater. However, there are some problems in the pyrolysis process, such as the generation of harmful gases and the low content of silico-oxygen functional groups to promote adsorption. Straw biochar (Ac-BCbm) was prepared by sulfuric acid co-ball milling method. The adsorption performance and adsorption mechanism of rhodamine B (RhB) under different preparation conditions and factors were investigated. The results showed that the adsorption rate of Ac-BCbm on RhB was up to 94.9%, which was 60.5% and 55.8% higher than that of ball-milling straw (STbm) and biochar prepared by pyrolysis (STBC600), respectively. The Ac-BCbm had better adaptability under different pH and common interfering ions for remove RhB. Characterization and DFT simulation analysis revealed that the sulfuric acid co-ball milling process promoted the formation of Si-OH and Si-O-CH3 oxygen-containing functional groups of Si component in straw, which enhanced the hydrogen bonding interactions and effectively improved the adsorption efficiency. This study investigated a new strategy for biochar preparation by sulfuric acid co-ball milling, which provides an additional development direction for the efficient resource utilization of straw.

Adsorption effect and mechanism of Cd(II) by different phosphorus-enriched biochars

The resource utilization of agricultural and forestry waste, especially the high-value transformation of low-grade phosphate rock and derivatives, is an important way to achieve sustainable development. This study focuses on the impregnation and co-pyrolysis of rice straw (RS) with fused calcium magnesium phosphate (FMP), FMP modified with citric acid (CA-FMP), and calcium dihydrogen phosphate (MCP) to produce three phosphorous-enriched biochars (PBC). The Cd(II) removal efficiency of biochars before and after phosphorus modification was investigated, along with the adsorption mechanism and contribution of biochars modified with different phosphorus sources to Cd(II) adsorption. The result indicated that CA-FMP and MCP could be more uniformly loaded onto biochar, effectively increasing the specific surface area (SSA) and total pore volume. The adsorption of Cd(II) onto PBC followed a mono-layer chemisorption process accompanied by intraparticle diffusion. The adsorption of Cd(II) by PBC involved ion exchange, mineral precipitation, complexation with oxygen-containing functional groups (OFGs), cation-π interaction, electrostatic interaction, and physical adsorption. Ion exchange was identified as the primary adsorption mechanism for Cd(II) by BC and FBC (51.53% and 53.15% respectively), while mineral precipitation played a major role in the adsorption of Cd(II) by CBC and MBC (51.10% and 47.98% respectively). Moreover, CBC and MBC significantly enhanced the adsorption capacity of Cd(II), with maximum adsorption amounts of 128.1 and 111.5 mg g-1 respectively.

High efficiency adsorption of uranium by magnesia-silica-fluoride co-doped hydroxyapatite

Hydroxyapatite has a high affinity to uranium, and element doping can effectively improve its adsorption performance. In this study, magnesia-silica-fluoride co-doped hydroxyapatite composite was prepared by hydrothermal method, and the effect of single-phase and multiphase doping on the structure and properties of the composites was investigated. The results showed that the specific surface area of Mg-Si-F-nHA composites increased by 63.01% after doping. Comparing with nHA, U(VI) adsorption capacity of Si-nHA, Mg-Si-nHA and Mg-Si-F-nHA composites increased by 13.01%, 17.39% and 22.03%, respectively. The adsorption capacity of Mg-Si-F-nHA composite reached 1286.76 mg/g. Adsorbent dosage and pH obviously affected U(VI) adsorption, and the experimental data can be fitted well by PSO and Sips models. The physicochemical characterization before and after adsorption suggested that complexation, ion exchange and precipitation participated in uranium adsorption. In conclusion, different elements doping can effectively improve the uranium adsorption properties of hydroxyapatite composites.

Retention of Ciprofloxacin and Carbamazepine from Aqueous Solutions Using Chitosan-Based Cryostructured Composites

Water pollution is becoming a great concern at the global level due to highly polluted effluents, which are charged year by year with increasing amounts of organic residues, dyes, pharmaceuticals and heavy metals. For some of these pollutants, the industrial treatment of wastewater is still relevant. Yet, in some cases, such as pharmaceuticals, specific treatment schemes are urgently required. Therefore, the present study describes the synthesis and evaluation of promising cryostructured composite adsorbents based on chitosan containing native minerals and two types of reinforcement materials (functionalized kaolin and synthetic silicate microparticles). The targeted pharmaceuticals refer to the ciprofloxacin (CIP) antibiotic and the carbamazepine (CBZ) drug, for which the current water treatment process seem to be less efficient, making them appear in exceedingly high concentrations, even in tap water. The study reveals first the progress made for improving the mechanical stability and resilience to water disintegration, as a function of pH, of chitosan-based cryostructures. Further on, a retention study shows that both pharmaceuticals are retained with high efficiency (up to 85.94% CIP and 86.38% CBZ) from diluted aqueous solutions.

Adsorption of cationic/anionic dyes and endocrine disruptors by yeast/cyclodextrin polymer composites

Factory and natural wastewaters contain a wide range of organic pollutants. Therefore, multifunctional adsorbents must be developed that can purify wastewater. Phytic acid-cross-linked Baker's yeast cyclodextrin polymer composites (IBY-PA-CDP) were prepared using a one-pot method. IBY-PA-CDP was used to adsorb methylene blue (MB), bisphenol A (BPA), and methyl orange (MO). Studies on the ionic strength and strongly acidic ion salts confirmed that IBY-PA-CDP adsorbs MO through hydrophobic interactions. This also shows that Na+ was the direct cause of the increased MO removal. Adsorption studies on binary systems showed that MB/MO inhibited the adsorption of BPA by IBY-PA-CDP. The presence of MB increased the removal rate of MO by IBY-PA-CDP due to the bridging effect. The Langmuir isotherm model calculated the maximum adsorption capacities for MB and BPA to be 630.96 and 83.31 mg g-1, respectively. However, the Freundlich model is more suitable for fitting the experimental data for MO adsorption. To understand the rate-limiting stage of adsorption, a mass-transfer mechanism model was employed. The fitting results show that adsorption onto the active sites is the rate-determining step. After five regeneration cycles, IBY-PA-CDP could be reused with good stability and recyclability.

Rapid sand filtration for <10 μm-sized microplastic removal in tap water treatment: Efficiency and adsorption mechanisms

The omnipresence of microplastics (MPs) in potable water has become a major concern due to their potential disruptive effect on human health. Therefore, the effective removal of MPs in drinking water is essential for life preservation. In this study, tap water containing microplastic <10 μm in size was treated using constructed pilot-scale rapid sand filtration (RSF) system to investigate the removal efficiency and the mechanisms involved. The results show that the RSF provides significant capacity for the removal and immobilization of MPs < 10 μm diameter (achieving 98 %). Results showed that silicate sand reacted with MPs through a cooperative assembly process, which mainly involved interception, trapping, entanglement, and adsorption. The MPs were quantified by Flow cytometry instrument. A kinetics study underlined the pivotal role of physio-chemisorption in the removal process. MP particles smaller than absorbents, saturation of adsorbents, and reactor hydrodynamics were identified as limiting factors, which were alleviated by backwashing. Backwashing promoted the desorption of up to 97 % MPs, conducive for adsorbent active site regeneration. These findings revealed the critical role of RSF and the importance of backwashing in removing MPs. Understanding the mechanisms involved in removing microplastics from drinking water is crucial in developing more efficient strategies to eliminate them.

Aminated Rapeseed Husks (Brassica napus) as an Effective Sorbent for Removing Anionic Dyes from Aqueous Solutions

The study investigated the effect of modifying rapeseed husks with ammonia and epichlorohydrin on their sorption capacity against anionic reactive dyes: Reactive Black 5 (RB5) and Reactive Yellow 84 (RY84). Its scope included sorbents characterization (FTIR, pHPZC), determination of pH influence on the sorption effectiveness of dyes, the adsorption kinetics of dyes, as well as the maximum sorption capacity. The study proved that the reaction of rapeseed husk biomass with ammonia can lead to its amination, namely to the introduction of amine functional groups into the material's structure. The sorption effectiveness of RB5 and RY84 on the tested sorbents was the highest in the pH range of 2-3. The dye sorption kinetics was well described by the pseudo-second-order model. The sorption equilibrium time ranged from 90 to 180 min, and depended on the initial concentration of dyes and the number of amino groups on the sorbent's surface. The most efficient of the sorbents tested were rapeseed husks pre-activated with epichlorohydrin and then aminated with ammonia. Their sorption capacity determined for RB5 and RY84 was 135.83 mg/g and 114.23 mg/g, respectively, which was 794% and 737% higher than that of the non-modified husks.

Sustainable aerogels based on biobased poly (itaconic acid) for adsorption of cationic dyes

This work reports the synthesis of poly (itaconic acid) by thermal polymerization mediated by 2,2'-Azobis(2-methylpropionamidine) dihydrochloride. Furthermore, physical hydrogels were prepared by using high molecular weight poly (itaconic acid) characterized by low dispersity and laponite RD. The hydrogels presented porous 3D network structures, with a high-water penetration of almost 2000 g/g of swelling ratio, which can allow the adsorption sites of both poly (itaconic acid) and laponite RD to be easily exposed and facilitate the adsorption of dyes. The water adsorption followed Schott's pseudo-second-order model. The mechanism of the adsorption process was investigated using 1H and 31P NMR. The hydrogel is able to fast adsorb by a combination of electrostatic interactions and hydrogen bonding by the synergic effect of the clay and poly (itaconic acid). Moreover, the prepared aerogels exhibited a fast removal of Basic Fuchsin, with an adsorption capacity of 67.56 mg/g and a high removal efficiency (~99 %). The adsorption followed the pseudo-second-order kinetic model and Langmuir isotherm model. Furthermore, the thermodynamic parameters showed that the BF process of adsorption was spontaneous and feasible, endothermic, and followed physisorption. These results indicated that the PIA/laponite-based aerogel can be considered a promising adsorbent material in textile wastewater treatment.

Adsorption of uranium (VI) complexes with polymer-based spherical activated carbon

Adsorption processes with carbon-based adsorbents have received substantial attention as a solution to remove uranium from drinking water. This study investigated uranium adsorption by a polymer-based spherical activated carbon (PBSAC) characterised by a uniformly smooth exterior and an extended surface of internal cavities accessible via mesopores. The static adsorption of uranium was investigated applying varying PBSAC properties and relevant solution chemistry. Spatial time-of-flight secondary ion mass spectrometry (ToF-SIMS) was employed to visualise the distribution of the different uranium species in the PBSAC. The isotherms and thermodynamics calculations revealed monolayer adsorption capacities of 28-667 mg/g and physical adsorption energies of 13-21 kJ/mol. Increasing the surface oxygen content of the PBSAC to 10 % enhanced the adsorption and reduced the equilibrium time to 2 h, while the WHO drinking water guideline of 30 µgU/L could be achieved for an initial concentration of 250 µgU/L. Uranium adsorption with PBSAC was favourable at the pH 6-8. At this pH range, uranyl carbonate complexes (UO2CO3(aq), UO2(CO3)22-, (UO2)2CO3(OH)3-) predominated in the solution, and the ToF-SIMS analysis revealed that the adsorption of these complexes occurred on the surface and inside the PBSAC due to intra-particle diffusion. For the uranyl cations (UO22+, UO2OH+) at pH 2-4, only shallow adsorption in the outermost PBSAC layers was observed. The work demonstrated the effective removal of uranium from contaminated natural water (67 µgU/L) and meeting both German (10 µgU/L) and WHO guideline concentrations. These findings also open opportunities to consider PBSAC in hybrid treatment technologies for uranium removal, for instance, from high-level radioactive waste.

Guideline for modeling solid-liquid adsorption: Kinetics, isotherm, fixed bed, and thermodynamics

During the years, adsorption has garnered considerable attention being one of the most cost-effective and efficient methods for separating contaminants out of liquid phase. A comprehensive understanding of adsorption mechanisms entails several crucial steps, including adsorbent characterization, batch and column adsorption tests, fitting of predefined kinetic and isotherm models, and meticulous thermodynamic analysis. These combined efforts serve to provide clarity and insights into the intricate workings of adsorption phenomena. However, the vast amount of literature published in the field each year is riddled with ill-considered model selections and incorrect parameter analyses. Therefore, the aim of this paper is to establish guidelines for the proper employment of these numerous kinetic, isotherm, and fixed-bed models in various applications. A thorough review has been undertaken, encompassing more than 45 kinetic models, 70 isotherm models, and 45 fixed bed models available hitherto, with their classification determined based on the adsorption mechanisms expounded within each of them. Moreover, five general approaches for modifying fixed-bed models were provided. The physical meanings, assumptions, and interconversion relationships of the models were discussed in detail, along with the information criterion used to evaluate their validity. In addition to commonly used activation energy and Gibbs energy analysis, the methods for calculating site energy distribution were also summarized.

Precursor-oriented design of nano-alumina for efficient removal of antibiotics

Rapid and efficient removal of environmental antibiotics is vital to curb bacterial resistance. Through rational precursors-oriented design, we attain the best Al2O3 absorbent by 500 °C calcination of ammonium aluminium carbonate hydroxide (AACH) precursor from NH4HCO3 route (AACH-NH4HCO3-500) for fast and efficient removal of tetracycline (TC) and other antibiotics from environmental waters including high-salinity wastewater. AACH-NH4HCO3-500 (0.25 g·L-1) can remove (69.92 ± 1.78)% of aqueous TC (0.025 g·L-1) within 5 min and (97.62 ± 2.75)% within 2 h, and the adsorption capacity is 444.4 mg·g-1, which is the highest qmax of TC for the 2 h-adsorptions among numerous adsorbents. AACH-NH4HCO3-500 has fine tolerance to the coexisting substances, and can be easily regenerated and reused, and has no harm even discarded. The relations among the synthetic methods, the structural features, and the adsorption functions of Al2O3 are disclosed through a systematic comparison of the commercial Al2O3 and different Al2O3 nanomaterials attained from three precursors produced by five different routes. The reasons behind the exceptional adsorption performance are discussed throughout. Our findings would facilitate the development of excellent adsorbents for removal of other pollutants.

Effect of pyrolytic temperatures on the 2,4-dichlorophenol adsorption performance of biochar derived from Populus nigra

To investigate the correlation between the physicochemical properties of biochar and its adsorption performance for 2,4-dichlorophenol (2,4-DCP), Populus nigra was subjected to oxygen-limited pyrolysis at temperatures ranging from 300 to 600 ℃. The experimental results showed that as the pyrolysis temperature increased, the specific surface area and degree of graphitization of the resultant biochar increased, but the amount of oxygen-containing functional groups decreased. Populus nigra biochar produced at 450 ℃ exhibits the best adsorption performance for 2,4-DCP due to its excellent physicochemical properties and greater electron exchange capability. The removal of 2,4-DCP is a multi-step adsorption process dominated by chemisorption, which involved oxygen-containing functional groups-mediated hydrogen bonding, as well as π-π electron donor-acceptor (EDA) interaction between the aromatic rings and Cl atoms. The study highlights the potential of Populus nigra residues for producing biochar as an affordable and effective adsorbent for 2,4-DCP removal.

The Adsorption of Pb(II) from Aqueous Solution Using KOH-Modified Banana Peel Hydrothermal Carbon: Adsorption Properties and Mechanistic Studies

Adopting banana peel as a raw material, the adsorption properties of banana peel hydrothermal carbon modified with a KOH solution for lead ions in aqueous solution were studied. The surface structure and functional groups of the modified hydrothermal carbon were analyzed by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR) spectroscopy, the Brunner-Emmet-Teller (BET) method, element analysis, and Raman spectroscopy. The results showed that an adsorption capacity of 42.92 mg/g and a removal rate of 86.84% were achieved when the banana peel hydrothermal carbon was modified with a KOH solution of 0.5 mol/L, with a pH of 6 and a solid-liquid ratio of 1 g/L. The equilibrium adsorption time for lead ions in solution being adsorbed using KOH-modified hydrothermal carbon was 240 min, the adsorption process satisfied the quasi-second-order kinetic model and the Redlich-Peterson isotherm equation, and the equilibrium removal efficiency was 88.62%. The adsorption of lead ions using KOH-modified hydrothermal carbon is mainly chemical-physical adsorption.

Comparison of microalgal hydrochar and pyrochar: production, physicochemical properties, and environmental application

Microalgal biomass has been considered the third-generation biofuel production feedstock, but microalgae-derived biochar still needs to be thoroughly understood. This study aims to evaluate the production and physicochemical properties of microalgae-derived hydrochar produced by hydrothermal carbonization (HTC) process by comparison with pyrochar produced by dry thermal carbonization (DTC) process for environmental applications. Microalgal biochar was produced with commercially available Chlorella vulgaris microalgae using HTC and DTC processes under various temperature conditions. Pyrochar presented higher pH, ash contents, porosity, and surface area than hydrochar. Hydrochar gave more oxygen-containing functional groups on the surface and higher lead adsorption than pyrochar, making the microalgal hydrochar applicable in soil amendment and various environmental remediations. HTC could be an economically feasible thermochemical process for microalgal biochar production. It can produce hydrochar with high production yield from wet microalgae at low temperatures without a drying process.

CTAB-modified peanut husk pre-treated with KMnO4 as an eco-friendly adsorbent for the uptake of Congo red in solution: adsorption and mechanism study

A cationic surfactant (cetyltrimethylammonium bromide, CTAB)-modified peanut husk pretreated with potassium permanganate (KMnO4) was developed and applied as an adsorbent for the removal of Congo red (CR) in aqueous solution. The surface morphology and physicochemical characteristics of the adsorbent labelled as PNK-CTAB were assessed using well-established analytical techniques. The efficiency of PNK-CTAB was assessed via the batch adsorption method using distilled water, tap water and river water as aqueous medium. Results of the batch study showed that the adsorption capacity of PNK-CTAB could reach 70.5 mg g-1 at 313 K due to its improved surface properties and functionalities. Furthermore, the uptake of CR onto PNK-CTAB was found to be best described by the Elovich model thus suggesting adsorption on a heterogeneous surface, whereas fitting of intraparticle diffusion model indicated the significant role of mass transfer mechanism in the process. The equilibrium data was found to be well described by Langmuir, Temkin and Freundlich models albeit the latter was the best fit. Further analysis of the associated thermodynamics indicated the adsorption process to be endothermic, spontaneous in nature and likely mediated by physisorption processes. The excellent adsorption efficiency of PNK-CTAB toward CR within a wide pH range, negligible influence of some commonly occurring salts, good reusability efficiency, low cost (as confirmed by its cost analysis) and its ability to reduce the cytotoxicity of CR towards human embryonic kidney (HEK) 293 cells suggest the good prospects of this adsorbent for practical applications.

Preparation of magnetic sodium alginate/sodium carboxymethylcellulose interpenetrating network gel spheres and use in superefficient adsorption of direct dyes in water

The rapid development of the printing and dyeing industry has led to the production of a large amount of high-density printing and dyeing wastewater, and technology for its effective treatment has become a focus of research. To construct a polymeric adsorbent material with abundant functional groups for the efficient adsorption of dye wastewater, a novel magnetic sodium alginate/carboxymethylcellulose interpenetrating network gel sphere (Fe3O4@SA/CMC-Fe) was prepared by co-blending sodium alginate (SA) and sodium carboxymethylcellulose (CMC) with Fe3O4; Fe3O4@SA/CMC-Fe was characterized by SEM-EDS, XRD, TGA, FT-IR, UV-Vis, VSM, BET-BJH and XPS. Static adsorption experiments showed that the optimal rates for adsorption of DV 51 and DR 23 from solutions with neutral pH values by Fe3O4@SA/CMC-Fe were up to 96 %, the adsorption process exhibited a Langmuir adsorption isotherm, and the dynamic adsorption process was accurately described by the pseudo-second-order kinetic model. A thermodynamic study showed that the adsorption reactions were all spontaneous exothermic reactions with increasing entropy. The mechanism for adsorption of the dyes by Fe3O4@SA/CMC-Fe involved hydrogen bonding, complexation and electrostatic adsorption. In summary, Fe3O4@SA/CMC-Fe is a green, simple, recyclable and highly efficient magnetic adsorbent that is expected to be widely used in treating dye wastewaters over a wide pH range.

Removal of radionuclide 99Tc from aqueous solution by various adsorbents: A review

Technetium isotope 99Tc is a main radioactive waste produced in the process of nuclear reaction, which has the characteristics of long half-life and strong environmental mobility, and can be bio-accumulated in organisms, resulting in serious threat to human health and ecosystem. Adsorption method is widely used in the field of removing radionuclides from water due to the advantages of high treatment rate, simple and mature industrial application. In this review paper, the recent advances in research and application of various adsorption materials for 99Tc pollution treatment were summarized and analyzed for the first time, including inorganic adsorbents, such as activated carbon, zero-valent iron, metallic minerals, clay minerals, layered double hydroxides (LDHs), tin-based materials, and sulfur-based materials; organic adsorbents, such as porous organic polymers (POPs), covalent-organic frameworks (COFs), metal-organic frameworks (MOFs), and ion exchange resin; and biological adsorbents, such as biopolymers (chitosan, cellulose, alginate), and microbial cells. The performance characteristics and the adsorption kinetics and isotherms of various adsorption materials were discussed. This review could deepen the understanding of the adsorptive removal of 99Tc from aqueous solution, and provide a reference for the future research in this field.

Preparation of emulsion hydrogels encapsulating extractant by the Pickering emulsion template method to recover lanthanum ions in aqueous solutions

To solve the problem of liquid-liquid extraction of La(III), the oil-in-water Pickering emulsions were prepared by utilizing the aqueous solution of sodium alginate as the continuous phase, kerosene-diluted extractant di-(2-ethylhexyl) phosphate (P204) as the dispersed phase, and modified silica as an emulsifier. Then the emulsions were added to a calcium chloride solution to prepare the Pickering emulsion hydrogels (PEHGs) to better remove La(III). The PEHGs were characterized using Fourier transform infrared, thermogravimetric analysis, and scanning electron microscopy. The adsorption properties of PEHGs for La(III) in the aqueous solution were investigated using a UV-vis spectrophotometer. The study found that P204 was successfully coated by hydrogels and reached the highest adsorption capacity of 48 mg/g at pH 4. The amount of adsorption increased with the rise in temperature from 298 to 318 K. La(III) adsorption experimental data were more consistent with the pseudo-second-order kinetic model and the Langmuir isotherm model. Thermodynamic parameters showed that the adsorption of La(III) by PEHGs was a spontaneous endothermic process. The internal diffusion model revealed a linear relationship, indicating that internal diffusion played a role in the adsorption process. The encapsulating property of PEHGs indicated its potential usefulness in industrial wastewater for treating La(III).

Interaction of fluorene and its analogs with high-density polyethylene microplastics: An assessment of the adsorption mechanism to establish the effects of heteroatoms in the molecule

The threat of microplastics (MP) pollution in aquatic ecosystems can be even more severe for they are able to interact with organic pollutants that can migrate to adjacent environments. The presence of heteroatoms in organic pollutants can directly influence adsorption onto MP. This research evaluated the adsorption of fluorene (FLN) and its heteroatom analogs dibenzothiophene (DBT), dibenzofuran (DBF) and carbazole (CBZ) onto high-density polyethylene (HDPE) MP from residual (HDPEres) and commercial (HDPEcom) sources. The Langmuir isotherm showed a better fit, while DBT showed higher maximum adsorption capacity (19.2 and 15.8 μmol g-1) followed by FLN (13.4 and 11.7 μmol g-1), and DBF (13.5 and 10.3 μmol g-1) to the HDPEcom and HDPEres, respectively, which indicates a direct correlation with the hydrophobicity of the molecules determined by Log Kow. In contrast, CBZ showed no significant interaction with MP, due to their polar characteristic, thus, no kinetic and thermodynamic parameters could be determined. The adsorption process of all PAH was determined to be exothermic and spontaneous, with low temperatures favoring the process. The pseudo-second-order kinetic models have fitted to the adsorption onto both HDPE; intraparticle diffusion was also observed. Computational studies, physical characterization techniques and batch adsorption experiments demonstrated that the mechanism is governed by hydrophobic interactions, with van der Waals forces as a secondary effect in the adsorption of FLN, DBT and DBF onto HDPEres and HDPEcom. Thus, allowing a deeper understanding of the interactions between HDPE MP and FLN as well with its derivatives.

3D Monolayer Silanation of Porous Structure Facilitating Multi-Phase Pollutants Removal

Activated carbon (AC) is widely used to removing hazardous pollutants from air and water, owing to its exceptional adsorption properties. However, the high affinity of water molecules with the surface oxygen-containing functional groups can adversely affect the adsorption performance of AC. In this study, a facile and efficient method is presented for fabrication of hydrophobic AC through surface monolayer silanation. Compared to initial AC, the hydrophobic AC improves the water contact angle from 29.7° to 123.5° while maintaining high specific surface area and enhances the removal capacity of multi-phase pollutants (emulsified oil and toluene). Additionally, the hydrophobic AC exhibits excellent adsorption capability to harmful algal bloom species (Chlorella) (97.56%) and algal organic matter (AOM) (96.23%) owing to electrostatic interactions and surface hydrophobicity. The study demonstrates that this method of surface monolayer silanation can effectively weaken the effect of water molecules on AC adsorption capacity, which has significant potential for practical use in air and water purification, as well as in the control of harmful algal blooms.

Interaction between antibiotics and microplastics: Recent advances and perspective

Both microplastics and antibiotics are emerging pollutants, which are ubiquitous in aquatic environments. With small size, high specific surface area, and attached biofilm, microplastics are capable of adsorbing or biodegrading antibiotic pollutants across aquatic environments. However, the interactions between them are poorly understood, especially factors that affect microplastics' chemical vector effects and the mechanisms driving these interactions. In this review, the properties of microplastics and their interaction behavior and mechanisms towards antibiotics were comprehensively summarized. Particularly, the impact of weathering properties of microplastics and the growth of attached biofilm was highlighted. We concluded that compared with virgin microplastics, aged microplastics usually adsorb more types and quantities of antibiotics from aquatic environments, whilst the attached biofilm could further enhance the adsorption capacities and biodegrade some antibiotics. This review can answer the knowledge gaps of the interaction between microplastics and antibiotics (or other pollutants), offer basic information for evaluating their combined toxicity, provide insights into the distribution of both emerging pollutants in the global water chemical cycle, and inform measures to remove microplastic-antibiotic pollution.

Application of carbon from pomegranate husk for the removal of ibuprofen, cadmium and methylene blue from water

The presence of pharmaceutical products, dyes, and toxic metal ions in water is a major problem worldwide. This work developed low-cost pomegranate-based materials to uptake ibuprofen, cadmium and methylene blue from water. Pomegranate husks (PPH) were carbonized at 400 °C to form carbonized pomegranate husk (CPH), and nanoparticles were loaded into the carbon surface (NPH) by co-precipitation. SEM micrographs showed that the morphology of carbon was highly porous compared to pristine pomegranate husk. The data for BET revealed that CPH and NPH, had about a 20-fold increase in surface area of 142 m2/g and 190 m2/g respectively compared with 9.27 m2/g for PPH. The composites exhibited larger pore sizes and volumes. TEM images confirmed the loading of nanoparticles. The FTIR results showed that the materials had on their surface oxygenated groups such as -OH, -C]O, -COC and other groups like -NH and -C]C which are anticipated to play an essential role in the sorption of the pollutants. It was found that removal efficiency increased when there was a progressive increase in pollutant concentration for all adsorbents. The best pH value of the solution for the sorption processes was pH 8. The recorded adsorption capacities at pH 8 for Cd(II), IBU and MB were 92.85, 39.77 and 95.89 mg/g for NPH, 72.60, 32.58 and 80.59 mg/g for CPH and 32.78, 16.12 and 40.79 mg/g for PPH. Contact time studies showed three sorption steps. Step 1: rapid increase at the initial stage. Step 2: marginal uptake. Step 3: plateau. The trends indicated that sorption was influenced by temperature variation. The data for the thermodynamic parameter △Ho suggest that all the sorption processes were endothermic; the obtained positive values indicate this. The △Ho for PPH was between (64.33-69.08 kJ/mol), 82.84-86.03 kJ/mol for CPH and 87.17-88.96 kJ/mol for NPH. For PPH, molecular interactions were physisorption, and chemisorption for CPH and NPH. The △So has positive values, showing increased freedom during the sorption. The adsorbents followed PSO based on uptake processes involving syngenetic mechanisms.

Efficient adsorptive removal of Co2+ from aqueous solution using graphene oxide

This study aimed to utilize synthesized graphene oxide (GO) for adsorptive removal of cobalt ions and investigate the adsorption mechanism using advanced techniques such as X-ray absorption spectra (XAFS). The GO was synthesized via an improved Hummers method, resulting in high surface area (93.7 m2/g) and abundant oxygen-containing functional groups. Various characterizations, including SEM, TEM, Raman, FT-IR, TG, potentiometric titrations, and N2 sorption-desorption measurements, were employed to characterize the GO. The adsorption behavior of GO towards Co2+ was investigated, and the results showed that the adsorption process followed a pseudo-second-order kinetic model and the Langmuir model, with a maximum sorption capacity of 93.7 mg/g. The adsorption process was chemisorption and endothermic, with GO showing adsorption selectivity order of Co2+ > Sr2+ > Cs+. Based on various characterizations such as X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS), FT-IR, and XPS, the sorption mechanism of Co2+ onto GO was discussed, with the results indicating that coordination and electrostatic interaction were the primary adsorption mechanisms, with oxygen-containing functional groups playing a vital role. The first coordinating atom for Co2+ was O, and the coordination environment was similar to that of cobalt acetate and CoO. Overall, this study provides comprehensive understanding of the adsorption behavior and mechanism of Co2+ onto GO, highlighting its potential as an effective adsorbent for removing nuclides from aqueous solution.

Plant-Waste-Derived Sorbents for Nitazoxanide Adsorption

The increased application of drugs during the COVID-19 pandemic has resulted in their increased concentration in wastewater. Conventional wastewater treatment plants do not remove such pollutants effectively. Adsorption is a cheap, effective, and environmentally friendly method that can accomplish this. On the other hand, maintaining organic waste is required. Thus, in this study, plant waste-derived pelletized biochar obtained from different feedstock and pyrolyzed at 600 °C was applied for the adsorption of nitazoxanide, an antiparasitic drug used for the treatment of SARS-CoV-2. The adsorption was fast and enables one to remove the drug in one hour. The highest adsorption capacity was noted for biochar obtained from biogas production (14 mg/g). The process of NTZ adsorption was governed by chemisorption (k2 = 0.2371 g/mg min). The presence of inorganic ions had a detrimental effect on adsorption (Cl-, NO3- in 20-30%) and carbonates were the most effective in hindering the process (60%). The environmentally relevant concentration of DOM (10 mg/L) did not affect the process. The model studies were supported by the results with a real wastewater effluent (15% reduction). Depending on the applied feedstock, various models described nitazoxanide adsorption onto tested biochars. In summary, the application of carbonaceous adsorbents in the pelletized form is effective in nitazoxanide adsorption.

Pb(II) Uptake from Polluted Irrigation Water Using Anatase TiO2 Nanoadsorbent

The adsorption characteristics of titanium dioxide nanoparticles (nano-TiO₂) for the removal of Pb(II) from irrigation water were investigated in this work. To accomplish this, several adsorption factors, such as contact time and pH, were tested to assess adsorption efficiencies and mechanisms. Before and after the adsorption experiments, commercial nano-TiO₂ was studied using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The outcomes showed that anatase nano-TiO₂ was remarkably efficient in cleaning Pb(II) from water, with a removal efficiency of more than 99% after only one hour of contact time at a pH of 6.5. Adsorption isotherms and kinetic adsorption data matched the Langmuir and Sips models quite well, showing that the adsorption process occurred at homogenous sites on the surface of nano-TiO₂ by forming a Pb(II) adsorbate monolayer. The XRD and TEM analysis of nano-TiO₂ following the adsorption procedure revealed a non-affected single phase (anatase) with crystallite sizes of 9.9 nm and particle sizes of 22.46 nm, respectively. According to the XPS data and analyzed adsorption data, Pb ions accumulated on the surface of nano-TiO₂ through a three-step mechanism involving ion exchange and hydrogen bonding mechanisms. Overall, the findings indicate that nano-TiO₂ has the potential to be used as an effective and long-lasting mesoporous adsorbent in the treatment and cleaning of Pb(II) from water bodies.

Green synthesize of nano-MOF-ethylcellulose composite fibers for efficient adsorption of Congo red from water

Two novel MOF- ethyl cellulose (EC)- based nanocomposites have been designed and synthesized in water by electrospinning and applied for adsorption of congo red (CR) in water. Nano- Zeolitic Imidazolate Framework-67 (ZIF-67), and Materials of Institute Lavoisier (MIL-88A) were synthesized in aqueous solutions by a green method. To enhance the dye adsorption capacity and stability of MOFs, they have been incorporated into EC nanofiber to prepare composite adsorbents. The performance of both composites in the absorption of CR, a common pollutant in some industrial wastewaters, has then been investigated. Various parameters including initial dye concentration, the dosage of the adsorbent, pH, temperature and contact time were optimized. The results indicated 99.8 and 90.9% adsorption of CR by EC/ZIF-67 and EC/MIL-88A, respectively at pH = 7 and temperature at 25 °C after 50 min. Furthermore, the synthesized composites were separated conveniently and successfully reused five times without significant loss of their adsorption activity. For both composites, the adsorption behavior can be explained by pseudo-second-order kinetics, Intraparticular diffiusion and Elovich models demonstrated that the experimental data well matched to the pseudo-second-order kinetics. Intraparticular diffiusion model showed that the adsorption of CR on EC/ZIF-67 and EC/MIL-88a took place in one and two steps, respectively. Freundlich isotherm models and thermodynamic analysis indicated exothermic and spontaneous adsorption.

Detection and removal technologies for ammonium and antibiotics in agricultural wastewater: Recent advances and prospective

With the extensive development of industrial livestock and poultry production, a considerable part of agricultural wastewater containing tremendous ammonium and antibiotics have been indiscriminately released into the aquatic systems, causing serious harms to ecosystem and human health. In this review, ammonium detection technologies, including spectroscopy and fluorescence methods, and sensors were systematically summarized. Antibiotics analysis methodologies were critically reviewed, including chromatographic methods coupled with mass spectrometry, electrochemical sensors, fluorescence sensors, and biosensors. Current progress in remediation methods for ammonium removal were discussed and analyzed, including chemical precipitation, breakpoint chlorination, air stripping, reverse osmosis, adsorption, advanced oxidation processes (AOPs), and biological methods. Antibiotics removal approaches were comprehensively reviewed, including physical, AOPs, and biological processes. Furthermore, the simultaneous removal strategies for ammonium and antibiotics were reviewed and discussed, including physical adsorption processes, AOPs, biological processes. Finally, research gaps and the future perspectives were discussed. Through conducting comprehensive review, future research priorities include: (1) to improve the stabilities and adaptabilities of detection and analysis techniques for ammonium and antibiotics, (2) to develop innovative, efficient, and low cost approaches for simultaneous removal of ammonium and antibiotics, and (3) to explore the underlying mechanisms that governs the simultaneous removal of ammonium and antibiotics. This review could facilitate the evolution of innovative and efficient technologies for ammonium and antibiotics treatment in agricultural wastewater.

Isotherm and Kinetic Study of Metal Ions Sorption on Mustard Waste Biomass Functionalized with Polymeric Thiocarbamate

The presence of high concentrations of metal ions in effluents resulting from industrial metal coatings is a well-known fact. Most of the time, such metal ions, once they reach the environment, significantly contribute to its degradation. Therefore, it is essential that the concentration of metal ions is reduced (as much as possible) before such effluents are discharged into the environment to minimize the negative impact on the quality of the ecosystems. Among all methods that can be used to reduce the concentration of metal ions, sorption is one of the most viable options due to its high efficiency and low cost. Moreover, due to the fact that many industrial wastes have sorbent properties, this method is in accordance with the principles of circular economy. Based on these considerations, in this study, mustard waste biomass (resulting from oil extraction) was functionalized with an industrial polymeric thiocarbamate (METALSORB) and used as a sorbent to remove Cu(II), Zn(II) and Co(II) ions from aqueous media. The best conditions for the functionalization of mustard waste biomass were found to be: mixing ratio biomass: METASORB = 1 g: 1.0 mL and a temperature of 30 °C. The experimental sorption capacities of functionalized sorbent (MET-MWB) were 0.42 mmol/g for Cu(II), 0.29 mmol/g for Zn(II) and 0.47 mmol/g for Co(II), which were obtained under the following conditions: pH of 5.0, 5.0 g sorbent/L and a temperature of 21 °C. The modeling of isotherms and kinetic curves as well as the analysis of the results obtained from desorption processes demonstrate the usefulness of this sorbent in the treatment of effluents contaminated with metal ions. In addition, tests on real wastewater samples highlight the potential of MET-MWB for large-scale applications.

Interaction behaviors of sulfamethoxazole and microplastics in marine condition: Focusing on the synergistic effects of salinity and temperature

Microplastics and antibiotics are two common pollutants in the ocean. However, due to changes of salinity and temperature in the ocean, their interaction are significantly different from that of fresh water, and the mechanism remains unclear. Here, the interactions of sulfamethoxazole (SMZ) and microplastics were studied at different temperatures and salinities. The saturation adsorption capacity of SMZ in polypropylene (PP), polyethylene (PE), styrene (PS), polyvinyl chloride (PVC), and synthetic resins (ABS) were highest at the temperature of 20 °C, with 0.118 ± 0.002 mg·g^-1, 0.106 ± 0.004 mg·g^-1, 0.083 ± 0.002 mg·g^-1, 0.062 ± 0.007 mg·g^-1 and 0.056 ± 0.003 mg·g^-1, respectively. The effect of temperature reduction is more significant than temperature rise. The intraparticle diffusion model is appropriate to PP, when film diffusion model suited for PS. The salinity has a more significant effect than temperature on different microplastics, due to the electrostatic adsorption and iron exchange. With the increase in salinity from 0.05% to 3.5%, the adsorption capacity of microplastics on SMZ fell by 53.3 ± 5%, and there was no discernible difference of various microplastics. The hydrogen bond and π-π conjugation of microplastics play an important role in the adsorption of SMZ. These findings further deepen the understanding of the interaction between microplastics and antibiotics in the marine environment.

Promoted wet peroxide oxidation of chlorinated volatile organic compounds catalyzed by FeOCl supported on macro-microporous biomass-derived activated carbon

Chlorinated volatile organic compounds (CVOCs) are a recalcitrant class of air pollutants, and the strongly oxidizing reactive oxygen species (ROS) generated in advanced oxidation processes (AOPs) are promising to degrade them. In this study, a FeOCl-loaded biomass-derived activated carbon (BAC) has been used as an adsorbent for accumulating CVOCs and catalyst for activating H₂O₂ to construct a wet scrubber for the removal of airborne CVOCs. In addition to well-developed micropores, the BAC has macropores mimicking those of biostructures, which allows CVOCs to diffuse easily to its adsorption sites and catalytic sites. Probe experiments have revealed HO^• to be the dominant ROS in the FeOCl/BAC + H₂O₂ system. The wet scrubber performs well at pH 3 and H₂O₂ concentrations as low as a few mM. It is capable of removing over 90% of dichloroethane, trichloroethylene, dichloromethane and chlorobenzene from air. By applying pulsed dosing or continuous dosing to replenish H₂O₂ to maintain its appropriate concentration, the system achieves good long-term efficiency. A dichloroethane degradation pathway is proposed based on the analysis of intermediates. This work may provide inspiration for the design of catalyst exploiting the inherent structure of biomass for catalytic wet oxidation of CVOCs or other contaminants.

Potential Application of Innovative Aspergillus terreus/ Sodium Alginate Composite Beads as Eco-Friendly and Sustainable Adsorbents for Alizarin Red S Dye: Isotherms and Kinetics Models

Fungi were used as one of the most common bioremediation methods. From this perspective, our study highlights the optimization of Alizarin Red S (ARS) dye adsorption performance for the sodium alginate (SA) by using the fungus Aspergillus terreus (A. terreus) to form a composite bead and the possibility of its reusability. This was accomplished by mixing SA with different ratios of biomass powder of A. terreus, including 0%, 10%, 20%, 30%, and 40%, to form composite beads of A. terreus/SA-0%, A. terreus/SA-10%, A. terreus/SA-20%, A. terreus/SA-30%, and A. terreus/SA-40%, respectively. The ARS adsorption characteristics of these composite mixtures were analyzed at various mass ratios, temperatures, pH values, and initial concentrations. Moreover, sophisticated techniques, such as scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR), were employed to detect the morphological and chemical properties of this composite, respectively. The experimental results revealed that A. terreus/SA-20% composite beads have the highest adsorption capacity of 188 mg/g. Its optimum adsorption conditions were achieved at 45 ∘C and pH 3. Moreover, the ARS adsorption was well explained by the Langmuir isotherm (q_m = 192.30 mg/g) and pseudo-second-order and intra-particle diffusion kinetics. The SEM and FTIR findings corroborated the superior uptake of A. terreus/SA-20% composite beads. Lastly, the A. terreus/SA-20% composite beads can be employed as an eco-friendly and sustainable alternative to other common adsorbents for ARS.

Adsorption of Hg(II) on polyethyleneimine-functionalized carboxymethylcellulose beads: Characterization, toxicity tests, and adsorption experiments

Mercury (Hg) is widely used in many industrial processes and is released into the environment. Therefore, efficient removal of Hg from water is of vital importance worldwide. Here, we explored the adsorption characteristics of Hg(II) on polyethyleneimine-functionalized carboxymethylcellulose (PEI-CMC) beads and studied the toxicity of the beads toward Daphnia magna and Pseudokirchneriella subcapitata. The PEI-CMC beads had an average particle size of 2.04 ± 0.25 mm, a point of zero charge (pH_pzc) of 5.8, and a swelling ratio of 2.45. Acute toxicity tests demonstrated that the PEI-CMC beads had no toxic effects on D. magna. The growth inhibition tests revealed that growth inhibition of P. subcapitata could be attributed to adsorption of trace elements in growth media on the PEI-CMC beads. The adsorption experiments exhibited that the Matthews and Weber model best described the kinetic data, whereas the Redlich-Peterson model was well fitted to the isotherm data. The theoretical maximum Hg(II) adsorption capacity of the PEI-CMC beads was 313.1 mg/g. The thermodynamic experiments showed endothermic nature of the Hg(II) adsorption on the PEI-CMC beads at 10-40 °C. The adsorption experiments exhibited that the Hg(II) adsorption capacity decreased gradually as pH increased from 2 to 12. The adsorption of Hg(II) on the PEI-CMC beads can occur through chelation and electrostatic attraction. The FTIR and XPS spectra before and after Hg(II) adsorption confirmed that chelation of neutral Hg(II) species (HgCl₂, HgClOH, and Hg(OH)₂) can occur with amino and oxygen-containing functional groups on the PEI-CMC beads. Considering species distribution of Hg(II) and the pH_pzc of the PEI-CMC beads, electrostatic attraction between the positively-charged beads and anionic Hg(II) species (HgCl₃^- and HgCl₄^2-) can take place in highly acidic solutions. The PEI-CMC beads were regenerated and reused for Hg(II) adsorption using 0.1 M HCl.

Remediation of perfluorooctanoic acid (PFOA) with nano ceramic clay: Synthesis, characterization, scale-up and regenerations

Perfluorooctanoic acid (PFOA) in the ecosystem, resulting from industrial effluent and water bodies, has attracted greater concern. An economical treatment is in demand to optimize the current issue. In this research work, Perfluorooctanoic Acid was treated from drinking water sources with nano-ceramic clay. The ceramic clay was synthesized and characterized with Fourier infrared transformation, scanning electron micrograph, transmission electron micrograph, x-ray diffraction, and thermal analysis. An adsorption process was performed in batch and continuous modes for the effective conditions for maximum removal. In batch mode 82 ± 12 nm ceramic clay particle size; 3.0 initial pH; 210 rpm agitation 1.2 mg/L PFOA concentration; 100 mg/L clay dosage; 27 °C temperature, and 20hrs experimental time shows maximum 99.15% adsorption. The experimental data is well fitted with kinetics, isotherms, and thermodynamics calculated data. In fixed bed, continuous column study 10 h treatment time, 10 cm of bed height, and 2 ml/min were adsorbed 99.99% of PFOA. The experimental data from the fixed bed adsorption equipment was correlated using a number of different mathematical models, including the Thomas, Adams-Bohart, Yoon-Nelson, and Clark models. Overall nano ceramic clay was found to potential adsorbent for Perfluorooctanoic acid removal.