Adsorption of a textile dye onto piaçava fibers: kinetic, equilibrium, thermodynamics, and application in simulated effluents

Impact of seawater temperature and physical-chemical properties on sorption of pharmaceuticals, stimulants, and biocides to marine particles

Pharmaceuticals, stimulants, and biocides enter the environment via wastewater from urban, domestic, and industrial areas, in addition to sewage, aquaculture and agriculture runoff. While some of these compounds are easily degradable in environmental conditions, others are more persistent, meaning they are less easily degraded and can stay in the environment for long periods of time. By exploring the adsorptive properties of a wide range of pharmaceuticals, stimulants, and biocides onto particles relevant for marine conditions, we can better understand their environmental behaviour and transport potential. Here, the sorption of 27 such compounds to inorganic (kaolin) and biotic (the microalgae Cryptomonas baltica) marine particles was investigated. Only two compounds sorbed to microalgae, while 23 sorbed to kaolin. The sorption mechanisms between select pharmaceuticals and stimulants and kaolin was assessed through exploring adsorption kinetics (caffeine, ciprofloxacin, citalopram, fluoxetine, and oxolinic acid) and isotherms (ciprofloxacin, citalopram, and fluoxetine). Temperature was shown to have a significant impact on partitioning, and the impact was more pronounced closer to maximum sorption capacity for the individual compounds.

Magnetic graphene derivates for efficient herbicide removal from aqueous solution through adsorption

2,4-Dichlorophenoxyacetic acid (2,4-D) is an herbicide and is among the most widely distributed pollutant in the environment and wastewater. Herein is presented a complete comparison of adsorption performance between two different magnetic carbon nanomaterials: graphene oxide (GO) and its reduced form (rGO). Magnetic functionalization was performed employing a coprecipitation method, using only one source of Fe2+, requiring low energy, and potentially allowing the control of the amount of incorporated magnetite. For the first time in literature, a green reduction approach for GO with and without Fe3O4, maintaining the magnetic behavior after the reaction, and an adsorption performance comparison between both carbon nanomaterials are demonstrated. The nanoadsorbents were characterized by FTIR, XRD, Raman, VSM, XPS, and SEM analyses, which demonstrates the successful synthesis of graphene derivate, with different amounts of incorporate magnetite, resulting in distinct magnetization values. The reduction was confirmed by XPS and FTIR techniques. The type of adsorbent reveals that the amount of magnetite on nanomaterial surfaces has significant influence on adsorption capacity and removal efficiency. The procedure demonstrated that the best performance, for magnetic nanocomposites, was obtained by GO∙Fe3O4 1:1 and rGO∙Fe3O4 1:1, presenting values of removal percentage of 70.49 and 91.19%, respectively. The highest adsorption capacity was reached at pH 2.0 for GO∙Fe3O4 1:1 (69.98 mg g-1) and rGO∙Fe3O4 1:1 (89.27 mg g-1), through different interactions: π-π, cation-π, and hydrogen bonds. The adsorption phenomenon exhibited a high dependence on pH, initial concentration of adsorbate, and coexisting ions. Sips and PSO models demonstrate the best adjustment for experimental data, suggesting a heterogeneous surface and different energy sites, respectively. The thermodynamic parameters showed that the process was spontaneous and exothermic. Finally, the nanoadsorbents demonstrated a high efficiency in 2,4-D adsorption even after five adsorption/desorption cycles.

Kinetics, Equilibrium, and Thermodynamics for Conjugation of Chitosan with Insulin-Mimetic [meso-Tetrakis(4-sulfonatophenyl)porphyrinato]oxovanadate(IV)(4-) in an Aqueous Solution

This study investigated the conjugation of chitosan with the insulin-mimetic [meso-tetrakis(4-sulfonatophenyl)porphyrinato]oxovanadate(IV)(4-), VO(tpps), in an aqueous medium as a function of conjugation time, VO(tpps) concentrations, and temperatures. To validate the synthesis of chitosan-VO(tpps) conjugate, UV-visible and Fourier transform infrared spectrophotometric techniques were utilized. Conjugate formation is ascribed to the electrostatic interaction between the NH3+ units of chitosan and the SO3- units of VO(tpps). Chitosan enhances the stability of VO(tpps) in an aqueous medium (pH 2.5). VO(tpps) conjugation with chitosan was best explained by pseudo-second-order kinetic and Langmuir isotherm models based on kinetic and isotherm studies. The Langmuir equation determined that the maximal ability of VO(tpps) conjugated with each gram of chitosan was 39.22 μmol at a solution temperature of 45 °C. Activation energy and thermodynamic studies (Ea: 8.78 kJ/mol, ΔG: -24.52 to -27.55 kJ/mol, ΔS: 204.22 J/(mol K), and ΔH: 37.30 kJ/mol) reveal that conjugation is endothermic and physical in nature. The discharge of VO(tpps) from conjugate was analyzed in freshly prepared 0.1 mol/L phosphate buffer (pH 7.4) at 37 °C. The release of VO(tpps) from the conjugate is a two-phase process best explained by the Higuchi model, according to a kinetic analysis of the release data. Taking into consideration all experimental findings, it is proposed that chitosan can be used to formulate both solid and liquid insulin-mimetic chitosan-VO(tpps) conjugates.

Biochar supported metallo-inorganic nanocomposite: A green approach for decontamination of heavy metals from water

Heavy metal contamination of water has become a global environmental burden, which has stirred up agitation worldwide. Fabrication of adsorbents utilizing either low cost, environment friendly materials or waste products can be helpful in remediating environmental pollution. The current study evolved around the synthesis of nanocomposites derived from such raw precursors like spent tea waste biochar, hydroxyapatite, and clays. In this context, two nanocomposites, namely manganese ferrite doped hydroxyapatite/kaolinite/biochar (TK-NC) and manganese ferrite doped hydroxyapatite/vermiculite/biochar (TV-NC), were synthesized followed by their employment for decontamination of heavy metals from aqueous media. TK-NC and TV-NC exhibited the crystallite sizes in the range of 2.55-5.94 nm as obtained by Debye Scherrer Equation and Williamsons-Hall equation The fabricated nanocomposites were characterized using FT-IR, SEM-EDX, and powder XRD. Batch adsorption studies were performed, and influence of different adsorption parameters (contact time, reaction temperature, solution pH, adsorbent dose, and initial adsorbate concentration) on metal adsorption was examined. Thermodynamic studies revealed that the adsorption of Cr(VI), Ni(II) and Cu(II) on TK-NC and TV-NC was endothermic (+ΔH°) and indicates disorderness (+ΔS°) at the solid-liquid interface owing to the strong affinity of metal ions with adsorbent. The heavy metal uptake selectivity followed the following decreasing order; Cr(VI) > Cu(II) > Ni(II) by both nanocomposites, with adsorption capacities falling in the range of 204.68-343.05 mg g-1. Several adsorption kinetic and isotherm models were applied to experimentally calculated data, which suggest favorable adsorption of Cr(VI), Ni(II) and Cu(II) by TK-NC and TV-NC from the system while obeying general-order kinetics and R-P adsorption model, conferring the transition in adsorption kinetics order and involvement of multiple adsorption process.

Active carbon-based waste packaging materials for uranium sorption from aqueous solution

Waste (packaging plastic and industrial water) accumulation is one of the great global challenges over the world. Combining waste recycling science and water treatment knowledge are fascinating as applied sciences add value to the safe disposal of waste plastic packaging materials and wastewater. Active carbons (ACs) are prepared from polyethylene terephthalate (PET) at two pyrolysis temperatures (i.e. 450 and 500 °C) and compressed in well-defined designed molds to form cylinder shapes as applied in industry. Particle size (817 and 1074 nm), zeta potential (- 7.17 and - 25.6 mV), surface area (544 and 632 m2/g), and topography of prepared ACs were investigated and discussed. Zeta potential exhibited nice dispersion in accordance to charge value and surficial SEM images prove space hole filling with adsorbed materials after treatment. The prepared activated carbon sorbents have been applied for the removal of radioactive elements from wastewater. The displayed data declare that both sorbents have the same sorption performance, whereas the uranium sorption process using both sorbents is obeyed to pseudo-second-order kinetic model and Langmuir isotherm model. Nevertheless, it is worth noting that the prepared AC at a pyrolysis temperature of 500 °C exhibits higher sorption capacity (38.9 mg g^-1) than that prepared at lower temperature, i.e., 450 °C (36.2 mg g^-1) which indicates that the increase in pyrolysis temperature improves the sorption characteristics of the yield-activated carbon.

Cassava bagasse as an alternative biosorbent to uptake methylene blue environmental pollutant from water

Herein, the methylene blue (MB) biosorption from the agroindustrial residue (cassava bagasse) is reported. The cassava bagasse residue presented an irregular surface, anionic character, and low specific surface area. The experiments were performed in batch mode. The biosorption behavior was investigated through the experimental variables, initial concentration of MB, pH, and temperature. The maximum biosorption capacity (170.13 mg g^-1) reached 328 K and pH 10.0. The equilibrium and kinetics were better fitted by the Sips and general order (R² ≥ 0.997 and R²_adj ≥ 0.996) models, respectively. Furthermore, the thermodynamic study revealed a spontaneous (ΔG⁰ < 0) and endothermic process. Finally, the results showed cassava bagasse is a potential material for biosorption dyes from the aqueous medium. In addition, the biosorbent has a low aggregate cost and high availability, which contributes to the destination of large amounts of waste and inspires engineering applications.

Construction of efficient Ni-FeLDH@MWCNT@Cellulose acetate floatable microbeads for Cr(VI) removal: Performance and mechanism

Water pollution is an aggravating dilemma that is extending around the world, threatening human survival. Strikingly, the notorious heavy metals like hexavalent chromium ions (Cr⁶⁺) cause environmental problems raising awareness of the essentials for finding feasible solutions. For this purpose, the self-floating Ni-FeLDH@MWCNT@CA microbeads were prepared for removing Cr⁶⁺. The morphological, thermal, and composition characteristics of Ni-FeLDH@MWCNT@CA microbeads were analyzed using XRD, FTIR, TGA, SEM, XPS, and zeta potential. Notably, the adsorption aptitude of Cr⁶⁺ was enhanced by raising the MWCNTs proportion to 5 wt% in microbeads. The Cr⁶⁺ adsorption onto Ni-FeLDH@MWCNT@CA fitted Langmuir and Freundlich isotherm models with q_m of 384.62 mg/g at pH 3 and 298 K. The adsorption process was described kinetically by the pseudo-2nd order model. More importantly, the adsorption of Cr⁶⁺ onto Ni-FeLDH@MWCNT@CA occurred via electrostatic interactions, inner/outer sphere complexations, ion exchange, and reduction mechanisms. Besides, the cycling test showed the remarkable reusability of Ni-FeLDH@MWCNT@CA floatable microbeads for five subsequent cycles. The self-floating Ni-FeLDH@MWCNT@CA microbeads in this work provide essential support for the potential applications for the remediation of heavy metals-containing wastewater.

Use of activated Chromolaena odorata biomass for the removal of crystal violet from aqueous solution: kinetic, equilibrium, and thermodynamic study

In the present study, biomass from the Chromolaena odorata plant's stem was activated using sulfuric acid to adsorb crystal violet (CV) dye. The adsorption operation of CV dye was studied considering the effect of variables like pH, initial dye concentration, time, adsorbent dosage, and temperature. The pseudo-second-order equation best fitted the kinetic study. The thermodynamic parameters such as activation energy (9.56 kJ/mol), change in Gibbs energy (81.43 to 96.7 kJ/mol), enthalpy change (6.89 kJ/mol), and entropy change (-254.4 J/mol K) were calculated. Response surface methodology estimated that at pH (4.902), adsorbent dosage (8.33 g/L), dye concentration (82.30 ppm), and temperature (300.13 K) dye removal of 97.53% is possible. FTIR, SEM, XRD, BJH, and BET confirmed adsorption operation. The adsorbent can be reused for 3 cycles effectively. Langmuir isotherm which best fitted the adsorption operation was used for designing a theoretical single-stage batch adsorber for large-scale operation.

Use of artificial intelligence for optimizing biosorption of textile wastewater using agricultural waste

Most of the dyes are toxic and non-biodegradable in textile industry wastewaters. Therefore, removal of textile dye using agriculture waste becomes crucial for the environment. This can be accomplished by the biosorption process which is the passive uptake of pollutants by agricultural waste. In this study, Response Surface Methodology (RSM), Artificial Neural Network (ANN) and Adaptive Neuro-Fuzzy Inference System (ANFIS) were used to obtain optimum conditions for Methylene Blue (MB) removal using sugarcane bagasse and peanut hulls as low-cost agricultural waste. The experimental design was carried out to study the effect of temperature, pH, biosorbent amount and dye concentration. The maximum MB dye removal considering the effect of total dissolved solids from aqueous solutions of 74.49% and 67.99% by sugarcane bagasse and peanut hulls, respectively. The models specify that they could predict biosorption with high accuracy having R²-value above 0.9. Statistical studies for RSM, ANFIS and ANN models were compared. Further, the models were optimized for maximum dye removal was at 1.21 g of biosorbent, pH 5.24, 31.24 mg/L MB concentration, 22.29°C of dye solution using sugarcane bagasse and at 1.37 g of biosorbent, pH 5.77, 36.7 mg/L MB concentration, 26.8°C of dye solution using peanut hulls. Additionally, Fourier Transform Infra-Red (FTIR) spectral analysis was also carried out to confirm the biosorption.

Fabrication of Cellulose Nanocrystal (CNCs) Based Biosorbent From Oil Palm Trunks Through Acid Hydrolysis With Sonication Assisted and Adsorption Kinetic Study

Developing cellulose nanocrystal (CNCs) preparation techniques is a challenge confronted by many researchers. The advantages of property remain the reason for research to be developed. To deal with this issue, it is essential to conduct research related to process optimization, particularly in the hydrolysis process, which is the primary step in forming CNCs. In this study, the effect of sonication-assisted hydrolysis time was investigated. XRD characterization showed that the CNCs formed where the first group with specific peaks indicated. The crystallinity of CNCs decreased with increasing sonication duration, indicating that sonication-assisted hydrolysis was nonselective. The crystallinity of CNCs obtained for 15, 30, and 45 min was 61.6, 55.0, and 48.4 %, respectively. For sonication duration variations of 15, 30, and 45 min, the hydration diameter of CNCs was nearly identical at 42.35 ± 27.10, 42.99 ± 29.46, and 42.63 ± 29.49 nm, respectively. Similarly, the removal of methylene blue can be achieved using CNCs bio-adsorbent. The results of percent removal of methylene blue under sonication treatment of 15, 30, and 45 min of sonication were 73.34; 73.62; 72.86 %, respectively. The adsorption rate of CNCs follows the pseudo-second-order kinetic model, with the adsorption values under sonication treatment of 15, 30, and 45 min were 0.075 ± 0.008; 0.166 ± 0.013; 0.078 ± 0.005 g mg-1 min-1, respectively.

Adsorption of Cr6+ ion using activated Pisum sativum peels-triethylenetetramine

The adsorption of Cr6+ ions from water-soluble solution onto activated pea peels (PPs) embellished with triethylenetetramine (TETA) was studied. The synthesized activated TETA-PP biosorbent was further characterized by SEM together with EDX, FTIR and BET to determine the morphology and elementary composition, functional groups (FGs) present and the biosorbent surface area. The confiscation of Cr6+ ions to activated TETA-PP biosorbent was observed to be pH-reliant, with optimum removal noticed at pH 1.6 (99%). Cr6+ ion adsorption to activated TETA-PP biosorbent was well defined using the Langmuir (LNR) and the pseudo-second-order (PSO) models, with a determined biosorption capacity of 312.50 mg/g. Also, it was found that the activated TETA-PP biosorbent can be restored up to six regeneration cycles for the sequestration of Cr6+ ions in this study. In comparison with other biosorbents, it was found that this biosorbent was a cost-effective and resourceful agro-waste for the Cr6+ ion confiscation. The possible mechanism of Cr6+ to the biosorbent was by electrostatic attraction following the surface protonation of the activated TETA-PP biosorbent sites.

Influence of magnetite incorporation into chitosan on the adsorption of the methotrexate and in vitro cytotoxicity

Emerging pollutants are a group of substances involved in environmental contamination resulting mostly from incomplete drug metabolism, associated with inadequate disposal and ineffective effluent treatment techniques. Methotrexate (MTX), for instance, is excreted at high concentrations in unchanged form through the urine. Although the MTX is still effective in cancer and autoimmune disease treatment, this drug shows the ability of bioaccumulation and toxicity to the organism. Thus, the present work aimed to evaluate the adsorption of the MTX drug onto magnetic nanocomposites containing different amounts of incorporated magnetite (1:1, 1:5, and 1:10 wt%), combining the theoretical-experimental study as well as the in vitro cytotoxicity. Moreover, equilibrium studies (Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Hill, Redlich-Peterson, and Sips), kinetic (PFO, PSO, and IPD), and thermodynamic (ΔG°, ΔH°, and ΔS°) were used to describe the experimental data, and ab initio simulations were employed in the theoretical study. Magnetic nanocomposites were synthesized by the co-precipitation method using only FeCl₂ as the iron precursor. Adsorbents were characterized by FTIR, XRD, Raman, SEM-EDS, BET, and VSM analysis. Meanwhile, cytotoxic effects on L929 and A375 cell lines were evaluated through MTT, NR, and LDH assays. The adsorption of the MTX was carried out in a typical batch system, exploring the different experimental conditions. The theoretical study suggests the occurrence of chemisorption between CS·Fe₃O₄-MTX. The maximum adsorption capacity of MTX was 285.92 mg g^-1, using 0.125 g L^-1 of CS·Fe₃O₄ 1:1, with an initial concentration of the MTX (50 mg L^-1), pH 4.0 at 293 ± 1.00 K. The best adjustment of equilibrium and kinetic data were the Sips (low values for statistical errors) and PSO (q_e = 96.73 mg g^-1) models, respectively. Thermodynamic study shows that the adsorption occurred spontaneously (ΔG° < 0), with exothermic (ΔH° =  - 4698.89 kJ mol^-1) and random at the solid-solution interface (ΔS° = 1,476,022.00 kJ mol^-1 k^-1) behavior. Finally, the in vitro study shows that magnetic nanomaterials exhibit higher cytotoxicity in melanoma cells. Therefore, the magnetic nanocomposite reveals to be not only an excellent tool for water remediation studies but also a promising platform for drug delivery.

Adaptation of advanced physical models to interpret the adsorption isotherms of lead and cadmium ions onto activated carbon in single-compound and binary systems

The work reports a modeling analysis of single-compound and binary adsorption of Pb²⁺ and Cd²⁺ ions from polluted water onto the activated carbon at room temperature. The homogeneous model for single adsorption (HM) and the exclusive extended monolayer model for binary adsorption (EEMM) are applied for the interpretation of the experimental data set. The adopted models correlate the entire set of adsorption data, allowing a thorough description of the occurring phenomena. The overall objective of the study is to determine the adsorption mechanisms, also through a comparative analysis between the single-compound and binary modeling data. The parameters of both models are used for to retrieve useful indications about the adsorption of these two ions. In particular, the number of ions adsorbed per single functional groups changed from single-compound to binary adsorption, allowing to explain the competitive behavior of the investigated system. The adsorption energy values vary between 21.39 (Pb²⁺) and 24.06 kJ/mol (Cd²⁺), and 27.17 (Pb²⁺) and 32.59 kJ/mol (Cd²⁺) in single-compound and binary systems, respectively, indicating that adsorption is a physisorption process.

Using an enhanced multilayer model to analyze the performance of nickel alginate/graphene oxide aerogel, nickel alginate aerogel/activated carbon, and activated carbon in the adsorption of a textile dye pollutant

This work describes the modeling and analysis of methylene blue molecule on different adsorbents, namely, nickel alginate/graphene oxide (NA/GO) aerogel, nickel alginate/activated carbon (NA/AC) aerogel, and Trichosanthes kirilowii maxim shell activated carbon (TKAC). A multilayer statistical physics model was used to calculate the energetic and steric parameters of the adsorption of methylene blue on these adsorbents. Based on the modeling investigation, it was concluded that the formation of multiple dye adsorbed layers on these adsorbents could be feasible where physical adsorption interactions could be involved. Adsorption capacities at saturation of these adsorbents ranged from 542.97 to 470.03 mg/g, 790.66 to 684.47 mg/g, and 401.11 to 1236.24 mg/g for NA-GO aerogel, NA-AC aerogel, and TKAC, respectively. This research contributes with new findings for the understanding of dye adsorption on novel materials, which can be used in water pollution control.

Multifunctional porous β-cyclodextrin polymer for water purification

Keeping water clean is of vital significance for human health and environmental protection. In order to remove organic micro-pollutants and natural organic substances in water bodies and kill pathogenic microorganisms simultaneously, this study synthesized a multifunctional porous β-cyclodextrin polymer with a high specific surface area by introducing quaternary ammonium groups and rigid benzene rings, respectively, which was then polymerized with crosslinking agent-4,4'-bis (chloromethyl)-1,1'-biphenyl (BCMBP) in an ionic liquid system. The grafting of quaternary ammonium groups was beneficial for the removal of negative-charged humic acid (HA) and sterilization. The introduction of numerous rigid structures during benzylation and Friedel-Crafts alkylation reaction could significantly improve the porosity and specific surface area of the polymer, conducive to the exposure of cyclodextrin binding sites and contaminant adsorption. By changing the proportions of quaternization and benzylation, the structure and surface properties of the polymer could be adjusted, thus further regulating the adsorption performance. Compared with activated carbon, the polymer named BQCD-BP with a huge surface area of 1133 m² g^-1 prepared under optimized conditions showed outstanding adsorption performance and sterilization ability. The pseudo-second-order kinetic constant of BQCD-BP reached 1.2058 g·mg^-1·min^-1, which was approximately 50 times greater than that of activated carbon (0.0256 g·mg^-1·min^-1) under the same experimental condition. The adsorption capacity of BQCD-BP to HA was twice as high as that to AC, and the antibacterial ability of BQCD-BP was significant, achieving 90% at the dosage of 1g L^-1. Moreover, the adsorption process was hardly affected by the hydrochemical conditions, and the polymer was easy to regenerate. In addition, the excellent adsorption and antibacterial performance of the polymer were also identified by natural water treatment. COD was almost completely removed, and the removal efficiency of TP reached 92% after contact with BQCD-BP. The sterilization rate of BQCD-BP to viable bacteria in complex water bodies reached 82%. Undoubtedly, BQCD-BP is a potential multifunctional water treatment material with reasonable design in the actual water purification.

Kinetics and Adsorption Equilibrium in the Removal of Azo-Anionic Dyes by Modified Cellulose

This study introduces a new and bio-friendly adsorbent based on natural and cetyltrimethylammonium chloride (CTAC)-modified adsorbent prepared from wheat straw residues for the removal of Congo red (CR) and tartrazine azo-anionic dyes from aqueous solution. The adsorbent was characterized by thermogravimetric analysis (TGA), calorimetric differential (DSC), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX), and pH point of zero charge (pHPZC) techniques. It was found that decreasing the adsorbent dose and increasing the initial concentration favors the removal of tartrazine and Congo red. Tartrazine adsorption capacities were 2.31 mg/g for the cellulose extracted from wheat residues (WC) and 18.85 mg/g for the modified wheat residue cellulose (MWC) for tartrazine as well as 18.5 mg/g for WC and 19.92 for MWC during Congo red (CR) adsorption, respectively. Increasing the initial and decreasing the adsorbent dose concentration favored the adsorption process. From time effect analysis, it was found that the equilibrium time was reached at 120 min when modified wheat cellulose was used and at 480 min when wheat cellulose was used. The kinetics of adsorption were described by pseudo-second-order in all cases with R2 > 0.95. The obtained data equilibrium from this research was well-fitted by the Freundlich isotherm model.

Adsorption isotherm models: A comprehensive and systematic review (2010-2020)

Among numerous methods developed in purification and separation industries, the adsorption process has received considerable attention due to its inexpensive, facile, and eco-friendly nature. The importance of the adsorption process causes extraordinary endeavors for modeling the adsorption isotherms during the years; thus, myriads of research have been conducted and many reviews have been published. In this paper, we have attempted to gather the most widely used adsorption isotherms and their related definitions, along with examples of correlated work of the recent decade. In the present review, 37 adsorption isotherms with about 400 references have been collected from the research published in the period of 2010-2020. The adsorption isotherms utilized are alphabetically organized for ease of access. The parameters of each isotherm, as well as the applicable definitions, are presented in the table, in addition to being discussed in the text. Another table is provided for the practical use of researchers, featuring the usage of the related isotherms in peer-reviewed studies.

Physicochemical Modeling of the Adsorption of Pharmaceuticals on MIL-100-Fe and MIL-101-Fe MOFs

The adsorption of naproxen (NAP), diclofenac (DFC), and acetaminophen (APAP) molecules from aqueous solutions using MIL-100-Fe and MIL-101-Fe metal organic frameworks (MOFs) has been analyzed and modeled. Adsorption isotherms of these pharmaceuticals were experimentally quantified at 30 and 40°C and pH 7. Textural parameters and surface chemistry of these MOFs were analyzed, and results were utilized to explain the pharmaceutical adsorption mechanism. Density Functional Theory (DFT) calculations were performed to understand the reactivity of pharmaceutical molecules, and a statistical physics model was employed to calculate the main physicochemical parameters related to the adsorption mechanism. Results showed that the adsorption of these pharmaceuticals on MOFs was multimolecular and exothermic. Both MOFs displayed the highest adsorption capacities, up to 2.19 and 1.71 mmol/g, for NAP and DFC molecules, respectively. MIL-101-Fe showed better pharmaceutical adsorption properties than MIL-100-Fe due to its highest content of Fe-O clusters and mesopore volume. Adsorption mechanism of these organic molecules could involve hydrogen bond, van der Waals forces, and electrostatic interactions with MOF surfaces. In particular, MIL-101-Fe MOF is a promising material to prepare composites with competitive adsorption capacities for facing the water pollution caused by pharmaceutical compounds.

Evaluation of Three Biomaterials from Coconut Mesocarp for Use in Water Treatments Polluted with an Anionic Dye

Coconut consumption leads to the generation of a large number of fibrous residues such as epicarp and mesocarp. In this study, bioadsorbents were prepared from coconut shells (CS), coconut cellulose (CC) and treated coconut cellulose (MCC) with cetyl trimethyl ammonium chloride (CTAC) for the elimination of Congo red (CR) in a watery solution. The impact of the adsorbent quantity (15, 25 and 35 mg) and initial concentration (40, 70 and 100 mg/L) were evaluated. Fourier transform infrared spectra (FTIR) confirmed the existence of OH−, C=O, COOH and CH2 groups in the adsorbents as well as the deformation of the bands between 3400 and 3800 cm−1 after the adsorption of CR, which was attributed to its capture in the bioadsorbent. From the bromatological analysis, a content of 48.94% lignin, 35.99% cellulose and 10.51% hemicellulose was found. SEM images showed a lignocellulosic essential surface origin for all adsorbents with presence of folds, roughness of an irregular exposed area and fibrous filaments. The average particle size was 0.45 mm and adsorbents had a mean porosity of 0.58. Increasing the initial concentration had a beneficial influence on the removal efficiency of CR, achieving a 99.9% removal with MCC. CS showed slow kinetics in the initial stages whereas CC and MCC achieved 78% and 99.98% removal at 120 min, respectively; an equilibrium was reached at 480 and 20 min, respectively. MCC, CC and CS achieved a maximum qe of 256.12 mg/g, 121.62 mg/g and 17.76 mg/g, respectively.

Raphia-Microorganism Composite Biosorbent for Lead Ion Removal from Aqueous Solutions

This study investigated the possibility of obtaining a raphia-microorganism composite for removing lead ions from aqueous solutions using immobilized yeast cells Saccharomyces cerevisiae on Raphia farinifera fibers. The obtained biocomposite was characterized using scanning electron microscopy and Fourier transform infrared spectroscopy. Studies were conducted to determine the influence of contact time, initial concentration of Pb(II), and pH allowed for the selection of nonlinear equilibrium and kinetic models. The results showed that the biocomposite had a better Pb(II) removal capacity in comparison to the raphia fibers alone, and its maximum Pb(II) adsorption capacity was 94.8 mg/g. The model that best describes Pb(II) sorption was the Temkin isotherm model, while kinetic studies confirmed the chemical nature of the sorption process following the Elovich model. The obtained research results provide new information on the full use of the adsorption function of biomass and the ubiquitous microbial resources and their use in the remediation of aqueous environments contaminated with heavy metals.

Phosphate removal from aqueous solution by Fe-La binary (hydr)oxides: characterizations and mechanisms

In this study, Fe-La binary (hydr)oxides were prepared by a co-precipitation method for phosphate removal. Various techniques, including secondary electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), powder X-ray diffraction (p-XRD), and Brunauer-Emmett-Teller (BET) surface area analysis, were employed to characterize the synthesized Fe-La binary (hydr)oxides. Batch experiments indicated that the performance of phosphate removal by Fe-La binary (hydr)oxides was excellent and increased with increasing the concentrations of La. The kinetics study showed that the adsorption was rapid and described better by the pseudo-second-order equation. The maximum adsorption capacities of Fe/La 3:1, Fe/La 1:1, and Fe/La 1:3 binary (hydr)oxides at pH 4.0 calculated by Langmuir model were 49.02, 69.44, and 136.99 mg/g, respectively. The uptake of phosphate was highly affected by solution pH and significantly reduced with the increase of pH value. The analyses of p-XRD, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) suggested that the predominant mechanisms of phosphate removal involved surface hydroxyl exchange reactions and co-precipitation of released La³⁺ and phosphate ions, which resulted into the formation of amorphous phase of rhabdophane (LaPO₄·0.5H₂O). The results show great potential for the application on the treatment of phosphate decontamination for their high efficiency of phosphate removal.

Optimization of synergistic biosorption of oxytetracycline and cadmium from binary mixtures on reed-based beads: modeling study using Brouers-Sotolongo models

The first aim of this study was to synthesize and characterize reed-based-beads (BBR), an enhanced adsorbent from Tunisian reed. The second purpose was to evaluate and optimize the BBR efficiency for the simultaneous removal of oxytetracycline (OTC) and cadmium (Cd(II)), using central composite design under response surface methodology. The third goal was to elucidate the biosorption mechanisms taking place. It was shown that under optimum conditions (4.19 g L^-1 of BBR, 165.54 μmol L^-1 of OTC, 362.16 μmol L^-1 of Cd(II), pH of 6, and 25.14-h contact time) the highest adsorption percentages (63.66% for OTC and 99.99% for Cd(II)) were obtained. It was revealed that OTC adsorption mechanism was better described by Brouers-Sotolongo fractal equation, with regression coefficient (R²) of 0.99876, and a Person's chi-square (χ²) of 0.01132. The Weibull kinetic equation better explained Cd(II) biosorption (R² = 0.99959 and χ² = 0.00194). FTIR and isotherm studies confirmed that the BBR surface was heterogeneous, and that adsorption mechanisms were better described by the Freundlich/Jovanovich equation (R² = 0.99276 and χ² = 0.04864) for OTC adsorption, and by the Brouers-Sotolongo model (R² = 0.9851 and χ² = 0.77547) for Cd(II) biosorption. Overall results indicate that, at last, the BBR lignocellulosic biocomposite beads could be considered as cost-effective and efficient adsorbent, which could be of socioeconomic and environmental relevance. Graphical abstract.

Efficient Adsorption of Anionic Dyes by Ammoniated Waste Polyacrylonitrile Fiber: Mechanism and Practicability

Adsorption is one of the commonly used methods in wastewater treatment, but it has the problem of high cost and a complicated production process. In this paper, a low-cost and efficient decolorizing adsorbent was successfully prepared based on waste polyacrylonitrile fiber (PANF). The waste PANF was ammoniated by propylene diamine derivates (PANAMF), and benzylamine (PANABMF) and quaternary ammonium ions (PANQMF) were introduced for PANAMF to regulate hydrophilicity and hydrophobicity. With acidic red 249 as the model anionic dye, influences of the adsorption center structure, the degree of modification, the concentration of acid, the dye structure, and the auxiliary agent in the solution on the dye adsorption performance were studied. Isothermal models, kinetic models, reusability, and continuous application ability of the fiber adsorbent were discussed. PANAMF, PANABMF, and PANAQF exhibit excellent adsorption performance compared to the common adsorbent. After protonation, the saturation adsorption value can reach 2051.3 mg/g for PANAMF. PANAMF also exhibited excellent reusability, and the adsorption capacity after being reused eight times still can keep 72.7% of that for the first time. The adsorption of the anionic dye for PANAMF is a chemisorption process, and the rate-determining step is changed from the diffuse step to the adsorption on the surface with the adsorption time. PANAMF can also be used in the continuous flow process, and the absorption amount is similar to that in the batch adsorption, which shows excellent commercial application potential.

Adsorption of Azo-Anionic Dyes in a Solution Using Modified Coconut (Cocos nucifera) Mesocarp: Kinetic and Equilibrium Study

The effect of adsorbent dose and initial concentration on removing the azo-anionic dyes Congo Red andtartrazine present in a synthetic aqueous solution was studied using natural cellulose (CC) and modified cationic cellulose (MCC) from coconut mesocarp. Three levels of adsorbent dosage (5, 8 and 12 mg/L) and initial concentration (40, 70 and 100 mg/L) were used. Cetyl trimethyl ammonium chloride (CTAC) was used as a modifying agent. TGA and DSC showed that the extracted cellulose was of good quality, composed mostly of cellulose with lignin and hemicellulose traces, and 8% moisture. The FTIR spectrum showed the effectiveness of the modification in the structure of the material with symmetric deformation of the C6H6-Cl group in 1472 cm−1 present in the CTAC. It was found that decreasing the adsorbent dosage and increasing the initial concentration favored the dyes’ adsorption capacity on the two bioadsorbents. Tartrazine removals of 5.67 mg/g on CC and 19.61 mg/g on MCC were achieved, and for CR of 15.52 mg/g on CC and 19.99 with MCC with removal percentages over 97% with the quaternized biomass in all cases. The kinetic and equilibrium study was carried out to identify the mechanisms involved in the adsorption process. The Freundlich model can describe the equilibrium isotherm data of tartrazine on CC and MCC. In contrast, those of CR is defined by the Langmuir and Dubinin–Radushkevic models for CC and MCC, respectively Adsorption kinetics showed that equilibrium was reached at 30 min, with rapid adsorption in the initial minutes with the removal of about 97% of the contaminant in the first 5 min; fitting to kinetic models showed that the kinetics of tartrazine on CC was fitted by Elovich (R2 = 0.756), and on MCC the Elovich (R2 = 0.887) and pseudo-second-order (R2 = 0.999) models. Removing CR on CC was fitted by pseudo-first-order, pseudo-second-order and Elovich models (R2 > 0.98), and when using MCC, all models show a good fitting with R2 = 0.99 in all cases.

Removal of color from real textile dyeing effluent utilizing tannin immobilized jute fiber as biosorbent: optimization with response surface methodology

The present study explored an efficient technoeconomic method for treating intensely colored dyeing effluents from a commercial source. Firstly, the adsorption efficacy of jute fiber (JF) was enhanced through grafting with tannin, a natural polyphenol, via incorporation of active epoxy groups by epichlorohydrin onto fiber surface. The effect of different experimental parameters (e.g., initial pH, adsorbent dose, temperature, and contact time) on extent of color removal was evaluated performing batch studies. A full factorial central composite design (CCD) in response surface methodology (RSM) was applied to optimize the decolorization process for achieving maximum color removal (99.5%) at pH 4.9, adsorbent dose 11.8 g/L, temperature 30 °C, and time of contact 117.8 min. The isotherm and kinetic studies of the process revealed that Langmuir model and pseudo-second-order model provided best fit, yielding high correlation coefficients (R² > 0.997). Significant desorption (76%) of the spent adsorbent by 0.1 M NaOH solution suggested that this tannin-modified JF can find a prospective practical application as a novel, inexpensive, and potential bioadsorbent to treat the dyeing effluent.

Sorption of U(VI), Mn (II), Cu(II), Zn(II), and Cd(II) from multi-component phosphoric acid solutions using MARATHON C resin

Crude phosphoric acid is a vital component used in making phosphate fertilizers. Depending on the processes used in producing the crude phosphoric acid, it usually contains organic and inorganic contaminants. To make environmentally friendly phosphate fertilizers, these contaminants must be removed from the crude phosphoric acid stock used in making fertilizers. In this paper, commercially available strong cation exchange resin, Marathon C, was used to study the adsorptive removal of U(IV), Mn(II), Cd(II), Zn(II), and Cu(II) from synthetic multi-component phosphoric acid solutions and commercial crude phosphoric acid. Important parameters on the adsorption process such as the effects of contact time, initial metal ion concentration, sorbent dose, and concentration of phosphoric acid were investigated. The results suggested that the adsorption process reached equilibrium within 240 min for the five metal ions studied and the resin had adsorptive affinity for the metal ions in the order of U(IV) > Zn(II) > Cu(II) > Mn(II) > Cd(II). The results from the kinetics and isotherm models from the studies are very consistent with pseudo-second-order kinetic and Langmuir isotherm models. Simultaneous adsorptive removal of metal ions from the crude phosphoric acid strongly suggests that the Marathon C resin could be used in removing toxic metal ions from crude phosphoric acids used in making phosphate fertilizer.

Removal behaviour of NSAIDs from wastewater using a P-functionalised microporous carbon

Diclofenac (DCF), naproxen (NPX) and ibuprofen (IBF) are three of the most commonly used non-steroidal anti-inflammatory drugs (NSAIDs) worldwide. They are widely detected in natural waters due to their persistence in wastewater treatment, and their removal is desirable in future wastewater management worldwide. In this study, "acid catalyst" functionalisation and subsequent carbonisation were adopted to synthesise a P-doped microporous carbonous adsorbent (CScPA) for NSAID removal. The CScPA was evaluated in depth for its adsorption performance (i.e., isotherms, kinetics and thermodynamics of adsorption at lab-scale). The CScPA had a large surface area (791.1 m²/g) and good porosity (0.392 cm³/g), which facilitated a high maximum adsorption capacity of 62.02 mg/g for a NSAID mixture. Thermodynamic data indicated that the adsorption of these NSAIDs was an endothermic process determined by physisorption (low-energy interactions). XPS analysis revealed the specific interactions involved in the adsorption process, including π-π and n-π electron donor-acceptor (EDA) interactions and hydrogen (H-) bonding. The Freundlich isotherm and Elovich kinetic model provided the best fit to the experimental results, which indicated surface heterogeneity (of the CScPA) and cooperative adsorption mechanisms. The adsorption process was shown to have potential to be applied to real wastewater effluent containing NSAIDs at low environmentally relevant concentrations (removal reached > 90% at 10 μg/L). Analysis of different implementation and cost related factors suggested that the CScPA has the potential for use with "real-world" water matrices, offering a sustainable treatment process for pharmaceutical remediation in wastewater.

Transforming pods of the species Capparis flexuosa into effective biosorbent to remove blue methylene and bright blue in discontinuous and continuous systems

This study investigates, for the first time, the applicability of seed pods from Capparis flexuosa as an alternative biosorbent to remove methylene blue and bright blue from aqueous medium using continuous and batch systems. The biosorbent was characterized by different techniques, whose particles presented rough surface and large pores and functional groups existing on its surface. In the batch system, an adsorptive capacity of 96.40 mg g^-1 and 80% of methylene blue removal was reached with 0.9 g L^-1 of adsorbent at pH 10, whereas 109.7 mg g^-1 and 83% of bright blue removal was observed using 0.8 g L^-1 of adsorbent at pH 2.0. The Elovich model adjusted the experimental data satisfactorily for both dyes. Tóth model for the MB best described the equilibrium data, and the Langmuir model for the bright blue both favored by the increase of temperature and dyes' concentration. The maximum capacities obtained were 280.78 mg g^-1 and 342.85 mg g^-1 for methylene blue and bright blue, respectively. The thermodynamic parameters indicated spontaneous processes, with endothermic behavior for both dyes. The fixed adsorption experiments using Capparis flexuosa seed pods showed adsorptive capacities of 158.65 and 205.81 mg g^-1 for the methylene blue and bright blue, respectively. The overall results indicated that the pods of the Capparis flexuosa could be an ecological, effective, and economical alternative in the removal of dyes for both continuous and batch systems.

Lead ion adsorption on functionalized sugarcane bagasse prepared by concerted oxidation and deprotonation

Targeting the removal of Pb²⁺ in wastewater, sugarcane bagasse was treated with nitric acid and an alkaline solution to prepare adsorbents. On a typical adsorbent, the adsorption isotherms agreed well with the Langmuir expression, and the maximum adsorption capacity reached 200.3 mg/g. In the presence of 150 ppm Ca²⁺, a common cation in natural water, the Pb²⁺ adsorption capacity slightly declined. In contrast, Mg²⁺ obviously prohibited the adsorption for Pb²⁺. The spent adsorbent could be regenerated at least five times through elution with an EDTA solution. EDS and XPS results demonstrated that nitric acid functioned as an oxidant instead of nitrification agent in the treatment of bagasse. The adsorption process was consistent with quasi-second-order kinetics. Based on thermodynamic studies, the changes in enthalpy and Gibbs free energy were calculated to be - 33.3 and ca. - 18 kJ/mol, indicating that the adsorption process was exothermic and spontaneous. The equilibrium Pb²⁺ adsorption amounts were proportional to the numbers of carboxylate groups on different adsorbents. The binding energies of Pd 4f_5/2 and Pd 4f_7/2 XPS spectra of Pb²⁺ adsorbed were 0.6-0.7 eV lower than those of free Pb(NO₃)₂, indicating the transfer of electrons during adsorption. The conversion of hydroxymethyl groups in sugarcane bagasse into carboxylate groups, as well as the chelation between Pb²⁺ ions and carboxylate groups, was validated in this work, which is beneficial for the treatment of wastewater polluted by lead ions.

Clay-activated carbon adsorbent obtained by activation of spent bleaching earth and its application for removing Pb(II) ion

BE/C-A750-1/1 is prepared by carbonizing SBE and then activating with KOH. BE/C-A750-1/1 has good adsorption capacity for Pb(II), and the adsorption capacity for Pb(II) is 206.65 mg/g. The harmful effects of coexisting cations are listed in ascending order: K⁺ < Na⁺ < Mg²⁺. Adsorption and desorption studies show that the adsorption capacity of BE/C-A750-1/1 for Pb(II) after adsorption and desorption 3 times is 183.62 mg/g. The adsorption mechanism mainly includes electrostatic attraction, ion exchange, physical adsorption, and chemical complexation. This suggests that activated BE/C may be a promising candidate for removing Pb(II) from industrial wastewater. Clay/carbon nanocomposites were prepared by carbonizing and activating the spent bleaching earth served as adsorbents for the efficient removal of Pb(II) from wastewater.

Lead adsorption on loess under high ammonium environment

Lead (Pb) is one of the most toxic, hazardous pollutants available in landfill leachate. Loess-amended soil buffers are found suitable and effective in attenuating migration of Pb and the other trace metals. High concentration of ammonium (NH₄⁺ > 1000 mg/l) is also reported in landfill leachate, and therefore, it is essential to investigate the transport of lead under such condition. In this study, the mechanisms and the capacity of loess to adsorb Pb under high NH₄⁺ concentration were investigated. Adsorption isotherm test data were obtained for 25 °C, 35 °C and 45 °C. The maximum adsorption capacity is estimated to be 2101.97 mg/g at 25 °C and 4292.8 mg/g at 45 °C under 1000 mg/l NH₄⁺. The binding sites of Pb on loess are positively related to each other at low temperatures (25-35 °C). The thermodynamic analysis indicates that adsorption process is endothermic and non-spontaneous and the system randomness increases with reaction time. The kinetic test data, fitted with a pseudo-second-order kinetic model and an intraparticle diffusion model, suggests that removal of Pb is driven by both membrane and intraparticle diffusions. The SEM, XRD and FTIR analyses indicate flocculation, precipitations as well as some ion exchange processes, which perhaps combinedly increases adsorption of both NH₄⁺ and Pb in loess. The two kinds of precipitations are involved for the removal of Pb. The precipitations of PbCO₃, Pb(OH)₂ and PbCO₃·2H₂O are formed by the reactions between calcite and lead. The other precipitation of white basic salt (Pb₂O(NO₃)₂) is formed by the reactions among Pb²⁺, NO₃^- and aqueous ammonia under alkaline environment of loess slurry.

Comprehensive evaluation of adsorption performances of carbonaceous materials for sulfonamide antibiotics removal

Sulfonamide antibiotics have highly toxic effects on humans and other organisms within the food chain. Adsorption by various carbonaceous materials is an effective method for removing them from the aqueous environment. Batch adsorption experiments were conducted between adsorbents and sulfamethoxazole (SMX) by studies of characterization, isotherm model, and kinetic model. The adsorption performances and mechanism of fifteen carbonaceous materials to remove SMX have been comprehensively evaluated. Results of the characterization showed that not only porosity, but also surface chemistry plays an important role in the adsorption process. Changes in the type and quantity of functional groups before and after adsorption are positive for the recyclability of carbonaceous materials. Moreover, kinetic studies showed that the adsorption process followed the pseudo-second-kinetic model and the intra-particle diffusion model. Four adsorbents (i.e., W-GAC, 3M-GAC, GP, and PAC) in this study have the best performance in each corresponding category in terms of the adsorption of SMX. Therefore, the results provide an indispensable reference for evaluating the adsorption performances of a variety of carbonaceous materials, and thus can support the selection of adsorbents for different applications. Graphical abstract.

Adsorption of sulfamethoxazole and sulfadiazine on phosphorus-containing stalk cellulose under different water pH studied by quantitative evaluation

To improve the high-value application of corn stalk, phosphorus-containing stalk cellulose (PFC) was prepared, characterized, and utilized for the adsorption of sulfamethoxazole (SMZ) and sulfadiazine (SD), with maximum adsorption capacities of 1.385 and 2.527 mg/g at pH 7. As expected, the adsorption efficiency of PFC was strongly affected by pH, and the preferential adsorption order of SMZ^- (SD⁰) > SMZ⁰ (SD^-) > SMZ⁺ (SD⁺) was obtained from the experimental results and due to the charges of PFC and the SMZ and SD species. Furthermore, these results were qualitatively linked to the adsorption mechanism, e.g., π⁺-π electron donor-acceptor (EDA), anion-π bond electrostatic, and hydrophobic interactions. In particular, the adsorption mechanism was further characterized in terms of structure and analyzed systematically using density functional theory (DFT), frontier orbital theory (FOT), and molecular dynamics (MD) simulation, with the aim to explain the theoretical calculation and experimental results. As a result, the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) orbitals revealed the key role of the rings and functional groups of PFC and SMZ (or SD) and validated the optimized structures of PFC⁺ sulfonamides (SAs)⁺, PFC^- SAs⁰, and PFC^- SAs^-, in which their binding energy values, energy gaps, and relevant molecular lengths determined their stability. Additionally, the van der Waals (vdW) energy confirmed the effect of various interactions on adsorption.

Lanthanum hydroxide: a highly efficient and selective adsorbent for arsenate removal from aqueous solution

In the present work, a lanthanum hydroxide adsorbent was prepared by a simple precipitation process, and its arsenic removal performances and adsorption mechanisms were investigated by batch experiments and various techniques including field emission scanning electron microscopy with energy-dispersive X-ray spectrophotometry (FESEM-EDX), Brunauer-Emmett-Teller (BET) analysis, powder X-ray diffraction (p-XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The influence of pH on arsenic removal showed that the lanthanum hydroxide adsorbent can effectively remove As(V) from solution, whereas the As(III) removal was very low, indicating that the lanthanum hydroxide adsorbent can selectively remove As(V) but not As(III). The isotherm study showed that the maximum adsorption capacities of As(V) at pH 5.0 and 9.0 were 299.4 and 192.3 mg/g, respectively, much higher than those of the widely used ferrihydrite. Significant interference on As(V) removal was caused by the presence of phosphate and natural organic acids (NOAs), such as citric acid. Powder XRD, FTIR, and XPS analysis showed that the lanthanum hydroxide was almost transformed into lanthanum arsenate after As(V) adsorption at pH 4.0, while a portion of lanthanum hydroxide remained after As(V) adsorption at pH 6.0 and 9.0. Furthermore, ligand exchange between the hydroxyl groups of the adsorbent and As(V) and the formation of inner-sphere surface complexes could play a central role in arsenic removal which needs further investigation.

Chitosan-coated sand and its application in a fixed-bed column to remove dyes in simple, binary, and real systems

Adsorption of tartrazine yellow food dye, in a fixed-bed column, was carried out using a single system, a binary system (in the presence of sunset yellow food dye), and in a real effluent provides from an ice cream industry. Chitosan was used to coat sand particles by the dip-coating technique, and these particles were applied in fixed-bed adsorption. The assays were performed in flow rates of 3 mL min^-1 and 5 mL min^-1. The best performance was reached at 3 mL min^-1. In this flow rate, for single and binary systems, the breakthrough time was 95 min and 65 min, and the maximum capacity of the column was around 595 mg g^-1 and 497 mg g^-1, respectively. In the assay conducted with the real effluent, the breakthrough time was 10 min, and the maximum adsorption capacity of the column was reduced to 191 mg g^-1 for tartrazine dye. The dynamic models of Thomas and Yoon-Nelson were used, and both were suitable to represent the breakthrough curves.

Adsorption of Cu(II) and Ni(II) ions from wastewater onto bentonite and bentonite/GO composite

Two superior adsorbents, namely bentonite and graphene oxide (GO), were hybridised to study the removal of copper and nickel ions from synthetic and industrial wastewater. The as-synthesised GO, bentonite/GO and bentonite were characterised by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and N₂ adsorption-desorption analysis. The factors influencing the adsorption behaviours including contact time, initial solution pH, ionic strength, initial concentration of metal ions, temperature and adsorbent dosage were systematically investigated by batch equilibrium method. The adsorption equilibrium for copper and nickel onto bentonite was attained in 90 min while equilibrium was reached in 60 min on bentonite/GO. The adsorption of copper and nickel was pH-dependent in the range from pH 2 to pH 7 and from pH 2 to pH 8. Pseudo-first-order kinetic model excellently described the adsorption of copper and nickel onto bentonite and bentonite/GO. The equilibrium adsorption data was well described by the Langmuir isotherm model and the maximum adsorption capacity was 248.9 mg/g, 558.4 mg/g, 215.8 mg/g and 402.5 mg/g for bentonite-copper, bentonite/GO-copper, bentonite-nickel and bentonite/GO-nickel adsorption systems, respectively. The bentonite/GO composite exhibited a higher adsorption capacity of both cations from synthetic wastewater than pure bentonite owning to the synergistic effect between bentonite and GO. In all adsorption studies, copper was more efficiently removed than nickel due to its higher tendency to form bond with adsorbent surfaces. The adsorption of copper and nickel on bentonite/GO was mainly due to cation exchange, intermolecular and electrostatic interactions and physisorption dominated the adsorption processes. The practical application of bentonite/GO on adsorption of copper was investigated using real wastewater and its removal efficiency was beyond 98%. The excellent adsorption performances of composites for the copper and nickel removal from wastewater demonstrated its significant potential for pollution mitigations.

Eco-friendly synthesis of self-regenerative low-cost biosorbent by the incorporation of CuO: a photocatalyst sensitive to visible light irradiation for azo dye removal

Acid pretreated biomass Lemna minor (BM-H3PO4) was used as support for CuO nanoparticles loading, to investigate the dye biosorption capacity and the photocatalytic performance under artificial visible light. The surface morphology, crystal structure, elemental composition, and the bandgap of modified biomass have been determined using FE-SEM, XRD, EDX, XPS, FTIR, and UV-DR analysis. The results showed that NH2 and P-O functional groups of (BM-H3PO4) can attract the copper ions (Cu2+), which can facilitate the loading of CuO nanoparticles hence, smaller nanoparticles with an average diameter of 21 nm was obtained. It was also found that when the CuO was incorporated in BM-H3PO4 in a proper mass ratio of 0.4, the biosorption efficiency was enhanced to 3 times compared with BM-H3PO4 and reached a maximum of 91%, at a dye concentration of 20 mg/L, solution pH equal to 5, and an ambient temperature of 25 °C. Furthermore, CuO-modified BM-H3PO4 exhibits a better photocatalytic activity than pure CuO in the presence of H2O2 and visible light irradiation, where the dye was completely removed and mineralized after 240 min, evidenced by COD measurement. The photocatalytic regeneration also shows that the biosorption efficiency was maintained at 91% over 3 cycles, indicating the significant self-regenerative capacity of the biosorbent.

Ultrasonic-assisted synthesis of natural clay/Fe3O4/graphene oxide for enhance removal of Cr (VI) from aqueous media

In this study, Fe3O4/graphene oxide (GO)/clay composite was used to remove chromium (VI) ion from aqueous media. The structure and characteristics of the Fe3O4/GO/clay composite were investigated using FT-IR, SEM, EDX/Map, VSM, BET, and XRD analyses. The BET analysis indicated that the specific surface area and mean pore size of the Fe3O4/GO/clay composite were calculated as 61.64 m2/g and 16.2 nm respectively, which indicate that the composite has a mesoporous structure. Also, the VSM analysis showed that the Fe3O4/GO/clay composite has a superparamagnetic property. Moreover, the highest removal efficiency of Cr (VI) from aqueous media was obtained to be 98.84%, which achieved at pH 3, Cr (VI) ion concentration of 10 mg/L, the composite dosage of 1 g/L, contact time of 60 min, and temperature of 25 °C. Furthermore, the kinetic and equilibrium studies showed that the quasi second-order kinetic model and the Langmuir model could better describe the sorption behavior of the clay and the Fe3O4/clay composite, while the behavior of the Fe3O4/GO/clay composite can be better explained by the Freundlich model. Besides, the maximum sorption capacities of the clay, Fe3O4/clay, and Fe3O4/GO/clay composite were obtained to be 49.61, 62.26, and 71.47 mg/g, respectively, which shows that the maximum sorption capacity of the clay increases with improving the surface properties of the clay. Also, the thermodynamic study indicated that the Cr (VI) sorption process was exothermic and spontaneous in nature. In general, the results indicated that the Fe3O4/GO/clay composite was more effective than the clay and the Fe3O4/clay in Cr (VI) ion removal.

Methylene blue adsorption by timbaúva (Enterolobium contortisiliquum)-derived materials

Liquid effluents from various dyeing industries often have a high concentration of dyes that diffuse into river systems and can be toxic and non-degradable in the environment. In this study, the potential of the use of timbaúva seed husks in the preparation of four adsorbents tested in the removal of methylene blue was analyzed: in natura, chemically activated material (q_max = 1.24 ± 0.04 mg g^-1), carbonized (q_max = 1.96 ± 0.03 mg g^-1), and activated carbon (q_max = 1.983 ± 0.04 mg g^-1). The adsorbents were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and CHN elemental analysis to assist in the proposed dye adsorption mechanism in the adsorbents tested. In the adjustment of the kinetic parameters, the pseudo-second order model was predominant by the statistical analysis of the ARE and R². The carbonized samples were better adjusted to Langmuir isotherms. The removal efficiency of the methylene blue dye in aqueous solutions at the concentrations and conditions studied was 86.78%. The coal from the seed husks of timbaúva has shown excellent performance in adsorption of the methylene blue dye and, therefore, can have technological application.

Adsorption of dichromate ions from aqueous solution onto magnetic graphene oxide modified by β-cyclodextrin

In this work, the β-cyclodextrin modified magnetic graphene oxide (β-CD/MGO) composite was fabricated by the in situ co-precipitation method and characterized by Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), and particle size analysis. The adsorption behavior of dichromate ions on the β-CD/MGO was investigated, and the mechanism of adsorption was also studied using FT-IR and XPS. The results from SEM and TEM showed that the graphene oxide (GO) layer became rough, and many fine particles were attached after compounding with ferroferric oxide and β-cyclodextrin. The characterization results of FT-IR and XPS show that that β-cyclodextrin and ferroferric oxide have been perfectly compounded to the graphene oxide layer and β-CD/MGO has a particle size of about 460 nm, a specific surface area of 252.3 m²g^-1, and a saturation magnetization of 73.5 emu g^-1. The adsorption amount of dichromate ions on the β-CD/MGO is affected by pH, adsorbent dosage, and adsorption time. Kinetic studies showed that the adsorption process followed a pseudo-second-order kinetic model. Equilibrium data agreed very well with the Langmuir model, the maximum adsorption amount of dichromate ions on the β-CD/MGO was 49.95 mg g^-1. After five successive adsorbent reuses, the reuse rate is still 73%, indicating the excellent potential reusability of β-CD/MGO adsorbent. β-CD/MGO exhibits excellent adsorption performance for dichromate ions. As an environmentally friendly magnetic adsorbent, β-CD/MGO is suitable for the treatment of dichromate-containing wastewater.

Conversion synthesis of manganese sulfate residue into iron hydroxide adsorbent for Cu(II) removal from aqueous solution

Manganese sulfate residue (MSR) is a by-product derived from the manganese sulfate production process. In this study, an iron hydroxide adsorbent was prepared from MSR using the hydrothermal conversion method. The adsorbent was characterized and used to remove copper(II) ions from aqueous solution. Batch experiments were performed to investigate the adsorption efficiency of copper ions at different contact times, initial concentrations, solution pH levels, and reaction temperatures. Adsorption equilibrium was observed in 3 h, and the best pH was under natural conditions (pH ∼ 5.5). Increasing the initial Cu²⁺ concentration and reaction temperature can increase the adsorption quantity. The adsorption capacity of iron hydroxide at an initial concentration of 50 mg L^-1 was 14.515 mg g^-1 Cu(II) under the conditions of a nature pH and room temperature. According to the adsorption data, the pseudo-second-order model can describe the adsorption kinetics of copper ions well, and the Freundlich model provides an excellent fit to the adsorption isotherm. XRD and FTIR were applied to characterize the raw materials and adsorbents to reveal the adsorption mechanism. The results suggest that the adsorbent converted from MSR is a promising material for the removal of Cu(II) in aqueous solutions.