Zeolite nanoparticle as a superior adsorbent with high capacity: Synthesis, surface modification and pollutant adsorption ability from wastewater

Theory guided engineering of zeolite adsorbents for acaricide residue adsorption from the environment

CONTEXT

Zeolites have attracted attention for their potential in adsorbing environmental contaminants. However, contaminants, such as acaricides used extensively in livestock production to control ticks and mites, have received limited exploration regarding their adsorption onto zeolite surfaces. This study aimed to identify the most appropriate zeolite frameworks for the adsorption of acaricide residues, deduce the mechanism underlying the adsorption process, and evaluate the impact of surface modification on the adsorption capabilities of zeolites.

METHODS

Grand Canonical Monte Carlo (GCMC) was used to screen the entire zeolite database to analyze their adsorption properties, where the cloverite zeolite framework (CLO) exhibits the highest adsorption capacity (percentage weight, 54%). Machine learning was employed to rank structural feature importance on adsorption. Density and helium void fraction appeared to be the most important structural features. Thus, engineering these features is of utmost significance in harvesting the desired acaricides. The second step involved engineering the structural and electronic properties of the shortlisted zeolite frameworks via cation substitution with suitable atoms. DFT calculations involving natural bond orbital (NBO) analysis and quantum theory of atoms in molecules (QTAIM) have been done to understand the influence of cation substitution on the electronic structure.

Heterogeneous MIL-88A on MIL-88B hybrid: A promising eco-friendly hybrid from green synthesis to dual application (Adsorption and photocatalysis) in tetracycline and dyes removal

Herein, the green synthesis of heterogeneous dual functional MIL88A-on-MIL88B hybrids (MIL: Materials InstituteLavoisier) with different amounts of MIL88B compared to MIL88A, including 1:2, 1:1, and 2:1, has been carried out. The photocatalytic degradation of tetracycline and adsorption of tetracycline and dyes (Direct Red 80, Direct Red 23, Acid Blue 92, and Reactive Orange 14) were investigated. Although the ratio of MIL88A-on-MIL88B (1:1) hybrid displayed the best activity, there is a slight difference in the photocatalytic performance of the other mass ratios studied. The result revealed that after 70 min of forming MIL88A on MIL88B, the best pollutant removal performance is obtained. During the limited synthesis time, the lopsided growth of MIL88A on the MIL88B surface limits the formation of sufficient functional groups and new pores between MIL88B as the substrate and MIL88A, which are effective and decisive in the performance. In the photocatalytic studies, the synthesized composite had good compatibility with the zero-order kinetics, and hydroxyl radicals were recognized as the most active species in the photocatalytic reaction. In the adsorption process, the MIL88A-on-MIL88A composite followed pseudo-second-order kinetics and the Langmuir isotherm. Besides, mechanisms such as π-π interaction/stacking, hydrogen bonding, and π-metal interaction were proposed for the pollutant adsorption process.

Impact of graphene oxide on visible light photocatalytic performance of graphene oxide/graphitic carbon nitride three-dimensional structure composites

The non-metallic catalyst graphitic carbon nitride (g-C3N4) has attracted a significant amount of attention due to its excellent photocatalytic performance. The photocatalytic performance of g-C3N4 has been further enhanced by the incorporation of graphene oxide (GO) as a composite catalyst. However, the enrichment and recovery of these two-dimensional composites after photocatalysis is still a difficult challenge. In this work, a visible light responsive graphene oxide/graphitic carbon nitride coated sponge three-dimensional composite (PU-GO/g-C3N4) was prepared by electrostatic self-assembly using polyurethane sponge (PU) as a skeleton and g-C3N4 as a photocatalyst. The degradation rate of rhodamine B (RhB) under visible light was used as an index to evaluate the photocatalytic performance of PU-GO/g-C3N4. The results demonstrate that during the photocatalytic degradation of RhB by PU-GO/g-C3N4, g-C3N4 is the main photocatalyst, while the holes and the superoxide radicals generated by electron excitation are the main agents. As a bridge connecting PU and g-C3N4, GO improves the agglomeration phenomenon of g-C3N4 on PU. Meanwhile, GO has excellent carrier mobility and inhibits the recombination of photogenerated electrons and holes. Moreover, the presence of GO enhances the absorption of light and dyes. Overall, the addition of GO effectively enhances the photocatalytic performance of PU-GO/g-C3N4 due to it enhances dye absorption, improves light energy utilization rate, and expedites transfer of photogenerated electrons. After 5 cycles, PU-GO/g-C3N4 still exhibits an RhB degradation rate of 92.06%, demonstrating good stability and recycling performance. This material shows great promise for practical environmental remediation applications.

Amino-Functionalized Silica@Resorcinol-Formaldehyde Nanocomposites for the Removal of Cr(VI) from Aqueous Solutions

Amino-functionalized silica@resorcinol-formaldehyde nanocomposites (NH2-SiO2@RF) were synthesized for the removal of Cr(VI) from aqueous solutions using the sol-gel technique with two simple preparation steps, including the one-pot synthesis of SiO2@RF using the Stöber method and (3-aminopropyl)triethoxysilane (APTES) modification. The morphology, particle size, functional group, and thermal stability of the obtained nanocomposites were systematically characterized, with the results indicating a uniform sphericity with a particle size of 200 nm and high thermal stability. The adsorption results demonstrated that the preferred pH value was 2, and the data were well fitted with the Langmuir and Temkin isotherm models and quasi-second-order kinetic equation, indicating a high adsorption capacity. The maximum Cr(VI) adsorption capacity from the nonlinear form of the Langmuir model was 272.6 mg·g-1. The intra-particle diffusion model accurately described the adsorption of Cr(VI) onto NH2-SiO2@RF. The changes in Gibb's free energy, enthalpy, and entropy revealed that Cr(VI) adsorption onto NH2-SiO2@RF was a spontaneous and endothermic process. Furthermore, high selectivity was demonstrated in the material for the removal of Cr(VI) from commonly coexisting ions. The obtained nanocomposites had good regeneration properties and maintained a removal rate above 85% in the fifth adsorption-desorption experiments. Moreover, under the optimized adsorption conditions, the obtained nanocomposites were preliminarily applied to tannery wastewater, demonstrating an excellent removal effect, which indicates their potential application value.

Photo-assisted degradation of Rhodamine B by a heterogeneous Fenton-like process: performance and kinetics

This study presents the degradation of rhodamine B (RhB) by photo Fenton-like (PF-like) process under visible light irradiation (λ > 380 nm) using cobalt phosphate microparticles (CoP-MPs). The effects of the initial concentration of RhB, pH value, CoP-MPs dosage, hydrogen peroxide (H2O2) concentration, and salts found in textile wastewater (such as NaNO3, Na2SO4, and NaCl) were investigated in detail. It was found that CoP-MPs can maintain high catalytic activity with wide pH values varying from 4 to 8. This indicated that the use of CoP-MPs overcame the low efficiency of Fenton-like reaction at neutral and even weakly alkaline pH. The PF-like degradation of RhB followed pseudo-first order kinetics in various conditions. Moreover, a comparison of experimental results showed that the PF-like system has good degradation ability for RhB and methyl blue (MB) solution, but is poor for methyl orange (MO) solution. The repeat experiments indicated that the chemical structures of CoP-MPs were stable. Furthermore, the Co2+ ions leaching to the solutions were measured by an inductively coupled plasma mass spectrometer (ICP-MS). Analysis of UV-vis spectra suggested that RhB was degraded by the formation of a series of N-de-ethylated intermediates followed by cleavage of the whole conjugate chromophore structure.HighlightsRhB can be effectively degraded in the PF-like process under visible light irradiation by CoP-MPs.The PF-like process can maintain high catalytic activity at neutral and even weakly alkaline pH.Degradation kinetics exhibited pseudo-first-order kinetics and were influenced by the key parameters.The variation in the UV-vis spectra of RhB was analyzed in detail to infer a possible degradation pathway.

Photocatalytic degradation of a typical macrolide antibiotic roxithromycin using polypropylene fibre sheet supported N-TiO2/graphene oxide composite materials

The post-treatment of recycling the fine photocatalyst nanoparticles restricts their application. In this study, a new photocatalytic material was synthesized by immobilizing the N-doped TiO2 and graphene oxide (GO) composite on polypropylene (PP) (N-TiO2/GO/PP) fibre sheet, and characterized based on X-ray diffraction spectroscopy (XRD), Raman spectroscopy and Scanning Electron Microscope (SEM). The photocatalytic activity was evaluated using roxithromycin (ROX) as a typical antibiotic pollutant. XRD, Raman spectra and SEM images proved that N-TiO2/GO/PP fibre sheet was successfully synthesized. The photocatalytic degradation of 10 mg L-1 ROX can reach up to 90% and the degradation rate constant was 0.2299 h-1 in surface water with the application amount of TiO2/GO/PP fibre sheet of 24.6 cm × 2.7 cm and reaction time of 9 h under the irradiation of simulated sunlight. The application amount of TiO2/GO/PP fibre sheet, initial concentration of ROX and water matrix significantly affect the degradation of ROX. A low concentration of natural organic matter (NOM) slightly promoted the degradation of ROX, while a high concentration of NOM significantly inhibited the degradation of ROX. Alkaline condition (pH 8-9) is favourable for the photocatalytic degradation of ROX by TiO2/GO/PP fibre sheet. The photocatalytic reactivity of the TiO2/GO/PP fibre sheet showed no significant decrease after three runs. Two primary degradation products of ROX were identified and they showed lower ecotoxicity than ROX. The results demonstrate that the new synthesized TiO2/GO/PP fibre sheet shows promising application prospects in the treatment of antibiotics in wastewater and surface waters.

Ionic liquids assisted preparation of BiPO4 photocatalyst with enhanced photocatalytic activity for tetracycline and rhodamine B removal

In this work, BiPO4 (BPO)-based photocatalyst was successfully synthesized by a conventional hydrothermal strategy using bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) and 1-ethyl-3-methylimidazolium dihydro phosphate ([EMIm]H2PO4). [EMIm]H2PO4 can serve as a phosphorus source and surfactant. Photocatalytic activities of the photocatalysts prepared were evaluated by the destruction of rhodamine B (RhB) and tetracycline (TC) under UV light irradiation, respectively. The results reveal that the sample (IL-BPO) synthesized with the assistance of ionic liquid exhibits enhanced photocatalytic activity in comparison with the reference BiPO4. The significantly improved photocatalytic activity of IL-BPO can be mainly attributed to the boosted separation of photoinduced electron-hole pairs (e-/h+) and richer oxygen vacancies (OVs).

Production of Ni0.5Co0.5Fe2O4/activated carbon@chitosan magnetic nanobiocomposite as a novel adsorbent of methylene blue in aqueous solutions

Methylene blue is a cationic dye, not degraded naturally due to its aromatic rings. Accordingly, biological, chemical, and physical water treatment methods have been proposed for its removal. Adsorption is an economical and effective method in this regard. In this study, the nickel-cobalt ferrite/activated carbon@chitosan magnetic nanobiocomposite was synthesized as an adsorbent. The nano-adsorbent was evaluated with FESEM, which estimated the particle size at ~ 16.64 nm. According to EDAX analysis, the purity of particles was 99%. XRD characterization showed the successful coverage of chitosan, correct placement of nickel-cobalt ferrite, and the nono-structure of crystallites. The specific surface area was 316 m²/g using the BET theory and 285 m²/g using the Langmuir theory, and the porosity volume was 0.18 cm³/g. According to the VSM analysis, magnetic reluctance and coercive force were 1.1 emu/g and 499 Oe, respectively. The FTIR analysis showed that the reaction was successful, and methylene blue was present on the adsorbent surface. The methylene blue adsorption test indicated that 388 mg/g of the dye was adsorbed (97% dye removal), and the final concentration reached 6 mg/L after 8 h. The point of zero charge (pHpzc) was 6.8.

Mesoporous calcium hydroxide nanoparticle synthesis from waste bivalve clamshells and evaluation of its adsorptive potential for the removal of Acid Blue 113 dye

Calcium hydroxide nanoadsorbent was prepared from waste bivalve clamshells and used for the adsorptive removal of Acid Blue 113 (AB113) dye. The morphology, elemental nature, functional groups, and thermal stability of the nanoadsorbent were characterized by various methods. The nanoadsorbent had a high monolayer adsorption capacity (153.53 mg/g) for AB113 dye. Langmuir and Temkin isotherms better fitted (R² > 0.95) the experimental data. The adsorption rate followed pseudo-second-order kinetics (R² > 0.99). The thermodynamic study ascertained spontaneous and exothermic adsorption. This study confirmed the possibility of using calcium hydroxide as an adsorbent to effectively remove AB113 dye from aqueous solutions.

Application of ZIF-8 nanocomposite membrane in microbial desalination cells for simultaneous heavy metal removal and biofouling prevention

Microbial desalination cells (MDC) syndicate the advantage of physical separation by using membranes to create conditions required for Bioelectrochemical processes for the treatment of various domestic and industrial wastewater, while simultaneously desalinating saline water and generating bioenergy. However, since the introduction of this technology, heavy metal removal has been a challenge, and membrane fouling has become a major bottleneck limiting the optimum performance and efficiency of this technology. This study incorporated the use of ZIF-8 nanocomposite membrane via phase inversion mechanism in MDC for simultaneous heavy metal removal and membrane biofouling prevention. The study was conducted in two MDC systems; MDC-Control (without the ZIF-8 nanocomposite membrane) and MDC with ZIF-8 nanocomposite membrane. The results from the experiment shown that maximum removal efficiency of 85.7%, 84.3%, 84.0%, and 90.61% was obtained for Cu²⁺, Zn²⁺, Pb^2+, and Cd²⁺ respectively in MDC-ZIF-8, while MDC control showed 54.17%, 59.71%, 51.94%, and 54.17%. The results were well fitted to the Langmuir adsorption isotherm with correlation coefficients (R²) > 0.99 in all cases for MDC-ZIF-8. A maximum adsorption capacity (Q_max) of 292 mg g^-1 was attained for all four metal ions in MDC-ZIF-8. Besides, after 38 days of continuous operation with two complete desalination for both systems, the SEM-EDS characterization analysis, polarization characteristics, and power generation revealed antifouling characteristics of ZIF-8 nanocomposite membrane incorporated in MDC. The integration of the ZIF-8 nanocomposite membrane proved to be simultaneously efficient in biofouling prevention and heavy metal removal without jeopardizing the system's ability for wastewater treatment, bioelectricity generation, and desalination processes.

Nanomaterials in membrane bioreactors: Recent progresses, challenges, and potentials

The use of nanomaterials (NMs) in the fabrication and modification of membranes as well as the coupling of nanomaterial-based processes with membrane processes have been attracted many researchers today. The NMs due to a wide range of types, different chemistry, the possibility of various kinds of functionality, different properties like antibacterial activity, hydrophilicity, and large surface area were applied to enhance the membrane properties. In the membrane bioreactors (MBRs) as a highly successful process of membrane technology in wastewater treatment, the NMs have been applied for improving the efficiency of MBR process. This review assessed the application of NMs both as the modifiers of membrane and as the effective part of hybrid techniques with MBR system for wastewater treatment. The efficiency of NMs blended membranes in the MBR process has been reviewed in terms of antifouling and antibacterial improvement and removal performance of the pollutants. Novel kinds of NMs were recognized and discussed based on their properties and advantages. The NMs-based photocatalytic and electrochemical processes integrated with MBR were reviewed with their benefits and drawbacks. In addition, the effect of the presence of mobilized NPs in the sludge on MBR performance was surveyed. As a result of this review, it can be concluded that nanomaterials generally improve MBR performance. The high flux and antifouling properties can be obtained by adding nanomaterials with hydrophilic and antibacterial properties to the membrane, and further studies are required for photocatalytic NMs applications. In addition, this review shows that the low amounts of NMs in the membrane structure could have an effective influence on the MBR process. Besides, since many studies in the literature are carried out at the laboratory scale, it is thought that pilot and real-scale studies should be carried out to obtain more reliable data.

Mesoporous crosslinked chitosan-activated clinoptilolite biocomposite for the removal of anionic and cationic dyes

A mesoporous crosslinked chitosan-activated clinoptilolite biocomposite (CS-GA/ACP) was prepared with chitosan (CS) as the substrate and glutaraldehyde (GA) as the crosslinking agent. Structural analysis of the CS-GA/ACP composite beads was performed using FTIR, SEM, and BET techniques. The adsorption properties of the CS-GA/ACP for Congo red (CR) and methylene blue (MB) removal were examined using a batch method. The effects of CS loading, CS-GA/ACP dosages (0.005-0.25 g), pH values (3-11), initial concentrations (30-300 mg/L), contact time (5-120 min), ionic strength, and temperatures (25-65 ℃) on the adsorption of CR and MB on the CS-GA/ACP composite beads were investigated. The pseudo-second-order kinetics could better describe the adsorption process than the pseudo-first-order kinetics, and the Langmuir isotherms model agreed well with the experimental data. The maximum adsorption capacities of the CS-GA/ACP for CR and MB were 180.59 mg/g and 143.67 mg/g at 25 ℃, respectively. The proposed mechanism studies showed that the possible interaction between the adsorbent and dye molecules were Yoshida H-bonding, dipole-dipole H-bonding, electrostatic interaction and n-π interaction. The CS-GA/ACP can be recycled to remove dyes without significant loss of efficacy, and the adsorption of dyes on the CS-GA/ACP is spontaneous endothermic adsorption. Overall, the CS-GA/ACP showed an excellent performance for dyes removal in aqueous solution and could be a practical candidate for industrial applications.

Facile method to synthesize fluorescent chitosan hydrogels for selective detection and adsorption of Hg2+/Hg. Carbohydr Polym 2022;288:119417. [PMID: 35450660 DOI: 10.1016/j.carbpol.2022.119417]

Fluorescent chitosan-based hydrogel for the selective detection and adsorption of Hg²⁺/Hg⁺ in aqueous environment was prepared through three-step synthesis strategy. NO₂-Boron-dipyrrolemethene (BODIPY) was prepared firstly, and then the -NO₂ group was reduced to -NH₂ group. Finally, the NH₂-BODIPY was introduced to chitosan by Schiff base formation reaction through bi-aldehyde. Eventually, fluorescent chitosan hydrogel was obtained. The as-prepared fluorescent hydrogel probe could detect Hg²⁺/Hg⁺ through PET mechanism with the detection limit of 0.3 μM. The recognition site which combines Hg²⁺/Hg⁺ is CN, it is just formed in the reaction with chitosan and the amino group on BODIPY. Adsorption capacity of the fluorescent hydrogel is 121 mg·g^-1, which is almost seven times of the original chitosan. The isotherm and kinetics of Hg²⁺/Hg⁺ removal follows Langmuir isotherm and pseudo-second order kinetics, respectively. Besides, a series of fluorescent hydrogels were prepared to compare the elasticity, hydropHilicity, fluorescence intensity and adsorption capacity.

Dynamics of Adsorption of Copper Ions in Fixed-Bed Column and Mathematical Interpretation of the First Stage of the Process

The dynamics of the adsorption process in the fixed-bed column was experimentally studied on the example of the system natural zeolite - water solution of copper salt with low concentrations, which are characteristic for wastewater treatment processes from toxic contaminants. The initial curves of the adsorption process for the height of the sorbent layer of 5 and 7 cm were constructed. The equilibrium of such processes can be described by Henry's linear equation. The adsorption process in the layer consists of two stages, which are examined in the study. The first stage is the formation of concentration front and the second one – its moving. The sum of the time of the first and second stages is the total adsorption time, which is determined before breakthrough time. The first stage of adsorption is mathematically formulated by the differential equation of molecular diffusion with a boundary condition of the first type. The second stage is supplemented by the balance equation, which takes into account not only the change of concentration in time, but also in the vertical coordinate and determines the time of movement of concentration front to breakthrough time. A mathematical model of the adsorption process in a fixed-bed column has been developed. Experimental data and theoretical calculations were compared. The results of statistical calculation of research results showed a satisfactory convergence of experimental and theoretical data.

Application of Attapulgite Clay-Based Fe-Zeolite 5A in UV-Assisted Catalytic Ozonation for the Removal of Ciprofloxacin

For the first time, Fe-zeolite 5A (Fe-Z5A) efficacy in the UV-assisted ozonation process to remove ciprofloxacin (CF) in wastewater is investigated. FTIR, SEM, EDX, BET, and the mass transfer process for point of zero charge are used to characterize the catalyst. Furthermore, the synergic process (UV/O3/Fe-Z5A) is compared with O3, O3/UV, and Fe-Z5A/O3 processes. The influence of catalyst dose, hydroxyl radical scavenger, and off-gas ozone released is discussed. The removal efficiency of CF in wastewater (for the synergic process) is compared with a single ozonation process. The results indicate that the synergic process was more efficient than others, with about 73% CF being removed (in 60 minutes) in the synergic process. The results also show that synergic processes produce less off-gas ozone than other processes, suggesting more ozone consumption in the synergic process, and confirmed by the radical scavenger effect and hydrogen peroxide decomposition studies. The Fe-Z5A was found to operate through a hydroxyl mechanism in which Fe worked as an active site that promotes the formation of hydroxyl radicals. Finally, the synergic process was more efficient than the ozonation process in the wastewater matrix. Hence, Fe-Z5A/O3/UV pathway is highly efficient for the degradation of pharmaceuticals in wastewater.

Green route for recycling of low-cost waste resources for the biosynthesis of nanoparticles (NPs) and nanomaterials (NMs)-A review

Nowadays, nanoparticles (NPs) and nanomaterials (NMs) are used extensively in various streams such as medical science, solar energy, drug delivery, water treatment, and detection of persistent pollutants. Intensive synthesis of NPs/NMs carried out via physico-chemical technologies is deteriorating the environment globally. Therefore, an urgent need to adopt cost-effective and green technologies to synthesize NPs/NMs by recycling of secondary waste resources is highly required. Environmental wastes such as metallurgical slag, electronics (e-waste), and acid mine drainage (AMD) are rich sources of metals to produce NPs. This concept can remediate the environment on the one hand and the other hand, it can provide a future roadmap for economic benefits at industrial scale operations. The waste-derived NPs will reduce the industrial consumption of limited primary resources. In this review article, green emerging technologies involving lignocellulosic waste to synthesize the NPs from the waste streams and the role of potential microorganisms such as microalgae, fungi, yeast, bacteria for the synthesis of NPs have been discussed. A critical insight is also given on use of recycling technologies and the incorporation of NMs in the membrane bioreactors (MBRs) to improve membrane functioning and process performance. Finally, this study aims to mitigate various persisting scientific and technological challenges for the safe disposal and recycling of organic and inorganic waste for future use in the circular economy.

Removal of aqueous pharmaceuticals by magnetically functionalized Zr-MOFs: Adsorption Kinetics, Isotherms, and regeneration

The functionalization of metal-organic frameworks (MOFs) is imperative and challenging for the development of practical MOF-based materials. Herein, a magnetically functionalized Zr-MOF (Fe₃O₄@MOF-525) was synthesized via secondary-growth approach to obtain an easily-separated and recyclable adsorbent for the removal of pharmaceuticals (tetracycline (TC) and diclofenac sodium (DF)). After loading Fe₃O₄ nanoparticles (NPs), due to the increase of micropore volume and specific surface area caused by defects, the adsorption performance of Fe₃O₄@MOF-525 was improved. The kinetics could be described by the pseudo-second-order kinetic model. The different adsorption capacity and initial rate were attributed to the properties of the pharmaceuticals, including the molecular size and hydrophobicity/hydrophilicity. In isotherm experiments, the maximum adsorption capacities of DF and TC on Fe₃O₄@MOF-525 calculated by Sips model reached 745 and 277 mg·g^-1, respectively. The thermodynamic studies indicated the adsorption was endothermic and spontaneous. The effect of pH suggested that electrostatic interaction, π-π interaction, anion-π interaction, and H-bonding were possibly involved in the adsorption process. The adsorbent was separated by magnetic and regenerated. Washed with ethanol, Fe₃O₄@MOF-525 remained about 80% adsorption capacity after four cycles. In-situ photo-regeneration under visible-light irradiation was another attractive method, where > 95% TC was degraded in 4 h. The reaction with scavengers revealed that ¹O₂ was the dominant reactive species in our system, indicating the occurrence of Type II photosensitization. The separability, excellent adsorption performance, and recyclability of Fe₃O₄@MOF-525 may lead to its beneficial applications in water treatment.

Cellulose Nanofiber-Based Aerogels from Wheat Straw: Influence of Surface Load and Lignin Content on Their Properties and Dye Removal Capacity

Water pollution is one of the most serious problems worldwide. Nanocellulose-based aerogels usually show excellent adsorption capacities due to their high aspect ratio, specific surface area and surface charge, making them ideal for water purification. In this work, (ligno)cellulose nanofibers (LCNFs/CNFs) from wheat straw residues were obtained using two types of pre-treatments: mechanical (Mec) and TEMPO-mediated oxidization (TO), to obtain different consistency (0.2, 0.4, 0.6 and 0.8) bioaerogels, and their adsorption capacities as dye removers were further studied. The materials were characterized in terms of density, porosity and mechanical properties. An inversely proportional relationship was observed between the consistencies of the aerogels and their achieved densities. Despite the increase in density, all samples showed porosities above 99%. In terms of mechanical properties, the best results were obtained for the 0.8% consistency LCNF and CNF-Mec aerogels, reaching 67.87 kPa and 64.6 kPa for tensile strength and Young’s modulus, respectively. In contrast, the adsorption capacity of the aerogels was better for TEMPO-oxidized aerogels, reaching removal rates of almost 100% for the CNF-TO5 samples. Furthermore, the residual lignin content in LCNF-Mec aerogels showed a great improvement in the removal capacity, reaching rates higher than 80%, further improving the cost efficiency of the samples due to the reduction in chemical treatments.

Emerging novel polymeric adsorbents for removing dyes from wastewater: A comprehensive review and comparison with other adsorbents

Dye molecules are one of the most hazardous compounds for human and animal health and the excess intake of these materials can create toxic impacts. Several studies show the practicality of the adsorption process for dye uptake from wastewaters. In recent years, various adsorbents were used to be efficient in this process. Among all, polymeric adsorbents demonstrate great applicability in different environmental conditions and attract many researchers to work on them, although there is not enough reliable and precise information regarding these adsorbents. This study aims to investigate some influential parameters such as their type, physical properties, experimental conditions, their capacity, and further modeling along with a comparison with non-polymeric adsorbents. The influence of the main factors of adsorption capacity was studied and the dominant mechanism is explained extensively.

Utilization of red mud waste into mesoporous ZSM-5 for methylene blue adsorption-desorption studies

Red mud as industrial waste from bauxite was utilized as a precursor for the synthesis of mesoporous ZSM-5. A high concentration of iron oxide in red mud was successfully removed using alkali fusion treatment. Mesoporous ZSM-5 was synthesized using cetyltrimethylammonium bromide (CTABr) as a template via dual-hydrothermal method, and the effect of crystallization time was investigated towards the formation of mesopores. Characterization using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption-desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) indicated the formation of cubic crystallite ZSM-5 with high surface area and mesopore volume within 6 h of crystallization. Increasing the crystallization time revealed the evolution of highly crystalline ZSM-5; however, the surface area and mesoporosity were significantly reduced. The effect of mesoporosity was investigated on the adsorption of methylene blue (MB). Kinetic and thermodynamic analysis of MB adsorption on mesoporous ZSM-5 was carried out at a variation of adsorption parameters such as the concentration of MB solution, the temperatures of solution, and the amount of adsorbent. Finally, methanol, 1-butanol, acetone, hydrochloric acid (HCl), and acetonitrile were used as desorbing agents to investigate the reusability and stability of mesoporous ZSM-5 as an adsorbent for MB removal.

The Potential Use of Zeolite, Montmorillonite, and Biochar for the Removal of Radium-226 from Aqueous Solutions and Contaminated Groundwater

The present work investigated the potential of using zeolite (clinoptilolite), montmorillonite (Swy2), and Conocarpus biochar as adsorbents to remove 226Ra from aqueous solution. The effect of the initial 226Ra concentrations on sorbents’ equilibrium activity concentrations and sorbents’ radium removal efficiency were investigated. The results showed that zeolite has a higher removal efficiency for 226Ra in comparison with the efficiencies of montmorillonite and biochar. In addition to the linear isotherm model, the Freundlich model, followed by Temkin’s model, provided a better description of the adsorption process than the Langmuir model. Kinetic studies indicated that a pseudo-second-order kinetic model could be the best fit for the adsorption of 226Ra onto the three investigated sorbents, which suggests that the mechanism of adsorption of 226Ra by sorbents was chemisorption. The intraparticle diffusion model indicated that adsorption of 226Ra onto the sorbents involves a multistep process: (i) boundary layer diffusion and (ii) intraparticle diffusion. Moreover, the remediation of groundwater samples polluted with 226Ra was assessed using the investigated sorbents; the results showed that zeolite also has the highest removal efficiency among other sorbents. Thus, the low cost, availability, and the high adsorption efficiency of zeolite can be a promising sorbent on 226Ra removal from aqueous solutions and groundwater remediation.

Eco-Efficient Green Seaweed Codium decorticatum Biosorbent for Textile Dyes: Characterization, Mechanism, Recyclability, and RSM Optimization

Biosorption using natural waste has emerged as a potential and promising strategy for removal of toxic dyes from wastewaters in comparison to conventional ones. Herein, the Codium decorticatum alga (CDA) was biologically identified and used as a biosorbent for anionic and cationic dyes from aqueous solutions. SEM analysis showed a rough surface with an irregular edge and shape while hydroxyl, amine, sulfur and carboxyl functional groups were identified using FTIR analysis. TGA/DTG confirmed the stability of CDA and the adsorption process. Batch studies were conducted to investigate the effect of operational factors such as initial pH, biosorbent dosage, temperature, initial concentration, and solid/liquid contact time on the biosorption of crystal violet (CV) and Congo red (CR) dyes. For both CV and CR dyes, the biosorption kinetics was accurately described by the pseudo-second-order model and the Langmuir isotherm was found to be best fitted for equilibrium data. Maximum uptake capacities have attained up to 278.46 mg/g for CV and 191.01 mg/g for CR. The CV and CR dye biosorption mechanism was ultimately manifested through the electrostatic interactions. The regeneration study showed that the CDA presents excellent reuse performance up to four consecutive cycles. The process optimization was performed using the response surface methodology based on Box-Behnken design (RSM-BDD). Accordingly, the optimum predicted removal efficiencies using RSM-BBD for CV and CR were obtained, respectively, at 96.9 and 89.8% using a CDA dose of 1.5 g/L, dye concentration of 20 mg/L, pH of 10 for CV, and pH of 4 for CR. Overall, CDA behaves as an efficient, recyclable, cheap, and eco-friendly adsorbent for cleaning-up of dyed effluents.

Ammonium removal using a calcined natural zeolite modified with sodium nitrate

Ammonium is one of the key factors responsible for the eutrophication of water bodies. The purpose of this study was to remove ammonium from water using a natural zeolite (NZ) modified with sodium nitrate (NaNO₃) by impregnation and calcination. The ability of the NZ to remove ammonium from water was determined by single calcination; however, its efficiency was significantly enhanced by impregnation with a NaNO₃ solution. Zeolite modified with 3.00 M NaNO₃ and calcination at 673 K yielded the best ammonium removal efficiency, which was 39.88 % higher than the NZ alone. The zeolites that were regenerated over six times maintained a removal rate of 79.35-84.79 % by mixing 25.0 mg of the NZ into 50 mL of a 5.0 mg/L ammonium solution. The improved performance of the modified zeolite (q_m, 16.96 mg/g) was mainly attributed to its relatively elevated mesopore volumes and higher ion-exchange capacity that results from nitrate decomposition, oxygen release, and sodium-ion exchange. The adsorption kinetics and isotherms are best described by the pseudo-first-order (PFO) and Freundlich model, respectively, and the process was endothermic. The effects of other factors, including coexisting ions, pH, and dosage, on ammonium adsorption were also determined.

Phosphoric Acid Activated Carbon from Melia azedarach Waste Sawdust for Adsorptive Removal of Reactive Orange 16: Equilibrium Modelling and Thermodynamic Analysis

Waste wood biomass as precursor for manufacturing activated carbon (AC) can provide a solution to ever increasing global water quality concerns. In our current work, Melia azedarach derived phosphoric acid-treated AC (MA-AC400) was manufactured at a laboratory scale. This novel MA-AC400 was tested for RO16 dye removal performance as a function of contact time, adsorbent dosage, pH, temperature and initial dye concentration in a batch scale arrangement. MA-AC400 was characterized via scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering (DLS) and fluorescence spectroscopy. MA-AC400 is characterized as mesoporous with BET surface area of 293.13 m² g^-1 and average pore width of 20.33 Å. pH_PZC and Boehm titration confirm the acidic surface charges with dominance of phenolic functional groups. The average DLS particle size of MA-AC400 was found in the narrow range of 0.12 to 0.30 µm and this polydispersity was confirmed with multiple excitation fluorescence wavelengths. MA-AC400 showed equilibrium adsorption efficiency of 97.8% for RO16 dye at its initial concentration of 30 mg L^-1 and adsorbent dose of 1 g L^-1. Thermodynamic study endorsed the spontaneous, favorable, irreversible and exothermic process for RO16 adsorption onto MA-AC400. Equilibrium adsorption data was better explained by Langmuir with high goodness of fit (R², 0.9964) and this fitness was endorsed with lower error functions. The kinetics data was found well fitted to pseudo-second order (PSO), and intra-particle diffusion kinetic models. Increasing diffusion constant values confirm the intraparticle diffusion at higher RO16 initial concentration and reverse was true for PSO chemisorption kinetics. MA-AC400 exhibited low desorption with studied eluents and its cost was calculated to be $8.36/kg.