Adsorption of arsenic onto films based on chitosan and chitosan/nano-iron oxide

Research progress on environmental behavior of arsenic in Qinghai-Tibet Plateau soil

The Qinghai-Tibet Plateau, with its high altitude and cold climate, is one of the most fragile ecological environments in China and is distinguished by its naturally elevated arsenic (As) levels in the soil, largely due to its rich mineral and geothermal resources. This review provides a comprehensive analysis of As content, focusing on its distribution, environmental migration, and transformation behavior across the plateau. The review further evaluates the distribution of As in different functional areas, revealing that geothermal fields (107.2 mg/kg), mining areas (53.8 mg/kg), and croplands (39.3 mg/kg) have the highest As concentrations, followed by river and lake sediments and adjacent areas (33.1 mg/kg). These elevated levels are primarily attributed to the presence of As-rich minerals, such as arsenopyrite and pyrite. Additionally, human activities, including mining and geothermal energy production, exacerbate the release of As into the environment. The review also highlights the role of local microorganisms, particularly those from the phyla Proteobacteria and Actinobacteria, which possess As metabolic genes that facilitate As translocation. Given the unique climatic conditions of the plateau, conventional methods for As control may not be fully effective. However, the review identifies promising remediation strategies that are environmentally adaptable, such as the use of local microorganisms, specific adsorbents, and integrated technologies, which offer potential solutions for managing and utilizing As-contaminated soils on the plateau.

Preparation of ultra-light, highly compressible, and biodegradable chitosan porous materials for heavy metal adsorption, dye adsorption and oil-water separation

Chitosan materials are much important in adsorption, separation and water treatment due to their hydrophilicity, biodegradability and easy functionalization. However, they were difficult to form structural materials, which limited its application in engineering. In this paper, a new type of chitosan porous materials was prepared with two-step strategy involving the freezing crosslinking of chitosan with glutaraldehyde to form cryogels, and their subsequent reduction with NaBH4 to transform CN bonds into CN bonds, resulting in remarkable improvement of mechanical property. That is, the strength remained almost unchanged after 80 % deformation. The abundant -NH2 and -OH on the surface of materials, as well as the unique pore structure from cryogels, gave relatively high adsorption capacity for metals and dyes (88.73 ± 4.25 mg·g-1 for Cu(II) and 3261.05 ± 36.10 mg·g-1 for Congo red). The surface hydrophilicity of materials made it possible for selective water permeation with over 95 % separation efficiency for oil-water mixtures. In addition, simple hydrophobic modification using bromotetradecane achieved selective oil permeation with over 96 % separation efficiency for oil-water mixtures. This study not only provides a new strategy to endow chitosan materials with excellent mechanical property, large adsorption capacity and good oil-water separation performance, but also offers environmentally friendly materials for sewage treatment applications.

Green synthesis of graphene oxide and magnetite nanoparticles and their arsenic removal efficiency from arsenic contaminated soil

Graphene-based nanomaterials have been proved to be robust sorbents for efficient removal of environmental contaminants including arsenic (As). Biobased graphene oxide (bGO-P) derived from sugarcane bagasse via pyrolysis, GO-C via chemical exfoliation, and magnetite nanoparticles (FeNPs) via green approach using Azadirachta indica leaf extract were synthesized and characterized by Ultraviolet-Visible Spectrophotometer (UV-vis.), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), mean particle size and Scanning electron microscopy (SEM) along with Energy dispersive spectroscopy (EDX) analysis. Compared to cellulose and hemicellulose, the lignin fraction was less in the precursor material. The GOC, bGO-P and FeNPs displayed maximum absorption at 230, 236, and 374 nm, respectively. FTIR spectrum showed different functional groups (C-OH, C-O-C, COOH and O-H) modifying the surfaces of synthesized materials. Graphene based nanomaterials showed clustered dense flakes of GO-C and thin transparent flakes of bGO-P. Elemental composition by EDX analysis of GO-C (71.26% C and 27.36% O), bGO-P (74.54% C and 24.61% O) and FeNPs (55.61% Fe, 4.1% C and 35.72% O) confirmed the presence of carbon, oxygen, and iron in synthesized nanomaterials. Sorption study was conducted with soil amended with different doses of synthesized nanomaterials (10, 50 and 250 mg) and exposed to 100, 300 and 500 ppm of As. Arsenic concentrations were estimated by colorimetry and atomic absorption spectroscopy (AAS). GO-C, bGO-P, and FeNPs showed substantial As removal efficiency i.e., 81 to 99.3%, 65 to 98.8% and 73.1-89.9%, respectively. Green synthesis of bGO-P and magnetite nanoparticles removed substantial amounts of As compared to GO-C and can be effectively deployed for As removal or immobilization. Higher and medium sorbent doses (250 and 50 mg) exhibited greater As removal and data was best fitted for Freundlich isotherm evidencing favorable sorption. Nevertheless, at low sorbent doses, data was best fitted for both models. Newly synthesized nanomaterials emerged as promising materials for As removal strategy for soil nano-remediation and can be effectively deployed in As contaminated soils.

Preparation of silver-based metal-organic framework and chitosan hybrid material for removing drug and dye

Pharmaceuticals and personal care products and dyes have low biodegradability and high toxicity, seriously threaten the human health and ecological environment. Therefore, seeking effective removal methods has become the focus of research. In this study, silver-based metal-organic framework (Ag-MOF) and chitosan (CS) hybrid adsorbent (Ag-MOF-CS) was synthesized via solvothermal one-pot synthesis to remove diclofenac sodium (DCF) and acid Red 1 (AR1) from water for the first time. The morphology and structure of Ag-MOF-CS were confirmed by various characterizations. The effect on adsorption was investigated by changing the adsorbent dosage, pH and other conditions. The adsorption kinetics, adsorption isotherms and thermodynamics were analyzed. Ag-MOF-CS showed a high adsorption capacity. And the maximum adsorption capacity of Ag-MOF-CS for DCF and AR1 was 351.75 mg/g and 678.83 mg/g, respectively. The adsorbent bound to DCF and AR1 may via electrostatic forces, π-π interactions, hydrogen bonding. Even after four cycles of Ag-MOF-CS, the DCF removal can still be higher than 80 %. The eco-friendly Ag-MOF-CS demonstrated significant potential for utilization in treating wastewater.

Critical assessment of recent advancements in chitosan-functionalized iron and geopolymer-based adsorbents for the selective removal of arsenic from water

Inorganic arsenic (As), a known carcinogen and major contaminant in drinking water, affects over 140 million people globally, with levels exceeding the World Health Organization's (WHO) guidelines of 10 μg L-1. Developing innovative technologies for effluent handling and decontaminating polluted water is critical. This paper summarizes the fundamental characteristics of chitosan-embedded composites for As adsorption from water. The primary challenge in selectively removing As ions is the presence of phosphate, which is chemically similar to As(V). This study evaluates and summarizes innovative As adsorbents based on chitosan and its composite modifications, focusing on factors influencing their adsorption affinity. The kinetics, isotherms, column models, and thermodynamic aspects of the sorption processes were also explored. Finally, the adsorption process and implications of functionalized chitosan for wastewater treatment were analyzed. There have been minimal developments in water disinfection using metal-biopolymer composites for environmental purposes. This field of study offers numerous research opportunities to expand the use of biopolymer composites as detoxifying materials and to gain deeper insights into the foundations of biopolymer composite adsorbents, which merit further investigation to enhance adsorbent stability.

Lanthanum-calcium bimetallic-modified attapulgite- chitosan hydrogel beads for efficient phosphate removal from water: Performance evaluation, mechanistic and life cycle assessment

Phosphorus is a critical factor in the control of eutrophication. We developed a three-dimensional porous, bimetallic-modified adsorbent La-Ca-CS/ATP to remove excess phosphate from water. Langmuir model showed that the theoretical adsorption capacity of La-Ca-CS/ATP was up to 123 mg P/g. The amount of La and Ca leached by La-Ca-CS/ATP was small, and the adsorption of 36.08 mg P/g was maintained during the five cycles of La-Ca-CS/ATP. The La-Ca-CS/ATP adsorption mechanism mainly involved surface precipitation, ligand exchange, electrostatic attraction, and inner-sphere complexation. Molecular dynamics demonstrated that La and Ca had complementary effects on binding sites and energy barriers within the range of 0.5-0.7 nm and 1.2-2 nm, enhancing the adsorption effect of La-Ca-CS/ATP. The life cycle assessment results showed that adding calcium could help reduce the environmental impact of lanthanum and chitosan. The production of La-Ca-CS/ATP adsorbed 73.88 P mg/g and emitted 24.73 kg CO2 eq, which was less than other adsorbents.

Adsorption Study of Neodymium from the Aqueous Phase Using Fabricated Magnetic Chitosan-Functionalized Graphene Oxide Composites

This work reports the performances of the magnetic chitosan@graphene oxide composite (MCh@GO) for the sorption of Nd(III) from aqueous medium. The prepared composite was synthesized by a coprecipitation method and then examined by FT-IR, XRD, SEM, and TGA. XRD analysis proved physical interactions between magnetic chitosan and graphene oxide through (inter- and intramolecular H-bonding and peptide bonding). TGA data approved the thermal stability of the prepared MCh@GO nanocomposite over their constituents. The optimum pH for the sorption process was 4.5. The Langmuir model and PSO fitted the experimental data. The adsorption process was found to be endothermic and spontaneous with a Q max of 56.6 mg g-1. Indeed, the MCh@GO composite proved to be an excellent adsorbent for the purification, remediation, and separation of Nd due to its promising properties.

Advanced technologies in water treatment: Chitosan and its modifications as effective agents in the adsorption of contaminants

Chitosan, derived from the abundant biopolymer chitin, has emerged as a promising option for water treatment due to its intrinsic bioavailability. This review emphasizes the notable characteristics of chitosan, which allow for various modifications, expanding its applications. The polymer's effectiveness in adsorbing contaminants, particularly in advanced water treatment technologies, is highlighted. The review underscores the potential of chitosan-based hybrid materials, including nanocomposites, hydrogels, membranes, films, sponges, nanoparticles, microspheres, and flakes, as innovative alternatives to traditional chemical-based adsorbents. The advantages of using these materials in wastewater treatment, especially in removing heavy metals, dyes, and emerging compounds, are explored. The study delves into the mechanisms involved in wastewater treatment with chitosan, emphasizing the interactions between the polymer and various contaminants. Additionally, the application of chitosan as a contaminant removal agent in a post-pandemic context is addressed, considering the challenges related to waste management and environmental preservation. The analysis highlights the potential contribution of chitosan in mitigating environmental impacts post-pandemic, offering practical solutions for treating contaminated effluents and promoting sustainability. The study addresses current obstacles and prospects for chitosan-based wastewater treatment, emphasizing its promising role in sustainable water management.

Recent advances in chitosan-based nanocomposites for adsorption and removal of heavy metal ions

Due to the high concentration of various toxic and dangerous pollutants, industrial effluents have imposed increasing threats. Among the various processes for wastewater treatment, adsorption is widely used due to its simplicity, good treatment efficiency, availability of a wide range of adsorbents, and cost-effectiveness. Chitosan (CS) has received great attention as a pollutant adsorbent due to its low cost and many -OH and -NH2 functional groups that can bind heavy metal ions. However, weaknesses such as sensitivity to pH, low thermal stability and low mechanical strength, limit the application of CS in wastewater treatment. The modification of these functional groups can improve its performance via cross-linking and grafting agents. The porosity and specific surface area of CS in powder form are not ideal, so physical modification of CS via integration with other materials (e.g., metal oxide, zeolite, clay, etc.) leads to the creation of composite materials with improved absorption performance. This review provides reports on the application of CS and its nanocomposites (NCs) for the removal of various heavy metal ions. Synthesis strategy, adsorption mechanism and influencing factors on sorbents for heavy metals are discussed in detail.

Static and dynamic adsorption of arsenate from water by Fe3+ complexed with 3-aminopropyltriethoxysilane-modified carboxymethyl chitosan

Fe3+ complexed with 3-aminopropyltriethoxysilane (APTES)-modified carboxymethyl chitosan (CMC) named Fe-ACMC was synthesized by a one-step method at room temperature and pressure. The surface morphology and chemical structure of Fe-ACMC were characterized by SEM-EDS, XRD, BET, FT-IR, XPS, and ζ-potential. In batch adsorption, the optimum pH for arsenate [As(V)] adsorption onto Fe-ACMC was 3-9 with removal efficiency > 99%. The adsorption of As(V) could reach equilibrium within 25 min and the maximum adsorption capacity was 84.18 mg g-1. The pseudo-second-order model fitted well the kinetic data (R2 = 0.995), while the Freundlich model well described the adsorption isotherm of As(V) on Fe-ACMC (R2 = 0.979). The co-existing anions (NO3-, CO32-, and SO42-) exhibited a slight impact on the As(V) adsorption efficiency, whereas PO43- inhibited As(V) adsorption on Fe-ACMC. The real applicability of Fe-ACMC was achieved to remove ca. 10.0 mg L-1 of As(V) from natural waters to below 0.05 mg L-1. The regeneration and reuse of Fe-ACMC for As(V) adsorption were achieved by adding 0.2 mol L-1 HCl. The main adsorption mechanism of As(V) on Fe-ACMC was attributed to electrostatic attraction and inner-sphere complexation between -NH2···Fe3+ and As(V). In fixed-bed column adsorption, the Thomas model was the most suitable model to elucidate the dynamic adsorption behavior of As(V). The loading capacity of the Fe-ACMC packed column for As(V) was 47.04 mg g-1 at pH 7 with an initial concentration of 60 mg L-1, flow rate of 3 mL min-1, and bed height of 0.6 cm.

Enhancing cationic dye removal via biocomposite formation between chitosan and food grade algae: Optimization of algae loading and adsorption parameters

Herein, a natural material including chitosan (CTS) and algae (food-grade algae, FGA) was exploited to attain a bio-adsorbent (CTS/FGA) for enhanced methyl violet 2B dye removal. A study of the FGA loading into CTS matrix showed that the best mixing ratio between CTS and FGA to be used for the MV 2B removal was 50 %:50 % (CTS/FGA; 50:50 w/w). The present study employed the Box-Behnken design (RSM-BBD) to investigate the impact of three processing factors, namely CTS/FGA-(50:50) dose (0.02-0.1 g/100 mL), pH of solution (4-10), and contact time (5-15 min) on the decolorization rate of MV 2B dye. The results obtained from the equilibrium and kinetic experiments indicate that the adsorption of MV 2B dye on CTS/FGA-(50:50) follows the Langmuir and pseudo-second-order models, respectively. The CTS/FGA exhibits an adsorption capacity of 179.8 mg/g. The characterization of CTS/FGA-(50:50) involves the proposed mechanism of MV 2B adsorption, which primarily encompasses various interactions such as electrostatic forces, n-π stacking, and H-bonding. The present study demonstrates that CTS/FGA-(50:50) synthesized material exhibits a distinctive structure and excellent adsorption properties, thereby providing a viable option for the elimination of toxic cationic dyes from polluted water.

Aldehyde-free and bio-based durable coatings for cellulose fabrics with high flame retardancy, antibacteria and well wearing performance

The bio-based coatings of cellulose fabrics (cotton) had attracted increasing attention for multifunction and sustainability but suffered from poor durability and low efficiency. Here, the aldehyde-free and durable coatings for cotton fabrics (CPZ@CF) with satisfactory flame retardancy, antibacteria as well as wearing performance were prepared through the interfacial coordination effect where the well-organized zinc phytate complex were in situ grew on the pre-treated surface of cotton fabrics with chitosan (CS) and Zn2+. The CZP@CF exhibited excellent antibacterial activity for Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) with 99.99 % antibacterial rates benefiting from the synergistic effect between Zn2+ and CS. Meanwhile, even the CPZ coatings loading was only 1.5 wt%, the fire safety of CZP@CF remarkably enhanced owing to the excellent synergistic catalytic charring and free radical capture. More importantly, the antibacterial rates of CZP@CF for S. aureus and E. coli still reached 99.99 % and 91.67 % after 50 washing cycles. Additionally, this treatment method did not deteriorate the fabrics properties, including mechanical and breathability as well as wearing performance, which provided the approach to fabricate the flame retardant and antibacterial textiles with well durability and wearing performance.

Superior capacity and easy separation of zirconium functionalized chitosan melamine foam for antimony(III/V) removal

Nowadays, highly toxic antimony has severely posed threat to water sources and jeopardized human health. Fabricating adsorbents with the capability of easy separation, high efficiency and large adsorption capacity remains a major challenge. In this paper, zirconium functionalized chitosan melamine foam (ZCMF) was fabricated with zirconium and chitosan crosslinked onto melamine foam, then utilized for the removal of antimony(III/V) in water. The characterization of SEM and EDS collectively showed that ZCMF has a porous structure which could boost the mass transfer rate and zirconium ions on the surface could provide plentiful active adsorption sites. Systematic adsorption experiments demonstrated that the experimental data of Sb(III) and Sb(V) were consistent with the pseudo-second-order and Elovich kinetic models, respectively, and the Langmuir maximum adsorption capacities were separately 255.35 mg g-1 (Sb(III)) and 414.41 mg g-1 (Sb(V)), which displayed prominent performance among adsorbents derived from biomass. Combining the XPS and FTIR characterization with experimental data, it is rational to speculate that ZCMF could remove Sb from aqueous solution through ligand exchange, electrostatic attraction, and surface complexation mechanisms. ZCMF exhibited excellent performance, including large adsorption capacity, easy separation, facile preparation and eco-friendliness. It could be a promising new adsorbent for the treatment of antimony-containing wastewater.

A review on chitosan/metal oxide nanocomposites for applications in environmental remediation

A cleaner and safer environment is one of the most important requirements in the future. It has become increasingly urgent and important to fabricate novel environmentally-friendly materials to remove various hazardous pollutants. Compared with traditional materials, chitosan is a more environmentally friendly material due to its abundance, biocompatibility, biodegradability, film-forming ability and hydrophilicity. As an abundant of -NH2 and -OH groups on chitosan molecular chain could chelate with all kinds of metal ions efficiently, chitosan-based materials hold great potential as a versatile supporting matrix for metal oxide nanomaterials (MONMs) (TiO2, ZnO, SnO2, Fe3O4, etc.). Recently, many chitosan/metal oxide nanomaterials (CS/MONMs) have been reported as adsorbents, photocatalysts, heterogeneous Fenton-like agents, and sensors for potential and practical applications in environmental remediation and monitoring. This review analyzed and summarized the recent advances in CS/MONMs composites, which will provide plentiful and meaningful information on the preparation and application of CS/MONMs composites for wastewater treatment and help researchers to better understand the potential of CS/MONMs composites for environmental remediation and monitoring. In addition, the challenges of CS/MONM have been proposed.

Biodegradable chitosan‑zirconium composite adsorptive membranes for potential arsenic (III/V) capture electrodialysis

Combining adsorption with other technologies holds great potential in fast and deep arsenic ion removal. Herein, chitosan‑zirconium composite adsorptive membranes (CS-Zr CM) were successfully prepared using simple casting and sodium hydroxide coagulation strategies, which was demonstrated the use in arsenic ion-capture electrodialysis based on their good adsorption performance. In the batch adsorption tests, the maximum adsorption capacities of CS-Zr CM for As(III) and As(V) were 134.2 mg/g and 119.5 mg/g, respectively. CS-Zr CM also exhibited satisfying adsorption selectivity and good reusability toward As(III) and As(V). However, the adsorption kinetics showed that they needed 48 h to reach the adsorption equilibrium and the adsorption ability toward trace arsenic ion was ineffective. Furthermore, CS-Zr CM was applied as the adsorptive membrane in the electrodialysis process. Under the influence of electric field, the As(III) and As(V) removal equilibrium time was shortened to 12 h and the concentrations of As(III) and As(V) ions could be efficiently reduced to below the WHO limit in drinking water (10 μg/L), which far surpassed the physicochemical adsorption method. Such good arsenic ion removal ability of CS-Zr CM together with the ease scalable fabrication, low cost, and biodegradable properties shows its huge prospects in arsenic-containing wastewater treatment.

Review on arsenic environment behaviors in aqueous solution and soil

Arsenic pollution in environment has always been an important environmental problem that has attracted wide attention in recent years. Adsorption is one of the main methods of treatment for arsenic in the aqueous solution and soil because of the advantages of high efficiency, low cost and wide application. Firstly, this report summarizes the commonly and widely used adsorbent materials such as metal-organic frameworks, layered bimetallic hydroxides, chitosan, biochar and their derivatives. The adsorption effects and mechanisms of these materials are further discussed, and the application prospects of these adsorbents are considered. Meanwhile, the gaps and deficiencies in the study of adsorption mechanism was pointed out. Then, this study comprehensively evaluated the effects of various factors on arsenic transport, including (i) the effects of pH and redox potential on the existing form of As; (ii) complexation mechanism of dissolved organic matter and As; (iii) factors affecting the plant enrichment of As. Finally, the latest scientific researches on microbial remediation of arsenic and the mechanisms were summarized. The review finally enlightens the subsequent development of more efficient and practical adsorption material.

Adsorption of Copper and Arsenic from Water Using a Semi-Interpenetrating Polymer Network Based on Alginate and Chitosan

New biobased hydrogels were prepared via a semi-interpenetrating polymer network (semi-IPN) using polyacrylamide/chitosan (PAAM/chitosan) hydrogel for the adsorption of As(V) or poly acrylic acid/alginate (PAA/alginate) hydrogel for the adsorption of Cu(II). Both systems were crosslinked using N,N'-methylenebisacrylamide as the crosslinker and ammonium persulfate as the initiating agent. The hydrogels were characterized by SEM, Z-potential, and FTIR. Their performance was studied under different variables, such as the biopolymer effect, adsorbent dose, pH, contact time, and concentration of metal ions. The characterization of hydrogels revealed the morphology of the material, with and without biopolymers. In both cases, the added biopolymer provided porosity and cavities' formation, which improved the removal capacity. The Z-potential informed the surface charge of hydrogels, and the addition of biopolymers modified it, which explains the further metal removal ability. The FTIR spectra showed the functional groups of the hydrogels, confirming its chemical structure. In addition, the adsorption results showed that PAAM/chitosan can efficiently remove arsenic, reaching a capacity of 17.8 mg/g at pH 5.0, and it can also be regenerated by HNO3 for six cycles. On the other hand, copper-ion absorption was studied on PAA/alginate, which can remove with an adsorption capacity of 63.59 mg/g at pH 4.0, and the results indicate that it can also be regenerated by HNO3 for five cycles.

Phosphorylation improved the competitive U/V adsorption on chitosan-based adsorbent containing amidoxime for rapid uranium extraction from seawater

A novel chitosan-based porous composite adsorbent with multifunctional groups, such as phosphoric acid, amidoxime, and quaternary ammonium groups, was prepared to improve the adsorption rate and competitive uranium‑vanadium adsorption of amidoxime group adsorbents. The maximum uranium adsorption capacity of PACNC was 962.226 mg g^-1 at 308 K and pH = 7. The maximum adsorption rate constant of PACNC for uranium was 2.83E-2 g mg^-1 min^-1, which is 2.38 times that of ACNC (1.19E-2 g mg^-1 min^-1). Moreover, the adsorption equilibrium time was shortened from 300 (ACNC) to 50 (PACNC) min. In simulated and real seawater, the K_d and adsorption capacity of PACNC for uranium were approximately 8 and 6.62 times those for vanadium, respectively. These results suggest that phosphorylation significantly improved the competitive adsorption of uranium‑vanadium and uranium adsorption rate. PACNC also exhibited good recycling performance and maintained stable adsorption capacity after five cycles. DFT calculations were used to analyze and calculate the possible co-complex structure of PACNC and uranium. The binding structure of phosphate and amidoxime is the most stable, and its synergistic effect effectively improves the competitive adsorption of uranium-vanadium of amidoxime. All the results demonstrated that PACNC has substantial application potential for uranium extraction from seawater.

Bentonite binding with mercury(II) ion through promotion of reactive oxygen species derived from manure-based dissolved organic matter

This study reports the mercury binding by bentonite clay influenced by cattle manure-derived dissolved organic matter (DOM). The DOM (as total organic carbon; TOC) was reacted with bentonite at 5.2 pH to monitor the subsequent uptake of Hg²⁺ for 5 days. The binding kinetics of Hg²⁺ to the resulting composite was studied (metal = 350 µM/L, pH 5.2). Bentonite-DOM bound much more Hg²⁺ than original bentonite and accredited to the establishment of further binding sites. On the other hand, the presence of DOM was found to decrease the Hg²⁺ binding on the clay surface, specifically, the percent decrease of metal with increasing DOM concentration. Post to binding of DOM with bentonite resulted in increased particle size diameter (~ 33.37- ~ 87.67 nm) by inducing the mineral modification of the pore size distribution, thus increasing the binding sites. The XPS and FTIR results confirm the pronounced physico-chemical features of bentonite-DOM more than that of bentonite. Hydroxyl and oxygen vacancies on the surface were found actively involved in Hg²⁺ uptake by bentonite-DOM composite. Furthermore, DOM increased the content of Hg²⁺ binding by ~ 10% (pseudo-second-order q_e = 90.9-100.0) through boosting up Fe³⁺ reduction with the DOM. The quenching experiment revealed that more oxygen functionalities were generated in bentonite-DOM, where hydroxyl was found to be dominant specie for Hg²⁺ binding. The findings of this study can be used as theoretical reference for mineral metal interaction under inhibitory or facilitating role of DOM, risk assessment, management, and mobilization/immobilization of mercury in organic matter-containing environment.

Novel magnetic Fe@NSC nanohybrid material for arsenic removal from aqueous media

Polymer-derived carbon nanohybrids present a remarkable potential for the elimination of water pollutants. Herein, an Fe-modified C, N, and S (Fe@NSC) nanohybrid network, synthesized via polymerization of aniline followed by calcination, is used for As removal from aquatic media. The Langmuir isotherm and pseudo-second-order kinetic models fit well the experimental data for the adsorptive removal of As(III) and As(V) by the as-synthesized Fe@NSC nanohybrid, indicating that adsorption is a monolayer chemisorption process. The maximum adsorption capacities of the fabricated Fe@NSC nanohybrid for As(III) and As(V) were 129.54 and 178.65 mg/g, respectively, which are considerably higher than those reported previously for other adsorbents. In particular, the Fe₃O₄/FeS nanoparticles (18.4-38.7 nm) of the prepared Fe@NSC nanohybrid play a critical role in As adsorption and oxidation. Spectroscopy data indicate that the adsorption of As on Fe@NSC nanohybrid involved oxidation, ligand exchange, surface complexation, and electrostatic attraction. Furthermore, the magnetic Fe@NSC nanohybrid was easily separated after As adsorption using an external magnet and did not induce acute toxicity (48 h) in Daphnia magna. Moreover, the Fe@NSC nanohybrid selectively removed As species in the presence of competing anions and was effectively regenerated for up to three cycles using a 0.1 M HNO₃ solution. These findings suggest that Fe@NSC nanohybrid is a promising adsorbent for As remediation in aquatic media.

Development of novel Core-shell impregnated polyuronate composite beads for an eco-efficient removal of arsenic

Arsenic (As) can geogenically and anthropogenically contaminate the potable water resources and undoubtedly reduces its availability for human consumption. To circumvent this predicament, present study focuses on the development of a novel biosorbent by impregnating calcium cross-linked polyuronate (alginate) beads (CABs) with bilayer-oleic coated magnetite nanoparticles (CAB@BOFe) for As(V) removal. Initially, the system parameters (i.e., adsorbents dose (0.1- 3.0 g L-1), pH (4.0-13), reaction times (0-180 min) and sorbate concentrations (10-150 µg L-1)) were optimized to establish adsorbent at the lab-scale. CAB@BOFe had higher monolayer (ad)sorption capacity (∼62.5 µg g-1, 120 min) than CABs (∼17.9 µg g-1, 180 min). Electrostatic/Ion-dipole interactions and surface-complexation mechanisms mediated As(V) sorption onto CAB@BOFe mainly obeyed Langmuir isotherm (R2 ∼ 0.9) and well described by intraparticle diffusion process. Furthermore, it demonstrated an excellent arsenate removal performance from the single/multiple anionic contaminants simulated water samples which supported its prospective field applicability.

A comparative study on Fe(III)-chitosan and Fe(III)-chitosan-CTAB composites for As(V) removal from water: preparation, characterization and reaction mechanism

Fe(III)-chitosan and Fe(III)-chitosan-CTAB composites were prepared using an ionotropic gelation method. Various techniques were used to analyze the morphology, structure, and property of the adsorbents, including SEM, EDS, FT-IR, XPS, and zeta potential. Compared with Fe(III)-chitosan, Fe(III)-chitosan-CTAB was more effective for As(V) adsorption at a wide range of pH (3.0-8.0). The adsorption of As(V) onto Fe(III)-chitosan and Fe(III)-chitosan-CTAB could reach equilibrium in 20 min, and their maximum adsorption capacities were 33.85 and 31.69 mg g^‒1, respectively. The adsorption kinetics was best described by the pseudo-second-order model (R² = 0.998 and 0.992), whereas the adsorption isotherm was fitted well by the Freundlich model (R² = 0.963 and 0.987). The presence of H₂PO₄^- significantly inhibited the adsorption of As(V) onto Fe(III)-chitosan and Fe(III)-chitosan-CTAB, and humic acid also led to a slight decrease in As(V) adsorption by Fe(III)-chitosan-CTAB. Over 94% of As(V) at the initial concentration of no more than 5 mg L^-1 was removed from real water by the two adsorbents. 1% (w/v) NaOH solution was determined to be the most suitable desorption agent. Fe(III)-chitosan and Fe(III)-chitosan-CTAB still maintained their initial adsorption capacities after five adsorption-desorption cycles. Based on different characterization results, both electrostatic attraction and surface complexation mechanisms played important roles in As(V) adsorption on Fe(III)-chitosan and Fe(III)-chitosan-CTAB.

Preparation and Adsorption Properties of Nanostructured Composites Derived from Al/Fe Nanoparticles with Respect to Arsenic

Composite nanostructures containing iron in different forms exhibit a high adsorption capacity with respect to arsenic. The aim of our study was to investigate the adsorption activity of an adsorbent composite prepared by the oxidation of bimetallic Al/Fe nanoparticles under different conditions. Depending on the oxidation conditions, nanostructures with different morphologies in the form of nanosheets, nanoplates and nanorods with different compositions and textural characteristics could be obtained. The nanostructures obtained had a positive zeta potential and were characterized by a high specific surface area: 330 m²/g for the AlOOH/FeAl₂ nanosheets; 75 m²/g for the AlOOH/Fe₂O₃/FeAl₂ nanoplates; and 43 m²/g for the Al(OH)₃/FeAl₂ nanorods. The distribution of an FeAl₂ intermetallide over the surface of the AlOOH nanostructures led to an increase in arsenic adsorption of 25% for the AlOOH/FeAl₂ nanosheets and of 34% for the AlOOH/Fe₂O₃/FeAl₂ nanoplates and Al(OH)₃/FeAl₂ nanorods. The adsorption isotherms matched most preciously to the Freundlich model. This fact indicated the energy heterogeneity of the adsorbent surface and multilayer adsorption. The nanostructures studied can be used to purify water contaminated with arsenic.

Arsenic in drinking water: overview of removal strategies and role of chitosan biosorbent for its remediation

Accessibility to clean drinking water often remains a crucial task at times. Among other water pollutants, arsenic is considered a more lethal contaminant and has become a serious threat to human life globally. This review discussed the sources, chemistry, distribution, and toxicity of arsenic and various conventional technologies that are in option for its removal from the water system. Nowadays, biosorbents are considered the best option for arsenic-contaminated water treatment. We have mainly focused on the need and potential of biosorbents especially the role of chitosan-based composites for arsenic removal. The chitosan-based sorbents are economically more efficient in terms of their, low toxicity, cost-effectiveness, biodegradability, eco-friendly nature, and reusability. The role of various modification techniques, such as physical and chemical, has also been evaluated to improve the physicochemical properties of biosorbent. The importance of adsorption kinetic and isotherm models and the role of solution pH and pHPZC for arsenic uptake from the polluted water have also been investigated. Some other potential applications of chitosan-based biosorbents have also been discussed along with its sustainability aspect. Finally, some suggestions have been highlighted for further improvements in this field.

Preparation of new MOF-808/chitosan composite for Cr(VI) adsorption from aqueous solution: Experimental and DFT study

In this study, a series of Zirconium-based MOF and chitosan composites (MOF-808/chitosan) were synthesized as efficient adsorbent for Cr(VI) ions elimination from aqueous solution. MOF-808/chitosan structure and morphology was characterized by FE-SEM, EDX, XRD, BET, zeta potential analysis, FT-IR, XPS techniques. The kinetic studies ascertained that Cr(VI) adsorption over MOF-808/chitosan followed pseudo-second-order kinetic model. The adsorption isotherms fitted the Langmuir isotherm model, implying on homogeneously adsorption of Cr(VI) on the surface of MOF-808/chitosan. According to the Langmuir model, the maximum capacity was obtained to be 320.0 mg/g at pH 5. Thermodynamic investigation proposed spontaneous (ΔG° < 0), disordered (ΔS° > 0) and endothermic (ΔH° > 0) for adsorption process. Besides, MOF-808/chitosan displayed an appropriate reusability for the elimination of Cr(VI) ions from their aqueous solutions for six successive cycles. DFT study of the adsorption process displayed and confirmed the role of hydrogen bonding and electrostatic attraction simultaneously.

Antioxidant and antibacterial properties of essential oils-loaded β-cyclodextrin-epichlorohydrin oligomer and chitosan composite films

Chitosan (CS) is becoming increasingly popular in food packaging due to its natural degradability and great film-forming properties. Nevertheless, its poor antibacterial properties and inadequate antioxidant properties prevent it from being used effectively. In this study, β-cyclodextrin-epichlorohydrin (β-CD-EP) oligomers were prepared and encapsulated with natural essential oils cinnamaldehyde and thymol, and then the inclusion complexes (IC) were incorporated into chitosan in various contents to afford a series of CS-IC composite films. The impacts of IC on the morphological, mechanical, thermal, and water resistance properties, antioxidant and antibacterial activities of chitosan films, as well as the loading and sustained release behavior of IC, were thoroughly examined. The results turned out that the essential oils were well-loaded with high encapsulation efficiency and showed a significant slow-release effect. It was also found that the tensile strength and the elongation at break decreased with increasing IC contents, while the thermal stability was enhanced. The incorporation of IC dramatically promoted the antioxidant and antibacterial properties of the chitosan films towards Gram-positive bacteria. Based on our findings, chitosan films containing essential oils-loaded β-CD-EP oligomers may serve as an effective food packaging material.

Chitosan magnetic graphene grafted polyaniline doped with cobalt oxide for removal of Arsenic(V) from water

The present study reports the successful functionalization/magnetization of bio-polymer to produce chitosan-magnetic graphene oxide grafted polyaniline doped with cobalt oxide (ChMGOP-Co₃O₄). Analytical techniques furrier transform infra-red (FT-IR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were used to confirm the formation of ChMGOP-Co₃O₄. The effects of several experimental factors (solution pH, adsorbent dosage and coexisting ions) on the uptake of As(V) ions using ChMGOP-Co₃O₄ were examined through batch experiments. As(V) removal process was validated by experimentally and theoretically investigating the adsorption capacity, rate, and thermal effects. Thermodynamic parameters such as free energy (ΔG°), entropy (ΔS°) and enthalpy (ΔH°) were also calculated and were used to explain the mechanism of adsorption. Based on the results, the sorbent showed a high adsorption capacities (90.91 mg/g) at favorable neutral pH and superior removal efficiencies as high as 89% within 50 min. In addition, the adsorption isotherm followed the Langmuir isotherm in compare to the Freundlich, due to its higher R² value (0.992 < 0.941). Meanwhile, the kinetic data revealed that the of As(V) adsorption was controlled by pseudo-second-order. Overall, the adsorption mechanism studies revealed a spontaneous endothermic nature with predominance of physisorption over chemisorption. This study indicated that ChMGOP-Co₃O₄ is an exceptional novel adsorbent material for the efficient isolation of As(V) from aqueous media.

Adsorption performance and its mechanism of aqueous As(III) on polyporous calcined oyster shell-supported Fe-Mn binary oxide

Fe-Mn binary oxide (FMBO) is a promising adsorbent for As(III) removal through combined adsorption and oxidation. The calcined oyster shell-supported Fe-Mn binary oxide (FMBO/OS) adsorbent was synthesized by the co-precipitation method. Results indicated that the calcined oyster shell, as a carrier, improved the stability of FMBO and its adsorption capacity for As(III). The maximum adsorption capacity of FMBO/OS on As(III) reached 140.5 mg·g^-1 . Under pH 5.0 and 25°C, the removal efficiency of FMBO/OS to As(III) solution (C₀  = 10 mg·L^-1 ) reached 87% within 12 h. Moreover, based on the characterization analyses, the removal mechanisms of As(III) were deduced to include the combined adsorption and oxidation process of FMBO and the synergistic effect of oyster shells. This work provides new insights into synthesizing efficient and green adsorbents to remove aqueous As(III). Meanwhile, it provides technical support for reusing waste biomass materials such as the oyster shell. PRACTITIONER POINTS: FMBO/OS was prepared by a simple hydrothermal co-precipitation method. The carrier alleviates the agglomeration of Fe-Mn oxides. The adsorbent shows a strong adsorption capacity of As(III) and good selectivity. The good results benefit from the synergistic effect of calcium arsenate generation. The prepared adsorbent can adsorb arsenic in real samples.

Arsenic removal approaches: A focus on chitosan biosorption to conserve the water sources

Globally, millions of people have no access to clean drinking water and are either striving for that or oppressed to intake polluted water. Arsenic is considered one of the most hazardous contaminants in water bodies that reaches there due to various natural and anthropogenic activities. Modified chitosan has gained much attention from researchers due to its potential for arsenic removal. This review focuses on the need and potential of chitosan-based biosorbents for arsenic removal from water systems. Chitosan is a low-cost, abundant, biodegradable biopolymer that possesses unique structural aspects and functional sites for the adsorption of contaminants like arsenic species from contaminated water. The chitosan-based biosorbents had also been modified using various techniques to enhance their arsenic removal efficiencies. This article reviews various forms of chitosan and parameters involved in chitosan modification which eventually affect the arsenic removal efficiency of the resultant sorbents. The literature revealed that the modified chitosan-based sorbents could express higher adsorption efficiency compared to those prepared from native chitosan. The sustainability of the chitosan-based sorbents has also been considered in terms of reusability. Finally, some recommendations have been underlined for further improvements in this domain.

Flocculation of combined contaminants of dye and heavy metal by nano-chitosan flocculants

In this study, two multifunctional nano-chitosan flocculants (CPAM-NCS1 and CPAM-NCS2) were made through the graft modification of cationic monomer and carboxymethylchitosan (CMCTS) to remove combined contaminants. The effects of various factors (pH, flocculant dosage and hydraulic mixing conditions) on the flocculation performance under single and composite pollution conditions were systematically investigated, the optimal chemical oxygen demand (COD) and the chromaticity removal rates in the dye wastewater were 79.9% and 83.9% at wastewater pH 7, the fast stirring rate 300 rpm, the fast stirring time 8 min, and the dosage of CPAM-NCS1 80 mg/L, respectively. The optimal removal rates of Cu (II) obtained by CPAM-NCS1 and CPAM-NCS2 at were 80.3% and 75.2% at 60 mg/L and the wastewater pH 7, respectively. The optimal removal rates of Cu (II) and disperse orange were 85.3% and 89.4%, respectively, in a composite pollutant system in which Cu (II) and disperse orange coexisted when the pH of the composite system was 9 and the dosage of CPAM -NCS1 was 60 mg/L. This study proved that nanoflocculants made by modifying CMCTS with different structures can demonstrate ideal flocculation removal performance for dye and heavy metal wastewaters.

An Overview on Composite Sorbents Based on Polyelectrolytes Used in Advanced Wastewater Treatment

Advanced wastewater treatment processes are required to implement wastewater reuse in agriculture or industry, the efficient removal of targeted priority and emerging organic & inorganic pollutants being compulsory (due to their eco-toxicological and human health effects, bio-accumulative, and degradation characteristics). Various processes such as membrane separations, adsorption, advanced oxidation, filtration, disinfection may be used in combination with one or more conventional treatment stages, but technical and environmental criteria are important to assess their application. Natural and synthetic polyelectrolytes combined with some inorganic materials or other organic or inorganic polymers create new materials (composites) that are currently used in sorption of toxic pollutants. The recent developments on the synthesis and characterization of composites based on polyelectrolytes, divided according to their macroscopic shape-beads, core-shell, gels, nanofibers, membranes-are discussed, and a correlation of their actual structure and properties with the adsorption mechanisms and removal efficiencies of various pollutants in aqueous media (priority and emerging pollutants or other model pollutants) are presented.

A detailed insight on fabricated porous chitosan in eliminating synthetic anionic dyes from single and multi-adsorptive systems with related studies

Chitosan was fabricated via gelation method using CaBr₂.xH₂O/methanol solution and was studied as a potential adsorbent (MCh) in adsorbing anionic synthetic dyes like Bromophenol blue (BB), Direct blue 6 (DB) and Congo red (CR) from single (one dye species at a time) and multi (having two dyes; binary and all three dyes; tertiary) adsorptive systems. Physico-chemical modifications of MCh surface prior and post modification and dye adsorption were evaluated using scanning electron microscopy, Energy-dispersive X-ray spectroscopy, powder X-ray diffraction analysis, surface area analysis and Fourier-transformed infrared spectroscopy. Influential parameters influencing the adsorption process viz. initial pH of dye solution, MCh dosage, adsorption temperature and initial concentration of dye species were optimised. Adsorptive studies involving single adsorptive setups verified formation of sorbate's (dye species) monolayer over the sorbent's (MCh) surface via chemisorption; as established by Langmuir isotherm and pseudo-second order kinetics model analysis. Theoretical maximum adsorption capacities of MCh for BB, DB and CR was found to be 81.301 mg/g, 163.934 mg/g and 75.758 mg/g, respectively. Meanwhile, for all multi-adsorptive systems, competitive Langmuir isotherm model verified antagonistic behaviour of an individual dye over other dye adsorption over MCh surface in their respective adsorptive systems. Thermodynamics of the sorbate-sorbent interaction was exothermic, spontaneous, with elevated degree of disorderedness; concluding the interaction as thermodynamically favourable. Co-existing metal cations and anionic salts had minimal effect on MCh's adsorption efficiency. Phytotoxicity assay via germination of Vigna mungo seeds verified the efficacy of the adsorbent in eliminating the dye species from single and multi-adsorptive systems.

Removal of arsenate using graphene oxide-iron modified clinoptilolite-based composites: adsorption kinetic and column study

In this study, graphene oxide (GO), iron modified clinoptilolite (FeZ), and composites of GO-FeZ (GOFeZA and GOFeZB) were synthesized and characterized using SEM, EDS, XRF, FTIR, and pHpzc. The arsenate uptake on composites of GOFeZA and GOFeZB was examined by both kinetic and column studies. The adsorption capacity increases with the increase of the initial arsenate concentration at equilibrium for both composites. At the initial arsenate concentration of 450 μg/L, the arsenate adsorption on GOFeZA and GOFeZB was 557.86 and 554.64 μg/g, respectively. Arsenate adsorption on both composites showed good compatibility with the pseudo second order kinetic model. The adsorption process was explained by the surface complexation or ion exchange and electrostatic attraction between GOFeZA or GOFeZB and arsenate ions in the aqueous solution due to the relatively low equilibrium time and fairly rapid adsorption of arsenate at the beginning of the process. The adsorption mechanism was confirmed by characterization studies performed after arsenate was loaded onto the composites. The fixed-bed column experiments showed that the increasing the flow rate of the arsenate solution through the column resulted in a decrease in empty bed contact time, breakthrough time, and volume of treated water. As a result of the continuous operation column study with regenerated GOFeZA, it was demonstrated that the regenerated GOFeZA has lower breakthrough time and volume of treated water compared to fresh GOFeZA.

Graphene oxide-iron modified clinoptilolite based composites for adsorption of arsenate and optimization using response surface methodology

In this study, graphene oxide and composites of graphene oxide-iron modified clinoptilolite were synthesized and used for arsenate removal from aqueous solution. All adsorbents were characterized using X-ray diffraction and specific surface area analysis. The specific surface areas of composites were found to be less than the iron modified clinoptilolite. The time required to reach equilibrium was determined as 3 hours for all adsorbents. The Box-Behnken statistical experiment design method was used to determine the effects of initial arsenate concentration, pH and the amount of adsorbent on the percent arsenate removal. Graphene oxide was not as effective as composites for arsenate adsorption from water. Arsenate adsorption on composites was showed good compatibility with the Freundlich isotherm. The maximum arsenate uptake was realized at pH 4 for graphene oxide and at pH 7 for composites. The maximum adsorption capacities obtained at the optimum points determined by using the Box-Behnken design method were calculated as 39.49, 117.98 and 124.64 µg.g^-1 for graphene oxide and composites, respectively.

Enhanced removal of As(III) and As(V) from water by a novel zirconium-chitosan modified spherical sodium alginate composite

Most nano-scaled adsorbents have trouble in separating from aqueous solution, thus, a need for new materials of facile separation and predominant adsorption performance has arisen. This present study focused on a novel segregative zirconium-chitosan modified sodium alginate (Zr-CTS/SA) composite preparation and its performance for As(III/V) removal from aqueous solution. The obtained composite presented a spherical structure with a diameter of 2.0-3.0 mm and favorable thermal stability. Experimental data showed that Zr-CTS/SA had considerable adsorbability for As(III) and As(V), the adsorption capacities were enhanced about at least 20 and 6 times separately compared with pristine SA beads. The adsorption processes of As(III) and As(V) could both be described with Langmuir isotherm model and the maximum adsorption capacities reached 43.19 and 76.78 mg g^-1, respectively. The kinetic data of As(III) followed the intra-particle diffusion model while As(V) fitted the pseudo-first-order model. Moreover, the adsorption mechanisms of As(III/V) involved ligand exchange with Cl on the surface of Zr-CTS/SA, another reaction pathway for As(V) was the electrostatic attraction with protonated -OH and -NH₂ groups. Note that the employment of Zr-CTS/SA in low-concentration arsenic solution exhibited a residue concentration as low as the 10 μg L^-1 WHO guideline for drinking water.

Excellent selectivity and high capacity of As (V) removal by a novel lignin-based adsorbent doped with N element and modified with Ca2

As one of the most significant natural polymer with the highest annual yield, lignin has been applied in the treatment of wastewater to remove heavy metal ions. However, there are still some shortages, such as low reactivity, difficulties in adsorbing oxyanions and low selectivity on specific oxyanions. To improve its adsorption properties, a novel lignin-based adsorbent was prepared in this study, doped with nitrogen by Mannich reaction, using triethylenetetramine (TETA) as N source, and further modified with Ca²⁺. The adsorption of Ca, N-co-doped lignin (Ca@N-Lig) for As (V), Cr (VI) and P (V) was studied. The Ca@N-Lig shows high capacity, excellent selectivity and prominent regeneration ability for As (V) adsorption. The adsorption of Ca@N-Lig for As (V) followed the Langmuir isotherm model and the pseudo-second-order kinetics model, yielding a maximum adsorption capacity of 681.59 mg·g^-1 and a fast adsorption equilibrium within 30 min. Ca@N-Lig has an excellent regeneration ability on the adsorption of As (V) with a decrease of about 15.60% after 5 adsorption/desorption cycles. This study offers an efficient way to remove As (V) from polluted water.