A novel quaternized chitosan–melamine–glutaraldehyde resin for the removal of nitrate and phosphate anions

Structure properties and industrial applications of anion exchange resins for the removal of electroactive nitrate ions from contaminated water

The presence of nitrates in lakes, rivers, and groundwater is common. Anion exchange resins (AER) are polymeric structures that contain functional groups as well as a variety of particle sizes that are used for removing nitrate ions from solutions. This article provides a concise review of the types and properties of AER, synthesis methods, characterization, and environmental applications of AER. It discusses how different factors affect the adsorption process, isotherm and kinetic parameters, the adsorption mechanism, and the maximum adsorption capacities. Additionally, the present review addresses AER's regeneration and practical stability. It emphasizes the progress and proposes future strategies for addressing nitrate pollution using AER to overcome the challenges. This review aims to act as a reference for researchers working in the advancement of ion exchange resins and presents a clear and concise scientific analysis of the use of AER in nitrate adsorption. It is evident from the literature survey that AER is highly effective at removing nitrate ions from wastewater effluents.

Surface modifications of biopolymers for removal of per- and polyfluoroalkyl substances from water: Current research and perspectives

Per- and polyfluoroalkyl substances (PFAS) are highly recalcitrant organic contaminants that have attracted ever-increasing attention from the general public, government agencies and scientific communities. To remove PFAS from water, especially the enormous volume of drinking water, stormwater, and groundwater, sorption is the most practical approach. Success of this approach demands green, renewable, and sustainable materials for capturing PFAS at ng/L or µg/L levels. To meet this demand, this manuscript critically reviewed sorbents developed from biopolymers, such as chitosan (CTN), alginate (ALG), and cellulose (CEL) covering the period from 2008 to 2023. The use of different cross-linkers for the surface modifications of biopolymers were described. The underlying removal mechanism of biosorbents for PFAS adsorption from molecular perspectives was discussed. Besides reviewing and comparing the performance of different bio-based sorbents with respect to environmental factors like pH, and sorption kinetics and capacity, strategies for modifying biosorbents for better performance were proposed. Additionally, approaches for regeneration and reuse of the biosorbents were discussed. This was followed by further discussion of challenges facing the development of biosorbents for PFAS removal.

Chitosan Biocomposites with Variable Cross-Linking and Copper-Doping for Enhanced Phosphate Removal

The fabrication of chitosan (CH) biocomposite beads with variable copper (Cu2+) ion doping was achieved with a glutaraldehyde cross-linker (CL) through three distinct methods: (1) formation of CH beads was followed by imbibition of Cu(II) ions (CH-b-Cu) without CL; (2) cross-linking of the CH beads, followed by imbibition of Cu(II) ions (CH-b-CL-Cu); and (3) cross-linking of pristine CH, followed by bead formation with Cu(II) imbibing onto the beads (CH-CL-b-Cu). The biocomposites (CH-b-Cu, CH-b-CL-Cu, and CH-CL-b-Cu) were characterized via spectroscopy (FTIR, 13C solid NMR, XPS), SEM, TGA, equilibrium solvent swelling methods, and phosphate adsorption isotherms. The results reveal variable cross-linking and Cu(II) doping of the CH beads, in accordance with the step-wise design strategy. CH-CL-b-Cu exhibited the greatest pillaring of chitosan fibrils with greater cross-linking, along with low Cu(II) loading, reduced solvent swelling, and attenuated uptake of phosphate dianions. Equilibrium and kinetic uptake results at pH 8.5 and 295 K reveal that the non-CL Cu-imbibed beads (CH-b-Cu) display the highest affinity for phosphate (Qm = 133 ± 45 mg/g), in agreement with the highest loading of Cu(II) and enhanced water swelling. Regeneration studies demonstrated the sustainability and cost-effectiveness of Cu-imbibed chitosan beads for controlled phosphate removal, whilst maintaining over 80% regenerability across several adsorption-desorption cycles. This study offers a facile synthetic approach for controlled Cu2+ ion doping onto chitosan-based beads, enabling tailored phosphate oxyanion uptake from aqueous media by employing a sustainable polysaccharide biocomposite adsorbent for water remediation by mitigation of eutrophication.

Recent advances in removal of inorganic anions from water by chitosan-based composites: A comprehensive review

Chitosan is a modified natural carbohydrate polymer that has been found in the exoskeletons of crustaceans (e.g., lobsters, shrimps, krill, barnacles, crayfish, etc.), mollusks (octopus, oysters, squids, snails), algae (diatoms, brown algae, green algae), insects (silkworms, beetles, scorpions), and the cell walls of fungi (such as Ascomycetes, Basidiomycetes, and Phycomycetes; for example, Aspergillus niger and Penicillium notatum). However, it is mostly acquired from marine crustaceans such as shrimp shells. Chitosan-based composites often present superior chemical, physical, and mechanical properties compared to single chitosan by incorporating the benefits of both counterparts in the nanocomposites. The tunable surface chemistry, abundant surface-active sites, facilitation synthesize and functionalization, good recyclability, and economic viability make the chitosan-based materials potential adsorbents for effective and fast removal of a broad range of inorganic anions. This article reviews the different types of inorganic anions and their effects on the environment and human health. The development of the chitosan-based composites synthesis, the various parameters like initial concentration, pH, adsorbent dosage, temperature, the mechanism of adsorption, and regeneration of adsorbents are discussed in detail. Finally, the prospects and technical challenges are emphasized to improve the performance of chitosan-based composites in actual applications on a pilot or industrial scale.

Recovery of Phosphate(V) Ions from Water and Wastewater Using Chitosan-Based Sorbents Modified-A Literature Review

Over the past two decades, there has been increasing interest in the use of low-cost and effective sorbents in water treatment. Hybrid chitosan sorbents are potential materials for the adsorptive removal of phosphorus, which occurs in natural waters mainly in the form of orthophosphate(V). Even though there are numerous publications on this topic, the use of such sorbents in industrial water treatment and purification is limited and controversial. However, due to the explosive human population growth, the ever-increasing global demand for food has contributed to the consumption of phosphorus compounds and other biogenic elements (such as nitrogen, potassium, or sodium) in plant cultivation and animal husbandry. Therefore, the recovery and reuse of phosphorus compounds is an important issue to investigate for the development and maintenance of a circular economy. This paper characterizes the problem of the presence of excess phosphorus in water reservoirs and presents methods for the adsorptive removal of phosphate(V) from water matrices using chitosan composites. Additionally, we compare the impact of modifications, structure, and form of chitosan composites on the efficiency of phosphate ion removal and adsorption capacity. The state of knowledge regarding the mechanism of adsorption is detailed, and the results of research on the desorption of phosphates are described.

Combination of adsorption/desorption and photocatalytic reduction processes for PFOA removal from water by using an aminated biosorbent and a UV/sulfite system

Per- and polyfluoroalkyl substances (PFAS) are stable organic chemicals, which have been used globally since the 1940s and have caused PFAS contamination around the world. This study explores perfluorooctanoic acid (PFOA) enrichment and destruction by a combined method of sorption/desorption and photocatalytic reduction. A novel biosorbent (PG-PB) was developed from raw pine bark by grafting amine groups and quaternary ammonium groups onto the surface of bark particles. The results of PFOA adsorption at low concentration suggest that PG-PB has excellent removal efficiency (94.8%-99.1%, PG-PB dosage: 0.4 g/L) to PFOA in the concentration range of 10 μg/L to 2 mg/L. The PG-PB exhibited high adsorption efficiency regarding PFOA, being 456.0 mg/g at pH 3.3 and 258.0 mg/g at pH 7 with an initial concentration of 200 mg/L. The groundwater treatment reduced the total concentration of 28 PFAS from 18 000 ng/L to 9900 ng/L with 0.8 g/L of PG-PB. Desorption experiments examined 18 types of desorption solutions, and the results showed that 0.05% NaOH and a mixture of 0.05% NaOH + 20% methanol were efficient for PFOA desorption from the spent PG-PB. More than 70% (>70 mg/L in 50 mL) and 85% (>85 mg/L in 50 mL) of PFOA were recovered from the first and second desorption processes, respectively. Since high pH promotes PFOA degradation, the desorption eluents with NaOH were directly treated with a UV/sulfite system without further adjustment. The final PFOA degradation and defluorination efficiency in the desorption eluents with 0.05% NaOH + 20% methanol reached 100% and 83.1% after 24 h reaction. This study proved that the combination of adsorption/desorption and a UV/sulfite system for PFAS removal is a feasible solution for environmental remediation.

Removal performance and mechanism of phosphorus by different Fe-based layered double hydroxides

Phosphorus pollution has the potential to cause both aquatic eutrophication and global phosphorus scarcity. Fe-based layered double hydroxides (LDHs) have received much attention due to their high phosphorus adsorption and recovery. The composition of Fe-based LDHs is an important factor in determining their adsorption performance. However, the mechanism by which single component regulation of Fe-based LDHs affects phosphorus adsorption performance remains unknown. In this study, two typical types of Fe-based LDHs were prepared: Mg/Fe LDH and Zn/Fe LDH. Results showed that the equilibrium adsorption capacity of Zn/Fe LDH was much greater than that of Mg/Fe LDH, reaching 65.85 mg/g with a phosphorus concentration of 150 mg/L. Calcination facilitated a substantial increase of adsorption capacity for Mg/Fe LDH rather than Zn/Fe LDH. Meanwhile, the phosphorus removal efficiency of Fe-based LDHs both exceeded 90% with an initial pH of 3.0, but it decreased as pH increased, and pH inhibition was relatively weaker for Zn/Fe LDH than Mg/Fe LDH. The common coexisting anions caused a phosphorus adsorption loss, with SO₄^2- possessing the most competition with phosphorus. Combined with FTIR, XRD, XPS, and BET analyses, a superior adsorption performance of Zn/Fe-LDH over Mg/Fe-LDH was probably attributed to a higher surface complexation and larger specific surface area. It was also concluded that Fe-based LDHs are a promising method for removing phosphorus from recirculating aquaculture wastewater.

Facile Synthesis of Hydrogel-Based Ion-Exchange Resins for Nitrite/Nitrate Removal and Studies of Adsorption Behavior

This research aimed to create facile, reusable, hydrogel-based anion exchange resins that have been modified with two different amines to test their ability to adsorb nitrate and nitrite in water using batch and continuous systems. In the batch experiment, maximum adsorption capacities of nitrate and nitrite onto poly (ethylene glycol) diacrylate methacryloxyethyltrimethyl ammonium chloride (PEGDA-MTAC) and poly (ethylene glycol) diacrylate 2-aminoethyl methacrylate hydrochloride (PEGDA-AMHC) adsorbents can be obtained as 13.51 and 13.16 mg NO₃⁻-N/g sorbent; and 12.36 and 10.99 mg NO₂⁻-N/g sorbent respectively through the Langmuir isotherm model. After 15 adsorption/desorption cycles, PEGDA-MTAC and PEGDA-AMHC retained nitrate adsorption efficiencies of 94.71% and 83.02% and nitrite adsorption efficiencies of 97.38% and 81.15% respectively. In a column experiment, modified adsorbents demonstrated adsorption efficiencies greater than 45% after being recycled five times. Proposed hydrogel-based adsorbents can be more effective than several types of carbon-based sorbents for nitrate and nitrite removal in water and have benefits such as reduced waste generation, cost-effectiveness, and a facile synthesis method.

Preparation of resin-based composites containing Ce and cationic polymers with abundant promotional affinity sites for phosphate capture

A new type of composite, D301-Ce+, for efficient and selective phosphate removal.

A review on the use of chitosan and chitosan derivatives as the bio-adsorbents for the water treatment: Removal of nitrogen-containing pollutants

Chitosan and its derivatives have been widely used as the adsorbents for different types of water pollutants. This review paper lists various physically and chemically modified chitosan-based adsorbents such as chitosan beads, cross-linked chitosan, chitosan-polymer composites, chitosan-inorganic material composites, and chitosan-metal complexes for the removal of nitrogen-containing pollutants (nitrate, nitrite, ammonia, and ammonium ions) from aqueous solutions. It covers preparation strategies, the effect of modification on adsorbent structure, and the impact of adsorption variables using batch and fixed-bed column studies. In addition to demonstrating the applications of chitosan and its derivatives in the removal of nitrogenous pollutants from water, it helps researchers understand the influence of modification of chitosan on its adsorption capacity as well as physical and chemical properties.

Modified Grape Seeds: A Promising Alternative for Nitrate Removal from Water

The aim of this work was to investigate grape seeds as a potential adsorbent for nitrate removal from water. Grape seeds were modified by quaternization and the applicability of the modified grape seeds (MGS) was evaluated in batch adsorption experiments. Fixed bed adsorption and regeneration studies were carried out to determine the regeneration capacity of MGS. The maximum adsorption capacity of 25.626 mg g⁻¹ at native pH (6.3) for nitrate removal by MSG was comparable to that of the commercial anion exchange resin Relite A490 under similar conditions. The percent removal of nitrate from model nitrate solution was 86.47% and 93.25% for MGS, and Relite A490, respectively, and in synthetic wastewater 57.54% and 78.37%. Analysis of the batch adsorption data using isotherm models revealed that the Freundlich model provided a better fit to the data obtained than the Langmuir model, indicating multilayer adsorption. In kinetic terms, the results showed that the adsorption followed the pseudo-first order model. By investigating the adsorption mechanism, the results suggest that the intraparticle diffusion model was not the only process controlling the adsorption of nitrate on MGS. In column experiments (adsorption/desorption studies), three adsorption cycles were tested with minimal decrease in adsorption capacities, implying that this alternative adsorbent can be successfully regenerated and reused.

Preparation of TiO2/cellulose nanocomposites as antibacterial bio-adsorbents for effective phosphate removal from aqueous medium

The design of environmentally benign bio-adsorbents for the removal of phosphate from aqueous medium was an economic and effective way for controlling eutrophication. Herein, we prepared three kinds of TiO₂/cellulose (CE-Ti) nanocomposites by a facile hydrolysis-precipitation method, and used them as antibacterial bio-adsorbents for the removal of phosphate from aqueous medium. Multiple techniques including Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and thermogravimetric analysis (TGA) were employed to characterize the nanostructure and characteristics of the prepared CE-Ti nanocomposite. The adsorption capacity of the CE-Ti was 19.57 mg P g^-1 according to the Langmuir model, which was 6 times higher than that of CE. Importantly, the bacterial inhibition zone of the CE-Ti was 2.88 mm (that of CE was 0 mm), indicating that CE-Ti had good antibacterial activity that could reduce the attachment of the microorganism to the surface of CE-Ti, which was suitable for long-term phosphate removal. Moreover, the CE-Ti had good adsorption selectivity and anti-interference capability, according to interfering ions and ion strength experiments. Furthermore, Ti⁴⁺ leakage tests suggested that CE-Ti was highly stable under acidic, neutral and alkali conditions. These results indicated that the CE-Ti nanocomposite could be utilized as a promising antibacterial bio-adsorbent for effective phosphate removal from aqueous medium.

Development of triaminotriazine functionalized graphene oxide capped chitosan porous composite beads for nutrients remediation towards water purification

The porous, definite and nitrogen rich triaminotriazine (TAT) grafted graphene oxide (GO) known as TATGO composite was developed for nutrients (NO₃^- and PO₄^3-) retention. Additionally, the structural property of TATGO composite was improved with the use of chitosan (CS) to produce easily separable TATGO@CS hybrid beads which possess the significant NO₃^- and PO₄^3- adsorption capacities of 58.46 and 61.38 mg/g respectively than their individual materials. The instrumentations such as SEM, TGA, FTIR, EDAX, XRD and BET studies were executed for adsorbents. The optimization of the parameters accountable for adsorption process was performed in batch scale. The effect of isotherms (Langmuir, Freundlich and Dubinin-Radushkevich (D-R)), kinetics (pseudo-first/second order and particle/intraparticle diffusion) and thermodynamic parameters (ΔG°, ΔH° and ΔS°) of the adsorption was explored. The removal mechanism of TATGO@CS hybrid beads was to be electrostatic attraction on NO₃^- and PO₄^3-. The field applicability and reuse of TATGO@CS hybrid beads was also inspected.

Production of aminated peat from branched polyethylenimine and glycidyltrimethylammonium chloride for sulphate removal from mining water

A novel bio-based anion exchanger was developed to remove sulphate from synthetic solutions and mine water. Different modification parameters such as chemical dosage and reaction time were tested when using a unique combination of branched polyethylenimine (PEI) and glycidyltrimethylammonium chloride (GTMAC) to produce an aminated biosorbent (termed PG-Peat). The novel and environment-friendly modification method was shown by FTIR and XPS analyses to be able to introduce quaternary ammonium and N-H groups into PG-Peat. The optimal modification conditions (PEI: 0.26 mmol/g, GTMAC: 0.0447 mol/g, reaction time: 18 h) resulted in the maximum sulphate uptake capacity (189.5 ± 2.7 mg/g) with a partition coefficient value of 0.02 mg/g/μM under acidic conditions. At low pH, amine groups on the peat surface became cationized, thereby resulting in a higher sulphate removal capacity. Batch sorption tests using PG-Peat exhibited rapid sulphate sorption after only five minutes of contact. The sulphate uptake by PG-Peat was unaffected by the presence of varying chloride concentrations, while slightly lower uptake capacity was observed when different concentrations of nitrate were present. The biosorbent showed high recyclability, which was revealed in regeneration studies. Tests were performed involving real mine water, where PG-Peat showed its potential to be a highly efficient biosorbent for sulphate removal at low pH values, indicating its suitability for treating acidic mine waters.

Q-Graphene-loaded metal organic framework nanocomposites with water-triggered fluorescence turn-on: fluorimetric test strips for directly sensing trace water in organic solvents

Q-Graphene-loaded MOF nanocomposites were coated onto test strips with H₂O-triggered fluorescence turn-on for probing H₂O in organic solvents.

Cu (II) binded chitosan/Fe3O4 nanocomomposite as a new biosorbent for efficient and selective removal of phosphate

The aim of this study was to develop a chitosan-based magnetic adsorbent for selective and effective removal of phosphate from aqueous solutions. For this purpose, Cu-chitosan/Fe₃O₄ nanocomposite was prepared using a facile method and characterized. The prepared adsorbent exhibited more porous surface with higher specific area compared to neat chitosan based on SEM and BET studies. The FTIR and EDX studies indicated the presence of Cu(II) bonded to the adsorbent surface. Crystalline properties of the adsorbent were also studied using XRD. Experimental isotherm data were fitted to nonlinear forms of Langmuir and Freunlich models. The maximum capacity for the modified adsorbent was calculated to be 88mg P₂O₅/g, much higher than that for neat chitosan and chitosan/Fe₃O₄ according to the Langmuir isotherm. The adsorption by the modified adsorbent had fast kinetics and obeyed pseudo-second-order kinetic model. Interestingly, the maximum removal efficiency for the modified adsorbent was observed in neutral pH values, pHs of natural waters. A high selectivity against natural waters common anions as well as good regeneration ability was obtained for the introduced adsorbent.

Application of modified chitosan microspheres for nitrate and phosphate adsorption from aqueous solution

Modified chitosan microspheres were prepared by inverse suspension crosslinking and used for nitrate and phosphate adsorption from aqueous solution. Their surface was coarse and porous compared to pure chitosan microspheres and they were about 100 μm in size.

Preparation of cross-linked magnetic chitosan with quaternary ammonium and its application for Cr(VI) and P(V) removal

Pollutants that exist in anionic species are issues of concern in water treatment. Compared to cationic pollutants, the removal of anionic pollutants by adsorption is more difficult because most adsorbents carry predominantly negative charges in neutral and alkaline environments. In this study, a cross-linked chitosan derivative with quaternary ammonium and magnetic properties (QM-chitosan) was prepared and employed to remove chromium (VI) and phosphorus (V) (Cr(VI) and P(V)) from aqueous environments. The QM-chitosan was characterized by Fourier transform infrared spectrometry (FT-IR), thermogravimetric analysis (TGA), energy dispersive X-ray (SEM-EDX) and zeta potential. Batch experiments show that QM-chitosan can effectively remove Cr(VI) and P(V), and the main mechanism was believed to be electrostatic interaction. A pseudo second-order model was fitted to describe the kinetic processes of Cr(VI) and P(V) removal. The adsorption isotherms of both Cr(VI) and P(V) on the QM-chitosan were well fitted by the Langmuir isotherm equation. The saturated adsorption capacity of P(V) (2.783 mmol/g) was found to be higher than that of Cr(VI) (2.323 mmol/g), resulting from the size of the H(2)PO(4)(-) ions being smaller than that of the HCrO(4)(-) ions. However, the theoretical calculation and experimental results showed that QM-chitosan had a stronger affinity for Cr(VI) than P(V). The adsorption-desorption of the QM-chitosan was evaluated, and high regeneration rates were demonstrated.