Adsorption of Cu(II), Co(II), and Ni(II) ions by modified magnetic chitosan chelating resin

Alginate-based adsorbents with adjustable slit-shaped pore structure for selective removal of copper ions

Adopting effective and efficient techniques for the treatment of heavy metal pollution in water bodies plays an important role in guaranteeing the quality of water and the sustainable development of water resources. In this study, GO, MMT and SA were used as raw materials to compare the adsorption behaviors of three alginate-based adsorbents crosslinked with different valence metal ions (Ca2+, Fe3+ and Zr4+) on Cu(II). The aerogels were based on sodium alginate as the matrix material with unique slit-shaped pore structures formed by stacking effect of sheets and chemical bonding. It was found that the pore structures of the aerogels were denser and more orderly with the increase of the valence states of the crosslinked ions, and the affinity for Cu(II) in planar configuration was stronger. The Zr4+-GMSA aerogel had the maximum adsorption capacity of 126.68 mg/g and the Kd of Cu(II) was up to 50.80 L/g, which exhibited good preferential adsorption performance. The adsorption mechanism of Mn+-GMSA aerogels on Cu(II) was mainly ionic exchange, surface complexation and physical adsorption, which was explored by combining XPS and EDS characterizations of Mn+-GMSA before and after adsorption. This scheme can provide valuable and meaningful contribution to realize the selective recovery of Cu(II).

Optimization of simultaneous adsorption of nickel, copper, cadmium and zinc from sulfuric solutions using weakly acidic resins

In this research, the adsorption of nickel (Ni), copper (Cu), cadmium (Cd), and zinc (Zn) from real sulfuric leaching solution with weakly acidic resins has been studied using response surface methodology (RSM). The adsorption process on two weakly acidic resins has been investigated as a function of pH, time, temperature, and resin dosage. The experimental results indicate that the amino phosphoric acid resin removed Ni, Cu, Cd, and Zn from an acidic solution very efficiently. Based on the central composite design (CCD) on the RSM, the statistical criteria of correlation coefficient (R2) values of Ni, Cu, Cd, and Zn are 0.9418, 0.9753, 0.9657, and 0.9189, respectively. The adsorption process followed the pseudo-second-order kinetic model and the thermodynamic calculations indicated the chemical interaction between the resin surface and the metal ions. Enthalpy values greater than zero indicate that the adsorption reaction of the metals is endothermic. The optimal adsorption process was carried out at time of 20 min, temperature of 30 0C, pH of 5, and resin dosage of 4 g/L. In these conditions, the adsorption capacity of nickel, copper, cadmium, and zinc were obtained 13.408, 7.087, 4.357, and 15.040 mg/g, respectively.

One-pot synthesis of novel mesoporous FeOOH modified NaZrH(PO4)2·H2O for the enhanced removal of Co(II) from aqueous solution

One-pot synthesis of a novel mesoporous hydroxyl oxidize iron functional Na-zirconium phosphate (FeOOH-NaZrH(PO4)2·H2O) composites was firstly characterized and investigated its Co(II) adsorption from aqueous solution. Compared to NaZrH(PO4)2·H2O (65.7 mg⋅g-1), the maximum Co(II) adsorption capacity of FeOOH-NaZrH(PO4)2·H2O was improved to be 95.1 mg⋅g-1. BET verified the mesoporous structures of FeOOH-NaZrH(PO4)2·H2O with a larger pore volume than NaZrH(PO4)2·H2O. High pH values, initial Co(II) concentration, and temperature benefited the Co(II) adsorption. Kinetics, isotherms, and thermodynamics indicated an endothermic, spontaneous chemisorption process. FeOOH-NaZrH(PO4)2·H2O has a better Co(II) adsorption selectivity than that of NaZrH(PO4)2·H2O. In particular, FeOOH-NaZrH(PO4)2·H2O exhibited an outstanding reusability after ten cycles of tests. The main possible mechanism for adsorbents uptake Co(II) involved in ion exchange, electrostatic interaction, and -OH, Zr-O bond coordination based on FTIR and XPS analysis. This work presents a feasible strategy to prepare novel modified zirconium phosphate composites for extracting Co(II) from solutions and providing a new insight into the understanding of Co(II) adsorption in the real nuclear Co(II)-containing wastewater.

Novel cellulose derivative containing aminophenylacetic acid as sustainable adsorbent for removal of cationic and anionic dyes

The synthesis and characterization of a novel cellulose derivative as a potential sustainable adsorbent for cationic and anionic dyes are described through processing in ionic liquids. Cellulose was solubilized in ionic liquid with tosyl chloride to form tosyl cellulose which reacted with 4-aminophenylacetic acid through nucleophilic substitution mechanism. The new cellulose derivative was characterized and explored as an effective adsorbent for methylene blue (MB) and methyl orange (MO) removal, and the adsorption behaviors were investigated with various models. The adsorption behavior of the cellulose derivative followed Langmuir and pseudo-second-order models, and the maximum adsorption efficiency recorded 135 and 106 mg/g for MB and MO, respectively. There is possibility that the enhanced adsorption capacity of the cellulose derivative is due to the carboxylic and amino functional groups that provide sufficient active sites to enhance dye molecule affinity. The adsorption results demonstrate that the cellulose derivative containing aminophenylacetic acid was efficient adsorbent for removals of MB and MO.

Eco-Friendly Recycling of Lithium Batteries for Extraction of High-Purity Metals

The significant increase in lithium batteries consumption produces a significant quantity of discarded lithium-ion batteries (LIBs). On the one hand, the shortage of high-grade ores leads to the necessity of processing low-grade ores, which contain a low percentage of valuable metals in comparison to the discarded LIBs that contain a high percentage of these metals, which enhances the processing of the discarded LIBs. On the other hand, the processing of discarded LIBs reduces the negative environmental effects that result from their storage and the harmful elements contained in their composition. Hence, the current study aims at developing cost-effective and ecofriendly technology for cobalt and lithium metal ion recovery based on discarded LIBs. A novel synthesized solid-phase adsorbent (TZAB) was utilized for the selective removal of cobalt from synthetic solutions and spent LIBs. The synthesized TZAB adsorbent was characterized by using 13C-NMR, GC-MS, FT-IR, 1H-NMR, and TGA. The factors affecting the adsorption of cobalt and lithium ions from synthetic solutions and spent LIBs, including the sorbent dose, pH, contact time, temperature, and cobalt concentration were investigated. The conditions surrounding the recovery of cobalt and lithium from processing discarded LIBs, were investigated to optimize the maximum recovery. The Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models were used to study the kinetics of the adsorption process. The obtained results showed that high-purity CoC₂O₄ and Li₃PO₄ were obtained with a purity of 95% and 98.3% and a percent recovery of 93.48% and 95.76%, respectively. The maximum recovery of Co(II) from synthetic solutions was obtained at C₀ = 500 mg·L^-1, dose of 0.08 g, pH 7.5, T = 25 °C, and reaction time = 90 min. The collected data from Langmuir's isotherm and the adsorption processes of Co agree with the data predicted by the D-R isotherm models, which shows that the adsorption of Co(II) onto the TZAB seems to be chemisorption, and the results agree with the Langmuir and D-R isotherm models.

A Porous Geopolymer Containing Ti-Bearing Blast Furnace Slag: Synthesis, Characterization, and Adsorption-Photodegradation Studies towards Methylene Blue Removal under Visible Light Condition

A porous geopolymer with adsorption and photocatalytic degradation functions was successfully developed by utilizing Ti-bearing blast furnace slag (TBBFS) as the raw material. The prepared porous geopolymers were characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, and Fourier transform infrared spectrum. Selective crystallization, water quenching, and natural cooling methods were employed to investigate the influences of these modifications on the applicability of TBBFS as a precursor for geopolymer synthesis. Water-quenched slag with amorphous content was prone to alkali dissolution, and the resulting geopolymer exhibited the highest adsorption capacity (97.18 mg/g) for methylene blue (MB) removal. Selective crystallization at 1400 °C generated a hybrid microstructure consisting of a non-cementitious CaTiO₃ crystallization phase and a cementitious amorphous fraction. The retention of CaTiO₃ in the final geopolymer enables a bifunctionality in adsorption-photodegradation. Particularly, the adsorption and photodegradation processes under various conditions were investigated. The superior removal efficiency for MB could be attributed to the synergistic effects between the geopolymer matrix and CaTiO₃, leading to an enhancement in the formation of hydroxyl radicals. The conversion of TBBFS into porous geopolymer offers an efficient and straightforward solution for slag utilization and dye removal.

Preparation of polyamidoamine dendrimer-functionalized chitosan beads for the removal of Ag(I), Cu(II), and Pb(II)

Chitosan bead grafted by third-generation dendrimers (CB-G3) with a diameter of 1.40 mm was synthesized to investigate their performance in recovering Ag(I), Cu(II), and Pb(II) ions in aqueous media. The prepared adsorbents were characterized by XRD, FT-IR, elemental analysis, TGA, and SEM, and the effects of pH, contact time, concentration, and temperature were examined. The results showed that the adsorbents were successfully fabricated. The optimum pH value was 5, and the increased generation number contributed to adsorption capacity improvement, indicating that electrostatic interactions between amine groups and metal ions are the governing mechanism of adsorption by the CB-G3. The kinetics, isotherms, and thermodynamics of Ag(I), Cu(II), and Pb(II) adsorption onto the CB-G3 were investigated. The adsorption processes can be described using pseudo-second-order kinetic and Langmuir models. The maximum monolayer adsorption capacities were 105.62, 88.82, and 97.87 mg·g^-1 for Ag(I), Cu(II), and Pb(II) at 30 °C within 210 min, respectively. Electrostatic interactions and hydrogen bonds are the main mechanisms between metal ions and N atoms. Therefore, the CB-G3 is a promising candidate for Ag(I), Cu(II), and Pb(II) adsorption owing to its splendid ability in easy separation, good adsorptivity, and reusability for efficiently adsorbing Ag(I), Cu(II), and Pb(II) ions.

Synthesis and adsorption performance of functionalized chitosan and carboxyethylsilanetriol hybrids

A novel adsorbent from cationic chitosan derivative and anionic silica precursor was fabricated to remove methylene blue (MB). The hybrid material was prepared from N-guanidinium chitosan acetate (GChi) and carboxyethylsilanetriol sodium salt by a simple ionic interaction followed by sol-gel approach. Multiple characterization methods were used to analyze the morphology and the structure of the well-prepared functionalized material. Batch experiments were conducted to optimize the various operational parameters. The Langmuir isotherm was used to fit the data, and it predicted monolayer adsorption with a maximum capacity of 334 mg g^-1. A pseudo-second-order equation fit the adsorption process well. Chitosan/silica hybrids containing carboxylic groups are efficient and cost-effective adsorbents for cationic dyes adsorption from aqueous solutions.

Synthesis, Characterization and Investigation of Cross-Linked Chitosan/(MnFe2O4) Nanocomposite Adsorption Potential to Extract U(VI) and Th(IV)

A cross-linked chitosan/(MnFe2O4) CCsMFO nanocomposite was prepared using co-precipitation methods and used as a nanomaterial to extract U(VI) and Th(IV) from an aqueous solution based on adsorption phenomena. The contact time of experiments shows a rapid extraction process within 30 min by the CCsMFO nanocomposite. The solution pH acts a critical role in determining qm value, where pH 3.0 was the best pH value to extract both ions. The pseudo-second-order equilibrium model illustrated the kinetics equilibrium modal extraction process. Adsorption isotherm of U(VI) at pH 3.0 by CCsMFO nanocomposite is an endothermic process. In contrast, the adsorption isotherm of Th(IV) at pH 3.0 by CCsMFO nanocomposite is an exothermic process. The reusability of CCsMFO nanocomposite was tested using basic eluents as suitable conditions for the chemical stability of CCsMFO nanocomposite; the reusability results show promising results for the removal of U(VI) adsorbed onto CCsMFO nanocomposite with 77.27%, after 12 h by Na2CO3 as eluent. At the same time, the reusability results show good reusability for removal of U(VI) adsorbed onto CCsMFO nanocomposite with 21.82%, after 8 h by EDTA as eluent.

Suspension polymerization for synthesis of new hypercrosslinked polymers nanoparticles for removal of copper ions from aqueous solutions

Novel hypercrosslinked polymers nanoparticles (HCPNs) were designed by suspension polymerization technique with high surface area as well as HCPNs with functional groups have the affinity to removal of copper ions from aqueous solutions. Two HCPNs were synthesized through a two-step reaction, initially including the suspension polymerization of N-methacryloxytetrachlorophthalimide (NMTPA) with divinyl benzene (DVB) to give poly(NMTPA-co-DVB) and followed by the treatment of poly(NMTP-co-DVB) with triethylenetetramine (TETA) to give HCPNs (1) and with tetraethylenepentamine (TEPA) to give HCPNs (2). Using scanning electron microscopy and transmission electron microscopy, the surface morphology of the particles of the synthesized HCPNs was detected, and also, the particle size was measured. Also, the chemical structures of the synthesized compounds were illustrated by Fourier transform infrared spectroscopy and 1H-nuclear magnetic resonance (1H NMR). Thermal stability of the synthesized HCPNs was characterized by thermogravimetric analysis. The results illustrated that the particle size of the synthesized HCPNs is in range of 25–50 nm. The synthesized HCPNs compounds were reported for the separation of copper ions from wastewater, in which the results showed a very good affinity for these compounds for separation of copper ions from wastewater.

Evaluation of diethylenetriaminepentaacetic acid modified chitosan immobilized in amino-carbmated alginate matrix as a low cost adsorbent for effective Cu(II) recovery

In present work, facile synthesis of a biocompatible hybrid biosorbent based on diethylenetriaminepentaacetic acid (DTPA) modified chitosan immobilized in organo-functionalized sodium alginate matrix (DTPA-MCSA) was carried out. DTPA-MCSA was casted in microspherical hydrogel beads. Three dimensional microporous geometry of the biosorbent remained well preserved as observed in SEM analysis which revealed the improved mechanical strength of the alginate matrix. Surface functionalization of base biopolymers was confirmed by FTIR and SEM analysis. Equilibrium sorption studies using DTPA-MCSA for Cu(II) from aqueous medium were carried out in batch mode and found considerably dependent on pH, contact sorption time, temperature and initial copper concentration. Isothermal sorption data showed close correlation with Langmuir model as evident from nonlinear fitting of data (R 2 ˜ 0.99) at different temperatures. The experimental sorption capacity (q e) was found nearly 67 mg/g using 100 mg/L initial concentration of copper ions. Kinetic studies were conducted using different initial concentrations for better elucidation of results and it showed better correlation with pseudo second order rate equation which unveiled that strong ion pair coordination and complexation exist between Cu(II) and newly grafted chelating sites of DTPA-MCSA. Thermodynamic parameters suggested that the adsorption process is spontaneous and endothermic. The results concluded that DTPA-MCSA could be a better candidate for adsorptive remediation of copper ions from liquid waste.

Water Saturated with Pressurized CO2 as a Tool to Create Various 3D Morphologies of Composites Based on Chitosan and Copper Nanoparticles

Methods for creating various 3D morphologies of composites based on chitosan and copper nanoparticles stabilized by it in carbonic acid solutions formed under high pressure of saturating CO2 were developed. This work includes a comprehensive analysis of the regularities of copper nanoparticles stabilization and reduction with chitosan, studied by IR and UV-vis spectroscopies, XPS, TEM and rheology. Chitosan can partially reduce Cu2+ ions in aqueous solutions to small-sized, spherical copper nanoparticles with a low degree of polydispersity; the process is accompanied by the formation of an elastic polymer hydrogel. The resulting composites demonstrate antimicrobial activity against both fungi and bacteria. Exposing the hydrogels to the mixture of He or H2 gases and CO2 fluid under high pressure makes it possible to increase the porosity of hydrogels significantly, as well as decrease their pore size. Composite capsules show sufficient resistance to various conditions and reusable catalytic activity in the reduction of nitrobenzene to aniline reaction. The relative simplicity of the proposed method and at the same time its profound advantages (such as environmental friendliness, extra purity) indicate an interesting role of this study for various applications of materials based on chitosan and metals.

Polyethyleneimine incorporated chitosan/α-MnO2 nanorod honeycomb-like composite foams with remarkable elasticity and ultralight property for the effective removal of U(VI) from aqueous solution

The development of new adsorbents is needed to address the environmental challenges of radioactive wastewater treatment. Herein we reported a novel polyethyleneimine incorporated chitosan/α-MnO₂ nanorod honeycomb-like composite (PCM) foam with remarkable elasticity and ultralight property for U(VI) removal. Among different PCM sorbents, PCM-40 possessed the highest sorption capacity for U(VI) due to its highly developed macroporous structure and high content of amine/imine groups. The kinetics were well-simulated by the pseudo-second-order model, indicating chemisorption as the rate-controlling step. The isotherms could be described by the Langmuir model, suggesting mono-layer homogeneous sorption of U(VI). The maximum sorption U(VI) capacity for PCM-40 reaches up to 301.9 mg/g at pH 4.5 and 298 K. The thermodynamic parameters revealed the spontaneous and endothermic nature of the adsorption process. The main sorption mechanism is related to the complexation of uranyl ions with the amine/imine and hydroxyl groups. The high sorption capacity, fast kinetic rate and relatively good selectivity of PCM-40 highlights its promising application in radioactive pollution cleanup.

Hydroxypicolinic acid tethered on magnetite core-silica shell (HPCA@SiO2@Fe3O4) as an effective and reusable adsorbent for practical Co(II) recovery

The soaring demand and future supply risk for cobalt (Co) necessitate more efficient adsorbents for its recycling from electronic wastes, as a cheaper and less hazardous option for its production. Herein, a magnetic adsorbent covalently tethered with 5-hydroxypicolinic acid (HPCA) as Co(II) ligand was developed. The magnetic component (Fe₃O₄) was protected with silica (SiO₂), then silanized with chloroalkyl linker and subsequently functionalized with HPCA via S_N2 nucleophilic substitution (HPCA@SiO₂@Fe₃O₄). Results from FTIR, TGA, EA, and XPS confirm the successful adsorbent preparation with high HPCA loading of 2.62 mmol g^-1. TEM-EDS reveal its imperfect spherical morphology with ligands well-distributed on its surface. HPCA@SiO₂@Fe₃O₄ is hydrophilic, water-dispersible and magnetically retrievable, which is highly convenient for its recovery. The Co(II) capture on HPCA@SiO₂@Fe₃O₄ involves monodentate coordination with carboxylate (COO^-) and lone pair acceptance from pyridine (aromatic -N = ) moiety of HPCA, with minor interaction from acidic silanols (Si-O^-). The binding occurs at 2 HPCA: 1 Co(II) ratio, that follows the Sips isotherm model with competitive Q_max = 92.35 mg g^-1 and pseudo-second order kinetics (k₂ = 0.0042 g mg^-1 min^-1). In a simulated LIB liquid waste, HPCA@SiO₂@Fe₃O₄ preferentially captures Co(II) over Li(I) with α_Li(I)^Co(II)=166 and Mn(II) with α_Mn(II)^Co(II)=55, which highlights the importance of HPCA for Co(II) recovery. Silica protection of Fe₃O₄ rendered the adsorbent chemically stable in acidic thiourea solution for its regeneration by preventing the deterioration of the magnetic component. Covalent functionalization averted ligand loss, which allowed HPCA@SiO₂@Fe₃O₄ to deliver consistent and reversible adsorption/desorption performance. Overall results demonstrate the potential of HPCA@SiO₂@Fe₃O₄ as a competitive and practical adsorbent for Co(II) recovery in liquid waste sources.

Photocatalytic Removal of Cr(VI) by Thiourea Modified Sodium Alginate/Biochar Composite Gel

Heavy metal pollution is an important problem in current water treatments. Traditional methods for treating chromium-containing wastewater have limitations such as having complicated processes and causing secondary pollution. Therefore, seeking efficient and fast processing methods is an important research topic at present. Photocatalysis is an efficient method to remove Cr(VI) from aqueous solutions; however, conventional photocatalysts suffer from a low metal absorption capacity, high investment cost, and slow desorption of trivalent chromium from the catalyst surface. In this study, a novel composite gel was synthesized by chemically modifying thiourea onto sodium alginate, which was then mixed with biochar. The composite gel (T-BSA) can effectively remove 99.98% of Cr(VI) in aqueous solution through synergistic adsorption and photocatalytic reduction under UV light irradiation. The removal mechanism of Cr(VI) was analyzed by FT-IR, FESEM, UV-DRS and XPS. The results show that under acidic conditions, the amino group introduced by chemical modification can be protonated to adsorb Cr(VI) through electrostatic interaction. In addition, the biochar as a functional material has a large specific surface area and pore structure, which can provide active sites for the adsorption of Cr(VI), while the photo-reduced Cr(III) is released into the solution through electrostatic repulsion, regenerating the adsorption sites, thereby improving the removal performance of Cr(VI). Biochar significantly intensifies the Cr(VI) removal performance by providing a porous structure and transferring electrons during photoreduction. This study demonstrates that polysaccharide-derived materials can serve as efficient photocatalysts for wastewater treatment.

Bi-layered hollow amphoteric composites: Rational construction and ultra-efficient sorption performance for anionic Cr(VI) and cationic Cu(II) ions

Here, we have developed a novel bilayer hollow amphiphilic biosorbent (BHAB-3) with large adsorption capacity, rapid adsorption kinetics, and cost-effective for the removal of Cr(VI) and Cu(II) from aqueous solutions. The synthesis was based on the clever use of freeze-drying to fix the structure, secondary modification of the carboxymethyl cellulose microspheres with polyethyleneimine and cross-linking by glutaraldehyde. The consequences of pH, initial concentration, contact time and temperature on adsorption were investigated. The Langmuir model fits showed that the maximum adsorption capacities of the two target heavy metal ions reached 835.91 and 294.79 mg/g, respectively. Moreover, BHAB-3 was characterized by SEM, FT-IR, TGA, and XPS synergistically, showing that it exhibits a strong complexation ability for Cu(II) and a strong electrostatic effect for Cr(VI). Adsorption and desorption experiments showed only a slight decrease in the adsorption capacity of the BHAB-3 for Cr(VI) and Cu(II) ions after 5 and 26 cycles, respectively. Given the excellent properties of this adsorbent, it is a promising candidate for heavy metal ion removal.

Ionic chitosan/silica nanocomposite as efficient adsorbent for organic dyes

A new adsorbent from chitosan and anionic silica was prepared by ionic interaction followed by sol-gel process. The obtained nanocomposite was characterized by different techniques: FTIR, XRD, SEM/EDX, TGA, and TEM. The results showed that silica precursor interacts with chitosan and deposits as regular spherical nanoparticles. The methylene blue (MB) adsorption by chitosan/silica nanocomposite achieved the adsorption equilibrium within 60 min. The adsorption method is fitted to the pseudo-second-order kinetic model and the Langmuir adsorption model with a maximum adsorption capacity of 847.5 mg/g at slight alkaline solution. Chitosan/silica composite displayed high regeneration capability and recovery of MB up to five cycles without the loss of the adsorption efficiency. The current study showed that as-prepared chitosan/silica nanocomposite is an appropriate material for the adsorption of organic pollutants from wastewater.

Highly selective removal and recovery of Ni(II) from aqueous solution using magnetic ion-imprinted chitosan nanoparticles

Nickel (Ni) is one of the most common heavy metals. In this study, nano-sized magnetic ion-imprinted polymers (MIIPs) were synthesized using chitosan as the functional monomer, and used for selective adsorption and recovery of Ni(II) from solutions. The results showed MIIPs possessed high sorption selectivity for Ni(II), and the change in pH (5.0-9.0) exerted insignificant influence on the ion adsorption, allowing almost complete elution and recovery of adsorbed Ni(II) ions by using 0.5% EDTA-Na solution. Moreover, the sorption capacity of the recycled MIIPs decreased by only about 10% after 15 adsorption-desorption cycles. The time required for establishing the adsorption equilibrium was less than 1 h. The sorption process was predominant and endothermic, and could be well described by both Langmuir isotherm model and pseudo-second-order kinetic model. Therefore, the synthesized MIIPs was a suitable adsorbent for highly selective, fast and efficient removal and recovery of low-concentration Ni(II) ions from wastewaters.

Chitosan-derived hydrothermally carbonized materials and its applications: A review of recent literature

Chitosan (CS) is a linear polysaccharide biopolymer, one of the most abundant biowastes in the environment. This makes chitosan a potential material for a wide range of applications. To improve CS's properties, chitosan has to be chemically modified. Hydrothermal carbonization (HTC) is a sustainable process for converting chitosan to solid carbonized material. This article presents a review on the applications of hydrothermally treated chitosan in different fields such as water treatment, heavy metals adsorption, carbon dioxide capturing, solar cells, energy storage, biosensing, supercapacitors, and catalysis. Moreover, this review covers the impact of HTC process parameters on the properties of the produced carbon material. The diversity of applications indicates the great possibilities and multifunctionality of hydrothermally carbonized chitosan and its derivatives. The utilization of HTC-CS is expected to further expand as a result of the movement toward sustainable, environmentally-friendly resources. Thus, this review also recommends a few suggestions to improve the properties of HTC chitosan and its comprehensive applications.

Carboxymethylcellulose-chitosan film modified magnetic alkaline Ca-bentonite for the efficient removal of Pb(II) and Cd(II) from aqueous solution

In order to endow alkaline Ca-bentonite (ACB) with magnetic separation ability, simultaneously obtain better magnetic stability and stronger removal capacity of heavy metal cations; magnetic alkaline Ca-bentonite/carboxymethylcellulose-chitosan film (MACB/C-C) was prepared by organic modification of magnetic alkaline Ca-bentonite (MACB) using non-toxic carboxymethylcellulose and chitosan. Textural characterization results revealed that magnetic Fe3O4 nanoparticles were successfully immobilized on ACB and modified with C-C. The functionalized layer of C-C concurrently enhanced the stability of Fe3O4 and removal performances of heavy metal cations. Adsorption results indicated that MACB/C-C exhibited thorough separation from aqueous solution and greater uptake ability for Pb(II) and Cd(II) (483 mg·g-1 and 123 mg·g-1) than the nascent MACB (335 mg·g-1 and 76 mg·g-1), respectively, at pH 5 and 25 °C temperature. The adsorption of Pb(II) and Cd(II) on MACB/C-C mainly occurred via surface precipitation and complexation when pH > 2. MACB/C-C could be efficiently recycled with marginal decrease in adsorption capacity. The current approach credited to the convenient operation, simplified synthesis, and high efficiency of MACB/C-C could be deemed as a promising alternative for the removal of heavy metal cations from wastewater.

Preparation of EDTA-modified magnetic attapulgite chitosan gel bead adsorbent for the removal of Cu(II), Pb(II), and Ni(II)

Attapulgite (ATP) has a unique porous layered chain structure and is an excellent environment-friendly decolorizer. However, its high viscosity makes it difficult to separate. First, it was combined with magnetic Fe₃O₄ nanoparticles to obtain Fe₃O₄-ATP that is easy to recycle and reuse. Then, Fe₃O₄-ATP nanoparticles were embedded in chitosan (CS) gel beads, and glutaraldehyde was used for cross-linking and curing. Lastly, ethylenediaminetetraacetic acid (EDTA) was successfully connected to Fe₃O₄-ATP/CS gel beads through amidation reaction, which further increased the capability of the adsorbent to adsorb heavy metal ions. The prepared magnetic composite adsorbent is a sphere with a rough surface and porous structure. The maximum adsorption capacity of the prepared Fe₃O₄-ATP/EDTA/CS adsorbent for Pb(II), Cu(II), and Ni(II) is 368.32, 267.94, and 220.31 mg g^-1, respectively. After 5 times of repeated use, Fe₃O₄-ATP/EDTA/CS still showed good adsorption capacity for Cu(II), Pb(II), and Ni(II). Fe₃O₄-ATP/EDTA/CS has a large adsorption capacity for heavy metal ions, a wide pH applicability, good reuse, and rapid magnetic separation. In addition, Cu(II) loaded Fe₃O₄-ATP/EDTA/CS also showed good catalytic degradation performance for bisphenol A. This study prepared a new type of adsorbent with good adsorption performance and provided a promising method for the treatment of wastewater.

Facile preparation of EDTA-functionalized magnetic chitosan for removal of co(II) from aqueous solutions

In this study, an efficient adsorption and reusable magnetic ligand material (Fe₃O₄@Chitosan-EDTA) was synthesized by binding EDTA dianhydride onto magnetic chitosan, and it was employed in removal of Co(II) from aqueous solution. The maximum adsorption capacity of Co(II) onto Fe₃O₄@CS-EDTA was 48.78 mg/g at pH = 5 (303 K), which is much higher than that of Fe₃O₄@Chitosan as well as chitosan. The kinetics of Co(II) on the Fe₃O₄@CS-EDTA was consistent with the pseudo-second-order model. The equilibrium data were better fit with the Langmuir isothermal model than with the Freundlich isothermal model, suggesting that the adsorption mechanism was chemical monolayer homogeneous adsorption. The thermodynamic data showed that the sorption of Co(II) was spontaneous. Furthermore, after four cycles, the adsorption capacity of Co(II) onto the Fe₃O₄@CS-EDTA still retained 84.5% of the capacity of the fresh adsorbent, indicating that Fe₃O₄@CS-EDTA can be considered a promising recyclable adsorbent to remove heavy-metal ions from wastewater.

Antimonate removal by diatomite modified with Fe-Mn oxides: application and mechanism study

In this study, diatomite coated with Fe-Mn oxides (DFMO) was synthesized through calcination. The adsorption of antimonate (Sb(V)) by DFMO was studied, and environmental factors affecting the adsorption were investigated. The components of DFMO were identified as γ-Fe₂O₃, γ-MnO₂, and SiO₂, in the presence of diatomite covered with nanoscale metal oxides. Batch experiments were carried out to evaluate the antimonate adsorption performance in aqueous solution. Results showed that maximum Sb(V) adsorption capacity of DFMO reached 10.7 mg/g at pH 4, corresponding to 22.2 mg/g per unit metal oxides. Antimonate adsorption occurred on heterogenous surface, following the Freundlich and Pseudo-second order model. Overall, antimonate adsorption was favored at acidic condition due to low point of zero charge. However, when treating electroplating wastewater, neutral pH condition exhibited a higher efficiency than acidic pH, because co-existing ions in electroplating wastewater significantly affects antimony adsorption. Further investigation showed that among different potential co-existing ions, fluoride can strongly inhibit the adsorption of antimonate at 5 mg/L under pH 4. Density functional theory (DFT) analysis confirmed that adsorption energy on DFMO follows: HF < F^- < Sb(OH)₆^-, indicating that fluoride is easier to bind with DFMO compared to antimonate, especially under pH 3.5 at which fluoride exists as HF. Moreover, the competitive adsorption of fluoride toward antimonate indicated the necessity of pre-treatment like neutralization and precipitation before adsorption process.

Adsorption behavior of heavy metal ions on a polymer-immobilized amphoteric biosorbent: Surface interaction assessment

Here we unveiled a novel magnetically separable amphoteric biosorbent (PD-Fe₃O₄@CCS) and investigated its adsorption behavior toward two classes of heavy metals, hexavalent chromium (Cr(VI)) and copper (Cu(II)) ions from water. Results indicated that the adsorption behavior of PD-Fe₃O₄@CCS for Cr(VI) was well described by Langmuir model; while for Cu(II) adsorption, the Freundlich model was the better one. Based on the kinetic results, both Cr(VI) and Cu(II) adsorption on PD-Fe₃O₄@CCS fitted well with the pseudo-second-order kinetic model. To evaluate the reusability and stability of PD-Fe₃O₄@CCS, regeneration tests were carried out for five cycles. Furthermore, the applicable feasibility of PD-Fe₃O₄@CCS in the real water matrix (including the single and binary pollutant systems) was studied, and results suggested the promising potential of PD-Fe₃O₄@CCS for large-scale application. Apart from these, the surface interactions between PD-Fe₃O₄@CCS and heavy metal ions in single and binary systems were systematically investigated based on FTIR and XPS analyses, which provided an essential implication for comprehending the interactions between biosorbents and contaminants in wastewater.

A systematic review on carbohydrate biopolymers for adsorptive remediation of copper ions from aqueous environments-Part B: Isotherms, thermokinetics and reusability

The presence of copper in aquatic environment is a serious threat for human health and ecosystem conservation. Adsorption is a powerful, operable and economic method for remediation of copper ions from aqueous phase. Carbohydrate biopolymers have emerged as promising, effective and environmental-friendly adsorbents for copper remediation. In part A of this review, different types of carbohydrate biopolymer adsorbents were surveyed focusing on prevalent and novel synthesis and modification methods. In current work (part B of the review), isothermal, thermodynamic and kinetic aspects of the copper adsorption by carbohydrate-based adsorbents as well as the regeneration and reusability of the biopolymer adsorbents are overviewed. Adsorption capacity, time required for equilibrium (adsorption rate), thermal-sensitivity of the adsorption, favorability extent, and sustainability of the adsorbents and adsorption processes are valuable and useful outcomes, resulted from the thermokinetic and reusability investigations. Such considerations are critical for the process design and scale up regarding technical, economical and sustainability of the adsorption process.

Adsorption Evaluation for the Removal of Nickel, Mercury, and Barium Ions from Single-Component and Mixtures of Aqueous Solutions by Using an Optimized Biobased Chitosan Derivative

In this experimental study, the use of 5-hydroxymethyl-furfural (HMF) organic compound as a grafting agent to chitosan natural polymer (CS) was examined. One optimized chitosan derivative was synthesized, and then tested (CS-HMF), in order to uptake nickel, mercury, and barium metal ions from single- and triple-component (multi-component) aqueous solutions. The characterization of the material before and after the metal uptake was achieved by scanning electron microscopy (SEM). The ability of the adsorption of CS-HMF was tested at pH = 6. The adjusting of temperature from 25 to 65 °C caused the increase in the adsorption capacity. The equilibrium data were fitted to the models of Langmuir and Freundlich, while the data from kinetic experiments were fitted to pseudo-1st and pseudo-2nd order models. The best fitting was achieved for the Langmuir model (higher R²). The adsorption capacity for nickel, mercury, and barium removal at 25 °C (single component) was 147, 107, and 64 (mg/g), respectively. However, the total adsorption capacity for the multi-component was 204 mg/g. A thermodynamic study was also done, and the values of ΔG⁰, ΔH⁰, and ΔS⁰ were evaluated.

Starch, cellulose, pectin, gum, alginate, chitin and chitosan derived (nano)materials for sustainable water treatment: A review

Natural biopolymers, polymeric organic molecules produced by living organisms and/or renewable resources, are considered greener, sustainable, and eco-friendly materials. Natural polysaccharides comprising cellulose, chitin/chitosan, starch, gum, alginate, and pectin are sustainable materials owing to their outstanding structural features, abundant availability, and nontoxicity, ease of modification, biocompatibility, and promissing potentials. Plentiful polysaccharides have been utilized for making assorted (nano)catalysts in recent years; fabrication of polysaccharides-supported metal/metal oxide (nano)materials is one of the effective strategies in nanotechnology. Water is one of the world's foremost environmental stress concerns. Nanomaterial-adorned polysaccharides-based entities have functioned as novel and more efficient (nano)catalysts or sorbents in eliminating an array of aqueous pollutants and contaminants, including ionic metals and organic/inorganic pollutants from wastewater. This review encompasses recent advancements, trends and challenges for natural biopolymers assembled from renewable resources for exploitation in the production of starch, cellulose, pectin, gum, alginate, chitin and chitosan-derived (nano)materials.

Chitosan-based molecular imprinted polymer for extraction and spectrophotometric determination of ketorolac in human plasma

A selective chitosan-based ion exchange molecular imprinted polymer (MIP) was prepared for ketorolac (KET) using the sol-gel method and glutaraldehyde as a crosslinker. The nonimprinted polymer (NIP) was prepared and used as a control, during the whole experiment. The chemical and morphological characteristics of the prepared polymers were investigated using FTIR and SEM, respectively. The prepared MIP was applied to determine the optimum operational conditions for KET extraction from dilute aqueous solutions. The adsorption step was performed at pH 5 and a contact time of 20 min, using 0.1 N HCl as an elution solvent for 30 min. The specificity of the prepared polymer was indicated by an imprinting factor of 1.45. The prepared MIP was successfully applied for selective solid phase extraction and subsequent determination of KET in spiked human plasma samples over a range of 2-20 μg/mL, with a mean % recovery of 94.62% using derivative spectroscopy.

CTAB-intercalated molybdenum disulfide nanosheets for enhanced simultaneous removal of Cr(VI) and Ni(II) from aqueous solutions

The treatment of heavy metal pollution in aquatic environment, especially the pollution caused by multiple heavy metal ions, has been a growing global concern for decades. To address this problem, it is urgent to explore effective and low cost adsorbents which can remove multiple heavy metal ions simultaneously. Herein, Cr(VI) and Ni(II) removal from water by MoS₂ with widened interlayer spacing was systematically investigated in comparison with pure MoS₂. A series of techniques, including X-ray powder diffraction (XRD), Transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) surface area and porosimetry analysis were applied to characterize the nanocomposites. The XRD results confirmed the enlarged interlayer spacing of MoS₂ by intercalating cetyl trimethyl ammonium bromide (CTAB) into the interlamination. The maximum adsorption capacities of Cr(VI) and Ni(II) for MoS₂/CTAB were 79.4 mg g^-1 and 88.3 mg g^-1, respectively. Moreover, a synergistic effect in the simultaneous removal of Cr(VI) and Ni(II) was observed. A new Cr(VI) removal mechanism involving redox reaction between Cr(VI) and Mo(IV) in MoS₂/CTAB was verified. The removal efficiencies of Cr(VI) and Ni(II) still remained high at the end of fifth cycle, indicating that MoS₂/CTAB has a great potential to remove heavy metals from wastewater.

Selenium(VI) and copper(II) adsorption using polyethyleneimine-based resins: Effect of glutaraldehyde crosslinking and storage condition

This study synthesizes polyethyleneimine-glutaraldehyde (PEI-GA) resins using different amounts of GA to crosslink with a certain amount of PEI and compares these adsorbents for the adsorption of Cu(II) (cations) and Se(VI) (anions). Moreover, the stability of adsorption affinity of PEI-GA resins stored in open or sealed conditions is also studied. Results show that the amount of GA for PEI crosslinking does not affect the adsorption performance for Se(VI), especially when PEI/GA mass ratio is less than 2, while for Cu(II), the increase on GA amount decreases Cu(II) adsorption capacity. This difference is directly correlated to the change in the adsorption mechanism from electrostatic attraction to chelation. The primary and secondary amine groups on PEI can easily react with CO₂ in the air to form carbamate, potentially affecting the adsorption performance of PEI. Results also indicate that the adsorption efficiency for Se(VI) is hardly affected by the storage condition, while that for Cu(II) decreases significantly after 20-day storage compared to the freshly prepared ones. In addition, all of the adsorbents can selectively remove Se(VI) from Se(VI)-As(V) system and Cu(II) from Pb(II)-Cu(II) system, indicating that the crosslinking has no significant influence on the selectivity.

New effective 3-aminopropyltrimethoxysilane functionalized magnetic sporopollenin-based silica coated graphene oxide adsorbent for removal of Pb(II) from aqueous environment

A new effective adsorbent, 3-aminopropyltrimethoxysilane functionalized magnetic sporopollenin (MSp@SiO₂NH₂) based silica-coated graphene oxide (GO), (GO@SiO₂-MSp@SiO₂NH₂) was successfully synthesized and applied for the first time in the removal of hazardous Pb(II) ions from aqueous solution. The properties of the composite were characterized using Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX) and vibrating-sample magnetometery (VSM). Evaluation of GO@SiO₂-MSp@SiO₂NH₂ adsorption performance at optimum conditions revealed that the adsorbent has a maximum adsorption capacity of 323.5 mg/g for Pb(II) using 50-200 mg/L initial Pb(II) ions concentrations. Initial and final concentrations of Pb(II) ions in aqueous solution were analyzed using graphite furnace atomic absorption spectroscopy (GF-ASS). The adsorption behavior of Pb(II) ions onto GO@SiO₂-MSp@SiO₂NH₂ was studied using Langmuir, Freundlich and Temkin isotherms models. The values of coefficient of determination showed that the adsorption best fitted the Langmuir model (R² = 0.9994). Kinetic studies suggested that the adsorption of Pb(II) ion followed a pseudo-second-order rate model (R² = 1.00) and thermodynamic studies revealed that the adsorption process is endothermic and spontaneous. The effect of co-existing ions on Pb(II) ion adsorption were also studied and found to have considerable effects only at higher matrix concentration. The adsorbent can be reused up to ten times and retain its good adsorption capacity. In addition, GO@SiO₂-MSp@SiO₂NH₂ showed great potential for Pb(II)removal from industrial wastewater samples.