Characteristics of equilibrium, kinetics studies for adsorption of Hg(II), Cu(II), and Ni(II) ions by thiourea-modified magnetic chitosan microspheres

Intelligent-activated carbon prepared from pistachio shells precursor for effective adsorption of heavy metals from industrial waste of copper mine

A novel and efficient bio-adsorbent based on magnetic activated carbon nanocomposites (MAC NCs)-modified by sulfamic acid (H₃NSO₃) has been developed from pistachio shell precursor as agricultural by-products and then was applied for heavy metal removal. Design an experimental model (Central Composite Design (CCD)) for adopting surface response could efficiently be used for adsorption process, and it is an economical way of obtaining the optimal adsorption conditions based on the limited number of experiments. The variants of adsorbent dosage, metal ion concentration, and contact time were optimized for Cu(II) metal by CCD. In addition, adsorption capacity and isoelectric point (pHzpc) of adsorbent were studied at different pH values. Kinetic and isotherm of adsorption were investigated via the Langmuir and the pseudo-second-order model. The maximum adsorption capacity using the Langmuir model was 277.77 mg g^-1 for Cu(II) ions on H₂NSO₃-MAC NCs. Then adsorption process was investigated for ions of Fe(II), Zn(II), and Ni(II) under optimized condition. Also, the competitive adsorption of Fe(II), Zn(II), and Ni(II) ions mixed solution onto H₂NSO₃-MAC NCs was conducted. Adsorption-desorption results exhibited that the H₂NSO₃-MAC NCs can be used up to seven cycles while they have excellent performance. Finally, to evaluate the efficiency of this bio-adsorbent, the removal of heavy metals from wastewater of the Sarcheshmeh copper mine as a real sample was studied. Graphical abstract.

Synthesis of Fe3O4@PVBC-TMT nanoparticles for the efficient removal of heavy metals ions

Core–shell magnetic Fe₃O₄@PVBC–TMT (Fe₃O₄@polyvinylbenzyl chloride–trithiocyanuric acid) nanoparticles containing trithiocyanuric acid groups were fabricated and employed for the fast removal of heavy metals from an aquatic environment. The morphology, structure and properties of Fe₃O₄@PVBC–TMT nanoparticles were characterized by a series of modern analytical tools. The adsorption behavior of the Fe₃O₄@PVBC–TMT nanoparticles for heavy metals ions in aqueous solutions was investigated by batch experiments. The maximum removal capacities of the Fe₃O₄@PVBC–TMT nanoparticles toward Mn²⁺, Ni²⁺, Cu²⁺, Cd²⁺ and Pb²⁺ ions were 127.4, 146.6, 180.5, 311.5, and 528.8 mg g⁻¹, respectively. Importantly, it is found that Pb²⁺ ions can be completely and quickly removed by the Fe₃O₄@PVBC–TMT nanoparticles. The equilibrium was established within 6 min, and the removal efficiencies were found to be 99.9%, 99.8% and 99.5% for Pb²⁺ ions at the initial concentrations of 100 mg L⁻¹, 200 mg L⁻¹ and 300 mg L⁻¹, respectively. It is hoped that the core–shell magnetic Fe₃O₄@PVBC–TMT nanoparticles may find application in wastewater treatment.

Core–shell Fe₃O₄@PVBC–TMT nanoparticles were fabricated and served as a valid magnetic adsorbent for the removal of heavy metals ions.

Adsorptive removal of lead (Pb), copper (Cu), nickel (Ni) and mercury (Hg) ions from water using chitosan silica gel composite

Silica gel chitosan composite was prepared to perform adsorptive experiment of different heavy metal ion solutions. The characterization of chitosan + silica gel (Ch + Sg) composite was done by FTIR and SEM-EDS to understand the presence of active sites and to have an insight on the surface morphology. The adsorption study of heavy metal ions by Ch + Sg composite gives maximum removal percent for Cu, Pb and Ni which were obtained at pH 5 and for Hg at pH 6.The trend of removal by Ch + Sg signifies that maximum removal percent was attained at 120 min. The surface of Ch + Sg is heterogeneous for the adsorption of Hg, Ni and Cu and homogeneous for Pb adsorption. The values obtained for Pb signify that its adsorption best fitted to pseudo first order with the R² value of 0.986, whereas pseudo second order best fitted to the experimental data of Cu, Ni and Hg as R² values which are 0.983, 0.819 and 0.957 respectively. The values of change in entropy (⊿S) obtained for Pb, Cu, Ni and Hg are - 69.33, - 118, - 63.33 and - 98.52 J/mol K respectively. Negative values of change in enthalpy, ⊿H in (kJ/mol) are in the range of - 18.2 to - 37.66 which indicates both physical and chemical adsorption involves in the process of adsorption.

Applications of Hydrogels with Special Physical Properties in Biomedicine

As a polymer matrix containing a large amount of water, hydrogels have been widely used in many fields such as biology and medicine due to its similarity to extracellular matrix components, and its contact with blood, body fluids, and human tissue does not affect the metabolic processes of living organisms. However, due to the lack of unique physical properties of traditional polymer hydrogels, its further application in the high-end field is limited. With the progress of study, a series of hydrogels with special structures, such as double network hydrogel, composite hydrogel, Tetra-PEG gel, and topological gel, have improved the situation to a large extent. At the same time, the progress of research on the biocompatibility and biodegradability of hydrogels, which are expected to be used in biomedical fields, is also worthy of attention. This review introduces four such types of high-strength polymeric hydrogels and the mechanisms for improving their mechanical strength. Moreover, a discussion will be made around specific methods for imparting special physical properties to hydrogels and applications in the field of biomedicine such as cell culture, medical surgery, tissue engineering, and biosensing. At the end of the review, the main reasons and contradictions for the limits of the current applications are explained. An outlook on the future research in related fields and the importance of carrying out research in this area to promote medical progress are emphasized.

An environment-friendly composite as an adsorbent for removal Cu (II) ions

The low-cost composite film was prepared by incorporating chitosan, berry soap fruit extract (rarasaponin), and bentonite as the raw materials. The produced chitosan/rarasaponin/bentonite (CRB) composite exhibits outstanding adsorption capability toward copper metal ions (Cu(II)). A series of static adsorption experiments were carried out to determine the isotherm and kinetic properties of CRB composite in the adsorption process. The adsorption equilibrium shows a good fit with the Langmuir isotherm model; the CRB composite has maximum uptake of Cu (II) of 412.70 mg/g; the kinetic adsorption data exhibit a good fit with the pseudo-second-order model. The thermodynamic parameters, ΔH°, ΔG°, and ΔS°, obtained from the isotherm data indicate that the uptake of copper ions by CRB composite is more favored at low temperatures. This study shows that physicochemical modified adsorbent, namely CRB composite, can remove Cu (II) better than pristine adsorbent of AAB and chitosan. The CRB composite also shows potential reusability.

Magnetic apple pomace biochar: Simple preparation, characterization, and application for enriching Ag(I) in effluents

In order to manage and utilize a large amount of wasted apple pomace, the magnetic biochar was prepared through pyrolysis of apple pomace at 600 °C in nitrogen environment, followed by immersion aging in Fe(II)/Fe(III) aqueous solution. The characterization of the resulting magnetic biochar, herein called the M600APB, showed that the saturation magnetization value and the Brunauer-Emmett-Teller (BET) specific surface area of M600APB were 9.52 emu/g and 102.18 m²/g, respectively. The batch adsorption showed that M600APB could preferentially enrich the low concentration of Ag(I) with the maximum adsorption capacity of 818.4 mg/g in an Ag(I)-Pb(II)-Cu(II)-Ni(II)-Zn(II) aqueous system at ambient temperature. The column adsorption experiments indicated that M600APB could effectively enrich and separate Ag(I) from the same aqueous mixture. The presumable mechanism of Ag(I) adsorption on M600APB involves intra-particle diffusion, coordination, ion exchange and reduction. This study provided an effective approach to both utilize wasted apple pomace and enrich the low concentration of Ag(I) in a sustainable way.

Theoretical modeling of sorption of metal ions on amino-functionalized macroporous copolymer in aqueous solution

With regard to the harmful effects of heavy metals on human health and the environment, the demand for synthesis and investigation of macromolecules with large capacity of harmful substances sorption is ever greater. Quantum-chemical methods may be applied in structural modeling, prediction, and characterization of such molecules and reactions. Sorption of metal ions (Cu²⁺, Cd²⁺, Co²⁺, and Ni²⁺) to triethylenetetramine-functionalized copolymer poly(GMA-co-EGDMA)-teta was successfully modeled by quantum chemical calculations, at the B3LYP//6-311++G**/lanl2dz level. Optimized structures of metal complexes were used for calculation of real binding energy of metal ion within the complex (ΔEr). Solvent and hydrolyzation effects were essential for obtaining the objective values. Solvent effect was included in ΔEr by using the total solvation energy for reaction of formation of tetaOH complex (ΔEs1, the first approach) or by using dehydration energy of free metal ion (ΔEs2, the second approach). Experimental results were confirmed in our theoretical analyses (using the second approach). Graphical abstract Theoretical modeling of divalent metal ions sorption on triethylenetetramine-functionalized copolymer poly(GMA-co-EGDMA)-teta.

Microfluidics combined with ionic gelation method for production of nanoparticles based on thiol-functionalized chitosan to adsorb Hg (II) from aqueous solutions

This work aimed at producing nanoparticles (NPs) based on thiol-functionalized chitosan (CS) using capillary microfluidic (MF) device combined with ionic gelation method to adsorb mercury ion [Hg (II)] from aqueous solutions. In this line, CS was functionalized with epichlorohydrin/cysteaminium chloride (2.73 M ratio) followed by fabricating NPs via MF and bulk mixing (BM) methods. To characterize the morphology, zeta potential, functionality, structure, and magnetic property of the samples, a series of tests such as SEM, TEM, DLS, FTIR, XRD, and VSM were carried out, respectively. The obtained results showed that MF technique was able to produce NPs with a diameter as small as 18 ± 3 nm, and a uniform shape compared to BM method. Thiol groups (-SH) functionalization on CS surface was confirmed by appearing a characteristic peak at 2579 cm^-1. Also, the XRD patterns indicated the appropriate synthesis of Fe₃O₄ (magnetite), and no change in the structure of CS NPs in the presence of magnetite. Moreover, adding the magnetite to thiol-functionalized CS NPs led to suitable saturation magnetization about 26 emu/g to facilitate their separation using a magnetic field. To evaluate the performance of the nanoadsorbent, it has been exposed to Hg (II) in an aqueous solution which in turn the parameters optimization for the adsorption was done via Box-Behnken design (BBD) method, exhibiting the effect of adsorbent dose and the initial concentration of Hg (II) was much more significant than that of pH. Different concentrations of total dissolved solids up to 1000 mg/L had no adverse impact on the adsorption process confirmed by EDAX spectra. The least value of RMSE (5.023) and χ² (0.3) were observed for Redlich-Peterson, Radke-Prausnitz, and UT isotherms. Maximum adsorption capacities calculated using Langmuir and UT models were 1192 mg/g and 1126 mg/g, respectively. Thermodynamic studies demonstrated that the nature of the adsorption process was spontaneous and endothermic. Recovery of nanoadsorbent was successfully carried out using HCl 0.5 mol/L. The adsorption studies revealed that the prepared nanoadsorbent is promising candidate used in mercury removal from a real wastewater potentially.

Chitosan-TiO2 composite: A potential 68Ge/68Ga generator column material

A durable and ready to use ⁶⁸Ge-⁶⁸Ga generator column material is required for its routine use in radiopharmaceutical procedures. The present work comprises preliminary studies for development and evaluation of chitosan-TiO₂ based microsphere (C-TOM) composite towards its competence as a column material. The batch uptake studies showed higher distribution coefficients for ⁶⁸Ge vis-à-vis ⁶⁸Ga in the complete concentration range of HCl examined (0.01-1 mol.L^-1). Furthermore, C-TOM showed enduring physical and chemical stability in 0.01 mol.L^-1 HCl with persistent ⁶⁸Ga elution profiles (>95%) and negligible ⁶⁸Ge breakthrough (2 × 10^-4%) for the preliminary evaluation period of ∼2 months. Overall, the studies indicated that, ⁶⁸Ga with high radionuclidic purity (≥99.99%) can be eluted routinely in a small volume (∼1.5 mL) of 0.01 mol.L^-1 HCl proving its potentials as a novel solid phase extractant for ⁶⁸Ge/⁶⁸Ge generator system.

Preparation and characterization of poly aniline modified chitosan embedded with ZnO-Fe3O4 for Cu(II) removal from aqueous solution

Poly aniline modified chitosan embedded with ZnO/Fe₃O₄ nanocomposites were synthesized using a precipitation method and applied to the removal of Cu(II) from aqueous solution. The synthesized nanocomposite was characterized by FT-IR, XRD, FESEM, TEM, EDS, TGA, BET and zeta-potential analyses. The adsorption batch experiments were conducted as a function of five effective parameters including pH, contact time, initial concentration of copper, temperature, and adsorbent dosage using a central composite design (CCD) in response surface methodology (RSM). Contour and surface plots were used to determine the interaction effects of main factors and optimum conditions of process. The regression equation coefficients were calculated and the data confirmed the validity of second-order polynomial equation for the removal of Cu(II) with novel absorbent. Analysis of variance (ANOVA) showed a high coefficient of determination value (R²) for copper removal being 0.99. The optimum level of the pH, temperature, initial concentration of copper, adsorbent dosage and contact time for maximum Cu(II) removal (94.51%) were found to be 6.5, 31 °C, 82 mg L^-1, 0.81 g L^-1, and 51 min, respectively. It was confirmed from XPS and EDS analyses that heavy metal ions were present on the surface of nanocomposite after adsorption. The adsorption equilibrium data fitted well with the Langmuir isotherm model and the adsorption process followed the pseudo-second-order and intra-particle diffusion kinetic model. The saturated adsorption capacity is found to be 328.4 mg/g. Thermodynamics analysis suggests that the adsorption process is endothermic, with increasing entropy and spontaneous in nature. Further recycling experiments show that nanocomposite still retains 95% of the original adsorption following the 5th adsorption-desorption cycle. The effects of coexist cation ions on the adsorption of Cu(II) was also investigated under optimal condition. All the results demonstrate that nanocomposite is a potential recyclable adsorbent for hazardous metal ions in wastewater.

Synthesis of novel modified magnetic chitosan particles and their adsorption performance toward Cr(VI)

Novel adsorbents, poly([2-(methacryloxy)ethyl]trimethylammonium chloride) modified magnetic chitosan particles (DMCPs), were synthesized via free radical polymerization and applied to adsorb Cr(VI) from aqueous solution. The effects of pH (2-11), Cr(VI) concentration (10-200 mg/L) and contact time (0-420 min) on the adsorption performance were evaluated. The results showed that the adsorption capacity of DMCPs was much larger than that of magnetic chitosan particles (MCPs) in the examined pH range and decreased with Cl^- concentration increasing, indicating that electrostatic interaction and ion exchange are the governing mechanisms of Cr(VI) adsorption by DMCPs. The Langmuir isotherm model and pseudo-second-order kinetic model fitted the experimental data well. The maximum adsorption capacity of DMCPs is 153.85 mg/g. Besides, Cr(VI)-loaded DMCPs could be easily separated and efficiently regenerated. Therefore, DMCPs are promising candidates for Cr(VI) adsorption owing to their excellent performance in a wide pH range, easy separation and good reusability.

Chitosan-Thiobarbituric Acid: A Superadsorbent for Mercury

In the present investigation, chitosan (CH) was supramolecularly cross-linked with thiobarbituric acid to form CT. CT was well characterized by UV, scanning electron microscopy-energy-dispersive X-ray analysis, Fourier transform infrared, NMR, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction analyses, and its adsorption potential for elemental mercury (Hg⁰), inorganic mercury (Hg²⁺), and methyl mercury (CH₃Hg⁺) was investigated. Adsorption experiments were conducted to optimize the parameters for removal of the mercury species under study, and the data were analyzed using Langmuir, Freundlich, and Temkin adsorption isotherm models. CT was found to have high adsorption capacities of 1357.69, 2504.86, and 2475.38 mg/g for Hg⁰, Hg²⁺, and CH₃Hg⁺, respectively. The adsorbent CT could be reused up to three cycles by eluting elemental mercury using 0.01 N thiourea, inorganic mercury using 0.01 N perchloric acid, and methyl mercury with 0.2 N NaCl.

Water-Soluble and Insoluble Polymers, Nanoparticles, Nanocomposites and Hybrids With Ability to Remove Hazardous Inorganic Pollutants in Water

The polymeric materials have presented a great development in adsorption processes for the treatment of polluted waters. The aim of the current review is to present the recent developments in this field of study by examining research of systems like functional water-soluble polymers and water-soluble polymer-metal complexes coupled to ultrafiltration membranes for decontamination processes in liquid-liquid phase. Noticing that a water-soluble polymer can be turned into insoluble compounds by setting a crosslinking point, connecting the polymer chains leading to polymer resins suitable for solid-liquid extraction processes. Moreover, these crosslinked polymers can be used to develop more complex systems such as (nano)composite and hybrid adsorbents, combining the polymers with inorganic moieties such as metal oxides. This combination results in novel materials that overcome some drawbacks of each separated components and enhance the sorption performance. In addition, new trends in hybrid methods combining of water-soluble polymers, membranes, and electrocatalysis/photocatalysis to remove inorganic pollutants have been discussed in this review.

Evaluation of magnetic chitosan beads for adsorption of heavy metal ions

Although many magnetic chitosan materials have been prepared for adsorption of metal ions, there is no standard method for comprehensive evaluation of material performance. The common practice simply compares either adsorption capacity (Q) or saturation magnetization (M_s) of interested materials; however, these two important parameters often work in opposite way. This study aims to establish two methods for evaluation of the overall performance of magnetic materials. The proposed methods consider both heavy metal ion adsorption capacity and magnetic recovery of the material after use. The first method introduces adsorption recovery index (ARI, ARI=Qt), which is calculated using Q and recovery time (t) needed for achieving 98% material recovery. Higher ARI value shows better performance of a magnetic material. The second method uses effort-vector data visualization, in which the position of a magnetic material is shown on a coordinate depicted using normalized Q and M_s value. The distance of the data point to the target (ideal Q and M_s value) indicates the performance of the material. The shorter the distance, the better the overall performance is. Two series of MCBs with different Fe₃O₄ chitosan mass ratios were prepared by using embedding method and chemical co-precipitation method respectively. They were used as model compounds for investigation of the feasibility of the proposed evaluation methods through adsorption of various metal ions (Ag⁺, Cu²⁺, Hg²⁺, Cr³⁺ and Cr⁶⁺) and MCBs recovery test. The best performers were able to be identified by using both methods and the results agreed with each other. Compared with ARI, the effort-vector data visualization was more straightforward and easier to use. This method was successfully applied to evaluate a wide selection of magnetic materials, including those prepared in this work and reported from literatures, for their overall performance.

Facile Preparation of Magnetic Chitosan Coprecipitated by Ethanol/NH3·H2O for Highly Efficient Removal toward Cr(VI)

The adsorption ability of chitosan (CS) usually decreases with the introduction of magnetic particles, and thus magnetic CS has to be chemically modified further to improve its adsorption performance. Herein, a novel magnetic chitosan composite (Fe₃O₄-CS3) with porous structure and evenly distributed Fe₃O₄ was successfully prepared via the reduction of the solubility of CS by ethanol (physical reaction), and followed the coprecipitation of the mixture of FeCl₃/FeCl₂/CS by ethanol/NH₃·H₂O. Without any modification, its maximum adsorption capacity toward Cr(VI) ions can achieve 242.1 mg/g (≈468.6 mg/g of CS). This significant progress could be ascribed to the very fast precipitate rate of CS due to the decrease in solubility induced by ethanol. Ethanol causes rigorous solidification of CS, so that there is not enough time to densify, resulting in a looser CS matrix with a larger pore size. After adsorption, this Fe₃O₄-CS3 could not only be easily separated but also be effectively regenerated by NaOH solution in a rather wider concentration range, showing great potential in the field of heavy metal wastewater treatment.

Synthesis of KMnO4-treated magnetic graphene oxide nanocomposite (Fe3O4@GO/MnO x ) and its application for removing of Cu2+ ions from aqueous solution

A magnetic KMnO₄-treated graphene-oxide-based nanocomposite, Fe₃O₄@GO/MnO _x , was synthesized through a facile hydrothermal technique. The properties of the Fe₃O₄@GO/MnO _x nanocomposite were characterized by SEM, XRD and FTIR. Batch experiments showed that the maximum adsorption capacity calculated by the Langmuir model for Cu²⁺ was 62.65 mg g^-1 at T = 303.15 K. Kinetics and XPS analysis also revealed that the mechanism of Cu²⁺ removal was mainly a chemical adsorption process involving both the MnO _x particles and oxygen functional groups. The prepared Fe₃O₄@GO/MnO _x was found to be an ideal adsorbent for the removal of Cu²⁺ ions due to the MnO _x particle coating, and was easily separated using a magnetic field after utilization. Reusability studies imply that Fe₃O₄@GO/MnO _x is a suitable material for heavy metal ion removal from aqueous solutions in real applications.

Sorption of Hg(II) and Pb(II) Ions on Chitosan-Iron(III) from Aqueous Solutions: Single and Binary Systems

The present work describes the study of mercury Hg(II) and lead Pb(II) removal in single and binary component systems into easily prepared chitosan-iron(III) bio-composite beads. Scanning electron microscopy and energy-dispersive X-ray (SEM-EDX) analysis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and point of zero charge (pHpzc) analysis were carried out. The experimental set covered pH study, single and competitive equilibrium, kinetics, chloride and sulfate effects as well as sorption⁻desorption cycles. In single systems, the Langmuir nonlinear model fitted the experimental data better than the Freundlich and Sips equations. The sorbent material has more affinity to Hg(II) rather than Pb(II) ions, the maximum sorption capacities were 1.8 mmol·g-1 and 0.56 mmol·g-1 for Hg(II) and Pb(II), respectively. The binary systems data were adjusted with competitive Langmuir isotherm model. The presence of sulfate ions in the multicomponent system [Hg(II)-Pb(II)] had a lesser impact on the sorption efficiency than did chloride ions, however, the presence of chloride ions improves the selectivity towards Hg(II) ions. The bio-based material showed good recovery performance of metal ions along three sorption⁻desorption cycles.

The use of new chemically modified cellulose for heavy metal ion adsorption

We have developed a simple one-step method to synthesize novel supramolecular polysaccharide composite from cellulose (CEL) and dibenzo-18-crown 6 using ceric ammonium nitrate as initiator. The [CEL+DB18C6] composites obtained retain properties of their components, namely superior mechanical strength (from CEL), excellent adsorption capability for heavy metal ions from DB18C6. More importantly, the [CEL+DB18C6] composites exhibit truly supramolecular properties. By itself CEL and DB18C6 can adsorb heavy metals. However, adsorption capability of the composite was substantially and synergistically enhanced by adding DB18C6 to CEL. That is, the removal percentage value for Cd²⁺, Zn²⁺, Ni²⁺, Pb²⁺ and Cu²⁺ by [CEL+DB18C6] composites are much higher than removal percentage values of individual CEL and DB18C6 composites. It seems that DB18C6 synergistically interact with CEL to form more stable complexes with heavy metals, and as a consequence, the [CEL+DB18C6] composite can adsorb relatively larger amount heavy metals. The adsorption parameters, such as pH, adsorbent dose, contact time, initial metal ion concentration and temperature were optimized. Desorption studies revealed that the regeneration of modified cellulose saturated with these metallic ions depends on the type and concentration of the regenerating solution (NH₄Cl, HNO₃, NaCl and CaCl₂).

Polymer-based nanocomposites for heavy metal ions removal from aqueous solution: a review

A review of versatile polymer-based composites containing different functional organic and/or inorganic counterparts for the removal of hazardous metal ions from wastewater solutions.

Enhanced adsorption behaviors of Co2+on robust chitosan hydrogel microspheres derived from an alkali solution system: kinetics and isotherm analysis

Chitosan hydrogel microspheres derived from the LiOH/KOH/urea aqueous system demonstrate great characteristics of high mechanical strength, relative chemical inertness, renewability and 3-D fibrous network, making them promising functional supports. This work aims to investigate the tunable Co²⁺ adsorption behaviors on these robust chitosan microspheres in detail, providing the theoretical basis for optimizing the preparation procedure of chitosan microspheres supported Co₃O₄ catalysts in the future. The experimental results revealed that the fabricated original chitosan microspheres with more extended chain conformation could display enhanced adsorption capacity for Co²⁺ at determined concentration both in water and alcohol solutions, which is about 2–7 times higher than that of the conventional chitosan hydrogel microspheres prepared from the acetic acid solution. The kinetic experiments indicated that the adsorption process in water solution agreed with the pseudo-second-order kinetic equation mostly, while the chemical and physical adsorptions commonly contribute to the higher Co²⁺ adsorption on chitosan microspheres in alcohol solution. Moreover, in both cases, the film diffusion or chemical reaction is the rate limiting process in the initial adsorption stage, and the adsorption of Co²⁺ on chitosan microspheres can well fit to the Langmuir isotherm. Thermodynamic analysis demonstrated that such adsorption behaviors were dominated by an endothermic (ΔH° > 0) and spontaneous (ΔG° < 0) process.

The 3-D fibrous network endows the chitosan hydrogel microspheres fabricated from the alkaline solvent system with high mechanical strength and enhanced adsorption capacity of Co²⁺, making them as the ideal and stable catalyst supports.

Chitosan-derived three-dimensional porous carbon for fast removal of methylene blue from wastewater

The chitosan-derived three-dimensional porous carbon (CTC) consisting of large-diameter channels and mesopores was prepared by two steps activation and used for the removal of methylene blue (MB) from wastewater.

Preparation of a novel resin with acyl and thiourea groups and its properties for Cu(II) removal from aqueous solution

In this paper, a new resin (PIDTR) containing acyl and thiourea chelating groups was synthesized and its adsorption performances and mechanism to Cu(II) were investigated by adsorption tests, BET, SEM, FTIR and XPS analyses. Equilibrium data were fitted well with Langmuir model with the maximum adsorption capacity of 1.1608 mmol g^-1 for Cu(II) at pH 5.0. The regeneration and reusability test showed that the adsorption capacities decreased from 0.917 mmol g^-1 to 0.88 mmol g^-1 after five cycles of adsorption and desorption. The thermodynamics showed that the adsorption process was spontaneous and endothermic. The adsorption dynamic demonstrated that two stages in the adsorption process: liquid film diffusion and chemical adsorption. The studies of SEM indicated that Cu(II) ions were adsorbed on the surface of PIDTR. FTIR and XPS analysis further proved that Cu(II) ions were chemisorbed on the surface of PIDTR by formation of CuN, CuO and CuS bonds with the breakage of NH, C=O and S=C bonds in PIDTR.