Fabrication of xanthate-modified chitosan/poly(N-isopropylacrylamide) composite hydrogel for the selective adsorption of Cu(II), Pb(II) and Ni(II) metal ions

Adsorptive removal of heavy metal ions from wastewater using shrimp chitosan-cysteine-glutaraldehyde hydrogel as a sustainable biosorbent

A new biosorbent, crosslinked chitosan-cysteine-glutaraldehyde hydrogel (CSCys-HG), was successfully synthesized and characterized using microanalytical and spectroscopic methods. CSCys-HG exhibited a high gel fraction and swelling capacity, indicating the highest degree of crosslinking and porosity. To optimize the performance of CSCys-HG as a scavenger for heavy metal ions (HMIs), its adsorptive removal of Cu(II) and Pb(II) ions from wastewater was studied through batch adsorption experiments under various conditions. The optimal parameters were determined to be an adsorbent dose of 5 mg/mL, contact times of 90 and 5 min, pH levels of 5 and 4, initial concentration of 25 ppm, and temperatures of 303 K and 308 K for Cu(II) and Pb(II), respectively. The CSCys-HG efficiently removed Cu(II) and Pb(II) ions, achieving adsorption capacities of 171.10 and 132.56 mg/g, respectively. CSCys-HG exhibited M(II) ion sorption performance that aligned with the nonlinear Langmuir isotherm model. For Cu(II), the parameters were b = 0.01411 L/mg and R2 = 0.99151, whereas for Pb(II), they were b = 0.02571 L/mg and R2 = 0.98908. The kinetics followed a pseudo-second-order model, with Cu(II) showing k2 = 4.34 × 10-4 g/mg min and R2 = 0.99924, and Pb(II) displaying k2 = 6.54 × 10-4 g/mg min and R2 = 0.99918.

Optimization of facile synthesis of xanthan gum xanthate based hydrogel for the capturing of heavy metal ions from aqueous solutions

This study investigated the elimination of Co2+, Ni2+ and Cu2+ ions from water using a mesoporous, cost-effective, reusable, biodegradable and efficient xanthan gum xanthate-based hydrogel (XGmXHs hydrogel) as an adsorbent. The XGmXHs hydrogel was prepared via free radical polymerization process with varying the ratios of 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) as monomers. These ratios were optimized based on grafting efficiency, swelling capacity and point of zero charge (ΔpHPZC) analysis. The results demonstrate that the XGmXHs hydrogel containing copolymer of HEMA: AA in a 1:3 ratio is optimal for grafting on xanthan gum (XGm) during polymerization process. The 1:3 ratio of monomer grafted on xanthan gum xanthate (XGmX) is referred to as XGmXHs-3 hydrogel. The XGmXHs-3 hydrogel showed a consistently negative surface charge across a diverse pH range, resulting the AA content was enhanced. Consequently, the swelling and adsorption capacity of the XGmXHs-3 hydrogel is significantly high. The optimum swelling capacity of the XGmXHs-3 hydrogel was found 40,128 % in water at pH 11. The maximum removal efficiency was 92.21 % for Co2+, 95.45 % for Ni2+ and 98.30 % for Cu2+ ions at pH 7. According to isothermal studies, the adsorption data aligns most closely with Langmuir isotherm model, resulting the adsorption capacities of 358.42, 469.48 and 555.55 mg/g Co2+, Ni2+ and Cu2+ ions, respectively. The adsorption kinetics were consistent with a pseudo-first-order kinetic model, showing rate constant of -2.6 × 10-2, -4.0 × 10-2 and - 6.3 × 10-2 min-1 for Co2+, Ni2+ and Cu2+ ions, respectively. The desorption efficiencies were 64.76 % for Co2+, 68.83 % for Ni2+ and 72.11 % for Cu2+ ions to the XGmXHs-3 hydrogel after being regenerated for the fifth cycle.

Fabrication of Cerium Metal-Organic Frameworks Functionalized with Glutamic Acid for Adsorption of Basic Red 46 from Aqueous Solutions: Kinetics, Thermodynamics, and Optimization

This research investigated the efficient removal of cationic Basic red 46 (BR46) dye from aqueous solutions, by means of cerium metal-organic frameworks (Ce-MOF) functionalized with glutamic acid to create NH2-Ce-MOF. The NH2-Ce-MOF was easily produced through a postsynthesis functionalization strategy and extensively analyzed through numerous methods with X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX), and N2 adsorption/desorption isotherm. The findings revealed that the synthesized adsorbent had a high surface area of 1158.8 m2/g, a pore size of 1.511 nm, and a pore volume of 0.875 cm3/g. Upon adsorption of the BR46 dye, the surface area decreased to 872.6 m2/g, the pore size reduced to 1.18 nm, and the pore volume released to 0.53 cm3/g. The decreases in surface area, pore size, and volume demonstrate the material's strong ability to adsorb substances, as the dye molecules can fill the tiny pores. They exhibited an increased adsorption capability of 454.8 mg/g. The Langmuir isotherm and pseudo-second-order kinetic models performed the best at simulating adsorption isotherm and kinetic curves, respectively. The exhibition of chemisorption and adsorption energy of 28.4 kJ/mol was supported by various adsorption driving forces, including hydrogen bonding, electrostatic interaction, π-π conjugation, pore filling, and van der Waals force. After conducting thorough research on the impact of temperature, it was established that the adsorption procedure is both endothermic, indicated by a positive ΔH° of 83.7 kJ/mol.K, and spontaneous, as confirmed by the increase in negativity of ΔG° with rising temperatures. Additionally, the increase in randomness with increasing temperatures is evident in the ΔS° value of 289.32 J/mol. Employed Box-Behnken design (BBD) and response surface methodology (RSM) to enhance the results of the adsorption procedure. The NH2-Ce-MOF proposal is a practical, affordable solution for eliminating BR46 dye from wastewater streams because the adsorbent was composed of reusable materials and reused over five times with excellent efficiency.

Accessing renewable magnetic cellulose nanofiber adsorbent to enhance separation efficiency for adsorption and recovery of Cd2

To address the issue of toxic cadmium pollution and meet the need for rapid separation from water body, a magnetic bio-composite material, marked as CFeMg, was prepared via a facile method. It explicitly includes components of cellulose nanofiber (CNF), Fe3O4 and Mg (OH)2. The microstructures and morphology were characterized and analyzed using XRD, FT-IR, SEM, and TEM. CNF was chemically coupled by Fe3O4, which together constructed the overall layered structure. Between layers were Mg(OH)2 flakes attached. While dealing with Cd2+, qmax of the best sample reached 361.5 mg g-1 with high adsorption efficiency. The roles of three components were explored and the adsorption mechanism was proposed. Assisted by magnetic CNF, it only took 3 min to efficiently and completely salvage the spent CFeMg sample from water after adsorption. Due to its high adsorption capacity and facile recovery performance, the prepared composite has promising application as water treatment.

Concurrent removal of Fe(II), Cu(II), and Zn(II) cations from acid mine drainage by an industrial solid waste - Steel slag: Behaviors and mechanisms

Acid mine drainage (AMD) contamination poses a severe environmental threat and is a significant risk to human health. There is an urgent need to develop environmentally sustainable and technically viable solutions for water contamination caused by heavy metals. In this study, steel slag (SS) was used as a secondary resource to concurrently remove Fe(II), Cu(II), and Zn(II) from AMD. Because of the loose and porous structure, abundant functional groups, fast sedimentation velocity, and excellent solid-liquid separation, SS showed exceptional removal performance for heavy metal ions. The adsorption kinetic data of Fe(II),Cu(II), and Zn(II) showed good regression with the pseudo-second-order model. Besides, the adsorption of Fe(II) by SS conformed to the Freundlich model, whereas the adsorption of Cu(II) and Zn(II) followed the Langmuir model, with the maximum adsorption amounts of Cu(II) and Zn(II) being 170.69 mg/g and 155.98 mg/g. Furthermore, competitive adsorption was observed among Fe(II), Cu(II), and Zn(II) in a multi-component system, with the adsorption priority being Fe(II)>Cu(II)>Zn(II). The removal mechanism of Fe(II), Cu(II), and Zn(II) in AMD by SS mainly includes electrostatic attraction, chemical precipitation, and surface complexation. Interestingly, the leached concentrations of Fe(II), Cu(II), and Zn(II) from the spent slag after calcination were all within the detection limit of the Chinese emission standard, demonstrating excellent environmental stability. Theoretically, this renders it a viable candidate for use as an additive in construction materials. Meaningfully, the work offers a practical approach for energy-efficient and eco-friendly heavy metal ions adsorption, and the secondary utilization of SS also contributes to the sustainable development of the steel industry. It is beneficial to implement the development concepts of clean production and efficient utilization of industrial solid waste.

Waste refractory brick material added chitosan/oxidized pullulan complex gel production and removal of heavy metals from waste water

Wastewater is a by-product of numerous industrial processes that have been demonstrated to have adverse effects on human and natural health due to the pollutants it contains. The pollutants in these substances are organic or inorganic molecules and heavy metal ions that significantly harm the environment and human health. A variety of techniques have been devised for the removal of heavy metal ions from wastewater. The adsorption process has attracted significant attention due to its straightforward implementation, cost-effectiveness, and the environmentally friendly production of adsorbent materials using biocompatible substances. In this study, the removal of Cu2+ ions from wastewater was conducted using chitosan pullulan, a biocompatible and biodegradable polymer. In addition to chitosan and pullulan, waste refractory materials from a furnace used in iron and steel production were added to these polymer materials to increase the adsorption capacity. The initial step involved grinding the waste refractory brick material. Subsequently, chitosan was dissolved in acetic acid. After that, the refractory material was suspended in this solution, facilitating the formation of hydrogel beads using a NaOH solution. The obtained hydrogels were coated with pullulan to produce polyelectrolyte gel. Pullulan was oxidized to 6-carboxypullulan by the TEMPO (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl) oxidation method and the negatively charged groups in its structure interacted with the positively charged groups in the chitosan structure to produce a complex gel. The chemical structure, morphological analysis, thermal analysis, and water release analysis of the produced waste refractory brick material added chitosan/oxidized pullulan complex gels were examined. The impact of the 6-carboxypullulan coating on the gels' properties was elucidated. Furthermore, the adsorption of Cu2⁺ was conducted using solutions containing 100, 500, and 1000 ppm Cu2⁺ ions. It has been observed that the material can clean water with over 98% efficiency, even in solutions that exceed the standards set for wastewater. The material's efficacy in cleaning solutions with concentrations above the standard for wastewater cleaning is evidence of its high performance. Furthermore, the kinetics and isotherm of the adsorption reaction were examined. The kinetics were determined to be consistent with the Pseudo Second Order (chemical reaction controlled) and aligned with the Langmuir and Freundlich Isotherm (mixed adsorption occurred on homogeneous and heterogeneous surfaces).

Development of ruthenium complexes with S-donor ligands for application in synthesis, catalytic acceptorless alcohol dehydrogenation and crossed-aldol condensation

The reaction of [Ru(dmso)4Cl2] with a potassium salt of four xanthate (RO-C(S)S-; R = Me, Et, iPr and tBu) ligands (depicted as Ln; n = 1-4) in hot methanol afforded a group of mixed-ligand complexes of type [Ru(Ln)2(dmso)2]. The crystal structures of all the four complexes have been determined, which show that the xanthate ligands are bound to the metal center forming four-membered chelates and dmso is coordinated through sulfur and they are mutually cis. The relative thermodynamic stability of this cis and the other possible trans-isomers of these complexes has been assessed with the help of DFT calculations, which have revealed that the cis-isomer is the more stable isomer. The coordinated dmso in the [Ru(Ln)2(dmso)2] complexes could be easily displaced by chelating bidentate ligands (depicted as L') to furnish complexes of type [Ru(Ln)2(L')], as demonstrated through isolation of two such complexes, viz. [Ru(L3)2(bpy)] and [Ru(L2)2(phen)] (bpy = 2,2'-bipyridine and phen = 1,10-phenanthroline). The crystal structure of [Ru(L3)2(bpy)] has been determined and the structure of [Ru(L2)2(phen)] has been optimized by the DFT method. The electronic spectra of the four [Ru(Ln)2(dmso)2] complexes and the two derivatives ([Ru(Ln)2(L')]; n = 3, L' = bpy; n = 2, L' = phen), recorded in dichloromethane solutions, show intense absorptions spanning the visible and ultraviolet regions, which have been analyzed by the TDDFT method. The [Ru(Ln)2(dmso)2] complexes are found to serve as efficient catalyst precursors for the acceptorless dehydrogenation of 2-propanol followed by crossed-aldol condensation with substituted benzaldehydes (and related aldehydes), using tert-butoxide as the co-catalyst, producing dibenzylideneacetone derivatives in good yields.

Enhancing brilliant green dye removal via bio composite chitosan and food-grade algae capsulated ruthenium metal-organic framework: Optimization of adsorption parameters by box-behnken design

A natural material made of chitosan (CS) and algae (food-grade algae, FGA) was cross-linked and loaded onto a ruthenium metal organic framework to create a bio-adsorbent (Ru-MOF@CS/FGA composite sponge) with the aim of adsorbing and eliminating Brilliant green (BG) from aqueous solutions. A range of methods were employed to analyze the Ru-MOF@CS/FGA composite sponge, such as X-ray photoelectron spectroscopy (XPS) for elemental analysis, Fourier transform infrared spectroscopy (FTIR) to ascertain the function groups, and scanning electron microscopy (SEM) to establish the surface morphology, and powder X-ray diffraction (PXRD) to study of single and multi-phase polycrystalline materials. Brunauer-Emmett-Teller surface area (BET) confirmed the adsorbent's high surface area and pore volume (826.85 m2/g and 1.28 cm3/g, respectively) and decreased to 475.62 m2/g and 0.74 cm3/g after adsorption. Determine the several factors that affect the adsorption process, such as pH, the adsorbent's dose, the initial BG concentration, and the effect of salinity. The adsorption process was fitted to pseudo-second-order kinetics and Langmuir isotherms. Dubinin-Radushkevich analysis revealed that the adsorption energy was 23.8 kJ/mol, indicating chemisorption as the mode of adsorption. It was discovered through examining the impact of temperature and computing positive-charged enthalpy and entropy that the adsorption process was endothermic, meaning that it increased in response to temperature. It is possible to reuse the Ru-MOF@CS/FGA composite sponge six times with acceptable efficiency, no change in its chemical composition, and comparable FT-IR, XPS, and XRD data before and after each reuse. Examine the mechanisms of adsorbent-adsorbate interaction, which may involve H-bonding, n-π stacking, electrostatic forces, and pore filling. The adsorption results were optimized with the Box Behnken-design (BBD).

Adsorbents prepared from epoxy-based porous materials of microcrystalline cellulose for excellent adsorption of anionic and cationic dyes

It reported a porous material prepared from microcrystalline cellulose (MCC), to achieve rapid preparation of adsorbents. The porous material was characterized by several tools including 1H NMR, FTIR, XPS, and SEM. Two adsorbents were prepared and subjected to adsorption experiments. Dye adsorption experiments show that the adsorption driving is electrostatic interactions and the process is chemisorption. The maximum capacity of Microcrystalline cellulose-g-Poly (glycidyl methacrylate)-Tannins (MPT) reached 191.3 (Methylene blue), 123.7 mg g-1 (Rhodamine B), and Microcrystalline cellulose-g-Poly (glycidyl methacrylate)-Lysine (MPL) attained 425.8 (Methylene blue), 480.7 mg g-1 (Methyl orange). The results were followed the pseudo-second-order (PSO) and agreed with the Langmuir fit model. Adsorption-desorption cycling experiments further indicate that the adsorbent possesses outstanding reproducibility. At last, epoxidized bio-porous materials are positive in the preparation of dye adsorbents with critical adsorption properties.

Chitosan-grafted hydrogels for heavy metal ion adsorption and catalytic reduction of nitroaromatic pollutants and dyes

Chitosan-grafted-poly(acrylic acid) (CS-g-PAA) and chitosan-grafted- poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (CS-g-P(AA-co-AMPS)) hydrogels were synthesized and then employed as adsorbents for the effective removal of Cu2+ and other heavy metal ions. The effect of hydrogel's composition on the Cu2+ adsorption was explored. The CS-g-PAA hydrogel demonstrated a superior adsorption capacity compared to pristine CS, PAA hydrogel, and CS-g-P(AA-co-AMPS) hydrogels. The adsorption followed the Langmuir isotherm model, and the pseudo-second order kinetic model. Additionally, the CS-g-PAA hydrogel exhibited relatively high adsorption performances toward Cr3+, Co2+, Ni2+, Pb2+, and Zn2+. Metal ions adsorbed within CS-g-PAA hydrogels underwent reduction to their corresponding metallic states and were reutilized as catalysts for the reduction of 4-nitrophenol. The comparative catalytic performances of the metal species in the hydrogel were in the order of Cu > Ni > Co > Zn. The reduction efficiency of Cu-CS-g-PAA increased with increased catalyst dosage, NaBH4 concentration, and temperature. A very low activation energy of 3.7 kJ/mol was observed. The catalyst maintained high catalytic performance even when subjected to real water samples and proved its reusability for up to three cycles. Moreover, the catalyst could effectively reduce 2-nitrophenol and methyl orange.

Fluorescent starch-based hydrogel with cellulose nanofibrils and carbon dots for simultaneous adsorption and detection of Pb(II)

The adsorption removal of lead (Pb) ions has become a crucial area of research due to the potential health hazards associated with Pb contamination. Developing cost-effective adsorbents for the removal of Pb(II) ions is significantly important. Hence, a novel fluorescent starch-based hydrogel (FSH) using starch (ST), cellulose nanofibrils (CN), and carbon dots (CD) was fabricated for simultaneous adsorption and detection of Pb(II). A comprehensive characterization of FSH, including its morphological features, chemical composition, and fluorescence characteristics, was conducted. Notably, FSH exhibited a maximum theoretical adsorption capacity of 265.9 mg/g, which was 13.0 times higher than that of pure ST. Moreover, FSH was employed as a fluorescent sensor for Pb(II) determination, achieving a limit of detection (LOD) of 0.06 μg/L. An analysis was further performed to investigate the adsorption and detection mechanisms of Pb(II) utilizing FSH. This study provides valuable insights into the production of a novel cost-effective ST-based adsorbent for the removal of Pb(II) ions.

Nd Recovery from Wastewater with Magnetic Calcium Alginate ((1,4)-β-d-Mannuronic Acid and α-L-Guluronic Acid) Hydrogels

In this study, a magnetic adsorbent material was produced, by environmentally friendly and inexpensive precursor materials, to clean wastewater that may result from primary and secondary rare earth metal (REM) production. Then, the absorption of Nd³⁺ ions from wastewater was done and this process's kinetic and isotherm models were developed. Thus, the removal of Nd³⁺ from wastewater with magnetic materials was accomplished, and then, this precious metal was recovered by using different acid media. First, Fe sub-micron particles were successfully produced by the polyol method. To increase the stability of Fe-based particles, their surfaces were covered with an oxide layer, and the average thickness was determined as 16 nm. The synthesized Fe particles were added into the calcium alginate beads and then coated with chitosan to increase the pH stability of the gels. The chemical composition of the gels was determined by Fourier transform infrared spectroscopy, the thermal properties were determined by differential scanning calorimetry, and the magnetic properties were determined by vibrating-sample magnetometer analysis. The magnetic saturation of the hydrogels was 0.297 emu/g. After the production of magnetic calcium alginate hydrogels, Nd³⁺ ion removal from wastewater was done. Wastewater was cleaned with 94.22% efficiency. The kinetic models of the adsorption study were derived, and isotherm studies were done. Adsorption reaction fitted different kinetic models at different time intervals and the Freundlich isotherm model. The effect of pH, temperature, and solid-liquid ratio on the system was determined and the thermodynamic constants of the system were calculated. After the adsorption studies, Nd³⁺ ions were regenerated in different acid environments and achieved an 87.48% efficiency value. The removal of Nd³⁺ ions from wastewater was carried out with high efficiency, the gels obtained as a result of adsorption were regenerated with high efficiency by using acid media, and it was predicted that the gels could be reused. This study is thought to have reference results not only for the removal of REM from wastewater by magnetic adsorption materials but also for the adsorption of heavy metals from wastewater.

Simple synthesis of chitosan/alginate/graphene oxide/UiO-67 amphoteric aerogels: Characterization, adsorption mechanism and application for removal of cationic and anionic dyes from complex dye media

A chitosan/alginate/graphene oxide/UiO-67 (CS/SA/GO/UiO-67) amphoteric aerogel was synthesized successfully. A series of characterization experiments of CS/SA/GO/UiO-67 amphoteric aerogel was performed by SEM, EDS, FT-IR, TGA, XRD, BET, and zeta potential. The competitive adsorption properties of different adsorbents for complex dyes wastewater (MB and CR) at room temperature (298 K) were compared. Langmuir isotherm model predicted that the maximum adsorption quantity of CS/SA/GO/UiO-67 for CR and MB was 1091.61 and 1313.95 mg/g, respectively. The optimum pH values of CS/SA/GO/UiO-67 for the adsorption of CR and MB were 5 and 10, respectively. The kinetic analysis showed that the adsorption of MB and CR on CS/SA/GO/UiO-67 was more suitable for the pseudo-second-order and pseudo-first-order kinetic model, respectively. The isotherm study revealed that the adsorption of MB and CR was consistent with the Langmuir isotherm model. The thermodynamic study demonstrated that the adsorption process of MB and CR was exothermic and spontaneous. FT-IR analysis and zeta potential characterization experiments revealed that the adsorption mechanism of MB and CR on CS/SA/GO/UiO-67 depended on π-π bond, hydrogen bond, and electrostatic attraction. Repeatable experiments showed that the removal rates of MB and CR of CS/SA/GO/UiO-67 after six cycles of adsorption were 67.19 and 60.82 %, respectively.

Extraction of Gold Based on Ionic Liquid Immobilized in UiO-66: An Efficient and Reusable Way to Avoid IL Loss Caused by Ion Exchange in Solvent Extraction

Ionic liquids (ILs) have received considerable attention as a promising green solvent for extracting metal ions from aqueous solutions. However, the recycling of ILs remains difficult and challenging because of the leaching of ILs, which is caused by the ion exchange extraction mechanism and hydrolysis of ILs in acidic aqueous conditions. In this study, a series of imidazolium-based ILs were confined in a metal-organic framework (MOF) material (UiO-66) to overcome the limitations when used in solvent extraction. The effect of the various anions and cations of the ILs on the adsorption ability of AuCl₄^- was studied, and 1-hexyl-3-methylimidazole tetrafluoroborate ([HMIm]⁺[BF₄]^-@UiO-66) was used for the construction of a stable composite. The adsorption properties and mechanism of [HMIm]⁺[BF₄]^-@UiO-66 for Au(III) adsorption were also studied. The concentrations of tetrafluoroborate ([BF₄]^-) in the aqueous phase after Au(III) adsorption by [HMIm]⁺[BF₄]^-@UiO-66 and liquid-liquid extraction by [HMIm]⁺[BF₄]^- IL were 0.122 mg/L and 18040 mg/L, respectively. The results reveal that Au(III) coordinated with the N-containing functional groups, while [BF₄]^- was effectively confined in UiO-66, instead of undergoing anion exchange in liquid-liquid extraction. Electrostatic interactions and the reduction of Au(III) to Au(0) were also important factors determining the adsorption ability of Au(III). [HMIm]⁺[BF₄]^-@UiO-66 could be easily regenerated and reused for three cycles without any significant drop in the adsorption capacity.

Fast-thermoresponsive carboxylated carbon nanotube/chitosan aerogels with switchable wettability for oil/water separation

The use of aerogels to selectively recover oil from oily wastewater is effective but challenging. In this study, a new carboxylated carbon nanotube/chitosan aerogel (CCNT/CA) with switchable wettability was developed as a smart adsorbent for fast oil absorption and oil recovery. Vinyltrimethoxysilane and thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) was grafted onto the surface of the CCNT/CA skeleton, and the resulting smart aerogel (PNI-Si@CCNT/CA) exhibited temperature responsiveness. PNI-Si@CCNT/CA exhibited an excellent reversible conversion between hydrophilicity and hydrophobicity when the temperature was changed to below or above the lower critical solution temperature (LCST) of PNIPAAm (~32 °C). Most importantly, CCNT significantly increased the oil absorption capacity, improved the mechanical properties, accelerated phonon conduction, enhanced thermal conductivity (80.57 mW m^-1 K^-1), improved the temperature response rate, shortened the oil desorption time (15 min), and improved the oil/water separation efficiency of PNI-Si@CCNT/CA because a strong interface interaction occurred between CCNT and chitosan. Moreover, PNI-Si@CCNT/CA absorbed oil at 45 °C and released the absorbed oil at 25 °C. It maintained its good adsorption performance after 15 cycles, and this was ascribed to its excellent mechanical properties and stable structure.

Removal of Zn(II) and Ni(II) heavy metal ions by new alginic acid-ester derivatives materials

The present work concerns the preparation of new materials based on alginic acid (AA) and diols in a facile and efficient process by improving the adsorption properties of Zn(II) and Ni(II) metal ions on the modified AA. The materials were analysed by zeta potential, thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), in addition to the Fourier Transform InfraRed spectroscopy (FTIR), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) before and after the adsorption behaviour was conducted. The results show that the esterification of AA with diols of different lengths significantly improves its adsorption efficiency of Zn(II) and Ni(II) with Q_max up to 200 mg/g and 185.185 mg/g respectively. Equilibrium and kinetic studies showed that the Langmuir and Freundlich adsorption isotherm models fit the experimental data well, and followed a pseudo-first order kinetic model and the particle diffusion model with correlation coefficients R² ≈ 1.

Single and Binary Adsorption Behaviour and Mechanisms of Cd2+, Cu2+ and Ni2+ onto Modified Biochar in Aqueous Solutions

The chitosan–EDTA modified magnetic biochar (E–CMBC) was successfully used as a novel adsorbent to remove heavy metals. The adsorption behaviour and mechanisms of E–CMBC to Cd2+, Cu2+ and Ni2+ were performed in single and binary system in aqueous solutions. In single–metal system, the adsorption process of Cd2+, Cu2+ and Ni2+ on E–CMBC fitted well with the Avrami fractional–order kinetics model and the Langmuir isotherm model. The measured maximum adsorption capacities were 61.08 mg g−1, 48.36 mg g−1 and 41.17 mg g−1 for Cd2+, Cu2+ and Ni2+, respectively. In binary–metal system, coexisting ions have obvious competitive adsorption behaviour on E–CMBC when the concentration of heavy meal beyond 20 mg L−1. The maximum adsorption capacities of the heavy metals were found to be lower than that in single–metal system. The order of the competitive adsorption ability was Cu2+ > Ni2+ > Cd2+. Interestingly, in Cd2+–Cu2+ system the earlier adsorbed Cd2+ could be completely replaced by Cu2+ from the solution. Different competitive adsorption ability of those heavy metal were due to the characteristics of heavy metal and resultant affinity of the adsorption sites on E–CMBC. The adsorption mechanism indicated that chemical adsorption played a dominating role. Therefore, E–CMBC could be a potential adsorbent for wastewater treatment.

The removal of Cu(II) and Pb(II) ions from aqueous solutions by temperature-sensitive hydrogels based on N-isopropylacrylamide and itaconic acid

This study deals with the potential use of poly(N-isopropylacrylamide-co-itaconic acid) temperature-sensitive hydrogels as an adsorbent for the removal of Cu(II) and Pb(II) ions from aqueous solutions. For this aim, the adsorption properties of hydrogels were examined by adsorption capacities, adsorption isotherm, and adsorption kinetics experiments. To describe the adsorption characteristics of hydrogels, the obtained experimental data were evaluated by Langmuir, Freundlich, Redlich-Peterson, and Dubinin-Radushkevich isotherm models. Adsorption kinetics experiments were carried out not only in single systems but also in binary systems where both ions were at equal initial concentrations for competitive adsorption studies. To predict the behaviors of the competitive and non-competitive adsorption process of ions onto hydrogels, the experimental adsorption data were analyzed by the pseudo-first-order model and the pseudo-second-order model. According to non-competitive ion removal findings, the adsorption capacities followed order Cu(II) > Pb(II) for all hydrogels, and the pseudo-second-order kinetic model explained the adsorption properties of the hydrogels. Competitive ion removal studies showed that all hydrogels were selective to Cu(II) ion. Furthermore, in the case of comparative investigations both of competitive Cu(II) and competitive Pb(II) removal by hydrogels, the metal ion removal capacity of N10 hydrogel was found as a bit higher than that of N7.5 and N5 in 48 h. That is, as the acidic group content increased in the hydrogel network, the adsorption capacity values also increased. In addition, the reusability of temperature-sensitive hydrogels seems possible without regeneration or after regenerating with acid, in case the temperature is increased above the LCST. Furthermore, even if it cannot be reused, these hydrogels that retain metal ions reach very small volumes by shrinking when the LSCT is exceeded, and thus they can be eliminated more easily than other conventional gels due to their small size. As a result, this temperature-sensitive hydrogel may propose as an alternative environmentally friendly adsorbent candidate for can be used for water purification and wastewater treatment.

Thiomers of Chitosan and Cellulose: Effective Biosorbents for Detection, Removal and Recovery of Metal Ions from Aqueous Medium

Removal of toxic metal ions using adsorbents is a well-known strategy for water treatment. While chitosan and cellulose can adsorb weakly some types of metals, incorporating thiols as metal chelating agents can improve their sorption behaviors significantly. Presented in this review are the various chemical modification strategies applicable for thiolation of chitosan and cellulose in the forms of mercaptans, xanthates and dithiocarbamates. Moreover, much attention has been paid to the specific strategies for controlling the thiolation degree and characterization approaches for establishing the structure-property relationship. Also, the kinetics and isotherm models that elucidate the adsorption processes and mechanisms induced by the thiomers have been explained. These thiomers have found great potentials in the applications associated with metal removal, metal recovery and metal detection.

Engineering of UiO-66-NH2 as selective and reusable adsorbent to enhance the removal of Au(III) from water: Kinetics, isotherm and thermodynamics

Efficient removal of gold ions from wastewater has become a hot research topic. A new metal-organic framework material (PAR-UiO-66) was prepared by post-modification of UiO-66-NH₂. A series of characterizations proved the successful preparation of PAR-UiO-66. The batch adsorption experiment was carried out. Under the room temperature (298 K) of and pH 4.0, the optimal adsorption capacity of PAR-UiO-66 for gold ions was 683.45 mg/g, which was an increase of 426.8 mg/g compared with that of UiO-66-NH₂. The adsorption of gold ions on PAR-UiO-66 accords with pseudo-second-order kinetics and Langmuir isotherm modles. The adsorption process was endothermic and spontaneous. PAR-UiO-66 has good selectivity and still has 92.5% adsorption efficiency after five repeated adsorptions. The adsorption mechanism is electrostatic attraction, reduction and chelation.

A graphene oxide modified cellulose nanocrystal/PNIPAAm IPN hydrogel for the adsorption of Congo red and methylene blue

A simple strategy is developed to fabricate a graphene oxide modified cellulose nanocrystal/PNIPAAm IPN (GO-CNC/PNIPAAm IPN) hydrogel. It is a high-efficiency and low-cost adsorbent for the removal the anionic dye CR and cationic dye MB.

Recent Advancement of Molecular Structure and Biomaterial Function of Chitosan from Marine Organisms for Pharmaceutical and Nutraceutical Application

Chitosan is an innate cationic biological polysaccharide polymer, naturally obtained from chitin deacetylation, that possesses broad-spectrum properties such as antibacterial, biodegradability, biocompatibility, non-toxic, non-immunogenicity, and so on. Chitosan can be easily modified owing to its molecular chain that contains abundant active amino and hydroxyl groups, through various modifications. Not only does it possess excellent properties but it also greatly accelerates its solubility and endows it with additional special properties. It can be developed into bioactive materials with innovative properties, functions, and multiple uses, especially in the biomedical fields. In this paper, the unique properties and the relationship between the molecular structure of chitosan and its derivatives are emphasized, an overview of various excellent biomedical properties of chitosan and its current progress in the pharmaceutical and nutraceutical field have prospected, to provide the theoretical basis for better development and utilization of new biomedical materials of chitosan and its derivatives.

The effects of carbon disulfide driven functionalization on graphene oxide for enhanced Pb(II) adsorption: Investigation of adsorption mechanism

The surface properties of graphene oxide (GO) have been identified as the key effects on the adsorption of Pb(II) from aqueous solutions in this study. This study reveals the effect of the surface reactivity of GO via Carbon Disulfide (CS₂) functionalization for Pb(II) adsorption. After successfully preparing CS₂ functionalized GO (GOCS), the specific techniques were applied to investigate Pb(II) adsorption onto GOCS. Results indicated that the new sulfur-containing functional groups incorporated onto GOCS significantly enhanced Pb(II) adsorption capacity on GOCS than that of GO, achieving an improvement of 31% in maximum adsorption capacity increasing from 292.8 to 383.4 mg g^-1. The equilibrium adsorption capacity for GOCS was 280.2 mg g^-1 having an improvement of 83.2% over that of 152.97 mg g^-1 for GO at the same initial concentration of 150 mg L^-1 under the optimal pH of 5.7. Moreover, the results of adsorption experiments showed an excellent fit to the Langmuir and Pseudo-Second-Order models indicating the monolayer and chemical adsorption, respectively. The mechanism for Pb(II) adsorption on GOCS was proposed as the coordination, electrostatic interactions, cation-pi interactions, and Lewis acid-base interactions. The regeneration study showed that GOCS had an appreciable reusability for Pb(II) adsorption with the adsorption capacity of 208.92 mg g^-1 after five regeneration cycles. In summary, GOCS has been proved to be a novel, useful, and potentially economic adsorbent for the high-efficiency removal of Pb(II) from aqueous solutions.

Carboxylated graphene oxide-chitosan spheres immobilize Cu2+ in soil and reduce its bioaccumulation in wheat plants

Due to the strong interaction with pollutants and the huge adsorption capacity, graphene adsorbents are widely applied in water decontamination. However, graphene adsorbents are seldom used in soil remediation, because the adsorptive sites on graphene would be occupied by soil components. In this study, we prepared carboxylated graphene oxide-chitosan (GO-COOH/CS) spheres for the immobilization of Cu²⁺ from water and soil. The pores in GO-COOH/CS allowed the internal diffusion of Cu²⁺ solution, while they blocked the direct contact between the solid soil and the adsorptive sites on graphene sheets. Therefore, the high adsorption capacity of GO-COOH/CS spheres (78 mg/g) was largely retained for the soil Cu²⁺ fixation. The partition coefficient (PC) for Cu²⁺ adsorption onto GO-COOH/CS spheres was 4.2 mg/g/μM at C_e of 0.48 mg/L and q_e of 31 mg/g, while the PC value decreased to 0.096 mg/g/μM at C_e of 91.4 mg/L and q_e of 78 mg/g. At initial Cu²⁺ concentrations of 120 mg/L and lower, the fixation efficiencies were all higher than 99% and the corresponding free Cu²⁺ concentrations in leachates were lower than 1.0 mg/L. The Cu²⁺ fixation on GO-COOH/CS spheres largely reduced its bioaccumulation in wheat roots from 127.8 μg/g to 51.2 μg/g. The toxicity evaluations suggested that GO-COOH/CS spheres were of low toxicity to wheat seedlings and did not amplify the toxicity of Cu²⁺. The implications to the design of graphene adsorbents for soil remediation are discussed. Overall, our results collectively indicated that porous GO-COOH/CS spheres were high-performance adsorbents for the immobilization of Cu²⁺ to reduce Cu²⁺ bioaccumulation in plants.