Copper, mercury and chromium adsorption on natural and crosslinked chitosan films: An XPS investigation of mechanism

Adjustable dielectric and bioactivity characteristics of chitosan-based composites via crosslinking approach and incorporation of graphene

This study explores the structural, electrical, dielectric, and bioactivity properties of chitosan (CS) composites incorporating graphene (G) nanoparticles. Characterization techniques, including Field Emission Scanning Electron Microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), dielectric spectroscopy, and in vitro testing in SBF, were employed to investigate the effects of G content and crosslinking. The XPS peak at 289.89 eV for CS-G10 indicates CC and CH bonds, suggesting significant interactions between chitosan's hydroxyl groups and graphene's carbon atoms, ensuring structural homogeneity. Dielectric constant (ε') gradually increased with G loading (0 %, 1 %, 5 %, and 10 %) for uncrosslinked composites, reaching 17.94, 18.92, 28.28, and 41.1, respectively. Crosslinked composites exhibited reduced ε' values (15.71, 15.42, 14.14, and 27.03) compared to non-crosslinked ones, with marginal increases post-percolation threshold (5 wt% G filling). XRD analysis revealed shifts in characteristic peaks of CS after SBF treatment, with new peaks at 28.9° and 48.5° indicating hydroxyapatite presence, confirming composite bioactivity. CS-G10/GA showed the highest bioactivity, suggesting promise for biomedical applications.

Corrosion Rate and Mechanism of Degradation of Chitosan/TiO2 Coatings Deposited on MgZnCa Alloy in Hank's Solution

Overly fast corrosion degradation of biodegradable magnesium alloys has been a major problem over the last several years. The development of protective coatings by using biocompatible, biodegradable, and non-toxic material such as chitosan ensures a reduction in the rate of corrosion of Mg alloys in simulated body fluids. In this study, chitosan/TiO2 nanocomposite coating was used for the first time to hinder the corrosion rate of Mg19Zn1Ca alloy in Hank's solution. The main goal of this research is to investigate and explain the corrosion degradation mechanism of Mg19Zn1Ca alloy coated by nanocomposite chitosan-based coating. The chemical composition, structural analyses, and corrosion tests were used to evaluate the protective properties of the chitosan/TiO2 coating deposited on the Mg19Zn1Ca substrate. The chitosan/TiO2 coating slows down the corrosion rate of the magnesium alloy by more than threefold (3.6 times). The interaction of TiO2 (NPs) with the hydroxy and amine groups present in the chitosan molecule cause their uniform distribution in the chitosan matrix. The chitosan/TiO2 coating limits the contact of the substrate with Hank's solution.

Modified phosphogypsum whiskers for decontamination of mercury tailings

Mercury (Hg) tailings are hazardous solid wastes because of their high Hg concentrations. Modified phosphogypsum (PG) can decrease the bioactivity and mobility of heavy metals through chemisorption or electrostatic interactions. In this study, PG whiskers were modified by ZnCl2 and S, chitosan-hydrochloric acid, and thioglycolic materials; the resulting modified whiskers were used to decontaminate Hg tailings. Leaching tests and orthogonal experiments were conducted to optimize the modification parameters, including modifier quantity, pH, reaction temperature, and reaction time. The structure and physicochemical properties of the whiskers before and after modification were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The stabilization efficiency of the modified PG whiskers ranged from 93.05 to 97.50%, demonstrating excellent stabilization effects. The stabilization was achieved through chemisorption or complexation. The decontamination process using modified whiskers reduced the pH and total nitrogen of the tailings; increased the cation exchange, total phosphorus, organic carbon, and total carbon; and made the tailings suitable for planting. In addition, the modified PG promoted the morphological transformation of Hg in the tailings, thereby significantly decreasing the Hg content in the effective states and mitigating the risk of Hg contamination.

Humic acid-nanoceria composite as a sustainable adsorbent for simultaneous removal of uranium(VI), chromium(VI), and fluoride ions from aqueous solutions

In this article, the multifunctional behavior of novel, efficient, and cost-effective humic acid-coated nanoceria (HA@CeO2 NPs) was utilized for the sorptive removal of U(VI), Cr(VI), and F- ions at different conditions. The production cost of HA@CeO2 was $19.28/kg and was well characterized by DLS, FESEM, HRTEM, FTIR, XRD, XPS, and TGA. Batch adsorption study for U(VI) (at pH ~ 8), Cr(VI) (at pH ~ 1), and F- (at pH ~ 2) revealed that the maximum percentage of sorption was > 80% for all the cases. From the contact time experiment, it was concluded that pseudo-second-order kinetics followed, and hence, the process should be a chemisorption. The adsorption study revealed that U(VI) and Cr(VI) followed the Freundlich isotherm, whereas F- followed the Langmuir isotherm. Maximum adsorption capacity for F- was 96 mg g-1. Experiments in real water suggest that adsorption is decreased in Kaljani River water (~ 12% for Cr(VI) and ~ 11% for F-) and Kochbihar Lake water (25.04% for Cr(VI) and 20.5% for F-) because of competing ion effect. Mechanism was well established by the kinetic study as well as XPS analysis. Because of high adsorption efficiency, HA@CeO2 NPs can be used for the removal of other harmful water contaminants to make healthy aquatic life as well as purified drinking water.

Mercury remediation from wastewater through its spontaneous adsorption on non-functionalized inverse spinel magnetic ferrite nanoparticles

In this study, inverse spinel cubic ferrites MFe2O4 (M = Fe2+, and Co2+) have been fabricated for the high-capacity adsorptive removal of Hg(II) ions. The PXRD analysis confirmed ferrites with the presence of residual NaCl. The surface area of Fe3O4 (Fe-F) and CoFe2O4 (Co-F) material was 69.1 and 45.2 m2 g-1, respectively. The Co-F and Fe-F showed the maximum Hg(II) adsorption capacity of 459 and 436 mg g-1 at pH 6. The kinetic and isotherms models suggested a spontaneous adsorption process involving chemical forces over the ferrite adsorbents. The Hg(II) adsorption process, probed by X-ray photoelectron spectroscopy (XPS), confirmed the interaction of Hg(II) ions with the surface hydroxyl groups via a complexation mechanism instead of proton exchange at pH 6 with the involvement of chloride ions. Thus, this study demonstrates a viable and cost-effective solution for the efficient remediation of Hg ions from wastewater using non-functionalized ferrite adsorbents. This study also systematically investigates the kinetics and isotherm mechanism of Hg(II) adsorption onto ferrites and reports one of the highest Hg(II) adsorption capacities among other ferrite-based adsorbents.

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

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

RSM approach for process optimization of the photodegradation of congo red by a novel NiCo2S4/chitosan photocatalyst

The current study reported a facile co-precipitation technique for synthesizing novel NiCo2S4/chitosan nanocomposite. The photocatalytic activity of the prepared nanocomposite was evaluated using congo red (CR) dye as a target pollutant. The central composite design was employed to examine the impact of different reaction conditions on CR dye degradation. This study selected the pH, photocatalyst loading, initial CR concentration and reaction time as reaction parameters, while the degradation efficiency (%) was selected as the response. A desirability factor of 1 suggested the adequacy of the model. Maximum degradation of 93.46% of 35 ppm dye solution was observed after 60 min of visible light irradiation. The response to surface methodology (RSM) is a helpful technique to predict the optimum reaction conditions of the photodegradation of CR dye. Moreover, NiCo2S4/Ch displayed high recyclability and reusability up to four consecutive cycles. The present study suggests that the prepared NiCo2S4/chitosan nanocomposite could prove to be a viable photocatalyst for the treatment of dye-contaminated wastewater.

Synthesis of magnetic bentonite-gelatin hydrogel beads and their applications in Cu2+ capturing

Heavy metal ions that exist in groundwater and farmland jeopardize the ecological environment and are very difficult to remove because of the complicated actual environment. Raw bentonite-gelatin beads (RB-GT) and magnetic bentonite-gelatin beads (MB-GT) synthesized in this work would be an appropriate tool to solve this problem. Those beads are synthesized by a facile hybrid injection method. Their adsorption behaviors on Cu(II) ions were systematically investigated using the batch adsorption method. The beads were characterized by scan electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS). The adsorption isotherm and adsorption kinetic study showed that the Cu2+ adsorption by MB-GT beads fitted the Langmuir model and the pseudo-second model. The adsorption maximum capacities reached 192.5 mg/g and 236.5 mg/g with Cu concentration of 1000 mg/L for RB-GT and MB-GT beads, respectively. The competitive adsorption with other heavy metal ions (Ni(II), Pd(II) and Cd(II)) were compared. The adsorption of Cu(II) mechanisms is also further discussed.

A review on heavy metal biosorption utilizing modified chitosan

Heavy metal pollution in water bodies is a global concern. The prominent source of metal contamination in aqueous streams and groundwater is wastewater containing heavy metal ions. Elevated concentrations of heavy metals in water bodies can have a negative impact on water quality and public health. The most effective way to remove metal contaminants from drinking water is thought to be adsorption. A deacetylated derivative of chitin, chitosan, has a wide range of commercial uses since it is biocompatible, nontoxic, and biodegradable. Due to its exceptional adsorption behavior toward numerous hazardous heavy metals from aqueous solutions, chitosan and its modifications have drawn a lot of interest in recent years. Due to its remarkable adsorption behavior toward a range of dangerous heavy metals, chitosan is a possible agent for eliminating metals from aqueous solutions. The review has focused on the ideas of biosorption, its kinds, architectures, and characteristics, as well as using modified (physically and chemically modified) chitosan, blends, and composites to remove heavy metals from water. The main objective of the review is to describe the most important aspects of chitosan-based adsorbents that might be beneficial for enhancing the adsorption capabilities of modified chitosan and promoting the usage of this material in the removal of heavy metal pollutants.

Development of chitosan/konjac glucomannan/tragacanth gum tri-layer food packaging films incorporated with tannic acid and ε-polylysine based on mussel-inspired strategy

Constructing biodegradable food packaging with good mechanics, gas barrier and antibacterial properties to maintain food quality is still challenge. In this work, mussel-inspired bio-interface emerged as a tool for constructing functional multilayer films. Konjac glucomannan (KGM) and tragacanth gum (TG) with physical entangled network are introduced in the core layer. Cationic polypeptide ε-polylysine (ε-PLL) and chitosan (CS) producing cationic-π interaction with adjacent aromatic residues in tannic acid (TA) are introduced in the two-sided outer layer. The triple-layer film mimics the mussel adhesive bio-interface, where cationic residues in outer layers interact with negatively charged TG in the core layer. Furthermore, a series of physical tests showed excellent performance of triple-layer film with great mechanical properties (tensile strength (TS): 21.4 MPa, elongation at break (EAB): 7.9 %), UV-shielding (almost 0 % UV transmittance), thermal stability, water, and oxygen barrier (oxygen permeability (OP): 1.14 × 10^-3 g/m s Pa and water vapor permeability (WVP): 2.15 g mm/m² day kPa). In addition, the triple-layer film demonstrated advanced degradability, antimicrobial functions, and presented good moisture-proof performance for crackers, which can be potentially applied as dry food packaging.

Chitosan, Chitosan/IgG-Loaded, and N-Trimethyl Chitosan Chloride Nanoparticles as Potential Adjuvant and Carrier-Delivery Systems

This work proposes a feasible, reproducible, and low-cost modified method to manufacture chitosan, chitosan/IgG-protein-loaded, and trimethylated chitosan nanoparticles, using microfluidics combined with the microemulsion technique, which differs from the traditional batch process of chitosan-based nanoparticles. The synthesis process consists of generating microreactors of chitosan-based polymer in a poly-dimethylsiloxane ψ-shaped microfluidic device and then crosslinking with sodium tripolyphosphate outside the cell. Transmission electron microscopy demonstrates an improvement in size control and distribution of the solid-shape chitosan nanoparticles (~80 nm) compared to the batch synthesis. Regarding chitosan/IgG-protein-loaded nanoparticles, these presented a core-shell morphology having a diameter of close to 15 nm. Raman and X-ray photoelectron spectroscopies confirmed the ionic crosslinking between the amino groups of chitosan and the phosphate groups of sodium tripolyphosphate in the fabricated samples and the total encapsulation of IgG protein during the fabrication of chitosan/IgG-loaded nanoparticles. Then, an ionic crosslinking and nucleation-diffusion process of chitosan-sodium tripolyphosphate was carried out during the nanoparticle formation, with and without IgG protein loading. The use of N-trimethyl chloride chitosan nanoparticles in vitro on human-keratinocyte-derived cell line HaCaT did not show side effects independently of its concentration from 1 to 10 μg/mL. Therefore, the proposed materials could be used as potential carrier-delivery systems.

One-pot synthesis of iron oxide - Gamma irradiated chitosan modified SBA-15 mesoporous silica for effective methylene blue dye removal

The development of adsorption technology and the processing of radiation have both been influenced by chitosan adsorbent (γ-chitosan), a raw material with unique features. The goal of the current work was to improve the synthesis of Fe-SBA-15 utilizing chitosan that has undergone gamma radiation (Fe-γ-CS-SBA-15) in order to investigate the removal of methylene blue dye in a single hydrothermal procedure. High-resolution transmission electron microscopy (HRTEM), High angle annular dark field scanning transmission electron microscopy (HAADF-STEM), small- and wide-angle X-ray powder diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR) and Energydispersive X-ray spectroscopy (EDS) were used to characterize γ-CS-SBA-15 that had been exposed to Fe. By using N₂-physisorption (BET, BJH), the structure of Fe-γ-CS-SBA-15 was investigated. The study parameters also included the effect of solution pH, adsorbent dose and contact time on the methylene blue adsorption. The elimination efficiency of the methylene blue dye was compiled using a UV-VIS spectrophotometer. The results of the characterization show that the Fe-γ-CS-SBA-15 has a substantial pore volume of 504 m² g^-1 and a surface area of 0.88 cm³ g^-1. Furthermore, the maximum adsorption capacity (Q_max) of the methylene blue is 176.70 mg/g. The γ-CS can make SBA-15 operate better. It proves that the distribution of Fe and chitosan (the C and N components) in SBA-15 channels is uniform.

Biocompatible and biodegradable copper-protocatechuic metal-organic frameworks as rifampicin carrier

Tuberculosis (TB) is a disease caused by the M. tuberculosis bacteria infection and is listed as one of the deadliest diseases to date. Despite the development of antituberculosis drugs, the need for long-term drug consumption and low patient commitment are obstacles to the success of TB treatment. A continuous drug delivery system that has a long-term effect is needed to reduce routine drug consumption intervals, suppress infection, and prevent the emergence of drug-resistant strains of M. tuberculosis. For this reason, biomolecule metal-organic framework (BioMOF) with good biocompatibility, nontoxicity, bioactivity, and high stability are becoming potential drug carriers. This study used a bioactive protocatechuic acid (PCA) as organic linker to prepare copper-based BioMOF Cu-PCA under base-modulated conditions. Detailed crystal analysis by the powder X-ray diffraction demonstrated that the Cu-PCA, with a chemical formula of C₁₄H₁₆O₁₃Cu₃, crystalizes as triclinic in space group P1. Comprehensive physicochemical characterizations were provided using FTIR, SEM, XPS, TGA, EA, and N₂ sorption. As a drug carrier, Cu-PCA showed a high maximum rifampicin (RIF) drug loading of 443.01 mg/g. Upon resuspension in PBS, the RIF and linkers release profile exhibited two-stage release kinetic profiles, which are well described by the Biphasic Dose Response (BiDoseResp) model. A complete release of these compounds (RIF and PCA) was achieved after ~9 h of mixing in PBS. Cu-PCA and RIF@Cu-PCA possessed antibacterial activity against Escherichia coli, and good biocompatibility is evidenced by the high viability of MH-S mice alveolar macrophage cells upon supplementations.

CeO2@PU sandwiched in chitosan and cellulose acetate layer as Cs-CeO2@PU-CA triple-layered membrane for chromium removal

The single or blended polymer membrane lacks a few advantages based on the durability of the membrane. The novel triple-layered sandwich membrane Cs-CeO₂@PU-CA membrane is cast through the phase inversion technique for chromium removal. This approach involves an arrangement of the top layer as chitosan which acts as a protective layer, and the sandwich layer of CeO₂@PU membrane which acts as source for stability, and a supportive layer of cellulose acetate is arranged accordingly. The incorporation of cerium oxide nanoparticles into the polyurethane can create pores on the surface of the membrane due to the high aspect ratio of cerium oxide. The triple-layered arrangement shows higher porosity via water contact angle, the network of pores present on the membrane which is visible through morphology, and also the intermediate sandwich layer CeO₂@PU provided with better mechanical strength which would be significant for changes achieved in adsorption technique. The batch adsorption was carried out with various ppm of Cr(VI) solution. The effect of pH, contact time, initial concentration, and temperature were analyzed and optimized for determining efficiency of chromium removal. Furthermore, the suitable adsorption isotherm and kinetics of the system were also determined for better fit via Langmuir, Freundlich, Temkin, and Sips along with pseudo-first-order and pseudo-second-order. The efficiency in adsorption is due to the prominent presence of hydroxyl, carboxyl, and hydrophilic group in the prepared membrane. Thus, the resultant prepared membrane can act as a potential chromium removal substrate.

Superparamagnetic Multifunctionalized Chitosan Nanohybrids for Efficient Copper Adsorption: Comparative Performance, Stability, and Mechanism Insights

To limit the dangers posed by Cu(II) pollution, chitosan-nanohybrid derivatives were developed for selective and rapid copper adsorption. A magnetic chitosan nanohybrid (r-MCS) was obtained via the co-precipitation nucleation of ferroferric oxide (Fe₃O₄) co-stabilized within chitosan, followed by further multifunctionalization with amine (diethylenetriamine) and amino acid moieties (alanine, cysteine, and serine types) to give the TA-type, A-type, C-type, and S-type, respectively. The physiochemical characteristics of the as-prepared adsorbents were thoroughly elucidated. The superparamagnetic Fe₃O₄ nanoparticles were mono-dispersed spherical shapes with typical sizes (~8.5-14.7 nm). The adsorption properties toward Cu(II) were compared, and the interaction behaviors were explained with XPS and FTIR analysis. The saturation adsorption capacities (in mmol.Cu.g^-1) have the following order: TA-type (3.29) > C-type (1.92) > S-type (1.75) > A-type(1.70) > r-MCS (0.99) at optimal pH₀ 5.0. The adsorption was endothermic with fast kinetics (except TA-type was exothermic). Langmuir and pseudo-second-order equations fit well with the experimental data. The nanohybrids exhibit selective adsorption for Cu(II) from multicomponent solutions. These adsorbents show high durability over multiple cycles with desorption efficiency > 93% over six cycles using acidified thiourea. Ultimately, QSAR tools (quantitative structure-activity relationships) were employed to examine the relationship between essential metal properties and adsorbent sensitivities. Moreover, the adsorption process was described quantitatively, using a novel three-dimensional (3D) nonlinear mathematical model.

The interaction of ZnO nanoparticles, Cr(VI), and microorganisms triggers a novel ROS scavenging strategy to inhibit microbial Cr(VI) reduction

Cr(VI) contaminated water usually contains other contaminants like engineered nanomaterials (ENMs). During the process of microbial treatment, the inevitable interaction of Cr(VI), ENMs, and microorganisms probably determines the efficiency of Cr(VI) biotransformation, however, the corresponding information remains elusive. This study investigated the interaction of ZnO nanoparticles (NPs), Cr(VI), and Pannonibacter phragmitetus BB (hereafter BB), which changed the process of microbial Cr(VI) reduction. ZnO NPs inhibited Cr(VI) reduction, but had no effect on bacterial viability. In particular, Cr(VI) induced BB to produce organic acids and to drive Zn²⁺ dissolution from ZnO NPs inside and outside of cells. The dissolved Zn²⁺ not only promoted Cr(VI) reduction to Cr(V)/Cr(IV) by strengthening sugar metabolism and inducing increase in NAD(P)H production, but also hindered Cr(V)/Cr(IV) transformation to Cr(III) through down-regulating Cr(VI) reductase genes. A novel bacterial driven ROS scavenging mechanism leading to the inhibition of Cr(VI) reduction was elucidated. Specifically, the accumulated Cr(VI) and Cr(V)/Cr(IV) formed a redox dynamic equilibrium, which triggered the disproportionation of superoxide radicals mimicking superoxide dismutase through the flip-flop of Cr(VI) and Cr(V)/Cr(IV) in bacterial cells. This study provided a realistic insight into design the applicability of biological remediation technology for Cr(VI) contaminant and evaluating environmental risks of ENMs.

Post-treatment of matured landfill leachate: Synthesis and evaluation of chitosan biomaterial based derivatives as adsorbents

Matured landfill leachate is complex in nature, hence, a single conventional treatment unit is insufficient to remove the contaminants of the leachate to achieve the discharge standards. Furthermore, high levels of organic matter, colour compounds, and iron-based materials form a dark black/brown colour in leachate which is not removed by the biological treatment units. Hence, an Anoxic-Oxic Membrane Bioreactor coupled with a tertiary adsorption unit composed of crosslinked-protonated chitosan was tested for effective removal of the colour of the permeate. Several operational parameters such a pH, contact time, and adsorbent dosage on the adsorptive removal of colour were quantified using sorption-desorption experiments. Furthermore, the biosorbent was characterized using FTIR, SEM, XRD, BET-specific surface area, and pH_ZPC. Response Surface analysis confirmed the optimization of operational parameters conducted through traditional batch experiments. Langmuir isotherm model fitted with equilibrium data (R² = 0.979) indicating a monolayer homogeneous adsorption. Kinetic data followed the Pseudo-Second-Order model (R² = 0.9861), showing that the adsorbent material has abundant active sites. The percentage removal values show that the colour removal increases with time of contact and dosage of adsorbent, but removal is mainly influenced by the solution pH levels. The experimental results manifested a colour removal efficiency of 96 ± 3.8% obtained at optimum conditions (pH = 2, adsorbent dosage = 20 g/L, contact time = 48 h) along with an adsorption capacity of 123.8 Pt-Co/g suggesting that the studied adsorbent can be used as an environmentally friendly biosorbent in a tertiary unit for colour removal in a treatment system which is used to treat matured landfill leachate.

Divalent metal ion removal from simulated water using sustainable starch aerogels: Effect of crosslinking agent concentration and sorption conditions

This paper evaluates corn starch aerogels, studying different crosslinking agent (trisodium citrate) concentrations (1:1, 1:1.5, and 1:2) and sorption conditions (contact time, adsorbent weight, and initial concentration) regarding the potentially toxic elements (PTEs) [Cd(II) or Zn(II)] adsorption of the aqueous systems. Besides, other properties of aerogels, such as structural properties, specific surface area, and mechanical performance, were evaluated. For adsorption results, better values were observed in adsorption capacity and efficiency for the initial concentration of 100 ppm. In addition, an adsorption time of 12 h and an adsorbent weight of 3.0 g obtained better results due to the possible balance in this time and the high specific surface area available for Cd(II) adsorption. As for the type of adsorbent, the Aero 1:1.5 sample (intermediate crosslinking agent concentration) obtained better results, possibly due to the high porosity, smaller pore sizes, high pore density, and high specific surface area (198 m²·g^-1). In addition, hydroxyl groups in the starch aerogel removed Cd(II) ions with 30 % adsorption efficiency. Lastly, Aero 1:1.5 obtained a high mechanical strength at compression and a satisfactory compressive modulus. In contrast, starch aerogels did not absorb the Zn(II) ion.

Self-Standing Bioinspired Polymer Films Doped with Ultrafine Silver Nanoparticles as Innovative Antimicrobial Material

Thin self-standing films with potential antimicrobial synergistic activity have been produced by a simple green chemical synthesis with overnight thermal treatment. Their properties have been studied by scanning electron microscopy, X-ray photoelectron spectroscopy and other techniques to understand their potential range of applications. In this work, the focus was set on the development of a potential novel and effective alternative to conventional antimicrobial materials. By creating an antimicrobial polymer blend, and using it to develop and immobilize fine (~25 nm) silver nanophases, we further aimed to exploit its film-forming properties and create a solid composite material. The resulting polymer matrix showed improved water uptake percentage and better stability in the presence of water. Moreover, the antimicrobial activity of the films, which is due to both organic and inorganic components, has been evaluated by Kirby-Bauer assay against common foodborne pathogens (Staphylococcus aureus and Salmonella enterica) and resulted in a clear inhibition zone of 1.2 cm for the most complex nanocomposition. The excellent performance against bacteria of fresh and 6-month-old samples proves the prospects of this material for the development of smart and biodegradable food packaging applications.

Design and optimization of an innovative lanthanum/chitosan bead for efficient phosphate removal and study of process performance and mechanisms

Presence of excessive phosphorus in surface waters is the main cause for eutrophication. In this study, a lanthanum/chitosan (La/CS) bead was prepared so as to provide a cost-effective solution to the problem. The optimization of bead for the treatment was conducted, leading to the optimal condition: 30 wt% La/CS bead at a dosage of 30 g L^-1 (wet weight). A higher phosphate removal around 90% was obtained in pH 4.0-10.0. Most of uptake occurred in the first 2 h and the equilibrium was reached in about 6 h. Coexisting ions of Cl^-, [Formula: see text] , [Formula: see text] , and [Formula: see text] had negligible effects on the treatment, while the presence of F^- reduced the uptake by 10.39%. The maximum adsorption capacity of 261.1 mg-PO₄·g^-1 (dried weight) at pH 5.0 was achieved, which is much better than many reported La-based adsorbents. The adsorbed phosphate can be effectively recovered with an alkaline solution. A multi-cycle regeneration-reuse study illustrated that the treated water still met the phosphorus discharge standard. The characterization results demonstrated the disappearance of La(OH)₃ and La₂(CO₃)₃ on the bead and the formation of NH₃⁺ … P and La-P groups after the adsorption, indicating the significant roles of ion exchange and electrostatic attraction on the uptake. The excellent performance found in this study clearly indicates that the optimized La/CS bead is promising in the treatment of phosphate and perhaps its recovery for industrial use.

Green synthesis of multifunctional ZnO/chitosan nanocomposite film using wild Mentha pulegium extract for packaging applications

Following the global corona virus pandemic and environmental contamination caused by chemical plastic packaging, awareness of the need for environmentally friendly biofilms and antibacterial coatings is increasing. In this study, a biodegradable hybrid film, comprising of green-synthesized zinc oxide nanoparticles (ZnO NPs) with a chitosan (CS) matrix, was fabricated using a simple casting procedure. The ZnO NPs were synthesized using wild Mentha pulegium extract, and the synthesized NPs and films were characterized using different approaches. The structural, morphological, mechanical, antibacterial, and optical properties, as well as the hydrophilicity, of the prepared samples were investigated using various techniques. Gas chromatography-mass spectrometry measurements revealed the presence of phenolic compounds in the M. pulegium extract. In addition, a strong coordination connection between Zn²⁺ and the chitosan matrix was confirmed, which resulted in a good dispersion of ZnO in the chitosan film. The surface of the composite films was transparent, smooth, and uniform, and the flexible bio-based hybrid films exhibited significant antibacterial and antioxidant characteristics, strong visible emission in the 480 nm region, and UV-blocking properties. The ZnO/CS films displayed a potential to extend the shelf life of fruits by up to eight days when stored at 23°C, and also acted as an acceptable barrier against oxygen and water. The biodegradable ZnO/CS film is expected to keep fruit fresher than general chemical plastic films and be used for the packaging of active ingredients.

UV-Cured Chitosan-Based Hydrogels Strengthened by Tannic Acid for the Removal of Copper Ions from Water

In this work, a new environmentally friendly material for the removal of heavy metal ions was developed to enhance the adsorption efficiency of photocurable chitosan-based hydrogels (CHg). The acknowledged affinity of tannic acid (TA) to metal ions was investigated to improve the properties of hydrogels obtained from natural and renewable sources (CHg-TA). The hydrogel preparation was performed via a simple two-step method consisting of the photocrosslinking of methacrylated chitosan and its subsequent swelling in the TA solution. The samples were characterized using ATR-FTIR, SEM, and Folin-Ciocalteu (F&C) assay. Moreover, the mechanical properties and the ζ potential of CHg and CHg-TA were tested. The copper ion was selected as a pollutant model. The adsorption capacity (Qe) of CHg and CHg-TA was assessed as a function of pH. Under acidic conditions, CHg-TA shows a higher Qe than CHg through the coordination of copper ions by TA. At an alkaline pH, the phenols convert into a quinone form, decreasing the Qe of CHg-TA, and the performance of CHg was found to be improved. A partial TA release can occur in the copper solution due to its high hydrophilicity and strong acidic pH conditions. Additionally, the reusability of hydrogels was assessed, and the high number of recycling cycles of CHg-TA was related to its high mechanical performance (compression tests). These findings suggest CHg-TA as a promising green candidate for heavy metal ion removal from acidic wastewater.

Degradation of Methylene Blue with a Cu(II)-Quinoline Complex Immobilized on a Silica Support as a Photo-Fenton-Like Catalyst

A Cu(II)-quinoline complex immobilized on a silica support was prepared to enhance the degradation of dyes. Mesoporous silica functionalized with this Cu(II) complex was turned into a photo-Fenton-like catalyst. Various techniques were used to characterize the resulting material, and the catalytic activity was determined by the degradation of methylene blue (MB) under UV light irradiation. The Cu(II) ion was successfully coordinated to the quinoline ligand on a silica support. The dye degradation investigation has shown that 95% of the dye was degraded in 2.5 h. The active radical species involved in the reaction were OH^• and O₂ ^•-, suggesting that a peroxo complex intermediate might be formed during degradation processes.

Speciation of heavy metals in soils and their immobilization at micro-scale interfaces among diverse soil components

Heavy metal (HM) pollution of soils is a globally important ecological and environmental problem. Previous studies have focused on i) tracking pollution sources in HM-contaminated soils, ii) exploring the adsorption capacity and distribution of HMs, and iii) assessing phyto-uptake of HMs and their ecotoxicity. However, few reviews have systematically summarized HM pollution in soil-plant systems over the past decade. Understanding the mechanisms of interaction between HMs and solid soil components is consequently key to effectively controlling and remediating HM pollution. However, the compositions of solid soil phases are diverse, their structures are complex, and their spatial arrangements are heterogeneous, all leading to the formation of soil micro-domains that exhibit different particle sizes and surface properties. The various soil components and their interactions ultimately control the speciation, transformation, and bioavailability of HMs in soils. Over the past few decades, the extensive application of advanced instrumental techniques and methods has greatly expanded our understanding of the behavior of HMs in organic mineral assemblages. In this review, studies investigating the immobilization of HMs by minerals, organic compounds, microorganisms, and their associated complexes are summarized, with a particular emphasis on the interfacial adsorption and immobilization of HMs. In addition, methods for analyzing the speciation and distribution of HMs in aggregates of natural soils with different particle sizes are also discussed. Moreover, we also review the methods for speciating HMs at mineral-organic micro-scale interfaces. Lastly, developmental prospects for HM research at inorganic-organic interfaces are outlined. In future research, the most advanced methods should be used to characterize the interfaces and in situ characteristics of metals and metal complexes. In particular, the roles and contributions of microorganisms in the immobilization of HMs at complex mineral-organic interfaces require significant further investigation.

Nano-Porous Composites of Activated Carbon–Metal Organic Frameworks (Fe-BDC@AC) for Rapid Removal of Cr (VI): Synthesis, Adsorption, Mechanism, and Kinetics Studies

Metal–organic frameworks (MOFs) are a group of porous materials that display potential in the elimination of toxic industrial compounds (TICs) from polluted water streams. However, their applications have so far been held up by issues due to their physical nature and cost. In this study, activated carbon (AC) is modified with an Fe-based MOF, iron terephthalate (Fe-BDC). A facile and cost-effective impregnation method is used for enhanced removal from aqueous solutions. The new adsorbent is characterized by SEM, FTIR, PXRD, and BET. The composite displays excellent uptake of Cr (VI) when compared to un-impregnated AC with a maximum monolayer adsorption capacity of 100 mg·g−1. The experimental data shows a high correlation to the Langmuir adsorption model. The adsorption kinetic study reveals that the adsorption of Cr (VI) to Fe-BDC@AC obeys the pseudo-first-order equation. The composite shows high reusability after five cycles and high adsorption rates reaching equilibrium in just 50 min. Such properties make the nanocomposite promising for water decontamination on larger scales compared to powder-based alternatives, such as individual MOF crystals.

Physicochemical and Photocatalytic Properties under Visible Light of ZnO-Bentonite/Chitosan Hybrid-Biocompositefor Water Remediation

In this investigation, a hybrid-biocomposite "ZnO-Bentonite/Chitosan" was synthesized using inexpensive and environmentally friendly materials (Bentonitechitosan) and (ZnO). It was used as a photocatalyst for water remediation. The structural, optical, thermal, and morphological properties of the synthesized hybrid-biocomposite were investigated using XRD, FTIR spectroscopy, UV-vis diffuse reflectance spectroscopy, TGA, XPS, and SEM-EDS. The thermal measurements showed that the decomposition of CS was postponed progressively by adding PB and ZnO, and the thermal stability of the synthesized hybrid-biocomposite was improved. The characterization results highlighted strong interactions between the C-O, C=O, -NH₂, and OH groups of chitosan and the alumina-silica sheets of bentonite on the one side, and between the functional groups of chitosan (-NH₂, OH) and ZnO on the other side. The photocatalytic efficiency of the prepared hybrid-biocomposite was assessed in the presence of Methyl Orange (MO). The experiments carried out in the dark showed that the MO removal increased in the presence of Zn-PB/CS hybrid-biocomposite (86.1%) by comparison with PB (75.8%) and CS (65.4%) materials. The photocatalytic experiments carried out under visible light showed that the MO removal increased 268 times in the presence of Zn-PB/CS by comparison withZnO.The holes trapping experiments indicated that they are the main oxidative active species involved in the MO degradation under both UV-A and visible light irradiations.

Heterogeneous Hybrid Nanocomposite Based on Chitosan/Magnesia Hybrid Films: Ecofriendly and Recyclable Solid Catalysts for Organic Reactions

Chitosan/magnesia hybrid films (CS-Mg) have been prepared via sol-gel process and employed as heterogeneous catalysts. An in situ generation of a magnesia network in the chitosan matrix was performed through hydrolysis/condensation reactions of magnesium ethoxide. The synthesized hybrid films were characterized using various analytical techniques, such as X-ray photo-electron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The hybrid films display excellent catalytic activities in Michael and Knoevenagel reactions via one pot or solvent-free approaches under microwave irradiation conditions. Chitosan/magnesia hybrid films, catalysed pyrimidine, benzochromene, coumarin and arylidene-malononitriles derivatives formation reactions occurred with highly efficient yields of 97%, 92%, 86% and 95% respectively. Due to the fact that the films are durable and insoluble in common organic solvents, they were easily separated and can be recycled up to five times without a considerable loss of their catalytic activity.

Effective removal of levofloxacin drug and Cr(VI) from water by a composed nanobiosorbent of vanadium pentoxide@chitosan@MOFs

Wastewaters is generally polluted with various inorganic and organic contaminants which require effective multipurpose purification technology. In this respect, a novel V₂O₅@Ch/Cu-TMA nanobiosorbent was constructed via encapsulation of nanoscale metal organic frameworks (Cu-TMA) into vanadium pentoxide-imbedded-chitosan matrix to comprehensively investigate its efficiency in removal of levofloxacin drug (LEVO) (e.g., organic pollutant) and chromium (VI) (e.g., inorganic pollutant) from water. Both LEVO drug and Cr(VI) adsorptions were correlated to pseudo-second order (R² = 1) and Langmuir isotherm (R² = 0.9924 for LEVO and R² = 0.9815 for Cr(VI)). Adsorption of Cr(VI) was confirmed to be spontaneous and endothermic reactions, while LEVO was found to proceed via spontaneous and exothermic reactions based on the thermodynamic parameters. The emerged V₂O₅@Ch/Cu-TMA is regarded as an excellent nanobiosorbent for removal of inorganic contaminant as Cr(VI) from all natural water samples (tap, sea and wastewater) with percentages range 92.43%-96.95% and organic contaminant as LEVO drug from tap and wastewater (91.99%-97.20%).

Facile one pot preparation of magnetic chitosan-palygorskite nanocomposite for efficient removal of lead from water

Development of polymeric magnetic adsorbents is a promising approach to obtain efficient treatment of contaminated water. However, the synthesis of magnetic composites involving multiple components frequently involves tedious preparation steps. In the present study, a magnetic chitosan-palygorskite (MCP) nanocomposite was prepared through a straight-forward one pot synthesis approach to evaluate its lead (Pb²⁺) removal capacity from aqueous solution. The nano-architectural and physicochemical properties of the newly-developed MCP composite were described via micro- and nano-morphological analyses, and crystallinity, surface porosity and magnetic susceptibility measurements. The MCP nanocomposite was capable to remove up to 58.5 mg Pb²⁺ g^-1 of MCP from water with a good agreement of experimental data to the Langmuir isotherm model (R² = 0.98). The Pb²⁺ adsorption process on MCP was a multistep diffusion-controlled phenomenon evidenced by the well-fitting of kinetic adsorption data to the intra-particle diffusion model (R² = 0.96). Thermodynamic analysis suggested that the adsorption process at low Pb²⁺ concentration was controlled by chemisorption, whereas that at high Pb²⁺ concentration was dominated by physical adsorption. X-ray photoelectron and Fourier transform infrared spectroscopy results suggested that the Pb adsorption on MCP was governed by surface complexation and chemical reduction mechanisms. During regeneration, the MCP retained 82% Pb²⁺ adsorption capacity following four adsorption-desorption cycles with ease to recover the adsorbent using its strong magnetic property. These findings highlight the enhanced structural properties of the easily-prepared nanocomposite which holds outstanding potential to be used as an inexpensive and green adsorbent for remediating Pb²⁺ contaminated water.

Chitosan Functionalized with 2-Methylpyridine Cross-Linker Cellulose to Adsorb Pb(II) from Water

In this study, chitosan was chemically modified with 2-methylpyridine. Subsequently, the modified chitosan was cross-linked to cellulose using succinic anhydride. Additionally, the capacity of cellulose derivatives to adsorb Pb(II) ions in an aqueous solution was studied through the determination of Pb(II) ions concentration in water, using microwave plasma atomic emission spectroscopy (MP-AES). A maximum adsorption capacity of 6.62, 43.14, 60.6, and 80.26 mg/g was found for cellulose, cellulose-succinic acid, cellulose-chitosan, and cellulose-chitosan-pyridine, respectively. The kinetic data analysis of the adsorption process showed a pseudo-second-order behavior. The increase in metal removal from water is possibly due to metal chelation with the carbonyl group of succinic acid, and the pyridine groups incorporated into chitosan.

Efficient heavy metal removal from water by alginate-based porous nanocomposite hydrogels: The enhanced removal mechanism and influencing factor insight

Novel porous alginate-based nanocomposite hydrogels were prepared by incorporating polyaniline-polypyrrole modified graphene oxide (GO@PAN-PPy) as reinforcing fillers into the alginate matrix (GO@PAN-PPy/SA) for Cr(VI) and Cu(II) removal from water. Different in-situ co-polymerization functionalized GO with Py-to-An mass ratios of monomers (from nil to 1:1) and contents of GO@PAN-PPy (from nil to 2.0%(w/v)) were embedded into the alginate backbone to improve the sorption performance. Key factors, such as pH, coexisting metal ions, and swelling states were investigated in batch adsorption modes. The synergistic effect combined from polymer backbone and fillers could lower the impact of the pH-dependent adsorption reaction. With an adsorption ability superior to that of plain SA and GO/SA, the optimized GO@PAN-PPy-2(1)/SA exhibited good experimental maximum adsorption capacities for Cr(VI) (~133.7 mg/g) and Cu(II) (~87.2 mg/g) at pH 3.0, which were better than those of many other similar sorbents. The sorbents possessed excellent adaptability for 0.2 M salt for Cr(VI) removal but poor for Cu(II) removal. Pre-swelling treatment and co-adsorption could enhance the adsorption performance. The excellent reusability of hydrogel was demonstrated after five cycles in single/binary system. Overall, this work reveals that the resultant hydrogel holds potential as candidate sorbent to remove anionic-cationic heavy metal ions from water.

Self-Assembled Hierarchical Cu x O@C18H36O2 Nanoflakes for Superior Fenton-like Catalysis over a Wide Range of pH

A novel copper-based catalyst supported by a long-chain hydrocarbon stearic acid (Cu _x O@C₁₈H₃₆O₂) was synthesized by a hydrothermal method and double replacement reactions. The as-prepared catalyst is shown as self-assembled hierarchical nanoflakes with an average size of ∼22 nm and a specific surface area of 51.4 m² g^-1. The catalyst has a good performance on adsorption as well as Fenton-like catalytic degradation of Rhodamine B (RhB). The catalyst (10 mg/L) showed an excellent adsorption efficiency toward RhB (20 mg/L) for pH ranging from 5 to 13, with the highest adsorption rate (99%) exhibited at pH 13. The Fenton-like catalytic degradation reaction of RhB (20 mg/L) by Cu _x O@C₁₈H₃₆O₂ nanoflakes was effective over a wide range of pH of 3-11, and ^•OH radicals were generated via Cu₂O/H₂O₂ interactions in acidic conditions and CuO/H₂O₂ reactions in a neutral solution. The highest efficiency catalytic degradation of RhB (20 mg/L) was 99.2% under acidic conditions (pH = 3, H₂O₂ = 0.05 M), with an excellent reusability of 96% at the 6th cycle. The results demonstrated that the as-prepared Cu _x O@C₁₈H₃₆O₂ nanoflakes are an efficient candidate for wastewater treatment, with excellent adsorption capacity and superior Fenton-like catalytic efficiency and stability for RhB.

Fabrication of a Cu Nanoparticles/Poly(ε-caprolactone)/Gelatin Fiber Membrane with Good Antibacterial Activity and Mechanical Property via Green Electrospinning

To improve the antibacterial effect of a poly(ε-caprolactone)/gelatin (PCL/Gt) composite, Cu nanoparticles (Cu NPs) were synthesized as an antibacterial agent, and a Cu NPs/PCL/Gt fiber membrane was thus fabricated via green electrospinning. The results showed that the Cu NPs/PCL/Gt fiber membrane with a uniform and complete structure exhibited high porosity and water absorption, favorable hydrophilicity, good mechanical and thermal properties, and satisfactory antibacterial activity. The easy preparation and good comprehensive property implied the great potential application of the Cu NPs/PCL/Gt fiber membrane in various fields (e.g., wound dressing and antibacterial clothing). In addition, the synthesis in this work would offer a promising approach for the preparation of a metal nanoparticle/polymer fiber material with good antibacterial property.

Amino acid-functionalized chitosan beads for in vitro copper ions uptake in the presence of histidine

One of the hallmarks of Alzheimer's Disease (AD) is the anomalous binding involving amyloid-β (Aβ) peptide and metal ions, such as copper, formed through histidine (His) residues. Herein, adsorption experiments were performed to test the in vitro ability of chitosan to uptake copper ions in the presence of histidine. The characterization of the beads was assessed before and after the adsorption process by scanning electron microscope, X-ray diffraction and Fourier-transform infrared spectroscopy. Amino acid functionalization of chitosan-based beads promoted an increase in the copper ions adsorption capacity (2.47 mmol of Cu(II)/gram of adsorbent). Nevertheless, depending on the order of addition of histidine to the system, different adsorption behaviors were observed. The kinetics showed that, once the Cu(II)-His bond was established, functionalized beads were less efficient to capture Cu(II), which promoted a decrease in the overall adsorption capacity. However, when chitosan and histidine were simultaneously added to the Cu(II) solution, there was no decrease in adsorption capacity. To sum up, chitosan-based materials are an interesting model to provide a better understanding on the biomolecules‑copper interactions that occur in AD, as well as a possible chelating agent that can interfere in the bonds between Aβ residues and copper ions.

Corrosion Resistance of MgZn Alloy Covered by Chitosan-Based Coatings

Chitosan coatings are deposited on the surface of Mg20Zn magnesium alloy by means of the spin coating technique. Their structure was investigated using Fourier Transform Infrared Spectroscopy (FTIR) an X-ray photoelectron spectroscopy (XPS). The surface morphology of the magnesium alloy substrate and chitosan coatings was determined using Scanning Electron Microscope (FE-SEM) analysis. Corrosion tests (linear sweep voltamperometry and chronoamperometry) were performed on uncoated and coated magnesium alloy in the Hank's solution. In both cases, the hydrogen evolution method was used to calculate the corrosion rate after 7-days immersion in the Hank's solution at 37 °C. It was found that the corrosion rate is 3.2 mm/year and 1.2 mm/year for uncoated and coated substrates, respectively. High corrosion resistance of Mg20Zn alloy covered by multilayer coating (CaP coating + chitosan water glass) is caused by formation of CaSiO₃ and Ca₃(PO₄)₂ compounds on its surface.

Chitosan grafted butein: A metal-free transducer for electrochemical genosensing of exosomal CD24

Metal-free cost-efficient biocompatible molecules are beneficial for opto-electrochemical bioassays. Herein, chitosan (CS) conjugated butein is prepared via graft polymerization. Structural integrity between radical active sites of CS and its probable conjugation routes with reactive OH group of butein during grafting were comprehensively studied using optical absorbance/emission property, NMR, FT-IR and XPS analysis. Fluorescence emission of CS-conjugated butein (CSB) was studied in dried flaky state as well as in drop casted form. Cyclic voltammetric study of CSB modified glassy carbon electrode exhibits 2e^-/2H⁺ transfer reaction in phosphate buffered saline electrolyte following a surface-confined process with a correlation coefficient of 0.99. Unlike pristine butein, CSB modified electrode display a highly reversible redox behavior under various pH ranging from 4 to 9. For the proof-of-concept CSB-modified flexible screen printed electrodes were processed for electrochemical biosensing of exosomal CD24 specific nucleic acid at an ultralow sample concentration, promising for ovarian cancer diagnosis.

Quantum mechanical study on physisorption of dissolved metal ions in seawater using cellulose, chitosan and chitin

Density Functional Theory (DFT) calculations were performed to investigate the adsorption of alkali and alkaline earth metal ions, Na⁺, K⁺, Mg²⁺, and Ca²⁺ present in seawater by biopolymers, cellulose, chitosan, and chitin. Analysis of the optimized geometries of the complexes formed by physisorption of metal ions on biopolymers reveals that monomer of chitin is the best biopolymer for adsorption of Mg²⁺ ion. Water as a solvent reduces the reactivity of complexes formed, playing a significant role in complex stability, which further proved the effective use of cellulose, chitosan and chitin for real-time applications. Natural Bond Orbital (NBO) analysis and quantum reactivity descriptors of the optimized geometries indicate that the electronic charge transfer between the biopolymer and metal ions acts as a driving force for the complex formation. This study also highlights the significant role of water in physisorption of metal ions on biopolymer.

Immobilization properties and adsorption mechanism of nickel(II) in soil by biochar combined with humic acid-wood vinegar

Biochar (BC) combined with humic acid (HA) and wood vinegar (WV) was designed and prepared as an inexpensive, effective, and environmentally friendly immobilization material (BHW) for metal-polluted soil. The influences of the wood vinegar and humic acid on the immobilization properties and adsorption mechanism of this new material were also investigated. The remediation performance was evaluated using a laboratory-made, nickel-contaminated soil with a Ni²⁺ concentration of 200 mg per kg surface soil (top 20 cm from agricultural land). The results indicated that the immobilization ratio sequence of nickel (II) in the soil was BC< BH< BHW. The maximum adsorption capacity increased in the same order: BC< BH< BHW. All three adsorption isotherms were better fitted by the Freundlich model, which were consistent with the surface heterogeneity of the remediation materials. The cause of this surface heterogeneous migration may be due to the increase in oxygen-containing groups in the BC introduced by the HA and WV. The WV can increase the number of the oxygen-containing groups in the BC combined with HA, which enhanced the adsorption and immobilization of Ni²⁺ ions. The results suggested that BHW is recommended for the remediation of metal-contaminated soils, because of its high efficacy, economic feasibility, environmental and food safety.

Chitosan as capping agent in a robust one-pot procedure for a magnetic catalyst synthesis

Here, we report a one-pot solvothermal method for the development of magnetically recoverable catalysts with Ru or Ag nanoparticles (NPs) capped by chitosan (CS), a derivative of natural chitin. The formation of iron oxide NPs was carried out in situ in the presence of CS and iron acetylacetonate in boiling triethyleneglycol (TEG) due to CS solubilization in warm TEG. Coordination with Ru or Ag species and the NP formation take place in the same reaction solution, eliminating intermediate steps. In optimal conditions the method developed allows stabilization of 2.2 nm monodisperse Ru NPs (containing both Ru⁰ and Ru⁴⁺ species) that are evenly distributed through the catalyst, while for Ag NPs, this stabilizing medium is inferior, leading to exceptionally large Ag nanocrystals. Catalytic testing of CS-Ru magnetically recoverable catalysts in the reduction of 4-nitrophenol to 4-aminophenol with excess NaBH₄ revealed that the catalyst with 2.2 nm Ru NPs exhibits the highest catalytic activity compared to samples with larger Ru NPs (2.9-3.2 nm). Moreover, this catalyst displayed extraordinary shelf-life in the aqueous solution (up to ten months) and excellent reusability in ten consecutive reactions with easy magnetic separation at each step which were assigned to its conformational rigidity at a constant pH. These characteristics as well as favorable environmental factors of the catalyst fabrication, make it promising for nitroarene reduction.

Understanding mechanisms in the adsorption of lead and copper ions on chili seed waste in single and multicomponent systems: a combined experimental and computational study

In the current work, a deep study to understand the adsorption phenomena occurring in single and multicomponent systems was conducted by using spectroscopic characterization, and computational tools. The experimental results showed that the adsorption capacity of chili seed is higher for Pb2+ (48 mg/g) than Cu2+ (4.1 mg/g) ions in single systems. However, the adsorption study in multicomponent systems provides important conclusions of the concentration effect of the metal ions, showing a significant antagonistic and competitive effect of both ions under equivalent concentrations of them (qPb2+ is 56% reduced) or high concentration of Pb2+ (qCu2+ is 50% reduced). Computational results correlated well with the experimental ones and evidenced all interactions proposed from spectroscopy results, accounting for the occurrence of complexation and electrostatic mechanisms between metal ions and the surface oxygenated functional groups (hydroxyl, carboxyl, and carboxylate) onto chili seed. Chemistry quantum descriptors supported the reactivity behavior of the chemical species implicated. All results evidenced that Pb2+ and Cu2+ adsorption on chili seed surface is governed by the occurrence of combined ionic exchange, π-interaction, complexation, and electrostatic attraction.

Self-decoration of N-doped graphene oxide 3-D hydrogel onto magnetic shrimp shell biochar for enhanced removal of hexavalent chromium

In this work, a novel decorated and combined N-doped graphene oxide hydrogel with shrimp shell magnetic biochar (NGO3DH-MSSB) biosorbent was fabricated as an effective material for Cr(VI) removal. Three-dimensional self-assembled graphene oxide hydrogel was synthesized using nitrogen source, ethylenediamine (EDA). Characterizations of NGO3DH-MSSB biosorbent were established by FT-IR, TGA, SEM and BET, where high surface area (398.05 m²/g) compared with that of MSSB (138.64 m²/g) was characterized. The maximum achieved swelling ratio (800%) was only after 300 min. The binding mechanisms between Cr(VI) ions and NGO3DH-MSSB biosorbent were controlled by electrostatic adsorption (ion-pair), pore filling, and reduction-coordination reaction. Adsorption was described by the pseudo-second order kinetic (R² =0.9994, 0.9983 and 0.9992) at 10, 50 and 100 mg/L and Langmuir isotherm model (R² =0.9997, 0.9957 and 0.9912) at 25, 40 and 50 °C. The adsorption capacity (350.42 mg/g) was achieved at pH 1.0, using initial Cr(VI) concentration (100 mg/L) and contact time (180 min) at room temperature. NGO3DH-MSSB biosorbent could be successfully reused after eight cycles. The percentage removal of Cr(VI) were confirmed as 99.79%, 99.20% and 98.00% from tap water, sea water and wastewater, respectively.