Ca-alginate/carboxymethyl chitosan/Ni0.2Zn0.2Fe2.6O4 magnetic bionanocomposite: Synthesis, characterization and application for single adsorption of Nd+3, Tb+3, and Dy+3 rare earth elements from aqueous media

Recent developments in conductive polysaccharide adsorbent formulations for environmental remediation: A review

Environmental remediation is crucial for human life and ecosystems, involving the cleanup of contaminated water to protect health and restore ecological balance. However, rapid industrialization and population growth have worsened pollution, particularly in water bodies, making effective wastewater treatment a key challenge in ensuring clean drinking water, and the adsorption of toxic gases for air treatment are the main strategies for environmental remediation. Among the various treatment methods, adsorption stands out for its high selectivity, low energy and chemical use, ease of operation, and cost-effectiveness. To date, innovative, highly efficient, non-toxic, engineered adsorbent materials have received potential interest from scientific and governmental communities. Conducting polymer-modified polysaccharide formulations are crucial in wastewater treatment due to their high surface area, adsorption efficiency, excellent stability, and eco-friendly, biodegradable properties. This review offers an extensive overview of recent progress in synthesizing conducting polymer-modified polysaccharide formulations (hydrogels, aerogels, nanofibers, and nanocomposites) for capturing toxic heavy metal ions, organic dyes, pharmaceuticals, phenols as well as adsorbing different toxic gases using various adsorption mechanisms. It also emphasizes the integration of different nanofillers, including carbon-based materials, Mxenes, nanoclay, metal/metal oxides, and hybrid nanomaterials, into conductive polysaccharide chains to improve their physicochemical properties and adsorption efficiency. The reported data showed that these engineered adsorbent materials based on conductive polysaccharide formulations have immense potential for wastewater treatment applications, offering more effective and sustainable solutions.

Biosorption of Cu2+ on magnetic calcium alginate immobilized Phanerochaete chrysosporium

Phanerochaete chrysosporium were immobilized in magnetic Fe3O4 nanoparticles and calcium alginate to form MC microspheres. The obtained MC microsphere was characterized by SEM, EDS, XRD, BET, VSM and TGA. The results indicated that MC microsphere was a three-dimensional structure with relatively large specific surface area and good porosity. MC microspheres had excellent magnetic recovery performance and thermal stability. The characteristics and performance of MC microspheres on adsorption of Cu2+ were evaluated based on batch adsorption experiments. The maximum adsorption capacity of Cu2+ by MC microspheres was 35.07 mg g-1 at pH of 5.0, temperature of 35 °C and adsorption time of 8 h. MC microspheres can still effectively adsorb Cu2+ at 400 mg L-1. Integrating simulation results from pseudo-second-order kinetic model, Intra-particle diffusion model and Freundlich model, the process was mainly dominated by chemical adsorption, and it is a multi-molecular layer adsorption. The results of XPS and FTIR showed that complexation, ion replacement, and reduction are important mechanisms for adsorption of Cu2+ on MC microspheres. -OH and C-O/C=O mainly complexes with Cu2+ in the biosorption process. After five adsorption-desorption cycles, the adsorption efficiency can still reach 32.40 %. Therefore, MC microspheres are a potential adsorbent that can achieve effective recovery.

Facile synthesis of eco-friendly alginate-chitosan bio-adsorbent for critical raw materials adsorption: A comprehensive study

Sustainable management of critical raw materials is of paramount importance to ensure a steady supply and reduce environmental impact. The application of newly synthesized and environmentally friendly ALG@CS material as a bio-adsorbent for the effective rare earth elements removal from aqueous solution has been presented. The synthesized material underwent FTIR, XPS, EDX, and SEM analysis to determine its suitability for metal uptake. To evaluate the adsorption capacity of ALG@CS for rare earth elements several factors were taken into consideration. These factors included alginate:chitosan ratios, bead size, pH level, composite mass, interaction time, metal ion concentration, and temperature, being all varied during the batch mode evaluation process. Under the optimal conditions, the maximum adsorption capacities were found to be 145.90 mg La(III)/g, 168.44 mg Ce(III)/g, 132.51 mg Pr(III)/g, 128.40 mg Nd(III)/g, 154.36 mg Sm(III)/g, and 165.10 mg Ho(III)/g. The equilibrium data fits well with non-linear three-parameter Sips and Redlich-Peterson isotherm models. The PSO model finds the highest process suitability. The synthesized ALG@CS bio-adsorbent showed excellent regenerative capacity in ten cycles, making it a suitable adsorbent for rare earth elements uptake. The unique bio-adsorbents combination allows for efficient critical raw materials adsorption providing a promising solution for their recovery and recycling.

Adsorption Study of Neodymium from the Aqueous Phase Using Fabricated Magnetic Chitosan-Functionalized Graphene Oxide Composites

This work reports the performances of the magnetic chitosan@graphene oxide composite (MCh@GO) for the sorption of Nd(III) from aqueous medium. The prepared composite was synthesized by a coprecipitation method and then examined by FT-IR, XRD, SEM, and TGA. XRD analysis proved physical interactions between magnetic chitosan and graphene oxide through (inter- and intramolecular H-bonding and peptide bonding). TGA data approved the thermal stability of the prepared MCh@GO nanocomposite over their constituents. The optimum pH for the sorption process was 4.5. The Langmuir model and PSO fitted the experimental data. The adsorption process was found to be endothermic and spontaneous with a Q max of 56.6 mg g-1. Indeed, the MCh@GO composite proved to be an excellent adsorbent for the purification, remediation, and separation of Nd due to its promising properties.

Innovative Green Alginate-Cellulose Composite for Light Lanthanides: Experimental Design and Comprehensive Studies on Kinetics, Equilibrium, Thermodynamics, and Reusability

Nowadays, there is a great interest in efficient adsorbent development due to the recent demand for lanthanides, which are widely used in high-tech technology. Alginates, owing to their natural occurrence, gel formation capability, and safety, could be promising feasible adsorbents for lanthanide removal. This study proposes the alginate-cellulose composite as an ecological, sustainable adsorbent for light lanthanide sorption. The structure, morphology, qualitative and quantitative compositions, average diameter, and pHpzc of the composite were discussed in great detail. Using the batch approach, sorption trials were performed to evaluate the metal sorption performance. The maximum lanthanide accumulation was attained at pH 5.0 and a dosage of 0.05 g. The uptake kinetics are successfully explained by the Ho and McKay model, whereas the equilibrium data is best represented by the Langmuir equation. The presence of Cl-, NO3 -, SO4 2-, Ni(II), and Co(II) did not have any impact on the adsorption capacity. In turn, the presence of Fe(III) ions led to a 15 % reduction in the adsorption. The lanthanide ions were eluted from the adsorbent following the treatment with 0.1 M HNO3. The adsorbent retained over 95 % of its initial adsorption capacity after 6 series of sorption/desorption studies.

Regulating Chemisorption and Electrosorption Activity for Efficient Uptake of Rare Earth Elements in Low Concentration on Oxygen-Doped Molybdenum Disulfide

Recovery of rare earth elements (REEs) with trace amount in environmental applications and nuclear energy is becoming an increasingly urgent issue due to their genotoxicity and important role in society. Here, highly efficient recovery of low-concentration REEs from aqueous solutions by an enhanced chemisorption and electrosorption process of oxygen-doped molybdenum disulfide (O-doped MoS2) electrodes is performed. All REEs could be extremely recovered through a chemisorption and electrosorption coupling (CEC) method, and sorption behaviors were related with their outer-shell electrons. Light, medium, and heavy ((La(III), Gd(III), and Y(III)) rare earth elements were chosen for further investigating the adsorption and recovery performances under low-concentration conditions. Recovery of REEs could approach 100% under a low initial concentration condition where different recovery behaviors occurred with variable chemisorption interactions between REEs and O-doped MoS2. Experimental and theoretical results proved that doping O in MoS2 not only reduced the transfer resistance and improved the electrical double layer thickness of ion storage but also enhanced the chemical interaction of REEs and MoS2. Various outer-shell electrons of REEs performed different surficial chemisorption interactions with exposed sulfur and oxygen atoms of O-doped MoS2. Effects of variants including environmental conditions and operating parameters, such as applied voltage, initial concentration, pH condition, and electrode distance on adsorption capacity and recovery of REEs were examined to optimize the recovery process in order to achieve an ideal selective recovery of REEs. The total desorption of REEs from the O-doped MoS2 electrode was realized within 120 min while the electrode demonstrated a good cycling performance. This work presented a prospective way in establishing a CEC process with a two-dimensional metal sulfide electrode through structure engineering for efficient recovery of REEs within a low concentration range.

Novel phosphate functionalized sodium alginate hydrogel for efficient adsorption and separation of Nd and Dy from Co

The recovery of rare earth elements (REEs) including neodymium (Nd) and dysprosium (Dy) from NdFeB permanent magnets has become one of the main ways to solve the increased demand for rare earth. Herein, n-dodecyl phosphate (DPPA) was used for the first time as the adsorption functional group donor, sodium alginate as the substrate, and calcium chloride solution as the reactive solvent, a hybrid hydrogel adsorbent DPPA/CaALG was synthesized by sol-gel method for application in the adsorption and separation of Nd and Dy from the Co-Nd-Dy ternary system. SEM-EDS, and N2 adsorption-desorption analysis showed the successful preparation of DDPA/CaALG with mesoporous structure. Batch experiments showed the superiority of the hybrid hydrogel for the good selective adsorption of Nd and Dy, such as large adsorption capacity (Nd: 162.5 mg/g, Dy: 183.5 mg/g), and no adsorption for Co. FT-IR, XPS showed that PO and P-O groups are involved in the adsorption process of Nd and Dy as electron acceptors, where the ion exchange of P-OH is dominant. Furthermore, the chemical properties of ligands and complexes were analyzed by Density Functional Theory (DFT) calculations and revealed their adsorption behaviors as well as the competition between different metal ions.

Biochar supported nanoscale zerovalent iron-calcium alginate composite for simultaneous removal of Mn(II) and Cr(VI) from wastewater: Sorption performance and mechanisms

Heavy metal pollution in water caused by industrial activities has become a global environmental issue. Among them, manganese mining and smelting activities have caused the combined pollution of Cr(VI) and Mn(II) in water, posing a serious ecotoxicological risk to ecological environments and human health. To efficiently remove Cr(VI) and Mn(II) from wastewater, a novel biochar supported nanoscale zerovalent iron-calcium alginate composite (CA/nZVI/RSBC) was synthesized by liquid-phase reduction and calcium alginate embedding methods. The adsorption performance and mechanisms of Cr(VI) and Mn(II) by CA/nZVI/RSBC were investigated. The maximum adsorption capacities of Cr(VI) and Mn(II) onto CA/nZVI/RSBC fitted by the Langmuir model were 5.38 and 39.78 mg/g, respectively, which were much higher than the pristine biochar. The iron release from CA/nZVI/RSBC was comparatively lower than that of nZVI/RSBC. Mn(II) presence enhanced the reduction of Cr(VI) by CA/nZVI/RSBC. The results of XRD, XPS, and site energy distribution analysis indicated that redox was the predominant mechanism of Cr(VI) adsorption, while electrostatic attraction dominated Mn(II) adsorption. This study provides a novel alternative way for the simultaneous removal of Cr(VI) and Mn(II) in wastewater.

Stripped: contribution of cyanobacterial extracellular polymeric substances to the adsorption of rare earth elements from aqueous solutions

The transformation of modern industries towards enhanced sustainability is facilitated by green technologies that rely extensively on rare earth elements (REEs) such as cerium (Ce), neodymium (Nd), terbium (Tb), and lanthanum (La). The occurrence of productive mining sites, e.g., is limited, and production is often costly and environmentally harmful. As a consequence of increased utilization, REEs enter our ecosystem as industrial process water or wastewater and become highly diluted. Once diluted, they can hardly be recovered by conventional techniques, but using cyanobacterial biomass in a biosorption-based process is a promising eco-friendly approach. Cyanobacteria can produce extracellular polymeric substances (EPS) that show high affinity to metal cations. However, the adsorption of REEs by EPS has not been part of extensive research. Thus, we evaluated the role of EPS in the biosorption of Ce, Nd, Tb, and La for three terrestrial, heterocystous cyanobacterial strains. We cultivated them under N-limited and non-limited conditions and extracted their EPS for compositional analyses. Subsequently, we investigated the metal uptake of a) the extracted EPS, b) the biomass extracted from EPS, and c) the intact biomass with EPS by comparing the amount of sorbed REEs. Maximum adsorption capacities for the tested REEs of extracted EPS were 123.9-138.2 mg g-1 for Komarekiella sp. 89.12, 133.1-137.4 mg g-1 for Desmonostoc muscorum 90.03, and 103.5-129.3 mg g-1 for Nostoc sp. 20.02. A comparison of extracted biomass with intact biomass showed that 16% (Komarekiella sp. 89.12), 28% (Desmonostoc muscorum 90.03), and 41% (Nostoc sp. 20.02) of REE adsorption was due to the biosorption of the extracellular EPS. The glucose- rich EPS (15%-43% relative concentration) of all three strains grown under nitrogen-limited conditions showed significantly higher biosorption rates for all REEs. We also found a significantly higher maximum adsorption capacity of all REEs for the extracted EPS compared to cells without EPS and untreated biomass, highlighting the important role of the EPS as a binding site for REEs in the biosorption process. EPS from cyanobacteria could thus be used as efficient biosorbents in future applications for REE recycling, e.g., industrial process water and wastewater streams.

Advancements in Composite Materials and Their Expanding Role in Biomedical Applications

The synthesis of a Ni-doped ZnO nanocomposite incorporating chitosan (CS/Ni-doped ZnO) was achieved via a precipitation method, followed by annealing at 250 °C. This study comprehensively examined the nanocomposite's structural, functional, morphological, and porosity properties using various analytical techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), high-resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analysis. The presence of chitosan (CS) and nickel (Ni) within the nanocomposite, along with their influence on reducing the band gap of ZnO particles and enhancing the generation of electron-hole pairs, was confirmed using UV-visible near-infrared spectroscopy (UV-vis-NIR). The electrochemical properties of the CS/Ni-doped ZnO nanocomposite were investigated via electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) by utilizing a phosphate buffer solution with a pH of 6, which closely resembled the typical pH of bacterial cell walls. Finally, the prepared CS/Ni-doped ZnO nanocomposite was evaluated for its antibacterial and anticancer activities. The results demonstrated the highest inhibition of bacterial growth in P. vulgaris, whereas the lowest inhibition was found in S. aureus across various concentrations, thus highlighting its potential in antimicrobial applications. The cytotoxicity of CS/Ni-doped ZnO nanocomposites demonstrated remarkable effects with a half-maximum inhibitory concentration of approximately 80 ± 0.23 µg mL-1 against MCF-7 breast cancer cell lines, following a dose-dependent manner.

Tuning the Dual Active Sites of Functionalized UiO-66 for Selective Adsorption of Yb(III)

The recovery of rare earth elements (REEs) from discharged electronic devices or mineral waste water is highly essential but still facing challenges. In this work, two amino-functionalized carboxyl-UiO-66 (UiO-66-COOH-TETA and UiO-66-(COOH)₂-ED) prepared via the postmodification method were employed as the adsorbents for Yb(III) capture. The experimental results revealed their superior adsorption capacities of 161.5 and 202.6 mg/g, respectively. Meanwhile, their adsorption processes can be described by the pseudo-second-order kinetic model and Langmuir model. Effects of initial pH and temperature on adsorptions were systematically evaluated, affording an optimal operating condition (i.e., pH of 5.5-6, T of 65 °C, t of 10 h). Moreover, the fabricated materials exhibited great reusability after five adsorption-regeneration cycles. UiO-66-COOH-TETA demonstrated good separation selectivity for Yb(III) over light REEs (i.e., 3.98 of Yb/Ce, 3.51 of Yb/Nd). Based on the density functional theory calculations and characterization analysis (XPS, Zeta, mapping, and IR), the adsorption mechanisms were mainly attributed to significant electrostatic attraction and strong surface complexation between N and O sites and Yb(III).

Hybrid lignin particles via ion-crosslinked for selective removal of anionic dyes from water

Hybrid lignin (HL) particles were synthesized by compounding lignosulfonate and carboxylated chitosan through a simple ionic cross-linking method, and modifying by polyvinylpolyamine. Due to the synergistic effect of recombination and modification, the material exhibits excellent adsorption performance for anionic dyes in water. The structural characteristics and adsorptive behavior were systematically investigated. The pseudo-second-order kinetic model and the Langmuir model were revealed to well describe the sorption procedure of HL for anionic dyes. The results exhibited that the sorption capacities of HL on sodium indigo disulfonate and tartrazine were 1099.01 mg/g and 436.68 mg/g, respectively. Simultaneously, the adsorbent behaved no significant adsorption capacity loss after five adsorption-desorption cycles, indicating its superb stability and recyclability. Additionally, the HL exhibited excellent selective adsorption of anionic dyes form binary dye adsorption systems. The interaction forces between adsorbent and dye molecules, such as hydrogen bonding, π-π stacking, electrostatic attraction and cation bonding bridge, are discussed in detail. The facile preparation process and superior dyes removal performance of HL were considered a potential adsorbent to remove anionic dyes from wastewater.

Tailoring abundant active-oxygen sites of Prussian blue analogues-derived adsorbents for highly efficient Yb(III) capture

The removal of rare earth elements in mineral processing wastewater is highly desirable but still challenging. In this study, three bimetallic Prussian blue analogues (PBA) and six corresponding oxides are prepared by co-precipitation and calcination methods, and then utilized to adsorb aqueous Yb(III) solution. The results of XRD, SEM, BET, and XPS indicate the successful synthesis of all the adsorbents. Among them, three PBA-oxide samples (PBO-800) exhibit the superior adsorption capacities (˃250 mg/g). The adsorption processes of Yb(III) are in accordance with the pseudo-second-order kinetic model and Langmuir model, simultaneously showing the spontaneous and endothermic thermodynamics. Moreover, PBO-800 can be reused after alkaline solution regeneration with less than 10% degradation after five consecutive adsorption-desorption cycles. More importantly, PBO-800 exhibits the impressive separation selectivity of Yb(III) and most light rare earth ions (e.g., 5.51 of Yb/La, 4.03 of Yb/Pr), as well as the selectivity of Yb(III) and alkali metal ions (e.g., 300.5 of Yb/Na, 256.2 of Yb/Ca). According to the characterization analysis and DFT calculation, the adsorption mechanism of Yb(III) by PBO-800 is mainly attributed to the strong interaction between the abundant active-oxygen sites and Yb(III), and the significant electrostatic attraction.

Recent advances in the application of magnetic bio-polymers as catalysts in multicomponent reactions

Magnetic nanoparticles have attracted significant attention due to their high surface area and superparamagnetic properties. Bio-polymers composed of polysaccharides including alginate, cellulose, glucose, dextrin, chitosan, and starch can be immobilized on magnetic nanoparticles. Bio-polymers can be obtained from natural sources, such as plants, tunicates, algae, and bacteria. Bio-polymers obtained from natural sources have attracted attention due to their various properties including efficient functional groups, non-toxicity, low cost, availability, and biocompatibility. According to the targets of "green chemistry", the application of bio-polymers is effective in reducing pollution. Furthermore, they are excellent agents for the functionalization of magnetic nanoparticles to yield nanomagnetic bio-polymers, which can be applied as recoverable and eco-friendly catalysts in multicomponent reactions.

Synthesis and characterization of chitosan-vermiculite-lignin ternary composite as an adsorbent for effective removal of uranyl ions from aqueous solution: Experimental and theoretical analyses

Chitosan (Ch), vermiculite (V) and lignin (L) were used as the components of a natural composite adsorbent (Ch-VL) for the removal of the UO₂²⁺ ions in aqueous solutions. During the study, we recorded and analyzed the initial UO₂²⁺ ion concentration, initial pH, contact time, temperature, and recovery. The recycling performance of the Ch-VL composite was assessed by three sequential adsorption/desorption experiments. Adsorption performance of the Ch-VL composite for UO₂²⁺ ions was 600 mg L^-1 at pH 4.5 and temperature of 25 °C. Thermodynamic findings, ΔH⁰:28.1 kJ mol^-1, and ΔG⁰:-14.1 kJ mol^-1 showed that adsorption behavior was endothermic and spontaneous. Its maximum adsorption capacity was 0.322 mol kg^-1, obtained from the Langmuir isotherm model. The adsorption kinetics indicated that it followed the pseudo-second-order and intraparticle diffusion rate kinetics. The adsorption thermodynamic shown indicated that the UO₂²⁺ ion adsorption was both spontaneous and endothermic. The adsorption process was enlightened by FT-IR and SEM-EDX analyses. The study suggested a simple and cost-effective approach for the removal of toxic UO₂²⁺ ions from wastewater. To highlight the adsorption mechanism, DFT calculations were performed. Theoretical results are in good agreement with experimental observations.

Photocatalytic Efficacy of Heterocyclic Base Grafted Chitosan Magnetite Nanoparticles on Sorption of Pb(II); Application on Mining Effluent

Development of bio-based sorbents (i.e., chitosan moieties) at nanoscale size for the removal of metal contaminants is the main target of this research. Grafting with thiazole heterocyclic derivative gives fast kinetics sorption, highly metal loading, and good recyclability for mining leaching solution. Different analyses tools including (thermogravimetric analysis (TGA), scanning electron microscope and energy dispersive spectroscopy (SEM-EDX), X-ray diffraction (XRD), Fourier transform infrared (FTIR), BET surface area (nitrogen sorption desorption), titration, and TEM (transmission electron microscopy)) were used to investigate the chemical and textural properties of the functionalized sorbent. The sorption was measured in normal visible light and under UV emission. The highest capacity was measured at pH 5, which reached 0.251 mmol Pb g−1 in visible light compared with 0.346 mmol Pb g−1 under UV for the pristine crosslinked chitosan (MCc). The sorption performances were improved by functionalization; (0.7814 and 1.014 mmol Pb g−1) for the functionalized sorbent (MCa-ATA) under visible light and UV, respectively. PFORE (pseudo-first-order rate equation) and RIDE (resistance to intraparticle diffusion) fit kinetics, the Sips equation is the most fit profile for the sorption isotherms for the MCc in either light and UV processes, while PFORE and RIDE for kinetics under light and UV for MCa-ATA and Sips in light and Sips and Langmuir under the UV emission. Finally, the sorbent was investigated toward a raffinate solution from ore processing and shows promising extraction tools for the most interesting elements.

Engineering DNA/Fe-N-C single-atom nanozymes interface for colorimetric biosensing of cancer cells

Single atom nanozymes (SAzymes) represent the state-of-the-art technology in nanomaterial-based catalysis, which have attracted attentions in catalysis, cancer treatment, disinfection and biosensing fields. However, numerous SAzymes suffered from low aqueous dispersion and without recognition capacity, which impeded their applications in bioanalysis. Herein, we engineered DNA onto SAzymes to obtain the DNA/SAzymes conjugates, which significantly improved the aqueous dispersion and recognition ability of SAzymes. We synthesized iron SAzymes (Fe-N-C SAzymes) as the catalytic nanomaterials, and investigated the interactions between Fe-N-C SAzymes and DNA. We compared A₁₅, T₁₅ and C₁₅ adsorption of Fe-N-C SAzymes in HEPES containing 2 mM MgCl₂. We found that 50 μg mL^-1 Fe-N-C SAzymes produced nearly 100% A₁₅ adsorption, 90% T₁₅ adsorption and only 69% C₁₅ adsorption, indicating that adenine and thymine had higher adsorption affinity on Fe-N-C SAzymes. More importantly, DNA modification did not affect the peroxidase-like activity of Fe-N-C SAzymes and the bioactivity of the adsorbed DNA. Taking the advantage of the diblock DNA with one DNA sequence (adenine) binding to Fe-N-C SAzymes and the other DNA sequence (i.e., aptamer) binding to cancer cells, we designed Apt/Fe-N-C SAzymes for colorimetric detection of cancer cells, which offered new insights for the use of SAzymes in biomedicine.

Adsorption of Uranium, Mercury, and Rare Earth Elements from Aqueous Solutions onto Magnetic Chitosan Adsorbents: A Review

The compound of chitin is the second most important and abundant natural biopolymer in the world. The main extraction and exploitation sources of this natural polysaccharide polymer are mainly crustaceans species, such as shrimps and crabs. Chitosan (CS) (poly-β-(1 → 4)-2-amino-2-deoxy-d-glucose) can be derived from chitin and can be mentioned as a compound that has high value-added applications due to its wide variety of uses, including pharmaceutical, biomedical, and cosmetics applications, food etc. Furthermore, chitosan is a biopolymer that can be used for adsorption applications because it contains amino and hydroxyl groups in its chemical structure (molecules), resulting in possible interactions of adsorption between chitosan and pollutants (uranium, mercury, rare earth elements (REEs), phenols, etc.). However, adsorption is a very effective, fast, simple, and low-cost process. This review article places emphasis on recent demonstrated research papers (2014–2020) where the chemical modifications of CS are explained briefly (grafting, cross-linking etc.) for the uptake of uranium, mercury, and REEs in synthesized aqueous solutions. Finally, figures and tables from selected synthetic routes of CS are presented and the effects of pH and the best mathematical fitting of isotherm and kinetic equations are discussed. In addition, the adsorption mechanisms are discussed.

Phosphorylation of Guar Gum/Magnetite/Chitosan Nanocomposites for Uranium (VI) Sorption and Antibacterial Applications

The development of new materials is needed to address the environmental challenges of wastewater treatment. The phosphorylation of guar gum combined with its association to chitosan allows preparing an efficient sorbent for the removal of U(VI) from slightly acidic solutions. The incorporation of magnetite nanoparticles enhances solid/liquid. Functional groups are characterized by FTIR spectroscopy while textural properties are qualified by N2 adsorption. The optimum pH is close to 4 (deprotonation of amine and phosphonate groups). Uptake kinetics are fast (60 min of contact), fitted by a pseudo-first order rate equation. Maximum sorption capacities are close to 1.28 and 1.16 mmol U g-1 (non-magnetic and magnetic, respectively), while the sorption isotherms are fitted by Langmuir equation. Uranyl desorption (using 0.2 M HCl solutions) is achieved within 20-30 min; the sorbents can be recycled for at least five cycles (5-6% loss in sorption performance, complete desorption). In multi-component solutions, the sorbents show marked preference for U(VI) and Nd(III) over alkali-earth metals and Si(IV). The zone of exclusion method shows that magnetic sorbent has antibacterial effects against both Gram+ and Gram- bacteria, contrary to non-magnetic material (only Gram+ bacteria). The magnetic composite is highly promising as antimicrobial support and for recovery of valuable metals.

Application of a Low-Cost Cellulose-Based Bioadsorbent for the Effective Recovery of Terbium Ions from Aqueous Solutions

The preparation of a low-cost cellulose-based bioadsorbent from cellulosic material extracted from rose stems (CRS) was carried out; rose stems are considered agricultural waste. After the required pretreatment of this waste and further treatment with an acidic mixture of acetic and nitric acids, the CRS product was produced. The resulting bioadsorbent was characterized by several techniques, such as X-ray diffraction, which revealed diffraction maxima related to the cellulose structure, whose calculated crystallinity index (CrI) was 75%. In addition, Fourier Transform Infrared spectroscopy (FTIR), 13C Nuclear Magnetic Resonance (NMR), and X-ray Photoelectron Spectroscopy (XPS) showed signs of acetylation of the sample. The thermal properties of the solid were also evaluated through Thermogravimetric Analysis (TGA). Scanning Electron Microscopy (SEM) showed cellulose fibers before and after the adsorption process, and some particles with irregular shapes were also observed. The CRS bioadsorbent was used for the effective adsorption of valuable Tb(III) from an aqueous solution. The adsorption data showed a good fit to the Freundlich isotherm and pseudo-second-order kinetic models; however, chemisorption was not ruled out. Finally, desorption experiments revealed the recovery of terbium ions with an efficiency of 97% from the terbium-loaded bioadsorbent.

Treatment of oil refinery effluent using bio-adsorbent developed from activated palm kernel shell and zeolite

This study investigated the potential of palm kernel shell (PKS) as a biomass feed for adsorbent production. This work aims at synthesizing green adsorbent from activated PKS by integrating iron oxide and zeolite. The newly developed adsorbents, zeolite-Fe/AC and Fe/AC, were analyzed for surface area, chemical composition, magnetic properties, crystallinity, and stability. The adsorbent efficiency in removing effluent from the palm oil mill was evaluated. The influence of operating parameters, including adsorbent dosage, H2O2, reaction time, and initial solution pH for adsorption performance was studied. The Fourier transform infrared analysis revealed that the adsorbents contain functional groups including OH, N-H, C[double bond, length as m-dash]O and C[double bond, length as m-dash]C, which are essential for removing pollutants. The SEM-EDX analysis shows holes in the adsorbent surface and that it is smooth. The adsorption study revealed that under optimized conditions, by using 4 g L-1 of adsorbent and 67.7 mM H2O2, zeolite-Fe/AC was able to remove 83.1% colour and 67.2% COD within 30 min. However, Fe/AC requires 5 g L-1 of adsorbent and 87.7 mM to remove 86.8 percent and 65.6 percent, respectively. This study also showed that zeolite-Fe/AC has higher reusability compared to Fe/AC. Among Freundlich and Temkin models, the experimental data were found to be best fitted with the Langmuir isotherm model. The kinetic analysis revealed that for both adsorbents, the adsorption process fitted the pseudo-second-order model (R 2 = 0.9724). The finding reflects monolayer adsorption of zeolite-Fe/AC and Fe/AC. This study thus demonstrates the applicability of low-cost green adsorbents produced from PKS to treat oil refinery effluent and other recalcitrant wastewaters.