Modified chitosan and calcium alginate biopolymer sorbents for removal of nickel (II) through adsorption

Immobilized chitosan as an efficient adsorbent for columnar adsorption of Cr (VI) from aqueous solution

The current effort focuses on creating an effective adsorbent for Cr (VI) adsorption due to the growing need to address Cr (VI) pollution in aqueous solutions. Chitosan, a biopolymer and polysaccharide with several functional sites, is immobilized on alginate using the ion exchange technique. Both prior to and following Cr (VI) adsorption, the material's shape, crystallinity, and functional groups are reported. Immobilized chitosan was employed to adsorb Cr (VI) in a fixed bed column with variable operational parameters (flow rate, initial chromium content, and bed height). The analysis of breakthrough curves showed that at a flow rate of 10 mL/min, Cr (VI) concentration of 50 mg/L and a bed height of 18 cm, a maximum adsorption of 78.41 % was achieved. The adsorption system and the breakthrough curves were thoroughly understood by using Thomas, Yoon-Nelson and Adams-Bohart kinetic models. There is promise for the large-scale use of synthesized immobilized chitosan because the current adsorption process fits the Thomas and Yoon-Nelson model well and confirms the homogenous bed, low mass transfer resistance, and constant operating conditions throughout the experiment. Furthermore, an exploration of the adsorption mechanism is undertaken and the outcomes are compared with existing literature. The regeneration and reuse tests up to four cycles provided insight into the immobilized chitosan's stability, dependability, and potential for scaling up.

Novel High-Performance Functionalized and Grafted Bio-Based Chitosan Adsorbents for the Efficient and Selective Removal of Toxic Heavy Metals from Contaminated Water

Novel functionalized and/or grafted crosslinked chitosan adsorbents were synthesized and used to remove several toxic heavy metal ions such as nickel, lead, chromium, and cadmium ions from contaminated water. The chitosan biopolymer was functionalized by maleic anhydride (CS_MA) acting also as a crosslinking agent. Glutaraldehyde-crosslinked chitosan (CS_GA) grafted with poly(methyl methacrylate) (CS_MMA) was also synthesized. The synthesized adsorbents were characterized using a variety of analytical techniques such as SEM, TGA, and FTIR, which confirmed their chemical structures and morphology. The adsorption capacity of the adsorbents was analyzed under various conditions of contact time, adsorbent dose, initial concertation, temperature, and pH and evaluated against those of pure chitosan (CS) and the crosslinked chitosan(CS_GA). The ultimate removal conditions were 0.5 g/100 mL adsorbent dose, an initial metal ion concentration of 50 ppm, a temperature of 45 °C, and pH 9. CS_MMA had the highest removal percentages for all metal ions, ranging from 92% to 94%. The adsorption was demonstrated to fit a pseudo-first-order model that followed a Langmuir adsorption isotherm. The results highlight the capacity of the synthesized polymers to efficiently remove major toxic contaminants at low cost from contaminated water, present especially in low-income areas, without harming the environment.

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.

Plant-based Biomass/Polyvinyl Alcohol Gels for Flexible Sensors

Flexible sensors show great application potential in wearable electronics, human-computer interaction, medical health, bionic electronic skin and other fields. Compared with rigid sensors, hydrogel-based devices are more flexible and biocompatible and can easily fit the skin or be implanted into the body, making them more advantageous in the field of flexible electronics. In all designs, polyvinyl alcohol (PVA) series hydrogels exhibit high mechanical strength, excellent sensitivity and fatigue resistance, which make them promising candidates for flexible electronic sensing devices. This paper has reviewed the latest progress of PVA/plant-based biomass hydrogels in the construction of flexible sensor applications. We first briefly introduced representative plant biomass materials, including sodium alginate, phytic acid, starch, cellulose and lignin, and summarized their unique physical and chemical properties. After that, the design principles and performance indicators of hydrogel sensors are highlighted, and representative examples of PVA/plant-based biomass hydrogel applications in wearable electronics are illustrated. Finally, the future research is briefly prospected. We hope it can promote the research of novel green flexible sensors based on PVA/biomass hydrogel.

Alginate microbeads incorporated with anthocyanins from purple corn (Zea mays L.) using electrostatic extrusion: Microencapsulation optimization, characterization, and stability studies

Microencapsulation of purple corn anthocyanins was carried out via an electrostatic extruder using alginate as a wall material. The influence of alginate concentration (1-2 %), extract concentration (20-30 %), and extrusion voltage (3-5 kV) on encapsulation efficiency and mean particle size was evaluated using response surface methodology. Optimal conditions were obtained to produce two different extract-loaded microbeads. Microbeads with the highest encapsulation efficiency (EE) and minimum particle size were achieved at 1 % alginate, 20 % extract, and 5 kV extrusion voltage (EEC3G = 70.26 %, EETPC = 91.59 %, particle size = 1.29 mm). In comparison, the microbeads with the efficient entrapment and maximum particle size were obtained at 1 % alginate, 26 % extract, and 3 kV (EEC3G = 81.15 %, EETPC = 91.01 %, particle size = 1.87 mm). Brunauer-Emmett-Teller (BET) surface area, pore size, and pore volume decreased after the inclusion of extract, with the lowest values reported for the smallest microbeads containing the extract. Scanning electron microscopy confirmed the results obtained by BET method and demonstrated fewer cracks and lower shrinkage of encapsulated samples. Fourier-transform infrared results proved the presence of anthocyanins and further possible interactions between phenolics and alginate. Stability studies revealed the color maintenance of anthocyanins-loaded microbeads during 4 weeks of storage at 4 °C and 8 °C. Moreover, the small and large particles showed a 7.6 and 3.4-fold reduction in degradation rate at 4 °C compared to their unencapsulated counterparts. Anthocyanins-loaded alginate microbeads retained over 80 % of cyanidin-3-glucoside at 4 °C and 8 °C, suggesting a promising potential of optimized microbeads for intelligent packaging applications.

Magnetic chitosan/calcium alginate double-network hydrogel beads: Preparation, adsorption of anionic and cationic surfactants, and reuse in the removal of methylene blue

Robust and reusable magnetic chitosan/calcium alginate double-network hydrogel beads (CSMAB) with an environmentally benign biocomposite material synthesis approach were used adsorption of surfactant and removal of methylene blue dye sequentially for the first time. Double network hydrogel structure with sodium alginate and chitosan and acidification of the surface with HCl provided the reusability of the beads at the pollutant removal in water. The CSMAB beads were characterized for structural analysis by FESEM, EDX, BET, VSM, and FTIR techniques. They were used for the adsorption of cationic hexadecylpyridinium chloride (HDPCl) and anionic sodium dodecyl sulfate (SDS) surfactants and reused in the removal of cationic methylene blue dye without any pretreatment. The effect of pH, adsorbent dose, and temperature on surfactant removal efficiency was analyzed and pH was found the statistical significance. The adsorption capacity of CSMAB beads with a surface area of 0.65 m² g^-1 was calculated as 1.9 mg g^-1 for HDPCl, and 1.2 mg g^-1 for SDS, respectively. The SDS and HDPCl adsorption followed the pseudo-second-order kinetic and Freundlich isotherm model. The thermodynamic results showed that the surfactant adsorption process is an exothermic and spontaneous process. SDS-reacted CSMAB beads showed higher efficiency with 61 % in the removal of methylene blue dye.

Biopolymer - A sustainable and efficacious material system for effluent removal

Undesired discharge of various effluents directly into the aquatic ecosystem can adversely affect water quality, endangering aquatic and terrestrial flora and fauna. Therefore, the conceptual design and fabrication of a sustainable system for alleviating the harmful toxins that are discharged into the atmosphere and water bodies using a green sustainable approach is a fundamental standpoint. Adsorptive removal of toxins (∼99% removal efficacy) is one of the most attractive and facile approaches for cleaner technologies that remediate the environmental impacts and provide a safe operating space. Recently, the introduction of biopolymers for the adsorptive abstraction of toxins from water has received considerable attention due to their eclectic accessibility, biodegradability, biocompatibility, non-toxicity, and enhanced removal efficacy (∼ 80-90% for electrospun fibers). This review summarizes the recent literature on the biosorption of various toxins by biopolymers and the possible interaction between the adsorbent and adsorbate, providing an in-depth perspective of the adsorption mechanism. Most of the observed results are explained in terms of (1) biopolymers classification and application, (2) toxicity of various effluents, (3) biopolymers in wastewater treatment and their removal mechanism, and (4) regeneration, reuse, and biodegradation of the adsorbent biopolymer.

Contribution of halloysite as nanotubular clay mineral on mechanism and adsorption rate of Cd(II) onto nanocomposites alginate-halloysite

In this work nanocomposites based on alginate (Alg) and halloysite as a nanotubular clay (Hy) were developed. Characterization techniques reveal that Hy/Alg nanocomposites are cation exchangers with predominantly negative charge density and good thermal stability. The adsorption equilibrium of Cd(II) in aqueous solution onto Hy/Alg nanocomposites revealed that by increasing the mass of halloysite in the nanocomposite, the adsorption capacity diminished significantly due to the halloysite-alginate interactions. Maximum adsorption capacities of 8, 65, 88, and 132 mg/g of Cd(II) were obtained for samples Hy, Hy/Alg 50%, Hy/Alg 95%, and Alg, respectively. In addition, the adsorption equilibrium of Cd(II) on the Hy/Alg bionanocomposites was affected by the pH and temperature of the solution, demonstrating the presence of electrostatic interactions during adsorption and that this is an exothermic process. The controlling mechanism of adsorption was cation exchange influenced by electrostatic forces. The Cd(II) adsorption rate studies were interpreted by the diffusion-permeation model and reveal that the presence of Hy in the structure of the nanocomposites enhances the permeation coefficient, that is, the adsorption rate was increased. The values of the permeation coefficient varied from 1.95 × 10^-7 to 8.50 × 10^-7 cm²/s for Hy/Alg 50% and from 1.70 × 10^-7 to 3.55 × 10^-7 cm²/s for Hy/Alg 95%.

Review on biopolymers and composites - Evolving material as adsorbents in removal of environmental pollutants

The presence of pollutants and toxic contaminants in water sources makes it unfit to run through. Though various conventional techniques are on deck, development of new technologies are vital for wastewater treatment and recycling. Polymers have been intensively utilized recently in many industries owing to their unique characteristics. Biopolymers resembles natural alternative to synthetic polymers that can be prepared by linking the monomeric units covalently. Despite the obvious advantages of biopolymers, few reviews have been conducted. This review focuses on biopolymers and composites as suitable adsorbent material for removing pollutants present in environment. The classification of biopolymers and their composites based on the sources, methods of preparation and their potential applications are discussed in detail. Biopolymers have the potentiality of substituting conventional adsorbents due to its unique characteristics. Biopolymer based membranes and effective methods of utilization of biopolymers as suitable adsorbent materials are also briefly elaborated. The mechanism of biopolymers and their membrane-based adsorption has been briefly reviewed. In addition, the methods of regeneration and reuse of used biopolymer based adsorbents are highlighted. The comprehensive content on fate of biopolymer after adsorption is given in brief. Finally, this review concludes the future investigations in recent trends in application of biopolymer in various fields in view of eco-friendly and economic perspectives.

Amine-bilayer-functionalized cellulose-chitosan composite hydrogel for the efficient uptake of hazardous metal cations and catalysis in polluted water

Herein, we represent a novel ecofriendly bilayer-amine group incorporated microcrystalline cellulose (MCC)/chitosan (CS) hydrogel, fabricated via integrating polydopamine (PDA) and polyethyleneimine (PEI) for reliable and effective extraction of copper (Cu²⁺), zinc (Zn²⁺), and nickel (Ni²⁺) ions from effluents. Owing to abundant adsorptive sites, the MCC-PDA-PEI/CS-PDA-PEI hydrogel showed excellent Cu²⁺, Zn²⁺, and Ni²⁺ adsorbabilities of ~434.8, ~277.7, and ~261.8 mg/g, respectively, in a single-ion adsorption system with the adsorption kinetics and isotherm complied with pseudo-second-order and Langmuir models, respectively. In a multi-ion adsorption system, hydrogel removes mixed metal cations with slightly higher selectivity for Cu²⁺. In accordance with X-ray photoelectron and Fourier-transform-infrared spectrometric analyses, a plausible binding mechanism of metal cations on the as-prepared hydrogel was proposed by chelation between hydrogel functional groups and metal ions. In the repetitive adsorption/desorption experiments, the hydrogel retained >40% metal ion adsorption and desorption capacities after four cycles. Furthermore, the Cu²⁺-adsorbing hydrogel could serve as a support for the in situ development of Cu nanoparticles, which showed excellent catalytic performance as demonstrated by the transformation of 4-nitrophenol (4-NP) to 4-aminophenol. This work provides a novel ecofriendly, reusable, and highly-efficient adsorbent, as well as a biocatalyst for remediation of heavy metal cations and 4-NP polluted effluents.

Buckwheat hull-derived biochar immobilized in alginate beads for the adsorptive removal of cobalt from aqueous solutions

Buckwheat hull-derived biochar (BHBC) beads were synthesized by immobilizing biochar powder with alginate. Due to their cation-exchange ability, abundant functional groups, microporous structure, and large surface area, BHBC beads were successfully applied for the removal of cobalt from aqueous solution. The adsorption behavior followed pseudo-second-order kinetics and the Langmuir isotherm model showed a better fit to adsorption data than the Freundlich or Temkin isotherm models. The maximum adsorption capacity of BHBC beads was 24.0 mg/g at pH 5, 35 °C, and an initial cobalt concentration of 1.0 g/L, which was higher than those of previously reported natural resource-based adsorbents. In a fixed-bed column study, the effects of operating parameters such as flow rate, bed height, and bed diameter were investigated. Both the Thomas and Yoon-Nelson models were applied to the experimental data to predict the breakthrough curves using nonlinear regression. Overall, BHBC beads can be used as an efficient adsorbent for removal of radioactive cobalt from aqueous solution.

Nickel adsorption from waters onto Fe3O4/sugar beet pulp nanocomposite

In this study the magnetic nanocomposite material was synthesized with Fe₃O₄ impregnated to sugar beet pulp using chemical precipitation technique. Ni(II) removal performance of magnetic nanocomposite was investigated under different environmental conditions such as contact time, adsorbent dose, pH, initial heavy metal concentration, etc. The experimental studies have shown that, 81.2% Ni(II) removal efficiency was achieved at optimal conditions (25 mg/L initial Ni(II) concentration at 40 minute contact time, 200 rpm shaking speed, 5 g/L nanocomposite dose and pH 6.6). Freundlich and Langmuir isotherm experiments were performed and correlation coefficients were determined as 94.5% and 99.4%, respectively. The maximum adsorption capacity of material was achieved as 9.36 mg/g. These findings indicate that the adsorption that takes place is a monolayer process. The results of the pseudo-second order kinetic model (R² = 0.9947) indicate the chemisorptions process is used for Ni(II) removal using the electrostatic interaction. Thermodynamic studies illustrated that Ni(II) adsorption onto nanocomposite are exothermic and causes a decrease in the entropy. The adsorption of Ni(II) ions is non-spontaneous except for at low temperature and low initial concentrations. Nanocomposite characterization was illuminated with XRD, FT-IR, BET, TGA, TEM, SEM/EDX analysis.

Synthesis and characterization of a new meso-tetrakis (2,4,6-trimethylphenyl) porphyrinto) zinc(II) supported sodium alginate gel beads for improved adsorption of methylene blue dye

Chemical modification of a biopolymer offers a simple strategy to realize new materials with added benefits. In this paper, meso-tetrakis(2,4,6-trimethylphenyl) porphyrinto) zinc(II) supported sodium alginate gel beads were successfully prepared, characterized, and used for the removal of a cationic dye from aqueous solution. The chemical structure of the prepared composite beads was confirmed by FT-IR, SEM, XRD and TGA/DTG techniques. Analytical data suggested that the sodium alginate beads and meso-tetrakis(2,4,6-trimethylphenyl) porphyrinto) zinc(II) complex interacted via non-covalent interaction (H-bonding) mode. The morphological micrographs showed spherical and smooth composite beads. The crosslinking of hydroxyl and carboxylate groups of the biopolymer with calcium ions and the incorporation of meso-tetrakis(2,4,6-trimethylphenyl) porphyrinto) zinc(II) into alginate matrix resulted in a small decrease of residual mass. The maximum adsorption capacities of methylene blue, at 20 °C, were found to be 52.3 mg/g and 34.8 mg/g for sodium alginate composite beads (3%) and plain sodium alginate beads, respectively. The adsorption process followed Freundlich isotherm and pseudo second order kinetics. The thermodynamic study displayed an exothermic and non-spontaneous process.

Chitosan@Carboxymethylcellulose/CuO-Co2O3 Nanoadsorbent as a Super Catalyst for the Removal of Water Pollutants

In this work, an efficient nanocatalyst was developed based on nanoadsorbent beads. Herein, carboxymethyl cellulose-copper oxide-cobalt oxide nanocomposite beads (CMC/CuO-Co2O3) crosslinked by using AlCl3 were successfully prepared. The beads were then coated with chitosan (Cs), Cs@CMC/CuO-Co2O3. The prepared beads, CMC/CuO-Co2O3 and Cs@CMC/CuO-Co2O3, were utilized as adsorbents for heavy metal ions (Ni, Fe, Ag and Zn). By using CMC/CuO-Co2O3 and Cs@CMC/CuO-Co2O3, the distribution coefficients (Kd) for Ni, Fe, Ag and Zn were (41.166 and 6173.6 mLg-1), (136.3 and 1500 mLg-1), (20,739.1 and 1941.1 mLg-1) and (86.9 and 2333.3 mLg-1), respectively. Thus, Ni was highly adsorbed by Cs@CMC/CuO-Co2O3 beads. The metal ion adsorbed on the beads were converted into nanoparticles by treating with reducing agent (NaBH4) and named Ni/Cs@CMC/CuO-Co2O3. Further, the prepared nanoparticles-decorated beads (Ni/Cs@CMC/CuO-Co2O3) were utilized as nanocatalysts for the reduction of organic and inorganic pollutants (4-nitophenol, MO, EY dyes and potassium ferricyanide K3[Fe(CN)6]) in the presence of NaBH4. Among all catalysts, Ni/Cs@CMC/CuO-Co2O3 had the highest catalytic activity toward MO, EY and K3[Fe(CN)6], removing up to 98% in 2.0 min, 90 % in 6.0 min and 91% in 6.0 min, respectively. The reduction rate constants of MO, EY, 4-NP and K3[Fe(CN)6] were 1.06 × 10-1, 4.58 × 10-3, 4.26 × 10-3 and 5.1 × 10-3 s-1, respectively. Additionally, the catalytic activity of the Ni/Cs@CMC/CuO-Co2O3 beads was effectively optimized. The stability and recyclability of the beads were tested up to five times for the catalytic reduction of MO, EY and K3[Fe(CN)6]. It was confirmed that the designed nanocomposite beads are ecofriendly and efficient with high strength and stability as catalysts for the reduction of organic and inorganic pollutants.

Modified alginate-chitosan-TiO2 composites for adsorptive removal of Ni(II) ions from aqueous medium

In this study, organo-funtionalization of sodium-alginate has been carried out using phenylsemicarbazide as modifier to graft N, O-donor atoms containing functional groups (amino-carbamate moieties) to offer novel support for TiO₂ immobilization. Hybrid composite made of aminocarbamated alginate, carboxymethyl chitosan (CMC) and titanium oxide TiO₂ (MCA-TiO₂) was prepared for the promising adsorptive remediation of Ni(II). FT-IR, SEM-EDX were employed to characterize MCA-TiO₂. The optimization of TiO₂ to modified alginate mass ratio was carried out and hydrogel beads with TiO₂/MCA mass ratio of 10.0% (2MCA-TiO₂) revealed highest sorption efficiency. The produced sorbents were adapted in the form of hydrogel beads for operation. Organic functionalization based on aminocarbamate (OCONHNH₂) moieties on linear chains of alginate embedded additional chelating functional sites which enhanced sorption and selectivity. Batch mode experiments were conducted for optimization of pH and sorbent dose. Equilibrium sorption, kinetic and thermodynamic studies were performed to pattern the nature of sorption. Kinetic data was found in close agreement with pseudo-second order rate expression (PSORE). Isothermal equilibrium sorption data was well fitted with Langmuir adsorption model. Maximum sorption capacity was evaluated as 229 mg/g at 298 K and pH = 6.0.

Simultaneous removal of radioactive cesium and strontium from seawater using a highly efficient Prussian blue-embedded alginate aerogel

Radioactive cesium (¹³⁷Cs) and strontium (⁹⁰Sr) contaminants in seawater have been a serious problem since the Fukushima accident in 2011 due to their long-term health risks. For the effective and simultaneous removal of radioactive cesium (¹³⁷Cs) and strontium (⁹⁰Sr) from seawater, a Prussian blue (PB)-immobilized alginate aerogel (PB-alginate aerogel) was fabricated and its adsorption performance was evaluated. PB nanoparticles were homogeneously dispersed in the three-dimensional porous alginate aerogel matrix, which enabled facile contact with seawater. The PB-alginate aerogel exhibited Cs⁺ and Sr²⁺ adsorption capacities of 19.88 and 20.10 mg/g, respectively, without substantial interference because Cs⁺ and Sr²⁺ adsorption occurred at different adsorption sites on the composite. The Cs⁺ and Sr²⁺ adsorption onto the PB-alginate aerogel was completed within 3 h due to the highly porous morphology of the aerogel. The Cs⁺ and Sr²⁺ adsorption behaviors on the PB-alginate aerogel were systematically investigated under various conditions. Compared with Cs⁺ adsorption, Sr²⁺ adsorption onto the PB-alginate aerogel was more strongly influenced by competing cations (Na⁺, Mg²⁺, Ca²⁺, and K⁺) in seawater. ¹³⁷Cs and ⁹⁰Sr removal tests in real seawater demonstrated the practical feasibility of the PB-alginate aerogel as an adsorbent.

Selective biosorption mechanism of methylene blue by a novel and reusable sugar beet pulp cellulose/sodium alginate/iron hydroxide composite hydrogel

A cellulose-based sodium alginate/iron hydroxide (C/SA/Fe) composite hydrogel was fabricated by using epichlorohydrin as cross-linking agent as an effective adsorbent for dye. The physicochemical structure of the C/SA/Fe hydrogel was characterized by SEM, FTIR, XRD and TG. The adsorption performance for the removal of methylene blue (MB) was investigated. In addition, the selective adsorption of cationic dye was also studied. The FTIR analysis revealed that the Fe(OH)₃ colloidal particles was successfully combined in the cellulose/sodium alginate hydrogel. The modified hydrogel had better adsorption performance, and the maximum adsorption capacity of C/SA/Fe0.5 for MB was 105.93 mg/g according to the fitting results of adsorption isotherm. The kinetic study showed that MB adsorption of C/SA/Fe was more consistent with the pseudo-second-order model, and the adsorption of MB in C/SA/Fe was dominated by chemisorption mechanism such as ion exchange or electron sharing. The adsorption data fits well with the Langmuir model. Thermodynamics analysis showed that the MB adsorption by C/SA/Fe was exothermic, spontaneous, favorable and feasible. After five adsorption-desorption cycles, the adsorption capacity was almost unchanged. So, the C/SA/Fe hydrogel is a potential material in the field of the recovery of agricultural by-products or other bio-based cellulose, or environmental protection, etc.

Novel Adsorbent Based on Banana Peel Waste for Removal of Heavy Metal Ions from Synthetic Solutions

Due to its valuable compounds, food waste has been gaining attention in different applications, such as life quality and environment. Combined with circular economy requirements, a valorization method for waste, especially banana waste, was to convert them into adsorbents with advanced properties. The banana waste, after thermal treatment, was used with high removal performances (100%) for the removal of heavy metals, such as Cr, Cu, Pb, and Zn, but their small particle size makes them very hard to recover and reuse. For this reason, a biopolymeric matrix was used to incorporate the banana waste. The matrix was chosen for its remarkable properties, such as low cost, biodegradability, low carbon footprint, and reduced environmental impact. In this research, different types of materials (simple banana peel ash BPA and combined with biopolymeric matrix, ALG–BPA, CS–BPA) were prepared, characterized, and tested. The materials were characterized by means of attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), optical microscopy (OM), scanning electron microscopy (SEM), and tested for the removal of metal ions from synthetic solutions using atomic absorption spectroscopy (AAS). The ALG–BPA material proved to be the most efficient in the removal of heavy metal ions from synthetic solution, reaching even 100% metal removal for Cr, Fe, Pb, and Zn, while the CS-based materials were the least efficient, presenting the best values for Cr and Fe ions with a removal efficiency of 34.14% and 28.38%, respectively. By adding BPA to CS, the adsorption properties of the material were slightly improved, but also only for Cr and Fe ions, to 37.09% and 57.78%.

Adsorption of U(VI) on the natural soil around a very low-level waste repository

The behaviors of U(VI) in environmental media around radioactive waste disposal site are important for safety assessment of geological repositories. However, the estimation of environmental behaviors of U(VI) in natural media was insufficient. This work aimed to determine the adsorption of U(VI) on natural soil surrounding a candidate very low-level radioactive waste (VLLW) disposal site in southwest China. Results showed that the adsorption process of U(VI) on soils could be well supported by pseudo-second-order kinetic and Freundlich model. The adsorption of U(VI) was pH-dependent but temperature-independent. High ionic strength (NaCl) strongly affected the adsorption process at low pH (2.0-5.5). CO₃^2- remarkably inhibited the U(VI) adsorption, while the adsorption of U(VI) was promoted by PO₄^3- and SO₄^2-. Naturally occurred soil organic matters (SOMs) showed high affinity for U(VI), while the presence of additional humic acid (HA) strongly inhibited U(VI) adsorption. The occurrence of ferrous iron could result in the reduction of U(VI) at low pH values (pH < 4), leading to the promotion of immobilization of U(VI). These findings would provide some guidance for the safety assessments of the VLLW disposal as well as the remediation of contaminated soil.

Highly Active Cellulose-Supported Poly(hydroxamic acid)-Cu(II) Complex for Ullmann Etherification

Highly active natural pandanus-extracted cellulose-supported poly(hydroxamic acid)-Cu(II) complex 4 was synthesized. The surface of pandanus cellulose was modified through graft copolymerization using purified methyl acrylate as a monomer. Then, copolymer methyl acrylate was converted into a bidentate chelating ligand poly(hydroxamic acid) via a Loosen rearrangement in the presence of an aqueous solution of hydroxylamine. Finally, copper species were incorporated into poly(hydroxamic acid) via the adsorption process. Cu(II) complex 4 was fully characterized by Fourier transform infrared (FTIR), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectrometry (ICP-OES), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses. The cellulose-supported Cu(II) complex 4 was successfully applied (0.005 mol %) to the Ullmann etherification of aryl, benzyl halides, and phenacyl bromide with a number of aromatic phenols to provide the corresponding ethers with excellent yield [benzyl halide (70-99%); aryl halide (20-90%)]. Cu(II) complex 4 showed high stability and was easily recovered from the reaction mixture. It could be reused up to seven times without loss of its original catalytic activity. Therefore, Cu(II) complex 4 can be commercially utilized for the preparation of various ethers, and this synthetic technique could be a part in the synthesis of natural products and medicinal compounds.

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

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

Removal of Nickel from Aqueous Solutions by Natural Bentonites from Slovakia

In this study, the removal of nickel (Ni(II)) by adsorption from synthetically prepared solutions using natural bentonites (Lieskovec (L), Hliník nad Hronom (S), Jelšový Potok (JP), and Stará Kremnička (SK)) was investigated. All experiments were carried out under batch processing conditions, with the concentration of Ni(II), temperature, and time as the variables. The adsorption process was fast, approaching equilibrium within 30 min. The Langmuir maximum adsorption capacities of the four bentonite samples used were found to be 8.41, 12.24, 21.79, and 21.93 mg g^–1, respectively. The results best fitted the pseudo-second-order kinetic model, with constant rates in a range of 0.0948–0.3153 g mg^–1 min. The effect of temperature was investigated at temperatures of 20, 30, and 40 °C. Thermodynamic parameters, including standard enthalpy (ΔH⁰), Gibbs energy (ΔG⁰), and standard entropy (ΔS⁰), were calculated. The adsorption of Ni(II) by bentonite samples was an endothermic and spontaneous process. These results indicated that, of the bentonite samples used, the natural bentonites from JP and SK were most suitable for the removal of nickel from synthetically prepared solutions.

Xanthation of alginate for heavy metal ions removal. Characterization of xanthate-modified alginates and its metal derivatives

Xanthates are widely used in mining industry as collectors for its high affinity towards metal sulfides and precious metal ores. The possibility of using alginate for xanthation has not been explored yet despite the feasibility by the presence of hydroxyl groups alongside the polymeric chains. Therefore, this work aims to evaluate the alginate as a matrix for xanthation and its application on heavy metal ions removal. In order to obtain green materials, important pararmeter were explored such as the effect of reaction time (4-12 h), type of base (NaOH/KOH) and amount of carbon disulfide (2-10%v/v). Xanthated alginates were analyzed by NMR techniques and evidence of β-elimination was detected at 5.45 ppm. Furthermore, the presence of S element was confirmed by EDS mapping technique, while XRD showed a semi-crystalline structure. On the other hand, the chemical shifts of δ(C=S) and ν(C=S) bands were found around 863-805 cm^-1 and 662-602 cm^-1 respectively. Also, a shoulder at 182 ppm is appreciated by NMR in solid state attributed to CS group. According to FESEM analyses, morphology of xanthated alginates is affected by interaction with heavy metal ions. Finally, suitable materials for the removal of heavy metal ions were established at optimum pH values.

Cytotoxic aquatic pollutants and their removal by nanocomposite-based sorbents

Water is an extremely essential compound for human life and, hence, accessing drinking water is very important all over the world. Nowadays, due to the urbanization and industrialization, several noxious pollutants are discharged into water. Water pollution by various cytotoxic contaminants, e.g. heavy metal ions, drugs, pesticides, dyes, residues a drastic public health issue for human beings; hence, this topic has been receiving much attention for the specific approaches and technologies to remove hazardous contaminants from water and wastewater. In the current review, the cytotoxicity of different sorts of aquatic pollutants for mammalian is presented. In addition, we will overview the recent advances in various nanocomposite-based adsorbents and different approaches of pollutants removal from water/wastewater with several examples to provide a backdrop for future research.

Chitosan: A Natural Biopolymer with a Wide and Varied Range of Applications

Although chitin is of the most available biopolymers on Earth its uses and applications are limited due to its low solubility. The deacetylation of chitin leads to chitosan. This biopolymer, composed of randomly distributed β-(1-4)-linked D-units, has better physicochemical properties due to the facts that it is possible to dissolve this biopolymer under acidic conditions, it can adopt several conformations or structures and it can be functionalized with a wide range of functional groups to modulate its superficial composition to a specific application. Chitosan is considered a highly biocompatible biopolymer due to its biodegradability, bioadhesivity and bioactivity in such a way this biopolymer displays a wide range of applications. Thus, chitosan is a promising biopolymer for numerous applications in the biomedical field (skin, bone, tissue engineering, artificial kidneys, nerves, livers, wound healing). This biopolymer is also employed to trap both organic compounds and dyes or for the selective separation of binary mixtures. In addition, chitosan can also be used as catalyst or can be used as starting molecule to obtain high added value products. Considering these premises, this review is focused on the structure and modification of chitosan as well as its uses and applications.

Enhanced adsorption properties of zirconium modified chitosan-zeolite nanocomposites for vanadium ion removal

The novel hybrid adsorbents, which were composed of nanozeolite and nanochitosan (NZ@NCT) and nanozeolite-multi walled carbon nanotube and nanochitosan (CNZ@NCT) were produced by simple method. The adsorption capacity of synthesized nanocomposites towards vanadium (V) was compared with that of a clinoptilolite-nanochitosan nanocomposite (CPL@NCT) obtained from natural zeolite. Zirconium (Zr) was employed to modify prepared nanocomposites because Zr (IV) has a strong affinity towards oxyanions such as V. Zr-modified nanocomposites and their pristine nanocomposites were comparatively characterized by different techniques. Batch experiments were conducted to find out the influence of different experimental factors. The adsorption capacities of all prepared materials towards V ions decreased with temperature increasing from 298 to 348 K. The calculated values of the thermodynamic parameters ΔH and ΔG demonstrated that the adsorption was exothermic and spontaneous. The adsorption process was described by the Freundlich isotherm and pseudo-second order model. The V species loaded nanocomposites could be regenerated by 0.5 M HCl-1.0 M thiourea solution. The adsorption performance was not considerably influenced by the coexistence of the nickel ( Ni²⁺) but nitrate (NO₃^-) and sulfate (SO₄^2-) revealed slightly greater negative effects. The as-prepared nanocomposites can be used in three adsorption cycles without specific changing its adsorption efficiency.

Fixed-bed adsorption of copper from aqueous media using chitosan-coated bentonite, chitosan-coated sand, and chitosan-coated kaolinite

Fixed-bed studies were performed to evaluate the removal efficiency of copper (Cu(II)) from aqueous solution using chitosan-coated bentonite (CCB), chitosan-coated sand (CCS), and chitosan-coated kaolinite (CCK). The thermal and morphological properties of CCB, CCK, and CCS were characterized using thermogravimetric analysis, Fourier transform infrared spectroscopy, and the Brunauer-Emmett-Teller method. Dynamic experiments were carried out to investigate the effect of solution pH (3.0 to 5.0) and initial Cu(II) concentration (200 to 1000 mg/L) on the time to reach breakthrough (t_b), total volume of treated effluent (V_eff), and adsorption capacity at breakthrough (q_b). Results show that increasing the initial Cu(II) concentration inhibits the column performance where lower V_eff, t_b, and q_b were obtained. Decreasing the pH from 5.0 to 3.0 led to improved removal efficiency with higher values of V_eff, t_b, and q_b. Under pH 3.0 and 200 mg/L, the maximum removal efficiency of 68.60%, 56.10%, and 58.90% for Cu(II) was attained using CCB, CCS, and CCK, respectively. The Thomas model was determined to adequately predict the breakthrough curves based on high values of coefficient of determination (R² ≥ 0.8503). Regeneration studies were carried out using 0.1 M HCl and 0.1 M NaOH solution in the saturated column of CCB, CCK, and CCS.

The sorption performance of corroded Gaomiaozi bentonite by evolved cement water at different temperatures: the case of europium removal

In the Chinese high-level radioactive waste geological disposal program, Gaomiaozi (GMZ) bentonite has been selected as the potential buffer/backfill material. After the closure of the repository, the Ca-OH-type alkaline solution (evolved cement water) released by cement degradation may last for more than 100,000 years. The bentonite will undergo the corrosion of evolved cement water (ECW) for a long period. This work focuses on the sorption property of GMZ bentonite altered by ECW. Firstly, the corrosion experiments on compacted GMZ specimens with the dry density of 1.70 Mg/m³ were carried out under constant volume conditions at two temperatures. Then, the sorption of europium (Eu (III)) onto the corroded GMZ bentonite was studied by batch experiments. The results of batch sorption tests indicate that the altered GMZ bentonite keeps an effective removal property with the uptake of Eu (III) more than 99%. The effect of high-temperature conditions of the repository on the sorption property of bentonite is not significant. The results also suggest that the evolved cement water presents no detrimental effect on the long-term adsorption performance of bentonite even under higher temperature conditions.

Diminishing Cohesion of Chitosan Films in Acidic Solution by Multivalent Metal Cations

Chitosan is a natural polymer with good biocompatibility, biodegradability, and bioactivity that has great potential for biomedical and industrial applications. Like other natural sugar-based polymers, chitosan molecules own versatile adhesion abilities to bind with various surfaces, owing to multiple functional moieties contained in the chain. To develop the promising biomaterials based on the chitosan chemistry, it is fundamentally important to figure out its adhesion mechanism under a certain condition, which leaves us numbers of open questions. In this work, we characterized the chitosan films adsorbed on a mica substrate in acidic solution and investigated the effects of multivalent salts on the cohesive behaviors of the films by means of the surface forces apparatus. The results showed that the cohesion capacities of chitosan films were reduced to around 30% of their original states after the addition of 10^-7 M LaCl₃ into 150 mM acetic acid, which could be partially recovered by holding the films at the contact position for a longer time. Surprisingly, the cohesion loss in the films exhibited the dependence on the properties of the metal cations including valance and concentration. The topography of the chitosan-coated surface also showed obvious aggregation in the presence of submicromolar of the salts. Here, we attributed these phenomena regarding cohesion loss to the mechanisms involved in the absorption of metal cations by the chitosan chains, which not only consumed the binding sites but also induced conformation change in the polymer network. Our findings may offer a suggestion for the production of chitosan-based materials to notice the potential impacts of ultralow concentrated salts that are usually neglected even under acidic conditions.

Chromium (III) coordination capacity of chitosan

Polycationic chitosan has a strong coordination to heavy metal ions due to its multifunctional hydroxyl and amino groups. However, due to the fast and facile dissolution of chitosan in acidic medium, it is difficult to measure the exact adsorption amount or coordination capacity accurately. In this work, a simple method of lyophilization plus ethanol-washing was employed to separate and purify chitosan/Cr(III) complex for further determining the coordination capacity. Meanwhile, the coordination structure of Bridge-chitosan-N(OH)₃(H₂O) and morphology of regenerated fibrillar sponge of CS/Cr(III) were further certified. The coordination capacity of Cr(III) on chitosan increased with the rising concentration of Cr(III) ions till the maximum coordination capacity was reached up to 355.03 mg/g. The mechanisms and characteristic parameters of the adsorption process were fit using two-parameter isotherm models which revealed the following order (based on the coefficient of determination) of Langmuir > Halsey > Freundlich > Temkin > Dubinin-Radushkevich. A proposed coordination formula of CS/Cr (III) might be a good certificate for the homogeneous chemical combination nature of Cr(III) on the monolayer surface of chitosan in a molecular scale.

Facile Synthesis of Novel Carboxymethyl-Chitosan/Sodium Alginate Grafted with Amino-Carbamate Moiety/Bentonite Clay Composite for Effective Biosorption of Ni (II) from Aqueous Solution

In the present study, a novel biosorbent clay composite, based on carboxymethyl-chitosan/sodium alginate grafted with amino-carbamate moiety/bentonite clay (CA-CMC/Bt) was prepared. The produced sorbent was conditioned in the form of hydrogel beads by ionotropic gelation with Ca(II) ions, and thoroughly characterized using FTIR, XRF, XRD, SEM and zeta potential measurements. FTIR and SEM confirmed the successful grafting and intercalation of clay mineral into modified biopolymer. Hydrogel beads were observed to be very integrated and stable under a wide pH working range (from 2.0 to 12.0). CA-CMC/Bt was employed for adsorptive remediation of Ni(II) from aqueous media. Sorption process was found as a function of various parameters such as sorbent dosage, contact time, pH and initial concentration. Kinetic data could be well explained by pseudo second order rate equation (PSORE), suggesting that complexation or valence forces are playing significant role in the uptake of Ni(II) ions. Isothermal sorption data was analysed using different sorption models such as Langmuir, Freundlich and Sips. Data was well fitted with Langmuir and Sips model, maximum monolayer sorption capacity (qm) was calculated (by non-linear fitting of data) as 159 mg/g at 298 K and pH 5.5. Separation factor (RL) was found as 0 < RL < 1 which indicated favourable sorption. Thermodynamic parameters i.e. ΔGo, ΔHo and ΔSo were quantified and patterned the sorption process as exothermic, spontaneous with increase in system entropy. CA-CMC/Bt was found cost-effective, efficient and reusable material in Ni(II) competitive recovery.

The Innovation Comes from the Sea: Chitosan and Alginate Hybrid Gels and Films as Sustainable Materials for Wastewater Remediation

The growing utilization of renewable and residual biomasses for environmental preservation and remediation are important goals to be pursued to minimize the environmental impact of human activities. In this paper, sodium alginate (derived from brown algae) was crosslinked using chitosan (mainly derived from the exoskeleton of crustaceans) in the presence of biowaste-derived substances isolated from green compost (BBS-GC), to produce hydrogels and dried films. The obtained materials were tested as adsorbents for wastewater remediation. To this purpose, gels were characterized using a multi-analytical approach and used as active substrates for the removal of three differently-charged molecules, chosen as model pollutants: crystal violet, rhodamine B, and orange II. The effectiveness of the gel formulations was demonstrated and attributed to the variety of active functionalities introduced by the different precursors, the structural factors and the peculiar physicochemical properties of the resulting materials.

Nickel ion removal from aqueous solutions through the adsorption process: a review

Recently, removal of nickel ions has been gaining a lot of attention because of the negative impact of nickel ions on the environment. The aim of this review paper is to organize the scattered available information on removal of nickel ions from aqueous solutions through the adsorption process. Survey on investigated materials suggests that composite- and polymer-based adsorbents have the most effective capability for nickel adsorption. The composite material class, i.e. CaCO3-maltose, followed by biopolymer-based material showed the highest Ni(II) adsorption capacity of 769.23 and 500 mg/g, respectively. The importance of treatment parameters (i.e. pH, temperature, contact time, and metal ion concentration) is discussed, together with their effect on the underlying physicochemical phenomena, giving particular attention to the adsorption/desorption mechanism. It was ascertained that adsorption of nickel ions is pH dependent and the optimal pH range for adsorption of Ni(II) ions was in range of 6–8. In general, nickel adsorption is an endothermic and spontaneous process that mainly occurs by forming a monolayer on the adsorbent (experimental data are often fitted by Langmuir isotherms and pseudo-second-order kinetics). Regeneration (i.e. desorption) is also reviewed, suggesting that acidic eluents (e.g. HCl and HNO3) allow, in most of the cases, an efficacious spent adsorbent recovery. The percentage use of desorption agents followed the order of acids (77%) > chelators (8.5%) > alkalis (8%) > salts (4.5%) > water (2%). Helpful information about adsorption and desorption of nickel ions from aqueous solutions is provided.