Adsorption and desorption of Cu(II), Cd(II) and Pb(II) ions using chitosan crosslinked with epichlorohydrin-triphosphate as the adsorbent

Efficient removal of Cu2+ and methylene blue pollutants from an aqueous solution by applying a new hybrid adsorbent based on alginate-chitosan and HAP derived from Moroccan rock phosphate

Alginate-chitosan/hydroxyapatite (Alg-Cs/HAP) beads were prepared as adsorbent to remove methylene blue (MB) and copper ions from an aqueous solution using a batch system. FTIR, TGA, point of zero charge (pHpzc), SEM, XRD, and BET analysis were used to characterize the elaborated material. The effect of several parameters such as initial pH value, adsorbent dose, temperature, contact time, and initial pollutant concentration were also investigated. The obtained results showed that Alg-Cs/HAP exhibit excellent adsorption properties for Cu (II) and MB removal, with high adsorption capacities of copper ions (208.34 mg/g) and methylene blue (454.54 mg/g). The kinetic of the adsorption process is correlated with the pseudo-first-order for methylene blue and the pseudo-second-order for copper ions. The equilibrium data for MB dye fitted the Freundlich isotherm model, thus implying that the adsorption process consists of multilayer adsorption as well as interactions between the adsorbate and the adsorbent. The equilibrium data for copper ions corresponds closely with the Langmuir model which suggests that the adsorbed molecules occur over a monolayer. Various thermodynamic parameters such as the standard Gibbs energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°) were calculated. All results indicated that Alg-Cs/HAP material has a good potential for the treatment of wastewater.

Reprocessed construction and demolition waste as an adsorbent: An appraisal

Construction and Demolition (C&D) waste is solid wastes generated from the construction, demolition, and renovation activities that constitute almost 30-40 % of globally generated solid wastes. Improper disposal and management of these materials can cause negative impacts on the environment, economy, and human health. Most research on C&D waste is limited to reduction, recycling, and reuse of the wastes. However, there is no systematic review dedicated entirely to the applicability of C&D wastes as adsorbent for waste management. This review presents the utilization of C&D wastes-based adsorbents for removing contaminants from environmental matrices covering triple edge benefits in the viewpoints of waste treatment, solid waste management, and disposal. The properties, the capability of C&D waste adsorbents on contaminant removal, and the influence of various factors on the adsorptive removal is detailed. Further, the mechanisms involved in contaminant removal by C&D waste are summarized. The review revealed that, chemisorption is the prominent mechanism of contaminant removal by most C&D wastes. Among the three types of C&D waste reviewed; concrete-based adsorbents were the most efficient for contaminant removal. Limited studies are avaiable in the literature on binary and multiple contaminant systems, reusability studies, and high dependence on solution pH, therefore further studies are warrated. As C&D waste contain trace concentration of heavy metals and contaminants, its leaching potential at different pH levels and adsorbate concentration need to be conducted, which has been hitherto neglected. Finally, the approaches, obstacles, and potential solutions to build an industrially and economically efficient C&D adsorbent are discussed.

Nitrogen-doped biochar (N-doped BC) and iron/nitrogen co-doped biochar (Fe/N co-doped BC) for removal of refractory organic pollutants

The presence of refractory organic pollutants (ROPs) in the ecosystem is a serious concern because of their impact on environmental constituents as well as their known or suspected ecotoxicity and adverse health effects. According to previous studies, carbonaceous materials, such as biochar (BC), have been widely used to remove pollutants from ecosystems owing to their desirable features, such as relative stability, tunable porosity, and abundant functionalities. Nitrogen (N)-doping and iron/nitrogen (Fe/N) co-doping can tailor BC properties and provide supplementary functional groups as well as extensive active sites on the N-doped and Fe/N co-doped BC surface, which is advantageous for interaction with and removal of ROPs. This review investigates the impact of N-doped and Fe/N co-doped BC on the removal of ROPs through adsorption, activation oxidation, and catalytic reduction due to the synergistic Fe, N, and BC features that modify the physicochemical properties, surface functional groups, and persistent free radicals of BC to aid in the degradation of ROPs. Owing to the attractive properties of N-doped and Fe/N co-doped BCs for the removal of ROPs, this review focuses and evaluates previous experimental investigations on the manufacturing (including precursors and influencing parameters during manufacturing) and characterizations of N-doped and Fe/N co-doped BCs. Additionally, the effective applications and mechanisms of N-doped and Fe/N co-doped BCs in adsorption, activation oxidation, and reductive remediation of ROPs are investigated herein. Moreover, the application of N-doped and Fe/N co-doped BC for progressive environmental remediation based on their effectiveness against co-pollutants, regeneration, stability, affordability, and future research prospects are discussed.

Hydrophobization of aerogels based on chitosan, nanocellulose and tannic acid: Improvements on the aerogel features and the adsorption of contaminants in water

Hydrophobic chitosan aerogels are promising adsorbents for immiscible contaminants such as oils and organic solvents. However, few studies have reported the application of hydrophobic aerogels as adsorbent for organic contaminants dissolved in water. Herein, novel highly hydrophobic chitosan (CS) beads containing cellulose nanocrystals (CNC) and hydrophobized tannic acid (HTA) composite were prepared with different CS and CNC-HTA content to achieve an optimized adsorbent to remove emerging contaminants from water in batch and fixed-bed assays. The CS@CNC-HTA beads properties were assessed by FTIR, XRD, SEM, XPS, Micro-CT, WCA, and zeta potential. Supramolecular interactions and physical interlacements between CS and CNC-HTA enabled the formation of CS@CNC-HTA beads with high porosity (98.6%), great volume of open pore space (10.16 mm³) and hydrophobicity (121.8°). The 1:1 CS@CNC-HTA beads showed the best performance for removing the pharmaceutical sildenafil citrate, the basic blue 26 dye, and the surfactant cetylpyridinium chloride, reaching adsorption capacities of 86 (73%), 375 (84%), and 390 (90%) mg.g^-1, respectively. The 1:1 CS@CNC-HTA beads efficiently removed sildenafil citrate, basic blue 26 and cetylpyridinium chloride in fixed-bed experiments with exhaustion times of 890, 300, and 470 min, respectively. Theoretical calculations and adsorption assays indicate that the main attractive interactions are pyridinium-π, π-π, electrostatic and hydrophobic.

Dietary chitooligosaccharide supplementation improves mineral deposition, meat quality and intramuscular oxidant status in broilers

BACKGROUND

The present study aimed at evaluating the in vitro adsorption capability of chitooligosaccharide (COS) with some metal elements (Fe, Zn, Cd, Pb) at different pH values along with potential effects of dietary COS supplementation on growth performance, mineral content, meat quality and oxidant status in broilers. Day-old male chicks were randomly distributed into two groups and offered a basal diet supplemented with or without 30 mg kg^-1 COS for 42 days.

RESULTS

In vitro trials demonstrated that Fe levels were higher (P < 0.001) in the COS-treated group compared with the non-treated group at pH of 2.5. However, these levels became lowered when pH values were raised to 5 (P < 0.01) or 6 (P < 0.001). Similarly, COS adsorbed more (P < 0.05) Zn at pH values of 2.5 and 6, and Cd contents at pH of 2.5 for 70 min when compared with the control. For in vivo trial, the feed-to-gain ratio, serum Cu (P < 0.01), hepatic Mn, Cr (P < 0.05) and intramuscular Cd (P < 0.01) were lower in response to COS treatment. Supplementation of COS improved (P < 0.05) meat quality of broilers in terms of lower drip loss, cooking loss and malondialdehyde content with a concomitant increase (P < 0.01) in the pH of breast meat at 24 h post mortem.

CONCLUSION

COS adsorbed heavy metal ions not only in vitro but also in broilers, and dietary supplementation with 30 mg kg^-1 COS improved growth performance, breast meat quality and oxidant status in broilers. © 2022 Society of Chemical Industry.

Insights into the Synergistic Removal of Copper(II), Cadmium(II), and Chromium(III) Ions Using Modified Chitosan Based on Schiff Bases-g-poly(acrylonitrile)

Chitosan has received broad consideration as an adsorbent for all pollutants because of its low cost and great adsorption potential. However, its shortcomings, including sensitivity to pH, poor thermal stability, and poor mechanical strength, limit its use. The functional groups of chitosan can be modified to enhance its performance by the grafting technique and Schiff base modification. The grafting process used acrylonitrile (Ch-g-PAN) as a monomer and potassium persulfate as an initiator. After that, the modification via preparation of the Schiff base reaction using salicylaldehyde (Ch-g-Sch I) and P-anisaldehyde (Ch-g-Sch II) was carried out. The synthesized copolymers were detailed and characterized through several spectroscopic and microscopic techniques including infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. In addition, Ch-g-Sch I and Ch-g-Sch II were applied in the removal of different metal ions such as Cu²⁺, Cd²⁺, and Cr³⁺. The maximum adsorption capacity of Ch-g-Sch I for Cd²⁺ was 183.7 mg g^-1 in 24 h, while in the case of Ch-g-Sch II, the maximum adsorption capacity for Cd²⁺ was improved to 322.9 mg g^-1 for the same time. Moreover, adsorption thermodynamic analysis displays that the all ion adsorption process was not random and the pseudo-second-order model fitted with experimental results. Finally, Ch-g-Sch I and Ch-g-Sch II were applied as designs for industrial wastewater treatment with significant efficiency.

Multivariate optimization applied to the synthesis and reuse of a new sugarcane bagasse-based biosorbent to remove Cd(II) and Pb(II) from aqueous solutions

This study reports the use of multivariate tools to optimize the synthesis of a new agricultural-based biosorbent derived from sugarcane bagasse (SB) for the removal of Cd(II) and Pb(II) from aqueous solutions, as well as to optimize the process of desorption of these ions from the spent biosorbent using an acidic solution. The effects of the reaction parameters temperature (T), time (t), and the ratio of 1,2,3,4-butanetetracarboxylic acid dianhydride (BTCAD) to raw SB (wBTCAD wraw SB-1) on the chemical modification of raw SB with BTCAD and on the equilibrium adsorption capacity (qe) for Cd(II) and Pb(II) were investigated by application of a 23 Doehlert experimental design (DED), followed by optimization using a statistical desirability tool to produce the best adsorbent in terms of performance and cost. The best reaction condition was wBTCAD wraw SB-1 of 4.0 g g-1, t of 1 h, and T of 70 ºC. The optimal synthesis condition resulted in a modified sugarcane bagasse (MSB) that provided qe values for Cd(II) and Pb(II) of 0.50 and 0.61 mmol g-1, respectively, obtained under the following conditions: 0.311 mmol Cd(II) L-1, 0.632 mmol Pb(II) L-1, pH 5.0, 4 h, 0.2 g L-1 MSB, 130 rpm, and 25 °C. The desorption of Cd(II) and Pb(II) from MSB was investigated by a 22 DED, with optimization using the desirability tool to obtain the best desorption condition in terms of HNO3 solution concentration ([Formula: see text]) and t. The desorption efficiencies for Cd(II) and Pb(II) were 90 ± 4% and 88 ± 3%, respectively, obtained using 0.7 mol L-1 HNO3, t of 42 min, and 1.0 g L-1 MSB-M(II) (M = Pb or Cd). Infrared spectroscopy was used to investigate the natures of the interactions involved in the adsorption of Cd(II) and Pb(II) on MSB, as well as possible changes in the chemical structure of MSB after desorption. The synthesis of MSB can be performed under mild reaction conditions (t = 1 h, T = 70 ºC), and the solvents used can be recovered by distillation. BTCA is commercially available at moderate cost and can alternatively be obtained employing microbial succinic acid, metal-free catalysis, and modest use of petrochemical feedstocks. Furthermore, MSB can be reused, which could contribute to increasing the economic feasibility of water and wastewater treatment processes.

Methacrylate-Based Polymeric Sorbents for Recovery of Metals from Aqueous Solutions

The industrialization and urbanization expansion have increased the demand for precious and rare earth elements (REEs). In addition, environmental concerns regarding the toxic effects of heavy metals on living organisms imposed an urgent need for efficient methods for their removal from wastewaters and aqueous solutions. The most efficient technique for metal ions removal from wastewaters is adsorption due to its reversibility and high efficiency. Numerous adsorbents were mentioned as possible metal ions adsorbents in the literature. Chelating polymer ligands (CPLs) with adaptable surface chemistry, high affinity towards targeted metal ions, high capacity, fast kinetics, chemically stable, and reusable are especially attractive. This review is focused on methacrylate-based magnetic and non-magnetic porous sorbents. Special attention was devoted to amino-modified glycidyl methacrylate (GMA) copolymers. Main adsorption parameters, kinetic models, adsorption isotherms, thermodynamics of the adsorption process, as well as regeneration of the polymeric sorbents were discussed.

Some Well-Known Alginate and Chitosan Modifications Used in Adsorption: A Review

Owing to environmental pollution and increasingly strict regulations, heavy metals have attracted the attention of many researchers in various disciplines. Alginate and chitosan derivatives have gained popularity as biosorbents for water treatment. An increase in the number of publications on modified biosorbents for the biosorption of toxic compounds reveals widespread interest in examining the requirements and positive contribution of each modification type. This paper reviews the advantages and disadvantages of using alginate and chitosan for adsorption. Well-known modifications based on chitosan and alginate, namely, grafting, functionalization, copolymerization and cross-linking, as well as applications in the field of adsorption processes, especially amino acid functionalization, are reviewed. The selection criteria for the best biosorbents and their effectiveness and proposed mechanism of adsorption are discussed critically. In the conclusion, the question of why these adsorbents need modification before use is addressed.

Study on the SBA-15 Silica and ETS-10 Titanosilicate as Efficient Adsorbents for Cu(II) Removal from Aqueous Solution

The efficiency of Cu(II) removal from aqueous solution by two adsorbents, silica SBA-15 and titanosilicate ETS-10, was investigated. Effects of various experimental parameters such as: contact time, pH, initial copper concentration, adsorbent dosage, temperature were investigated in order to determine the maximum adsorption capacity of the adsorbents. The maximum adsorption capacity of silica SBA-15 was achieved at pH 5.0, and of titanosilicate ETS-10 at pH 6.0. The Freundlich, Langmuir, and Temkin isotherm models were applied in order to describe the equilibrium adsorption of Cu(II) by the studied adsorbents. Equilibrium data fitted well to the Langmuir model with a higher adsorption capacity of ETS-10 (172.53 mg·g−1) towards Cu(II) than SBA-15 (52.71 mg·g−1). Pseudo-first- and pseudo-second-order, Elovich, and Weber–Morris intraparticle diffusion models were used for description of the experimental kinetic data. It was found that the pseudo-first-order and pseudo-second-order kinetic models were the best applicable models to describe the adsorption kinetic data. Thermodynamic parameters that characterize the process indicated that the adsorption of Cu(II) onto the two adsorbents is spontaneous and endothermic.

Gelatin–Siloxane Hybrid Monoliths as Novel Heavy Metal Adsorbents

Novel gelatin-siloxane hybrid monoliths for heavy metal removal were prepared in the chemical reaction of gelatin with organomodified silicone containing epoxy group. Obtained porous hybrid materials were applied for adsorption of Cu(II), Cd(II) and Pb(II) from aqueous solutions. In this paper, the influence of siloxane amount used for the modification of gelatin on adsorbent stability and heavy metal removal was examined. The effect of pH values of the immersion liquid, as well as the contact time, was studied. Morphology, compressive strength and water absorption of hybrid monoliths were investigated. Desorption tests were also performed. The results showed that the higher the amount of the siloxane, the better stability of the hybrid monoliths in aqueous solutions. The highest values of adsorption capacity were observed for Pb(II) ions. The experimental maximum adsorption capacity determined for hybrid monoliths was 3.75 mg/g for Pb(II), 1.76 mg/g for Cu(II) and 1.5 mg/g for Cd(II). The desorption of metal ions for hybrid monoliths stable in aqueous solutions reached 70%.

Highly efficient and rapid Pb(ii) removal from acidic wastewater using superhydrophilic polystyrene phosphate resin

Novel superhydrophilic polystyrene phosphate resin was synthesized for efficient and rapid Pb(ii) removal from acidic wastewater.

Synthesis of chitosan/silver nanocomposites by phase inversion with the assistance of carbon dioxide

Carbon dioxide (CO₂) assisted synthesis of water-soluble silver nanoparticle with a narrow particle size distribution is reported here based on the phase-inversion procedure. Bio-derived chitosan (CS) is used to stabilize the metal nanoparticles according to its abundant functional groups. Formic acid is employed as both a solvent (for the polymer) and a reductant for in-situ reducing the silver precursor along with the solvent evaporation. CO₂ is utilized to combine with the amino groups of CS, reducing the viscosity of chitosan/formic acid solution and limiting the formation of hydrogen bonds. This promotes the stabilization and reduction efficiency of silver nanoparticles. In particular, 100% of Ag metal nanoparticles with the size of 7.5 ± 2.3 nm is successfully synthesized with the assistance of CO₂. Interestingly, the synthesized CS/Ag nanocomposites are water-soluble owing to the formation of carbamate groups. This water-soluble silver nanoparticle presents an exceptional performance in the selective reduction of 4-nitrophenol, where the turnover frequency (TOF = 599 h^-1) is even double with respect to the CO₂ free system.

Ultrafast and efficient removal of Pb(II) from acidic aqueous solution using a novel polyvinyl alcohol superabsorbent

The direct removal of heavy metal ions from acidic wastewater is a hard problem. In this study, a novel superabsorbent, polyvinyl alcohol phosphate ester (PVAP), was designed and prepared to remove Pb(II) from acidic wastewater (pH = 3). The PVAP can absorb water and swell to reach equilibrium within 30 s, which provides the conditions for ultrafast kinetic adsorption. For 100 mg/L Pb(II) solution, the adsorption reaches equilibrium within 5 min, and the removal ratio is more than 99.9% over a wide pH range of 3-6. Adsorption kinetics and isotherm data are consistent with pseudo-second-order and Langmuir model, respectively. The calculated maximum adsorption capacity for Pb(II) is 558.66 mg/g. Thermodynamic results show that the adsorption is spontaneous and exothermic process. The removal ratio for Pb(II) of PVAP still maintains above 99% after ten recycles. The PVAP can also simultaneously remove more than 97% of other heavy metal ions (Cu(II), Cd(II), Zn(II), Co(II), and Ni(II)) from an acidic solution. Moreover, the PVAP can efficiently purify simulated acid mine heavy metal wastewater, and the results meet EPA drinking water standards. The studies of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy prove that the adsorption mechanism involves surface complexation. This new superabsorbent is a promising candidate for acidic heavy metal sewage disposal.

Recovery of Heavy Metal Ions Using Magnetic Glycine-Modified Chitosan—Application to Aqueous Solutions and Tailing Leachate

The necessity of decontaminating effluents for the dual purpose of environmental beneficiation and valorization of low-grade resources is driving the development of new sorbents. The functionalization of biopolymers is a promising strategy for improving sorption performance. Incorporating magnetic micro-particles offers an opportunity for the facilitated recovery of spent micron-size sorbent. Combining magnetic facilities and biopolymer functionalization represents a winning strategy. Magnetic glycine-grafted chitosan (G@MChs) was synthesized for the sorption of Ni(II), Zn(II), and Hg(II) before being applied to the removal of hazardous and strategic metals from tailing leachates. The sorbent was characterized using Fourier transform infrared spectroscopy and scanning electron microscopy, before and after metal sorption. The acid–base properties of functionalized sorbent were also determined (pHPZC). Uptake kinetics were studied in mono- and multi-component solutions using different equations for kinetic modeling at optimized pH (i.e., pH0: 5.5). Langmuir and Sips equations were applied to model sorption isotherms in single-component solutions. In addition, sorption isotherms in multi-component solutions were used to evaluate the preference for selected metals. Maximum sorption capacities were 0.35 mmol Hg g−1, 0.47 mmol Zn g−1, and 0.50 mmol Ni g−1. Acidified urea solution (pH 2.7) successfully desorbs metal ions from G@MChs (desorption > 90%). The sorbent was tested for the recovery of hazardous and strategic metal ions from acidic leachates of tailings. This study demonstrates the promising performance of G@MChs for the treatment of complex metal-bearing solutions.

Dual-functional calcium alginate hydrogel beads for disinfection control and removal of dyes in water

For the decontamination of both pathogenic microorganism and toxic dye from wastewater, new type of materials should be exploited to fabricate more cost-effective, eco-friendly biosorbent. Herein, a promising hydrogel beads based on the incorporation of nano‑silver/diatomite into calcium alginate (named as Ag-DE@CAH) was designed to disinfect water and remove methylene blue (MB). Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM), etc. were utilized for characterization analysis. Compared with nano‑silver/diatomite (Ag-DE), the novel Ag-DE@CAH beads displayed a better sustained release profile for Ag⁺, and it noteworthy that the concentration of Ag⁺ in aqueous media is below the limit of the World Health Organization (WHO) standard (100 ppb) for a 30-days release experiment. It was found that Ag-DE@CAH beads exhibited better disinfection ability towards Escherichia coli (E. coli) than Staphylococcus aureus (S. aureus), and the maximum adsorption capacities of Ag-DE@CAH for MB was 128.21 mg/g. In addition, the as-prepared Ag-DE@CAH beads showed superior and reusable performance in the process of adsorption experiments for MB. Overall, the study indicates that the materials with both excellent disinfection and adsorption properties have potential application prospects for water purification.

Highly selective removal and recovery of Ni(II) from aqueous solution using magnetic ion-imprinted chitosan nanoparticles

Nickel (Ni) is one of the most common heavy metals. In this study, nano-sized magnetic ion-imprinted polymers (MIIPs) were synthesized using chitosan as the functional monomer, and used for selective adsorption and recovery of Ni(II) from solutions. The results showed MIIPs possessed high sorption selectivity for Ni(II), and the change in pH (5.0-9.0) exerted insignificant influence on the ion adsorption, allowing almost complete elution and recovery of adsorbed Ni(II) ions by using 0.5% EDTA-Na solution. Moreover, the sorption capacity of the recycled MIIPs decreased by only about 10% after 15 adsorption-desorption cycles. The time required for establishing the adsorption equilibrium was less than 1 h. The sorption process was predominant and endothermic, and could be well described by both Langmuir isotherm model and pseudo-second-order kinetic model. Therefore, the synthesized MIIPs was a suitable adsorbent for highly selective, fast and efficient removal and recovery of low-concentration Ni(II) ions from wastewaters.

The influence mechanism of dissolved organic matter on the adsorption of Cd (II) by calcite

Dissolved organic matter (DOM) has been widely existed in the soil, which has great influence on the adsorption of heavy metals by minerals. In this paper, the effects of DOM on Cd (II) adsorption by calcite were studied. In the presence of DOM (5 mg/L, 10 mg/L, and 20 mg/L), the maximum sorption of Cd (II) by calcite reduced from 48.94 mg/g to 44.14 mg/g, 28.11 mg/g, and 22.30 mg/g, respectively. The characterizations (XRD, SEM, XPS, FTIR, 3D-EEM, and UHPLC-Q-Orbitrap) were used to further study the mechanism about the effects of DOM on the adsorption of Cd (II) by calcite. These results showed calcite exhibited a significant adsorption capacity for Cd (II) at pH = 6.0, and CdCO₃ was formed on the surface of calcite after calcite reaction with Cd (II). Meanwhile, the fractionation of DOM by calcite could change the binding characteristics of DOM to calcite, which would increase the migration of Cd (II) in the solution. After the reaction of DOM with Cd (II) and calcite, Cd (II)-DOM complex was formed, and part of calcite was dissolved in the solution which would further increase the migration of Cd (II) and decrease the adsorption of Cd (II) by calcite. This paper might help further understand the effect of calcite and DOM on the environmental behavior of Cd (II) in the soil environment.

Formaldehyde and tripolyphosphate crosslinked chitosan hydrogels: Synthesis, characterization and modeling

In this work, the synthesis of crosslinked chitosan hydrogels was performed by ionic and covalent interactions using tripolyphosphate (TPP) and formaldehyde (CH₂O), respectively. The hydrogels synthesis was performed using a D-Optimal combined experiment design with two mixing variables, A and B representing the TPP weight fraction (slack variable) and CH₂O weight fraction, respectively, and three (3) process variables C-chitosan concentration, D-cross-linker concentration, and E-Contact time. The response variables studied were the point of zero charge (pH_PZC), the swelling ratio (SW), and the equilibrium water content (EWC), which are relevant physicochemical properties in applications such as the pollutant removal from water. According to the ANOVA results, the model obtained was significant; this means it can be adequately used to predicting pH_PZC, SW, and EWC from the mixing and process variables, obtaining coefficients of determination R² of 0.9572, 0.8900, and 0.8447, respectively. The pH_PZC is affected by chitosan concentration, while the crosslinker concentration influences the SW, and the contact time most significantly affected the EWC. Morphology and hardness tests, thermal stability, infrared spectroscopy, and scanning electron microscopy, allowed verifying the types of crosslinking of chitosan with TPP and CH₂O.

Low-cost hydrogel adsorbent enhanced by trihydroxy melamine and β-cyclodextrin for the removal of Pb(II) and Ni(II) in water

Hydrogels have extensively studied as adsorbents, raw materials for the preparation of adsorbent hydrogels have low strength, while high strength hydrogels have weak adsorption capacity. In this study, PVA hydrogel was crosslinked via trihydroxy melamine and epichlorohydrin, and β-cyclodextrin with strong adsorption capacity was added to remove the heavy metal ions. Results showed that the addition of trihydroxy melamine with 8%, the compressive strength of the hydrogel was increased by approximately 20%. The Langmuir isotherm model showed that the adsorption capacity of the hydrogel for Pb(II) and Ni(II) reached 505.9 mg/g and 286.7 mg/g, respectively, and the efficiency of removing the low-concentration heavy metal ions in water more than 99%. The hydrogel is low cost, and maintained highly removal efficiency under low pH. The removal efficiency of the hydrogel remained above 90% after five repeated adsorption-desorption experiments. The hydrogels have a potential to be used in wastewater treatment as adsorbents.

Carbohydrate biopolymers, lignin based adsorbents for removal of heavy metals (Cd2+, Pb2+, Zn2+) from wastewater, regeneration and reuse for spent adsorbents including latent fingerprint detection: A review

Living organisms are created by carbohydrate biopolymers such as chitosan, carboxymethyl cellulose, alginate and lignin. These carbohydrate biopolymers have been extensively used for environmental applications because they are bio-degradable, bio-compatible, non-toxic and inexpensive. Recently, carbohydrate biopolymers have been used to prepare different nanocomposite adsorbents for treatment of wastewater. These adsorbents explored the removal effectiveness of inorganic pollutants from aqueous solution. This review article discusses the synthesis and application of chitosan, carboxymethyl cellulose, alginate and lignin nanocomposites as adsorbents for heavy metals. Toxic metals can be efficiently absorbed by cross-linkers, distributed in aqueous solutions of divalent heavy metal ions to examine their polymer absorption capacity. These nanocomposites were used for the adsorption of highly toxic metals such as Cd2+, Pb2+ and Zn2+ in water. To make heavy metal ion uptake more effective, more functionalization has been implemented such as blending, grafting, or mixing with different nanomaterials with an extra functional group. The integration of the second part into the main polymer chain not only adds functionality but also increases mechanical efficiency, one of the core criteria for adsorbent recyclability. The remediation method of metal ions from wastewater is cheaper as long as the adsorbent is reused. Furthermore, they exhibited good performance for the reuse of spent adsorbents after adsorption-desorption processes including latent fingerprint detection with nanomaterials by using the powder dusting method. Chitosan, carboxymethyl cellulose, alginate and lignin based nanocomposites have demonstrated better adsorption activities due to great physical and chemical properties for the chelation of heavy metals such as Cd2+, Pb2+ and Zn2+ from water and also higher regeneration with various eluents after several desorption-adsorption cycles. In addition, reuse of the spent adsorbents in latent fingerprint detection with different nanomaterials is discussed. Finally, this review article makes recommendations for future studies in light of environmentally favourable and economical applications.

Preparation and Kinetic Studies of Cross-Linked Chitosan Beads Using Dual Crosslinkers of Tripolyphosphate and Epichlorohydrin for Adsorption of Methyl Orange

Preparation of cross-linked chitosan beads using dual crosslinkers of tripolyphosphate (TPP) and epichlorohydrin (ECH) for the adsorption and kinetic studies of methyl orange (MO) had been carried out. FTIR spectra showed that TPP could act as the protecting agent of the NH₂ group of chitosan and ECH reacted with the primary hydroxyl group of chitosan. Various concentrations of TPP, ECH, and immersing time in the TPP solution for bead formation were studied. The effect of pH and kinetics of adsorption were investigated to define the mechanism of adsorption and rate-limiting step. As a result, pH 3, 10% (w/v) TPP, 5% (v/v) ECH, and 12 h immersing time in TPP were selected as the optimum conditions for preparing the beads as indicated by the highest adsorption amount of MO. The cross-linked chitosan beads' adsorption capacity for MO under optimum condition was found to be 79.55 mg/g with the adsorption rate constant (k) of 1.29 × 10⁻³/min. Furthermore, it was found that a low concentration of ECH could maintain the stability of chitosan in acidic conditions, whereas the concentration of TPP and immersing time controlled pore size and morphology of chitosan beads. The mechanism of adsorption of MO was controlled by the pore and rigidity of cross-linked chitosan beads. Bulk diffusion acted as a rate-limiting step, and a high concentration of MO inhibited diffusion and adsorption itself.

A systematic review on carbohydrate biopolymers for adsorptive remediation of copper ions from aqueous environments-Part B: Isotherms, thermokinetics and reusability

The presence of copper in aquatic environment is a serious threat for human health and ecosystem conservation. Adsorption is a powerful, operable and economic method for remediation of copper ions from aqueous phase. Carbohydrate biopolymers have emerged as promising, effective and environmental-friendly adsorbents for copper remediation. In part A of this review, different types of carbohydrate biopolymer adsorbents were surveyed focusing on prevalent and novel synthesis and modification methods. In current work (part B of the review), isothermal, thermodynamic and kinetic aspects of the copper adsorption by carbohydrate-based adsorbents as well as the regeneration and reusability of the biopolymer adsorbents are overviewed. Adsorption capacity, time required for equilibrium (adsorption rate), thermal-sensitivity of the adsorption, favorability extent, and sustainability of the adsorbents and adsorption processes are valuable and useful outcomes, resulted from the thermokinetic and reusability investigations. Such considerations are critical for the process design and scale up regarding technical, economical and sustainability of the adsorption process.

Simultaneous removal of Congo red and cadmium(II) from aqueous solutions using graphene oxide-silica composite as a multifunctional adsorbent

Graphene oxide is a very high capacity adsorbent due to its functional groups and π-π interactions with other compounds. Adsorption capacity of graphene oxide, however, can be further enhanced by having synergistic effects through the use of mixed-matrix composite. In this study, silica-decorated graphene oxide (SGO) was used as a high-efficiency adsorbent to remove Congo red (CR) and Cadmium (II) from aqueous solutions. The effects of solution initial concentration (20 to 120 mg/l), solution pH (pH 2 to 7), adsorption duration (0 to 140 min) and temperature (298 to 323 K) were measured in order to optimize the adsorption conditions using the SGO adsorbent. Morphological analysis indicated that the silica nanoparticles could be dispersed uniformly on the graphene oxide surfaces. The maximum capacities of adsorbent for effective removal of Cd (II) and CR were 43.45 and 333.33 mg/g based on Freundlich and Langmuir isotherms, respectively. Langmuir and Freundlich isotherms displayed the highest values of Q_max for CR and Cd (II) adsorption in this study, which indicated monolayer adsorption of CR and multilayer adsorption of Cd (II) onto the SGO, respectively. Thermodynamic study showed that the enthalpy (ΔH) and Gibbs free energy(ΔG) values of the adsorption process for both pollutants were negative, suggesting that the process was spontaneous and exothermic in nature. This study showed active sites of SGO (π-π, hydroxyl, carboxyl, ketone, silane-based functional groups) contributed to an enormous enhancement in simultaneous removal of CR and Cd (II) from an aqueous solution, Therefore, SGO can be considered as a promising adsorbent for future water pollution control and removal of hazardous materials from aqueous solutions.

A systematic review on carbohydrate biopolymers for adsorptive remediation of copper ions from aqueous environments-part A: Classification and modification strategies

Copper is one of the most toxic heavy metals which must be eliminated from aqueous environments, according to the environmental standards. Carbohydrate biopolymers are promising candidates for synthesizing copper-adsorbent composites. It is due to unique properties such as having potential adsorptive functional sites, availability, biocompatibility and biodegradability, formability, blending capacity, and reusability. Different types of copper-adsorbent carbohydrate biopolymers like chitosan and cellulose with particular focus on the synthesizing and modification approaches have been tackled in this review. Composites, functionality and morphological aspects of the biopolymer adsorbents have also been surveyed. Further progress in the fabrication and application of biopolymer adsorbents would be achievable with special attention to some critical challenges such as the process economy, copolymer and/or (nano) additive selection, and the physicochemical stability of the biopolymer composites in aqueous media.

Adsorption of cadmium using modified zeolite-supported nanoscale zero-valent iron composites as a reactive material for PRBs

The main challenge in utilizing permeable reactive barriers (PRB) for remediation of metals-contaminated groundwater is determination of a proper low-cost reactive medium that can remove the desired contaminants simultaneously. In this study, the performance of different zeolite materials and nZVI-based adsorbents for cadmium (Cd) removal was compared. Further, a composite of the best nZVI and zeolite samples was synthesized with the removal efficiency of 20.6 g/kg and selected as the proposed adsorbent. Moreover, the characteristics of the composite were analyzed through different techniques (BET, XRF, XRD, FT-IR, FE-SEM and EDX). In addition, through kinetic and thermodynamic studies, the effect of temperature, pH, ionic strength and presence of other metal ions on Cd removal efficiency was investigated. According to the results, since sodium zeolite (NaZ) provides a large number of specific ion-exchange sites for decoration with nZVI, stabilizes nZVI, and prevents its aggregation and further leaching in the harsh environment, the NaZ-nZVI composite is capable of removing Cd by adsorption and is applicable in PRBs, and thus it seems that the aforementioned composite is a proper candidate for groundwater remediation from a wide range of metal ions.

Functionalized Glutathione on Chitosan-Genipin Cross-Linked Beads Used for the Removal of Trace Metals from Water

Functionalized glutathione on chitosan-genipin cross-linked beads (CS-GG) was synthesized and tested as an adsorbent for the removal of Fe(II) and Cu(II) from aqueous solution. The beads were characterized by several techniques, including Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), CNS elementary analysis, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The effect of several parameters such as the pH, the temperature, and the contact time was tested to optimize the condition for the adsorption reaction. The beads were incubated in aqueous solutions contaminated with different concentrations of Fe(II) and Cu(II) (under the range concentration from 10 to 400 mg·L-1), and the adsorption capacity was evaluated by inductively coupled plasma optical emission spectrometry (ICP-OES). The adsorption equilibrium was reached after 120 min of incubation under optimal pH 5 for Fe(II) and after 180 min under optimal pH 6 for Cu(II). According to the Langmuir isotherm, the maximum adsorption capacities (q max) for Fe(II) and Cu(II) were 208 mg·g-1 and 217 mg·g-1, respectively. Our results showed that the adsorption efficiency of both metals on CS-GG beads was correlated with the degree of temperature. In addition, the adsorption reaction was spontaneous and endothermic, indicated by the positive values of ΔG 0 and ΔH 0. Therefore, the present study demonstrated that the new synthesized CS-GG beads had a strong adsorption capacity for Fe(II) and Cu(II) and were efficient to remove these trace metals from aqueous solution.

Synthesis and Characterisation of Graphene Oxide-Silica-Chitosan for Eliminating the Pb(II) from Aqueous Solution

Heavy metal ions have a toxic and negative influences on the environment and human health even at low concentrations and need to be removed from wastewater. Chitosan and graphene oxide are suitable nano plate adsorbents with high adsorption potential because of their π-π interaction, and they are available functional groups that interact with other elements. In this study, graphene oxide was coated with silica to enhance the hydrophilicity of the adsorbent. Subsequently, the adsorbent was functionalised by various amounts of chitosan to improve the Pb(II) removal. The adsorbent was analysed using transmission electron microscopy (TEM), Raman, Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and mapping analysis techniques. An investigation of the influences of the initial concentration of Pb(II), pH and contact time were included to obtain the optimum amount of adsorption. The range of the initial Pb(II) concentration studied was from 10 to 120 mg/L. The pH factor ranged from 3 to 8 with contact time from 0 to 140 min. Freundlich, Temkin and Langmuir isotherm models were fit to the results, and a pseudo-second-order kinetic model was found to provide a good fit as well. The maximum Pb(II) removal capacity achieved was 256.41 (+/- 4%) mg/g based on Langmuir isotherms.

Anionic dye uptake via composite using chitosan-polyacrylamide hydrogel as matrix containing TiO2 nanoparticles; comprehensive adsorption studies

In the present study, TiO₂ nanoparticles dispersed in chitosan grafted polyacrylamide matrix (TiO₂-PAM-CS) was synthesized using in situ technique, and applied for the uptake of Sirius yellow K-CF dye from aqueous solution. The synthesized nano-composite was characterized by FE-SEM, TEM, XRD and FT-IR analysis. The effect of significant parameters such as pH, dose, time and temperature in batch adsorption experiments were investigated. The adsorption process was pH dependent and the optimum value of pH was obtained 2 with 96.81% dye removal at 40 °C. The equilibrium data were compatible well with the Langmuir isotherm having q_m value of 1000 mg/g. The Dubinin-Radushkevich (D-R) isotherm and thermodynamic studies prove that the adsorption is physical, endothermic and spontaneous. Kinetic study also verifies that pseudo second order kinetic model is the predominant model. The interactions between amin groups of polyacrylamide-chitosan (PAM-CS) composite in from of NH₃⁺ and molecules of anionic dye via hydrogen bond formation (Dye-NH₃⁺), also electrostatic interactions between Ti⁺⁴ available in PAM-CS composite and anionic dye (free energy of 1.66 kJ/mol calculated from D-R model) govern the adsorption mechanism. The reusability test showe that TiO₂-PAM-CS composite can be renewed easily with HCl solution as an efficient adsorbent for practical wastewater treatment.

Modifying alginate beads using polycarboxyl component for enhanced metal ions removal

Designing desirable adsorbent for highly efficient removal of heavy metal ions is of practical significance, given the cost-effectiveness, environmental benign, natural abundance and easy-handling collection features. Herein, a bead-like adsorbent with high adsorption capacity was prepared by modifying alginate beads using polyacrylate with high density of carboxyl groups. The developed alginate/polyacrylate beads were collaboratively characterized by FT-IR, TGA, SEM, XPS, etc., and various adsorption conditions were tested including the pH of the solution, contact time and the initial concentration. The experimental data were fitted well by the Freundlich isotherm model, and the maximum adsorption capacity was obtained from the Langmuir model was 611.0 mg/g, and adsorption process followed the Pseudo-second-order kinetic model. The adsorption mechanisms conformed to multi-layer adsorption, and mainly dominated by chemical interactions. The bead-like adsorbent exhibited excellent reusability after eight sequential cycles and displayed higher adsorption capacity towards lead ions. This type of adsorbent might possess promising role in treating heavy metals from water by virtue of degradable, cost-effective component and high adsorption efficiency.

Adsorption of Deoxynivalenol (DON) from Corn Steep Liquor (CSL) by the Microsphere Adsorbent SA/CMC Loaded with Calcium

The occurrence of deoxynivalenol (DON) in animal feed is a serious issue for the livestock industry. Approaches using mycotoxin adsorbents are key to decreasing mycotoxin carryover from contaminated feed to animals. In this paper, a novel functional microsphere adsorbent comprising an alginate/carboxymethyl cellulose sodium composite loaded with calcium (SA/CMC-Ca) was prepared by an emulsification process to adsorb DON from polluted corn steep liquor (CSL) containing DON at a concentration of 3.60 μg/mL. Batch experiments were conducted under different experimental conditions: CSL volumes, reaction times, desorption times, and microsphere recyclability. Results showed that 5 g of microspheres reacted with 5 mL of DON-polluted CSL for 5 min, the microspheres can be recycled 155 times, and the maximum DON adsorption for the microspheres was 2.34 μg/mL. During recycling, microspheres were regenerated by deionized water every time; after the microspheres were cleaned, DON in the deionized water was degraded by sodium hydroxide (NaOH) at 70 °C for 1 h at pH 12. The mechanism for physical adsorption and hydrogen bonding was analyzed by scanning electron microscopy (SEM) and Fourier transform infrared spectrometry (FTIR). To the best of our knowledge, this is the first report showing that the microsphere adsorbent SA/CMC-Ca adsorbs DON. Therefore, we suggest that using microsphere absorbents would be a possible way to address DON-contaminated CSL issues in animal feed.