Selective and enhanced nickel adsorption from sulfate- and calcium-rich solutions using chitosan

Nitric Acid-Treated Blue Coke-Based Activated Carbon's Structural Characteristics and Its Application in Hexavalent Chromium-Containing Wastewater Treatment

This study primarily focused on the efficient transformation of low-priced blue coke powder into a high-capacity adsorbent and aimed to address the pollution issue of hexavalent chromium (Cr (VI))-laden wastewater and to facilitate the effective utilization of blue coke powder. A two-step method was utilized to fabricate a blue coke-based nitric acid-modified material (LCN), and the impact of nitric acid modification on the material's structure and its efficacy in treating Cr (VI)-contaminated wastewater was evaluated. Our experimental results illustrated that, under identical conditions, LCN exhibited superior performance for Cr (VI) treatment compared to the method employing only potassium hydroxide (LCK). The specific surface area and pore volume of LCN were 1.39 and 1.36 times greater than those of LCK, respectively. Further chemical composition analysis revealed that the functional group structure on the LCN surface was more conducive to Cr (VI) adsorption. The highest amount of Cr (VI) that LCN could bind was measured at 181.962 mg/g at 318 K. This was mostly due to chemisorption, which is dominated by redox reactions. The Cr (VI) removal process by LCN was identified to be a spontaneous, exothermic, and entropy-increasing process. Several tests on recycling and reuse showed that LCN is a stable and effective chromium-containing wastewater adsorbent, showing that it could be used in many situations.

Mesoporous Materials for Metal-Laden Wastewater Treatment

Rapid technological, industrial and agricultural development has resulted in the release of large volumes of pollutants, including metal ions, into the environment. Heavy metals have become of great concern due to their toxicity, persistence, and adverse effects caused to the environment and population. In this regard, municipal and industrial effluents should be thoroughly treated before being discharged into natural water or used for irrigation. The physical, chemical, and biological techniques applied for wastewater treatment adsorption have a special place in enabling effective pollutant removal. Currently, plenty of adsorbents of different origins are applied for the treatment of metal-containing aqueous solution and wastewater. The present review is focused on mesoporous materials. In particular, the recent achievements in mesoporous materials' synthesis and application in wastewater treatment are discussed. The mechanisms of metal adsorption onto mesoporous materials are highlighted and examples of their multiple uses for metal removal are presented. The information contained in the review can be used by researchers and environmental engineers involved in the development of new adsorbents and the improvement of wastewater treatment technologies.

Thermoreversible and tunable supramolecular hydrogels based on chitosan and metal cations

A new thermoreversible and tunable hydrogel CS-M with high water content prepared by metal cation (M = Cu²⁺, Zn²⁺, Cd²⁺ and Ni²⁺) and chitosan (CS) was reported. The influence of metal cations on the thermosensitive gelation of CS-M systems were studied. All prepared CS-M systems were in the transparent and stable sol state and could become the gel state at gelation temperature (T_g). These systems after gelation could recover to its original sol state at low temperature. CS-Cu hydrogel was mainly investigated and characterized due to its large T_g scale (32-80 °C), appropriate pH range (4.0-4.6) and low Cu²⁺ concentration. The result showed that the T_g range was influenced and could be tuned by adjusting Cu²⁺ concentration and system pH within an appropriate range. The influence of anions (Cl^-, NO3^- and Ac^-) in cupric salts in the CS-Cu system was also investigated. Scale application as heat insulation window was investigated outdoors. The different supramolecular interactions of the -NH₂ group in chitosan at different temperatures were proposed to dominate the thermoreversible process of CS-Cu hydrogel.

Enhanced nickel removal and synchronous bioelectricity generation based on substrate types in microbial fuel cell coupled with constructed wetland: performance and microbial response

In this study, an attempt was made to clarify the impact of substrates on the microbial fuel cell coupled with constructed wetland (CW-MFC) towards the treatment of nickel-containing wastewater. Herein, zeolite (ZEO), coal cinder (COA), ceramsite (CER), and granular activated carbon (GAC) were respectively introduced into lab-scaled CW-MFCs to systematically investigate the operational performances and microbial community response. GAC was deemed as the most effective substrate, and the corresponding device yielded favorable nickel removal efficiencies over 99% at different initial concentrations of nickel. GAC-CW-MFC likewise produced a maximum output voltage of 573 mV, power density of 8.95 mW/m², and internal resistance of 177.9 Ω, respectively. The strong adsorptive capacity of nickel by GAC, accounting for 54.5% of total contaminant content, was mainly responsible for the favorable nickel removal performances of device GAC-CW-MFC. The high-valence Ni²⁺ was partially reduced to elemental Ni⁰ on the cathode, which provided evidence for the removal of heavy metals via the cathodic reduction of CW-MFC. The microbial community structure varied considerably as a result of substrates addition. For an introduction of GAC into the CW-MFC, a remarkably enriched population of genera Thermincola, norank_f__Geobacteraceae, Anaerovorax, Bacillus, etc. was noted. This study was dedicated to providing a theoretical guidance for an effective regulation of CW-MFC treatment on nickel-containing wastewater and accompanied by bioelectricity generation via the introduction of optimal substrate.

Study of phenobarbital removal from the aqueous solutions employing magnetite-functionalized chitosan

Due to its wide use in anticonvulsant pharmacotherapy, phenobarbital (PHEN) is an aquatic contaminant with a high prevalence in the environment. In this adsorption study, chitosan and chitosan-based magnetic adsorbents containing different amounts of incorporated magnetite (CS, CS·Fe₃O₄ 1:1, CS·Fe₃O₄ 1:5, and CS·Fe₃O₄ 1:10) were used for phenobarbital removal. The magnetic adsorbents were synthesized by co-precipitation method and characterized through FTIR, XRD, MEV, and VSM analysis. In PHEN adsorption, the equilibrium and adsorption kinetic were better adjusted by the Sips and pseudo-second-order model, respectively. Among the four nanoadsorbents used, the maximum phenobarbital adsorption capacity was 94.60 mg g^-1 using 25 mg of CS·Fe₃O₄ 1:5, with a concentration of PHEN (50 mg L^-1), pH 7.0 at room temperature. The parameters of pH, adsorbent dosage, ionic strength, and thermodynamic study were tested for the adsorbent with the highest performance (CS·Fe₃O₄ 1:5). The nanoadsorbent demonstrates efficiency in the removal of the contaminant for diverse adsorption cycles. Finally, the protocol employing magnetic adsorbents dispenses the subsequent steps of filtration and centrifugation.

Adsorption of Co2+ and Sr2+ in aqueous solution by a novel fibrous chitosan biosorbent

In this study, a novel fibrous chitosan biosorbent was prepared using LiOH/KOH/urea/H₂O (4.5:7:8:80.5 by weight) as spinning solvent. The fibrous chitosan exhibited a higher adsorption capacity and a faster adsorption rate for Co²⁺ and Sr²⁺, compared with spherical chitosan due to its high specific surface area (16.9 m² g^-1), uniform fineness (24.1 μm), and good mechanical strength. The adsorption capacity of fibrous chitosan for Co²⁺ and Sr²⁺ was 31.3 mg g^-1 and 20.0 mg g^-1, respectively, which was higher than that of spherical chitosan (22.5 mg g^-1for Co²⁺ and 8.9 mg g^-1 for Sr²⁺). The coordination between -NH₂/-OH of chitosan and the nuclide ions was the rate-limiting step. The improvement of adsorption performance was due to the higher specific surface area which increased the exposure degree of functional groups (adsorptive sites). This new wet-spun fibrous chitosan biosorbent showed great potential in the adsorptive removal of nuclides ions from aqueous solution.