Biosorption of Cd(II) Ions from Aqueous Solution Using Chitosan-iso-Vanillin as a Low-Cost Sorbent: Equilibrium, Kinetics, and Thermodynamic Studies

Crosslinked modified chitosan biopolymer for enhanced removal of toxic Cr(VI) from aqueous solution

Two new crosslinked modified chitosan biopolymers, namely (CTS-VAN) and (Fe₃O₄@CTS-VAN) bioadsorbents were prepared starting from chitosan and 4-hydroxy-3-methoxybenzaldehyde (VAN) in presence of epichlorohydrin. The analytical techniques FT-IR, EDS, XRD, SEM and XPS besides BET surface analysis were utilized for full characterization of the bioadsorbents. Batch experiments were conducted to study the effect of various influencing parameters in Cr (VI) removal such as initial pH, contact time, adsorbent amount and initial Cr (VI) concentration. The adsorption of Cr (VI) was found out to be maximum at pH = 3 for both bioadsorbents. Langmuir isotherm fit well the adsorption process with a maximum adsorption capacity of 188.68 and 98.04 mg/g for CTS-VAN and Fe₃O₄@CTS-VAN, respectively. The adsorption process followed pseudo second-order kinetics with R² values of 1 and 0.9938 for CTS-VAN and Fe₃O₄@CTS-VAN, respectively. X-ray photoelectron spectroscopy (XPS) analysis showed that Cr(III) accounted for 83 % of the total Cr bound to bioadsorbents surface, which indicated reductive adsorption was responsible for Cr(VI) removal by the bioadsorbents. Cr(VI) was initially adsorbed on the positively charged surface of the bioadsorbents and reduced to Cr(III) by electrons provided by oxygen-comprising functional groups (e.g., CO), and consequently part of the converted Cr(III) stayed on the surface and the rest released into solution.

Dual immobilization of magnetite nanoparticles and biosilica within alginate matrix for the adsorption of Cd(II) from aquatic phase

The adsorption of cadmium ions by magnetite (Fe3O4)@biosilica/alginate (MBA nano-hybrid) was the main aim of the present investigation. Herein, MBA nano-hybrid was synthesized via chemical precipitation technique. As-synthesized MBA nano-hybrid was characterized using FT-IR, FESEM and XRD analyzes. Based on the results, the maximum adsorption capacity of the adsorbent for the removal of Cd(II) was obtained at the initial pH of 7.0. At the initial Cd(II) concentration of 40 mg/L, increasing the reaction time to 180 min led to the Cd adsorption of 35.36 mg/g. Since the removal of Cd(II) after the reaction time of 60 min was insignificant, the reaction time of 60 min was considered as optimum reaction time for performing the experimental runs. According to the results, Langmuir isotherm and pseudo-second order kinetic models were the best fitted models with high correlation coefficients (R2 > 0.99). The results of thermodynamic study indicated exothermic (positive ΔH°) and spontaneous nature (negative ΔG°) of the adsorption of Cd(II) on the surface of MBA nano-hybrid. Negligible reduction in the adsorption capacity of the nano-hybrid was observed (16.57%) after fifth experimental runs, indicating high reusability potential of the as-synthesized nano-hybrid adsorbent.

Snail Shells Adsorbent for Copper Removal from Aqueous Solutions and the Production of Valuable Compounds

This research explored the efficiency of snail shells powder (SSP) for Cu(II) removal from aqueous solutions and the production of valuable compounds from the residual product. To confirm its chemical and mineral components, the material was characterized by different instrumental techniques. The effects of experimental parameters such as the pH of the solution, the effect of SSP dose, particle size, and initial concentration of Cu(II) on the removal process were studied. The removal of Cu(II) was reasonably fast to be completed within a time frame of 90 min. The kinetics following the pseudo-second-order model (R2 = 0.979) were better compared to the pseudo-first-order model (R2 = 0.896). The increase in pH values leads to an increase in the amount of Cu(II) adsorbed. Afterward, the adsorption capacity reaches stability at pH near 7. The maximum Cu(II) removal occurred with a mass of 8 g·L−1 and a particle size of 300 μm. This particle size presents approximately 44.5% of SSP particles, which is the largest proportion of the sample as shown by particle size analysis. The adsorption isotherm was well described by Langmuir and Freundlich equations. The thermodynamic parameters values showed that the Cu(II) adsorption was a spontaneous and exothermic process. Furthermore, with the presence of CaCO3, the precipitation of Cu(II) in the form of posnjakite occurred with a high Cu(II) removal rate close to 99%. The residual SSP was used for the production of valuable compounds through the thermal decomposition process at various temperatures.