Equilibrium, kinetic and mechanism studies of Cu(II) and Cd(II) ions adsorption by modified chitosan beads

Removal of Pb (II) from aqueous solution by sulfur-functionalized walnut shell

Heavy metal lead poses a great threat to organisms and the environment; the removal of lead has drawn more and more attention in recent years. In this paper, the sulfur-containing functional group was grafted onto the walnut shell with xanthate to synthesize a low-cost biosorbent (SWM) for the removal of lead in water. The synthesized adsorbent was characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunner-Emmet-Teller (BET). The effects of pH, adsorbent dosage, contact time, initial Pb (II) concentration, and temperature on adsorption were investigated, and the adsorption properties of walnut shells before and after modification were compared. Moreover, adsorption kinetics, adsorption isotherms, and adsorption thermodynamics were studied. The sulfur-containing functional group was confirmed to be successfully grafted onto the walnut shell. The results showed that the adsorption performance of SWM was much better than the unmodified walnut shell due to complexation by sulfur-containing functional group and ion exchange. The Pb (II) adsorption onto SWM was found to follow Temkin isotherm model and has a good correlation with the pseudo-second-order kinetic model. In addition, the adsorption process was spontaneous and exothermic. All the results showed that the high adsorption performance and low cost of SWM make it a potential biosorbent in the treatment of lead-contaminated water.

Carboxymethyl cellulose/polyacrylamide composite hydrogel for cascaded treatment/reuse of heavy metal ions in wastewater

A new bio-based bilateral hydrogel containing carboxymethyl cellulose (CMC) and polyacrylamide (PAM) was prepared for the wastewater remediation. The obtained CMC/PAM composite hydrogel reveals a strong single-ion affinity for copper (Cu^II), lead (Pb^II) and cadmium (Cd^II) ions, as well as multi-ion absorbability with its equilibrium data following the Langmuir adsorption model and its adsorption process abiding by a pseudo-second-order kinetics. To demonstrate its recycled use for the metal ions, the adsorbed Cu^II ions in the hydrogel were reduced in situ to form homogeneously dispersed Cu nanoparticles (NPs), leading to the Cu NPs-loaded CMC/PAM hydrogel. Reduction of 4-nitrophenol to 4-aminophenol with high efficiency was successfully achieved by this Cu NPs-loaded CMC/PAM hydrogel, verifying the hydrogel's dual functionalities towards the wastewater treatment and catalytic application.

Novel alginate/polyethyleneimine hydrogel adsorbent for cascaded removal and utilization of Cu2+ and Pb2+ ions

Heavy metal ion pollution leads to severe health risk to human beings. Herein, a natural and highly efficient sodium alginate (ALG)/polyethyleneimine (PEI) composite hydrogel was designed and fabricated for the removal of heavy metal ions from wastewater. The adsorption of heavy metal ions on the ALG based, 3D composite hydrogel were thoroughly investigated in this study. Furthermore, the in situ reduced metal nanoparticle-loaded ALG/PEI composite hydrogel provided us a sustainable utilization route of the heavy metal ion with a promising adsorption-catalysis ability. In general, this research will present an effective and practical paradigm for the cascaded treatment and recycling of heavy metal ions in wastewater.

Adsorption of Cu(II) and Zn(II) Ions from Aqueous Solution by Gel/PVA-Modified Super-Paramagnetic Iron Oxide Nanoparticles

Super-paramagnetic iron oxide nanoparticles (SPIONs)/gelatin (gel)/polyvinyl alcohol (PVA) nanoparticles were designed and synthesized by the co-precipitation method and further modified with gel and PVA. These nanoparticles were used for the removal of Cu(II) and Zn(II) from aqueous solutions. The adsorbents were rich in different functional groups for chemisorption and showed effective adsorption properties. The adsorption of Cu(II) and Zn(II) on the SPIONs/gel and SPIONs/gel/PVA materials were investigated with respect to pH, adsorption kinetics, and adsorption isotherms. The adsorption data was fitted to the Langmuir, Freundlich, and Sips models at the optimum pH 5.2 (±0.2) over 60 min; SPIONs/gel showed maximum adsorption capacities of 47.594 mg/g and 40.559 mg/g for Cu(II) and Zn(II); SPIONs/gel/PVA showed those of 56.051 mg/g and 40.865 mg/g, respectively. The experimental data fitted the pseudo-second-order model, indicating that the process followed chemical monolayer adsorption. In addition, the SPIONs/gel/PVA showed better stability and Cu(II) adsorption efficiency than SPIONs/gel.