Multiwall carbon nanotube promising route for removal of chromium from wastewater via batch column mechanism

Novel Thermosensitive-co-Zwitterionic Sulfobetaine Gels for Metal Ion Removal: Synthesis and Characterization

Zwitterionic betaine polymers are promising adsorbents for the removal of heavy metal ions from industrial effluents. Although the presence of both negative and positively charged groups imparts them the ability to simultaneously remove cations and anions, intra- and/or inter-chain interactions can significantly reduce their adsorption efficiencies. Therefore, in this study, novel gels based on crosslinked co-polymers of thermosensitive N-isopropylacrylamide (NIPAAM) and zwitterionic sulfobetaine N,N-dimethylacrylamido propyl ammonium propane sulfonate (DMAAPS) were synthesized, characterized, and evaluated for ion removal. Fourier-transform infrared (FTIR) and proton nuclear magnetic resonance (1H NMR) analyses confirmed the success of the co-polymerization of NIPAAM and DMAAPS to form poly(NIPAAM-co-DMAAPS). The phase transition temperature of the co-polymer increased with increasing DMAAPS content in the co-polymer, indicating temperature-dependent amphiphilic behavior, as evidenced by contact angle measurements. The ion adsorption analyses of the poly(NIPAAM-co-DMAAPS) gels indicated that co-polymerization increased the molecular distance and weakened the interaction between the DMAAPS-charged groups (SO3- and N+), thereby increasing the ion adsorption. The results confirmed that, with a low concentration of DMAAPS in the co-polymer gels (~10%), the maximum amount of Cr3+ ions adsorbed onto the gel was ~58.49% of the sulfonate content in the gel.

Effective adsorptive removal of Zn2+, Cu2+, and Cr3+ heavy metals from aqueous solutions using silica-based embedded with NiO and MgO nanoparticles

In this study, the adsorptive removal of Zn²⁺, Cu²⁺, and Cr³⁺ metal ions from aqueous solutions onto NiO-MgO silica-based nanoparticles (SBNs) has been studied. The effect of several factors such as solution pH, initial concentration, contact time, and coexisting ions on the adsorbed amounts of single Zn²⁺, Cu²⁺, and Cr³⁺ ions have been investigated within an array of batch mode experiments. Interestingly, the adsorption of Cr³⁺ at high and low concentrations was very fast, and equilibrium was achieved within 2 min compared to Cu²⁺ and Zn²⁺ which needed 30 and 60 min to reach equilibrium, respectively. The adsorption equilibrium data fitted very well with the Sips adsorption isotherm model for Cu²⁺ and Zn²⁺, and the BET model for Cr³⁺ ions. The maximum uptake was maintained at 7.23, 13.76, 41.36 (ions per nm²) for Zn²⁺, Cu²⁺, and Cr³⁺, respectively. This equals to 37.69, 69.68, 209.51 (mg adsorbate per g adsorbent), respectively, showing the promising industrial application of those SBNs. Moreover, the adsorption uptake results increase with increasing the pH in the range of 7.0-11.0 for all investigated metal ions. The thermodynamic parameters such as the changes in Gibbs free energy (ΔG^o), enthalpy (ΔH^o), and entropy (ΔS^o) were determined. The adsorption of Zn²⁺, Cu²⁺, and Cr³⁺ was spontaneous, endothermic, and physical for Cu²⁺ and Cr³⁺, while exothermic and chemical for Zn²⁺. The regeneration and reusability studies have proven that the NiO-MgO SBNs can be employed for the adsorptive of these metals repeatedly without impacting the adsorption capacity indicating their sustainability.