Characterization of radioactive cobalt on graphene oxide by macroscopic and spectroscopic techniques

Tunnel manganese oxides prepared using recovered LiMn2O4 from spent lithium-ion batteries: Co adsorption behavior and mechanism

The purpose of this study was to investigate Cobalt (Co) removal from wastewater using synthesized manganese oxides from the recovered LiMn₂O₄. An efficient ultrasonication leaching method was utilized to recycle LiMn₂O₄ from spent lithium-ion batteries (LIBs). The recovered LiMn₂O₄ was used to synthesize tunnel λ-MnO₂, γ-MnO₂ and β-MnO₂ by acid leaching and hydrothermal methods. Meanwhile, Li⁺ in the supernatant was recycled by the precipitation of Li₃PO₄. Subsequently, for the synthesized tunnel MnO₂, various characterizations and sodium hydroxide titration in NaNO₃ solution were performed. The effect of sorption studies presented the uptake of Co increased with the pH increasing from pH ~1 to pH ~8 and the isothermal sorption at pH ~6 showed that γ-MnO₂ possessed the highest uptake amount 0.44 meq/g, and the highest distribution coefficient 2.5 × 10⁵ mL/g. Moreover, γ-MnO₂ was found without Mn³⁺/Mn²⁺ leached during the sorption process. The ion exchange-surface complexation model was adopted to study the titration, effect of pH and isotherm sorption on the ion exchange reaction mechanism of Co adsorption. Overall, this work provides an economically feasible and environmentally friendly method to recycle the spent LIBs and the γ-MnO₂ synthesized from the recovered LiMn₂O₄ was proved to be promising adsorbents for Co removal.

Decontamination of U(VI) on graphene oxide/Al2O3 composites investigated by XRD, FT-IR and XPS techniques

The decontamination of U(VI) on graphene oxide/nano-alumina (GO/Al₂O₃) composites were investigated by batch, XRD, FT-IR and XPS techniques. The characterization results showed that GO/Al₂O₃ composites presented a variety of oxygen-containing functional groups, which provided the more surface reactive sites. The batch experiments indicated that sorption equilibrium of U(VI) on GO/Al₂O₃ composites was achieved within 30 min, and the maximum sorption capacity derived from Langmuir model was 142.8 mg/g at pH 6.5. In addition, the slight decrease of sorption capacity was observed even after fifth recycling times. These results indicated that GO/Al₂O₃ composites displayed the fast sorption rate, high sorption capacity and good regeneration performance. No effect of ionic strength revealed the inner-sphere surface complexation of U(VI) on GO/Al₂O₃ composites. FT-IR and XPS analysis demonstrated that the high adsorption of U(VI) on GO/Al₂O₃ was attributed to the various oxygen-bearing functional groups. In addition, the nano Al₂O₃ was transferred to amorphous AlO(OH) mineral phase by XRD pattern, which provided the additional reactive sorption sites. These observations indicated that GO-based composites can be regarded as a promising adsorbent for immobilization and pre-concentration of U(VI) from aqueous solutions in the environmental remediation.

Enhanced Adsorption of Zn(II) onto Graphene Oxides Investigated Using Batch and Modeling Techniques

Graphene oxide (GO) was synthesized and employed as an adsorbent for Zn(II) removal from an aqueous solution. The adsorption isotherms showed that Zn(II) adsorption can be better described using the Freundlich model than the Langmuir model. The maximum adsorption capacity of Zn(II) on GO determined using the Langmuir model at pH 7.0 and 293 K was 208.33 mg/g. The calculation of thermodynamic parameters revealed that the process of Zn(II) adsorption on GO was chemisorptions, endothermic, and spontaneous. Kinetic studies indicated that the pseudo-second-order kinetic model showed a better simulation of Zn(II) adsorption than the pseudo-first-order kinetic model. On the basis of surface complexation modeling, the double layer model provided a satisfactory prediction of Zn(II) by inner-sphere surface complexes (for example, SOZn⁺ and SOZnOH species), indicating that the interaction mechanism between Zn(II) and GO was mainly inner-sphere complexation. In terms of reusability, GO could maintain 92.23% of its initial capability after six cycles. These findings indicated that GO was a promising candidate for the immobilization and preconcentration of Zn(II) from aqueous solutions.

Removal of Pb(ii) by nano-titanium oxide investigated by batch, XPS and model techniques

The ion exchange and inner-sphere surface complexation were inferred as the adsorption mechanisms of Pb(ii) on nano-TiO₂.