Nonthermal plasma-activated polyvalent cerium-manganese bimetallic (hydro)oxide-functionalized nanographene for the removal of thallium(I) contaminants and mechanism exploration

Abstract

Thallium(I) (Tl(I)) is a highly toxic substance with significant environmental toxicity, belonging to the high-toxicity category, with characteristics of chronic accumulation. In this study, cerium(IV) (Ce(IV)) was incorporated into nonthermal plasma (NTP)-irradiated polyvalent manganese (hydro)oxides and synchronously grafted onto nanographene to synthesize a new type of Mn-based adsorbent (NTP-P-Ce-Mn-NGs) with excellent adsorption capacities for Tl(I) contaminants, aiming to overcome the weak adsorption capacity of existing adsorbents for Tl(I) and propose a new approach to enhance their adsorption performance. The factors including the molar ratios of Ce(SO4)2 to MnCl2, the dosage of nanographene, and the irradiation time of NTP all significantly affected the synthesis of NTP-P-Ce-Mn-NGs. Both the participation of NTP and the intercalation of Ce(IV) exerted a potential influence on the adsorption improvement of Mn-based adsorbents towards Tl(l) contaminants. Different chemical valences of Ce and Mn species were observed in the synthesized adsorbent. More flocculated and amorphous fillings were generated in the adsorbent samples with both Mn and Ce, visually presenting the incorporation effect of Ce into the NTP-irradiated Mn (oxy)hydroxides. A maximum adsorption capacity of 352.18 mg/g was obtained by NTP-P-Ce-Mn-NGs at an initial pH of 11, an initial concentration of Tl(I) of 250 mg/L, and a dosage of adsorbent of 0.15 g/L. The kinetics models, including the pseudofirst-order, pseudonth-order, mixed 1,2-order, and hyperbolic tangent Ⅱ models, were all appropriate for analysing the heterogeneous adsorption process of NTP-P-Ce-Mn-NG towards Tl(I) ions under different pH conditions. The excessive OH− ions in the alkaline environment intensified the adsorption of Tl(I) ions onto the active sites of NTP-P-Ce-Mn-NGs and further strengthened the relevant chemical reactions in which the polyvalent Mn and Ce further oxidized Tl species from Tl(I) to Tl(III), induced internal dispersion of Tl ions by the nanographene into the molecular structure and achieved chemical immobilization.