Facile synthesis of coal tar residue based porous carbon/MnO2 composite for eminent thallium(I) removal from wastewater

Thallium (Tl) is a typical hypertoxic heavy metal, its accumulation in the water environment can have serious impacts on ecosystems and human health. In this study, a composite material (PC@MnO 2 ) was designed for removing Tl(I) by grafting MnO 2 onto coal tar residue-based porous carbon (PC) via hydrothermal impregnation. δ-MnO 2 with nano flower-like structure was verified to be evenly distributed on PC surface through material characterizations. The adsorption performance was markedly elevated after loading MnO 2 on PC, and the optimal adsorbent (PC@MnO 2 -75) was prepared by hydrothermal process from KMnO 4 (75 mg) using PC (100 mg) as a reducing agent. The adsorption of Tl(I) onto PC@MnO 2 -75 has achieved equilibrium in 90 min, slightly affected by solution pH (4−12), and exhibited an outstanding adsorptive selectivity in the presence of high concentrations of K + , Na + , Ca 2+ , Mg 2+ , Cl - , CO 3 2- , humic acid, and fulvic acid. The pseudo second order kinetic and Freundlich isotherm models were preferably described as the adsorptive characteristics. And the Tl(I) removal was a spontaneous exothermic adsorptive process. Density functional theory (DFT) results manifested that Mn doping enhanced electron transfer rate during adsorption. The highly efficient removal of Tl(I) on PC@MnO 2 -75 was achieved via electrostatic interaction, complexation, and oxidation-adsorption. The porous carbon derived from coal tar residue was engineered into PC@MnO 2 composites for efficient Tl(I) removal, which was in line with the environmental protection concept of sustainable development and green production.