Cerium oxide modified activated carbon as an efficient and effective adsorbent for rapid uptake of arsenate and arsenite: Material development and study of performance and mechanisms

Co-existence of arsenate and arsenite in groundwater poses a great risk to humans. The objective of this study was to develop a cerium oxide modified activated carbon and to study its performance for removal of arsenic species. The adsorbent was prepared by a one-step solvothermal process. The FESEM-EDX analysis showed that the cerium oxide was mainly coated on the carbon surface. The thermal gravimetric analysis indicated the abundant presence of hydroxyl groups on the adsorbent. The point of zero charge was approximately 6.0. The uptake of arsenic species was highly affected by solution pH. The maximum adsorption capacities of As(V) and As(III) at pH 5 were 43.60 and 36.77 mg-As/g, respectively. A rapid adsorption causing 90% of ultimate uptake in 30 min was observed in the adsorption kinetics study, which outperformed other reported adsorbents; the better fitting of the experimental data was obtained by a pore diffusion model. The presence of phosphate exhibited the most significant interference on the adsorption. A limited interference was caused by the existence of humic acid, sulphate and carbonate, in particular at low concentration levels. Based on the results from the X-ray photoelectron spectroscopy analysis, nearly 90% of cerium element on the adsorbent was Ce(IV). The high redox potential of Ce(IV) was responsible for the partial oxidation of As(III) during the removal, which improved the As(III) uptake. The ligand exchange between hydroxyl groups on the adsorbent and arsenic species played a key role in the uptake of arsenic.