Effective removal of hexavalent chromium from aqueous system by biochar-supported titanium dioxide (TiO

Abstract

Environmental context Photocatalytic TiO2 materials are good prospects in water quality treatment due to their stable chemical properties and limited secondary pollution. TiO2 photocatalytic material prepared with biochar as a carrier can greatly improve the photocatalytic efficiency of CrVI, and the removal rate of CrVI can reach 84.4%. This study shows that biochar-supported TiO2 photocatalytic composites are feasible for the green and efficient removal of CrVI from an aqueous phase. Rationale TiO2 has great application prospects in the treatment of chromium-containing wastewater due to its photochemical stability and low toxicity. Loading TiO2 on solid adsorption materials can improve the photocatalytic efficiency and solve the problem of difficult separation and recovery of TiO2. Methodology In this study, biochar-supported TiO2 (BC-TiO2) and acid-washed biochar-supported TiO2 (HBC-TiO2) were prepared by a sol–gel method using biochar (BC) and acid-washed biochar (HBC) as adsorption carriers. The effects of various experimental parameters such as ultraviolet irradiation conditions, catalyst dose and pH on the removal efficiency of CrVI by BC, HBC, BC-TiO2 and HBC-TiO2 were investigated. The structure and morphology of the four materials were characterised. Results The results indicated that under the optimal reaction conditions (pH = 6, dosage of biochar materials/photocatalytic composites = 5 g/6 g), the removal percentage of CrVI changed as BC-TiO2 (Light) (84.43%) > HBC-TiO2 (Light) (80.19%) > BC-TiO2 (Dark) (57.9%) > HBC-TiO2 (Dark) (52.94%) > HBC (30.06%) > BC (14.66%). Loading TiO2 on biochar materials improved the specific surface area and increased the reaction sites when compared with BC and HBC. Discussion This study shows that BC-TiO2 is more suitable to remove CrVI from an aqueous system because of its high removal efficiency. The enrichment of CrVI on the biochars and the close contact between the biochar and TiO2 through the Ti–O–C dense heterojunction promote the interfacial transfer of CrVI, which is the key to the removal of CrVI. This study has great significance for the treatment of chromium-containing wastewater by photocatalytic composites.