Removal of chlorhexidine digluconate from aqueous solution by heterogenous photocatalysis using sunlight-driven Ni-doped TiO2 material

Abstract

Photoactive Ni-TiO2 was synthesized through green hydrothermal method with preferential photocatalytic performance in visible and solar light for synthetic and formulated wastewater treatment. Incorporation of this transition metal into TiO2 was examined by XRD, FTIR, UV–visible DRS, XPS, SEM-EDS and HRTEM analysis. According to the Langmuir–Hinshelwood model, the photodegradation of the chlorhexidine digluconate under solar (R2=0.986) and simulated visible light (R2=0.982), follows a pseudo-first-order kinetics. The interaction of operational fractions, such as S/C ratio, irradiation time, and pH of the reaction mixture, were evaluated using the RSM. Although complete mineralization of CHD was not achieved using Ni-TiO2 under visible light, but the parent compound was mineralized to some extent, as demonstrated by TOC reduction (85.71%-synthetic wastewater and 61.17%-formulated wastewater), UV254 (89.91% synthetic wastewater and 55.39%-formulated wastewater) and UV280 (68.23%-synthetic wastewater and 68.23%-formulated wastewater) absorbance variations. Based on the identified transformed products, the possible degradation pathway was proposed and bacterial susceptibility test on Bacillus cereus DPAML065 was performed to evaluate the toxicity of oxidation intermediates. Comparative studies about energy consumption and removal efficiency during simulated visible light/Ni-TiO2 and sunlight/ Ni-TiO2 mediated treatment system for formulated wastewater revealed that sunlight/ Ni-TiO2 mediated treatment system was high energy efficient (1.67 kWhKg-1) system.