Sustainable treatment of harmful dyeing industry pollutants using SrZnTiO3/g-C3N4 heterostructure with a light source-dependent charge transfer mechanism

Abstract

Abstract Herein, we build on the results of previous works describing the use of advanced photocatalytic processes for effective industrial wastewater treatment and investigate SrZnTiO3/g-C3N4 heterostructure (SZTO/CN)-catalyzed removal of rhodamine B (RhB) and indigo carmine (IC), probing the effects of the light source (UV and visible) on charge transfer (Z-scheme and non-Z-scheme) in the above heterostructure. Both RhB (cationic dye) and IC (anionic dye) could be efficiently removed by SZTO/CN, which also exhibited elevated photocurrent responses. In particular, the efficiencies of IC and RhB removal over a SZTO/CN sample with a CN/(SZTO\u2009+\u2009CN) mass ratio of 0.8 after 3-h visible-light irradiation equaled 93.1 and 82.2%, respectively, while the respective values for STO were obtained as 9.7 and 21.8%. Dye degradation under UV light irradiation (e.g., within 30\u2009min for IC) was much faster than under visible light irradiation (e.g., within 180\u2009min for IC), and optimal CN/(SZTO\u2009+\u2009CN) ratios were individually determined for both irradiation types. Notably, the best performing catalyst maintained over 95% of its initial photocatalytic performance after five consecutive IC decomposition runs, and the X-ray diffraction patterns of cycled and non-cycled catalysts indicated that cycling did not induce any notable crystalline structure changes. The reactive species involved in photocatalytic degradation were identified as O2•–, h+, and OH• for both light source types, which, together with the results of band energy structure analysis and hydroxyl radical population measurements allowed us to propose two light source-dependent photocatalytic dye removal mechanisms. Thus, it was concluded that the developed SZTO/CN heterostructure can be sustainably applied to the treatment of dye-contaminated wastewater.