Engineered BaTiO₃/SnIn₄S₈ step–scheme nanocomposite with interfacial coupling for energy-efficient piezo-photocatalytic oxidation of tetracycline

¹ University of Johannesburg, Department of Chemical Science, Doornfontein Campus, Johannesburg, 2028, South Africa
² Department of Chemistry, Faculty of Natural and Agricultural Sciences, University of Pretoria, Private Bag X20, Hatfield 0028, Pretoria, South Africa
³ Council for Scientific and Industrial Research (CSIR), Pretoria Campus, Pretoria, 0001, South Africa
⁴ Centre for Nanomaterial Science Research, Department of Chemical Sciences, Doornfontein Campus, Johannesburg, 2028, South Africa

^* Nonhlangabezo Mabuba: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Tetracycline hydrochloride (TCH) has been recognized as one of the most problematic pollutants in water systems due to its extensive uses in medical and veterinary systems. Poor removal leads to persistent residues that lead to antibiotic resistance and ecological disruption. The nanosphere-on-nanoflower architecture of BaTiO₃/SnIn₄S₈ (BTO/SIS) was designed and fabricated via solvothermal synthesis using ethanol as a solvent, as an energy-efficient catalyst for piezo-phototronic applications. Characterization such as Mott-Schottky (M-S), scanning electron microscopy (SEM), and XRD were used to substantiate the nanoflower-decorated nanosphere composite heterojunction contact leading to the Step-scheme (S-scheme) band alignment promoting partial recombination through the internal electric field for enhanced charge separation, generation, and migration within the heterostructure. Owing to the synergistic effects of the S-scheme alignment and the hierarchical morphology, BTO/SIS (1:1) ratio achieved the removal of ~85% of the persistent tetracycline hydrochloride (TCH) in 120 minutes with minimal 70 W light illumination and low ultrasonication power of 6.8 W (20 kHz). The optimized BTO/SIS possessed a synergistic factor of 1.74 (>1), way higher than the single photocatalytic and piezocatalytic processes. Photoluminescence (PL), and electrochemical impedance spectroscopy (EIS) indicated longer lifetimes of charge carriers, lower charge transfer resistance, and lower rates of recombination. Interestingly, TCH as an amphoteric molecule was efficiently removed at an optimum pH of 7 where it is at its zwitterionic form. Trapping studies revealed that superoxides (•O₂⁻) were the major oxidants responsible for the degradation caused by efficient electron transfer and via indirect oxidation especially in S-scheme heterojunctions. This study not only demonstrated the energy-efficient 0D/3D BTO/SIS system but also showed that the nanosphere piezoelectric BTO with a photo-active nanoflower in an architecture S-scheme enhances mechanical deformation sensitivity, while maintaining high stability in piezo-photocatalytic degradation of organic pollutants in water.