The design and fabrication of TiO2/Bi4O5Br2 step-scheme heterojunctions for the photodegradation of gaseous hydrogen sulfide: DFT calculation, kinetics, pathways, and mechanisms

Abstract

ABSTRACT

It is a challenging task to efficiently convert deleterious hydrogen sulfide (H₂S) into less harmful products such as SO₄^2– species. In an effort to address such issue, a step-scheme (S-scheme) heterojunction photocatalyst has been built by concatenating TiO₂ (P25) and ultrathin Bi₄O₅Br₂ into TiO₂/Bi₄O₅Br₂ (namely, x-TB-y: x and y denote the molar ratio of TiO₂:Bi₄O₅Br₂ and pH value for solution-based synthesis, respectively) via in-situ hydrothermal method. The S-scheme charge transfer pathway in TB is confirmed by electron spin resonance and band structure analysis while experimental data and density functional theory calculations suggest the formation of an internal electric field to facilitate the separation and transfer of photoinduced charge carriers. Accordingly, the optimized heterojunction photocatalyst, i.e., 5-TB-9, showcases significantly high (> 99%) removal efficiency against 10 ppm H₂S in a 17 L chamber within 12 minutes (removal kinetic rate r: 0.7 mmol·h^–1·g^–1, specific clean air delivery rate SCADR: 5554 L·h^–1·g^–1, quantum yield QY: 3.24 E-3 molecules·photon^–1, and space-time yield STY: 3.24 E-3 molecules·photon^–1·mg^–1). Combined analysis of in-situ diffuse reflectance infrared Fourier transform adsorption spectra and gas chromatography-mass spectrometry allows to evaluate the mechanisms leading to the complete degradation of H₂S (i.e., into SO₄^2– without forming any intermediate species). This work demonstrates the promising remediation potential of an S-scheme TiO₂/Bi₄O₅Br₂ photocatalyst against hazardous H₂S gas for sustainable environmental remediation.