Boosting photocatalytic CO2 reduction over S-scheme CTF–Bi–BiOBr using pre-oxidized dissolved effluent organic matter as an electron donor

Abstract

Photocatalytic conversion of CO₂ into value-added products is considered a sustainable strategy to mitigate CO₂ over-emission. However, achieving favorable performance generally relies on valuable additives such as sacrificial organic electron donors, which, in turn, limit its applicability. In this study, we tested dissolved effluent organic matter (dE_fOM) derived from domestic wastewater as an alternative hole scavenger during CO₂ photoreduction over a ternary photocatalyst (CTF-1–Bi–BiOBr) composed of CTF-1, Bi, and BiOBr. Impressively, the optimal CTF-1–Bi–BiOBr catalyst demonstrated remarkable dE_fOM degradation and CO production (2.933 μmol g⁻¹ h⁻¹) in a cascading oxic–anoxic photocatalytic process. This enhanced activity was attributed to the establishment of an S-scheme structure between CTF-1 and BiOBr, with Bi-metal serving as the carrier recombination centre, allowing holes and electrons with greater redox capacity to be retained. Importantly, we discovered that smaller intermediates formed during the oxic stage can serve as extraordinary electron donors in the succeeding anoxic stage. Spectroscopic and electrochemical characterization techniques revealed that pre-oxidized dE_fOM was more effective in preventing the recombination of photoinduced carriers compared to untreated dE_fOM, highlighting its improved electron donating propensity. This study provides innovative insights for simultaneously achieving wastewater purification and carbon emission reduction through a more economical pathway.