Dual-pathway reactive species evolution over novel N-doped Bi9O13.5Cl2/g-C3N4 scaffolding heterojunction: Investigation of dark and light-induced micropollutant decomposition

Abstract

The mechanism underlying reactive species (RSs) evolution in photo-based advanced oxidation processes (AOPs) under continuous conditions has not been well characterized and investigated in the existing scientific literatures. A scaffolding heterojunction comprising N-doped graphitic carbon nitride with novel Bi₉O_13.5Cl₂ photocatalyst (NBCN) was successfully fabricated, achieving 96.7 % for TC degradation compared to 63.4 % for non-doped BCN. Comprehensive characterization analyses demonstrated exceptional charge-carrier separation dynamic through composite heterojunction. Under illuminated conditions, we identified two main RSs formation routes: an O₂-mediated pathway and a h ⁺ -mediated pathway. Comparative kinetic analysis revealed the critical role of O₂ activation, showing a remarkable 6.2-fold enhancement in kinetic rate constant for organic pollutant degradation under O₂-ambient condition (k = 3.1 × 10⁻² min⁻¹) compared to the anaerobic environment (k = 5 × 10⁻³ min⁻¹). Primary RSs were identified and ranked in order of significance as ¹O₂ > ^•O₂⁻ > h⁺ > ^•OH. Theoretical calculations further revealed that the promoted photocatalytic performance was achieved through favorable adsorption energy, promoted electron redistribution by N-doping and well-defined formation pathways of O₂-mediated RSs. Under dark conditions, significant amounts of dark-generated h⁺ were detected in NBCN, where its hydrophilic nature facilitated the formation of transient ^•OH. The practical applicability of the system was validated through real water matrix tests, highlighting the robust performance of the O₂ activation and ¹O₂ production. By elucidating the mechanism of continuous contaminant degradation under entire round-the-clock scenarios, this study advances the development of sustainable environmental remediation technologies in low temperature environment across various water matrices.