A comparative study of metal-sulphide/ZnO for visible-light-induced photocatalysis and the six-flux photon absorption model of an external lamp photoreactor

Abstract

This study compares the photocatalytic performance of three metal-sulphide/ZnO nanocomposites (Ag2S/ZnO, FeS/ZnO and NiS/ZnO) for degrading tetracycline (TC) under visible light irradiation. The nanocomposites were synthesized using a novel one-pot solid-phase combustion method, analysed by various characterization techniques (XRD, SEM, TEM, BET, FTIR, PL, and UV–vis DRS). Photocatalytic tests revealed significantly higher efficiencies for Ag2S/ZnO (87.50 %), FeS/ZnO (80.53 %) and NiS/ZnO (77.27 %) nanocomposites exhibit much higher photocatalytic efficiency than pure ZnO (42.63 %). The improved performance is attributed to the reduced bandgap energy and suppressed electron-hole (e-/h+) recombination facilitated. This can also be attributed to the photocatalytic inhibition test which confirmed the holes (h+) as the main inhibitor and identified the superoxides (O2•−) radical as the main active specie responsible for the degradation. Additionally, this study innovatively applies the Six Flux radiation absorption-scattering models (SFM) to an external lamp photocatalytic reactor. This approach allows precise determination of reactor parameters and intrinsic reaction kinetics for TC degradation, independent of the radiation field. The TC degradation rate, calculated at 5.6 × 104EinL−1S−1 for every point in the reaction space, shows a half-order dependence on the local volumetric rate of photon absorption (LVRPA) of 142.3 W/m3, at a photon flux of 115.42 W/m2. These findings elucidate the mechanisms behind enhanced visible-light photocatalysis and demonstrate the innovative application of photon absorption and light-scattering models to optimize reactor design and efficiency. This work offers valuable insights for developing advanced photocatalytic systems with improved performance and practical applicability.