A dual-function photocatalytic system for simultaneous separating hydrogen from water splitting and photocatalytic degradation of phenol in a twin-reactor

Abstract

Coupling photocatalytic H2 evolution and phenol degradation have drawn much attention on H2 as clean energy and phenol as an organic pollutant to the environment. Such dual-function reaction can utilize the chemical potential of phenol oxidation to make up the chemical potential required for hydrogen evolution from water splitting. The production of H2 thus was enhanced via the phenol oxidation. However, H2 is still needed to be purified from the reaction products by traditional methods. In this study, we demonstrated the simultaneous separation of H2 using a photo twin-reactor under artificial sunlight, in which the photocatalytic efficiency was substantially increased due to the inhibition of backward reaction by separating H2 from the products directly. Three Rh-doped SrTiO3 (STO) photocatalysts calcined at 900, 1100, 1200 °C (named as STO:Rh900, STO:Rh1100, and STO:Rh1200, respectively) were prepared by solid-state fusion reaction, then photo-deposition method was applied to synthesize Pt loading STO:Rh. All photocatalysts were fully characterized by XRD, XPS, UV–vis, SEM, TEM, and DLS. A single reactor and a twin-reactor (Z-scheme system) were systematically designed by using Pt/STO:Rh for H2 evolution photocatalyst and WO3 for phenol oxidation photocatalyst, where Fe3+/Fe2+ pairs were served as electron transfer mediators to conduct the dual-function reaction. In the single reactor, the stoichiometric of the dual-function reaction was proposed and with high consistency to the experimental data. By using the twin-reactor, H2 production rate increased 2.7 times, reaching 1.90 μmol g−1 h−1, compared to that in the single reactor. Moreover, the H2 concentration of the gas-phase products increased from 70% (in the single reactor) to 94% owing to the separation function of the twin-reactor, which would significantly reduce the cost for further purification. The effect of phenol concentration on H2 production in the twin-reactor was also thoroughly investigated. The results showed that increased phenol initial concentration would enhance the production of H2. With 200 μmol L−1 phenol, the H2 yield (11.37 μmol g−1 in 6-h reaction) was increased by 20% compared to that of pure water splitting.