Hollow TiO₂@TpPa S-Scheme Photocatalyst for Efficient H₂O₂ Production Through ¹O₂ in Deionized Water Using...

Hydrogen peroxide (H₂O₂) production through photocatalytic O₂ reduction reaction (ORR) is a mild and cost-efficient alternative to the anthraquinone oxidation strategy. Of note, singlet state oxygen (¹O₂) plays a crucial role in ORR. Herein, a hollow TiO₂@TpPa (TOTP) S-scheme heterojunction by the Schiff base reactions involving 1,3,5-triformylphloroglucinol (Tp) and paraphenylenediamine (Pa) for efficient photocatalytic H₂O₂ production in deionized water has been developed. Upon irradiation, rapid phototautomerization of TaPa from enol to keto form expands π-electron delocalization, facilitating effective conversion of the triplet excited state and consequent generation of ¹O₂. This mechanism is supported by time-resolved electron paramagnetic resonance (EPR) spectral analysis. Additionally, density functional theory calculations, in situ irradiated X-ray photoelectron spectroscopy, and femtosecond transient absorption spectroscopy reveal superior separation of photogenerated carriers in the TOTP S-scheme composites. In deionized water, the TOTP2.4 S-scheme heterojunction exhibits exceptional H₂O₂ production activity, yielding 891 µmol g^-1 h^-1, underscoring the critical role of ¹O₂ in the process. This research offers insights into the S-scheme heterojunctions and emphasizes the pivotal role of ¹O₂ in enhancing H₂O₂ production efficiency.