The design of photocatalysts with hierarchical pore sizes is an effective method to improve mass transport, enhance light absorption, and increase specific surface area. Moreover, the construction of a heterojunction at the interface of two semiconductor photocatalysts with suitable band positions plays a crucial role in separating and transporting charge carriers. Herein, ZIF-8 and urea are used as precursors to prepare hierarchically porous ZnO/g-C3N4 S-scheme heterojunction photocatalysts through a two-step calcination method. This S-scheme heterojunction photocatalyst shows high activity toward photocatalytic H2O2 production, which is 3.4 and 5.0 times higher than that of pure g-C3N4 and ZnO, respectively. The mechanism of charge transfer and separation within the S-scheme heterojunction is studied by Kelvin probe, in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS), and electron paramagnetic resonance (EPR). This research provides an idea of designing S-scheme heterojunction photocatalysts with hierarchical pores in efficient photocatalytic hydrogen peroxide production.

Developing a high‐performance photocatalyst is important for realizing efficient photocatalytic H2O2 generation. Herein, a novel step‐scheme (S‐scheme) heterojunction photocatalyst C3N4/PDA (CNP) comprised of ultrathin g‐C3N4 (U‐CN) and polydopamine (PDA) is constructed by in situ self‐polymerization. The optimal photocatalyst presents an excellent H2O2 production rate of 3801.25 µmol g−1 h−1 under light irradiation, which is about 2 and 11 times higher than that of pure U‐CN and PDA, respectively, and exceeds most of the reported C3N4‐based photocatalysts. The improvement of photocatalytic activity is ascribed to the synergistic effect of improved light absorption and promoted charge separation and transfer induced by the S‐scheme heterojunction. In situ irradiated X‐ray photoelectron spectroscopy (ISI‐XPS) reveals that the charge transfer route matches the S‐scheme mechanism. Rotating disk electrode (RDE) measurements and electron spin resonance (ESR) spectroscopy verify that H2O2 is produced by a two‐step one‐electron process. This work highlights a promising method to construct high‐performance S‐scheme heterojunction photocatalysts through the hybridization of PDA and C3N4.

Catalytic conversion of aromatic olefins into carbonyl compounds is a critical reaction in chemical industries. Herein, we constructed a series of pyrene-alt-dibenzothiophene-S,S-dioxide (P16PySO)/tungsten trioxide (WO3) composites to investigate the mechanism of photocatalytic styrene oxidation under anaerobic and aerobic conditions. The S-scheme charge transfer pathway within P16PySO/WO3 was systematically analyzed. Under anaerobic conditions, the optimized P16PySO/WO3 photocatalyst exhibited a moderate styrene conversion rate with continuous H2 evolution. Under aerobic conditions, the activity of styrene oxidation was promoted, but H2 production was dramatically inhibited. The detection of reactive oxygen species and scavenger-assisted photocatalytic experiments revealed that triplet oxygen (3O2) could efficiently trap the energy of triplet excited P16PySO through an energy transfer process and convert to singlet oxygen (1O2). In situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory indicate that the highly reactive 1O2 plays an important role in styrene oxidation to dioxetane intermediates, realizing selective cleavage of styrene.

Photocatalytic production of H 2 O 2 from water and atmospheric oxygen has been recognized as a green and sustainable chemical process, due to the abundance of raw materials and sustainable solar energy. Herein, flower-like hierarchical ZnO microspheres were prepared by hydrothermal method followed by calcination at different temperatures, and their photocatalytic performance in H 2 O 2 production was examined under simulated sunlight irradiation. The calcination temperature plays a vital role in the structure, morphology, and surface area of the final ZnO products as well as their optical and electrochemical properties, which are determining factors in their photocatalytic activity. The ZnO calcined at 300 °C (Zn-300) exhibits the highest activity and optimal stability, showing productivity of 2793 μmol l −1 within 60 min of irradiation, which was 6.5 times higher than that of uncalcined ZnO precursor. The remarkable photocatalytic activity is attributed to enhanced light utilization, large surface area, abundant exposed active sites, improved separation efficiency, and prolonged carrier lifespan. Moreover, the results from cycling experiments indicate the as-prepared ZnO samples exhibit good stability and long-time performance. This work provides useful information for the preparation of hierarchical ZnO photocatalysts.

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