Semiconductor photocatalysis has long been considered as a promising approach for water pollution remediation. However, limited by the recombination of electrons and holes, low kinetics of photocatalysts and slow reaction rate impede large-scale applications. Herein, we addressed this limitation by developing a triphase photocatalytic system in which a photocatalytic reaction is carried out at air-liquid-solid joint interfaces. Such a triphase system allows the rapid delivery of oxygen, a natural electron scavenger, from air to the reaction interface. This enables the efficient removal of photogenerated electrons from the photocatalyst surface and minimization of electron-hole recombination even at high light intensities, thereby resulting in an approximate 10-fold enhancement in the photocatalytic reaction rate as compared to a conventional liquid/solid diphase system. The triphase system appears an enabling platform for understanding and maximizing photocatalyst kinetics, aiding in the application of semiconductor photocatalysis.

We compare a coherent Raman imaging modality, broadband coherent anti-Stokes Raman scattering (BCARS) microscopy, with spontaneous Raman microscopy for quantitative and qualitative assessment of multicomponent pharmaceuticals. Indomethacin was used as a model active pharmaceutical ingredient (API) and was analyzed in a tabulated solid dosage form, embedded within commonly used excipients. In comparison with wide-field spontaneous Raman chemical imaging, BCARS acquired images 10× faster, at higher spatiochemical resolution and with spectra of much higher SNR, eliminating the need for multivariate methods to identify chemical components. The significant increase in spatiochemical resolution allowed identification of an unanticipated API phase that was missed by the spontaneous wide-field method and bulk Raman spectroscopy. We confirmed the presence of the unanticipated API phase using confocal spontaneous Raman, which provided spatiochemical resolution similar to BCARS but at 100× slower acquisition times.

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Summary Photocatalytic oxygen reduction has garnered attention as an emerging alternative to traditional anthraquinone oxidation process to synthesize H 2 O 2 . However, despite great efforts to optimize photocatalyst activity, the formation rate has been largely limited by the deficient accessibility of the photocatalysts to sufficient O 2 in water. Here we boost the reaction by reporting an air-liquid-solid triphase photocatalytic system for efficient H 2 O 2 generation. The triphase system allows reactant O 2 to reach the reaction interface directly from the ambient atmosphere, greatly increasing the interface O 2 concentration, which in turn simultaneously enhanced the kinetics of formation constant and suppressed the unwanted electron-hole recombination and the kinetics of H 2 O 2 decomposition reaction. Compared with a conventional liquid-solid diphase reaction system, the triphase system enables an increase in H 2 O 2 formation by a factor of 44. The triphase system is generally applicable to fundamentally understand and maximize the kinetics of semiconductor-based photocatalytic oxygen reduction for H 2 O 2 generation.

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