In photocatalytic reactions, the interfacial transfer of electrons from semiconductor nanostructures to cocatalysts is the key step that determines the utilization of photogenerated charges and is sensitively influenced by the behaviors of this electronic process. Under weak illumination, photocatalytic reaction rates deviate from linearity to incident light intensity (r = k ss·P inc α, with α → 0.5), because charge recombination predominates interfacial transfer. When the irradiation intensity is high, theoretically, thermionic emission would be the major electronic process (r = k te·P inc α, with α → 2). The ratio of photocatalytic reaction rate to incident light intensity that mainly reflects the energy utilization would encounter a minimum along the variation of irradiation intensity. This crucial relationship, however, has hardly been consciously considered. In this work, inspired by theoretical simulation, we demonstrate that sunlight-driven photocatalysis is generally on the bottom of the energy utilization curves for certain common semiconductors (CdS, TiO2, or C3N4).

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We report a new and effective method to prepare high activity graphitic carbon nitride (g-C3N4) by a simple ammonia etching treatment. The obtained g-C3N4 displays a high BET surface area and enhanced electron/hole separation efficiency. The hydrogen evolution rates improved from 52 μmol h(-1) to 316.7 μmol h(-1) under visible light.

The construction of C−C bonds by coupling reactions is an important process in synthetic chemistry though expensive catalysts are required. Heterogeneous photocatalysis offers a platform for C−C coupling of aromatic halides via hydro-dehalogenation by employing alcohols as the hydrogen donor; however, a designed photocatalyst with high activity and selectivity is lacking. Here, we show that Cu is a promising candidate to promote the coupling of aromatic halides due to the optimized adsorption energy of the reaction intermediates (benzyl radical and Br atom) over a series of transition metals. The Cu-modified TiO 2 shows a remarkable apparent quantum efficiency (15%) and a great tolerance of harsh reaction conditions for the homocoupling of benzyl bromides into bibenzyl under UV irradiation. The low-cost photocatalyst also shows high performance upon scaling-up and selective coupling of a series of benzyl bromide derivatives, demonstrating the heterogeneous photocatalytic C−C coupling as an attractive process for applications. Additionally, the design strategy can be applied to modify other photocatalysts (i.e., g-C 3 N 4 ) to realize the C−C coupling of benzyl bromide under visible light.

Metal nanoparticles (NPs) are heavily involved in photocatalytic transformations to manipulate charge separation and storage, yet the catalytic role of metal NPs in tuning the selectivity of photoreactions is rarely addressed. Here, the photodehydrogenative coupling of primary amines is selected as the model reaction to probe the catalytic role of Pt and Pd NPs supported on graphitic carbon nitride (Pt/C 3 N 4 and Pd/C 3 N 4 ). When Pt/C 3 N 4 is employed as the photocatalyst, imine is produced via dehydrogenative homocoupling of primary amines owing to the weak adsorption of photogenerated imines and H atoms on Pt NPs. In comparison, Pd/C 3 N 4 promotes the consecutive hydrogenation of photogenerated imines into secondary amines due to a strong affinity of both imine and H atom for the surface of Pd NPs. This strategy is applicable for the synthesis of a series of imines and secondary amines with high yields.

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Despite thermodynamic feasibility, the high activation energy originating from potential barriers and trap states kinetically prevents the interfacial transfer of electrons from semiconductor nanostructures to reduction cocatalysts, resulting in a lowered utilization of photogenerated charge carriers in photocatalysis. Nanostructuring-induced narrowing of potential barriers offers a rational solution to kinetically facilitate interfacial electron transfer by tunneling. Here, inspired by theoretical simulation, we manage to promote the separation of photogenerated charge carriers by coating the semiconductor nanostructures with a homogeneous interlayer. The low activation energy for interfacial electron transfer endows photocatalysis with nearly constant quantum yields and a quasi-first-order reaction to the incident photons and grants evident superiority over the photocatalyst without interlayers, especially under sunlight. In our demonstrated sunlight-driven hydrogen evolution integrated with benzylamine oxidation, the production rates for both reduction and oxidation half-reactions reach as high as ∼0.77 mmol dm–2 h–1, which are ∼10 times higher than that without an interlayer.