To simultaneously improve the critical factors in photocatalytic H₂ production, the population of active photogenerated electrons, the adsorption and activation of H₂O molecules, and the surface dehydrogenation efficiency, we propose a synergistic strategy for TiO₂ modification by combining transition metal (TM) doping and N-doped carbon (N-C) coating. The targeted Cr-TiO₂@N-C heterojunction exhibits dramatically enhanced H₂ production under blue light irradiation, contrasting sharply with a negligible production by pristine TiO₂. Comprehensive structural characterization and theoretical calculations confirm the uniform substitution of Cr into the TiO₂ lattice, promoting the formation of adjacent oxygen vacancies (V_O). The synergistic effect of Cr doping and V_O extends the light absorption range into the visible region. The coated N-C layer facilitates the efficient separation of photogenerated charge carriers, boosting the population of active electrons. Critically, the combined action of V_O and N-C layer enhances the adsorption and activation of H₂O molecules while effectively improving the subsequent surface dehydrogenation efficiency. Significantly, this strategy demonstrates broad universality: Analogous TM-TiO₂@N-C heterojunctions (TM = Mn, Co, Ni, Cu, and Zn) synthesized via the same approach all show substantially improved H₂ production performance over pristine TiO₂.

The application of semiconductors-based photocatalysts in organic transformation has been limited by the low light utilization efficiency and the rapid recombination of photo-induced charge carriers. In this paper, we have successfully fabricated a hollow cuboctahedral nanostructure (CNNCH), which is composed of N-doped carbon layer and CuO/NiO p-n heterojunctions. The hollow structure in CNNCH can effectively favor the light utilization through the multiple light reflection and scattering. The separation of photo-induced charge carriers can be highly improved by the exitence of charge transfer pathways between the p-n heterojunctions and semiconductor/N-doped carbon layer interfaces. Due to the above advantages, hollow cuboctahedral CNNCH as the photocatalyst has behaved high performance towards the photocatalytic cross-dehydrogenative coupling reaction.