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 efficient utilization of visible light catalysts for organic reactions necessitates not only the effective separation of photogenerated electrons and holes to participate in the reaction, but also their ability to form key intermediates with reactant molecules. The present study successfully synthesized a crusiform-like mesoporous structure of nitrogen-doped carbon-coated Cu₂O/Cu (Cu₂O/Cu/N-C) with a Cu₂O/dual electron acceptor interface using etched HKUST-1 as the precursor. A series of theoretical and experimental studies have demonstrated that the Cu₂O/Cu/N-C interface in the photocatalytic homo-coupling of terminal alkynes not only effectively enhances the separation of photogenerated electron−hole pairs, but also facilitates the formation of the key intermediate [Cu₂O/Cu/N-C]-phenylacetylide and promotes the rearrangement of its internal charges. As a result, the homo-coupling reaction can be effectively facilitated. The primary reason for the functional role of Cu₂O/Cu/N-C interface lies in the downward bending of energy band from Cu₂O to N-doped C layers, induced by the different work functions of Cu₂O, Cu and N-doped C layers. Consequently, Cu₂O/Cu/N-C photocatalysts demonstrate exceptional photocatalytic activity in the homo-coupling reaction of terminal alkynes under blue-light irradiation and air atmosphere. The present study presents a novel research methodology for the development of highly efficient visible light catalysts to facilitate organic reactions in future applications.