Carbon Nitride-Modified Defective TiO2–x@Carbon Spheres for Photocatalytic H2 Evolution and Pollutants Removal: Synergistic Effect and Mechanism Insight

Inducing TiO2 sensitive to visible light and effectively restraining the possibility of electron–hole recombination are crucial for actual applications over TiO2-based catalysts. In this study, a facile strategy to fabricate three-dimensional (3D) defective TiO2–x@carbon spheres (CSs) composite modified with two-dimensional (2D) graphite-like carbon nitride (g-C3N4) nanosheets (NSs) is presented. During the synthesis process, zero-dimensional tiny TiO2–x nanoparticles were evenly loaded onto CSs with intimate chemically bonded (Ti–O–C) interfaces. Simultaneously, loose g-C3N4 NSs were tightly coated on the hierarchical spherelike TiO2–x@CSs, with the purpose of supporting an effectively protective layer to prevent the oxidation of the directly exposed Ti3+ and constructing highly efficient 2D/3D ternary heterostructures with strong interfacial interaction. The obtained CSs/TiO2–x@g-C3N4 heterojunction showed remarkably enhanced photocatalytic activity in hydrogen production and toxic pollutants degradation compared to the binary composites or pristine components, mainly due to the cooperative effects of the enhanced visible-light-harvesting capacity introduced by Ti3+ and CSs, effective interfacial charge separation (Ti–O–C structure and heterostructure), and the vectorial charge-transfer channel design. This work paves a green, gentle, and economical way to design more efficient TiO2–x new ternary materials with multistep electron transfer toward solar energy conversion (like CO2 reduction and H2 evolution).