The ultra-small Ag nanocrystallite-decorated TiO2 hollow sphere heterostructures were fabricated by using a two-step hydrothermal method. These heterostructures demonstrated an excellent photodegradation performance of rhodamine B. The photodegradation efficiency could reach up to 100 % within 20 min under simulated sunlight irradiation. XRD, field emission SEM, TEM, scanning TEM, high-resolution TEM coupled with energy-dispersive X-ray spectroscopy, UV/Vis absorption and photoluminescence spectroscopy, X-ray photoelectron spectroscopy, Mott–Schottky analysis, and hydroxyl radical measurements were used to correlate the structure, surface property, and energy band alignment of rhodamine B to its photocatalytic activity. In these metal–semiconductor heterostructures, the Ag nanocrystallites were highly crystalline and were distributed evenly on the surface of TiO2 hollow spheres with compact interfaces. They reduced the recombination rate of charge carriers and favoured the charge transfer across the interfaces. The increased surface adsorbed oxygen facilitated the generation of hydroxyl radicals, and the reduced surface defects increased the lifetime of charge carriers upon Ag loading. The Schottky barriers between Ag and illuminated TiO2, the upward shift of the Fermi level, and increased electron density due to Ag coupling contributed to the charge transfer and increase in quantum efficiency. These key factors involved in photocatalysis are of great importance to design functional and effective photocatalysts.
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