Small plasmonic Au nanoparticles (NPs)-decorated with TiO2 nanosheets were fabricated to improve the photocatalytic performance. The Au/TiO2 nanosheets with Au NPs of different sizes ranging from similar to 3 nm to 28 nm were prepared by using hydrothermally obtained TiO2 nanosheets as substrate via urea and light reduction method. During synthesis, the obtained Au NPs through urea reduction treatment in different calcination temperatures possessed smaller size (similar to 3-13 nm) than those of the light reduction method (similar to 28 nm). The introduced Au NPs were tightly loaded on the surface of TiO2 nanosheets through in situ growth reduction process of chloroauric acid. The emergence of smaller Au NPs promoted the photocatalytic performance over Au/TiO2 nanosheets. The as-prepared Au/TiO2 nanosheets with small Au NP sizes of similar to 3-5 nm showed the highest photocatalytic rate of hydrogen production (similar to 230 mu mol.h(-1)) under xenon lamp illumination, exceeding more than twice that of Au/TiO2 nanosheets with loading of larger Au NPs (similar to 28 nm). The favorable constituents and combination of Au/TiO2 nanosheets provided large surface adsorptive sites for reactant adsorption, introduced plasmonic effects and formed Schottky barrier junction via surface plasmon resonance. The Schottky barrier height was lower due to the presence of smaller Au NPs, thereby enhancing the charge separation through the Schottky transfer hub to neighboring TiO2 nanosheets. The synergistic effect between the plasmonic hot carrier-driven Au NPs and TiO2 nanosheets was discussed. The photocatalytic mechanism was also proposed for the fabrication of visible light restricted photocatalysts with smaller Au NPs. (C) 2019 Elsevier Inc. All rights reserved.