In this work, size-controllable Au NPs-coated TiO2 are synthesized by adjusting the pH of solutions based on sonoelectrochemical methods. The size-controlled Au NPs on TiO2, ranging from 2 to 80 nm in diameter, can be obtained by varying the pH of solutions from 3 to 7 and further placement for 3 h before sonoelectrochemical reductions. Experimental results indicate that the catalytic activity of synthesized Au NPs for the decomposition of acetaldehyde in solution increases with a decrease of particle size. However, bigger Au NPs with 80 nm in diameter still demonstrate slight activity for the decomposition of acetaldehyde due to the formation of Au/TiO2 nanocomposites. (C) 2012 Elsevier Ltd. All rights reserved.