Monolayer H1.4Ti1.65O4 center dot H2O nanosheet (denoted as NST) has been prepared as a photocatalyst for the oxidation of furfuryl alcohol (denoted as FA) to furaldehyde under visible light irradiation. The photocatalytic activity of NST is over 10 times higher than that of its layered counterpart. This enhanced activity may be attributed to the high percentage of exposed Lewis acid sites in NST. The in-situ FTIR result suggests that FA are efficiently chemosorbed on the exposed Lewis acid sites forming the surface coordination species via C-O groups, resulting in the activation of FA. The surface coordination species would respond to visible light absorption. Furthermore, The XAFS result shows that the signals for Ti-O and Ti-Ti in NST are weaker dramatically and the signals positions are shifted by 0.03 angstrom in the higher R direction as compared with those in layered counterpart, suggesting the more exposed Ti and 0 defects in NST. The oxygen molecules absorbed on these surface defects are activated forming center dot O-2(-) by photo-electrons under visible light irradiation. Finally, a possible mechanism has been proposed at a molecular level.