This study demonstrates the co-catalytic effect for selective hydrogenation of a particular group in a multifunctional organic compound. Transmission electron microscopy (TEM) studies revealed that Au loaded nanoparticles were found to be of similar to 3.89 nm and similar to 8.86 nm with 1 wt% and 3 wt% metal loading respectively by homogeneous deposition precipitation (HDP) method over synthesized mesoporous titanium dioxide (m-TiO2) nanoparticles. The Au particles were deposited in the metallic state which was confirmed from X-ray photoelectron spectroscopy (XPS) with a binding energy of 84.0 eV and 87.7 eV credited to 4f(5/2) and 4f(7/2) spin states respectively. In this Au-mTiO(2) heterojunction, metal particles found to be decisive for 100% selective hydrogenation of 1,3-dinitrobenzene under visible light. Predominantly, m-nitroaniline formed when 1,3-dinitrobenzene was treated with 1 wt% Au-mTiO(2) whereas 100% photoreduction of both nitro groups occurred with 3 wt% Au-mTiO(2). Hence, 1,3-dinitrobenzene exhibited particle size sensitive photocatalytic hydrogenation under mild conditions without using any reducing agent. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.