This paper highlights the comparative co-catalytic efficiency of different shapes of prepared Ag nanoparticles of size much larger as well as smaller than titania for the Ag-TiO2 photocatalysis. Quantum sized Ag nanospheres (4-8 nm), nanorod (length 70-75 nm and width 30-38 nm), polygonal nanosphere (80-120 nm) and truncated triangles (side length 70-140 nm) are prepared by solvothermal process. The co-catalytic activities of these Ag nanostructures were investigated by mixing them with TiO2 for the photocatalytic degradation of aqueous salicylic (0.5 mM) and benzoic acid (0.5 mM) under UV light (125 W-Hg arc, 10.4 mW cm(-2)) irradiation. The Ag co-catalysis effect imparted to TiO2 follows as polygonal nanosphere > nanorod > truncated triangle > small nanosphere due to the formation of many Ag-TiO2 interfaces by a single large-sized Ag nanoparticle than smaller one. As the surface coverage of Ag particles by TiO2 decreases, the Ag-TiO2 photoactivity is decreased accordingly. The efficient adsorption of salicylic acid to TiO2 surface through -COOH and -OH groups render its higher photo-degradation rate (1.8-2.7 x 10(-2) mu mol min(-1)) than benzoic acid (1.5-2.5 x 10(-2) mu mol min(-1)) having one chelating -COOH group. Zeta potential and conductance measurement of photoreaction mixture were carried out to investigate the ionic interaction-adsorption of reactant substrates over Ag-TiO2 surface. (C) 2013 Elsevier B.V. All rights reserved.