BACKGROUND: Surface modification by doping with metal ions and organic polymers has been proven to be an efficient route to improve the photocatalytic activity of TiO2. Pesticide photocatalysis has been conducted with fine TiO2 particles suspended in an aqueous phase. RESULTS: It has been found that the Ag dopant accelerates TiO2 anatase to rutile transformation. At relatively low Ag concentrations (2-6%), anatase grain sizes decreased and specific surface areas of the TiO2 powders increased. The presence of Ag in crystalline TiO2 was found to increase the photocatalytic activity of TiO2 in the photocatalytic degradation of acetamiprid at 25 degrees C. CONCLUSION: All photocatalytic degradations of acetamiprid followed pseudo-first-order degradation kinetics (C-t = C(0)e(-kt)) and parameters like the concentration of doped Ag appeared to play an important role affecting the reaction rate. The photocatalytic degradation velocity constant (k) was found to increase quickly with the Ag content, increasing from n = 0.02 to 0.06, and decreased slowly from n = 0.08 to 0.12. The half-lives of degradation 0112) were 18.8, 11.3, 16.2, 10.0, 6.9, 8.4 and 14.7 min at n = 0, 0.02, 0.04, 0.06, 0.08 and 0.12, respectively. The optimal mole percentage of Ag in TiO2 should be between 4% and 8%. (c) 2008 Society of Chemical Industry.