Control of morphology of silver clusters coated on titanium dioxide during photocatalysis

Supported metal catalysts have been used extensively in many current industrial processes. The morphology of coated metal on a support is usually an important factor affecting the efficiency of the catalyst. In this study, the investigation is focused on a photocatalytic process to coat silver clusters on titania (P-25 TiO2) with an emphasis on the morphology control of coated silver clusters. For the first time, the particle size and the deployment intervals of silver clusters are controlled with an innovative method that involves the in-situ formation of water-insoluble transitory species such as AgBr, AgCl, or Ag2O on the surface of titanium dioxide. Experimental results demonstrated that the transitory particles function as physical spacers, which temporarily occupy some of the active site on the titanium dioxide surface and act as reservoirs for Ag+ ions to keep the local Ag+ concentration on TiO2 extremely low. The silver clusters coated on titania are found to be stable in the spherical silver-3c syn crystalline form indicated by TEM, XRD, and XPS measurements.