Controllable Growth of Copper on TiO₂ Nanoparticles by Photodeposition Based on Coupled Effects of Solution Viscosity and Photoreduction Rate for Catalysis-Related Applications

The wet chemical growth of nanomaterials is widely reported as an alternative to high-vacuum growth. There have been numerous studies that investigate the morphology change of formed nanomaterials in solution, but no studies found have examined the effect of solution viscosity on the growth mechanism at the solid–liquid interface. Here, we report the impact of different solvents, methanol (MeOH) and water, on the formation of nanomaterials at the solid–liquid interface through an investigation of photocatalytic growth of copper on TiO2 nanoparticles supported on graphite. The postgrowth characterization of nanostructures has been made by using scanning/transmission electron microscopy (S/TEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). XPS analysis reveals an unexpected decrease in the amount of deposited material with increasing photocatalytic reduction rate in MeOH, whereas the expected increase is observed in water. S/TEM and EDS observations indicate a variation in the morphology of the copper, including small nanoparticles and flakes depending on the photocatalytic reduction rate and which solvent was used. By changing the solution viscosity and photocatalytic reduction rate, we demonstrate the way of controlling the growth of copper, regulated by classical growth mechanism at a slower reduction rate and cluster aggregation-mediated and viscosity-dependent growth mechanism at a faster reduction rate. Thus, these studies contribute to the development of knowledge that enables better control of the morphology of copper on TiO2, which is crucial for catalysis and related applications.