Preparation of gold nanoparticle dispersed TiO2-polymer composite film by a combined layer-by-layer and photocatalytic deposition method

Gold nanoparticles (AuNPs) can be generated by irradiating a TiO2 photocatalyst with UV, a process known as photocatalytic deposition. Since the AuNPs nucleate and grow only on UV irradiated TiO2 surfaces, their numbers cannot be increased by multiple stacking. In this study, multilayer composites of polysodium 4-stylene sulfonate (PSS), TiO2, and AuNPs were prepared by a combined electrostatic layer-by-layer and photocatalytic deposition method. To acquire a negatively charged AuNP surface, 3-mercapto-1-propanesulfonate (Na-MPS) was added to the HAuCl4 solution used in the photocatalytic deposition process. Under these conditions, positively charged TiO2 particles were electrostatically deposited on MPS-modified AuNPs, enabling good dispersion of AuNPs throughout the composite thin films. In the absence of Na-MPS, TiO2 particles were sparsely deposited on AuNP surfaces, and AuNPs grew through repetition of photocatalytic deposition. In addition, the size of the photocatalytically deposited AuNPs was decreased by increasing the amount of Na-MPS in the HAuCl4 solution. Four-layer samples were observed under a scanning transmission electron microscope. The AuNP size was reduced from 80 nm to 10 nm in the presence of Na-MPS. The composite thin films exhibited localized surface plasmon resonance sensitivity to the refractive index of the solvents around the films.