Solution plasma synthesis of Au nanoparticles for coating titanium dioxide to enhance its photocatalytic activity

A convenient method for coating titanium dioxide (TiO2) by Au nanoparticles (AuNPs) is demonstrated in solution plasma to improve the photocatalytic activity of TiO2. AuNPs from a metallic Au electrode were bonded to the surface of a commercial TiO2 powder, which acted as a catalyst support, with the reaction taking place in an electrolyte solution. The effect of diverse plasma conditions on the size and productivity of the AuNPs was investigated initially to provide a reference in the absence of TiO2. At 290 V, “partial plasma” was attained, with only a weak light emission surrounding the Au electrode. Conditions then evolved to “full plasma”, with a strong orange emission at 330 V. Partial or full status was maintained for 1 h at 300 and 400 V, respectively. At the transition to full, the AuNP particle size increased from 3.72 to 6.09 nm and the productivity increased dramatically from 0.025 to 0.87 mg h− 1 mm− 2. Stronger plasma very efficiently synthesized AuNPs, and therefore, it was adopted for further study. AuNP-TiO2 combinations were formed by applying 400 V to a TiO2-dispersed solution. In these experiments, TiO2 coated with AuNPs was synthesized; these combinations of AuNP-TiO2 had 0.44 mol% of Au. The photocatalytic activity of AuNP-TiO2 was investigated by measuring the degradation of Rhodamine B (RhB). Under UV irradiation, the AuNP-TiO2 particles removed up to 95% of the dye in 70 min. Commercial TiO2 achieves values closer to 85%. The results thus raise the possibility that solution plasma methods can be generalized as a means for achieving catalysis-enhancing coatings.