Facile synthesis of Ag nanoparticles supported on TiO2 inverse opal with enhanced visible-light photocatalytic activity

TiO₂ inverse opal films loaded with silver nanoparticles (ATIO) were synthesized on glass substrates. TiO₂ inverse opal (TIO) films were prepared via a sol-gel process using self-assembly of SiO₂ colloidal crystal template and a facile wet chemical route featuring an AgNO₃ precursor solution to fabricate silver nanoparticles on the TIO films. The inverse opal structure and Ag deposition physically and chemically modify titania, respectively. The catalysts were characterized by Raman spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), UV-vis absorption spectra, X-ray photoelectron spectroscopy and photoluminescence spectroscopy. The HRTEM results show that Ag nanoparticles measuring 5-10 nm were evenly distributed on TIO. Both the UV- and visible-light photocatalytic activities of the samples were evaluated by analyzing the degradation of methylene blue (MB) in aqueous solution. The results reveal that the apparent reaction rate constant (k_app) of MB degradation of the sample ATIO under UV-light irradiation is approximately 1.5 times that of the conventional Ag-loaded TiO₂ film (ATF) without an ordered porous structure at an AgNO₃ concentration of 5 mM in the precursor solution. At an AgNO₃ concentration of 10 mM, the sample exhibits a k_app value approximately 4.2 times that of ATF under visible-light irradiation. This enhanced visible-light photocatalytic performance can be attributed to the synergistic effect of optimized Ag nanoparticle deposition and an ordered macroporous TIO structure. Repeated cycling tests revealed that the samples showed stable photocatalytic activity, even after six repeated cycles.