Photocatalytic hybrid nanocomposites of metal oxide nanoparticles enhanced towards the visible spectral range

Abstract

We propose and demonstrate photocatalytic hybrid nanocomposites that co-integrate TiO(2) and ZnO nanoparticles in the same host resin to substantially enhance their combined photocatalytic activity in the near-UV and visible spectral ranges, where the intrinsic photocatalytic activity of TiO2 nanoparticles or that of ZnO nanoparticles is individually considerably weak For a comparative study, by embedding TiO(2) nanoparticles of ca. 6 nm and ZnO nanoparticles of ca. 40 nm in the sol-gel matrix of acrylic resin, we make thin film coatings of TiO(2)-ZnO nanoparticles (combination of TiO2 and ZnO, each with a mass ratio of 8.5%), as well as the composite films of TiO(2) nanoparticles alone (17.0%), and ZnO nanoparticles alone (17.0%), and a negative control group with no nanoparticles. For all of these thin films coated on polyvinyl chloride (PVC) polyester, we experimentally study photocatalytic activity and systematically measure spectral degradation (recovery obtained by photocatalytic reactions). This spectral characterization exhibits photodegradation levels of the contaminant at different excitation wavelengths (in the range of 310-469 nm) to distinguish different parts of optical spectrum where TiO(2) and ZnO nanopartides are individually and concurrently active. We observe that the photocatalytic activity is significantly improved towards the visible range with the use of TiO(2)-ZnO combination compared to the individual cases. Particularly for the excitation wavelengths of photochemical reactions longer than 400 nm, where the negative control group and ZnO nanoparticles alone yield no observable photodegradation level and TiO2 nanoparticles alone lead to a low photodegradation level of 14%, the synergic combination of TiO(2)-ZnO nanoparticles achieves a photodegradation level as high as 30%. Investigating their scanning electron microscopy (SEM), X-ray diffraction (XRD), and high resolution transmission electron microscopy (HRTEM), we present evidence of the heterostructure, crystallography, and chemical bonding states for the hybrid TiO(2)-ZnO nanocomposite films, in comparison to the films of only TiO(2) nanoparticles, only ZnO nanoparticles, and no nanoparticles.