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

We propose and demonstrate photocatalytic hybrid nanocomposites that co-integrate TiO2 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 TiO2 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 TiO2–ZnO nanoparticles (combination of TiO2 and ZnO, each with a mass ratio of 8.5%), as well as the composite films of TiO2 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 TiO2 and ZnO nanoparticles are individually and concurrently active. We observe that the photocatalytic activity is significantly improved towards the visible range with the use of TiO2–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 TiO2–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 TiO2–ZnO nanocomposite films, in comparison to the films of only TiO2 nanoparticles, only ZnO nanoparticles, and no nanoparticles.

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► Hybrid nanocomposites exhibit enhanced photocatalytic activity in the visible spectral range.
► The synergy is promising for large area decontamination applications that use outdoor sunlight.
► Thin films of integrated TiO2 (ca. 6 nm) and ZnO (ca. 40 nm) are optically characterized at different wavelengths.
► The structure of hybrid nanocomposite films is shown by SEM, XRD, and HRTEM.