Synergetic Effects of Pd Metal Nanoparticles and Pd Ions on Enhanced Photocatalytic Activity of ZnWO Nanorods for Nitric Oxide Removal.

Doping and novel metallic nanoparticles loading on the photocatalyst are two effective means to enhance its photocatalytic activity. In our study, Pd/Pd-co-modified ZnWO nanorods were fabricated by a two-step hydrothermal process and room-temperature reduction method. The performance of the as-prepared samples was evaluated through the photocatalytic nitric oxide (NO) removal under simulated solar and visible-light irradiation. Pd/Pd-co-modified ZnWO nanorods present a significantly enhanced photocatalytic activity for NO removal compared with Pd-loaded or Pd-doped ZnWO under simulated sunlight irradiation owing to a narrower band gap of Pd doping compared with that of pure ZnWO. The role of Pd nanoparticles is to act as an electron reservoir to restrain the recombination of e/h pairs. According to the trapping measurements, the photoinduced holes and electrons play critical roles during the photocatalytic process. In addition, electron spin resonance (ESR) results further confirm that O and OH radicals are present and assist in the photocatalysis under simulated solar light irradiation. Stability test demonstrated that 1.5% Pd/0.5% Pd-co-modified ZnWO nanorods as photocatalyst have high photocatalytic stability in NO removal. This work proved that Pd/Pd-co-modified ZnWO nanorods can be considered as an efficient photocatalyst for NO removal.