Constructing
oxygen vacancies (OVs) in metal-oxide semiconductors
is an effective and simple way to enhance the photocatalytic performance
via promoting the utilization of solar light and boosting the formation
of surface reactive oxygen species (ROS). The presence of different
oxygen atoms in the same crystal structure can possibly lead to the
formation of different types of OVs with distinct physicochemical
and optoelectronic properties. Particularly, the two different crystallographic
positions of oxygen atoms in the [BiO]2
2+ layer
of (BiO)2CO3 (BOC) allow the construction of
two types of OVs (OVs1 and OVs2). In this work, OVs1-BOC and OVs2-BOC
are synthesized via introducing the OVs1 and OVs2 on the surface of
the BOC. The influence of OVs1 and OVs2 on the generation of ROS in
the BOC is demonstrated based on theoretical and experimental studies
by analyzing the separation and redox potentials of photogenerated
charge carriers, absorption surface adsorbates (H2O and
O2), and reaction active energy. The photocatalytic performance
is evaluated by photo-oxidative nitric oxide (NO) removal efficiency
under visible light irradiation. The OVs1-BOC and OVs2-BOC exhibit
50.0 and 41.6% photo-oxidative NO removal efficiencies, while generating
15.6 and 16.54 ppb NO2, respectively. The in situ Fourier
transform infrared spectroscopy and estimated NO conversion pathway
reveal the photo-oxidative NO removal mechanism and suppression of
NO2 formation on the surfaces of OVs1-BOC and OVs2-BOC.
This work demonstrates a straightforward approach for enhancing the
photo-oxidative NO removal via manipulating the OV defect position
in semiconductors.
Doping and novel metallic nanoparticles loading on the photocatalyst are two effective means to enhance its photocatalytic activity. In our study, Pd 0 /Pd 2+ -co-modified ZnWO 4 nanorods were fabricated by a twostep hydrothermal process and room-temperature reduction method. The performance of the as-prepared samples was evaluated through the photocatalytic nitric oxide (NO x ) removal under simulated solar and visible-light irradiation. Pd 0 /Pd 2+ -co-modified ZnWO 4 nanorods present a significantly enhanced photocatalytic activity for NO x removal compared with Pd 0 -loaded or Pd 2+ -doped ZnWO 4 under simulated sunlight irradiation owing to a narrower band gap of Pd 2+ doping compared with that of pure ZnWO 4 . The role of Pd 0 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 2 − and • OH radicals are present and assist in the photocatalysis under simulated solar light irradiation. Stability test demonstrated that 1.5% Pd 0 /0.5% Pd 2+ -co-modified ZnWO 4 nanorods as photocatalyst have high photocatalytic stability in NO x removal. This work proved that Pd 0 /Pd 2+ -co-modified ZnWO 4 nanorods can be considered as an efficient photocatalyst for NO x removal.
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