Uniform Zn2+-Doped BiOI Microspheres Assembled by Ultrathin Nanosheets with Tunable Oxygen Vacancies for Super-Stable Removal of NO

Highly exposed active facets and surface oxygen vacancies (OVs) are beneficial for the photocatalytic removal of various harmful organic compounds. In this study, uniform Zn2+ -doped BiOI microspheres, assembled by ultrathin nanosheets with highly exposed {001} facets, with OVs were successfully synthesized for NO removal under visible light irradiation. The phase structure and chemical states are analyzed by means of X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The transmission electron microscopy observations reveal that replacing Bi3+ with Zn2+ can lead to the increased exposure of the {001} facets. X-ray photoelectron and electron paramagnetic resonance spectroscopy results confirm that low-state Zn2+ increases the number of OVs, indicating that an increased number of OVs and a reduced thickness of the nanosheets can enhance the photocatalytic activity for the removal of NO. The photo-oxidative removal efficiency of NO over 3%Zn-BiOI reaches 53.6% and remains highly stable (52.9%) for up to 210 min under visible light irradiation. The calculation of interface adsorption confirms that OVs and Zn2+ can not only offer a donor energy level to extend the solar response range but also act as adsorption sites for low concentration of NO and O-2 to optimize the transmission capacity of surface charge carriers. Moreover, this work systematically explains the function of OVs and Zn2+ in the adsorption process of NO. The in situ Fourier transform infrared spectroscopy supports understanding of the photo-oxidative removal mechanisms of NO over Zn-BiOI: (i) the byproducts were bidentate nitrites (bi-NO2-), chelate nitrites (ch-NO2-), and bridging nitrites (br-NO3-) in the dark condition and (ii) the final products were bridging nitrites and bidentate nitrites (bi-NO3-) under visible light irradiation. OVs are found to play an important role both in the dark adsorption and photo-oxidative removal of NO by the 3%Zn-BiOI sample.