(NH4)2CO3 mediated hydrothermal synthesis of N-doped (BiO)2CO3 hollow nanoplates microspheres as high-performance and durable visible light photocatalyst for air cleaning

This research represents an efficient visible light photocatalytic removal of 450 ppb level of NO in air by employing newly synthesized monodisperse N-doped (BiO)(2)CO3 hierarchical hollow microspheres (N-BOC). The N-BOC sample was synthesized by template-free hydrothermal treatment of aqueous solution of bismuth citrate and ammonium carbonate mixture. The resulting material was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, Scanning electron microscopy, Transmission electron microscopy, N-2 adsorption-desorption isotherms, and Fourier transform-infrared spectroscopy. The results indicated that the N-BOC sample was hierarchically self-assembled by single-crystalline nanoplates. The regular arrangement of 2D nanoplates at progressively increasing angles to the radial axis resulted in the formation of 3D porous hierarchical hollow architecture, which was favorable for efficient reactants transport and photo-energy utilization. It was found that ammonium carbonate played dual roles in the formation of N-doped (BiO)(2)CO3 hierarchical hollow microspheres, one as structure directing factor and the other as nitrogen doping source. The doped nitrogen substituted for oxygen in the lattice of (BiO)(2)CO3, leading to the formation of special two-band-gaps structure (3.25 and 2.0 eV) for N-BOC sample. The band gap of 3.25 eV is intrinsic for (BiO)(2)CO3 and the small band gap of 2.0 eV can be ascribed to the doped nitrogen forming mid-gap. The N-BOC sample not only exhibited efficient visible light photocatalytic activity but also high stability during long term photocatalytic reaction without deactivation toward purification of NO in air. The characterization of the used N-BOC sample after long term irradiation implied that the nitrogen doping and special hierarchical structure co-contributed to the durable photocatalytic activity. This work demonstrates that the facile hydrothermal synthesis method for N-BOC sample combined with the associated efficient and durable visible light photocatalytic performance could provide an attractive and feasible technology for air cleaning. (C) 2012 Elsevier B.V. All rights reserved.