Preparation And Photocatalytic Activity Study Of Modified Bi₂O₂CO₃

In recent years, with the worsening of environment, People urgently appeal to environmental technologies. As a new, environmental and energy-saving technology, great attention was paid to photocatalysis by scientists. Traditional TiO₂ photocatalyst is an ideal photocatalyst that was fully studied by scientists. However its band gap is about 3.2 eV,which greatly limites its application. As an ideal substitute for TiO₂,Bi₂O₂CO₃ has also been extensively studied nowadays. Bi₂O₂CO₃ is a typical bismuth layered compound which belongs to Aurivillius type oxide with typical "sellen" structure, and the structure of it consists of[Bi2O2]2+ layers and CO32- layers. Its band gap is about 2.8 ? 3.2 eV, and it has good photocatalytic decomposition of water and degradation of organic matter. In this paper, the influence of Pb dopant on Bi₂O₂CO₃ and the effect of Ag compound on the photocatalytic activity of Bi₂O₂CO₃ were studied. The influence of Pb doping on the band gap of Bi₂O₂CO₃ was verified theoretically by first-principles calculation. Specific studies include the following:?1? Pb doped Bi₂O₂CO₃ were successfully prepared by hydrothermal method. XRD, SEM, TEM, UV-vis were used to study the property of them. From the result, Pb2+ and Pb4+ replace some Bi3+ of crystal internal.The successful doping leads to rearrangement of the electrons in lattice,forming a new doping energy level and reducing the band gap of the semiconductors. By first-principles calculations, the reducing band gap is theoretically confirmed. The calculation of the density of states also shows that the presence of Pb2+?Pb4+? in lattice can form doping energy level near Fermi level. In the photocatalytic degradation of rhodamine B,Pb doped Bi₂O₂CO₃ showes better photocatalytic activity than pure Bi₂O₂CO₃. Among them, the 10% Pb doped Bi₂O₂CO₃ showed the best photocatalytic activity. When the doping amount is higher, the volume of the semiconductors becomes larger and the relative surface area decreases,which can reduce the effective photocatalytic sites.?2? The complex of Ag/Bi₂O₂CO₃ was successfully synthesized by one step hydrothermal method using Bi ?NO3?3·5H2O and Ag?NO3?3. It was found that Ag was uniformly distributed on the nanosheets of Bi₂O₂CO₃ and formed heterogeneous structure between them, and the heterogeneous structure of Ag/Bi₂O₂CO₃ was tested by XRD, SEM, TEM,UV-vis et. al. The red-shift of the UV-vis spectrum was observed, which proves the higher spectral efficiency. The photocatalytic efficiency of Ag/Bi₂O₂CO₃ was higher than pure Bi₂O₂CO₃, and the photocatalytic achieved the highest when the composite ratio was 20%. This phenomenon can be explained by the existence of silver that can change the surface electron distribution. The electron will redistribute from semiconductor to silver. So there are too many electrons on the surface of Ag while too much holes on the surface of the semiconductor, forming a Schottky that can capture the photogenerated electrons and hinder the recombination of the photogenerated electron-hole pairs, thus the photocatalysis is enhanced. However, too much silver nanoparticles will cover active sites on the surface of Bi₂O₂CO₃, affecting the photocatalytic efficiency.