The Study Of Photocatalytic Properties Of Layered Bismuth-based Borates

Semiconductor photocatalysts, applied to solve the industrial pollution and to effectively improve the energy and the environment issues, are of great significance. Although Ti02 has been widely studied as a representative of semiconductor photocatalysts, its defects caused by wide bandgap and carrier recombination inhibit the further application.Therefore, to develop new and efficient photocatalysts has become an inevitable trend. Bismuth-based compounds, because of their unique electronic structure and flattened layer morphology easy, are superior to other catalysts. Bismuth-based compounds not only benefit the catalytic reaction, but Bi 6s electrons hybrid with O 2p provides a more suitable band gap and dispersed valence band structure, which effectively suppress the recombination of photogenerated carriers. Therefore, the bismuth compound is a potential photocatalytic material based on the easy reaction and stable function.For the development of layered bismuth compounds,Bi2O2 (BO2OH),a novel compound, has been successfully prepared by the one-step hydrothermal method in which the metal lead ions successfully embedded in the native lattice, thus we obtain Bi2-xPbxO2 (BO2OH) nano-spheres.The results of X-ray diffraction pattern (XRD) and X-ray photoelectron spectroscopy (XPS) show that Pb has been embedded in the lattice of Bi2O2(?). Because of lead modifying, layered structureis arranged in the fon(?)nano-sphere. The final products with different molar ratio of bismuth and lead have various performance on photocatalysis. When the ratio is 1.5/0.5, the sample has the optimum photocatalytic efficiency even 30% higher than P25. The calculating results from density functional theory (DFT) show that hybridization of Pb 6p, Bi 6s6p and O 2s changes in the Fermi level near the electronic density distribution of electrons, which makes Fermi level band move to the conduction band,narrow the band gap, thus extending the optical wavelength and enhanced the utilization of light energy. The above two aspects enhance the catalytic activity. Finally, bismuth borate acts as a new type of layered compounds with high efficiency of photocatalysis by extending the carrier life.In addition, the heterojunctions of BiIO4/Bi2O2(BO2OH) with different mass fraction of BiI04 are successfully prepared by one-step hydrothermal method. The X-ray diffraction pattern demonstrates that the final sample is composed of two components. The composite with different mass fraction of bismuth/iodate are prepared firstly. The results show that composite with the mass fraction of 35% has the highest photocatalytic activity. Secondly, the comparison of the morphology and photocatalytic performance of 35% BiIO4/Bi2O2 (B020H) with different pH is achieved. pH=7 was observed at the highest reactivity in degradation. The optical absorption band gap of heterostructure is 2.68 eV under the condition of pH=7, with which the heterostructure can be motivated by longer optical wavelength. The efficiency of photocatalytic degradating rhodamine is improved.Apart from reducing the optical absorption band gap, the unique polar structures of IO3- and (BO2OH)2- anions prolong the carrier lifetime and facilitate the long-term effective degradation. The anion group B03 is distorted into a non-planar group with asymmetric structure under the interaction of atoms (mainly coulomb interactions) in the lattice, thus forming the internal polarization field in lattice, so that the photogenerated electrons and photogenerated holes are spontaneously polarized whileIO3cooperates with the polarized field induced by(BO2OH)2- along the c-axis, which effectively promoted the separation of the electron-hole pairs so that the composite material has higher photocatalytic activity.