Synthesis And Properties Of BiOCl Based Photocatalytic Materials

With energy shortage and environment pollution all over the world, the research focus on photocatalysis has been changed from basic theory to practical application.Key of the trend is to build a stable and efficient photocatalytic system by broadening range of light response and reducing recombination of photo-generated electron hole pairs. BiOCl has been widely used in photocatalytic research due to its unique layered structure. BiOCl is a semiconductor with wide band gap (?3.4 eV),i.e.,has response to only UV light, which makes it difficult in practical application.Consequently, two methods including semiconductor composite and metal deposition were used to modify BiOCl in this research to broaden the range of light response and reduce the recombination of photo-generated carrier. in order to enhance the photocatalytic activity of BiOCl in visible light range.(1) BiVO4 was grown on the surface of BiOCl microspheres by a simple hydrothermal method. BiVO4/BiOCl composites with different contents of BiOCl were prepared by adjusting the amount of V in reaction solutions. Samples were characterized by techniques including XRD, SEM, XPS, UV-Vis spectra, and the degradation of Rhodamine B as a probe reaction to evaluate the photocatalytic activity. The influence of BiVO4 content on crystal phase, morphology, light response range and photocatalytic properties of BiVO4/BiOCl composite was investigated. Results shows that BiOCl provides not only Bi source for the formation of BiVO4, but also a backbone to form a special BiV04 encapsulated BiOCl microspheres. Generation of BiVO4 in the semiconductor composites extends the light response range to the visible range, which greatly improves the utilization of the solar light. Semiconductor heterojunctions are formed on the interface of two semiconductors. Regulation of Fermi energy bands of the two components constitutes an internal electric field, which inhibits the recombination of photo-generated carriers and improves the quantum efficiency. Compared with pure BiOCl or monoclinic BiVO4,BiVO4 /BiOCl semiconducting photocatalysts exhibit enhanced photocatalytic activity for degradation of Rhodamine B solution under visible light irradiation, among which, 30% BiVO4/BiOCl possessed a optimal photocatalytic activity and Rhodamine B degrades completely within 2 h.(2) Via solvothermal reaction using ethylene glycol, BiOCl microspheres were formed with Bi metal, which was reduced from Bi3+ and grown in situ on its surface.The size and contents of Bi nanoparticles and the morphology of BiOCl can be controlled by reaction time. The influence of reaction time on light absorption and photocatalytic performance of Bi/BiOCl heterojunction was further investigated as well. Results show that BiOCl has a microsized spherical structure comprised of nanosheets within composites with reaction time of 12h or 18h. Metal Bi was successfully grown on the surface of BiOCl by the reduction of ethylene glycol. The light absorption ability of Bi/BiOCl composites within visible light range was enhanced by surface plasmon resonance. Metal Bi loaded BiOCl can separate charge carriers by heterojunctions, and enhanced the activity of degradation of Rhodamine B. However,with too long reaction time,the morphology of BiOCl microspheres is destroyed due to over-reduction, resulting in defects and decrease in the degradation activity.