The Preparation And Modification Of BiOCI Nanostructure And Their Photocatalytic Performances

Photocatalysis is proved with energy saving, economical, safe, non-toxic, non-pollution, strong oxidation ability and high degradation efficiency, which is considered as a green method to solve the energy problems and environment problems. Thus many scientists have been focusing on the study of photocatalysis. While the photocatalyst is the key factor of the photocatalysis. BiOCl is talent showing itself because of its high photocatalytic activity, which is caused by its layered structure. In this work, a solventhermal method was used to prepare BiOCl nanosheets with high photocatalytic activity, then used an in situ reduction, oxidation and hydrolysis method to synthesize Bi/BiOC1 and Bi2O3/BiOCl nanocomposites, which are confirmed with higher photocatalytic properties than that of BiOCl. The process and the mechanism of photocatalysis are also discussed. The main research results are showing as follows:(1) The bismuth oxychloride (BiOCl) with morphology of nanosheets were synthesized by solvothermal method using EG aqueous solution. The XRD, SEM, HRTEM and SAED characterizations show that the sample was squared like BiOCl nanosheets with 300～600 nm in size. The study on the samples synthesized with different hydrothermal time and different solutions gives the crystallization and grow up process of the BiOCl nanosheets. The hydrogen bonding between hydroxyl groups of EG and its selective adsorption result the squared like shape of BiOCl nanosheets. The degradation of MO solution proves that BiOCl nanosheets have a good photocatalytic activity in contrast to the BiOCl microspheres under UV light and 20 mg BiOCl nanosheets could photodegrade 15 mL 20 mg/L MO solution completely in 15 min. Recycling experiments and the photocatalysis experiment of the sample placed three months later also confirm the long term stability of the photocatalyst under UV light.(2) Bi nanoparticles modified BiOCl nanosheets were achieved via an in situ chemical reduction method in KBH4 aqueous solution. The nanoparticles are well dispersed on the surface of BiOCl nanosheets with size of approximately 5～20 nm. And the amount of Bi nanoparticles on BiOCl nanosheets can be controlled by changing the concentration of KBH4 solution. When the KBH4 concentration is around 25 mmol·L-1, Bi/BiOC1 nanosheets achieve the best photocatalytic performance with MO degradation rate of 100% in 8 min under UV irradiation and 75% in 2 h under visible light irradiation. The technical stability and recyclability test of Bi/BiOC1-25 nanosheets under UV light illumination show that the Bi/BiOCl-25 nanosheets not only possess high photocatalytic activity but also show excellent photocatalytic stability. Bi nanoparticles can enhance the photocatalytic performance of BiOCl nanosheets in the UV region due to the separation effect of photogenerated electrons and holes, and the improvement of photocatalytic performance in the visible light irradiation due to the indirect band gap transition of Bi nanoparticles. The O2" radicals are the dominant species in the photocatalytic process.(3) Bi2O3 nanoparticles modified BiOCl nanosheets were achieved via an oxidization of Bi/BiOCl nanosheets using H2O2 solutions as oxidization reagent. Bi2O3 nanoparticles are evenly distributed on BiOCl nanosheets with sizes ranging from 10 to 25 nm. The BiOCl nanosheets are in a hierarchical structure with interlaminary spacing of approximately 4 nm, and the biconvex lens structure of BiOCl nanosheets composed of several ultrathin layers can be observed. The hierarchical Bi2O3/BiOCl nanosheets show higher photocatalytic performances than that of BiOCl nanosheets, and the Bi2O3/BiOCl-0.02 sample achieves the highest photodegradation rate of 93.6% in 8 min under UV light illumination. The enhancement of the photocatalytic performance of Bi2O3-BiOCl can be ascribed to several aspects, including higher surface area, higher UV light absorption rate and separation of photogenerated electron-hole pairs. The photogenerated electrons on Bi2O3 nanoparticles play the dominant role on the photocatalytic process by forming·O2- radicals.(4) A facile hydrolysis method was used to synthesize the Bi2O3/BiOCl nanocomposites by the assistance of ascorbic acid and Pluronic F127. The results of XRD, SEM, TEM and XPS prove that Bi2O3 nanoparticles of about 10 nm in size modified BiOCl nanosheets were successfully prepared. The degradation of MO solution proves that Bi2O3/BiOCl nanocomposites have an excellent photocatalytic activity under UV light with MO degradation rate of 100% in 8 min. The technical stability and recyclability test of Bi2O3/BiOCl-20 nanosheets under UV light illumination show that the Bi2O3/BiOCl-20 nanosheets not only possess high photocatalytic activity but also show excellent photocatalytic stability. The photogenerated electrons play the dominant role on the photocatalytic process by forming·O2- radicals.