Prepration Of Ultrathin Bi₁₂O₁₇Cl₂ Nanobelts And Composites And Their Application In Photocatalysis

In 21st century,pollutants in various organic wastewater,such as pharmaceutical wastewater,have caused irreversible damage to the environment and human beings.For example,tetracycline as a typical antibiotic has attracted widespread attention,because excessive tetracycline may affect human health,and even cause cancer.With the process of industrialization,the content of CO₂in the air is increacing,which is the main cause of greenhouse effect.Whether it is tetracycline pollution in water,or the concentration of CO₂in the air exceeds the standard,we need to urgently find an effective solution.Fortunately,semiconductor photocatalytic technology can not only remove pollutants into carbon dioxide and water,but also use solar energy to directly convert CO₂and H₂O into hydrocarbon fuel and O₂.Therefore,semiconductor photocatalytic technology is considered to be an ideal choice to solve energy and environmental problems.In recent years,layered bismuth based compounds have attracted great attention as photocatalysts.Because of their unique layered structure,nontoxicity and suitable energy band position,they have become promising materials in the field of photocatalysis.Therefore,in this thesis,through the improvement of Bi₁₂O₁₇Cl₂material,we have successfully achieved the degradation of TC and the photocatalytic reduction of CO₂.The details are as follows:1.1D Bi₁₂O₁₇Cl₂ultra-thin nanobelts（1D-UBOC）,2D Bi₁₂O₁₇Cl₂nanoplates（2D-BOC）,and 3D Bi₁₂O₁₇Cl₂nanoflowers（3D-BOC）were synthesized by hydrothermal method.The degradation of aquoues tetracycline and the photocatalytic reduction of gaseous CO₂were investigated under simulated sunlight.The 1D-UBOC presents best photocatalytic performance.It could remove about 97.09%tetracycline in 3h.At the same time,the yield rate of CO and CH₄were 29.24 and 0.65μmol·g^-1?h^-1,respectively,which was 2.2 times of the CO yield rate and 1.5 times of CH₄yield rate of 2D-BOC and 3D-BOC.The highest CO₂conversion rate of 1D-UBOC was5.73%,which is 2～3 times of 2D-BOC（2.07%）and 3D-BOC（2.36%）.After 5cycles,the TC degradation efficiency and CO₂photoreduction ability of 1D-UBOC did not decrease significantly.Finally,the mechanism of TC degradation and CO₂reduction by three kinds of photocatalysts with different morphologies was obtained through the experiments of Mott Schottky and free radical capture.2.Direct Z-type 1D ultra-thin Bi₁₂O₁₇Cl₂/Cu Bi₂O₄（CBO/UBOC）materials were successfully prepared by hydrothermal method.Due to the structural advantages of Z-type heterojunction,it has excellent photocatalytic activity and high stability for CO₂photoreduction.At room temperature and simulated sunlight,the yield rate of CO and CH₄reduced by CBO/UBOC-50%composite catalyst were 77.28 and 0.87μmol·g^-1?h^-1,respectively.The yield rate of CO is about 15 and 2.6 times higher than that of pure CBO and UBOC,respectively,while the yield rate of CH₄is higher than that of pure UBOC.Meanwhile,the CO₂conversion rate of CBO/UBOC-50%is14.30%,while that of pure CBO and UBOC is only 1.46%and 5.73%.The excellent performance is assignd to the composite of Cu Bi₂O₄,which greatly improved the light absorption ability of the catalyst.Further,the formation of direct Z-type heterojunction promots the separation and transfer of photogenerated electrons and holes meanwhile maintains the strong redox ability of the material,which brings advantages for the photocatalytic reduction of CO₂.3.Ultra-thin 1D/2D Bi₁₂O₁₇Cl₂/g-C₃N₄（UBOC/UCNNs）composites were prepared by a simple reflux method,and their photocatalytic properties for CO₂reduction were investigated.The results showed that UBOC/UCNNs-5 exhibited excellent performance in CO₂photoreduction.Within 3 hours,the yield rate of CO and CH₄by the composite catalyst could reach 169.46 and 35.91μmol·g^-1?h^-1,respectively,and the CO yields were about 5.2 and 6 times higher than those of UCNNs and UBOC respectively.The yield of CH₄is about 50 times that of UCNNs and UBOC.The CO₂conversion rate of UBOC/UCNNs-5 composite catalyst can reach 25.45%,which is about 6 times that of UCNNs（6.09%）and UBOC（5.73%）.At the same time,the catalytic activity of the catalyst remained stable after 5 cycles.The mechanism of improving the photocatalytic performance of UBOC/UCNNs-5was analyzed by in situ infrared spectroscopy,photocurrent,EIS impedance,PL and Mott-Schottky experiments.The results showed that the improved performance of UBOC/UCNNs composite catalyst is mainly due to the effective separation of photogenerated e^--h⁺and more active sites for CO₂reaction.