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CQDs/Bi2WO6制备及可见光光催化降解VOCs的研究

作者:优质期刊论文发表网  来源:www.yzqkw.com  发布时间:2019/10/26 13:57:04  

摘要:挥发性有机物(VOCs)是一类有毒有害的大气污染物,对社会发展和人类健康造成较大影响。本课题通过在Bi2WO6掺杂CQDs增强光生电子的传输,提高材料去除VOCs的性能。研究主要包括三个方面:一是通过调控Bi2WO6的结构,探讨其形貌结构对光催化材料的吸附能力和光电效应等的影响;二是选择不同CQDs材料,研究CQDs对改善Bi2WO6性能的影响;三是改变光催化过程的工艺条件,寻找优化参数。在实验研究的基础上,总结出CQDs/Bi2WO6降解VOCs的一般规律。

Bi2WO6是一种良好的半导体材料,其表界面结构可以通过选用不同的表面活性剂和调节pH等方法,在水热反应下达到结构形貌的可控制备。采用SEM、XPS等表征分析材料的物理化学性质,此外通过UV-vis、TPR和PL等分析材料的光学性质。分析表明花状微球形Bi2WO6吸收波长达到440 nm,且电荷分离效率高,同时,它还具有较低的光生电子空穴复合效率。性能测试中,它的催化效率是微球形的10倍,因此后续实验中选择花状微球的纯Bi2WO6作主体材料。

CQDs具有优秀的光电性能,其制备原料是影响光电性能的一个重要因素。采用水热法,以五种不同有机物作碳源制备CQDs。再将五种CQDs负载到Bi2WO6载体上制备了CQDs/Bi2WO6光催化材料。XRD表明CQDs以物理方式与Bi2WO6表面相结合。BET测试显示CQDs的引入能够增加光催化材料的比表面积,以壳聚糖作碳源时,复合材料(C-CBW)的比表面积最高达到29 m2·g-1,增加了38%。从TEM图像和FT-IR看出CQDs纳米颗粒成功修饰在Bi2WO6材料表面。XPS显示添加CQDs后材料Bi4f和W4f轨道的结合能向高结合能方向偏移,最高偏移量达0.6 e-。TPR和PL分别分析了光催化材料光生电子空穴的分离效率和复合速率。TPR表明光照下C-CBW的电荷分离效率最高,且添加量为2%时效果最好。PL表明C-CBW电子空穴复合效率最低,且添加量为2%效果最好。高效的电荷分离且复合速度慢使得电子和空穴停留时间长,氧化还原反应能高效进行。通过实验表明C-CBW具有最好的光催化活性,且CQDs的添加量为2%时活性最高。这与表征结果相一致。性能测试中,可见光下C-CBW对甲苯和甲醛气体的催化效率是Bi2WO6的4.8倍和5.8倍。添加量为2%,催化效率分别是Bi2WO6的6.6倍和6倍。

CQDs/Bi2WO6在可见光条件下降解甲苯和甲醛气体实验中,甲苯和甲醛气体初始浓度升高,甲苯和甲醛的去除率效率降低。光催化反应环境中氧气浓度升高会对光催化反应起促进作用,当氧气浓度持续升高到25%时,污染物去除率趋于稳定。光催化反应环境的相对湿度升高会显著促进光催化反应进行。相对湿度为50%时,光催化反应速率最高,其中C-CBW能够完全降解甲苯和甲醛气体。这是因为水分子与空穴作用生成·OH的量增加,提高氧化能力。相对湿度继续升高后,会反过来抑制光催化反应,污染物的去除率和反应速率都会降低。因为水分子饱和后吸附在材料表面占据活性位点,使材料不能充分吸附污染物进行降解。光催化反应中,光照强度对光催化反应起促进作用,光照强度提高,光催化反应速率提高,对污染物的降解率也升高。

本课题研究的材料具有可控、高效等优点,提供了一个高效去除VOCs的方法,为开发去除VOCs的光催化材料提供了一个新思路,具有积极意义。

Volatile organic compounds (VOCs) are aclass of toxic and harmful atmospheric pollutants that have a major impact onsocial development and human health. In this paper, the performance ofphoto-generated electrons is increased by doping CQDs in Bi2WO6, and theperformance of materials to remove VOCs is improved. The research mainlyincludes three aspects: Firstly, by controlling the morphology of Bi2WO6, theinfluence of its morphology on the specific surface area, adsorption capacityand photoelectric effect of photocatalytic materials is discussed. The secondis to select different CQDs materials to investigate the effect of CQDs onimproving the performance improvement of Bi2WO6. The third is to change theprocess conditions of the photocatalytic process and find optimized parameters.On the basis of experimental research, the general rule of CQDs/Bi2WO6degradation of VOCs was summarized.

Bi2WO6 is a good semiconductor materialwith high controllability and control of the formation of Bi2WO6 with differentmorphologies by controlling surfactant and pH. In the screening process ofBi2WO6 catalytic materials, the physicochemical properties of the four Bi2WO6materials were analyzed by SEM, XPS and other characterization, and the opticalproperties of the materials were analyzed by DRS, TPR and PL. The analysisshows that the flower-like microspherical Bi2WO6 has an absorption wavelengthof 440 nm and high charge separation efficiency. At the same time, it also hasa low photogenerated electron-hole recombination efficiency. In the performancetest, its catalytic efficiency is 10 times that of the microsphere, so the pureBi2WO6 of the flower-like microspheres was selected as the host material in thesubsequent experiments.

CQDs have excellent optoelectronicproperties and their raw materials are an important factor in performance. TheCQDs were prepared by hydrothermal method, using five different organicmaterials as carbon sources and modified onto the Bi2WO6 carrier. XRD indicatedthat the CQDs were physically combined with the Bi2WO6 surface. The BETcharacterization shows that the introduction of CQDs can increase the specificsurface area of the photocatalytic material. When chitosan is used as thecarbon source, the specific surface area of the composite (C-CBW) is up to 29m2·g-1, an increase of 38%. It was found from the TEM and FT-IR images that theCQDs nanoparticles were successfully modified on the surface of the Bi2WO6material. XPS shows that the binding energy of the Bi4f and W4f orbitalsshifted toward the high binding energy after CQDs is added, the highest is 0.6e-. TPR and PL characterization analyzed the separation efficiency and recombinationefficiency of photogenerate electron holes in photocatalytic materials,respectively. TPR showed that C-CBW had the highest charge separationefficiency under illumination, and the best effect was obtained when theaddition was 2%. PL indicates that the electron hole recombination efficiencyof C-CBW is the lowest, and the amount of 2% is the best. The charge separationefficiency is high and the recombination rate is slow, so that electrons andholes have a long residence time, and the redox reaction can be efficientlyperformed. It has been shown by experiments that C-CBW has the bestphotocatalytic activity, and the activity is highest when the amount of CQDsadded is 2%. This is consistent with the characterization results. In theperformance test, the catalytic efficiency of C-CBW to toluene and formaldehydegas under visible light was 4.8 times and 5.8 times that of Bi2WO6. Theaddition amount was 2%, and the catalytic efficiency was 6.6 times and 6 timesthat of Bi2WO6, respectively.

In the experiment of degrading toluene andformaldehyde gas under visible light of CQDs/Bi2WO6, the initial concentrationof toluene and formaldehyde gas increased, and the removal efficiency oftoluene and formaldehyde decreased. The increase of oxygen concentration

关键词:光催化;VOCs;CQDs/Bi2WO6;可见光

Photocatalysis; VOCs; CQDs/Bi2WO6; Visiblelight

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