【作者】 张霞；

【导师】 樊静；

【作者基本信息】 河南师范大学 ， 环境科学， 2018， 博士

【摘要】 环境污染和能源危机是人类可持续发展所面临的两大难题。半导体光催化技术不仅可以利用太阳能来治理环境污染,而且还能直接将太阳能转化为氢气、低醇燃料等清洁能源,减少使用传统化石燃料时产生的废气及粉尘污染等环境问题,被人们誉为是一种理想的环境污染治理和清洁能源生产的绿色技术。TiO₂是应用最广泛的半导体光催化材料,但由于TiO₂带隙较大（3.0-3.2 eV）,只能利用紫外光激发,因此,研究开发能够利用可见光或太阳光做驱动能源的新型光催化剂具有重要的应用价值。近年来,铋系催化剂由于具有独特的层状晶体结构和优异的太阳光催化性能而得到学者们的广泛关注,而且我国铋资源比较丰富,这对研发具有较高催化活性的可见光铋系光催化剂十分有利。但是,单一的铋基光催化剂存在可见光吸收范围有限或量子效率偏低的缺点。而将碳基材料或其它半导体材料与可见光吸收性能优良的铋基光催化剂复合,对于拓宽光催化剂的光响应范围和催化效率都十分有效,有望解决当前光催化领域面临的能效和量子效率低的问题。本文采用低温水热法分别制备了具有较高催化活性的三种复合铋系光催化剂,借助X-射线粉末衍射仪（XRD）、扫描电子电镜（SEM）、透射电子电镜（TEM）、高分辨透射电子电镜（HRTEM）、傅里叶变换红外光谱仪（FT-IR）、X射线光电子能谱仪（XPS）、紫外可见漫反射光谱（UV-Vis DRS）和光致发光（PL）等手段对所制备材料的晶相、形貌和微观结构、表面态、光学性能等进行了表征和研究。以染料甲基橙（MO）或罗丹明B（RhB）作为评估对象,系统考察了复合光催化剂的催化活性。在此基础上,选用水体中的新型有机污染物和六价铬作为目标污染物,研究了在模拟阳光光源照射下,复合光催化剂对污染物的降解去除效果,结合材料的能带结构计算,提出了复合光催化材料催化降解有机物的催化作用机理,并根据中间降解产物推测了污染物的降解路径。论文的主要研究内容和结论如下:（1）采用原位水热法制备了多壁碳纳米管（MWCNTs）负载的MWCNTs/Bi₄VO₈Cl复合材料,采用XRD、SEM、TEM、XPS以及UV-Vis DRS等技术对所制得产品的晶体结构、形貌及微观结构、相组成以及光学性能进行了分析。在模拟阳光照射下,通过甲基橙的降解,评估了不同条件下制备的复合材料的光催化性能。在此基础上,进一步考察了染料光敏化的可能性、复合材料的广谱适用性以及在实际废水中的使用情况,同时将制备的复合材料应用于纯水和实际废水中重金属Cr（VI）和双酚A的同步去除,分析了协同去除效应的产生机制。研究结果表明:Bi₄VO₈Cl禁带宽度和价带电位分别为2.43 eV和2.81 eV,具有较强的氧化能力,对可见光具有较好响应;适量的碳纳米管的加入可有效提高Bi₄VO₈Cl材料的光催化活性,当碳纳米管含量为4wt.%时,复合光催化剂活性比单一Bi₄VO₈Cl的活性提高了30%;将复合光催化剂用于重金属Cr（VI）和有机物双酚A共存体系中,发现去除效果明显优于单一污染物体系。自由基等活性物质俘获实验表明,MWCNTs/Bi₄VO₈Cl复合光催化材料对有机污染物降解的作用机理是空穴氧化起主导作用,·OH氧化次之。该复合光催化剂对Cr（VI）和双酚A的协同去除效应来自于光催化产生的电子或空穴同时被Cr（VI）和双酚A俘获,大大减少了载流子的复合,从而有效提高了复合材料的光催化活性。（2）以冰乙酸和水为溶剂,采用简单一步低温混合溶剂热的方法制备了BiVO₄/CH₃COO（BiO）异质结光催化剂。通过多种技术手段对所制备材料的晶体结构、形貌及微观结构、相组成以及光学性能进行了分析。通过磺胺甲噁唑、甲基橙以及4-氨基安替比林的降解,评估了不同条件下制备的复合材料的光催化性能,并研究了复合材料的形成机理以及光催化活性提高的作用机理。此外,BiVO₄/CH₃COO（BiO）光催化剂还被用来降解双酚A和布洛芬,通过比较和分析目标污染物的降解情况,揭示了有机污染物的结构对降解效果的影响规律。根据对所检测到的活性物质和中间降解产物的分析,推测了有机污染物的降解途径。最后,评价了材料的稳定性及重复使用性能,并尝试将复合光催化剂用于实际废水中污染物中的去除。研究结果表明:前驱体溶液的pH值以及NH₄VO₃投加量对复合材料的形貌及催化活性有重要影响,当pH值为5.5、NH₄VO₃投加量为1.5mmol时,BiVO₄/CH₃COO（BiO）催化剂的活性最高,分别为单纯CH₃COO（BiO）和BiVO₄的2.5和14.8倍;目标污染物的矿化率可高达80-96%;污染物的降解路径主要包括侧链的断裂、杂环开环以及芳香环的羟基化过程,且所得中间产物还可以进一步被羟基氧化,直至完全矿化;此外,在实际废水中应用该复合光催化剂时,同样取得满意的处理效果;异质结光催化剂经连续循环四次使用后,材料仍然维持较高的催化活性,因此,预测该复合光催化剂对废水中新型难降解污染物的净化处理方面具有潜在的应用前景。（3）采用低温水热法制备了碘掺杂的BiOIO₃/[Bi₆O₆（OH）₃]（NO₃）₃·1.5H₂O复合光催化剂（I/BiOIO₃/BHN）。通过罗丹明B的降解,评估了前驱体溶液中不同BiOI投加量、水热反应温度和反应时间对所制备的复合材料光催化性能的影响,优化了复合光催化材料的制备条件。采用XRD、SEM、TEM、XPS、UV-Vis DRS和PL等技术对所制得材料的晶相、晶貌、表面氧化态以及光学性能等进行了表征及分析,推测了复合材料的形成机理及催化活性提高的作用机理,通过自由基俘获实验确定了主要的活性物种。此外,为了进一步了解复合材料的广谱适用性,还考察了复合光催化剂在模拟太阳光照射下对甲基橙和苯酚的降解。最后,通过多次循环使用实验评价了材料的稳定性及重复使用性。研究结果表明:当BiOI投加量为0.4398 g、反应温度为180℃、反应时间为12 h时,所制得光催化材料的活性最佳,与单纯[Bi₆O₆（OH）₃]（NO₃）₃·1.5H₂O、BiOI和BiOIO₃相比,BB-2复合材料的催化活性分别提高了69.1、10.4和2.2倍;经模拟太阳光照射40 min,罗丹明B即可被完全去除;甲基橙和苯酚分别经光照100 min和150 min后,去除率可高达94%和84%。机理分析结果表明:前驱体中的硝酸铋对BiOIO₃的生成起关键性的作用;碘掺杂及II型异质结构建的同步实现是复合光催化剂活性提高的主要原因;材料光催化降解有机污染物的机理是空穴氧化起主导作用。特别是该复合光催化剂经简单自由沉降即可快速分离,且在重复使用过程中能保持良好的稳定性和催化活性,因此预测该复合光催化剂在处理有机污染物方面具有良好的应用前景。更多还原

【Abstract】 Environmental pollution and energy crisis are two major problems faced by human sustainable development.Semiconductor photocatalytic technology can not only use solar energy to control environmental pollution,but also directly convert solar energy into clean energy such as hydrogen,low alcohol fuel,reducing environmental problems such as exhaust gas and dust pollution caused by the use of traditional fossil fuels,and has been praised as an ideal green technology for environmental pollution control and clean energy production.TiO₂ is the most widely used semiconductor photocatalytic material.However,the band gap of TiO₂ is large（3.0-3.2 eV）,it can only be excited by ultraviolet light.Therefore,research and development of new photocatalysts that can use visible light or sunlight as driving energy have important application value.In recent years,Bi-based photocatalysts have attracted much attention due to their unique lamellar crystal structure and excellent solar catalytic performance.Moreover,China is rich in bismuth resources,which is beneficial to the development of visible bismuth photocatalysts with high catalytic activity.However,the single bismuth-based photocatalyst has the disadvantages of limited visible light absorption range and low quantum efficiency.The combination of carbon-based materials or other semiconductor materials with bismuth-based photocatalysts with good visible light absorption can effectively broaden the light response range of photocatalyst and improve photocatalytic efficiency of photocatalysts,and is expected to solve the problems of low energy efficiency and quantum efficiency in the field of photocatalysis.In this paper,three composite bismuth based composite photocatalysts with high catalytic activity were prepared by low temperature hydrothermal method,respectively.The crystalline phase,morphology and microstructure,surface state and optical property were characterized by X-ray powder diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,high resolution transmission electron microscopy（HRTEM）,fourier transform infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,UV-Vis diffuse reflection spectroscopy（UV-Vis DRS）and photoluminescence（PL）.Methyl orange（MO）and rhodamine B（RhB）were selected as evaluation object to systematically investigate the photocatalytic activity of the composite photocatalyst.A variety of emerging organic pollutants and Cr（VI）in water were selected as the target pollutants and the removal efficiencies of these pollutants by composite photocatalysts under simulated sunlight irradiation were studied.Based on the calculation of the energy band structure,the photocatalytic mechanism of composite photocatalyst for the degradation of compounds was proposed,and the degradation pathway of pollutants was deduced according to the detected intermediate degradation products.The main contents of this paper are as follows:（1）Multiwalled carbon nanotubes（MWCNTs）loaded MWCNTs/Bi₄VO₈Cl composite photocatalyst was prepared by a facile in-situ hydrothermal method.XRD,SEM,TEM,XPS and UV-Vis DRS technologies were used to investigate the crystal structure,morphology and microstructure,phase composition and optical property of the samples.The photocatalytic performance of the composite materials prepared under different conditions was evaluated by degradation of methyl orange under simulated sunlight irradiation.In addition,in order to further investigate the possibility of photosensitization,the broad applicability of the composite materials and their application in actual wastewater,the composite materials were applied to the simultaneous removal of Cr（VI）and bisphenol A in pure water and wastewater,and the mechanism of synergistic removal effect was analyzed.The results show that the bandgap and valence band potential of Bi₄VO₈Cl is 2.43 and 2.81 eV,respectively,indicating that it has strong oxidation capacity and can effectively response to visible light.The presence of moderate amount of CNTs in the composite can improve the photocatalytic activity.When the content of carbon nanotubes is 4wt.%,the activity of composite photocatalyst is 30%higher than that of single Bi₄VO₈Cl.When the composite photocatalyst is used in the coexistence of Cr（VI）and bisphenol A,it is found that the removal efficiency of the combined pollution is better than that of the single pollutant.Active substances trapping experiments show that the holes play the major role and·OH radicals play the miner role for the degradation of organic pollutants by MWCNTs/Bi₄VO₈Cl composite photocatalyst under light irradiation.The synergistic removal of Cr（VI）and bisphenol A is attributed to the simultaneous capture of electron and hole generated by photocatalysis by Cr（VI）and bisphenol A,by which the photocatalytic activity of the composite photocatalyst is greatly improved.（2）A novel BiVO₄/CH₃COO（BiO）heterojunction was successfully synthesized by a simple one-step mixed solvothermal method with the mixture of deionized water and glacial acetic acid used as solvent.The crystal structure,phase composition,morphology and microstructure,and optical properties of the as-synthesized samples were characterized by a variety of techniques.The photocatalytic properties of the composites prepared under different conditions were evaluated by the degradation of sulfamethoxazole,methyl orange and 4-aminoantipyrine.The mechanisms for the formation of composite photocatalysts and photocatalytic degradation of organic contaminants were studied in detail.In addition,BiVO₄/CH₃COO（BiO）photocatalyst was also used to degrade bisphenol A and ibuprofen.Through the comparative analysis of the removal effects of four target pollutants,the influence of the structure of organic pollutants on the degradation effect was revealed.The degradation pathway of organic pollutants was speculated by analyzing the degradation products of active substances and intermediates.Finally,the stability and reusability of the composite photocatalyst were evaluated,and the composite photocatalyst was attempted to remove pollutants from the actual wastewater.The results show that the pH value of the precursor solution and NH₄VO₃ dosage play significant roles on the morphologies and photocatalytic activities of as-synthesized composite photocatalysts.The photocatalytic performance achieves the best when the pH value of precursor and NH₄VO₃ dosage is 5.5 and 1.5 mmol,respectively.Compared with CH₃COO（BiO）and BiVO₄,photocatalytic activity of the composite photocatalyst is 2.5 and 14.8 times higher than that of individual CH₃COO（BiO）and BiVO₄,respectively.The mineralization rate can reach as high as 80-96%.The degradation pathway includes the cleavage of the side chain,heterocyclic ring opening as well as the hydroxylation of aromatic ring,and these intermediate products can be further attacked by hydroxyl radical,leading to eventual mineralization.In addition,the application of composite photocatalyst in practical wastewater has also achieved satisfactory results.After four consecutive cycles,heterojunction photocatalyst still maintains high photocatalytic activity.Therefore,the composite photocatalyst has potential application prospects in the purification of refractory pollutants in wastewater.（3）A novel iodine doped BiOIO₃/[Bi₆O₆（OH）₃]（NO₃）₃·1.5H₂O composite photocatalyst（I/BiOIO₃/BHN）was prepared by a low temperature hydrothermal method.The effects of different BiOI dosage,hydrothermal reaction temperature and reaction time on the photocatalytic property of the composite materials were evaluated by degradation of rhodamine B.The preparation conditions of the composite photocatalytic materials were optimized.The crystal phase,crystal morphology,surface oxidation state and optical properties of the composites were characterized and analyzed by using XRD,SEM,TEM,XPS,UV-Vis DRS and PL technologies.The mechanisms for the formation of composite photocatalyst and enhancement of photocatalytic activity were speculated.The main active species were identified by free radical capture experiments.In addition,the degradations of methyl orange and phenol by the composite photocatalyst under simulated sunlight were also investigated to further confirm the broad applicability of the composite photocatalyst.Finally,the stability and reusability of the material were evaluated through recycling experiment.The results show that when the dosage of BiOI is 0.4398 g,the reaction temperature is 180℃and the reaction time is 12 h,the photocatalytic activity of composite photocatalyst achieves the best.Compared with pure[Bi₆O₆（OH）₃]（NO₃）₃·1.5H₂O,BiOI and BiOIO₃,the photocatalytic activity of BB-2 composite is increased by 69.1,10.4 and 2.2 times,respectively.Rhodamine B can be completely removed in 40 min irradiation,and the removal efficiency of methyl orange and phenol can reached 94%and 84%after 100 min and 150 min of irradiation,respectively.The mechanism analysis shows that bismuth nitrate in precursor plays a key role in the formation of BiOIO₃.The synchronization implementation of the iodine doping and construction of the II heterostructures is the main reason for the enhancement of photocatalytic activity.The mechanism for the photocatalytic degradation of organic pollutants is hole oxidation.Especially,the composite photocatalyst can be easily separated and reused by simple free sedimentation,and good stability and photocatalytic activity can be maintained in the reuse process,therefore,it is predicted that the composite photocatalyst has good application prospects in the treatment of organic pollutants.更多还原