




已阅读5页,还剩33页未读, 继续免费阅读
版权说明:本文档由用户提供并上传,收益归属内容提供方,若内容存在侵权,请进行举报或认领
文档简介
本科毕业设计 (论文 ) FINAL PROJECT/THESIS OF UNDERGRADUATE (2017 届 ) Preparation and application of g-C3N4/TiO2 composite with visible light photocatalytic activity 学 院 材料科学与工程 专 业 材料科学 (卓越班 ) 学生姓名 学 号 指导教师 完成日期 2017 年 05 月 承诺书 本人郑重承诺:所呈交的毕业论文“ Preparation and application of g-C3N4/TiO2 composite with visible light photocatalytic activity”是在导师的指导下, 严格按照学校和学院的有关规定由本人独立完成 。文中所引用的观点和参考资料均已标注并加以注释。论文研究过程中不存在抄袭他人研究成果和伪造相关数据等行为。如若出现任何侵犯他人知识产权等问题,本人愿意承担相关法律责任。 承诺人 (签名 ): _ 日期: 年 月 Abstract The collection of solar energy through photocatalysts and subsequent production of renewable energy sources (such as hydrogen) is an attractive and sustainable solution to our energy problem. Due to the potential in environmental and energy-related applications, metal oxide semiconductor photocatalysts have attracted worldwide attention. Most of the photocatalysts studied previously had the problem of low quantum efficiency, which was mainly due to the rapid recombination of charge within the photocatalyst,while the charge was slowly transferred at the interface of the photocatalyst. For example, electron-hole recombination in TiO2 usually occurs in the nanosecond time scale, whereas the interface charge transfer usually takes almost a microsecond time. This may be worse when applying internal modifications such as doping to improve their optical performance. However, when the heterojunction is formed among the different semiconductors, the charge recombination can be remarkably suppressed. g-C3N4 has been widely recognized as an ideal semiconductor for the manufacture of heterostructures with various semiconductors for the following reasons: (1) visible light absorption bandgap ( 2.75eV),and its efficient photocatalytic performance under visible light (2) minimum conduction band (CB) (-1.12eV vs. NHE) promoting the electron to another semiconductors CB and thus its photogenerated electrons have a strong reducing ability. (3) cheap and simple synthesis which can have a wide use in production practice. TiO2 (P25) is one of the polymorphs of titania having n-type electron conductivity. Relatively open structure , a large number of surface OH groups and simple synthesis method makes a variety of modifications and large-scale production becomes feasible. For the first time, g-C3N4/TiO2 is synthesized by hydrothermal method using melamine sponge and TiO2 (P25) as the raw materials.At the same time, g-C3N4/TiO2 is also prepared by the same hydrothermal method using TiO2 and bulk g-C3N4 which is calcinated by dicyandiamide directly. On this basis, the pure physical adsorption of raw materials and calcined products is used as a control experiment. Through the change of raw material ratio,we have found the best ratio of g-C3N4/TiO2,leading an-extended-life charge which is due to the efficient separation of electrons and holes. The improvement of photocatalytic activity was proved by the control experiment and the degradation of the dye. KEYWORDS: Titanium dioxide;Nanoparticle; heterostructures;Graphitic carbon nitride Content 1. INTRODUCTION. 1 1.1 HISTORICAL CONTEXT OF TIO2 .2 1.2 TIO2 FEATURE .2 1.3 TITANIUM DIOXIDE(TIO2)-BASED HETEROGENEOUS PHOTOCATALYSIS .3 1.3.1 a promising candidate for photocatalysis and electrocatalysis g-C3N4 . 3 1.3.2 main problem in g-C3N4 . 3 1.3.3 g-C3N4/TiO2 photocatalysts mechanism . 3 1.4 THE KEY TO THE G-C3N4/TIO2 PHOTOCATALYSTS .4 1.5 PROPERTIES OF MELAMINE SPONGE(MS) .4 1.6 SYNTHESIS OF G-C3N4/TIO2 COMPOSITE .6 1.5 SUBJECT SUPPORT AND MAIN RESEARCH CONTENTS . 10 2. EXPERIMENTAL DETAILS . 12 2.1 THE MAIN CHEMICAL REAGENTS AND INSTRUMENTS . 12 2.2 SAMPLE PREPARATION . 12 2.2.1 PREPARATION OF GRAPHENE OXIDE . 12 2.2.2 PREPARATION OF CRUMPLED GRAPHENE OXIDE . 13 2.2.3 MATERIAL PROCESSING-HEAT SHOCK (N-DOPED CRUMPLED GRAPHENE) . 13 2.2.4 MATERIAL PROCESSING-SLOW HEATING . 错误 !未定义书签。 2.3 CHARACTERIZATION . 13 2.3.1 Specific surface area measurement . 13 2.3.2 Scanning electron microscopy (SEM). 14 2.3.3 X-ray powder diffraction . 14 2.3.4 Fourier transform infrared spectroscopy . 15 2.4ELECTROCHEMICAL TEST . 15 2.4.1 Galvanostatic charge/discharge . 15 2.4.2 Cyclic voltammograms . 15 2.4.3 Electrochemical impedance spectroscopy . 15 3. RESULTS AND DISCUSSION . 17 3.1 INFLUENCE OF HEAT TREATMENT PROCESS ON ELECTROCHEMICAL PERFORMANCE OF THE SAMPLES . 17 3.1.1 Influence of heat treatment process on structure of N-doped CG . 17 3.1.2 Influence of heat treatment process on electrochemical performance of N-doped CG Figure 3.7 (A) Typical Galvanostatic charge/discharge curves of symmetric ultracapacitor devices at 0.1A/g, 0.5A/g, 1A/g, 2A/g, 5A/g, 10A/g, 20A/g using urea-CG . (B) Typical charge/discharge curves of symmetric ultracapacitor devices at 0.1A/g, 0.5A/g, 1A/g, 2A/g, 5A/g, 10A/g, 20A/g using urea-CG -600. . 21 3.1.3 Conclusion . 22 3.2 INFLUENCE OF UREA AMOUNT ON ELECTROCHEMICAL PERFORMANCE OF THE SAMPLES . 23 3.2.1 Influence of urea amount on the structure of N-doped CG . 23 3.2.2 Capacitance test of N-Doped CG prepared by different urea amounts . 25 3.2.3 Conclusion . 28 4. CONCLUSION . 29 REFERENCES . 30 ACKNOWLEDGMENT . 32 Preparation and application of g-C3N4/TiO2 composite with visible light photocatalytic activity 1 1. Introduction Since the beginning of the 20th century, the continuous progress of science and technology and the rapid development of industry have brought comfort and convenience to mankind.However it caused serious environmental pollution and deterioration, which has brought potential danger to human health and life. 1-3 Among the various environmental pollution, chemical pollution is the most common, dangerous and influential one.Therefore, the effective control of various chemical pollutants on the water,soil and atmospheric environment have been the focus of comprehensive environmental management. Over the years,people have been dedicated to manage environmental pollution, through such as physical,chemical or biological treatment and so on ,but there are many shortcomings. Therefore,finding a new solution on chemical pollution has a great significance. Photocatalysis is one of the unique properties of nanocrystals.In the light irradiation, nano-semiconductor materials absorb the light and produce the photogenerated electrons and holes ,which possessing super-oxidizing capacity and reducing ability, promoting the synthesis or degradation of compounds (organic or inorganic). 4 Figure 1.1 Air Quality Indexi in Shanghai 上海理工大学本科毕业设计 (论文 ) 2 1.1 historical context of TiO2 In 1972, Fujishima and Honda 5 firstly published a paper ,using TiO2 as a photocatalyst for hydrogen production, which marked the beginning of the era of photocatalysis.At that time, the energy crisis has broke out, and the development of photocatalyst and solar energy on the energy crisis has a great significance, which causing widespread concern from scientific research scholars. And then in-depth exploration on the mechanism of photocatalysis have been carried out. In 1977, Frank and Bard et al. 6 used TiO2 as a photocatalyst to decompose cyanide in water and oxidize CN to OCN , providing a new method to the treatment of sewage. These major research have also laid the foundation for the research of catalyst in environmental purification and new energy development. 1.2 TiO2 feature TiO2 ,which is non-toxic, high-catalytic-activity, good-stability and low-price, etc, is recognized as an excellent semiconductor photocatalyst. The strong oxidizing ability of the photogenerated holes of nano-TiO2 makes it possible to completely oxidize the unbiodegradable organic pollutants. A large number of studies have shown that most of the organic matter can be photocataly tic oxidation a nd degradation. In addition, many inorganic compounds or inorganic ions can also react with photocatalytic electrons on the surface of TiO2 to produce less toxic or non-toxic products.Thus in the atmospheric purification, antibacterial, water purification and anti-fouling,TiO2 has a broad application prospect. Figure 1.2 Nano titanium dioxide Preparation and application of g-C3N4/TiO2 composite with visible light photocatalytic activity 3 1.3 titanium dioxide(TiO2)-based heterogeneous photocatalysis Over the past few decades, titanium dioxide photocatalysis has been used for the efficient degradation of organic compounds, dyes, pesticides and drugs 7-10. However, the photocatalytic activity of TiO2 in visible light is poor ,owing to its high band gap (3.2 eV) and the recombination rate of the photo-generated electron-hole pairs, which limits its practical applications. To enhance the visible-light response and the lifetimes of its charge carriers, people have designed various strategies .11-15Whereas, it remains a long-standing problem unresolved and the efficiency remains insufficient. 1.3.1 a promising candidate for photocatalysis and electrocatalysis g-C3N4 Recently, the metal-free graphitic carbon nitride has attracted enormous interest due to its narrow band gap (2.7 eV), which could respond to the visible light about 460 nm.It is a promising candidate for photocatalysis and electrocatalysis owing to its unique structure and electronic properties. The two-dimensional planar structure consisted of -conjugation system facilitates the transmission of charge carriers. According to the study of Wang et al. 16, the conduction band (CB) of g-C3N4 were 1.3 V and the valence band (VB) were 1.4 V at pH 7 vs the normal hydrogen electrode (NHE), respectively. Therefore, light-excited electrons in the CB of g-C3N4 have a great thermodynamic driving force to reduce O2 (E(O2/O2)= 0.16 V). Figure 1.3 Mimic diagram of g-C3N4 1.3.2main problem in g-C3N4 Light holes in the VB of g-C3N4 is not enough to oxidize OH to hydroxyl radicals (E(-OH /OH) = 2.4V) 17. However, the photocatalytic performance of g-C3N4 is still limited due to its weak oxidative ability of photo-generated hole and the rapid recombination of charge within the photocatalyst. 1.3.3 g-C3N4/TiO2 photocatalysts mechanism To surmount the photocatalytic activity of semiconductor photocatalyst, development of g-C3N4/TiO2 photocatalysts has aroused increased attention due to its efficient separation of 上海理工大学本科毕业设计 (论文 ) 4 photogenerated electronhole pairs in two different semiconductors 18-20. There, the electrons in the CB of g-C3N4 migrate to the CB of TiO2 and recombine with the VB holes.Subsequently, the well-separated holes and electrons in the VB and CB of TiO2 and CN have stronger oxidation and reduction ability than single photocatalysts. 1.4 the key to the g-C3N4/TiO2 photocatalysts As has been mentioned above, the key to promote charge separations between heterostructures is to establish a strong interface between the two semiconductors. In the case of g-C3N4, most of the previous systems were prepared by simple mixing of g-C3N4 with TiO2, which could not guarantee large interface contact 21. On the other hand, TiO2 ,with large amounts of surface OH groups, strongly promote the formation of g-C3N4 during MS degradation. 22 More importantly, FT-IR shows that the formation of g-C3N4 will be firmly bound to the surface of TiO2, which indicates that it will establish a good interface connection. TiO2(P25) belongs to the mixed crystal type, consisting of anatase and rutile which weight ratio is about 80:20.Due to the hybrid of the two structure, the defect density in lattice of TiO2 increases, which increases carrier concentration.The number of electrons and holes increases, making it more capable of capturing the solution components (water, oxygen, organic) on the surface of TiO2. TiO2(P25) relatively open structure, a large number of surface OH groups and cheap price makes a variety of modifications and large-scale production becomes feasible. The synthesized g-C3N4/TiO2 makes the charge have an extended lifetime and the improved photocatalytic activity due to the efficient separation of electrons and holes. As far as l am concerned, this is the first report on the synthesis of g-C3N4 / TiO2 using melamine sponge(MS) condensation. 1.5 Properties of melamine sponge(MS) Melamine sponge is a new type of foam with a high porosity of the three-dimensional grid structure. It has excellent sound absorption, flame retardancy, adiabaticty, thermal stability, safety and secondary processing and other comprehensive performance. These features make the product have a wide range of applications (such as heat-insulation in buildings, transportation, aviation, electromechanical commodity and household appliances, etc.) and broad market prospects. sound-absorbing: melamine sponge has a fully open three-dimensional grid structure system, which length to diameter ratio ( L / D) is between about 10 to 20.Its Preparation and application of g-C3N4/TiO2 composite with visible light photocatalytic activity 5 high porosity characteristics make the sound waves get into the deep layer of sponge easily and effectively and transformed to the vibration energy which is consumed and absorbed late.And the reflected wave is effectively eliminate. The excellent absorption of low-frequency noise exhibited by melamine sponge has aroused great interest from experts in the acoustic industry. flame retardancy: melamine sponge begins to burn in the surface only when it is contacted with the fire.Once it starts to burn, a large number of inert non-combustible gas immediately generates,which slows down the burning speed.At the same time, the surface of melamine sponge will quickly form a dense coke bed which effectively prevent the process of combustion.The fire is automatically extinguished after leaving the fire. For a scientific evaluation standard, melamine sponge can meet the standards for B1 grade low flammable materials (German standard), UL94-V0 grade high flame retardant material standard without adding flame retardants. The general sponge such as polyolefins, polystyrene, polyurethane, etc. often need flame retardants for their own flammable characteristic.Many of flame retardant will be thermally decomposed at high temperatures, and release the poisonous gas,which causes secondary disasters and environmental pollution.The two important indicators in material combustion evaluation, which is often overlooked by the user, is flowing drop property and density of smoke. General sponge ,such as polyethylene, polystyrene, polyurethane, etc. are burning in the combustion and produce droplets, which will quickly cause the spread of fire. Flame retardant modification to these materials is useless in the above flaws. At the same time, polystyrene, polyurethane in the combustion process
温馨提示
- 1. 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
- 2. 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
- 3. 本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
- 4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
- 5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
- 6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
- 7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
最新文档
- 无线资金管理办法
- 抚顺疫情管理办法
- 新疆林地管理办法
- 2024年四川省盐源县普通外科学(副高)考试题含答案
- 房票安置管理办法
- 房屋拆改管理办法
- 战略咨询管理办法
- 房产测给管理办法
- 收费退费管理办法
- 林业用水管理办法
- 基于项目式学习的中考英语大单元复习设计探究
- 绿色高油酸花生种植技术规程(征求意见稿)-编制说明
- 成为司法鉴定机构的条件
- 心境稳定剂的合理应用
- 医疗废物处理登记表
- 卷烟真伪鉴别知识
- 药理学绪论-课件
- JGJ106-2014 建筑基桩检测技术规范
- 2022年06月辽宁经济管理干部学院(辽宁经济职业技术学院)公开招聘高层次人才笔试题库含答案解析
- 电脑基础知识培训ppt课件-电脑基础知识培训课件
- 龙湖集团招标管理原则
评论
0/150
提交评论