论文总字数：23423字

摘 要

随着社会的发展和进步，人类对化石燃料的过度依赖及其不可避免的消耗造成大量CO₂的排放，导致全球温室效应问题十分突出，进而引发了严重的能源和环境危机。因此，降低CO₂的排放量，将潜在的碳资源通过一定的技术手段进行转化，构建非化石燃料、环境友好型的可再生新能源成为化学、材料、物理、环境等领域的研究工作者的追求目标。这样既可以减轻环境污染危机，又可以实现碳资源的循环利用。近年来，降低大气中CO₂含量的主要方法有热化学转化法、光电化学转化法、电化学转化法、生物还原法等。但是这些方法反应条件苛刻、需要额外消耗不可再生能源、且转化效率不高。同时安全性和对生态的破坏等缺点使得其发展受到挑战。光催化转发技术因其反应条件温和、不需要额外提供其他能量、安全性能高等优点备受关注。光催化还原CO₂技术是利用丰富的太阳能、廉价的水和光催化剂将CO₂还原为碳氢燃料，反应过程中不会额外产生CO₂气体，最终降低了大气中的CO₂浓度，实现了人类发展的能源需求和环境资源可持续利用的平衡发展。然而，单一半导体光催化剂在光催化应用中存在光生载流子复合速度快，量子产率低等问题。为了克服单一半导体在应用中存在的弊端，常常采用助催化剂来解决这些问题。石墨烯因其具有突出的导热性能、力学性能、优异的导电性能以及巨大的比表面积等优点被用作光催化反应助剂。因此，本论文通过采用Stöber 法制备SiO₂ 微球，再以其为模板，通过油浴法和碱刻蚀法制备CdS空心微球，最后采用静电自组装的方法实现CdS与石墨烯复合。通过表征技术对该复合材料的微观形貌、晶相结构、表面性质以及光催化性能进行表征。结果表明，尺寸均一的CdS空心微球包裹在石墨烯纳米片中，在350 W氙灯模拟光照下照射下，CdS/石墨烯复合光催化材料显示出较高的CO₂光催化还原活性，当复合石墨烯的量为2%时，光催化还原性能达到最优，CO₂催化还原产物甲烷和一氧化碳的产率分别为2.234 μmol·g^-1·h^-1和5.960 μmol·g^-1·h^-1,较纯CdS材料分别提高了3倍和7倍之多，并且石墨烯的引入有利于甲醇的选择性生成。光催化还原性能的提升主要源于构建了助催化剂有效地将光生载流子进行了分离，其次石墨烯的独特层状结构为反应提供了大量的吸附位点。

关键词：CdS；石墨烯；光催化CO₂还原；复合光催化材料

Abstract

With the development and progress of society, the excessive dependence on fossil fuels and the inevitable consumption of fossil fuels cause a large amount of CO₂ emissions, leading to the global greenhouse effect problem is very prominent, which leads to a serious energy and environmental crisis. Therefore, reducing CO₂ emissions, transforming potential carbon resources through certain technical means, building non fossil fuel, environment-friendly renewable new energy has become the goal of researchers in the fields of chemistry, materials, physics, environment and so on. This can not only reduce the environmental pollution crisis, but also realize the recycling of carbon resources. In recent years, the main methods to reduce the content of CO₂ in the atmosphere are thermochemical conversion, photoelectrochemical conversion, electrochemical conversion and biological reduction. However, the reaction conditions of these methods are harsh, the additional consumption of non renewable energy is required, and the conversion efficiency is not high. At the same time, its development is challenged by its security and ecological damage. Due to its mild reaction conditions, no need to provide additional energy, high security and other advantages, photocatalytic transfer technology has attracted much attention. The technology of photocatalytic reduction of CO₂ is to use abundant solar energy, cheap water and photocatalyst to reduce CO₂ to hydrocarbon fuel, no additional CO₂ gas will be generated in the reaction process, and ultimately reduce the concentration of CO₂ in the atmosphere, achieving the balanced development of energy demand for human development and sustainable utilization of environmental resources. However, there are some problems in the application of single semiconductor photocatalyst, such as fast recombination speed of photocarriers and low quantum yield. In order to overcome the disadvantages of single semiconductor in application, cocatalyst is often used to solve these problems. Graphene is used as a photocatalyst because of its outstanding thermal conductivity, mechanical properties, excellent electrical conductivity and large specific surface area. Therefore, in this paper, we use Stöber method to prepare SiO₂ microspheres, then use it as template, and use oil bath method and alkali etching method to prepare CdS hollow microspheres. Finally, we use electrostatic self-assembly method to realize CdS and graphene composite. The morphology, crystal structure, surface properties and photocatalytic properties of the composite were characterized by characterization technology. The results showed that the CdS hollow microspheres with uniform size were encapsulated in graphene nanoflakes at 350 Under the simulated light of W xenon lamp, CdS / graphene composite photocatalysis material showed higher photocatalytic activity of CO₂ reduction. When the content of composite graphene was 2%, the photocatalytic reduction performance reached the best. The yields of methane and carbon monoxide were 2.234 μmol·g^-1·h^-1 and 5.960 μmol·g^-1·h^-1, respectively, Compared with the pure CdS material, it is 3 times and 7 times higher, and the introduction of graphene is conducive to the selective formation of methanol. The improvement of photocatalytic reduction performance is mainly due to the construction of cocatalyst to effectively separate the photocarriers. Secondly, the unique layered structure of graphene provides a large number of adsorption sites for the reaction.

Keywords：CdS; Graphene; Photocatalytic CO₂ reduction; Composite photocatalytic materials

目录

第1章 绪论 5

1.1 研究背景 5

1.1.1 CO₂过度排放的危害 5

1.1.2 CO₂工业回收利用的主要方法 5

1.2 光催化还原CO₂技术 6

1.2.1光催化还原CO₂的反应机理 6

1.2.2 光催化还原反应的影响因素 8

1.2.3光催化还原CO₂的研究进展 9

1.3 选题意义及研究思路 11

1.3.1 选题意义 11

1.3.2 研究思路 11

1.3.3 研究内容 12

第2章 实验 13

2.1 CdS/石墨烯复合光催化材料的制备 13

2.1.1 原料与试剂 13

2.1.2 材料的制备 13

2.1.3 CdS/石墨烯静电自组装过程 14

2.2 表征手段 15

2.3 光催化性能测试 16

第3章 结果与讨论 17

3.1 CdS/石墨烯复合光催化材料的形成机理 17

3.2 样品的微观形貌分析 17

3.3 样品的晶相结构分析 18

3.4 样品的光催化性能分析 19

第4章 总结与展望 22

4.1 工作总结 22

4.2 工作展望 22

参考文献 23

致 谢 25

第1章 绪论

1.1 研究背景

1.1.1 CO₂过度排放的危害

随着人类社会现代化进程的不断加速，人们不管在物质生活水平还是精神生活水平上都得到了前所未有的提高。然而，伴随着这些进步的却是人类对资源的爆炸式消耗和对环境的不注重保护，现阶段能源问题和环境问题俨然已经成为人类社会所面临的两大问题。目前，世界能源消耗的80%仍来自于以石油、煤、天然气等为主的传统化石能源，大量化石燃料的燃烧和消耗不可避免地造成了CO₂的过度排放。据有关机构预测，如果人类依照现阶段对化石燃料的消耗速度并且没有找到能够积极回收二氧化碳的方法，到22世纪初期，地球大气中的二氧化碳浓度可能将突破600 ppm，为现阶段大气中二氧化碳浓度水平的1.5倍之多。CO₂作为大气中最为主要的温室气体，如果浓度高居不下或者持续走高，由于其对地表长波辐射的大量吸收，所导致的温室效应将愈加显著，至此，全球气温将会明显升高，进而将引发一系列的问题^[1]，例如由于温度升高，两极冰川将会大部分融化，导致南极大陆将大部分消失，一些以冰原生态系统为主的动植物将失去生存环境，走向灭绝，两极冰川融化所形成的淡水还将会不断抬高海平面，使一些沿海的重要城市被海水淹没，人口不得不向内陆高海拔地区迁徙，由此人口密度将会不断扩大，生存条件将会变得更加紧迫，此外，大多数低海拔的地区如亚马逊雨林等将会全部消失，缺少“地球之肺”的碳氧循环后，地球大气条件将会更加极端、恶劣。此外，由于全球气温的升高，还会使赤道沿线的热带区域不断扩大，使热带风暴将变得更加频繁，一些原本降雨量较少的热带草原气候区，生态系统将直接破灭，土地沙漠化将会更加严重，病虫害将更加猖獗，人类粮食问题将会面临新的挑战等，这一系列变化，不仅对人类打击严重，对与许多野生动植物而言，无异于灭顶之灾^[2]。由此可见，如何稳定地控制大气中二氧化碳的浓度，已经成为了各国研究者研究和讨论的热点。

1.1.2 CO₂工业回收利用的主要方法

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