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石墨烯复合材料的性能研究及其在石油化工污染物处理上的应用
论文作者:童鞋论文网  论文来源:www.txlunwenw.com  发布时间:2019/10/8 8:59:30  

摘要:现如今环境问题的严峻性迫使环保技术开发迫在眉睫,而石油石化行业生产输运过程中产生的废水废液的处理是一大技术难题。含油废水中的污染物包括芳香烃、油污等有机污染物,及卤代烃、表面活性剂等无机污物染。传统手段无法完全处理此类污染物并且易造成二次污染。因此需要高效、洁净、无毒害的处理方法。

二氧化钛是最为常用的光催化剂,可以针对上述污染物进行较为彻底的降解,产物为无毒害的小分子无机物。而且二氧化钛本身无毒,性质稳定,价格低廉。但同样也存在光响应范围局限、产生降解作用的电子-空穴容易复合等问题从而影响光催化性能。

在此背景下,本文着眼于光催化处理技术,对于二氧化钛光催化剂做了简要介绍,综述了二氧化钛光催化剂及其改性方法的国内外研究现状。本文简化了反应制备过程,通过简单水热法制备石墨烯/二氧化钛复合光催化剂,并在此基础上以氨水为氮源,通过水热法合成氮掺杂石墨烯/二氧化钛,制备了不同反应条件下(时间、温度、质量分数等)的复合物样品。通过扫描电子显微镜、拉曼光谱、红外光谱等表征手段对其进行表征,并对结果进行了分析。另外针对复合物的光催化性能,选用亚甲基蓝、甲苯、二氯乙烷等具有鲜明代表性的物质作为目标污染物进行了降解实验。研究石墨烯负载及氮掺杂对二氧化钛光催化剂复合改性的影响以及针对不同污染物的降解机理。另外,进一步研究了石墨烯表面官能团对光催化剂性能的影响。

研究发现石墨烯及氮元素的引入对二氧化钛的团聚有抑制作用。尽管水热反应后样品比表面积较小,但特别的负载状态反而使得光催化性能有显著的提高。并且两种负载物质的质量分数提高会相应提升复合物光催化性能,通过催化实验找到最优配比。氮元素的掺杂会影响复合物的晶体生长结构,氨基在复合物中起桥接作用,会使产物尺寸增大,并且活化复合物的界面,提高与其他元素或基团结合。通过优化表面官能团种类和数量,发现催化剂对具有相同官能团的吸附质有更好的吸附作用,相应提升了对该物质的降解能力。

对不同污染物的降解实验进行分析后发现:降解效率的影响因素主要包括被降解物的性质,催化剂表面官能团的种类及石墨烯与二氧化钛的成键情况等。相对分子量不是降解快慢的首要因素,相对分子量相近,但官能团种类与催化剂相似度高,数量多,则更易降解。从成键情况分析,石墨烯与二氧化钛成键情况越好,两者之间的界面接触更好,电子传导能力更强,从而使光催化效率更高。

Recently, water pollution becomes one ofthe concerned environmental problems plaguing people throughout the world,which is caused by contamination of organic pollutants and heavy metalpollutants in water. Some serious threaten have be introduced to human healthand the living environment. Specially, the pollutants in oily wastewaterinclude aromatic hydrocarbon, oil pollution and inorganic contaminants,including halogenated hydrocarbons, surfactants and so on. Photocatalysis, as alow cost and green technology, shows huge potential in completely removing mostkinds of pollutants in water without using additional chemical reagents.

Titanium dioxide (TiO2) is one of thewidely used photocatalyst, and kinds of pollutants will degrade into smallmolecule inorganic substances under the illumination. Moreover, TiO2 possessessome advantages, such as non-toxic, high stability and low cost. However, theabsorption edge is in the UV light range due to its wide band-gap. Moreover,the high recombination of the photo-induced electron-hole pairs limits thephotocatalytic performance of the intrinsic TiO2.

Firstly, the photocatalytic mechanism andthe latest progress of the TiO2 based photocatalysts is reviewed. summarizesthe titanium dioxide photocatalyst and the experimental methods of graphenemodification, as well as the research status at home and abroad. In this paper,a facile hydrothermal method on preparing the graphene/TiO2 compositephotocatalyst was suggested, and the influence on the resulting photocatalyticperformance from the mass fraction of the graphene is discussed. Methyleneblue, toluene, dichloroethane and other representative substances are adoptedas the target pollutants to evaluated the photocatalytic performances of thesecomposites. Furthermore, the nitrogen-doped graphene/TiO2 was synthesized byhydrothermal method by using the ammonia water as nitrogen source, and thecorresponding photoactivities under UV- and visible-light irradiation arerevealed. The effect of the added graphene and N atoms are investigated, andthe distinctions on the photocatalytic performances from different reactionconditions (hydrothermal time and hydrothermal temperature, etc.) are alsoanalyzed. Based on the characterization resulting from the SEM, Raman spectrum,IR spectrum, the morphology and microstructure information of these compositephotocatalysts are detected. 

It was found that graphene and nitrogenelements could inhibit the agglomeration of titanium dioxide. Although the BETof the composite photocatalysts are small after hydrothermal reaction, the highphotocatalytic performances are achieved because of the special loading state.The photocatalytic properties of these composites are closely related to themass fraction of the loaded graphene and doped N atoms, and the optimum ratio arefound. The doping of N elements affects the crystal growth structure of thecomposite, in which amino group plays a bridging role to activate the interfacebetween the graphene basal plane and TiO2. By optimizing the type and quantityof surface functional groups, the catalyst performances enhance remarkable. Theadsorbates with the same functional groups have better adsorption ability, thusimproving the degradation ability of the substance accordingly.

The degradation experiments of differentpollutants show that the main determined factors for the photocatalyticperformances include the molecular weight of the pollutions, type and totalamount of functional groups on the graphene surface and mass fraction of thedoped N atoms. The type and total amount of the surface functional groups ofgraphene not only determine the adsorption ability to various adsorbates, butalso exert a significant influence on the visible-light activity of thecomposite photocatalysts. Similarly, the amount of doped N atoms imposes aremarkable effect on the photocatalytic performance under visible-lightirradiation.

关键词:二氧化钛;氮掺杂石墨烯;光催化机理;污染物降解

titanium dioxide modification;nitrogen-doped graphene;study onphotocatalytic Mechanism;pollutant degradation

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