中国科学院生态环境研究中心机构知识库
Advanced  
RCEES OpenIR  > 环境纳米技术与健康效应重点实验室  > 学位论文
题名: 二氧化钛石墨烯复合纳米材料制备及其对全氟辛酸的降解
作者: 张提亮
学位类别: 博士
答辩日期: 2015-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 潘纲
关键词: 二氧化钛石墨烯复合材料 ; 全氟辛酸 ; 直接光解 ; 光催化降解 ; PFOA,TiO2-Graphene nanocomposite ; Perfluorooctanoic acid ; direct photolysis ; Photocatalysis ; PFOA
其他题名: Synthesis of TiO2 graphene nanocomposites for photocatalysis degradation of Perfluorooctanoic acid
学位专业: 环境工程
中文摘要:       全氟辛酸(Perfluorooctanoic acid,PFOA)是一种持久性有机污染物,具有生物毒性与潜在健康威胁。常规污水处理工艺并不能有效去除PFOA,高效降解PFOA技术是当前的研究 热点,光降解被认为是其中最有效的技术之一。二氧化钛是光催化降解的明星材料,光稳定性好、成本低、使用广泛。石墨烯是一种二维纳米材料,有超高的热导电 率、极高的比表面积、优越的电子迁移率及良好的透光性。二者的复合二氧化钛石墨烯光催化材料具有较高的光催化活性。然而目前PFOA光化学降解还存在一些 问题,如PFOA的直接光解效率低,二氧化钛降解PFOA效率低、机理尚有争议,二氧化钛石墨烯复合材料降解PFOA研究缺乏等。      
      本文合成了二氧化钛石墨烯复合纳米材料(TiO2 Graphene nanocomposites,TiG),探索了复合材料结构与光催化活性的关系,以提高PFOA的光化学降解效率为目标,考察了温度效应对PFOA直接 光解的影响,尝试用TiG复合材料降解PFOA,并探索了其降解机理。具体研究结果如下:
      (1)TiG复合材料的结构特征。TiG复合材料中的TiO2为锐钛矿晶型,石墨烯在复合材料中是TiO2晶体的生长基底,因而其组分含量不影响晶体结 构。石墨烯的加入有效地增加了TiG复合材料的比表面积,且石墨烯组分含量越多,TiO2纳米晶体分布越均匀。TiO2纳米晶体是以Ti-O-C键结合在 石墨烯的含氧官能团位点上。相对于纯TiO2,Ti-O-C键改变了TiG复合材料中Ti的近边结构,但是石墨烯组分含量增加对Ti的近边结构影响甚微。 TiG复合材料具有锐钛矿晶型结构和较大的比表面积,组分之间以Ti-O-C键紧密结合。
      (2)TiG复合材料的光催化活性研究。TiG20(石墨烯组分含量为20%)复合材料在20 min内可以使罗丹明6G完全脱色,且表观速率常数是同条件下TiG1(石墨烯组分含量为1%)的6.3倍。这种影响与TiG复合材料中共轭大π键和 Ti-O-C键相关。共轭大π键一方面增强了罗丹明6G的π-π堆积吸附,另一方面可以接收光生电子;Ti-O-C键便于光生电子转移,抑制光生电子空穴 对的复合,从而提高光催化效率。TiG20复合材料的光催化活性还与用量相关,当用量在4.0 mg·L-1时,光催化效率最高。复合材料用量低不足以启动足够的降解反应,而用量过高会导致光散射或反射,降低光利用率,从而降低降解效率。TiG复合 材料具有良好的光催化活性,且随着石墨烯组分含量增加而增强。
      (3)温度对PFOA的直接光解的影响。为了更好地考察TiG复合材料在PFOA的降解中的作用机理,首先研究了反应温度对PFOA直接光解的影响。研究 发现,反应温度升高,PFOA光降解速率有较大提升。85 °C下,60 min内去除率即可达到99%(PFOA初始浓度30 mg·L-1)。提高反应温度可以提高光解的量子效率,85 °C下光量子效率比25 °C高约12倍。温度效应循环反复作用于每一次脱去CF2单元的化学反应过程,加快了氟离子的生成,从而提高了脱氟效率。85 °C下,180 min内脱氟率可达到72%。此外,去除1 μmol PFOA的能耗从25 °C的82.5 kJ降低到85 °C的10.9 kJ。反应温度升高促进了PFOA的直接光解和脱氟,并降低了能耗。
       (4)TiG复合材料催化降解PFOA及其机理。25 °C下,PFOA直接光解与TiG20催化降解的速率常数分别为0.693 × 10-2 min-1和1.406 × 10-2 min-1,常温下TiG20促进了PFOA的降解。60 °C下,PFOA直接光解与TiG20催化降解的速率常数分别为4.373 × 10-2 min-1和0.361 × 10-2 min-1,高温下TiG20抑制了PFOA的降解。在TiG20催化降解体系中,PFOA降解通过两个竞争的化学反应过程进行:β裂解和直接光解。25 oC下,PFOA主要以TiG20光生空穴引发的β裂解方式降解;60 oC下,PFOA主要以直接光解的方式降解,此条件下TiG复合材料倾向于生成羟基自由基,而羟基自由基不能有效降解PFOA,因而抑制了PFOA的直接 光解。TiG复合材料在室温下促进了PFOA降解,在高温下抑制了PFOA降解。
      本研究实现了PFOA的高效直接光解。观察了二氧化钛石墨烯复合材料(TiG)对PFOA的光催化降解。在TiG光催化体系中,存在两种竞争的PFOA降 解过程:直接光解和β裂解。室温下TiG复合材料通过β裂解的方式促进了PFOA降解。高温下TiG复合材料倾向于生成羟基自由基,而羟基自由基不能有效 降解PFOA,因而降低了降解效率。
英文摘要:
      Perfluorooctanoic acid (PFOA) is a persistent organic pollutant. PFOA is a toxicant in animals and enhances the health risks. It is difficult to remove PFOA using most conventional wastewater treatment techniques. Recently, the development of PFOA degradation techniques is one of the current research hotspots. Photodegradation is one of the most promising alternatives to decompose PFOA efficiently. TiO2 photocatalysis is widely used in the environmental fields due to its stability and low cost. Graphene is a two-dimensional nanomaterial and has great potential in various applications, due to its excellent features in a high electrical and thermal conductivity, high mechanical strength, high carrier mobility, high transparency and huge specific surface area. The nanocomposites of TiO2 and graphene exhibit high photocatalytic activity. Although PFOA degradation technology has made great process, there are also some thorny problems, such as the poor efficiency of PFOA direct photolysis, the controversial mechanisms of PFOA photocatalysis by TiO2 and the lack of investigate for the PFOA photocatalysis by the nanocomposites of TiO2 and graphene.
      In this study, we prepared the nanocomposites of TiO2 and graphene (TiG); explored the relationship between the structure of TiG and photocatalysis activity; investigated the temperature effect on PFOA direct photolysis; tried to degrade PFOA using TiG as photocatalyst and speculated the photocatalysis mechanism. The specific results are as follows:
      (1) The structure of TiG nanocomposites. The TiO2 component in TiG is anatase phase. TiO2 nanoparticles with a narrow size distribution disperse on the surface of graphene sheets uniformly when the graphene content increase. The graphene component increase the surface area of TiG nanocomposites greatly. The TiO2 is bond on the site of oxygen functional groups in graphene with Ti-O-C bond. The Ti-O-C bond modifies the near edge structure of Ti element in pure TiO2. In a word, TiG has high surface area and load anatase TiO2 grown on graphene with Ti-O-C bond.
      (2) The photocatalysis performance of different TiG nanomaterials. TiG20 (graphene content 20 wt. %) can completely decolor Rhodamine 6G in 20 min. The apparent rate constant of TiG20 is 6.3 times than that of TiG1. The aromatic structures of TiG enhance the π-π stack adsorption of Rhodamine 6G and accept photo-induced electron. The Ti-O-C bond is favorable for the transfer of photo-induced electron. The aromatic structures and Ti-O-C bonds inhibit the recombination of photo-induced electron-hole pair and thus promote the photodegradation. TiG20 has an optimal dosage (4.0 mg·L-1). The photodegradation is not enough to degrade Rhodamine 6G when the dosage is small. The degradation efficiency decreases when the dosage is big due to the light scattering and reflecting. In a word, the increase of graphene content in TiG nanocomposites enhances the photocatalysis activity.         
      (3) Temperature effect on PFOA photolysis. The high temperature enhances the decomposition of PFOA. At 85 °C, the direct photolysis could almost completely remove PFOA in 60 min. The quantum yield at 85 °C (1.72 × 10-3) is 12 times higher than that at 25 °C (1.55 × 10-4). The high temperature promotes each cyclical process of losing one CF2 unit and thus enhance the production of fluorine ions. At 85 °C, the defluorination ratio achieve 72% in 180 min. The energy consumption for removing one μmol PFOA reduced from 82.5 kJ at 25 °C to 10.9 kJ at 85 °C. The high temperature enhances PFOA photolysis and defluorination using low energy consumption.
      (4) PFOA photocatalysis by TiG nanocomposites. At 25 °C, the rate constant in direct photolysis is 0.693 × 10-2 min-1, the rate constant in TiG20 degrading system increase to 1.406 × 10-2 min-1. At 60 °C, the rate constant in direct photolysis was 4.373 × 10-2 min-1, the rate constant in TiG20 degrading system decreased to 0.361 × 10-2 min-1. In TiG photocatalysis system, there are  two different  kinds of  PFOA degradation min  ,  the rate  constant in  TiG20 degrading system processes, including  direct photolysis and  β-scission. At 25  °C, β-scission accounted for a large proportion of the  PFOA degradation. At 60 °C, direct photolysis accounted for a larger proportion. TiG20 nanocomposite is prone to produce •OH at 60 °C, which is not effective to  degrade PFOA. TiG20 nanocomposite enhances  PFOA degradation at 25 °C but inhibits PFOA degradation at 60 °C.
      We realized the efficiency enhancement of PFOA direct photolysis and investigated PFOA photocatalysis by the nanocomposites of  TiO2 and graphene (TiG). Both direct photolysis and β-scission  existed in TiG photocatalysis system.  At room temperature, TiG promoted the degradation  of PFOA through β-scission chemical process. At  high
temperature, TiG20 nanocomposite  was prone to  produce •OH and thus  inhibited the degradation of PFOA.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/34541
Appears in Collections:环境纳米技术与健康效应重点实验室_学位论文

Files in This Item:
File Name/ File Size Content Type Version Access License
张提亮--二氧化钛石墨烯复合纳米材料制备及其对全氟辛酸的降解.pdf(5019KB)学位论文--限制开放 联系获取全文

Recommended Citation:
张提亮. 二氧化钛石墨烯复合纳米材料制备及其对全氟辛酸的降解[D]. 北京. 中国科学院研究生院. 2015.
Service
Recommend this item
Sava as my favorate item
Show this item's statistics
Export Endnote File
Google Scholar
Similar articles in Google Scholar
[张提亮]'s Articles
CSDL cross search
Similar articles in CSDL Cross Search
[张提亮]‘s Articles
Related Copyright Policies
Null
Social Bookmarking
Add to CiteULike Add to Connotea Add to Del.icio.us Add to Digg Add to Reddit
所有评论 (0)
暂无评论
 
评注功能仅针对注册用户开放,请您登录
您对该条目有什么异议,请填写以下表单,管理员会尽快联系您。
内 容:
Email:  *
单位:
验证码:   刷新
您在IR的使用过程中有什么好的想法或者建议可以反馈给我们。
标 题:
 *
内 容:
Email:  *
验证码:   刷新

Items in IR are protected by copyright, with all rights reserved, unless otherwise indicated.

 

 

Valid XHTML 1.0!
Copyright © 2007-2018  中国科学院生态环境研究中心 - Feedback
Powered by CSpace