【作者】 苏碧泉；

【导师】 王春明；

【作者基本信息】 兰州大学 ， 分析化学， 2009， 博士

【摘要】 环境污染与防治已成为全球性普遍关注的重要课题,有机污染物的光电催化及电催化研究是环境化学领域的前沿热点方向之一,深入研究和了解有机污染物的降解机理及催化行为对于研发新型的污染治理方法具有重要的意义。本文利用电化学方法研究了亚甲基蓝（Methylene blue, MB）和对硝基苯酚（p-Nitrophenol,pNP）在修饰电极上的光电催化降解机理及电催化行为,主要包括以下内容:1.利用循环伏安法（Cyclic voltammetry, CV）和表面红外光谱法（IR spectra,IR）为主要研究手段,将有机污染物亚甲基蓝和光催化剂二氧化钛,通过Nafion修饰在铂电极（MB/Nf/TiO₂）上,对亚甲基蓝现场光电催化降解机理进行了研究。结果表明,在紫外光照条件下,亚甲基蓝分子对Nafion-TiO₂ （Nf/TiO₂）表面上的光电子清除具有一定的促进作用,而且降解过程中残余亚甲基蓝分子的循环伏安峰电流与光降解反应时间之间呈线性衰减关系。在光电催化降解过程中,红外光谱证明亚甲基蓝分子受到具有强氧化性羟基自由基的进攻而经历了去甲基化和C=N键的断裂。该研究为有机污染物的现场光电催化降解机理分析提供了一个简单有效的方法。2.利用聚苯胺-TiO₂-Nafion （PANI/TiO₂/Nf）复合膜修饰的铂电极为研究对象,通过扫描电子显微镜（Scanning electron microscopy, SEM）和电化学阻抗谱（Electrochemical impedance spectroscopy, EIS）技术对其形态和界面性质进行了表征,并利用循环伏安法、动力学伏安法对亚甲基蓝在PANI/TiO₂/Nf复合膜上的电化学行为进行了研究。结果表明,多孔性PANI/TiO₂/Nf复合膜具有较大的有效面积,该修饰电极对亚甲基蓝有较好的电催化活性,亚甲基蓝分子在PANI/TiO₂/Nf复合膜修饰电极上不发生二聚反应,而且亚甲基蓝分子在该修饰膜内表观扩散系数较大。该类复合膜用于传感膜材料以及光电反应中催化剂载体具有一定的可行性。3.在nano-TiO₂修饰的旋转环-盘铂电极（Rotating ring-disk electrode, RRDE）上,将旋转铂环电极作为检测工作电极,而将旋转铂盘电极用纳米TiO₂修饰后作为光电反应工作电极,利用动力学示差脉冲伏安法（Hydrodynamic differential pulsevoltammetry, HDPV）,研究了对硝基苯酚的光电催化降解过程。在旋转铂环电极上实时记录了动力学状态下对硝基苯酚光电催化降解中间产物的伏安响应信号。实验表明,在0.55 V附近的阳极峰是对硝基苯酚光电催化降解过程中形成电活性主要中间产物对苯二酚（Hydroquinone, HQ）的电氧化峰,实验证明它来自于具有强氧化能力的光生羟基自由基（·OH）与对硝基苯酚直接相互作用的结果。另外,阳极偏压的增大能够提高对硝基苯酚光电催化降解的效率,光电协同催化是这种修饰膜上对硝基苯酚催化降解的主要途径。这种将修饰旋转环-盘电极与动力学示差脉冲技术相结合的研究方法,对现场研究硝基酚类有毒污染物的光电催化降解反应机理是一种非常有效的技术手段。4.采用循环扫描电聚合法（Electropolymerization）和脉冲电沉积法（Pulsedelectrodeposition）制备了一种新型的聚多巴胺/纳米银（PDA/Ag）修饰玻碳电极。实验结果发现,聚多巴胺修饰层对纳米银的成核和生长具有影响作用,与裸电极相比,在修饰聚多巴胺基底上通过脉冲电沉积得到的纳米银颗粒更小、更均匀,单位面积上的沉积量也更多。另外,利用循环伏安法研究表明对硝基苯酚在该修饰电极上的电催化还原特性,聚多巴胺/纳米银修饰的玻碳电极对对硝基苯酚有很好的电催化活性,能使对硝基苯酚的还原电位明显降低;利用示差脉冲法研究发现对硝基苯酚还原电流的变化与浓度的变化呈线性关系,这为建立用聚多巴胺/纳米银修饰的玻碳电极对硝基酚类有毒污染物的检测方法提供了实验依据。更多还原

【Abstract】 The control of environmental pollution has become a global important issue ofcommon concern.Photoelectrocatalytic and electrocatalytic study of organicpollutants is one of the forefront of hot spots in the environmental chemistry field.The in-depth study and understanding of the degradation mechanism and catalyticbehavior of organic pollutants is of great significance for the development of newmethods of pollution control.In this paper,the degradation mechanism and catalyticbehavior of methylene blue （MB） and p-nitrophenol （pNP） at modified electrode havebeen investigated.The detailed contents can be summarized as follows:1.The investigation of in situ photoelectrocatalytic degradation of the MB moleculesmerged into a nano-TiO₂ modified film by electrochemical techniques is proposed.The MB-Nafion-TiO₂ （MB/Nf/TiO₂） modified platinum electrode shows reversibleand faster electron-transfer efficiency in photoelectrocatalytic degradation reactions ofsurrounding compounds adsorbed on photocatalyst.Open-circuit potential (E_oc) of theMB/Nf/TiO₂ electrode shows that the MB molecules have an assured effect withtransferred photogenerated electrons on the Nf/TiO₂ interface under UV illumination.A linear regression equation is obtained by the cyclic voltammetry peak current of theresidual MB and the reaction time in the degradation process,in which MB undergoesdemethylation and C=N bond breaking.It is a promising approach for investigating insitu the photoelectrocatalytic degradation of pollution.2.A porous Nafion-TiO₂-polyaniline （Nf/TiO₂/PANI） composite film with a largeelectrode effective surface area was prepared on a platinum electrode by a simplemethod.The morphology and the interfacial properties of the composite film wereevaluated by scanning electron microscopy （SEM） and electrochemical impedancespectroscopy （EIS）.The investigation of cyclic voltammetry （CV） confirmed that theNf/TiO₂/PANI film showed an excellent electrocatalytical response to the redox ofMB and was mechanically stable under hydrodynamic conditions.The resultsobtained reveal that the dimerization of MB in Nf/TiO₂/PANI film does not occurred and the introduction of the conducting polymer to electrocatalysts helps in increasingthe interfacial properties between the electrode and electrolyte.The composite filmwould be used as a promising support material in electrochemical orphotoelectrochemical applications.3.The photoelectrocatalytic degradation behavior of pNP was investigated by usinghydrodynamic differential pulse voltammetry （HDPV） technique.The method wasapplied on a nano-TiO₂ modified platinum rotating ring-disk electrode （RRDE） asversatile working electrode.The voltammetric response of the intermediate productwas recorded instantly at the rotating platinum-ring electrode under hydrodynamicconditions via compulsive transport during the photoelectrocatalytic degradationprocess of pNP.A distinct anodic peak at about 0.55 V is mainly attributed to theresult of the formation of electroactive intermediate product,namely hydroquinone（HQ）,through the direct reaction between photo-generated powerful oxidant（hydroxyl radicals,·OH） andpNP.The present work has demonstrated that HDPV canbe effectively used to in situ monitor the formation of intermediate product atnano-TiO₂ modified RRDE,providing a promising approach to investigate in situ thephotoelectrocatalytic degradation mechanism of organic pollutants like toxicnitrophenols.4.A glassy carbon electrode modified with silver particles under polydopamine filmwas prepared successfully by means of electropolymerization and pulsedelectrodeposition.A detailed analysis of the scanning electron microscope imagesreveals that silver deposit,obtained under pulsed electrodeposition conditions,appears as homogeneously compact and the crystallites are well dispersed on thepolydopamine substrate than that observed on the unmodified glassy carbon surfaces.The resulting silver nanoparticle/polydopamine modified glassy carbon electrode（Ag/PDA/GC） was electrochemically characterized through the reduction ofpNP.Thepotential needed for the reduction of the compound on the Ag/PDA/GC electrode issignificantly less negative than that observed on the unmodified glassy carbonelectrode substrates.A linear equation is obtained between the cyclic voltammetrypeak current and the concentration of pNP.The Ag/PDA/GC would be used in the practical application for detecting toxic nitrophenols.更多还原