钛基体增强掺硼金刚石电极电催化过程动力学研究

发布时间：2018-07-28 10:15

【摘要】：水环境中存在的有机污染物直接关乎人类身体健康,同时与社会发展有着至关重要的联系,去除水体中难降解有机污染物已成为水环境保护的迫切要求。电催化氧化技术以电极表面电化学产生强氧化性活性物质为媒介直接或间接氧化有机物,被环保工作者广泛的应用到有机物去除领域。掺硼金刚石(BDD)电极被认作为电催化氧化领域最为理想高效的电极材料,而具体的有机物电催化氧化过程、机理及动力学增强机制有待进一步研究。本论文以BDD电极电催化有机污染物为基础,重点围绕高效BDD电极的构筑及其在有机污染物的矿化过程,探索BDD电极电催化氧化有机污染物的机理、降解过程和钛基体结构与电催化之间的联系;同时针对电极/溶液界面的电催化机理及动力学过程,设计实现增强电催化氧化过程动力学的具体途径和方式。具体的主要研究成果如下:(1)基于提高BDD电极电催化活性的目的,在多孔钛基体上通过热丝化学气相沉积方法制备了三维多孔钛基掺硼金刚石(3D-Ti/BDD)薄膜,SEM、XRD和Raman测试表明多孔Ti/BDD薄膜保持了与二维BDD薄膜近似的质量、晶型及相成分。在保持BDD电极自身高析氧电位特点的前提下,基体结构由二维到多孔钛的改变使薄膜呈现三维多孔结构,增加了BDD薄膜电极的表面积,多孔钛/BDD电极的有效电化学面积由二维BDD电极的2.62 cm2 cm-2增加到8.37 cm2cm-2;循环伏安测试及电化学阻抗测试表明多孔钛BDD对铁氰化钾氧化还原对具有更高的电催化活性和更快的电荷转移速率,电荷转移电阻由128.3Ωcm2降低到31.3Ωcm2。同时bdd薄膜沉积过程的操作参数也发挥着重要的作用,碳源浓度、硼掺杂浓度及反应器压力等通过影响沉积过程中金刚石颗粒的成核和生长速率,直接影响bdd晶粒的表面形貌及质量,通过操作参数的控制能够实现微米及纳米级多孔bdd薄膜的可控制备。(2)抗炎药物在三维bdd电极上的降解过程及动力学研究。抗炎药物已成为当前水环境中出现的新型有机污染物,选取扑热息痛为模拟污染有机物,研究其在bdd电极上的降解过程及动力学。扑热息痛在循环伏安曲线的0.90v附近出现明显的氧化峰,证明在扑热息痛在bdd电极上的电催化过程存在电子转移反应,并且其在对应电位下的响应电流与有机物浓度呈现良好的线性关系。不同电流密度下的有机物降解过程表明,随着电流密度的升高,用于有机物电催化过程的电流逐渐增加,加快了扑热息痛的整体矿化速率;但高电流密度也加剧了电极表面析氧副反应的进行,造成电流效率逐渐下降。扑热息痛在bdd电极上的降解动力学符合准一级反应动力学,在二维及多孔bdd电极上对应的表观速率常数分别为0.208、0.344h-1。多孔bdd电极拥有更大的比表面积,为扑热息痛在bdd电极上的直接电子转移过程提供更多的反应活性位点,促进间接电催化氧化扑热息痛过程中强氧化活性羟基自由基的电生成,最终表现出更快的电化学反应动力学速率。最后,根据扑热息痛电催化降解过程的存在的中间产物,提出了其在bdd电极上的机理及降解途径。(3)对苯二酚在不同电极材料上的电催化矿化过程表明电极的电催化氧化活性与电极析氧电位及表面产生羟基自由基能力有着重要的联系;不同取代基团的对位取代酚类化合物在bdd电极上的电化学降解实验显示电催化反应的活性受取代官能团自身的电子效应制约,有机物矿化过程中取代基脱离苯环成为整个电催化反应过程的决速步骤,且电催化反应速率与取代基特征hammett常数σ呈近似线性关系。bdd电催化氧化机理主要以电产生强氧化活性羟基自由基为媒介,多孔bdd电极自身多孔结构的存在使多孔bdd电极表面产生羟基自由基的量约为二维电极的2.7倍,多孔bdd电极对于不同种类有机物的阶跃电流为二维电极的2倍,表现出更高的间接电催化氧化能力。电催化氧化不同种类有机物的降解结果表明,多孔bdd电极能够实现更快的去除速率和电流效率,但多孔电极内部不规则的孔道结构造成有机物在多孔电极内部的传质过程变得困难,成为整个降解过程的限制步骤,造成了多孔电极羟基自由基利用率只有50~60%,这在一定程度削弱了多孔BDD电极高催化氧化能力的优势。(4)针对于上述多孔电极孔洞内部传质受限的问题,进一步设计用于增强电极/溶液界面传质过程的三维网络BDD电极。以三维网络钛作为沉积基体制备得到具有表面微结构的三维网络BDD电极。电极微结构表面为电催化氧化反应提供更多的活性位点,有效电化学表面积为二维BDD电极的1.6倍。由于表面积的增强作用及天然的网络结构,三维网络BDD电极在铁氰化钾氧化还原对溶液中的相关电化学测试中表现出更高的电催化活性和较低的传质电阻;表面疏水性的增强作用使电极表面产生的羟基自由基更容易脱离电极表面进入本体溶液与有机物进行电化学氧化作用,增加了羟基自由基的利用效率;三维网络结构增强有机物在电极表面的传质过程使有机物在电极表面具有更快的传质系数,削弱了传质过程控制的限制,以上因素使三维网络BDD电极相在具体的不同种类有机物的矿化实验中表现出更快的去除速率及动力学过程。此外,将三维网络钛基体还可扩展到其他用于水处理的网络钛基体和活性涂层,制备得到的网络PbO2电极表现出比拟于BDD电极的优异电催化氧化性能,验证了此类网络电极的适用性和高效性。
[Abstract]:Organic pollutants in water environment are directly related to human health and have a vital relationship with social development. It has become an urgent requirement for water environmental protection to remove the difficult degradation of organic pollutants in water bodies. The electrocatalytic oxidation technology produces strong oxidizing active substances from the electrode surface electrochemistry as the direct or indirect oxygen. Organic compounds are widely used by environmentalists in the field of organic matter removal. Boron doped diamond (BDD) electrode is considered as the most ideal and efficient electrode material in the field of electrocatalytic oxidation. The mechanism and kinetics enhancement mechanism of the specific organic electrocatalytic oxidation process need further study. This paper uses BDD electrode to electrocatalysis organic pollution. On the basis of the dye, focusing on the construction of high efficiency BDD electrode and the mineralization process of organic pollutants, the mechanism of electrocatalytic oxidation of organic pollutants by BDD electrode, the relationship between the degradation process and the titanium matrix structure and electrocatalysis are explored. At the same time, the electro catalytic mechanism and the kinetic process of the electrode / solution interface are designed to enhance the electrical stimulation. The concrete main research results are as follows: (1) based on the purpose of improving the electrocatalytic activity of BDD electrode, a three-dimensional porous titanium based boron doped diamond (3D-Ti/BDD) film was prepared on porous titanium substrate by hot wire chemical vapor deposition. The SEM, XRD and Raman tests showed that the porous Ti/BDD film was preserved. On the premise of maintaining the high oxygen evolution potential of the BDD electrode, the matrix structure from the change of two-dimensional to porous titanium makes the thin film three-dimensional porous structure, increases the surface area of the BDD film electrode, and the effective electrochemical area of the porous titanium /BDD electrode is 2.62 from the two-dimensional BDD electrode, on the premise of maintaining the high oxygen evolution potential of the BDD electrode. Cm2 cm-2 increases to 8.37 cm2cm-2; cyclic voltammetry and electrochemical impedance tests indicate that porous titanium BDD has higher electrocatalytic activity and faster charge transfer rate for potassium ferricyanide redox, and the operation parameters of the charge transfer resistance from 128.3 Omega cm2 to 31.3 Omega cm2. and the BDD film deposition process are also important. The surface morphology and quality of BDD grains are directly affected by the influence of carbon source concentration, boron doping concentration and reactor pressure on the nucleation and growth rate of the diamond particles in the deposition process. The controllable preparation of micrometer and nanoscale porous BDD films can be achieved through the control of operating parameters. (2) the degradation of anti-inflammatory drugs on the three-dimensional BDD electrode Study of process and dynamics. Anti inflammatory drugs have become a new organic pollutant in the current water environment. The degradation process and kinetics of paracetamol on the BDD electrode are studied. Paracetamol appears obvious oxidation peak near the 0.90v of cyclic voltammetry curve. It is proved that paracetamol is on the BDD electrode. There is an electron transfer reaction in the electrocatalysis process, and the response current at the corresponding potential has a good linear relationship with the concentration of organic matter. The degradation process of organic matter under different current density shows that the current increase in the electrocatalytic process of organic matter increases with the increase of current density, accelerating the overall mineralization of acetaminophen. However, the high current density also aggravates the oxidation side reaction of the electrode surface, resulting in the gradual decrease of the current efficiency. The degradation kinetics of acetaminophen on the BDD electrode conforms to the quasi first order reaction kinetics, and the apparent rate constant on the two-dimensional and porous BDD electrode has a larger comparison table for the 0.208,0.344h-1. porous BDD electrode, respectively. The area provides more reactive sites for the direct electron transfer of paracetamol on the BDD electrode, promoting the electroformation of the strongly oxidized active hydroxyl radical in the process of indirect electrocatalytic oxidation acetaminophen, and eventually showing a faster electrochemical reaction kinetic rate. The mechanism and degradation pathway on the BDD electrode are proposed. (3) the electrocatalytic mineralization of hydroquinone on different electrode materials shows that the electrocatalytic oxidation activity of the electrode has an important relation with the electrode oxygen evolution potential and the surface generation of hydroxyl radical. The substituent phenols of different substituent groups are in the BD The electrochemical degradation experiments on the D electrode show that the activity of the electrocatalytic reaction is restricted by the electronic effect of the substituent functional group itself. The substituent is separated from the benzene ring in the mineralization process and becomes the quick step of the whole electrocatalytic reaction process, and the electrocatalytic reaction rate is approximately linear with the Hammett constant of the substituent group, which has an approximate linear relationship with the electrocatalytic oxygen (.Bdd). The mechanism mainly produces the strong oxidation active hydroxyl radical as the medium, and the existence of porous structure of porous BDD electrode makes the amount of hydroxyl radical produced on the surface of the porous BDD electrode is about 2.7 times that of the two-dimensional electrode, and the step current of the porous BDD electrode is 2 times that of the two dimensional electrode for different kinds of organic matter, showing a higher indirect electrical stimulation. The degradation of different kinds of organic compounds by electrocatalytic oxidation shows that the porous BDD electrode can achieve faster removal rate and current efficiency. However, the irregular pore structure inside the porous electrode leads to the difficulty in the mass transfer process of organic matter in the porous electrode, which is a limiting step for the whole degradation process and causes much more. The utilization rate of hydroxyl radical of hole electrode is only 50~60%, which weakens the advantage of high catalytic oxidation ability of porous BDD electrode. (4) to further design the three dimension network BDD electrode for enhancing the mass transfer process of electrode / solution interface for the problem of the internal mass transfer in the porous electrode hole. A three-dimensional network BDD electrode with surface microstructures is prepared. The electrode microstructural surface provides more active sites for the electrocatalytic oxidation reaction, and the effective electrochemical surface area is 1.6 times as high as that of the two-dimensional BDD electrode. Due to the enhancement of surface area and the natural network structure, the three-dimensional network BDD electrode redox to the solution of the solution of the potassium ferricyanide Higher electrocatalytic activity and lower mass transfer resistance were shown in the related electrochemical tests, and the enhancement of surface hydrophobicity made the hydroxyl radicals produced on the surface of the electrode more easily detached from the surface of the electrode to enter the bulk solution and the organic matter to be electrochemical oxidation, and increased the efficiency of the hydroxyl radical. The mass transfer process of organics on the electrode surface makes the organic matter have a faster mass transfer coefficient on the surface of the electrode and weakens the restriction of the mass transfer process control. The above factors make the three-dimensional network BDD electrode show a faster removal rate and dynamic process in the mineralizing experiment of different kinds of organic matter. In addition, the three-dimensional network is used. The complex titanium matrix can also be extended to other network titanium and active coatings for water treatment. The obtained network PbO2 electrode shows excellent electrocatalytic oxidation performance compared to the BDD electrode, and the applicability and efficiency of this kind of network electrode have been verified.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O646.5;O643.3

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