【作者】 钱功明；

【导师】 杨昌柱； 张敬东；

【作者基本信息】 华中科技大学 ， 环境工程， 2007， 博士

【摘要】 研制基于纳米材料修饰的电极,并将其应用于环境电化学方面的研究,是一个将纳米技术、环境工程和电分析化学有机结合起来的崭新领域,有利于建立电分析化学的新技术和新方法,促进环境电化学的发展。本论文的工作主要集中在纳米技术与电分析化学相结合的最活跃的研究领域之一——新型纳米材料修饰电极的制备和应用。本文采用了三种不同的方法制备出具有高催化活性的载铂纳米修饰电极,将其用于环境检测,并对苯酚电化学氧化进行了热力学分析。本文的主要内容如下:1.以抗坏血酸为还原剂,采用一步原位化学还原法将纳米金属铂直接修饰到玻碳电极表面制备了纳米铂修饰玻碳(PtNPs/GC)电极,结果表明,大量球形纳米铂颗粒修饰到玻碳电极表面,粒径为40-200 nm。研究了电极性能和半胱氨酸在PtNPs/GC电极上的电化学行为。该修饰电极具有优良的电化学性能,并对甲醇具有良好的催化氧化作用。较高的pH和温度有利于提高其氧化还原反应活性。研究发现:该修饰电极对半胱氨酸具有良好的催化氧化性能,与铂片电极相比,半胱氨酸的氧化峰电位降低了300 mV,氧化峰电流增加了12倍。半胱氨酸浓度在1.0×10-7 mol/L到1.3×10-5 mol/L范围内,其氧化峰电流与浓度呈良好的线性关系。可用于半胱氨酸的检测,检测下限为7.6×10-8 mol/L。2.利用循环伏安法研究了苯酚、邻苯二酚和对苯二酚在PtNPs/GC电极上的电化学氧化行为。温度、pH值和苯酚浓度对苯酚电化学氧化影响的实验结果表明,随着温度的升高,苯酚电催化氧化峰电位逐渐降低,而峰电流逐渐增大。随着pH值升高,氧化峰电位逐渐减小,氧化峰电流在pH小于7时逐渐减小,在pH=7.5时突然增大,超过7.5又减小。随着苯酚浓度的增大,苯酚的氧化峰电位逐渐减小,峰电流增大。苯酚在PtNPs/GC电极上的电化学氧化反应活化能为14.6 kJ/mol。在温度为187 K时只有聚合过程而没有其他的副反应发生。在温度超过375 K后,电极表面发生的主要反应是苯酚的降解和自发形成聚合膜。苯酚的氧化是在铂氧化物表面发生的。介质的类型和pH对苯酚的氧化机理没有影响。常温下,苯酚在PtNPs/GC电极上的氧化过程以聚合为主,邻苯二酚和对苯二酚的生成速率是其控制步骤。邻苯二酚在PtNPs/GC电极上的氧化过程是扩散控制过程,氧化峰电流随着温度的升高而增大,而氧化峰电位逐渐减小。在不同体系中,其电化学氧化反应的机理不同。在常温条件下,邻苯二酚可以自发的在电极表面发生聚合反应,生成具有导电性的聚合膜。反应的温度、邻苯二酚的浓度,介质类型和pH对其氧化过程均有较明显的影响。对苯二酚在PtNPs/GC电极上的催化氧化反应活化能为14.0 KJ/mol。且随温度的升高,反应可逆性降低,氧化峰电流的对数与温度的倒数呈线性关系。3.以血红蛋白(Hb)为组装分子,利用自组装技术成功地将Hb组装到PtNPs/GC电极上。使用交流阻抗技术对Hb修饰的PtNPs/GC电极(Hb/PtNPs/GC)的性能进行电化学表征。结果表明Hb自组装膜对H2O2的还原反应和Hb的直接电子转移具有催化作用。Hb/PtNPs/GC电极具有比PtNPs/GC电极更好的催化还原H2O2的能力。H2O2浓度在5.0×10-6 mol/L到4.5×10-4 mol/L范围内,Hb/PtNPs/GC电极对H2O2的催化还原电流与其浓度呈线性关系。最低检测限为7.4×10-7 mol/L。4.用电化学方法制备了聚合邻苯二酚/铂复合物修饰膜。电化学聚合的电位范围在-0.6~0.8 V可以得到具有良好电活性的聚合邻苯二酚膜。利用循环伏安法成功的将金属铂纳米颗粒引入聚合膜中。复合修饰膜对甲醇的催化氧化活性和铂颗粒的大小和分散性能有关。同时聚合膜对甲醇的催化氧化有协同作用,和直接在玻碳电极表面沉积金属铂相比,复合物对甲醇的催化氧化能力提高了70%。这种用电化学方法制备的复合膜可以作为一种新型电极材料。5.研究了甲醛在聚合邻苯二酚/铂复合物修饰膜电极上的电化学行为。利用循环伏安法研究了电解质、pH、扫速和甲醛浓度对甲醛氧化过程的影响。结果表明,该修饰电极对甲醛具有良好的催化氧化作用。在0.5 mol/L硫酸中,甲醛主要发生第一步氧化生成甲酸的反应;而在磷酸氢二钠—柠檬酸缓冲体系中,甲醛能够得到较彻底的氧化。甲醛的第一氧化峰电流随其浓度的增加而增大,并且呈线性关系,可用于甲醛的检测。更多还原

【Abstract】 The modified electrodes based on nanomaterials are prepared and applied to the environmental electrochemistry, which is an organic combination of nanotechnology, environmental technology and electroanalytical chemistry. It is a promising research field which is advantage to form the new technology and new method and accelerate the development of environmental electrochemistry.The main work of this paper focuses on one of the most active field where nanotechnology combines with electroanalytical chemistry, preparation and application of novel nanomaterial-modified electrodes. Three methods are applied in this thesis to fabricate nanoplatinum-modified electrodes with high catalytic activity. The emphasis of the study is to apply these modified electrodes to realize the environmental determination and thermodynamic analysis of phenol’s electrochemical oxidation. The details are listed below:1. Platinum nanoparticles directly attached to glassy carbon (PtNPs/GC) were successfully fabricated by using an in situ chemical reductive growth method with ascorbic acid was used as reducing agent. The results indicated that many spherical metallic platinum nanoparticles were presented on GC surface. The diameter of these spherical nanoparticles was in the range of 40 to 200 nm. The electrochemical activety of the PtNPs/GC electrode and the electrochemical behavior of L-cysteine (L-cys) on the modified electrodes were studied. It was found that the PtNPs/GC electrode characterized excellent electrochemical feature in improving the electrocatalytic activity for the oxidation of methanol. Excellent redox reaction activity was obtained at high pH value and high temperature. The electrochemical behavior of PtNPs/GC for the L-cys oxidation was apparently higher than those of the bulk platinum electrode. Compared with the response obtained on the bulk platinum electrode, the electrochemical oxidation potential of L-cys on the modified electrode shifted negatively by 0.3 V, and the oxidation peak current of L-cys increased 12 times. The oxidation peak current of L-cys was linear to the L-cys concentration in the range of 1.0×10-7 mol/L to 1.3×10-5 mol/L. The calculated detection limit was 7.6×10-8 mol/L, which could be used to detect L-cys.2. The electrochemical oxidation behavior of phenol, catechol and hydroquinone on PtNPs/GC electrode was investigated by cyclic voltammetry. Various influence factors such as temperature, the pH of electrolyte and the concentration of phenol were examined. The results indicated that the oxidation peak potentials of phenol shifted to more negative values when temperature, pH and the concentration of phenol increased. The peak current increased with temperature and the concentration of phenol. However, the peak current decreased with increasing pH valve between 3 and 7. The peak current increased obviously until pH=7.5, and then decreased with increasing pH value. Activation energy of phenol’s electro-oxidation on PtNPs/GC electrode obtained from the experimental data was 14.6 kJ/mol. The thermodynamicanalyses showed that polymerization process took place without any side reaction at 187 K. After 375 K the main reaction tended to be the degradation of phenol with a spontaneous polymerization process on the electrode surface. In addition, the electrolyte and pH did not influence the oxidation mechanism of phenol on platinum surface. Polymerization was the main oxidation process of phenol, which was controlled by the generation rate of catechol and hydroquinone.The electrochemical oxidation of catechol was a diffusion-controlled process. The oxidation peak current increased with temperature. However, the oxidation peak potential decreased with increasing temperature. The electrochemical oxidation mechanisms of catechol in different electrolyte were different. The polymerization of catechol could occur at room temperature and the formed polymer was an electronically conducting polymer. The oxidation process was significantly affected by temperature, the concentration of catechol and electrolyte. The activation energy of hydroquinone’s oxidation was 14.0 kJ/mol. The reaction became irreversible with increasing temperature. The logarithm of the oxidation peak current was linear to the reciprocal of the absolute temperature.3. The hemoglobin (Hb) was immobilized on the platinum nanoparticles modified glassy carbon surface successfully. The Hb immobilization was characterized by electrochemical impedance technique. The results indicated that the effect of Hb monolayer was contributed to catalyzing the direct electron transfer of Hb and improving the reduction of hydrogen peroxide (H2O2). The electrocatalytic reduction activity to H2O2 on Hb/PtNPs/GC electrode was apparently higher than those on the PtNPs/GC electrode. The linear relationship existed between the catalytic current and the H2O2 concentration in the range of 5.0×10-6 mol/L to 4.5×10-4 mol/L. The limited detection was 7.4×10-7 mol/L.4. This study has shown that the synthesis of polycatechol/platinum composites could be accomplished using the electrochemical method. A polymerization catechol film with excellent electrochemical activity was obtained by controlling the potential scan range from -0.6 V to 0.8 V. Metallic platinum nanoparticles was introduced in polycatechol film by cyclic voltammetry. The catalytic oxidation of methanol was influenced predominantly by the size and dispersion of platinum particles. The results indicated that the oxidation current of methanol at polycatechol/platinum composites was significantly higher (70%) than that at the platinum directly electrodeposited on the GC surface, illustrating that the polymer had a synergistic effect with platinum particles in improving the catalytic oxidation of methanol. Thus, the obtained composites may be used as novel electrode material with excellent electrochemical feature.5. The electrochemical behavior of formaldehyde was investigated on the polycatechol/platinum composites modified electrode. Various influence factors such as electrolyte, pH value,scan rate and the concentration of formaldehyde were examined by cyclic voltammetry. The results indicated that the polycatechol/platinum composites modified electrode had excellent electrochemical catalytic activity to the oxidation of formaldehyde. The main reaction occurred in 0.5 mol/L H2SO4 solution was the oxidation of formaldehyde to methyl acid. However, formaldehyde could be completely oxided in 0.1 mol/L citrate + 0.2 mol/L Na2HPO4 solution (pH=7.0). The first oxidation peak current was linear to the formaldehyde concentration, which could be used to detecte formaldehyde.更多还原