Raman Spectroscopic Studies of Thiourea in Nitric Acid Medium

硫脲在硝酸介质中的拉曼光谱研究钟起玲粟晓琼刘峰名＊田中群＊（江西师范大学化学系南昌330027）（＊厦门大学固体表面物理化学国家重点实验室厦门361005）rAMAnSPECTrOSCOPICSTudIESOfTHIOurEAInnITrICACI...Abstract Using normal Raman and surFace enhanced Raman (SERS) spectroscopies, we have studied the behaviours of thiourea(TU) adsorbed on the surFace of silver electrode in the nitric acid medium and in the mixed medium of nitric acid and perchloric acid.It was Found that TU can be vertically chemi adsorbed on the surFace of silver electrode through the S and can induce coadsorbed NO - 3 through its protonated amino of TU.The SERS active centers of the surFace of silver electrode are very stable since the SERS signals of TU can be observed even at the negative potential of -2.0V.国家自然科学基金;江西省自然科学基

粗糙铂电极上甲酸吸附氧化的电化学原位表面增强拉曼光谱研究

采用循环伏安法和电化学原位表面增强拉曼光谱 (SERS)技术研究甲酸的解离吸附与氧化行为 .首次报道了甲酸吸附、解离和氧化的电化学原位SERS谱 ,发现甲酸在粗糙铂电极上能自发解离吸附 ;首次成功地获得了粗糙铂电极上甲酸吸附解离的强吸附中间体CO和活性中间体COOH的表面增强拉曼光谱 ,同时首次检测到甲酸氧化最终产物CO2 的拉曼光谱信号 ,从分子水平证实甲酸解离吸附反应的双途径机理

表面增强拉曼光谱研究硫脲及其衍生物在银电极上的共吸附行为

用表面增强拉曼光谱技术（ＳＥＲＳ）研究了ＨＣｌＯ４介质中硫脲（ＴＵ），一甲基硫脲（ＭＴＵ）和烯丙基硫脲（ＡＴＵ）在银电极表面的共吸附行为．首次报道了它们的混合物在银电极表面上竞争共吸附随电极电位变化的行为以及在所研究的共吸附体系中作为支持电解质的弱吸附ＣｌＯ－４离子被诱导物理共吸附的现象．作者联系地址：江西师范大学化学

Raman Spectroscopy Study on Coadsorption of 1 Methyl 2 Thiourea with Electrolyte Anions at Ag Electrodes

本文用电化学现场表面增强拉曼散射光谱（SErS）技术研究了MTu在HClO4、H2SO4和HnO3介质中分别与一种或两种无机阴离子的共吸附行为，发现ClO-4、SO2-4和nO-3等弱吸附无机阴离子均能被MTu诱导物理吸附在其质子化了的氨基（nH＋3）上，这三种无机阴离子被MTu诱导物理吸附的强弱顺序是：在电极电位位于-0.2V~-0.7V区间时，SO2-4＞ClO-4＞nO-3，在电位位于-0.8V~-1.2V区间时，ClO-4＞SO2-4＞nO-3。Using surFace enhanced Raman spectroscopy (SERS), we have studied the coadsorption of 1 methyl 2 thiourea (MTU) with one or two kinds of inorganic anions in perchloric acid, sulphuric acid, nitric acid medium respectively at silver electrodes.The results indicate that inorganic anions with weak coadsorbability such as ClO - 4,SO 2- 4 and NO - 3 can be physically induced to absorb through the protonated amino group of MTU.It was Found that the coadsorbability of these anions with MTU is in the order of SO 2- 4>ClO - 4>NO - 3 in the potential region From -0 2V to -0 7V and ClO - 4>SO 2- 4>NO - 3 in the potential region From -0 8V to -1 2V.国家自然科学基金;江西省自然科学基

Preparation of nano-structured platinum electrode surfaces by electrochemical methods and its properties

The nano-sized constant potential roughened platinum (CPRPt) and constant current roughened platinum (CCRPt) electrode-surfaces have been prepared successfully by oxidation-reduction-cycle method. Many regularly shaped triangle-cones of the size of 10 similar to 30 nm were observed on the CPRPt electrode surface by the scan electron microscopy (SEM) technology. The electro-oxidation of methanol on the nano-CPRPt and the CCRPt electrode-surfaces was used to investigate the performances with the results of the peak current density 1.35 and 2.50 times greater than those of smooth Pt respectively. The in situ Raman spectra of these two kinds of electrode-surfaces indicated their high surface enhanced Raman spectrum (SERS) effects for pyridine adsorption. The CPRPt electrode surface has extraordinarily enhanced effect for adsorption-dissociation of small organic molecules. The mechanism of SERS on these platinum electrode-surfaces has been also discussed

In-situ SERS study on the electro-oxidation with HCOOH on a roughened platinum electrode

The dissociative adsorption and oxidation behavior of HCOOH on Pt was investigated by cyclic voltammogram (CV) and in-situ surface enhanced Raman spectroscopy (SERS) techniques. The in-stiu SERS of HCOOH adsorption, dissociation and oxidation on rough Pt is reported. It is found that HCOOH can spontaneously dissociate. The surface Raman spectra of CO, the strongly adsorbed intermediate and COOH, the weakly adsorbed intermediate of the dissociative adsorption of HCOOH were successfully obtained for the first time. At the same time, the Raman spectra of the finally oxidized product CO2 of HCOOH was also firstly detected. The dual path reaction mechanism for the oxidation of HCOOH was confirmed at molecular level

The Charge Transfer Effect of SERS Induced by the Electrochemical Hydrogen Evolution Reaction

应用高灵敏度的共焦显微拉曼技术 ,分别研究了水体系和不同pH值的硫脲体系中电化学反应与表面增强拉曼散射 (SERS)效应之间的关系 .研究结果表明 ,在电化学析氢反应电位区 ,电荷转移增强机制起主要作用 ,使表面物种的拉曼强度显著地增强 .As one of the important mechanisms of SERS, the charge transfer (CT) enhancement requires the strong interaction of the adsorbed species with the substrate in order to permit the transition of charge between the metal Fermi level (energy state) and the molecular orbital [1] . The high enhancement needs the match of the energy gap between the Fermi level (or surface state) and the orbital energy level of the adsorbed molecules with the energy of the incident light. The electrode Fermi level is usually adjusted by the applied potential to satisfy the CT resonance. For the electrochemical reaction process, the frontier orbital energy level of the reacting surface species should be greatly different from that of the adsorbed molecules. Thus, it is interesting to test the additional SERS enhancement induced by the electrochemical reaction. In the present study, the influence of the electrochemical reaction on SERS intensity of thiourea (TU) and water adsorbed on silver electrode surfaces were investigated, respectively. The Raman experiments were performed on a confocal microprobe Raman system (LabRam I). The details of the Raman system and pretreatment of the Ag electrode can be found elsewhere [2] . The SERS spectra of TU in pH 1 and 7 are showed in the Fig. 1 (a) and (b), respectively. The major bands of TU locate at～710 cm -1 and～1 091 cm -1 . The strong 933 cm -1 band is assigned to the symmetric stretching vibration of ClO 4 - as electrolyte anion, which coadsorbed on the surface. The electrochemical measurements indicate that TU can adsorb strongly at Ag electrode in a wide potential region from -0.2 V to -1.5 V (vs SCE). It is of interest that the SERS intensity reaches the maximum at different potential in acidic and neutral solutions. In the low pH solution, one can find that when the electrode potential shifted to -0.8 V, all the band intensities increase remarkably. In the high pH solution (Fig. 1 (b)), at potentials positive of -1.0 V only solution signal can be discerned. The intensity of the surface signals underwent a sharp increase at -1.2 V. Interestingly, we found the maximum intensities in the two pH solutions have a certain relation with the occurrence of the electrochemical hydrogen evolution reaction (HER). A systematic SERS experiments were performed in solutions with pH of 2.0, 2.5, 3..0, 3.5, 4.0 and 7.0 respectively. The profiles of the integrated band intensities (～710 cm -1 ) and the potentials are shown in Fig. 2. It can be found that the maxima of the intensities are located at -0.8 V, -1.1 V for pH 1.0 and 2.0 respectively and -1..2 V for pH 2.5 ～7.0. Correspondingly, the current densities for each potential in different pH solution were presented in Fig. 3. From the two figures, it can be found that the potentials of the maximum intensity of SERS are right at the initial potentials of HER. It implies that there must have some relation between the HER and the additional enhancement of the SERS. A study on the SERS of water will be helpful for further understanding of this relation.作者联系地址：厦门大学固体表面物理化学国家重点实验室!化学系厦门361005,厦门大学固体表面物理化学国家重点实验室!化学系厦门361005,厦门大学固体表面物理化学国家重点实验室!化学系厦门361005,江西师范大学化学系!南昌,330027,厦门大学固体表面物理化学国家重点实验室!化学系厦门361005,Author's Address: 1 State Key Lab. for Phys. Chem. of Sol. Surf., Inst. of Phys. Chem. and Dept. of Chem., Xiamen Univ., Xiamen 361005, China; 2 Dept. of Chem.,

Microwave radiation-assisted synthesis of Pt-CNTs

Carbon nanotube-supported platinum nanoparticles (Pt-CNTs) were synthesized using glycol as a reducer and H2PtCl6 as an oxidant under microwave radiation. The CNTs was first hydroxylated in refluxing concentrated HNO3. Transmission electron microscopy was used to investigate the influence of the hydroxylation time on the amount of supported platinum on the carbon nanotubes and the effect of the amount of platinum on the morphology of Pt-CNTs. Selected area electron diffraction, X-ray diffraction, and UV-visible spectroscopy were employed to characterize the structure of the Pt-CNTs and the results showed that Pt was of polycrystal nanoparticles. Cyclic voltarnmetric study indicated that the CNTs surface was covered by a compact layer of Pt when the loadings of platinum to CNTs was as high as 0.1875 mmol . g(-1). The result, on one hand, showed that cyclic voltammetry could be used to study the surface structure and properties of CNTs supported platinum nanoparticles, and on the other hand, indicated that it was possible to obtain novel electrode materials with good catalytic activity and stability by optimizing the synthesizing method for CNTs supported platinum nanoparticles

Electrocatalytic Oxidation of Formic Acid on Pt-Se Hollow Nanosphere Modified Glassy Carbon Electrodes

Corresponding authors. Email: [email protected],[email protected]; Tel:+86-13879159319.[中文文摘]以无定形硒溶胶为模板制备了不同硒覆盖度(θSe)(θSe=0.49,0.39,0.06,0)的Pt-Se和Pt纳米空球(分别记为(Pt-Se)HN和PtHN),发展了利用亚硫酸盐彻底除去核壳纳米粒子上Se的方法.对获得的纳米空球进行了形貌和结构的表征,结果表明所制备的(Pt-Se)HN粒径均匀,分散性好,球壳呈多孔结构.以其作为电催化剂制备了(Pt-Se)HN修饰的玻碳(GC)电极((Pt-Se)HN/GC),利用常规电化学方法比较该电极与PtHN/GC和商用碳载铂(Pt/C)修饰GC(Pt/C/GC)电极对甲酸的催化氧化作用,发现对甲酸氧化的活性顺序为(Pt-Se)HN/GC>PtHN/GC>Pt/C/GC.三种电极催化甲酸氧化的机理有所不同:前者更倾向于通过弱吸附中间体直接氧化成CO2的单途径机理进行,后两者则通过强吸附和弱吸附中间体的双途径机理进行.在一定Se覆盖度条件下,(Pt-Se)HN/GC对甲酸的氧化有助催化作用.[英文文摘]Platinum-selenium and platinum hollow nanospheres(denoted as(Pt-Se)HN and PtHN,respectively) with different coverages of Se(θSe)(θSe=0.49,0.39,0.06,0) were prepared using amorphous Se colloids as a sacrificial template.Sulfite was used to completely remove Se from the core-shell nanoparticles.The morphology and structure of the nanoparticles were characterized using various methods,which revealed a hollow structure with a very uniform size distribution and a porous structure on the shell.Assembly of Pt-Se hollow nanospheres ((Pt-Se)HN) on a glassy carbon (GC) electrode produced a (Pt-Se)HN/GC electrode. The electrocatalytic activity of the electrode for the oxidation of formic acid was compared with the PtHN/GC and commercial Pt/C/GC electrodes by cyclic voltammetry and chronoamperometry. The activity followed the order:(Pt-Se)HN/GC > PtHN/GC >Pt/C/GC. The electrooxidation of formic acid on (Pt-Se)HN/C, PtHN/C, and Pt/C catalysts follows different mechanisms: the former tends to directly oxidize formic acid to CO2 via weakly adsorbed intermediates, and the latter two via both weakly and strongly adsorbed intermediates.(Pt-Se)HN with a suitable selenium content showed optimal electrocatalytic activity for the oxidation of formic acid.国家自然科学基金(20663002); 厦门大学固体表面物理化学国家重点实验室基金(200511)资助项

In-situ SERS of formic acid electro-catalytic oxidation on Au-core@Pt-shell/Pt electrode

Au-core@Pt-shell nanoparticles were synthesized by chemical reduction method. The samples were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). In-situ surfac-enhanced Raman scattering (in-situ SERS) spectroscopy combined with cyclic voltammetry was utilized to investigate the electro-oxidation behavior of formic acid adsorbed on Au-core@Pt-shell nanoparticles coated on platinum electrode, and SERS spectra with high quality were acquired. Results showed that the intermediates COad and HCOOad, the dissociated products of HCOOH, were produced at open circuit potential. As the potential moved to positive, the first oxidation wave for CO, was observed at +0.10 V. The study demonstrated that the electrode prepared by Au-core@Pt-shell nanoparticles coated on platinum substrate exhibited good electro-catalytic properties and SERS activity for the oxidation of HCOOH, and the electro-oxidation proceeds of formic acid via "dual path" mechanism