胆碱与谷氨酸共价单层混合修饰玻碳电极的制作与表征及其测定亚硝酸根的分析应用

A choline and L-glutamic acid mixed monolayer covalently modified glassy carbon electrode (Ch-Glu/GCE) was fabricated and characterized by X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). It provided an excellent example of mixed covalent monolayer modification of carbon electrodes with alkanol and amino acid, and also a facile means for altering the interfacial architecture. The Ch-Glu/GCE displayed good catalytic activity toward the oxidation of nitrite anions. Differential pulse voltammetry was used for determination of nitrite at the Ch-Glu/GCE. The Ch-Glu/GCE showed higher capability for restraint of pollutions than a simple Ch modified electrode or a simple Glu modified electrode.     

Spontaneous attachment of amines to carbon and metallic surfaces

Primary alkylamines attach spontaneously from acetonitrile (ACN) solutions onto glassy carbon and metallic surfaces (Au, Pt, Cu, and Fe). The surface concentration of the organic layer measured from the integration of cyclic voltammograms appears close to or lower than that of a compact monolayer. The rate of the attachment depends on the concentration of the primary amino compound; it reaches a maximum after 3 h of immersion for the most concentrated solutions (20 mM). The modified surfaces have been characterized by cyclic voltammetry (CV), energy dispersive X-ray spectrometry (EDX), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (ATR). The possible reaction mechanisms are discussed.     

Electrochemical and surface characterization of 4-aminothiophenol adsorption at polycrystalline platinum electrodes

The formation of a self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) on polycrystalline platinum electrodes has been characterized by surface analysis and electrochemistry techniques. The 4-ATP monolayer was characterized by cyclic voltammetry (CV), linear sweep voltammetry, Raman spectroscopy, reflection-absorption infrared (RAIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). CV was used to study the dependence of the adsorption time and 4-ATP solution concentration on the relative degree of coverage of 4-ATP monolayers on polycrystalline Pt electrodes. The adsorption time range probed was 24-72 h. The optimal concentration of 4-ATP needed to obtain the highest surface at the lowest adsorption time was 10 mM. RAIR and Raman spectroscopy for 4-ATP-modified platinum electrodes showed the characteristic adsorption bands for 4-ATP, such as nuNH, nuCH(arom), and nuCS(arom), indicating the adsorption on the platinum surface. The XPS spectra for the modified Pt surface presented the binding energy peaks of sulfur and nitrogen. High energy resolution XPS studies, RAIR, and Raman spectrum for platinum electrodes modified with 4-ATP indicate that the molecules are sulfur-bonded to the platinum surface. The formation of a S-Pt bond suggests that ATP adsorption leads to an amino-terminated electrode surface. The thickness of the monolayer was evaluated via angle-resolved XPS (AR-XPS) analyses, giving a value of 8 A. As evidence of the terminal amino group on the electrode surface, the chemical derivatization of the 4-ATP SAM was done with 16-Br hexadecanoic acid. This surface reaction was followed by RAIR spectroscopy.     

Ni/Pt(111) bimetallic surfaces: unique chemistry at monolayer ni coverage.

We have utilized the dehydrogenation and hydrogenation of cyclohexene as probe reactions to compare the chemical reactivity of Ni overlayers that are grown epitaxially on a Pt(111) surface. The reaction pathways of cyclohexene were investigated using temperature-programmed desorption, high-resolution electron energy loss (HREELS), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Our results provide conclusive spectroscopic evidence that the adsorption and subsequent reactions of cyclohexene are unique on the monolayer Ni surface as compared to those on the clean Pt(111) surface or the thick Ni(111) film. HREELS and NEXAFS studies show that cyclohexene is weakly pi-bonded on monolayer Ni/Pt(111) but di-sigma-bonded to Pt(111) and Ni(111). In addition, a new hydrogenation pathway is detected on the monolayer Ni surface at temperatures as low as 245 K. By exposing the monolayer Ni/Pt(111) surface to D2 prior to the adsorption of cyclohexene, the total yield of the normal and deuterated cyclohexanes increases by approximately 5-fold. Furthermore, the reaction pathway for the complete decomposition of cyclohexene to atomic carbon and hydrogen, which has a selectivity of 69% on the thick Ni(111) film, is nearly negligible (<2%) on the monolayer Ni surface. Overall, the unique chemistry of the monolayer Ni/Pt(111) surface can be explained by the weaker interaction between adsorbates and the monolayer Ni film. These results also point out the possibility of manipulating the chemical properties of metals by controlling the overlayer thickness.     

Fabrication of layer-by-layer modified multilayer films containing choline and gold nanoparticles and its sensing application for electrochemical determination of dopamine and uric acid

A novel electrochemical sensor has been constructed by use of a glassy carbon electrode (GCE) coated with a gold nanoparticle/choline (GNP/Ch). Electrochemical impedance spectroscopy (EIS), field emission scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the properties of this modified electrode. It was demonstrated that choline was covalently bounded on the surface of glassy carbon electrode, and deposited gold nanoparticles with average size of about 100 nm uniformly distributed on the surface of Ch. Moreover, the modified electrode exhibits strong electrochemical catalytic activity toward the oxidation of dopamine (DA), ascorbic acid (AA) and uric acid (UA) with obviously reduction of overpotentials. For the ternary mixture containing DA, AA and UA, these three compounds can be well separated from each other, allowing simultaneously determination of DA and UA under coexistence of AA. The proposed method can be applied to detect DA and UA in real samples with satisfactory results.     

Pt–Ni alloy nanoparticles supported on multiwalled carbon nanotubes for methanol oxidation in alkaline media

The Pt–Ni alloy nanoparticles with different Pt/Ni atomic ratios supported on functionalized multiwalled carbon nanotubes surface were synthesized via an impregnation-reduction method. The nanocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques. XRD demonstrated that Pt was alloyed with Ni. TEM showed that the Pt–Ni alloy nanoparticles were uniformly dispersed on the multiwalled carbon nanotubes (MWCNTs) surface, indicating appropriate amount of Ni in Pt–Ni alloy which facilitates the dispersion of nanoparticles on the MWCNT surface. XPS revealed that the Pt 4f peak in Pt–Ni/MWCNT (4:1) catalyst shifted to a lower binding energy compared with Pt/MWCNT catalyst, and nickel oxides/hydroxides such as NiO, Ni(OH)₂, and NiOOH were on the surface of Pt–Ni nanoparticles. Electrochemical data based on cyclic voltammetry and chronoamperometric curves indicated that Pt–Ni (4:1) alloy nanoparticles exhibited distinctly higher activity and better stability than those of Pt/MWCNTs toward methanol oxidation in alkaline media.     

Preparation and electrocatalytic activities of platinum nanoclusters deposited on modified multi-walled carbon nanotubes supports

Multi-walled carbon nanotubes (MWNTs) were modified by oxyfluorination treatment at several different temperatures of 20, 100, 200, and 300 °C. The changes of surface properties of oxyfluorinated MWNTs were investigated using X-ray photoelectron spectroscopy (XPS) method. As a result, it was found that surface fluorine contents were varied with changing an oxyfluorination temperature and showed a maximum value at 100 °C. By changing the treatment temperature in the process of oxyfluorination for carbon supports, the surface characteristics of MWNTs had been modified, resulting that the size and loading content of deposited Pt on the modified carbon supports could be changed. Consequently, Pt deposited MWNTs that were treated at 100 °C (Pt/100-MWNTs) showed the best electroactivity among samples. The enhanced electroactivity was dependent on the higher surface area of electrochemical reaction for metal catalyst, which was related to the particle size and the morphology of the deposited particle catalysts.     

Cysteamine monolayer inducing the formation of platinum nanoclusters for methanol electrocatalytic oxidation

Platinum nanoclusters (Pt-NCs) were synthesized on the surface of a gold electrode that was modified with cysteamine to form a kind of self-assembled monolayer via in-situ cyclic voltammetry (CV). Scanning electron microscopy, electrochemical impedance spectroscopy, and CV were used to characterize the properties of the electrode. The Cys monolayer induces the aggregation of platinum nanoparticles due to electrostatic interaction between the positive amino groups of the cystein monolayer and the negative charge of the hexachloroplatinate ions and causes the formation of Pt-NCs on the surface of the electrode. The resulting electrode exhibits high elecrocatalytic activity towards the oxidation of methanol.     

Cyclic control of the surface properties of a monolayer-functionalized electrode by the electrochemical generation of Hg nanoclusters

Hg(2+) ions are bound to a 1,4-benzenedimethanethiol (BDMT) monolayer assembled on a Au electrode. Electrochemical reduction of the Hg(2+)-BDMT monolayer to Hg(+)-BDMT (at E degrees =0.48 V) and subsequently to Hg(0)-BDMT (at E degrees =0.2 V) proceeds with electron-transfer rate constants of 8 and 11 s(-1), respectively. The Hg(0) atoms cluster into aggregates that exhibit dimensions of 30 nm to 2 microm, within a time interval of minutes. Electrochemical oxidation of the nanoclusters to Hg(+) and further oxidation to Hg(2+) ions proceeds with electron-transfer rate constants corresponding to 9 and 43 s(-1), respectively, and the redistribution of Hg(2+) on the thiolated monolayer occurs within approximately 15 s. The reduction of the Hg(2+) ions to the Hg(0) nanoclusters and their reverse electrochemical oxidation proceed without the dissolution of mercury species to the electrolyte, implying high affinities of Hg(2+), Hg(+), and Hg(0) to the thiolated monolayer. The electrochemical transformation of the Hg(2+)-thiolated monolayer to the Hg(0)-nanocluster-functionalized monolayer is characterized by electrochemical means, surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact-angle measurements. The Hg(0)-nanocluster-modified surface reveals enhanced hydrophobicity (contact angle 76 degrees ) as compared to the Hg(2+)-thiolated monolayer (contact angle 57 degrees ). The hydrophobic properties of the Hg(0)-nanocluster-modified electrode are further supported by force measurements employing a hydrophobically modified AFM tip.     

高效组合型Pt-Fe/C 催化剂用于肉桂醛选择性加氢反应

采用有机金属化合物Pt2(dba)3(dba为二亚苄基丙酮)还原分解法制得均匀分布的Pt纳米颗粒(粒径在2.0nm左右),直接吸附到经预处理的Fe/C载体上,即得到了组合型Pt-Fe/C催化剂.采用透射电子显微镜(TEM)、X射线光电子能谱(XPS)和能量散射X射线谱(EDS)等技术表征了催化剂表面Pt颗粒大小分布,Pt、Fe化学态和催化剂表面元素等.将该组合型催化剂用于肉桂醛(CAL)选择性加氢反应,获得了良好的效果,其催化活性比浸渍法制备的Pt/C催化剂高1倍以上.在60°C、2.5h、4.0MPaH2反应条件下,1%(w,质量分数)Pt-1.5%(w)Fe/C催化剂肉桂醛加氢转化率为99.2%,肉桂醇(COL)选择性达到85.0%.     

Characterization of Pt@Cu core@shell dendrimer-encapsulated nanoparticles synthesized by Cu underpotential deposition

Dendrimer-encapsulated nanoparticles (DENs) containing averages of 55, 147, and 225 Pt atoms immobilized on glassy carbon electrodes served as the electroactive surface for the underpotential deposition (UPD) of a Cu monolayer. This results in formation of core@shell (Pt@Cu) DENs. Evidence for this conclusion comes from cyclic voltammetry, which shows that the Pt core DENs catalyze the hydrogen evolution reaction before Cu UPD, but that after Cu UPD this reaction is inhibited. Results obtained by in situ electrochemical X-ray absorption spectroscopy (XAS) confirm this finding.     

“非保护型”金属胶体纳米簇形成机理研究

碱-乙二醇法制备的"非保护型"金属及合金纳米簇由表面吸附的溶剂分子和简单离子实现稳定化,它们被广泛用于制备高性能复相催化剂和研究复相催化剂中的尺寸、组成、载体表面基团以及修饰剂对催化性能的影响。关于此类非保护金属纳米簇的形成过程及机理的认识尚有待进一步深化。本文采用原位快速扫描X射线吸收精细结构谱(QXAFS)、原位紫外-可见(UV-Vis)吸收光谱、透射电子显微镜和动态光散射技术研究了碱-乙二醇法合成中非保护型金属胶体纳米簇的形成过程与机理。结果表明,在碱-乙二醇法合成非保护型Pt金属纳米簇的过程中,室温下即有部分Pt(IV)被还原至Pt(II)。随着反应温度的升高,OH-逐渐取代与Pt离子配位的Cl-,在Pt―Pt键形成之前,反应体系的UV-Vis吸收光谱中可观察到明显的纳米粒子的散射信号,原位QXAFS分析表明Pt纳米簇是由Pt氧化物纳米粒子还原所形成的;在Ru金属纳米簇的形成过程中,OH-首先取代了Ru Cl_3中的Cl~-,形成羟基配合物Ru(OH) _6~(3-),后者进一步缩合形成氧化钌纳米粒子,最终Ru金属纳米簇由乙二醇还原氧化钌纳米粒子形成。由于先形成了氧化物纳米粒子,后续的还原反应被限制在氧化物纳米粒子内,使最终得到的非保护型金属纳米簇具有尺寸小、分布窄的特点。本工作所获得的知识对发展高性能能源转化催化剂、精细化学合成催化剂、传感器等功能体系具有重要意义。     

Pt(111) 表面上表层 Fe (FeO) 结构和次表层 Fe 结构的可控转变

 利用扫描隧道显微镜 (STM) 和 X 射线光电子能谱 (XPS) 对 Pt(111) 表面制备的 Fe 单层薄膜及其在不同环境气氛条件下的多种结构进行了研究. 在温度为 487 K 的 Pt(111) 表面制备出了完整的 Fe 单层薄膜Fe/Pt(111). 对 Fe/Pt(111) 依次升高温度进行超高真空退火, STM 和 XPS 结果表明退火温度高于 800 K 时, 表面 Fe 原子扩散到次表层区域, 形成次表层 Fe 结构Pt/Fe/Pt(111). Pt/Fe/Pt(111) 在 O2 氧化气氛中经 850 K 退火可转变成表面 FeO 薄膜FeO/Pt(111). FeO/Pt(111) 结构在温和的 H2 还原气氛中 (600 K) 转变成表面 Fe 结构, 进一步的还原处理 (800 K) 则可以重新生成 Pt/Fe/Pt(111). 控制样品的环境气氛在 O2 和 H2 之间切换, 使得表面 Fe (FeO) 和次表面 Fe 可以重复地转变. 本研究实现了多种 Fe-Pt 表面结构的可控制备, 可为合理地设计高效、价廉的催化剂提供借鉴.     

Determination of Formaldehyde with a Platinum–Palladium–Graphene Nanocomposite Glassy Carbon Electrode

The oxidation of formaldehyde on a platinum (Pt)–palladium (Pd)–graphene nanocomposite glassy carbon electrode prepared by chemical reduction was characterized in 0.5?M sulfuric acid. The surface and morphology of the catalyst were characterized by transmission electron microscopy, Raman spectroscopy, and X-ray diffraction. Bimetallic Pt–Pd nanoparticles were uniformly dispersed on the graphene sheets. Energy-dispersed X-ray spectroscopy was used to characterize the metal composition of the nanocomposite. The electrocatalytical characteristics of the modified electrode were investigated by cyclic voltammetry. The results show that the electrode displayed high activity for the oxidation of formaldehyde in sulfuric acid with a linear relationship from 4.50?µM to 0.180?mM and a detection limit of 2.85?µM. The low detection limit, wide linear dynamic range, and high sensitivity of the modified electrode suggests further applications.     

Inside/outside Pt nanoparticles decoration of functionalised carbon nanofibers (Pt(19.2)/f-CNF(80.8)) for sensitive non-enzymatic electrochemical glucose detection

A highly efficient and reproducible approach for effective Pt nanoparticles dispersion and excellent decoration (inside/outside) of functionalised carbon nanofibers (f-CNF) is presented. The surface morphological, compositional and structural characterisations of the synthesised Pt(19.2)/f-CNF(80.8) material were examined using transmission electron microscopy (TEM/STEM/DF-STEM), energy-dispersive X-ray spectrometry (EDS), thermogravimetric analysis (TGA/DTG), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) was employed in order to confirm the typical electrochemical response for Pt. The aim of the work was to improve the utility of both the supporting matrix (via the use of both inner/outer surfaces of nanofibers) and precious Pt, together with the sensitive glucose determination. TEM data indicated successful nanoparticle decoration with average Pt particle size 2.4 nm. The studies demonstrated that utilisation of the inner surface of the nanofibers, together with the modified outer surface characteristics using chemical treatment, enables excellent decoration, effective dispersion and efficient impregnation of Pt nanoparticles on carbon nanofibers. Pt(19.2)/f-CNF(80.8) exhibited excellent amperometric response (sensitivity = 22.7 μAmM(-1)cm(-2) and LoD = 0.42 μM) towards direct glucose sensing, over the range 0-10 mM glucose, in neutral conditions (pH 7.4). The improved carbon surface area for nanoparticle decoration, inner surface structure and morphology of nanofibers together with the presence of functional groups provided strong interactions and stability. These features together with the effective nanoparticle dispersion and decoration resulted in excellent catalytic response. The decorated nanoscaled material (Pt(19.2)/f-CNF(80.8)) is capable of large scale production, providing sensing capability in neutral conditions, while eliminating the temperature sensitivity, pH and lifetime issues associated with glucose enzymatic sensors and holds great promise in the quantification of glucose in real clinical samples.     

Covalent bonding of alkene and alkyne reagents to graphitic carbon surfaces

Various aromatic and aliphatic alkynes and one alkene were covalently bonded to sp(2)-hybridized carbon surfaces by heat treatment in an argon atmosphere. X-ray photoelectron spectroscopy, Raman, and FTIR spectra of the modified surfaces showed that the molecules were intact after the 400 degrees C heat treatment but that the alkyne group had reacted with the surface to form a covalent bond. Alkynes with ferrocene and porphyrin centers exhibited chemically reversible voltammetric waves that could be cycled many times. Atomic force microscopy of the modified surfaces indicated a thickness of the molecular layer consistent with monolayer coverage, and surface coverage determined by voltammetry was also in the monolayer range. Raman spectroscopy of the porphyrin monolayers formed from a porphyrin alkyne showed no evidence for dimer formation, although multilayer formation may occur at undetected levels. FTIR spectra of the porphyrin-modified carbon surfaces were well-defined, similar to the parent molecule, and indicative of an average tilt angle between the porphyrin plane and the surface normal of 37 degrees . The bond between the molecular monolayer and the carbon surface was quite stable, withstanding sonication in tetrahydrofuran, mild aqueous acid and base, and repeated voltammetric cycling in propylene carbonate electrolyte. Heat treatment of alkynes and alkenes appears to be a generally useful method for modifying carbon surfaces, which can be applied to both aromatic and aliphatic molecules.     

硅表面含二茂铁基团自组装单分子膜制备及电流-电压关系测量

合成了一种头基为二茂铁基团的长链烯烃分子(Fc-CO-NH-(CH₂)₉-CH=CH₂) (FcUA)，并用红外、核磁、质谱等手段对其进行了表征。用微波引发将该化合物嫁接到平面硅的表面，并用X射线光电子能谱、反射红外光谱、原子力显微镜表征了这一过程。最后，通过循环伏安电化学法和电敏感原子力显微镜的导电模式对其进行电学性质测试。结果表明这层单分子膜可以提高硅片的介电常数。同时还观察到了一种不稳定的类似负微分电流现象。     

Switchable surface properties through the electrochemical or biocatalytic generation of Ag0 nanoclusters on monolayer-functionalized electrodes

The electroswitchable and the biocatalytic/electrochemical switchable interfacial properties of a Ag(+)-biphenyldithiol (BPDT) monolayer associated with a Au surface are described. Upon the application of a potential corresponding to -0.2 V the Ag(+)-BPDT is reduced to the Ag(0)-BPDT interface, and silver nanoclusters are generated on the interface. The application of a potential that corresponds to 0.2 V reoxidizes the monolayer to the Ag(+)-BPDT monolayer. The reversible electrochemical transformation of the Ag(+)-BPDT monolayer and of the Ag(0)-BPDT surface was followed by electrochemical means and surface plasmon resonance spectroscopy (SPR). The SPR experiments enabled us to follow the kinetics of nanoclustering of Ag(0) on the surface. The hydrophobic/hydrophilic properties of the surface are controlled by the electrochemically induced transformation of the interface between the Ag(+)-BPDT and Ag(0)-BPDT states. The Ag(0)-BPDT monolayer reveals enhanced hydrophilicity. The hydrophobic/hydrophilic properties of the interface were probed by contact angle measurements and force interactions with a hydrophobically-functionalized AFM tip. The Ag(0)-BPDT interface was also biocatalytically generated using alkaline phosphatase, AlkPh, and p-aminophenyl phosphate as substrate. The biocatalytically generated p-aminophenol reduces Ag(+) ions associated with the surface to Ag(0) nanoclusters. This enables the cyclic biocatalytic/electrochemical control of the surface properties of the modified electrode.     

Methanol Oxidation over TiO_2-modified Multi-walled Carbon Nanotubes Supported Pt-Mo Electrocatalyst

In order to develop a novel and high-performance catalytic material for direct methanol fuel cells(DMFC), molybdenum oxide as a co-catalyst with Pt on multi-walled carbon nanotubes which were modified by titanium dio-xide(denoted as CNTs@TiO2) was investigated. The physicochemical characterizations of the catalysts were carried out via X-ray diffraction(XRD), transmission electron microscopy(TEM) and X-ray photoelectron spectroscopy(XPS). Cyclic voltammetry(CV) showed that the CO-tolerance performance incre...     

Electrodeposition of Pt nanoclusters on the surface modified by monolayer poly(amidoamine) dendrimer film

Preparation of Pt nanoclusters on the poly(amidoamine) (PAMAM) modified surface by electrodeposition was firstly reported. The presence of PAMAM could affect the growth of Pt nanostructures. Field-emitted scanning microscopy images showed that these nanoclusters were not common nanoparticles but were consisted of many small nanoparticles. The size of them could be controlled and the deposition mechanism was also discussed. This method would give a route of preparing novel nanostructures by electrodeposition.