Shape-dependent electrocatalysis: methanol and formic acid electrooxidation on preferentially oriented Pt nanoparticles

Reactivity towards methanol and formic acid electrooxidation on Pt nanoparticles with well characterised surfaces were studied and compared with the behaviour of single crystal electrodes with basal orientations. Polyoriented and preferential (100), (111) and (100)-(111) Pt nanoparticles were synthesised, cleaned preserving its surface structure, characterised and employed to evaluate the influence of the surface structure/shape of the Pt nanoparticles on these two relevant electrochemical reactions. The results pointed out that, in agreement with fundamental studies with Pt single crystal electrodes, the surface structure of the electrodes plays an important role on the reactivity of both oxidation processes, and thus the electrocatalytic properties strongly depend on the surface structure/shape of the nanoparticles, in particular on the presence of sites with (111) symmetry. These findings open the possibility of designing new and better electrocatalytic materials using decorated shape-controlled Pt nanoparticles as previously described with Pt single crystal electrodes.     

Shape-Controlled Nanocrystals for Catalytic Applications

The activity, selectivity, and long-term stability of catalyst nanoparticles can be enhanced by shape modulation. Such shaped catalytic nanocrystals have well-defined surface crystalline structures on which the cleavage and recombination of chemical bonds can be rationally controlled. Metal and metal oxide nanocrystals have been synthesized in various shapes using wet chemistry techniques such as reducing metal precursors in the presence of the surface-capping agents. The surface-capping agents should be removed prior to the catalytic chemical reaction, which necessitates clean catalytically active surface. The removal process should be performed very carefully because this removal often causes shape deformation. A few examples in which the surface-capping agents contribute positively to the chemical reactions have been reported. The examples described in this review include shaped metal, metal composite, and metal oxide nanocrystals that show enhanced catalytic activity, selectivity, and long-term stability for various gas-phase, liquid-phase, or electrocatalytic reactions. Although most of the studies using these shaped nanocrystals for catalytic applications have focused on low-index surfaces, nanocrystals with high-index facets and their catalytic applications have recently been reported. By bridging surface studies with nanoparticle catalysts using shape modulation, catalysts with improved properties can be rationally designed.     

Intrinsic therapeutic applications of noble metal nanoparticles: past, present and future

Biomedical nanotechnology is an evolving field having enormous potential to positively impact the health care system. Important biomedical applications of nanotechnology that may have potential clinical applications include targeted drug delivery, detection/diagnosis and imaging. Basic understanding of how nanomaterials, the building blocks of nanotechnology, interact with the cells and their biological consequences are beginning to evolve. Noble metal nanoparticles such as gold, silver and platinum are particularly interesting due to their size and shape dependent unique optoelectronic properties. These noble metal nanoparticles, particularly of gold, have elicited a lot of interest for important biomedical applications because of their ease of synthesis, characterization and surface functionalization. Furthermore, recent investigations are demonstrating another promising application of these nanomaterials as self-therapeutics. To realize the potential promise of these unique inorganic nanomaterials for future clinical translation, it is of utmost importance to understand a few critical parameters; (i) how these nanomaterials interact with the cells at the molecular level; (ii) how their biodistribution and pharmacokinetics influenced by their surface and routes of administration; (iii) mechanism of their detoxification and clearance and (iv) their therapeutic efficacy in appropriate disease model. Thus in this critical review, we will discuss the various clinical applications of gold, silver and platinum nanoparticles with relevance to above parameters. We will also mention various routes of synthesis of these noble metal nanoparticles. However, before we discuss present research, we will also look into the past. We need to understand the discoveries made before us in order to further our knowledge and technological development (318 references).     

Design of oxide nanoparticles by aqueous chemistry

The elaboration of nanoparticles designed for technological applications in various fields such as catalysis, optics, magnetism, electronics… needs the strict control of their characteristics, especially chemical composition, crystalline structure, size, and shape. These characteristics bring the physical properties (color, magnetism, band gap…) of the material, and also the surface to volume ratio of particles which is of high importance when they are used as a chemically active or reactive support, in catalysis for instance. The nanoparticles may have also to be surface functionalized by various species, and/or dispersed in aqueous or non aqueous media. We will show that the aqueous chemistry of metal cations is a very versatile and attractive way for the design of oxide nanomaterials, allowing the control of size, shape, and crystalline structure for polymorphic materials. Aqueous surface chemistry, including adsorption of various species, may be used to modify the morphology of nanoparticles. In some cases, redox processes can be involved to control the morphology of nanoparticles. Technologically important nanomaterials such as titania, alumina, and iron oxides are studied.     

Hollow and cage-bell structured nanomaterials of noble metals

Mastery of the structure of nanomaterials enables control of their properties to enhance their performance for a given application. Herein we demonstrate the synthesis of metal nanomaterials with hollow interiors or cage-bell structures based on the inside-out diffusion of Ag in core-shell structured nanoparticles. It begins with the synthesis of core-shell Ag-M or core-shell-shell M(A)-Ag-M(B) nanoparticles in an organic solvent. Ag is then extracted from the core or the inner shell by bis(p-sulfonatophenyl)phenylphosphane, which binds strongly with Ag(I)/Ag(0) to allow the complete removal of Ag in 24-48 h, leaving behind an organosol of hollow or cage-bell structured metal nanomaterials. Because of their relatively lower densities, which usually translate to a higher surface area than their solid counterparts, the hollow and cage-bell structured metal nanomaterials are especially relevant to catalysis. For example, cage-bell structured Pt-Ru nanoparticles were found to display outstanding methanol tolerance for the cathode reaction of direct methanol fuel cells (DMFCs) as a result of the differential diffusion of methanol and oxygen in the cage-bell structure.     

Poly(vinylpyrrolidone)-modified graphite carbon nanofibers as promising supports for PtRu catalysts in direct methanol fuel cells

Carbon nanomaterials, including herringbone graphite carbon nanofibers (GNFH), multiwalled carbon nanotubes (MWCNT), and carbon black, were surface-modified by a new poly(vinylpyrrolidone) (PVP) grafting process as well as by the conventional acid-oxidation (AO) process, and characterized by FTIR, TGA, Raman, HRTEM, XRD, and XPS measurements. Pt nanoparticles of 1.8 nm were evenly deposited on all PVP-grafted carbon nanomaterials. The effects of the two surface modification processes on the dispersion, average Pt nanoparticle sizes, the electrocatalytic performance, and electrical conductivities of Pt-carbon nanocomposites in direct methanol oxidation were systematically studied and compared. It was found that the PVP-grafted carbon nanomaterials have much less loss in the electric conductivity and thus better electrocatalytic performance, 17-463% higher, than their corresponding acid oxidation-treated nanocomposites. The electrocatalytic performance of the Pt-carbon nanocomposites decreases in the following order: Pt-PVP-GNFH > Pt-PVP-MWCNTarc > Pt-AO-MWCNTarc > Pt-PVP-MWCNTCVD > Pt-AO-MWCNTCVD > Pt-XC-72R > Pt-AO-GNFH, with the Pt-PVP-GNFH nanocomposite having approximately 270% higher performance than that of the Pt-Vulcan XC-72R nanocomposite. In addition, PtRu-PVP-GNFH shows even better (50% higher) electrocatalytic activity than the Pt-PVP-GNFH nanocomposite at a 0.6 V applied voltage.     

Strain‐Enhanced Metallic Intermixing in Shape‐Controlled Multilayered Core–Shell Nanostructures: Toward Shaped Intermetallics

Controlling the surface composition of shaped bimetallic nanoparticles could offer precise tunability of geometric and electronic surface structure for new nanocatalysts. To achieve this goal, a platform for studying the intermixing process in a shaped nanoparticle was designed, using multilayered Pd‐Ni‐Pt core–shell nanocubes as precursors. Under mild conditions, the intermixing between Ni and Pt could be tuned by changing layer thickness and number, triggering intermixing while preserving nanoparticle shape. Intermixing of the two metals is monitored using transmission electron microscopy. The surface structure evolution is characterized using electrochemical methanol oxidation. DFT calculations suggest that the low‐temperature mixing is enhanced by shorter diffusion lengths and strain introduced by the layered structure. The platform and insights presented are an advance toward the realization of shape‐controlled multimetallic nanoparticles tailored to each potential application.     

贵金属纳米材料的液相合成及其表面等离子体共振性质应用

金属中的表面等离子体共振是描述其导带电子在电磁场作用下集体振荡的一个物理概念。金属纳米颗粒由于其表面等离子体共振性质表现出独特的光学应用。本文在相关研究的基础上,综述了具备表面等离子体共振性质的不同形貌及多种复合结构的贵金属纳米材料的制备和应用,并对其发展及应用前景进行了展望。     

贵金属纳米材料的液相合成及其表面等离子体共振性质应用

金属中的表面等离子体共振是描述其导带电子在电磁场作用下集体振荡的一个物理概念。金属纳米颗粒由于其表面等离子体共振性质表现出独特的光学应用。本文在相关研究的基础上,综述了具备表面等离子体共振性质的不同形貌及多种复合结构的贵金属纳米材料的制备和应用,并对其发展及应用前景进行了展望。     

Nanomaterials for Biomedical Applications: Production,Characterisations, Recent Trends and Difficulties

Designing of nanomaterials has now become a top-priority research goal with a view to developing specific applications in the biomedical fields. In fact, the recent trends in the literature show that there is a lack of in-depth reviews that specifically highlight the current knowledge based on the design and production of nanomaterials. Considerations of size, shape, surface charge and microstructures are important factors in this regard as they affect the performance of nanoparticles (NPs). These parameters are also found to be dependent on their synthesis methods. The characterisation techniques that have been used for the investigation of these nanomaterials are relatively different in their concepts, sample preparation methods and obtained results. Consequently, this review article aims to carry out an in-depth discussion on the recent trends on nanomaterials for biomedical engineering, with a particular emphasis on the choices of the nanomaterials, preparation methods/instruments and characterisations techniques used for designing of nanomaterials. Key applications of these nanomaterials, such as tissue regeneration, medication delivery and wound healing, are also discussed briefly. Covering this knowledge gap will result in a better understanding of the role of nanomaterial design and subsequent larger-scale applications in terms of both its potential and difficulties.     

Tracking the Electrocatalytic Activity of a Single Palladium Nanoparticle for the Hydrogen Evolution Reaction

The nanoparticle-based electrocatalysts’ performance is directly related to their working conditions. In general, a number of nanoparticles are uncontrollably fixed on a millimetre-sized electrode for electrochemical measurements. However, it is hard to reveal the maximum electrocatalytic activity owing to the aggregation and detachment of nanoparticles on the electrode surface. To solve this problem, here, we take the hydrogen evolution reaction (HER) catalyzed by palladium nanoparticles (Pd NPs) as a model system to track the electrocatalytic activity of single Pd NPs by stochastic collision electrochemistry and ensemble electrochemistry, respectively. Compared with the nanoparticle fixed working condition, Pd NPs in the nanoparticle diffused working condition results in a 2–5 orders magnitude enhancement of electrocatalytic activity for HER at various bias potential. Stochastic collision electrochemistry with high temporal resolution gives further insights into the accurate study of NPs’ electrocatalytic performance, enabling to dramatically enhance electrocatalytic efficiency.     

Synthesis and characterization of polyhedral Pt nanoparticles: their catalytic property, surface attachment, self-aggregation and assembly

In this paper, we presented the preparation procedure of Pt nanoparticles with the well-controlled polyhedral morphology and size by a modified polyol method using AgNO(3) in accordance with the reduction of H(2)PtCl(6) in EG at high temperature around 160°C. The methods of UV-vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution (HR) TEM measurements were used to characterize their surface morphology, size, and crystal structure. We have observed that the polyhedral Pt nanoparticles of sharp edges and corners were produced in the preferential homogenous growth as well as the formation of porous and large Pt particles by self-aggregation and assembly originating from as-prepared polyhedral Pt nanoparticles. It is most impressive to find that the arrangement of Pt nanoparticles was observed in their surface attachments, self-aggregation, random and directed surface self-assembly by the bottom-up approach. Their high electrocatalytic activity for methanol oxidation was predicted. The findings and results showed that the polyhedral Pt nanoparticle-based catalysts exhibited the high electrocatalytic activity for their potential applications in developing the efficient Pt-based catalysts for direct methanol fuel cells.     

石墨烯负载的空心银钯纳米粒子的制备及其在过氧化氢检测中的应用

制备了在石墨烯上修饰的AgPd合金纳米粒子,并将其应用于对过氧化氢(H2O2)的电化学检测。通过两步合成得到此纳米复合物:利用柠檬酸钠作为保护剂和还原剂,合成石墨烯负载的Ag纳米粒子(Ag/GO);在100℃下,通过Ag与Pd2+之间的置换反应得到石墨烯负载的具有空心结构的AgPd合金纳米粒子(AgPd/GO)。用紫外-可见光谱(UV-vis),电子显微镜(TEM)等对此纳米复合物的结构及其吸收光谱和形貌进行了表征。电化学循环伏安法(CV)和计时安培法(i-t)的研究结果表明,修饰在石墨烯上的空心AgPd合金纳米粒子对H2O2还原具有显著的催化活性,对H2O2检测的线性范围为0.01～1.4 mmol/L(R=0.990);检出限为1.4μmol/L。     

天然模板辅助水/醇溶胶浸渍-煅烧法合成纳米SnO2

选择孔道丰富的竹炭、锯末、脱脂棉和滤纸等作为天然模板,结合水/醇溶胶浸渍-煅烧法成功地制备了纳米SnO2;采用X射线衍射仪(XRD)和透射电镜(TEM)分析了所制备的纳米材料的晶型、形貌、粒径.结果表明,纳米SnO2产物呈球形,具有四方相金红石型结构,平均粒径在10～25 nm范围内;其粒径大小与模板类型和溶胶体系有关...     

Various Current Responses of Single Silver Nanoparticle Collisions on a Gold Ultramicroelectrode Depending on the Collision Conditions

Collisions of silver nanoparticles (NPs) with a more electrocatalytic gold or platinum ultramicroelectrode (UME) surface have been observed by using an electrochemical method. Depending on the applied potential to the UME, the current response to the collision of Ag NPs on the UME resulted in various shape changes. A staircase decrease, a blip decrease, and a blip increase of the hydrazine oxidation current were obtained at an applied potential of 0.33, 0.80, and 1.3 V, respectively. Different collision behaviors of Ag NPs on the UME surface were suggested for each shape of current response. Ag NP attachment, which hindered the diffusion flux to the UME, caused a staircase decrease of the electrocatalytic current. Instantaneous blocking of the hydrazine oxidation by Ag NP collision and, following recovery of the current by means of oxidation of Ag NP, caused a blip decrease of the electrocatalytic current. The formation of a higher oxidation state of Ag on the Ag NP and its electrocatalytic hydrazine oxidation resulted in a blip increase of the electrocatalytic current. The analysis of the current response of a single NP collision experiment can be a useful tool to understand the various behaviors of NPs on the electrode surface.     

A Highly Efficient,Clean‐Surface,Porous Platinum Electrocatalyst and the Inhibition Effect of Surfactants on Catalytic Activity

Herein we report a gentle seedless and surfactant‐free method for the preparation of clean‐surface porous platinum nanoparticles. In terms of electrocatalytic CH₃OH oxidation, the clean‐surface porous platinum exhibited better performance than platinum nanoparticles and a commercial Pt/C catalyst. The porous nanostructures exhibited 2.26‐fold higher mass activity and 2.8‐fold greater specific activity than the Pt/C catalyst. More importantly, three typical surfactants, cetyltrimethylammonium bromide/chloride (CTAB/C), poly(vinylpyrrolidone), and sodium dodecyl sulfate, were chosen to study the inhibition effect of surfactants on electrocatalytic performance. It was observed that the surfactants led to a clear selective decrease in electrocatalytic performance. CTAB/C inhibited the catalytic activity the most due to the stronger interaction between the OH‐enriched platinum surface and the positively charged molecules. Thus, this work indicates that these clean‐surface porous platinum nanoparticles may be used as efficient catalysts for direct methanol fuel cells and provides a greater understanding of the inhibition effects of surfactants on catalytic activity.     

Dispersions, novel nanomaterial sensors and nanoconjugates based on carbon nanotubes

Nanomaterials are structures with dimensions characteristically much below 100 nm. The unique physical properties (e.g., conductivity, reactivity) have placed these nanomaterials in the forefront of emerging technologies. Significant enhancement of optical, mechanical, electrical, structural, and magnetic properties are commonly found through the use of novel nanomaterials. One of the most exciting classes of nanomaterials is represented by the carbon nanotubes. Carbon nanotubes, including single-wall carbon nanotubes, multi-wall carbon nanotubes, and concentric tubes have been shown to possess superior electronic, thermal, and mechanical properties to be attractive for a wide range of potential applications They sometimes bunch to form “ropes” and show great potential for use as highly sensitive electronic (bio)sensors due to the very small diameter, directly comparable to the size of single analyte molecules and that every single carbon atom is in direct contact with the environment, allowing optimal interaction with nearby molecules. Composite materials based on integration of carbon nanotubes and some other materials to possess properties of the individual components with a synergistic effect have gained growing interest. Materials for such purposes include conducting polymers, redox mediators and metal nanoparticles. These tubes provide the necessary building blocks for electronic circuits and afford new opportunities for chip miniaturization, which can dramatically improve the scaling prospects for the semiconductor technologies and the fabrication of devices, including field-effect transistors and sensors. Carbon nanotubes are one of the ideal materials for the preparation of nanoelectronic devices and nanosensors due to the unique electrical properties, outstanding electrocatalytic properties, high chemical stability and larger specific surface area of nanotubes. Carbon nanotubes are attractive material for supercapacitors due to their unique one-dimensional mesoporous structure, high specific surface area, low resistivity and good chemical stability. Nanoscaled composite materials based on carbon nanotubes have been broadly used due to their high chemical inertness, non-swelling effect, high purity and rigidity. The integration of carbon nanotubes with organics, biomaterials and metal nanoparticles has led to the development of new hybrid materials and sensors. Hybrid nanoscale materials are well established in various processes such as organic and inorganic compounds, nucleic acid detachment, protein separation, and immobilization of enzymes. Those nanostructures can be used as the building blocks for electronics and nanodevices because uniform organic and metal coatings with the small and monodisperse domain sizes are crucial to optimize nanoparticle conductivity and to detect changes in conductivity and absorption induced by analyte adsorption on these surfaces. The highly ordered assembly of zero-dimensional and one-dimensional nanoparticles is not only necessary for making functional devices, but also presents an opportunity to develop novel collective properties.     

Effect of aging on the electrocatalytic activity of gold nanoparticles

The electrocatalytic activities of freshly prepared nanomaterials do not represent normal activities, if they change with aging. We report the dependence of the electrocatalytic activity of gold nanoparticles (AuNPs) upon aging. The activities of AuNPs prepared by four different methods (electrodeposition; reduction of Au ions with NaBH₄, citrate, and ascorbate, respectively) slowly decrease with aging in the electrooxidation of H₂O₂ or formic acid, both in air and in solution. The possible origin of this effect is discussed.     

能源催化材料的电化学合成

电催化是发展可持续洁净能源技术的基础科学,是电化学能源转换和物质转化的关键环节.精准合成催化活性纳米结构是制约很多电催化反应走向实际应用的重要挑战.与湿化学合成、固相合成和气相沉积等传统方法相比,电化学合成是一种简单、快速、廉价及可控的高效催化材料制备方法,也是一种最为直接的一体化电极制备方法.本文综述了近年来利用电化...     

Recent Advances in Inorganic Nanomaterials Synthesis Using Sonochemistry: A Comprehensive Review on Iron Oxide,Gold and Iron Oxide Coated Gold Nanoparticles

Sonochemistry uses ultrasound to improve or modify chemical reactions. Sonochemistry occurs when the ultrasound causes chemical effects on the reaction system, such as the formation of free radicals, that intensify the reaction. Many studies have investigated the synthesis of nanomaterials by the sonochemical method, but there is still very limited information on the detailed characterization of these physicochemical and morphological nanoparticles. In this comprehensive review, recent advances in the sonochemical synthesis of nanomaterials based on iron oxide nanoparticles (Fe₃O₄NP), gold nanoparticles (AuNP) and iron oxide-coated gold nanoparticles (Fe₃O₄@Au NP) are discussed. These materials are the most studied materials for various applications, such as medical and commercial uses. This review will: (1) address the simple processing and observations on the principles of sonochemistry as a starting point for understanding the fundamental mechanisms, (2) summarize and review the most relevant publications and (3) describe the typical shape of the products provided in sonochemistry. All in all, this review’s main outcome will provide a comprehensive overview of the available literature knowledge that promotes and encourages future sonochemical work.