Selective growth of Au nanoparticles on (111) facets of Cu2O microcrystals with an enhanced electrocatalytic property

The selective growth of Au nanoparticles on (111) facets of truncated octahedral and cuboctahedral Cu(2)O crystals has been achieved by exploiting the differences in the standard potential between AuCl(4)(-)/Au and Cu(2+)/Cu(2)O pairs and in surface energies between (111) and (100) planes. The density and size of Au nanoparticles can be controlled by tuning the concentration of the gold precursor. Truncated octahedral Cu(2)O-Au nanocomposites have a 10 times higher electrochemically catalytic activity toward H(2)O(2) reduction than do pure Cu(2)O crystals. The enhanced catalysis may be derived from the polarization of Au NPs at the interface, which makes Cu(2)O more active for H(2)O(2) reduction.     

Molecular dynamics simulations of inverse sodium dodecyl sulfate (SDS) micelles in a mixed toluene/pentanol solvent in the absence and presence of poly(diallyldimethylammonium chloride) (PDADMAC)

Well-aligned ZnO nanorods (NRs) were grown on indium-tin-oxide (ITO) slide by the hydrothermal method and used as templates for preparing ZnO/Au composite nanoarrays. The optical and morphological properties of ZnO/Au composites under various HAuCl(4) concentrations were explored via UV-vis absorption spectroscopy, photoluminescence (PL) and scanning electron microscopy (SEM). The density and size of gold nanoparticles (Au NPs) on ZnO NRs can be controlled by adjusting the concentration of HAuCl(4). The optimal ZnO/Au composites display complete photocatalytic degradation of methyl blue (MB) within 60 min, which is superior to that with pure ZnO NRs prepared by the same method. The reason of better photocatalytic performance is that Au NPs act as electron traps and it prevents the rapid recombination of electrons and holes, resulting in the improvement of photocatalytic efficiency. The photocatalytic performance of ZnO/Au composites is mainly controlled by the density of Au NPs formed on ZnO NRs. The application in rapid photodegradation of MB shows the potential of ZnO/Au composite as a convenient catalyst for the environmental purification of organic pollutants.     

金/氧化亚铜异质球的制备及其可见光催化性能

使用L-半胱氨酸作为连接剂, 利用硼氢化钠原位还原预先吸附在介孔氧化亚铜表面的氯金酸根离子,得到了Au/Cu₂O异质结构. 应用X射线粉末衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、X射线光电子能谱(XPS)、紫外-可见(UV-Vis)光谱和N₂物理吸附等手段对催化剂进行表征, 并以λ>400 nm的可见光作为光源, 评价了该催化剂光催化降解亚甲基蓝(MB)的活性. 实验结果表明, 直径为4 nm的金颗粒完好地负载在介孔氧化亚铜的表面, 并且介孔氧化亚铜的细微结构与孔径均未发生变化. 研究表明, 以乙醇作为反应溶剂有效抑制了AuCl₄^-与Cu₂O之间的氧化还原反应, 从而有利于氧化亚铜介孔结构的保持及金颗粒的原位还原. 光催化降解亚甲基蓝的结果表明, Au/Cu₂O异质结构的光催化活性比纯氧化亚铜光催化活性有明显提高. 推测其光催化性能提高的主要原因如下: 一方面, 金颗粒良好的导电性有利于氧化亚铜表面电子的快速转移, 实现电子-空穴分离; 另一方面, 金颗粒可能存在的表面等离子共振现象加速了光生电子的产生.     

Electrocatalytic and photocatalytic applications of atomically precise gold-based nanoclusters

With advances in cluster chemistry, atomically precise gold nanoclusters(NCs) with well-defined composition and tunable structure provide an exciting opportunity to uncover the specific roles of the geometrical and electronic structures as well as the capped ligands in overall catalytic performances. The Au NCs possess quantum energy levels and unique optical properties,which have exhibited unexpected photocatalytic and electrocatalytic activities. In this review, we first highlight the electrocatalytic applications of Au NCs, including hydrogen evolution reaction, oxygen reduction reaction, CO_2 reduction and catalytic oxidation reactions, and then present Au NCs-driven photocatalytic applications such as selective organic reactions, decomposition of pollutants and energy conversion reactions. Finally, we conclude this review with a brief perspective on the catalytic field of Au NCs.     

Multifunctional PES fabrics modified with colloidal Ag and TiO2 nanoparticles

This study is aimed to highlight the possibility of engineering the multifunctional textile nanocomposite material based on the polyester (PES) fabric modified with colloidal Ag and TiO₂ nanoparticles (NPs). The effects of concentration of NPs as well as the order of Ag and TiO₂ NPs loading on antimicrobial, UV protective, and photocatalytic properties of PES fabrics were examined. The antimicrobial activity of differently modified PES fabrics was tested against Gram‐negative bacterium Escherichia coli, Gram‐positive bacterium Staphylococcus aureus, and fungus Candida albicans. The concentration of Ag colloid and the order of Ag and TiO₂ NPs loading considerably affected the antimicrobial efficiency of PES fabrics. The fabrics provided maximum UV protection upon surface modification with Ag and TiO₂ NPs. Ag NPs enhanced Ag NPs enhanced the photodegradation activity of TiO₂ NPs and total photodegradation of methylene blue was achieved after 24 hr of UV illumination. Copyright © 2010 John Wiley & Sons, Ltd.     

基于等离激元热电子调控的全谱光催化产氢增强（英文）

等离激元效应在光催化体系中的集成为实现广谱光吸收提供了一个新的途径,然而等离激元热电子的较低迁移率和不确定扩散方向使得其光催化效率仍较低.等离激元金属与n型半导体接触后,其界面间会形成肖特基结.在特定波长太阳光照射下,等离激元金属将其表面等离子体能量聚集在表面自由电子上,进而产生热电子.当这些热电子具有的能量高于肖特基势垒时,热电子便可注入到半导体导带上.与此同时,半导体上的电子可以通过肖特基接触发生回流,与金属上的空穴复合,进而降低半导体-等离激元金属复合材料的光催化性能.因此,为了提高光催化效率,如何调控等离激元热电子迁移和充分利用等离激元效应是一个重要挑战.本文尝试将"表面异质结"与肖特基结相结合的复合结构,得以有效地调控等离激元热电子的迁移.在该复合结构中,金纳米颗粒和铂纳米颗粒分别作为等离激元吸光单元和助催化剂,集成在TiO_2纳米片表面.其中"表面异质结"是由TiO_2纳米片的两种不同表面晶面所构成,我们选择由{001}和{101}两组晶面组成的TiO_2纳米片作为半导体衬底.该结构中的{001}晶面导带能级高于{101}导带能级,因而电子由高能级的{001}流向低能级的{101}晶面,可以用来引导等离激元热电子从可见光响应的金纳米颗粒向TiO_2进行高效转移.通过巯基丙酸的桥联作用,将等离激元Au纳米颗粒锚定在TiO_2纳米片的{001}晶面上,获得Au-TiO_2{001}样品.另一方面,利用TiO_2纳米片自身光生电荷导向性光沉积,得到与{101}晶面结合形成的Au-TiO_2{101}样品.我们对两组样品进行光电流和光催化产氢实验对比,确认在"表面异质结"诱导下Au-TiO_2{001}样品中Au产生的光生热电子可以更好地注入到TiO_2纳米片导带上.我们进一步通过光沉积Pt纳米颗粒来判定光生电子所能到达的区域,验证了以上结论.与此同时,肖特基结由铂纳米颗粒与TiO_2纳米片所形成,可以促使电子由TiO_2向铂纳米颗粒进行转移,而避免发生向金纳米颗粒的反向迁移,从而在Au-TiO_2体系中实现高效的单向载流子转移.基于该设计,等离激元光催化剂实现了明显改善的全谱光催化产氢性能.本文为全谱光催化的复合结构理性设计提供了一个新的思路.     

Wavelength Dependence of the Fluorescence Quenching Efficiency of Nearby Dyes by Gold Nanoclusters and Nanoparticles: The Roles of Spectral Overlap and Particle Size

The efficiency of the glutathione monolayer-protected gold nanocluster (NC) Au(25) (1.2 nm metal core diameter (d)) in quenching the emission of dyes intercalated into DNA is compared to that of 2 and 4 nm gold nanoparticles (NPs). In all cases, the DNA/dye moieties and the gold particles are not covalently attached but rather form non-covalent ground state complexes. Under these conditions, steady-state measurements reveal that the quenching efficiency of Au(25) is a factor of 10 lower than that of plasmonic 4 nm gold NPs but comparable to that of 2 nm particles which do not show a distinct plasmon band. Nonetheless, significant emission quenching is observed even at very low (nM) concentrations of Au(25). The quenching efficiency of the 4 nm NPs is significantly higher for dyes emitting near the wavelength of the plasmon peak whereas that of the 2 nm gold NPs is well described by the nano-surface energy transfer (NSET) model proposed by the Strouse group (J. Am. Chem. Soc. 127, 3115 2005). Interestingly, for Au(25) the maximum quenching efficiency occurs for dyes emitting in the same wavelength range as that of the 2 and 4 nm NPs (490-560 nm), where it shows no discrete absorption features, rather than for wavelengths coincident with its HOMO-LUMO, intra-band or inter-band transitions. The fluorescence quenching properties of Au(25) NCs are therefore found to be distinct from those of larger NCs and NPs but do not appear to conform to theoretical predictions advanced thus far.     

The density of surface ligands regulates the luminescence of thiolated gold nanoclusters and their metal ion response

The fascinating luminescence properties of gold nanoclusters(AuNCs) have drawn considerable research interests,and been widely harnessed for a wide range of applications.However,a fundamental understanding towards ligand density's role in the luminescence properties of these ultrasmall AuNCs remains unclear yet.In this communication,through systematic investigation of surface chemistries of glutathione-protected Au NCs(GSH-Au NCs) with diffe rent density of GSH as well as other thiolates,it is discovered that the density of surface ligands can significantly regulate the luminescence properties of AuNCs.Fluorescence lifetime spectroscopy and X-ray photoelectron spectroscopy showed that AuNCs with a higher density of electron-rich ligands facilitate their luminescence generation.Moreover,differences in the surface coverage of AuNCs can also affect their interactions with foreign species,as illustrated by significantly different fluorescence quenching capability of GSH-AuNCs with different ligand density towards Hg~(2+).This study provides new insight into the intriguing luminescence properties of metal NCs,which is hoped to stimulate further research on the design of metal NCs with strong luminescence and sensitive/specific responses for promising optoelectronic,sensing and imaging applications.     

Atomically precise Au25(GSH)18 nanoclusters versus plasmonic Au nanocrystals: Evaluating charge impetus in solar water oxidation

Atomically precise metal nanoclusters (NCs) have been deemed as an emerging class of metal nanomaterials owing to fascinating size-dependent physicochemical properties, discrete energy band structure, and quantum confinement effect, which are distinct from conventional metal nanoparticles (NPs). Nevertheless, metal NCs suffer from photoinduced self-oxidative aggregation accompanied by in-situ transformation to metal NPs, markedly reducing the photosensitization of metal NCs. Herein, maneuvering the generic instability of metal NCs, we perform the charge transport impetus comparison between atomically precise metal NCs and plasmonic metal NPs counterpart obtained from in-situ self-transformation of metal NCs in photoelectrochemical (PEC) water splitting reaction. For conceptual demonstration, we proposed two quintessential heterostructures, which include TNTAs-Au₂₅ heterostructure fabricated by electrostatically depositing glutathione (GSH)-protected Au₂₅(GSH)₁₈ NCs on the TiO₂ nanotube arrays (TNTAs) substrate, and TNTAs-Au heterostructure constructed by triggering self-transformation of Au₂₅(GSH)₁₈ NCs to plasmonic Au NPs in TNTAs-Au₂₅ via calcination. The results indicate that photoelectrons produced over Au₂₅ NCs are superior to hot electrons of plasmonic Au NPs in stimulating the interracial charge transport toward solar water oxidation. This is mainly ascribed to the significantly accelerated carrier transport kinetics, prolonged carrier lifespan, and substantial photosensitization effect of Au₂₅ NCs compared with plasmonic Au NPs, resulting in the considerably enhanced PEC water splitting performance of TNTAs-Au₂₅ relative to plasmonic TNTAs-Au counterpart under visible light irradiation. Our work would provide important implications for rationally designing atomically precise metal NCs-based photosystems toward solar energy conversion.     

Controllable synthesis and catalysis application of hierarchical PS/Au core-shell nanocomposites

Polystyrene (PS)/gold (Au) core-shell nanocomposites with tunable size, high stability, and excellent catalytic activity have been synthesized by a facile method that combines the ionic self-assembly with the in situ reduction. The composition and stoichiometry, as well as its morphology and optical properties of these nanocomposites have been examined and verified by various characterization techniques. The size and the coverage of gold nanoparticles (NPs) can be simply tailored by changing the amount of 3-aminopropyltrimethoxysilane (APTES), the functionalization time, the protonation time, and the amount of chloroauric acid (HAuCl₄). The continuous red shifts of the localized surface plasmon resonance absorption of the Au NPs on the PS spheres are observed. Importantly, the obtained Au NPs with controllable and uniform size on the surfaces of amino-functionalized PS spheres exhibit excellent size-dependent catalytic properties for the reduction of 4-nitrophenol (4-NP) by NaBH₄.     

Low polydispersed copper-sulfide nanocrystals derived from various Cu-alkyl amine complexes

Copper-sulfides, Cu2-xS nanocrystals (NCs) have been synthesized using the reaction between a Cu-alkyl amine complex and a sulfur/1-dodecanethiol. Here, 1-dodecanthiol plays an important role to reduce the reaction temperature of sulfuration. The Cu/S composition (the Cu-defect density) of Cu2-xS NCs depends on the stability of Cu-alkyl amine complex. XPS analyses reveal that the substance of Cu-defect is attributed to an introducing of Cu+2S2-2 species. There is a good correlation between an intensity of a near IR absorption peak and a Cu-defect density estimated by XPS analyses. These results demonstrate that optical properties of Cu2-xS NCs in a near IR region are tunable.     

Metal‐Enhanced Fluorescence of CdTe Nanocrystals in Aqueous Solution

Metal‐enhanced fluorescence of semiconductor nanocrystals (NCs) is investigated. There is very little attention paid to the metal‐enhanced fluorescence in aqueous solution, which has great potential applications in bioscience. In this work, we directly observe metal‐enhanced fluorescence of CdTe NC solution by simply mixing CdTe NCs and Au nanoparticles, both of which are negatively charged. In order to study this kind of photoluminescence enhancement in aqueous solutions, we propose a calibration method, which takes into account the light attenuation in solutions. After consideration of the light weakening in transmission, the maximal PL enhancement is about 3 times as large as the ones without Au NPs. Some factors related to the enhanced magnitude of fluorescence, for instance, the concentration and the molar feed ratio of CdTe NCs and Au NPs, are studied in detail. Furthermore, the decreased lifetimes of CdTe NCs induced by Au NPs are also obtained, which are in accord with the enhancement of the photoluminescence.     

Highly Facet‐Dependent Photocatalytic Properties of Cu2O Crystals Established through the Formation of Au‐Decorated Cu2O Heterostructures

This work confirms the presence of a large facet‐dependent photocatalytic activity of Cu₂O crystals through sparse deposition of gold particles on Cu₂O cubes, octahedra, and rhombic dodecahedra. Au‐decorated Cu₂O rhombic dodecahedra and octahedra showed greatly enhanced photodegradation rates of methyl orange resulting from a better separation of the photogenerated electrons and holes, with the rhombic dodecahedra giving the best efficiency. Au–Cu₂O core–shell rhombic dodecahedra also displayed a better photocatalytic activity than pristine rhombic dodecahedra. However, Au‐deposited Cu₂O cubes, pristine cubes, and Au‐deposited small nanocubes bound by entirely {100} facets are all photocatalytically inactive. X‐ray photoelectron spectra (XPS) showed identical copper peak positions for these Au‐decorated crystals. Remarkably, electron paramagnetic resonance (EPR) measurements indicated a higher production of hydroxyl radicals for the photoirradiated Cu₂O rhombic dodecahedra than for the octahedra, but no radicals were produced from photoirradiated Cu₂O cubes. The Cu₂O {100} face may present a high energy barrier through its large band edge bending and/or electrostatic repulsion, preventing charge carriers from reaching to this surface. The conventional photocatalysis model fails in this case. The facet‐dependent photocatalytic differences should be observable in other semiconductor systems whenever a photoinduced charge‐transfer process occurs across an interface.     

Self-Indicative Gold Nanozyme for H2O2 and Glucose Sensing

In addition to superior enzyme-mimicking abilities, nanozymes also have intrinsic physicochemical properties. Integrating the enzyme-like activities and tunable physicochemical properties into a single nanoparticle is a promising strategy for versatile nanozyme design and application. Herein, a composite nanozyme in which Au nanoparticles are encapsulated by Au nanoclusters (AuNP@AuNCs) is presented. By integrating the peroxidase-mimicking ability of fluorescent Au NCs with the glucose oxidase-like activity of Au NPs, the composite nanozyme realized cascade assay of glucose without the aid of external indicators. Compared to traditional multistep colorimetric methods, the analytical process was highly simplified by using the self-responsive nanozyme. This synthetic strategy provided valuable insights into exploring talented nanozymes for sensing diverse targets.     

真空离子溅射法制备TiO2∶Au复合纳米纤维新型光催化剂及其 降解乙醛性能研究

采用静电纺丝技术与真空离子溅射相结合的方法制备了TiO2∶Au复合纳米纤维, 并采用SEM和X射线电子能谱仪对其进行了表征. 结果表明TiO2∶Au纳米纤维的表面形态能通过Au沉积时间得到很好的控制. 同时在紫外光照射下采用乙醛体系考察了TiO2纳米纤维和TiO2∶Au复合纳米纤维催化剂降解乙醛性能, 结果证明TiO2∶Au复合纳米纤维具有更好的催化效率, 紫外光照射70 min后乙醛被完全降解.     

Photocatalytic reduction of carbon dioxide to methanol by Cu2O/SiC nanocrystallite under visible light irradiation

The Cu2O/SiC photocatalyst was obtained from SiC nanoparticles (NPs) modified by Cu2O. Their photocatalytic activities for reducing CO2 to CH3OH under visible light irradiation have been investigated. The results indicated that besides a small quantity of 6H-SiC, SiC NPs mainly consisted of 3C-SiC. The band gaps of SiC and Cu2O were estimated to be about 1.95 and 2.23 eV from UV-Vis spectra, respectively. The Cu2O modification can enhance the photocatalytic performance of SiC NPs, and the largest yields of methanol on SiC, Cu2O and Cu2O/SiC photocatalysts under visible light irradiation were 153, 104 and 191μmol/g, respectively.     

低温静电自组装法制备贵金属修饰TiO_2纳米结构薄膜及其增强的光催化性能(英文)

以碱-水热法在金属Ti片上原位生长了TiO2纳米结构(纳米花和纳米线)薄膜,并采用低温静电自组装方法将超细贵金属(金、铂、钯)纳米颗粒均匀沉积于多孔TiO2薄膜上.负载于Ti片上的贵金属/TiO2纳米结构薄膜具有一体化结构、多孔架构和高光催化活性.超高分辨率场发射扫描电子显微镜(FESEM)直接观察表明贵金属纳米颗粒在TiO2表面分布均匀,且颗粒之间相互分离,金、铂、钯纳米颗粒的平均粒径分别约为4.0、2.0和10.0nm.俄歇电子能谱(AES)纵深成分分析表明贵金属不仅沉积于薄膜表面,且大量分布于TiO2纳米结构薄膜内部,其深度超过580 nm.X射线光电子能谱(XPS)分析表明,经300°C下在空气中热处理后,纳米金仍保持金属态,纳米铂部分被氧化成PtOabs,而钯粒子则完全被氧化成氧化钯(PdO).以低温静电自组装法沉积贵金属,贵金属负载量可通过调节组装时间与溶胶pH值来控制.光催化降解甲基橙的结果表明,沉积的纳米金和铂能显著增加TiO2纳米结构薄膜的光催化活性,说明金和铂粒子可促进光生载流子的分离;但负载的PdO对TiO2薄膜的光催化性能增强几乎无作用.     

Cu2+/TiO2对甲基橙的光催化降解机理

以自制的掺铜离子的混晶型二氧化钛为光催化剂,考察了甲基橙光催化降解过程中pH值和光源的影响,提出了两种不同的光催化降解机理:在高压汞灯照射下,TiO2的价带电子被激发到导带,光生电子和空穴主要通过Cu2+ 的短路循环而复合,光催化剂的活性降低;在太阳光照射下,甲基橙发生自身光敏化氧化反应,受激电子从单线态或三线态的甲基橙分子跃迁到TiO2的导带,Cu2+起到电荷传递中继站的作用,加速了注入电子向H2O2的转移,从而促进了甲基橙的光催化降解。     

In situ synthesis and characterization of multiwalled carbon nanotube/Au nanoparticle composite materials

An effective and facile in situ reduction approach for the fabrication of carbon nanotube-supported Au nanoparticle (CNT/Au NP) composite nanomaterials is demonstrated in this article. Linear polyethyleneimine (PEI) is ingeniously used as both a functionalizing agent for the multiwalled carbon nanotubes (MWNTs) and a reducing agent for the formation of Au NPs. This method involves a simple mixing process followed by a mild heating process. This approach does not need the exhaustive surface oxidation process of CNTs. The coverage of Au NPs on CNTs is tunable by varying the experimental parameters, such as the initial molar ratio of PEI to HAuCl4, the relative concentration of PEI and HAuCl4 to MWNTs, and the temperature and duration of the heat treatment. More importantly, even the heterogeneous CNT/Au composite nanowires are obtainable through this method. TEM, XPS, and XRD are all used to characterize the CNT/Au composite materials. In addition, the optical and electrocatalytic properties are investigated.     

花状Cu2O/Cu的水热合成及其光催化性能

以硝酸铜为前驱体, 不采用任何模板, 通过逐步水热法合成了花状Cu2O/Cu复合纳米材料. 用扫描电镜(SEM)、X射线衍射(XRD)和紫外-可见漫反射光谱(DRS)对样品进行表征. 结果表明, 花状纳米Cu2O/Cu材料是由长为300-500 nm, 宽为30-70 nm的带状花瓣构成, 在可见光区域有很强的吸收. 复合材料中Cu的含量可以通过反应时间进行调控. 对染料Procion Red MX-5B(PR)的可见光催化降解, Cu能明显提高Cu2O的光催化性能. 当Cu质量分数为27%-71%时, 复合材料Cu2O/Cu的催化活性明显高于单相Cu2O. 与立方体形貌的Cu2O/Cu复合材料相比, 花状纳米Cu2O/Cu复合材料对染料PR有更高的催化降解性能. 且该复合材料有较高的循环回收利用率.