Ultrafast Laser Manufacture of Stable,Efficient Ultrafine Noble Metal Catalysts Mediated with MOF Derived High Density Defective Metal Oxides

Supported metal nanoparticles (MNPs) undergo severe aggregation, especially when the interaction between MNPs and their supports are limited and weak where their performance deteriorates dramatically. This becomes more severe when catalysts are operated under high temperature. Here, it is reported that MNPs including Pt, Au, Rh, and Ru, with sub‐2 nm size can be stabilized on densely packed defective CeO₂ nanoparticles with sub‐5 nm size via strong coupling by direct laser conversion of corresponding metal ions encapsulated cerous metal–organic frameworks (Ce‐MOFs). Ce‐MOF serves as an ideal dispersion precursor to uniformly encapsulate noble metal ions in their orderly arranged pores. Ultrafast laser vaporization and cooling forms uniform, ultrasmall, well‐mixed, and exceptionally dense nanoparticles of metal and metal oxide concurrently. The laser‐induced ultrafast reaction (within tens of nanoseconds) facilitates the precipitation of CeO₂ nanoparticles with abundant surficial defects. Due to the well‐mixed ultrasmall Pt and CeO₂ components with strong coupling, this catalyst exhibits exceptionally high stability and activity both at low and high temperatures (170–1100 °C) for CO oxidation in long‐term operation, significantly exceeding catalysts prepared by traditional methods. The scalable feature of laser and huge MOF family make it a versatile method for the production of MNP‐based nanocomposites in wide applications.     

Controlled self-assembly of metal-organic frameworks on metal nanoparticles for efficient synthesis of hybrid nanostructures

We report a novel approach for synthesizing inorganic nanoparticle/metal-organic frameworks (MOFs) heterostructured nanocomposites by self-assembly of MOFs on nanoparticles. This approach involves the synthesis of Au nanoparticles and preferential growth of [Cu(3)(btc)(2)](n) frameworks consisting of Cu(2+) ions and benzene-1,3,5-tricarboxylate (btc) on nanoparticles. Aggregates consisting of 11-mercaptoundecanoic acid (MUA)-stabilized Au nanoparticles linked by Cu(2+) ions were necessary for preferential self-assembly of [Cu(3)(btc)(2)](n) frameworks on the aggregates, resulting in the formation of Au nanoparticles/[Cu(3)(btc)(2)](n) nanocomposites. The present approach was confirmed to be applicable for other hybrids consisting of Au nanoparticles and tetragonal [Cu(2)(ndc)(2)(dabco)](n) frameworks.     

Integration of Metal Nanoparticles into Metal–Organic Frameworks for Composite Catalysts: Design and Synthetic Strategy

Metal–organic frameworks (MOFs) are constructed by periodically alternate metal ions with organic ligands, which offer structural diversity and a wide range of interesting properties as an attractive classification of crystalline porous materials. Integration of MOFs with other size‐limited functional centers can supply new multifunctional composites, which exhibit both the properties of the components and new characteristics due to the combination of MOFs with the selected loadings. In recent years, integration of metal/metal oxide nanoparticles (MNPs) into MOFs to form the composite catalysts has attracted considerable attention due to the superior performance. In this review, the latest studies and up‐to‐date developments on the design and synthetic strategy of new MNP@MOF composite catalysts are specifically highlighted. Both the achievements and problems are evaluated and proposed, and the opportunities and challenges of MNP@MOF composite catalysts are discussed.     

Ultrasmall Metal Nanoparticles Confined within Crystalline Nanoporous Materials: A Fascinating Class of Nanocatalysts

Crystalline nanoporous materials with uniform porous structures, such as zeolites and metal–organic frameworks (MOFs), have proven to be ideal supports to encapsulate ultrasmall metal nanoparticles (MNPs) inside their void nanospaces to generate high‐efficiency nanocatalysts. The nanopore‐encaged metal catalysts exhibit superior catalytic performance as well as high stability and catalytic shape selectivity endowed by the nanoporous matrix. In addition, the synergistic effect of confined MNPs and nanoporous frameworks with active sites can further promote the catalytic activities of the composite catalysts. Herein, recent progress in nanopore‐encaged metal nanocatalysts is reviewed, with a special focus on advances in synthetic strategies for ultrasmall MNPs (<5 nm), clusters, and even single atoms confined within zeolites and MOFs for various heterogeneous catalytic reactions. In addition, some advanced characterization methods to elucidate the atomic‐scale structures of the nanocatalysts are presented, and the current limitations of and future opportunities for these fantastic nanocatalysts are also highlighted and discussed. The aim is to provide some guidance for the rational synthesis of nanopore‐encaged metal catalysts and to inspire their further applications to meet the emerging demands in catalytic fields.     

Monodispersed Pt nanoparticles on reduced graphene oxide by a non-noble metal sacrificial approach for hydrolytic dehydrogenation of ammonia borane

Downsizing noble metal nanoparticles,such as Pt,is an essential goal for many catalytic reactions.A non-noble metal sacrificial approach was used to immobilize monodispersed Pt nanoparticles (NPs) with a mean size of 1.2 nm on reduced graphene oxide (RGO).ZnO co-precipitated with Pt NPs and subsequently sacrificed by acid etching impedes the diffusion of Pt atoms onto the primary Pt particles and also their aggregation during the reduction of precursors.The resulting ultrafine Pt nanoparticles exhibit high activity (a turnover frequency of 284 min-1 at 298 K) in the hydrolytic dehydrogenation of ammonia borane.The non-noble metal sacrificial approach is demonstrated as a general approach to synthesize well-dispersed noble metal NPs for catalysis.     

Two particle enhanced nano Raman microscopy and spectroscopy

The distance- and polarization-dependent near-field enhancement of two coupling metal nanoparticles (MNPs) is analyzed by means of the novel scanning particle enhanced Raman spectroscopy (SPRM) technique. In contrast to single MNP Raman experiments, the near-field coupling between two dissimilar MNPs as followed here leads to a Raman hot spot yielding an extra enhancement factor of 17.6 and 20, as proven here both in experiment and in theory. Three-dimensional electric field calculations for our two-particle arrangements were performed using the semianalytical multiple-multipole method. An excellent agreement is found to our experiments, in which we inspect the interaction between a "scanning" 30 nm gold MNP (Au30) and a "fixed" 80 nm Au MNP (Au80). The Au80 MNP is attached to the apex of an optical fiber manipulator and exposed to the Gaussian focus of a high NA = 1.45 objective at lambda = 532 nm. A monolayer of 1-octanethiol molecules covering the Au80 MNP serves as the electric field prober when scanning the Au30 MNP through the optical focus. This constellation allows recording the Raman signatures from a very low number of well-confined molecules. Moreover, also the spectral and spatial dependence could be explored with a superb sensitivity and very low integration time.     

Functionalization of silicon nanowire surfaces with metal-organic frameworks

Metal-organic frameworks (MOFs) and silicon nanowires (SiNWs) have been extensively studied due to their unique properties; MOFs have high porosity and specific surface area with well-defined nanoporous structure, while SiNWs have valuable one-dimensional electronic properties. Integration of the two materials into one composite could synergistically combine the advantages of both materials and lead to new applications. We report the first example of a MOF synthesized on surface-modified SiNWs. The synthesis of polycrystalline MOF-199 (also known as HKUST-1) on SiNWs was performed at room temperature using a step-by-step (SBS) approach, and X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy elemental mapping were used to characterize the material. Matching of the SiNW surface functional groups with the MOF organic linker coordinating groups was found to be critical for the growth. Additionally, the MOF morphology can by tuned by changing the soaking time, synthesis temperature and precursor solution concentration. This SiNW/MOF hybrid structure opens new avenues for rational design of materials with novel functionalities.      

Preparation and characterization of iminodiacetic acid-functionalized magnetic nanoparticles and its selective removal of bovine hemoglobin

In this study, a novel route for the preparation of magnetite (Fe(3)O(4)) nanoparticles (NPs) with immobilized metal affinity ligand iminodiacetic acid (IDA) charged with Cu(2+) was developed. First, magnetite nanoparticles were synthesized by a hydrothermal method. Charged with Cu(2+), the magnetic nanoparticles (MNPs) were applied to separate a model protein mixture of bovine hemoglobin (BHb) and bovine serum albumin (BSA). They could be separated completely and showed low non-specific adsorption. The morphology, structure and composition of the magnetite MNPs were characterized by transmission electron microscopy, power x-ray diffraction, x-ray photoelectron spectrometry and Fourier transform infrared spectroscopy. The resulting magnetite MNPs charged with Cu(2+) show not only a strong magnetic response to externally applied magnetic field, but are also highly specific to protein BHb. It is interesting that MNPs modified with metal ligands showed a property of magnetic colloid photonic crystals. Furthermore, they could efficiently remove the abundant protein bovine hemoglobin from bovine blood. They have potential application in removing abundant protein in proteomic analysis.     

Probing hot electron flow generated on Pt nanoparticles with Au/TiO2 Schottky diodes during catalytic CO oxidation

Hot electron flow generated on colloid platinum nanoparticles during exothermic catalytic carbon monoxide oxidation was directly detected with Au/TiO2 diodes. Although Au/TiO2 diodes are not catalytically active, platinum nanoparticles on Au/TiO2 exhibit both chemicurrent and catalytic turnover rate. Hot electrons are generated on the surface of the metal nanoparticles and go over the Schottky energy barrier between Au and TiO2. The continuous Au layer ensures that the metal nanoparticles are electrically connected to the device. The overall thickness of the metal assembly (nanoparticles and Au thin film) is comparable to the mean free path of hot electrons, resulting in ballistic transport through the metal. The chemicurrent and chemical reactivity of nanoparticles with citrate, hexadecylamine, hexadecylthiol, and TTAB (tetradecyltrimethylammonium bromide) capping agents were measured during catalytic CO oxidation at pressures of 100 Torr O2 and 40 Torr CO at 373-513 K. We found that chemicurrent yield varies with each capping agent but always decreases with increasing temperature. We suggest that this inverse temperature dependence is associated with the influence of charging effects due to the organic capping layer during hot electron transport through the metal-oxide interface.     

Microwave synthesis and voltammetric simultaneous determination of paracetamol and caffeine using an MOF-199-based electrode

In the present paper, the microwave synthesis of MOF-199 and its application as an electrode modifier for the simultaneous voltammetric determination of paracetamol (PAR) and caffeine (CAF) were demonstrated. The obtained materials were characterised by X-ray diffraction, a scanning electron microscope (SEM), nitrogen adsorption/desorption isotherms and thermal gravity. The microwave (MW) synthesis of MOF-199 has been compared to its conventional hydrothermal synthesis. It is found that by using the MW synthesis, MOF-199 can be obtained in a much shorter synthesis time with improved yield and textural properties. The electrode modified by MOF-199 was used in order to develop an electroanalytical method that can be used to simultaneously quantify PAR and CAF. The kinetic parameters of the electrode reaction process were also investigated. This proposed method was successfully employed for the simultaneous detection of PAR and CAF in pharmaceutical formulations using the standard addition method and the obtained results compared with the results determined by means of HPLC were found to be statistically similar.     

金属-有机骨架材料MOF-199对甲醛气体吸附行为的研究

初步探讨了金属-有机骨架材料MOF-199对甲醛气体的吸附性能.采用分光光度法测定MOF-199对甲醛气体的吸附量,研究了吸附量与吸附温度及吸附时间的关系,并探讨了MOF-199对甲醛的吸附机理,提出了一种测定MOF-199对甲醛吸附量的方法.结果表明,在50℃、6h的吸附条件下,MOF-199对甲醛气体的吸附量最大,达到83.84mg/g;MOF-199对甲醛气体具有较好的吸附效果.     

Adsorptive removal of methyl orange and methylene blue from aqueous solution with a metal-organic framework material, iron terephthalate (MOF-235)

An iron terephthalate (MOF-235), one of the metal-organic frameworks (MOFs), has been used for the removal of harmful dyes (anionic dye methyl orange (MO) and cationic dye methylene blue (MB)) from contaminated water via adsorption. The adsorption capacities of MOF-235 are much higher than those of an activated carbon. The performance of MOF-235 having high adsorption capacity is remarkable because the MOF-235 does not adsorb nitrogen at liquid nitrogen temperature. Based on this study, MOFs, even if they do not adsorb gases, can be suggested as potential adsorbents to remove harmful materials in the liquid phase. Adsorption of MO and MB at various temperatures shows that the adsorption is a spontaneous and endothermic process and that the entropy increases (the driving force of the adsorption) with adsorption of MO and MB.     

Gold nanoparticle enhanced electrochemiluminescence of CdS thin films for ultrasensitive thrombin detection

Interactions between surface plasmons (SP) of metallic surfaces and photoluminescence (PL) of semiconductor nanocrystal (S-NC) surfaces have been extensively investigated, and SP-induced PL enhancement has been used as a sensitive analytical technique. However, this SP induced electrochemiluminescence (ECL) enhancement is rarely studied. In this work, we report greatly enhanced ECL of CdS thin films by gold nanoparticles (Au NPs) for ultrasensitive detection of thrombin. The system was composed of a CdS NC film on glassy carbon electrode (GCE) as ECL emitter attached an aptamer of thrombin. Then, ssDNA-AuNP conjugates hybridized with the aptamer to form a separation length of ca. 12 nm between CdS NCs and Au NPs. The system showed 5-fold enhancement of ECL intensity as compared to that without Au NPs, which might be attributed to the long-distance interaction between the S-NCs and SPR field of noble metal nanoparticles (MNPs).We also found that the enhanced ECL could be influenced by the involving factors such as the separation distance, spectral overlap, and magnetic field. Such enhancement in combination with smart recognition of aptamer and target protein allowed us to construct an ultrasensitive aptasensor for attomolar detection of thrombin. The presence of target protein was reflected by the ECL signal decrease caused by the target-induced removal of ssDNA-AuNP conjugates. The decrease of ECL signal was logarithmically linear with the concentration of thrombin in a wide range from 100 aM to 100 fM. The principle described in this work could be also applied to many other bioassays.     

Ce改性金属有机骨架材料对氟的吸附

利用水热合成法，将金属Ce与合成金属有机骨架材料(MOFs)所需的反应前体混合，通过“一锅法”和“两步法”分别合成性能不同的Ce/MOF-5材料。采用SEM、XRD、BET等对合成材料进行表征。结果表明:不同的方法合成的Ce/MOF-5形貌有较大差异，对氟吸附性能也不同。并测定了初始浓度、pH值、吸附时间对F?吸附效果的影响。实验表明，通过“一锅法”合成的Ce/MOF-5材料对F?的吸附在pH=7、吸附时间为60 min左右即可达到吸附平衡，吸附量为109.6 mg·g?1，符合准二级动力学模型和Freundlich等温吸附模型。      

Au–ZnO hybrid nanostructures prepared by electro-exploding wire technique: Raman signal enhancement and photoluminescence emission quenching

Electro-exploding wire (EEW) technique was employed to prepare ZnO and Au–ZnO hybrid nanoparticles. Average size of the prepared ZnO nanoparticles is found to be 3.8 nm and uniform throughout. These ultrafine ZnO nanoparticles are found to agglomerate around the highly surface active Au nanoparticles. It also acts as a stabilizer for the Au nanoparticles by avoiding self agglomeration. The hybrid nanocrystals show strong crystallinity of face-centered cubic and hexagonal wurtzite structure of gold (Au) and zinc oxide (ZnO), respectively. Presence of Au₃Zn in pristine sample is a clear indication of a strong interaction between ZnO and Au systems. The hybrid system shows strong enhancement in the ZnO Raman signals and quenching in the visible Photoluminescence (PL) emission. Energy-dependent PL analysis shows the dominance of the surface defects over the bulk contribution in these ultrafine ZnO and Au–ZnO hybrid nanostructures.     

Carbonaceous materials passivation on amine functionalized magnetic nanoparticles and its application for metal affinity isolation of recombinant protein

Magnetic nanoparticles (MNPs) with an amine functionalized surface (MH) were passivated with carbonaceous materials (MH@C) by carbonization of glucose under hydrothermal reaction conditions. The carboxylate groups in carbonaceous shell could be enriched to 0.285 mmol/g when acrylic acid was added as a functional monomer in the carbonization reaction (MH@C-Ac). The carbonaceous shell not only protected the magnetic core from acidic erosion but also showed a high adsorption capacity toward Ni(2+) ion. The Ni(2+) ion complexed on MH@C and MH@C-Ac could specifically isolate 6×His tagged recombinant proteins from crude bacterial extracts via metal affinity interaction. The superparamagnetic property facilitates the easy retrieval of the carbonaceous material passivated MNPs from the viscous proteins solutions. Recombinant green fluorescence protein (GFP) and hyaluronic acid (HA) lyase of 9.4 mg and 2.3 mg could be isolated by 1 g of MH@C-Ac-Ni, respectively.     

Nanostructure characterization of polymer-stabilized gold nanoparticles and nanofilms derived from green synthesis

The fabrication and characterization of gold (Au) nanostructured materials draws significant attention because of their distinctive properties and their technological applications. The first objective of this study is to fabricate polymer-stabilized Au nanoparticles and nanofilms (PAN) through a cost effective and green synthetic methodology. In this study, the gold trication (Au³⁺) can be spontaneously converted into metallic gold atom using a non-toxic reductant (ascorbic acid). The ultrafine Au clusters were formed and stabilized through metallic bonds in the colloidal suspension, which was then deposited on a micro-glass or polymer-bead substrate to prepare thin films. It was found that ascorbic acid was the best reducing agent due to its rapid rate, spontaneity of reaction, and its non-toxic nature. In order to prevent aggregation of the nanoparticles, a dispersing agent (gum Arabic) was used. The second objective of this study was to analyze the PAN using a number of state-of-the-art instrumentation techniques and analytical approaches, such as X-ray powder diffraction (XRD), atomic force microscopy (AFM), scanning and transmission electron microscopy (SEM and TEM), ultraviolet–visible (UV–Vis) spectroscopy, and ZetaPALS. These techniques were applied to evaluate specific properties of the PAN, such as characterization of its crystalline phase, surface topology, characteristic plasmon, particle size distribution, and stability. From this study, it can be concluded that the ultrafine Au nanoparticles and uniform films were obtained using the green chemistry method. The ultrafine Au particles are highly stabilized and monodispersed as demonstrated by their high absolute value of zeta potential.     

Optically active poly(dimethylsiloxane) elastomer films through doping with gold nanoparticles

Poly(dimethylsiloxane) (PDMS) elastomer films synthesized through a cross-linking reaction between hydroxyl-terminated or vinyl-terminated PDMS have been homogeneously doped with silica-coated Au nanoparticles. The nanocomposite synthesis involves mixing a preformed colloid of surface-modified metal nanoparticles with the elastomer film precursors. The homogeneous distribution of nanoparticles is demonstrated through the presence of well defined plasmon absorbance bands in the visible, which clearly show that the composites retain the characteristic optical properties of single Au nanoparticles. The metal particle concentration could be easily tailored either through the amount or the concentration of the nanoparticle colloid added. Since the Au nanoparticles are not cross-linked to the polymer and the concentration of particles is relatively low, we postulate that the presence of the nanoparticles does not affect the mechanical properties of the films, though this remains to be confirmed.     

Preparation of SiO2/(PMMA/Fe3O4) nanoparticles using linolenic acid as crosslink agent for nucleic acid detection using chemiluminescent method

Usually, magnetic nanoparticles (MNPs) are prepared based on the famous St?ber process in which divinylbenzene (DVA) is often used as a crosslink agent to synthesize SiO2/(PMMA/Fe3O4) nanoparticles. Compared with DVA, linolenic acid (LNA) is innoxious and can polymerize more easily for it has three unsaturated double bonds. In this paper, LNA was used as a new crosslink agent instead of DVA to synthesize the SiO2/(PMMA/Fe3O4) nanoparticles. The results showed that the core-shell structure could be observed obviously. The sizes of nanoparticles with core-shell structure range from 200 to 500 nm. The DNA probes which was immobilized on the surface of MNPs were used to capture the biotin modified complementary sequence of the probe, and the formed complexes were bonded with streptavidin-modified alkaline phosphatase (SA-AP). Finally the chemiluminescent signals were detected by adding 3-(2'-spiroadamantane)-4-methoxy-4-(3"-phosphoryloxy) phenyl-1, 2-dioxetane (AMPPD) which was the substrate reagent of AP. The specificity and sensitivity of this approach were investigated in this paper.     

脉冲激光液相烧蚀贵金属Au/Ag产物的表征及反应机理研究

采用多波长(1064nm、532nm、248nm)脉冲激光在去离子水中对责金属Au、Ag片表面进行激光烧蚀(PLA).利用TEM、AFM、SEM对烧蚀金属片表层及产物(微/纳米尺度的金属颗粒)进行观察分析,认为在液相水环境中,整个烧蚀过程主要可分为激光诱导相沸腾爆炸和等离子体羽辉混合体膨胀2个过程.在这2个过程中分别产生得到具有微米尺度的球状金属颗粒和纳米尺度的金属颗粒.同时,具有纳米尺度金属Au/Ag颗粒经过强激光光子"二次"修饰改性过程,形成具有形状统一、分散性和稳定性较好的金属纳米胶体体系,这些胶体中金属纳米颗粒作为探针,在表面增强拉曼散射(SERS)光谱学方面有很好的应用价值.