Room-Temperature Laser Synthesis in Liquid of Oxide,Metal-Oxide Core-Shells,and Doped Oxide Nanoparticles

Although oxide nanoparticles are ubiquitous in science and technology, a multitude of compositions, phases, structures, and doping levels exist, each one requiring a variety of conditions for their synthesis and modification. Besides, experimental procedures are frequently dominated by high temperatures or pressures and by chemical contaminants or waste. In recent years, laser synthesis of colloids emerged as a versatile approach to access a library of clean oxide nanoparticles relying on only four main strategies running at room temperature and ambient pressure: laser ablation in liquid, laser fragmentation in liquid, laser melting in liquid and laser defect-engineering in liquid. Here, established laser-based methodologies are reviewed through the presentation of a panorama of oxide nanoparticles which include pure oxidic phases, as well as unconventional structures like defective or doped oxides, non-equilibrium compounds, metal-oxide core–shells and other anisotropic morphologies. So far, these materials showed several useful properties that are discussed with special emphasis on catalytic, biomedical and optical application. Yet, given the endless number of mixed compounds accessible by the laser-assisted methodologies, there is still a lot of room to expand the library of nano-crystals and to refine the control over products as well as to improve the understanding of the whole process of nanoparticle formation. To that end, this review aims to identify the perspectives and unique opportunities of laser-based synthesis and processing of colloids for future studies of oxide nanomaterial-oriented sciences.     

Application of Pulsed Traveling Hydrogen Arcs for Metal Oxide Reduction

A plasma reactor that has a transient traveling arc has been used to study hydrogen in relation to in-flight reduction of metal oxide particles. Experiments were done to determine the nature of the arc and its interaction with the reactor gas. The lifetime of the excited atomic hydrogen was measured and it was found to be more than 4 ms after the arc had ceased. Powders and tablets of oxides were exposed to the pulsed-arc treated hydrogen and found to react much more rapidly and intensely than when exposed to hot molecular hydrogen. The results suggest that atomic hydrogen will exist throughout the volume of such a reactor for a period that is sufficient to reduce particles of FeO, Cr₂O₃, and TiO₂.     

Thermally Induced Growth of ZnO Nanocrystals on Mixed Metal Oxide Surfaces

An in situ method for the growth of ZnO nanocrystals on Zn/Al mixed metal oxide (MMO) surfaces is presented. The key to this method is the thermal treatment of Zn/Al layered double hydroxides (Zn/Al LDHs) in the presence of nitrate anions, which results in partial demixing of the LDH/MMO structure and the subsequent crystallization of ZnO crystals on the surface of the forming MMO layers. In a first experimental series, thermal treatment of Zn/Al LDHs with different fractions of nitrate and carbonate in the interlayer space was examined by thermogravimetry coupled with mass spectrometry (TG‐MS) and in situ XRD. In a second experimental series, Zn/Al LDHs with only carbonate in the interlayer space were thermally treated in the presence of different amounts of an external nitrate source (NH₄NO₃). All obtained Zn/Al MMO samples were analysed by electron microscopy, nitrogen physisorption and powder X‐ray diffraction. The gas phase formed during nitrate decomposition turned out to be responsible for the formation of crystalline ZnO nanoparticles. Accordingly, both interlayer nitrate and the presence of ammonium nitrate led to the formation of supported ZnO nanocrystals with mean diameters between 100 and 400 nm, and both methods offer the possibility to tailor the amount and size of the ZnO crystals by means of the amount of nitrate.     

过渡金属氧化物对阻燃剂聚磷酸铵热分解的影响机制

过渡金属氧化物(MO)可以显著影响聚磷酸铵(APP)的热分解过程, 进而改善APP复配膨胀阻燃聚合物材料的阻燃效率。将ZnO、Fe₂O₃、TiO₂掺入到APP中, 采用热失重分析(TGA)、X射线光电子能谱(XPS)和X射线衍射分析(XRD), 考察了3种MO对APP热分解行为的影响, 分析了相互作用过程中金属原子和磷原子化学结合状态的变化以及高温热分解产物的物相结构。TGA和XPS图谱分析结果表明, MO可降低APP的起始热分解温度, 并催化APP释放NH₃和H₂O, 而在热分解后期由于金属磷酸盐的形成可显著增加APP的高温残留量。3种MO催化APP热分解脱NH₃和H₂O的活性由大到小的顺序是:ZnO>Fe₂O₃>TiO₂, 而对APP凝聚相热分解P-O产物的交联能力从大到小的顺序为:Fe₂O₃>ZnO>TiO₂。XRD结果显示, ZnO在高温下与APP反应生成了Zn(PO₃)₂晶体, 而Fe₂O₃和TiO₂与APP反应分别生成了Fe₄(P₂O₇)₃和TiP₂O₇晶体。     

过渡金属氧化物对阻燃剂聚磷酸铵热分解的影响机制

过渡金属氧化物(MO)可以显著影响聚磷酸铵(APP)的热分解过程,进而改善APP复配膨胀阻燃聚合物材料的阻燃效率。将ZnO、Fe2O3、TiO2掺入到APP中,采用热失重分析(TGA)、X射线光电子能谱(XPS)和X射线衍射分析(XRD),考察了3种MO对APP热分解行为的影响,分析了相互作用过程中金属原子和磷原子化学结合状态的变化以及高温热分解产物的物相结构。TGA和XPS图谱分析结果表明,MO可降低APP的起始热分解温度,并催化APP释放NH3和H2O,而在热分解后期由于金属磷酸盐的形成可显著增加APP的高温残留量。3种MO催化APP热分解脱NH3和H2O的活性由大到小的顺序是:ZnO>Fe2O3>TiO2,而对APP凝聚相热分解P-O产物的交联能力从大到小的顺序为:Fe2O3>ZnO>TiO2。XRD结果显示,ZnO在高温下与APP反应生成了Zn(PO3)2晶体,而Fe2O3和TiO2与APP反应分别生成了Fe4(P2O7)3和TiP2O7晶体。     

Synthesis of Iron Oxides by Co2 Laser vs. Thermally Induced Decomposition of Inorganic Salts

This paper reports on the synthesis of various iron oxides by the IR laser processing of different iron salts. X-ray diffraction techniques were used to characterize the reaction products. Some differences in terms of crystallite size and isotropy between these oxides and those obtained from the same salt by thermal means are described and explained. This revised version was published online in July 2006 with corrections to the Cover Date.     

脉冲激光法连续制备高蓝光荧光性的修饰纳米ZnO乙醇溶胶

采用聚焦脉冲激光束轰击浸于含有水杨酸的无水乙醇流动相中的ZnO固体靶, 连续制备得到了强度高达1.12×105的蓝色荧光(440 nm)的水杨酸修饰纳米ZnO乙醇溶胶. 考察了修饰剂的种类、浓度、添加顺序和流动相流速对其荧光性能的影响. 透射电镜结果表明, 所制备的纳米ZnO粒径分布在15—30 nm.     

过渡金属基MOF材料在选择性催化还原氮氧化物中的应用

选择性催化还原(SCR)技术是目前应用最广泛的工业脱硝技术,研发具有优良活性和抗毒化性能的催化剂体系是研究学者关注的重点。过渡金属氧化物和金属有机骨架(MOF)材料因其优良的氧化还原性能在脱硝领域受到了广泛关注和研究,且研究学者发现将过渡金属氧化物与MOF材料结合能够进一步提高催化剂的脱硝活性。本文综述了近年来主要应用于NH₃-SCR反应的系列单过渡金属基MOF脱硝催化剂和复合过渡金属基MOF脱硝催化剂的研究进展,阐述了过渡金属基MOF脱硝催化剂抗水抗硫中毒性能和热稳定性的强化方法,并展望了未来过渡金属基MOF脱硝催化剂的主要研究方向：综合利用不同过渡金属氧化物的特点并结合金属氧化物间的强相互作用,制备得到具有优良脱硝活性、抗水抗硫性能和热稳定性的新型过渡金属基MOF脱硝催化剂,进一步通过实验和仿真模拟相结合制备高效过渡金属基MOF脱硝催化剂以满足工业化需求。     

Kinetically Stable Nonequilibrium Gold-Cobalt Alloy Nanoparticles with Magnetic and Plasmonic Properties Obtained by Laser Ablation in Liquid

Nonequilibrium nanoalloys are metastable solids obtained at the nanoscale under nonequilibrium conditions that allow the study of kinetically frozen atoms and the discovery of new physical and chemical properties. However, the stabilization of metastable phases in the nanometric size regime is challenging and the synthetic route should be easy and sustainable, for the nonequilibrium nanoalloys to be practically available. Here we report on the one-step laser ablation synthesis in solution (LASiS) of nonequilibrium Au−Co alloy nanoparticles (NPs) and their characterization on ensembles and at the single nanoparticle level. The NPs are obtained as a polycrystalline solid solution stable in air and water, although surface cobalt atoms undergo oxidation to Co(II). Since gold is a renowned plasmonic material and metallic cobalt is ferromagnetic at room temperature, these properties are both found in the NPs. Besides, surface conjugation with thiolated molecules is possible and it was exploited to obtain colloidally stable solutions in water. Taking advantage of these features, an array of magnetic-plasmonic dots was obtained and used for surface-enhanced Raman scattering experiments. Overall, this study confirms that LASiS is an effective method for the formation of kinetically stable nonequilibrium nanoalloys and shows that Au−Co alloy NPs are appealing magnetically responsive plasmonic building blocks for several nanotechnological applications.     

Influence of Encapsulation on The Mechanism of Thermal Destruction of Cyanide Transition Metal Complexes

The results of investigation of the influence of encapsulation on the mechanism of thermal decomposition of cyanide transition metal complexes, based on data obtained by methods of differential thermal analysis (inert atmosphere) and thermodesorption (mass-spectral monitoring of gaseous products) are represented. It was established, that encapsulation of cyanide iron(II) and cobalt(III) complexes in faujasite type zeolite results in the hydrolytic mechanism of thermal destruction of complexes, unlike to bulk analogues, which is determined by essential decreasing of the temperature of complex anions encapsulated destruction beginning, up to temperatures while zeolite water molecules are saved; the gaseous products of thermal destruction composition is determined by the peculiarities of localization of cations of different nature in inclusion compounds. This revised version was published online in August 2006 with corrections to the Cover Date.     

二硫代钨酸铵晶体的合成、表征与热分解机理的研究

本工作用偏钨酸铵和硫化铵为原料，在水溶液中合成二硫代钨酸铵晶体[(NH₄)₂WO₂S₂]。用紫外-可见光谱(UV-Vis)的方法研究了二硫代钨酸铵晶体的形成机理。采用元素分析、X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、激光拉曼光谱(LRS)等对化合物进行了表征。结果表明采用该方法制备出的二硫代钨酸铵晶体，晶型良好。热重-差热分析(TG-DTA)、原位X射线衍射(in situ XRD)和FTIR等结果表明二硫代钨酸铵晶体在氢气气氛下的热分解主要发生在160～450 ℃之间，分两步进行，首先分解为{WOS₂}，随后转化为二硫化钨。     

Thermochemical Transition in Low Molecular Weight Substances: The Example of the Silybin Flavonoid

Silybin is a complex organic molecule with high bioactivity, extracted from the plant Silybum. As a pharmaceutical substance, silybin’s bioactivity has drawn considerable attention, while its other properties, e.g., thermodynamic properties and thermal stability, have been less studied. Silybin has been reported to exhibit a melting point, and values for its heat of fusion have been provided. In this work, differential scanning calorimetry, thermogravimetry including derivative thermogravimetry, infrared spectroscopy, and microscopy were used to provide evidence that silybin exhibits a thermochemical transition, i.e., softening occurring simultaneously with decomposition. Data from the available literature in combination with critical discussion of the results in a general framework suggest that thermochemical transition is a broad effect exhibited by various forms of matter (small molecules, macromolecules, natural, synthetic, organic, inorganic). The increased formation of hydrogen bonding contributes to this behavior through a dual influence: (a) inhibition of melting and (b) facilitation of decomposition due to weakening of chemical bonds.     

Identification of Catalytic Sites for Oxygen Reduction in Metal/Nitrogen‐Doped Carbons with Encapsulated Metal Nanoparticles

The development of metal‐N‐C materials as efficient non‐precious metal (NPM) catalysts for catalysing the oxygen reduction reaction (ORR) as alternatives to platinum is important for the practical use of proton exchange membrane fuel cells (PEMFCs). However, metal‐N‐C materials have high structural heterogeneity. As a result of their high‐temperature synthesis they often consist of metal‐N_x sites and graphene‐encapsulated metal nanoparticles. Thus it is hard to identify the active structure of metal‐N‐C catalysts. Herein, we report a low‐temperature NH₄Cl‐treatment to etch out graphene‐encapsulated nanoparticles from metal‐N‐C catalysts without destruction of co‐existing atomically dispersed metal‐N_x sites. Catalytic activity is much enhanced by this selective removal of metallic nanoparticles. Accordingly, we can confirm the spectator role of graphene‐encapsulated nanoparticles and the pivotal role of metal‐N_x sites in the metal‐N‐C materials for ORR in the acidic medium.     

Stress‐Induced Melting of Crystals in Natural Rubber: a New Way to Tailor the Transition Temperature of Shape Memory Polymers

Lightly cross‐linked natural rubber (NR, cis‐1,4‐polyisoprene) was found to be an exceptional cold programmable shape memory polymer (SMP) with strain storage of up to 1000%. These networks are stabilized by strain‐induced crystals. Here, we explore the influence of mechanical stress applied perpendicular to the elongation direction of the network on the stability of these crystals. We found that the material recovers its original shape at a critical transverse stress. It could be shown that this is due to a disruption of the strain‐stabilizing crystals, which represents a completely new trigger for SMPs. The variation of transverse stress allows tuning of the trigger temperature T_trig(σ) in a range of 45 to 0 °C, which is the first example of manipulating the transition of a crystal‐stabilized SMP after programming.     

Thermochemical Reactivity of Transition Metal Acetates and of A Novel DMSO Solvate of Iron(II) Acetate in Molecular Hydrogen

The thermal decomposition of acetates of the transition metals Fe, Co, Ni, Mn and Cu in molecular hydrogen has been investigated by means of combined thermogravimetry/mass spectrometry, X-ray diffraction, and transmission as well as scanning electron microscopy. In the context of the reproducible preparation of the parent phases, i.e. the hydrated or anhydrous metal(II) acetates, single crystalline Fe₃(CH₃COO)₆(DMSO)₂, a novel DMSO solvate of iron(II) acetate, has been isolated and its crystal structure has been determined by means of X-ray diffraction. For the series of metal(II) acetates it has been found that the course of the thermal degradation in molecular hydrogen, in particular the formation of the gaseous products, strongly depends on the transition metal ion present in the parent compound. The detailed characterisation of the solid products revealed, that phases exhibiting different catalytic activities and selectivities are formed as micro- or nanocrystalline metals and/or metal oxides.This revised version was published online in November 2005 with corrections to the Cover Date.     

Impact of Chemical and Physical Properties of Organic Solvents on the Gas and Hydrogen Formation during Laser Synthesis of Gold Nanoparticles

Laser ablation in liquids has been established as a scalable preparation method of nanoparticles for various applications. Particularly for materials prone to oxidation, it is established to suppress oxidation by using organic solvents as a liquid medium. While this often functionalizes the nanoparticles with a carbon shell, the related chemical processes that result from laser-induced decomposition reactions of the organic solvents remain uncertain. Using a systematic series of C₆ solvents complemented by n-pentane and n-heptane during the nanosecond laser ablation of gold, the present study focuses on the solvent-dependent influence on gas formation rates, nanoparticle productivity, and gas composition. Both the permanent gas and hydrogen formation was found to be linearly correlated with ablation rate, ΔH_vap, and pyrolysis activation energy. Based on this, a decomposition pathway linked to pyrolysis is proposed allowing the deduction of first selection rules for solvents that influence the formation of carbon or permanent gases.     

The Role of Reduced Graphite Oxide in Transition Metal Oxide Nanocomposites Used as Li Anode Material: An Operando Study on CoFe2O4/rGO

A composite consisting of CoFe₂O₄ spinel nanoparticles and reduced graphite oxide (rGO) is studied as an anode material during Li uptake and release by applying synchrotron operando X‐ray diffraction (XRD) and operando X‐ray absorption spectroscopy (XAS), yielding a comprehensive picture of the reaction mechanisms. In the early stages of Li uptake, a monoxide is formed as an intermediate phase containing Fe²⁺ and Co²⁺ ions; this observation is in contrast to reaction pathways proposed in the literature. In the fully discharged state, metallic Co and Fe nanoparticles are embedded in an amorphous Li₂O matrix. During charge, metallic Co and Fe are oxidized simultaneously to Co²⁺ and Fe³⁺, respectively, thus enabling a high and stable capacity to be achieved. Here, evidence is presented that the rGO acts as a support for the nanoparticles and prevents the particles from contact loss. The operando investigations are complemented by TEM, Raman spectroscopy, galvanostatic cycling, and cyclic voltammetry.     

不同组分过渡金属氧化物催化剂对介质阻挡放电固氮的影响机制

为了促进介质阻挡放电(DBD)协同催化固氮效果, 制备了不同组分Mn/Co/W元素的单一型、 二元和三元复合型负载催化剂, 并将催化剂置入DBD气隙中进行等离子体协同催化固氮反应. 通过X射线衍射(XRD)、 扫描电子显微镜(SEM)和X射线能谱(EDS)表征了催化剂的性质, 并采用紫外分光光度法测定了液相中的总氮浓度. 结果表明, 填充催化剂实验组比未填充催化剂组的总氮浓度明显提升. 采用傅里叶变换红外光谱仪对有/无催化剂填充两种情况下DBD的气相产物进行了检测, 结果表明, 填充催化剂能促进空间内NO₂和N₂O₅的生成. 通过DBD气相链式反应和催化原理揭示了总氮浓度得以提升的原因, 是由于催化剂在等离子协同过程中提供了大量的氧空位, 使得NO _x 充分氧化. 多元复合型催化剂能在单一型的基础上, 通过金属元素价态的变换和能量的传递进一步促进固氮效果, 三元复合型催化剂Mn₃WCo/γ-Al₂O₃在电压为22 kV时的固氮最高总氮浓度为119.13 mg/L, 较未填充催化剂组的最大值提升了71.61%, 能耗降低了21.70%.     

Metal Oxide Catalysts for Selective Reduction of NOx by Hydrocarbons: Toward Molecular Basis for Catalyst Design

Metal oxides are stable and highly durable catalysts for the selective catalytic reduction (SCR) of NO by hydrocarbons and potential candidates for practical use. This review focuses on the development as well as the fundamental understanding of metal oxide based catalysts for selective reduction of NO by hydrocarbons. Our studies on the SCR-deNOx properties of Ga₂O₃/Al₂O₃, Cu-Al₂O₃, and Ag-Al₂O₃ catalysts are presented and it is attempted to demonstrate the advantages of this type of catalysts. On the basis of several spectroscopic characterizations, the effect of important factors, such as dispersion, coordination, and the electronic states of the metal cation, on the intrinsic catalytic activity are quite well clarified. From the in situ FTIR results, the reaction mechanism is understood in terms of formation and reaction of surface molecules. The structural and kinetic information obtained at the molecular level provides a useful strategy for designing better deNOx catalysts using metal oxides.     

Determination of Kinetic Parameters and Metal Ions in Urea-Urease System Based on the Biochemical Reaction Heat Induced Laser Beam Deflection

Reaction heat induced laser beam deflection is a new analytical method which came in tobeing in 1993', by probing the gradient of the refraction index which was induced byreaction heat with a laser probe beam, one can relate the laser beam deflection to theconcentration of the sample.In this paper, the method was used for the study of the kinetic process for ureaurease system. It is well known that urease catalyzes the hydrolysis of urea as follows fUreaseNHZCONHZ HZO~ CO2 2NH3 QThe pro…