Facile solid-state synthesis of oxidation-resistant metal nanoparticles at ambient conditions

A simple and scalable method for the synthesis of metal nanoparticles in the solid-state was developed, which can produce nanoparticles in the absence of solvents. Nanoparticles of coinage metals were synthesized by grinding solid hydrazine and the metal precursors in their acetates and oxides at 25 °C. The silver and gold acetates converted completely within 6 min into Ag and Au nanoparticles, respectively, while complete conversion of the copper acetate to the Cu sub-micrometer particles took about 2 h. Metal oxide precursors were also converted into metal nanoparticles by grinding alone. The resulting particles exhibit distinctive crystalline lattice fringes, indicating the formation of highly crystalline phases. The Cu sub-micrometer particles are better resistant to oxidation and exhibit higher conductivity compared to conventional Cu nanoparticles. This solid-state method was also applied for the synthesis of platinum group metals and intermetallic Cu₃Au, which can be further extended to synthesize other metal nanoparticles.     

Amphiphilic block copolymers directed synthesis of mesoporous nickel-based oxides with bimodal mesopores and nanocrystal-assembled walls

Mesoporous late-transition metal oxides have great potential in applications of energy,catalysis and chemical sensing due to their unique physical and chemical properties.However,their synthesis via the flexible and scalable soft-template method remain a great challenge,due to the weak organic-inorganic interaction between the frequently used surfactants(e.g.,Pluronic-type block copolymers) and metal oxide precursors,and the low crystallization temperature of metal oxides.In this study,ordered mesoporous NiO with dual mesopores,high surface area and well-interconnected crystalline porous frameworks have been successfully synthesized via the facile solvent evaporation-induced co-assembly(EICA) method,by using lab-made amphiphilic diblock copolymer polystyrene-b-poly(4-vinylpyridine)(PS-b-P4 VP) as both the structure-directing agent(the soft template) and macromolecular chelating agents for nickel species,THF as the solvent,and nickel acetylacetonate(Ni(acac)2) as inorganic precursor.Similarly,by using Ni(acac)2 and Fe(acac)3 as the binary precursors,ordered mesoporous Fedoped NiO materials can be obtained,which have bimodal mesopores of large mesopores(32.5 nm) and secondary mesopores(4.0-11.5 nm) in the nanocrystal-assembled walls,high specific surface areas(～74.8 m~2/g) and large pore value(～0.167 cm~3/g).The obtained mesoporous Fe-doped NiO based gas sensor showed superior ethanol sensing performances with good sensitivity,high selectivity and fast response-recovery dynamics.     

A secondary ion mass spectrometric study of thallium oxide thin films grown via metal organic chemical vapour deposition

Within a comprehensive programme including synthesis via metal organic chemical vapour deposition (MOCVD) and characterization of inorganic compounds and materials of possible interest in technologies based on thin films, results concerning the deposition of metal oxides by means of volatile organometal precursors are reported. In particular, thallium oxide films obtained by the MOCVD technique and commercial powders of Tl₂O₃ and Tl₂O adsorbed on several metal substrates (stainless steel, Si, Cu, Mo, Pt) were studied by secondary ion mass Spectrometry (SIMS) under ion beam bombardment at different ion energies. The positive- and negative-ion mass spectra exhibit typical isotopic patterns of several ionic species produced by interesting interfacial reactions, and the analysis of their relative abundances provides a measure of oxide reactivity towards different substrates. SIMS measurements of metal substrates were also performed. The ability and limits of SIMS in the reactivity study of thallium oxide powders and films and, in addition, in the identification of reaction products evidencing impurity species that, in turn, can be ascribed to the substrates or to the precursors used for the oxide synthesis is pointed out.     

Cross-Linked Polymers as Scaffolds for the Low-Temperature Preparation of Nanostructured Metal Oxides

The current state of the art of the use of cross-linked organic polymers, both insoluble (resins or gels) and soluble (micro- and nanogels), as aids for the low-temperature preparation of stable metal oxide nanoparticles or nanostructured metal oxides is reviewed herein. Synthetic strategies for inorganic oxide nanomaterials of this kind can greatly benefit from the use of cross-linked polymers, which may act as scaffolds/exotemplates during inorganic nanoparticle synthesis, or as stabilizers following post-synthetic modification of the nanoparticles. Furthermore, the peculiar properties of the organic cross-linked polymers add to those of the inorganic oxide nanoparticles, producing materials with combined properties. The potential applications of such highly promising composite nanomaterials will be also briefly sketched.     

Synthesis and characterization of ordered hexagonal and cubic mesoporous tin oxides via mixed-surfactant templates route

Ordered hexagonal and cubic mesoporous tin oxides were synthesized for the first time in the presence of mixed cationic and neutral surfactants (a mixture of cetyltrimethylammonium bromide cationic surfactant and dodecylamine neutral surfactant) with different alkali and simple inorganic precursors at room temperature. In the synthesis systems, the dodecylamine neutral surfactant may function as a polar organic cosolvent and cosurfactant. The formation of the tin oxide mesostructured material was proposed to be due to the presence of hydrogen-bonding interactions between the supramolecular template and inorganic precursors Sn4+ and OH-, which were assumed to self-assemble around the cationic surfactant molecules. The materials are characterized by X-ray powder diffraction, transmission electron microscopy, thermogravimetric analysis, and N2 adsorption/desorption isotherm. The surface areas of materials evaluated from the N2 sorption isotherms are about 248 m(2)/g for hexagonal mesoporous tin oxide (SnH) and 281 m(2)/g for cubic mesoporous tin oxide (Sn-C) for calcination at 350 degrees C.     

Metal Oxide‐Coated Three‐Dimensional Graphene Prepared by the Use of Metal–Organic Frameworks as Precursors

A simple method for the preparation of metal‐oxide‐coated three‐dimensional (3D) graphene composites was developed. The metal–organic frameworks (MOFs) that served as the precursors of the metal oxides were first synthesized on the 3D graphene networks (3DGNs). The desired metal oxide/3DGN composites were then obtained by a two‐step annealing process. As a proof‐of‐concept application, the obtained ZnO/3DGN and Fe₂O₃/3DGN materials were used in a photocatalytic reaction and a lithium‐ion battery, respectively. We believe this method could be extended to the synthesis of other metal oxide/3DGN composites with 3D structures simply through the appropriate choice of specific MOFs as precursors.     

Surfactant-free nonaqueous synthesis of metal oxide nanostructures

Surfactant-free nonaqueous (and/or nonhydrolytic) sol-gel routes constitute one of the most versatile and powerful synthesis methodologies for nanocrystalline metal oxides with high compositional homogeneity and purity. Although the synthesis protocols are particularly simple, involving only metal oxide precursors and common organic solvents, the obtained uniform nanocrystals exhibit an immense variety of sizes and shapes. The small number of reactants in these routes enables the study of the chemical mechanisms involved in metal oxide formation. Nonhydrolytic routes to inorganic nanomaterials that used surfactants as size- and shape-controlling agents have been discussed recently. This Minireview supplements this topic by discussing surfactant-free processes, which have become a valuable alternative to surfactant-assisted as well as to traditional aqueous sol-gel chemistry routes.     

Poly(styrene–b–ethylene/butylene–b–styrene)/cobalt ferrite magnetic nanocomposites

Magnetic nanoparticles were created in or around the sulfonated (s) polystyrene domains in a poly[styrene–b–(ethylene–co–butylene)–b–styrene)] block copolymer (BCP) using an in situ inorganic precipitation procedure. The sBCP was neutralized with a mixed iron/cobalt chloride electrolyte, and the doped samples were converted to their oxides by reaction with sodium hydroxide. Transmission electron microscopy indicated the presence of nanoparticles having diameters of 20–50 nm. Metal oxide particle structures were studied using wide angle X–ray diffraction, which revealed that they were inverse spinel cobalt iron oxide crystals. Thermogravimetric analysis provided the weight percent of the inorganic component and nanocomposite thermal decomposition profile. Modulated differential scanning calorimetry studies suggested that the inorganic inclusions were selectively grown in the polystyrene hard block phase. These nanocomposites were shown, using alternating gradient magnetometry, to be ferrimagnetic at room temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1475–1485, 2005     

聚合物/无机纳米粒子复合膜在气体分离中的研究进展

由于聚合物膜具有可高度设计、机械性能好、易于加工 等优点,是理想的气体分离材料。然而,聚合物膜在气体选择性和渗透性方面存在平衡限制,在聚合物中引入纳米粒子,是提高气体分离性能的一种有效手段。本文基于聚合物/无机纳米粒子复合膜在气体分离领域的研究现状,重点阐述了零维纳米粒子（二氧化硅、二氧化钛）、一维纳米粒子（碳纳米管）、二维纳米粒子（氧化石墨烯、二维过渡金属氧化物）、三维纳米粒子（金属有机框架、沸石）对气体分离性能的影响,并展望了聚合物复合分离膜的发展趋势,为未来高效分离膜的研发提供了参考。     

Solid-state synthesis of embedded single-crystal metal oxide and phosphate nanoparticles and in situ crystallization

A new solid state organometallic route to embedded nanoparticle-containing inorganic materials is shown, through pyrolysis of metal-containing derivatives of cyclotriphosphazenes. Pyrolysis in air and at 800 °C of new molecular precursors gives individual single-crystal nanoparticles of SiP(2)O(7), TiO(2), P(4)O(7,) WP(2)O(7) and SiO(2), depending on the precursor used. High resolution transmission electron microscopy investigations reveal, in most cases, perfect single crystals of metal oxides and the first nanostructures of negative thermal expansion metal phosphates with diameters in the range 2-6 nm for all products. While all nanoparticles are new by this method, WP(2)O(7) and SiP(2)O(7) nanoparticles are reported for the first time. In situ recrystallization formation of nanocrystals of SiP(2)O(7) was also observed due to electron beam induced reactions during measurements of the nanoparticulate pyrolytic products SiO(2) and P(4)O(7). The possible mechanism for the formation of the nanoparticles at much lower temperatures than their bulk counterparts in both cases is discussed. Degrees of stabilization from the formation of P(4)O(7) affects the nanocrystalline products: nanoparticles are observed for WP(2)O(7), with coalescing crystallization occurring for the amorphous host in which SiP(2)O(7) crystals form as a solid within a solid. The approach allows the simple formation of multimetallic, monometallic, metal-oxide and metal phosphate nanocrystals embedded in an amorphous dielectric. The method and can be extended to nearly any metal capable of successful coordination as an organometallic to allow embedded nanoparticle layers and features to be deposited or written on surfaces for application as high mobility pyrophosphate lithium-ion cathode materials, catalysis and nanocrystal embedded dielectric layers.     

Synthesis of classes of ternary metal oxide nanostructures

Nanoscale structures, such as nanoparticles, nanorods, nanowires, nanocubes, and nanotubes, have attracted extensive synthetic attention as a result of their novel size-dependent properties. Ideally, the net result of nanoscale synthesis is the production of structures that achieve monodispersity, stability, and crystallinity with a predictable morphology. Many of the synthetic methods used to attain these goals have been based on principles derived from semiconductor technology, solid state chemistry, and molecular inorganic cluster chemistry. We describe a number of advances that have been made in the reproducible synthesis of various ternary oxide nanomaterials, including alkaline earth metal titanates, alkali metal titanates, bismuth ferrites, ABO(4)-type oxides, as well as miscellaneous classes of ternary metal oxides.     

Decoration carbon nanotubes with Pd and Ru nanocrystals via an inorganic reaction route in supercritical carbon dioxide-methanol solution

This work describes a method to decorate carbon nanotubes (CNTs) with metallic Pd and Ru nanocrystals via inorganic reactions in supercritical (SC) CO2-methanol solutions. In this route, PdCl2 or RuCl3.3H2O dissolved in SC CO2-methanol solution acted as a metal precursor and CNTs functioned as a template to direct the deposition of produced nanoparticles. Methanol served as the reductant for the precursors as well as cosolvent to enhance the dissolution of precursors in SC CO2. Dry products were readily obtained through in situ extraction with SC CO2 after reactions. The products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. It was demonstrated that the loading content and particle size of the nanoparticles deposited on CNTs could be tuned by changing the weight ratio of the precursor to CNTs. This simple and efficient approach may also be utilized to synthesize other high-purity materials using inorganic salt precursors in SC CO2-based solution.     

钼催化剂结构对其催化气相丙烯环氧化反应选择性的影响

考察了Mo基催化剂上空气气相氧化丙烯反应。从无机的和有机金属Mo前驱体出发,采用浸渍法和物理气相沉积法(PVD)制备了不同类型的SiO2负载氧化钼和Mo-Bi复合氧化物催化剂。透射电镜结果证实,所制催化剂上环氧化反应活性与其纳米结构直接有关。催化剂中出现部分或完全结晶的氧化钼相,它们与载体SiO2的相互作用较弱,使得反应生成环氧丙烷的选择性低于10%,而锚合在SiO2上的非结晶的八配位Mo物种上的环氧丙烷选择性达55%以上,此时丙烯转化率约为11%。不同形貌氧化钼的电化学表征结果证实了结构缺陷的重要性。另外,还讨论了Bi对氧化钼催化环氧化活性的直接促进效应。     

Ti-Si mixed oxides prepared by polymer in situ sol-gel chemistry with the aid of CO2

A method to prepare titania-silica binary oxides is proposed in this work. In this route, inorganic precursors tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TIP) were simultaneously or sequentially impregnated into a polypropylene (PP) matrix using supercritical carbon dioxide as a swelling agent and carrier. Hydrolysis and condensation reaction of the precursors confined in a polymer network were induced by treating the composites in 1 mol.dm(-3) (1 M) HCl. Then the PP matrix was decomposed at higher temperature, and titania-silica binary oxides were obtained. The mixed oxides were characterized by X-ray diffraction and Raman, FTIR, and X-ray photoelectron spectroscopy. It was demonstrated that the structure of the oxides depended strongly on the procedure to impregnate the precursors. The simultaneous method, in which the TEOS and TIP were simultaneously impregnated into a PP matrix, resulted in mixed oxides with highly dispersed titanium oxide species in the SiO2 matrix, while the sequential method produced the mixed oxide with separate SiO2 and TiO2 phases which were connected by Ti-O-Si bands at the interface. The method described in this work provides a new route to control the texture of TiO2-SiO2 mixed oxide simply by the impregnation sequence.     

Transition-Metal Oxides/Carbides@Carbon Nanotube Composites as Multifunctional Electrocatalysts for Challenging Oxidations and Reductions

The rapid development of renewable-energy technologies such as water splitting, rechargeable metal–air batteries, and fuel cells requires highly efficient electrocatalysts capable of the oxygen-reduction reaction (ORR) and the oxygen-evolution reaction (OER). Herein, we report a facile sonication-driven synthesis to deposit the molecular manganese vanadium oxide precursor [Mn₄V₄O₁₇(OAc)₃]³⁻ on multiwalled carbon nanotubes (MWCNTs). Thermal conversion of this composite at 900 °C gives nanostructured manganese vanadium oxides/carbides, which are stably linked to the MWCNTs. The resulting composites show excellent electrochemical reactivity for ORR and OER, and significant reactivity enhancements compared with the precursors and a Pt/C reference are reported. Notably, even under harsh acidic conditions, long-term OER activity at low overpotential is reported. In addition, we report exceptional activity of the composites for the industrially important Cl₂ evolution from an aqueous HCl electrolyte. The new composite material shows how molecular deposition routes leading to highly active and stable multifunctional electrocatalysts can be developed. The facile design could in principle be extended to multiple catalyst classes by tuning of the molecular metal oxide precursor employed.     

Synthesis of hybrid polysiloxane-MO<Subscript>2</Subscript> (M = Si,Ti, Zr) nanoparticles through a sol–gel route

Polysiloxanes in combination with metal oxides show interesting properties as nanocomposites for optical or medical applications. The formation of covalent connections between the metal oxide and the polysiloxane is an important method to overcome phase separation between the two components, but it also can have an influence on the morphology of the final materials. In this contribution we report a method for the synthesis of hybrid materials based on polysiloxanes and various metal oxides in which both components are tightly connected to each other. Alkoxysilane modified polysiloxanes were obtained by hydrosilation reactions between vinyl triethoxysilane and poly(dimethylsiloxane-co-methylhydrosiloxane) (PDMS-co-PMHS). The thus functionalized polymers were used in a sol-gel process applying Stöber conditions and hybrid nanoparticles were obtained. Following the same pathway, different metal alkoxides (M(OR)₄; M = Ti, Zr; R = ethyl, isopropyl) were coordinated to allyl acetoacetate (AAA) and the resulting complexes were applied in a hydrosilation reaction with PDMS-co-PMHS. Metal oxide hybrid nanoparticles were obtained through a sol–gel process.     

Recent advances in the preparation of hybrid nanoparticles in miniemulsions

In this review, we summarize recent advances in the synthesis of hybrid nanoparticles in miniemulsions since 2009. These hybrid nanoparticles include organic–inorganic, polymeric, and natural macromolecule/synthetic polymer hybrid nanoparticles. They may be prepared through encapsulation of inorganic components or natural macromolecules by miniemulsion (co)polymerization, simultaneous polymerization of vinyl monomers and vinyl-containing inorganic precursors, precipitation of preformed polymers in the presence of inorganic constituents through solvent displacement techniques, and grafting polymerization onto, from or through natural macromolecules. Characterization, properties, and applications of hybrid nanoparticles are also discussed.     

Nonaqueous synthesis of metal oxide nanoparticles:Review and indium oxide as case study for the dependence of particle morphology on precursors and solvents

Nonaqueous solution routes to metal oxide nanoparticles are a valuable alternative to the well-known aqueous sol-gel processes, offering advantages such as high crystallinity at low temperatures, robust synthesis parameters and ability to control the crystal growth without the use of surfactants. In the first part of the review, we give an overview of the various nonaqueous routes to metal oxides, their surface functionalization and their assembly into well-defined nanostructures. However, we will strongly focus on surfactant-free processes developed in our group. Within the various reaction systems such as metal halides—benzyl alcohol, metal alkoxides—benzyl alcohol, metal alkoxides—ketones, metal acetylacetonates—benzyl alcohol and metal acetylacetonates—benzylamine we will discuss representative examples in order to show the versatility of this approach. The careful characterization of the organic species in the final reaction mixtures provides information about possible condensation mechanisms. Depending on the system several reaction pathways have been postulated: (i) elimination of organic ethers as result of condensation between two metal alkoxide precursors; (ii) C–C bond formation between the alkoxy ligand of the metal alkoxide precursor and the solvent benzyl alcohol under formation of a metal hydroxyl species, which can undergo further condensation; (iii) ketimine and aldol-like condensation steps, which in the metal acetylacetonate systems are preceded by a solvolysis of the precursor, involving C–C bond cleavage. In the second part of the paper we will focus on the synthesis of indium oxide nanoparticles using different precursors and solvents. Indium oxide represents an instructive example how the oxide precursors and the solvents influence the particle morphology. These findings make it possible to tailor particle size and shape of a particular metal oxide by the appropriate choice of the reaction system.     

程序升温反应法由纳米氧化铁制备纳米氮化铁

先以廉价的无机铁盐为主要原料,采用沉淀法和溶胶凝胶法制备纳米氧化铁粒子,由此得到粒径大小在10～20nm,20～40nm和40～60nm的氧化铁,在此基础上,以纳米氧化铁为前体,在氨气气氛下由程序升温反应法制备纳米氮化铁.研究发现,纳米氧化铁经程序升温反应氮化后,可以制备出纳米尺度的氮化铁.不同大小的氧化铁纳米粒子氮化后尺寸存在明显的差异,在一定范围内,小粒径的纳米氧化铁氮化后更容易长大;对于大小相近的γ相与α相纳米氧化铁粒子,γ氧化铁纳米粒子氮化后尺寸增大更为显著.制得的氮化铁的形貌与其氧化铁前体保持一致.