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首页> 外文期刊>Journal of Sol-Gel Science and Technology >Sol-gel derived silica-based organic-inorganic hybrid materials as 'composite precursors' for the synthesis of highly homogeneous nanostructured mixed oxides: an overview
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Sol-gel derived silica-based organic-inorganic hybrid materials as 'composite precursors' for the synthesis of highly homogeneous nanostructured mixed oxides: an overview

机译：溶胶-凝胶衍生的基于二氧化硅的有机-无机杂化材料，作为“复合前体”，用于合成高度均一的纳米结构混合氧化物：概述

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摘要

The present contribution reports on our results concerning the synthesis of different binary and ternary oxide systems by using hybrid materials as "composite" precursors. In the last years, we have developed and explored a valuable strategy to yield a very homogeneous dispersion of nanopar-ticles of early metal transition oxide, MO2 (M = Zr, Hf) inside a silica matrix. This route is based on the use of the sol-gel process to obtain organic-inorganic hybrid silica-based materials embedding the oxide precursors (Zr and/or Hf oxoclusters), which are then calcined at high (T > 500 °C) temperatures to give the desired oxides. The "precursor" hybrid materials are prepared by a modified sol-gel process, involving the copolymerisation of the organically modified oxozirconium or oxohafnium clusters (M4O2(OMc)_(12) (M = Zr, Hf and OMc = methacrylate) with (methacryloxymeth-yl)triethoxysilane (MAMTES) or (methacryloxypropyl)tri-methoxysilane (MAPTMS). Free radical copolymerisation of the 12 methacrylate groups of the oxoclusters with the methacrylate-functionalised siloxanes allows a stable anchoring of the oxoclusters to the silica network formed by the hydrolysis and condensation of the alkoxy groups. The sol-gel reactions of the two methacrylate-modified silanes methacryloxymethyltriethoxysilane and methacry-loxypropyltrimethoxysilane were followed by using two independent time-resolved spectroscopic methods, viz., IR ATR and NMR with the aim to optimise their pre-hydrolysis times and consequently their use as precursors for hybrid materials. As mentioned, thermal treatment at high temperature of the hybrid yields a very homogeneous dispersion of ZrO2 and/or HfO2 nanoparticles in the silica matrix, since the molecular homogeneity of the starting hybrid is retained in the final mixed oxide. This route was successfully applied both to the synthesis of bulk materials and thin films characterised by different compositions (in term of M/Si molar ratios and M nature), heating route (conventional or microwave-assisted) and final temperature of annealing (from RT to 1,100 °C). The first example of the ZrO2-HfO2-SiO2 ternary oxide system was also prepared by this approach. The prepared systems, both in the form of hybrid materials as well as in the final form of binary or ternary oxides, were thoroughly characterised by a wide variety of analytical tools from a compositional, structural, morphological point of view. Moreover, in the case of the binary ZrO2-SiO2 bulk materials, also the evolution under heating was followed by different methods. In particular, the composition of the hybrid as well as of the final oxidic materials was determined by X-Ray Photoelectron Spectroscopy and elemental analysis, whereas FT-IR and multinuclear solid-state NMR spectroscopies shed light on the changes occurring in the composition upon thermal heating and the degree of condensation of the silica network. The morphology and the microstructure of the hybrids and of the oxides were studied by nitrogen sorption and Scanning Electron Microscopy. X-Ray Diffraction, Transmission Electron Microscopy and X-ray Absorption Fine Structure Spectroscopy X-ray Absorption Fine Structure Spectroscopy were used to follow the conversion of the amorphous oxides to the final materials consisting of crystalline zirconia or hafnia dispersed in amorphous silica. On selected systems, functional properties (surface reactivity, dielectric properties) were furthermore investigated. The obtained binary oxides were also used as substrates for functionalisation experiments with (1) dial-kycarbamates and (2) long alkyl chains to produce functional materials for catalysis and HPLC applications, respectively.
机译：本贡献报告了我们关于通过使用杂化材料作为“复合”前体来合成不同的二元和三元氧化物体系的结果。在过去的几年中，我们已经开发并探索了一种有价值的策略，可在二氧化硅基质中产生非常均匀的纳米颗粒，使早期金属过渡氧化物MO2（M = Zr，Hf）均匀分散。此路线基于使用溶胶-凝胶工艺获得嵌入氧化物前体（Zr和/或Hf氧簇）的有机-无机杂化二氧化硅基材料，然后在高温（T> 500°C）下煅烧得到所需的氧化物。 “前体”杂化材料是通过改良的溶胶-凝胶工艺制备的，涉及有机改性的氧锆或氧oh簇（M4O2（OMc）_（12）（M = Zr，Hf和OMc =甲基丙烯酸酯）与（甲基丙烯酰氧基甲基-基）三乙氧基硅烷（MAMTES）或（甲基丙烯酰氧基丙基）三甲氧基硅烷（MAPTMS）。羟基团的12个甲基丙烯酸酯基团与甲基丙烯酸酯官能化的硅氧烷的自由基共聚作用使羟基团稳定地锚定在水解形成的二氧化硅网络上两种甲基丙烯酸酯改性的硅烷甲基丙烯酰氧基甲基三乙氧基硅烷和甲基丙烯酸-丙氧基丙基三甲氧基硅烷的溶胶-凝胶反应之后，采用两种独立的时间分辨光谱方法，即IR ATR和NMR，以优化它们的预水解时间，因此将其用作杂化材料的前体如前所述，杂化yi的高温热处理由于起始杂化物的分子均质性保留在最终的混合氧化物中，因此在二氧化硅基质中产生了ZrO2和/或HfO2纳米粒子非常均匀的分散体。该路线已成功应用于具有不同组成（就M / Si摩尔比和M性质而言），加热路线（常规或微波辅助）和最终退火温度（来自RT）的散装材料和薄膜的合成中至1,100°C）。 ZrO2-HfO2-SiO2三元氧化物体系的第一个实例也通过这种方法制备。从组成，结构，形态学的观点来看，各种混合分析工具对混合系统以及最终形式的二元或三元氧化物形式的制备系统进行了全面表征。此外，在二元ZrO2-SiO2块状材料的情况下，也可以通过不同的方法跟踪加热下的析出。特别是，通过X射线光电子能谱和元素分析确定了杂化物以及最终氧化材料的组成，而FT-IR和多核固态NMR光谱则揭示了热后组成发生的变化加热和二氧化硅网络的缩合度。通过氮吸附和扫描电子显微镜研究了杂化物和氧化物的形态和微观结构。 X射线衍射，透射电子显微镜和X射线吸收精细结构光谱法X射线吸收精细结构光谱法用于追踪无定形氧化物向由分散在无定形二氧化硅中的结晶氧化锆或氧化f组成的最终材料的转化。在选定的系统上，还研究了功能特性（表面反应性，介电特性）。所获得的二元氧化物还可用作底物，用于与（1）二烷基氨基甲酸酯和（2）长烷基链进行功能化实验，以分别生产用于催化和HPLC应用的功能材料。

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