Use of epoxides in the sol-gel synthesis of porous iron(III) oxide monoliths from Fe(III) salts
Use of epoxides in the sol-gel synthesis of porous iron(III) oxide monoliths from Fe(III) salts
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DOI：
10.1021/cm0007611
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发表时间：
2001-03-01
影响因子：
8.6
通讯作者：
Simpson, RL
中科院分区：
文献类型：
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作者：
Gash, AE;Tillotson, TM;Simpson, RL
通过溶胶-凝胶法在各种溶剂中使用Fe（III）盐制备基于氧化铁的多孔固体。据观察，环氧丙烷的Fe（III）的解决方案，导致在形成透明的红棕色整体凝胶。通过大气干燥将所得凝胶转化为干凝胶，或通过用CO2超临界萃取将所得凝胶转化为气凝胶（1）。一些干燥的材料，其特征在于通过氮气吸附和脱附分析和透射电子显微镜（TEM）。这些分析的结果表明，该材料具有高的表面积（类似于300 - 400 m2/g），具有介孔尺寸（2 - 23 nm）的孔径，以及由5 - 10 nm直径的氧化铁（III）簇组成的微观结构。通过改变环氧化物/Fe（III）比率、Fe（III）前体盐、存在的水量（H2O/Fe（III））和所用溶剂来研究凝胶形成及其速率的依赖性。所有这些变量都被证明会影响凝胶形成的速率，并提供了一个方便的控制这个参数。最后，研究了Fe2O3凝胶的形成机理。pH值和核磁共振（NMR）的研究表明，添加的环氧化物作为一个不可逆的质子清除剂，诱导Fe（III）物种进行水解和缩合，形成无机氧化铁框架。该方法可推广到其它过渡族和主族金属氧化物材料的制备。
Iron oxide-based porous solids were prepared by a sol-gel process using Fe(III) salts in various solvents. It was observed that the addition of propylene oxide to Fe(III) solutions resulted in the formation of transparent red-brown monolithic gels. The resulting gels were converted to either xerogels by atmospheric drying or aerogels by supercritical extraction with CO2(1). Some of the dried materials were characterized by nitrogen adsorption and desorption analysis and transmission electron microscopy (TEM). The results of those analyses indicate that the materials have high surface areas (similar to 300-400 m(2)/g), pore sizes with mesoporic dimensions (2-23 nm), and a microstructure made up of 5-10 nm diameter clusters of iron(III) oxide. The dependence of both gel formation and its rate was studied by varying the epoxide/Fe(III) ratio, the Fe(III) precursor salt, amount of water (H2O/Fe(III)) present, and the solvent employed. All of these variables were shown to affect the rate of gel formation and provide a convenient control of this parameter. Finally, an investigation of the mechanism of Fe2O3 gel formation was performed. Both pH and nuclear magnetic resonance (NMR) studies suggest that the added epoxide acts as an irreversible proton scavenger that induces the Fe(III) species to undergo hydrolysis and condensation to form an inorganic iron oxide framework. This method can be extended to prepare other transition and main-group metal oxide materials.