溶胶-凝胶法是常见的制备金属氧化物的方法之一。在溶胶-凝胶法中，各种反应物能达到分子级的均匀混合，因此能制备成份复杂的氧化物材料。目前，溶胶-凝胶法也应用于设计与制备金属纳米材料，特别是合金纳米颗粒。例如，溶胶-凝胶法能应用于制备CoPt、FePt等磁性纳米合金材料以及CoCrCuNiAl高熵合金纳米材料，以及物相结构为有序相的Cu3Pt合金纳米材料。本文综述溶胶-凝胶法设计制备金属纳米材料的研究进展，包括溶胶-凝胶法实施的基本步骤、该方法在制备金属纳米材料方面的具体应用，并着重论述采用热力学计算设计金属及化合物的基本原理。该基本原理包括计算金属氧化物与还原性气体如氢气的还原反应的吉布斯自由能的变化量、金属氧化物的标准电极电位(不同于金属离子的标准电极电位)。最后探讨溶胶-凝胶法设计制备金属纳米材料存在的问题以及后续可能的发展方向。
The sol-gel method, developed for over 150 years, is a conventional route for designing and preparing various kinds of metal oxide materials. In the sol-gel method, different chemical agents are homogenously mixed together in aqueous or organic solutions. During the evaporation of the solvents, the solution transforms to sol and gel through polycondensation or polyesterification reaction, and the dried gel is obtained after the complete evaporation of the solvent. Then, the dried precursor is often heat-treated in air at high temperature to induce the formation of oxide materials, especially the multi-component oxide materials that are difficult to prepare using other methods. Recently, new developments have been achieved in the sol-gel method. The application of the sol-gel method has been extended to the preparation of metallic nanomaterials, especially the alloy nanocrystals. For instance, the sol-gel method can be used to prepare CoPt and FePt hard magnetic alloy nanocrystals; CoCrCuNiAl high-entropy alloy nanocrystals; Ni3Fe and Cu3Pt alloy nanocrystals with equilibrium-ordered crystalline phases; and Ni, Cu, Bi, Sb, Te, Ag, Pt, and Pd monometallic nanocrystals. This article reviews the recent progresses in the sol-gel method for designing and preparing metallic and alloy nanocrystals, as well as the detailed experimental procedures and the different metallic nanocrystals that can be obtained by the sol-gel method. The crystalline phase formed in the final calcined products can be determined from the thermodynamic calculations of the sol-gel method. The thermodynamic model involves the calculation of the Gibbs free energy change of the reaction between the metallic oxide and reducing gases, such as hydrogen. A negative change and a positive change in the Gibbs free energy of the reaction correspond to the formation of metallic and alloy crystalline phases, or oxide crystalline phase, respectively. Based on the thermodynamic calculations and the relationship between the Gibbs free energy and standard electrodynamic potential of the chemical reaction, a new parameter, metal oxide standard electrode potential, was proposed. This electrode potential is different from the conventional