An opportunity for utilizing earth-abundant metals through the mesostructural design of metal phosphate-based materials

Abstract

This review focused on the surfactant-assisted synthesis of metal phosphate-based materials and summarized their potential based on the design of a mesoporous structure as well as the composition and crystal structure of the inorganic frameworks. In the cases of Ti and Zr, metal phosphate frameworks are constructed through two synthetic pathways. One is a step-by-step process including phosphation of the as-synthesized metal oxides. The phosphation process is helpful for stabilizing the mesoporous structures constructed by thin inorganic frameworks. Direct synthesis is possible when the thickness of frameworks is enough for stabilizing mesoporous structures prepared using polymeric surfactants like EO_nPO_mEO_n type triblock copolymers. Other mesoporous metal (e.g., Nb, Ta, Cr, Ga, Sn) phosphates are directly obtained using C_nTMA type surfactants. In addition, unique mesostructural alterations are observed for some metal (e.g., Mn, Fe, Co, Ni, Ca as redox/ionic) phosphates. According to the nature of the metal oxide like units and surface properties of metal phosphate frameworks, the resultant mesoporous materials are broadly investigated as newly designed catalysts and/or catalyst supports for selective oxidation, acidity-dependent, photo-induced, and electrochemical reactions. For enrichment of electrochemical activities, crystallized frameworks with a suitable P/M ratio are required for fabricating electrodes for dye-sensitized solar cells, fuel cells and lithium-ion batteries. Consequently, the contents of this review provide an opportunity for designing mesostructures of a wide variety of metal phosphates containing earth-abundant metals.