Hydrothermal Synthesis of Layered Perovskite-Structured Metal Oxides and Cesium Tungstate Nanosheets

Abstract

The synthesis of layered metalates consisting of metalate layers with two types of metal ions and interlayer organic cations via an aqueous solution process was studied for the preparation of metalate nanosheets. First, layered perovskite Cs­[Sr2Nb3O10] was synthesized hydrothermally and featured Cs+ ions, but not organic cations, as interlayer cations; the formation of a strontium niobate layer required a high hydrothermal temperature (≥150 °C). Next, bulky organic interlayer cations N­(CH3)4 + and C16H33N­(CH3)3 + were used. However, bulky cations inhibited the formation of layered compounds at high temperature due to their thermal vibration. Then, layered cesium tungstates were hydrothermally synthesized using alkylamines at a temperature ≥150 °C. Alkylamines NH2C n H2n+1 with a long alkyl chain n ≥ 10 provided a robust layered structure at ≥150 °C, yielding layered cesium tungstates with interlayer organic cations. Upon dispersing the product in acetone solvent, cesium tungstate nanosheets [Cs4W11O36]2– were formed by exfoliation. Overall, high temperature is required for the hydrothermal synthesis of metalate layers featuring two types of metal ions, and the interlayer organic cations are needed to contribute to the formation of layered structures at high temperature.

Recent Advances in Perovskite Catalysts for Efficient Overall Water Splitting

“…The co-precipitation method could also be used to synthesize well-defined perovskites such as Sr 2 MIrO 6 (M = Fe, Co), which is explored as an excellent OER catalyst in acidic media [72]. Hydrothermal synthesis acts as one of the most attractive techniques for fabricating perovskites with various morphologies such as nanosheets [79], rod-like perovskites [80], nanoflakes [81], cubic perovskites [82], and nanoparticles [83]. However, the formation of perovskite oxides from hydrothermal synthesis usually involves subsequent annealing treatment, which requires a relatively high temperature.…”

Perovskite Oxides for Energy Applications

“…The difference of this method compared to the previously listed methods is that crystalline powders can be obtained without the calcination step. Furthermore, the advantage of this method is the possibility to change particle size and shape by controlling reaction temperature, pH, time and concentration of the reactants [12,18].…”

“…Although the nanostructured perovskite oxides can be synthesised by previously mentioned sol-geland hydrothermal methods [17,18], they are often prepared by the molten salt method [19]. In this method, sources of metal ions (oxides) are mixed with salt (NaCl and KCl) and then sintered at a temperature above the melting point (950 °C) of the salt.…”

Perovskite Oxides Prepared by Hydrothermal and Solvothermal Synthesis: A Review of Crystallisation, Chemistry, and Compositions

“…[161] Other niobates whose hydrothermal synthesis has been studied include AgNbO3, whose photocatalytic properties have been studied, [162] and Pb(Mg1/3Nb2/3O3), which was formed at high KOH concentrations in preference to a pyrochlore phase. [163] The hexagonal niobate perovskite Ba5Nb4O15 [164] and the layered Dion-Jacobson-type perovskite CsSr2Nb3O10 [165] have also been prepared by direct hydrothermal routes.…”