A simple and general route to prepare functional mesoporous double-metal oxy(hydroxide)

Abstract

The design and synthesis of functional mesoporous metal oxide materials while retaining their original morphology has still remained challenging over the past few decades. Herein, a simple and general route without using any surfactant has been developed to fabricate one-, two- and three-dimensional (1D, 2D and 3D) mesoporous double-metal oxy(hydroxides) from their corresponding metal hydroxides through the topotactic transformation and selective etching strategy. Taking ZnSn(OH)₆ 3D nanocubes as an example, after solvothermal treatment, ZnSn(OH)₆ was successfully converted into worm-like mesoporous Zn_0.7SnO_2.4(OH)_0.6 3D nanocubes with a large specific surface area of 369 m² g⁻¹ and pore size of 3.41 nm, and the shape of the nanocubes was maintained. This topotactic transformation is achieved by one-step solvothermal treatment in ethanol through solvothermal partial dehydration of a metal hydroxide precursor. Besides, ethanol serves as a weak reducing agent, and abundant oxygen vacancies are generated for mesoporous Zn_0.7SnO_2.4(OH)_0.6, which is responsible for the enhancement of catalytic performance. The as-prepared mesoporous nanocatalysts show excellent activity and stability towards highly selective visible-light photocatalytic aerobic oxidation of amines to imines with a conversion of over 90% and selectivity over 94%. Notably, this method is also successfully applied to other double-metal hydroxides such as CuSn(OH)₆ 1D nanorods and CoAl-layered double hydroxide (LDH) 2D nanosheets, and mesoporous CuSn_0.5O_1.7(OH)_0.48 and Co₂Al_0.5O_2.5(OH)_0.48 materials with large surface areas are obtained, while retaining their original morphology. Therefore, this promising strategy reported here is believed to be a universal approach to fabricate various other mesoporous metal oxy(hydroxides) with a large specific surface area and abundant oxygen vacancies, which could find a wide range of potential applications in photocatalysis, electrocatalysis, energy conversion and storage and so on.