Synthesis of ordered mesoporous metal oxides by solvent evaporation-induced cooperative assembly.

Abstract

Ordered mesoporous metal oxides (OMMOs) with periodically interconnected mesopores and crystalline framework have attracted ever-growing attention due to their high specific surface area, well-defined mesoscopic structures and adjustable pore-wall chemical microenvironment. It has been difficult to rationally design OMMO syntheses because the hydrolysis of metal salts is difficult to control; it is also difficult to find precursors that have a strong enough interaction with the structure-directing agents and oxides to overcome the formation of disordered metal oxide crystals rather than frameworks at the temperatures required for calcination. Here we describe an evaporation-induced cooperative assembly (EICA) approach for the controllable synthesis of high-quality OMMOs (for example, WO₃). The EICA approach endows precise control over the intermolecular interactions between metal oxide precursors and amphiphilic block copolymers such as poly(ethylene oxide)-block-polystyrene through ligand-assisted or cluster-involved assembly strategies and optimizes the thermal treatment process through carbon-supported crystallization. Based on this Protocol, a library of OMMOs with different framework compositions and desired pore sizes (10-35 nm, by changing the polystyrene length of poly(ethylene oxide)-block-polystyrene template) can be readily tuned, which can be further precisely modified by pore-wall engineering (for example, element doping, noble metal decoration and heterojunction construction). We describe the detailed experimental design and synthesis procedures to ensure the reproducibility of the experiments. Chemiresistive gas sensing and electrocatalytic hydrogen evolution reaction are introduced as potential applications of OMMOs. Except for the time (~2.5 d) needed for the preparation of amphiphilic block copolymers, the EICA approach for synthesizing OMMOs requires ~3.5 d without requiring special expertise.