Transformation of CuO from Cu‐MOF Templates and Their Enhanced Sensing Performance for HCHO

Abstract

In this study, porous CuO samples were prepared from Cu-Metal-organic frameworks (MOF) templates through thermal decomposition. Four types of porous CuO samples were prepared through different decomposition treatments at temperatures ranging from 400 to 800 C. The prepared CuO samples were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray powder diffraction. The CuO prepared at a calcination temperature of 500 C (CuO-500), showed outstanding sensing performance in terms of response and response/recovery speed. The micropores in the material provided numerous active sites whereas the mesopores functioned as passages for the HCHO gas molecules. Furthermore, CuO-500 shows an excellent selectivity to HCHO gas.Keywords: CuO, Gas sensor, HCHO, Metal-organic frameworks Gas sensors based on metal oxides have been widely investigated for their suitability in the detection of toxic gases and organic vapors. The chemisorbed oxygen species on the surface of these sensing materials interact with the gas molecules. This results in changes in the electric resistance of these semiconductor gas sensors.1-3 In order to improve sensing properties such as response, response/recovery speed and sensitivity, substantial efforts have been devoted to syntheses of particular structures (such as hollow, urchin and porous structure) that can increase the surface area of the metal oxides. [4][5][6][7][8][9] Among these structures, the porous structure in the sensing material provides considerable advantages in terms of gas diffusion. This occurs because the gas molecules can pass between grains through pores, leading to considerable resistance variation in the sensing material. [10][11][12] In this regard, the Knudsen diffusion is suggested through various investigations as the most persuasive model. It is proven that mesopores are ideal sites for gas diffusion. 13 However, the development of simpler and easier methods for the preparation of mesoporous structures of metal oxides still remains a challenge.Metal-organic frameworks (MOFs) are a burgeoning class of porous materials consisting of metal clusters and organic linkers with large specific surface areas, high porosity, and chemical tunability.14-18 Because of these advantages, they have been investigated extensively for various applications in gas storage, sensors, catalysis, and drug delivery. [19][20][21][22] Recently, MOFs have been used as sacrificial templates during the thermal decomposition of organic linkers and the formation of metal oxides for the preparation of new porous materials. This approach turns out to be a facile method for the synthesis of porous metal oxides, using only thermal decomposition. [23][24][25][26][27][28][29] Decomposition conditions, such as temperature, speed, and atmospheric environment, play key roles in control of structure, porosity, surface area, and grain size of the transformed porous metal oxide. During the thermal decomposition, the organic linkers are changed to carbonaceous materials, resulting in th...

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