Study of mechanochemical synthesis in the formation of the metal–organic framework Cu3(BTC)2 for hydrogen storage

A study was done to determine the effectiveness of mechanochemical synthesis for the preparation of a microporous metal–organic framework Cu3(BTC)2 from trimesic acid and various copper salts. The effect of parameters such as the nature of the starting materials, presence of solvent, and grinding conditions were carefully studied. It was found that using copper acetate as a starting material instead of copper nitrate resulted in a better yield of product. In addition, the presence of water of hydration in the reactants improved the crystallinity of the Cu3(BTC)2 that was produced. However, the addition of a small amount of solvent into the system prior to grinding was found to be even more effective in improving the crystallinity of Cu3(BTC)2, which leads to enhanced specific surface area and hydrogen storage capacity. Indications are that mechanochemical synthesis is a very fast method for the quantitative formation of Cu3(BTC)2 with complete synthesis achieved in as little as 10 min of grinding. A variety of thermal stability tests demonstrated that the as-synthesized Cu3(BTC)2 contains some residual reactants that could be removed in less than five hours by a heat treatment at 200 °C, which is less time than is typically required for samples synthesized by wet methods.

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► Water of hydration in the starting materials improves crystallinity of Cu3(BTC)2.
► Adding a small amount of solvent before grinding enhances surface area of Cu3(BTC)2.
► Mechanochemical synthesis is an efficient method for preparing Cu3(BTC)2.
► The rate of Cu3(BTC)2 formation is enhanced by water of hydration in the reactant.
► Reaction byproducts can be removed by heat treatment without prior washing.