Fabrication of [Cu2(bdc)2(bpy)]n thin films using coordination modulation-assisted layer-by-layer growth

The processing of metal-organic frameworks as films is the first step toward localizing them for device fabrication. Herein, we investigated the fabrication of polycrystalline, phase pure and highly oriented [Cu-2(bdc)(2)(bpy)](n) thin films on bare and chemically modified mesoporous titania surfaces, using a modified layer-by-layer method. While a film consisting of randomly oriented crystals was formed on a bare TiO2 surface, we were able to show that [Cu-2(bdc)(2)(bpy)](n) nanoplates in the thin film could adopt perpendicular alignment upon the addition of acetic acid as a modulating agent. It was found that the addition of acetic acid promotes the growth of crystals mostly along [010] direction, provided that it is added to the metal solution. The effects of the modulator addition sequence and amount, reaction temperature, immersion time and reactant concentrations have been investigated. In addition, 3,4-dihydroxybenzoic acid and isonicotinic acid were also used to study the effect of surface functionality. Our primary results indicate that large, oriented crystalline domains could be formed on both surfaces independent of the functionality type. Benefiting from their large crystalline domains, films grown on modified surfaces exhibit higher thermal and water stability in comparison with the film grown on a bare surface.