Alignment controllable synthesis of MOF films: From Cu(OH)2 nanowire array to highly oriented Cu-MOF film

This work applies a quasi-epitaxial growth method to synthesize the highly oriented Cu-MOF film with the Cu(OH)2 nanowire arrays. The Cu(OH)2 nanowires with high aspect ratio were first synthesized via an optimization of the reactant concentration, then deposited and arrayed with the gravity assistance on an ITO substrate via a fluid-assisted technique. Based on the template with the Cu(OH)2 nanowire arrays, the Cu-MOF film was synthesized via the displacement reaction at room temperature. By optimizing the number of times and the flow velocity of the fluid-assisted technique, a Cu-MOF film with a thickness of above 0.9 ​μm and a roughness below 84.73 ​nm was obtained. The calculated crystallographic preferred orientation (CPO) index of the (00l) direction showed that the film had a strong c-axis orientation. Furthermore, the fluorescence spectra of the DMASP dyes aligned in the channels of this oriented Cu-MOF film exhibited a polarization ratio of about 2.83. Synthesis of the highly oriented Cu-MOF film with the Cu(OH)2 nanowire arrays via a quasi-epitaxial growth method. The Cu(OH)2 nanowires with high aspect ratio are prepared, and then deposited on an ITO substrate via a fluid-assisted technique, in which the Cu(OH)2 nanowire suspension flows downward along the tank slope and the nanowires are arrayed with the gravity assistance. The sample with Cu(OH)2 nanowire arrays is immersed in the saturated organic ligand solution. The Cu-MOF film is synthesized via the displacement reaction between the Cu(OH)2 nanowires and the organic ligand. [Display omitted] •The Cu(OH)2 nanowires with high aspect ratio are synthesized via an optimization of the reactant.•The nanowires are arrayed with the gravity assistance when they flowed over a slope.•The flow velocity of nanowires is regulated by adjusting the slope angle.•The oriented Cu-MOF film is synthesized based on the arrayed Cu(OH)2 nanowires.