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. • 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.