A general electrochemical strategy for oriented porphyrin-based MOF films with enhanced charge-transport kinetics

The orientation is the key factor to determine the physicochemical properties of the metal-organic framework (MOF) films. New strategies for oriented MOF films are of fundamental importance in the advancement of science and technology. Here we report a unified approach to the synthesis of a large variety of porphyrin-based MOF films with different directions, chemistries and properties. This strategy is based on a general electrochemical regulation of coordination process of different metal cation (M₁=Zn, Co, Ni, Ce) and tetra (4-carboxyphenyl) porphyrin (M₂TCPP, M₂=H, Cu, Pt, Pd) on various conductive substrates. The cathode strategy relies on the reduction of M₂TCPP ligands and follows the electrochemical reaction mechanism to achieve effective control over crystallizing M₁-M₂TCPP MOF films oriented in the (110) direction. The highly oriented M₁-M₂TCPP MOF films are endowed with excellent crystalline, spatial network structure and hierarchical three-dimensional pore structure, which is conducive to charge transfer and material transmission and suitable for use as an electrochemical catalyst. The Zn-TCPP MOF films on conductive substrate could be used directly as an electrochemical sensor for electrocatalytic oxidation of NaNO₂, and showed wide linear range, low limit of detection (0.24 μM), high sensitivity (285.8 mA·mM^-1·cm^-2) and good anti-interference performance. We believe our methodology provides a simple and convenient route to a variety of oriented porphyrin-based MOF films for nanodevices with novel structure and function in nanotechnology.