Fast photo- and Moisture-Driven bidirectional actuation of a Shape-Programmable MOFLoading composite

Metal-organic frameworks (MOFs) emerge as promising candidates for developing stimuli-responsive actuators. However, currently reported MOF-loading actuators rely on the reversible volume change of MOF crystal lattice upon stimulation, which requires a much longer time than other types of hygroscopic fillers to accomplish the actuating process. In this work, we report the use of Zr-Fc to develop NIR light and moisture responsive actuators. Zr-Fc possesses a rigid structure and is prepared by a conventional solvent-thermal approach using ZrCl₄ and Fc(COOH)₂ as raw materials, and the composite is developed by introducing Zr-Fc into polyvinyl alcohol with a gradient distribution. The developed composite can reversibly bend toward different sides upon the stimulation of NIR light or moisture, and the actuation processes can be completed within seconds due to structural rigidity of Zr-Fc. Further by inducing the formation of chemical crosslinking between polyvinyl alcohol chains, the composite can be programmed into intricate 3D shapes, which enables the exhibition of different modes of deformation and motion upon stimulation. This work enriches the design and preparation of actuators by MOF-loading with advanced actuating behaviors.