Synthesis And Properties Of Metal- Organic Frameworks Functional Thin Films

Nowadays, metal-organic framworks (MOFs) have become very promising porous crystalline materials and demonstrated leading potentials for gas separation, chemical sensors, catalysts, and optical devices due to their large and accessible specific surface area, uniform and tunable pore size, and diverse properties. Pore size tailorability combined with tunable sorption behavior provides promising avenues for applications of MOFs as membranes for gas separation. In order to further enrich or expand the functionalization of MOFs, new synergistic properties have been achieved by incorporating functional species into MOFs to form composite materials, which can’t be obtained from the parent MOF counterparts. Typically, the encapsulation process has been widely used to incorporate hetero-particles with new functions into MOFs. Solution impregnation, gas-phase infiltration, and solid grinding have been applied to introduce the precursors into the preformed MOFs host, and then converted to the corresponding functional components encapsulated in MOFs. However, in this two-step approach, the nonselective deposition at the outer surface of the MOF host is unavoidable, and the particles size and morphology are limited by the cavities of the MOFs host. In addition, the framework may suffer degradation during the nanoparticle formation. And most of them are in powder forms. However, MOFs thin films are very important to be used as devices in thin film form. MOFs films have been synthesized on inn organic plate-like substrate under relative high temperature in toxic organic solvent for long time. They thickness of them are normal thick which are not good for high efficient separation membranes.Therefore, preparing well inter-growth MOFs membranes on the porous substrate or on the hollow fibers, or even free-standing MOFs membranes for gas separation at room temperature and non toxic solvent is very promising. Besides, developing a general method for synthesis of heterogeneous functional components encapsulated MOFs thin films with thickness of several micrometers on porous substrates and in free-standing form, respectively, is also imperative. Here, we developed several methods to synthesize free-standing, on the surface of polymer hollow fibers, face oriented, and diverse functional units encapsulated MOFs thin films by using highly positive charged and active metal hydroxide nanostrands, respectively, at room temperature and nontoxic solvent quikly. These results will contribute to promote the application of MOFs for thin film devices. See detail as follows:1. We have synthesized a HKUST-1 free-standing membrane from a solid mesoporous CHNs free-standing thin film in water/ethanol solution at room temperature. Then, continuous intergrown HKUST-1 film can be scale-up synthesized on the curved surface of the PVDF hollow fibers within 40 mins at room temperature through a pressure-assisted process. After that, HKUST-1 seeds with different morphologies were prepared on a porous support at room temperature, which were directly used to investigate the eefect of seeds for secondary growth of HKUST-1 membranes. Besides, metal hydroxide nanostrands induced oriented MIL-110 nanorod arrays on porous AAO were used as both hetero seeds and anchor bars for growing continuous, crack-free, well intergrown HKUST-1 membrane. All of the membranes above demonstrated nice gas separation performances.2. We developed an omnipotent method that can successfully encapsulate various kinds of functional components into the MOFs thin films at room temperature within one to two hours. The MHNs serve not only as metal source but also help to assemble the functional components embedded into the precursor networks, which is the key point to get the uniform functional components encapsulated MOFs composite thin films. The thin film form with new synergistic properties should be expected by combining the properties of the functional agents and the MOFs host, and promise for thin films related devices including catalytic membrane reactors, conductive and flexible electronic devices so on.3. In order to realize the facets controlled separation performance of MOFs membranes, three kinds HKUST-1 membranes with different orientation and specific exposed facets with different window sizes were prepared. For the first time, as a proof of concept, we investigated the difference in the permeance and gas separation factors of the prepared HKUST-1 membranes with different exposed crystal facets and small window size of 0.46 nm presented obvious size sieving separation for CO2/C3H8 mixture.4. Meso-HKUST-1 single crystals, macro-HKUST-1 single crystals and well intergrown meso-HKUST-1 membrane were prepared through a ligand-assisted etching process at 40 ℃. The hierarchical mesoporous structures significantly increase the CO2 capture capacity by increasing the surface area and the mass diffusion process at pressure close to 10 kPa. This might be promising for capture CO2 in flue gas since the CO2 partial pressure in flue gas is generally about 10 kPa.