Solvent-Free Crystallization of Zeolitic Imidazolate Framework Membrane via Layer-by-Layer Deposition

Searching for sustainable synthesis methods of metal–organic framework (MOF) membranes has received huge attention in both academia and industry. In this contribution, the compact ZIF-8 membrane with excellent gas separation performance was successfully prepared via an environmentally friendly and simple method, in which the artful layer-by-layer deposition approach was used to achieve the solvent-free crystallization of a well-intergrown and defect-free ZIF-8 membrane. The solvent-free process is a simple and generalized method for construction of MOF membranes, which can avoid using solvents and high autogenous pressure and brings great benefits for energy saving, emission reduction, and safety as well as scalable manufacturing. In addition, the solvent-free crystallization of MOF membranes exhibits more unprecedented advantages to fill the common intercrystalline cracks, pinhole defects, and grain boundary defects on the membrane. The resulting thin ZIF-8 membrane exhibited both competitive H<sub>2</sub> permeability of 6.7 × 10<sup>–7</sup> mol m<sup>–2</sup> s<sup>–1</sup> Pa<sup>–1</sup> and high H<sub>2</sub>/CO<sub>2</sub> selectivity of 12.3, simultaneously, which is one of the best ZIF-8 membranes ever reported.