Silk Fibroin Fibers with In Situ Growth of ZIF-67 Nanoparticles for Membranes with Highly Efficient Nanofluidic Ion Transport

Nanofluidic systems due to their unique transport properties play a crucial role in a lot of applications ranging from water desalination to sensors. Over the past few years, considering the simple structure of two-dimensional materials, significant efforts have been devoted to designing synthetic membranes for ion transport. However, expensive fabrication methods such as lithography techniques and some shortcomings such as scale-up difficulty, low pore density, poor mechanical stability, and biocompatibility limit their practical application. Herein, we demonstrate a scalable hierarchically porous membrane with three-dimensional (3D) interconnected nanochannels which is based on the silk fibroin (SF) fiber biomass and modifying the nanofluidic channels by in situ growth of zeolitic imidazolate framework-67 (ZIF-67) nanoparticles on the fiber surfaces. The ZIF-67/SF membrane with 400 μm thickness is a 3D interconnected network with a large positively charged surface area (54 m2 g-1) containing 1-5 nm pores estimated from density functional theory modeling. Surface-charge-governed ion transport through the nanofluidic channels of the ZIF-67/SF membrane is systematically explored, and characteristic higher-than-bulk ion conductivity was observed at low concentrations (≤10-3 M) of monovalent electrolytes (KCl, NaCl, NaOH, and HCl). Moreover, the ZIF-67/SF is stable and fully functional at elevated temperatures up to 60 °C and maintains its structural and operational properties under acidic and basic conditions.