Oriented 2D Metal Organic Framework Coatings on Modified Bacterial Cellulose for Separations

Bacterial cellulose (BC) is a fibril network composed of well-arranged three-dimensional nanofibers, which is synthesized by certain bacteria such as Gluconacetobacter hansenii, Rhizobium and Rhodobacter [1, 2]. Under appropriate conditions, the bacterium has the ability to secrete cellulose strands as part of its metabolism, forming a certain thickness of cellulose pellicles. BC has the same molecular formula as plant cellulose, which makes it easy to degrade, renewable, non-toxic, cheap and easily available. Originated from the unique and complex three-dimensional porous structure, BC demonstrates a serious of unique structural characteristics such as high purity, ultrafine network structure (20-80 nm), high degree of polymerization (up to 8000), high crystallinity (70-80%), high water content up to 99%, and high mechanical stability, which make a promising platform for supporting molecular sieve membranes [3, 4]. Continuous Metal Organic Frameworks (MOFs) on porous support is a candidate for membrane separation with high permeance and molecular recognition. The appropriate template has become the key to direct MOF attachment and thin film formation without any defects.

In this work, a BC template with -COOH was obtained by grafting hyaluronic acid on the fiber to improve the electrostatic interaction between metal ions and the BC surface, thereby forming a tight attached layer. Cu(bdc) was chosen for the well-known 2D morphology, stability in water, defined pore and unsaturated metal center for adsorption. By grafting -COOH, Cu(bdc) axis a (small dimension) is perpendicular to the surface of modified BC and forms 10 nm scale thickness continuous MOF layer. The oriented Cu(bdc)-BC composite would be ideal for isobutane/isobutane/n-butane separation and rose Bengal/methylene blue separation.

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