Microfluidic preparation of yolk/shell ZIF-8/alginate hybrid microcapsules from Pickering emulsion

We develop a facile method to fabricate yolk/shell and multi-yolk/shell ZIF-8/alginate hybrid microcapsules by first forming yolk/shell W/O ZIF-8 Pickering emulsions containing sodium alginate in water, followed by sodification of alginate to form the hybrid shell. Polymerization induced phase separation of a polyethylene glycol aqueous and acrylamide aqueous solution is used to form the yolk, and droplet coalescence is used to form multi-yolks. We examine the preparation conditions to obtain a stable ZIF-8 W/O Pickering emulsion. Further, these ZIF-8 Pickering emulsions can be converted to ZIF-8/alginate hybrid microcapsules with both hollow and yolk/shell structures by adding small amount of sodium alginate in the PEG solution, based on our finding that ZIF-8 can gelate sodium alginate. The ZIF-8/alginate hybrid microcapsules exhibit controlled release ability for Rhodamine B, with the yolk/shell one showing a lower dye release percentage. Furthermore, the release rate can be accelerated in an acid condition, resulting from the dissolution of ZIF-8.