Construction of site-specific immobilized lipase in bio-inspired “rigid and flexible” composite PVIm/ZIF-8 for long-cycle biodiesel synthesis from waste cooking oil

Maintaining the long-term stability of flexible polymer-immobilized lipase remains a significant challenge in enzyme catalysis. The deformation of the polymer during the process often damages the lipase, severely limiting its practical application. In this work, we in situ constructed rigid Zeolitic Imidazolate Framework-8 (ZIF-8) in porous hydrophobic polymer PVIm as “rigid and flexible” composite PVIm/ZIF-8 through a self-assemble strategy. The implanted rigid ZIF-8 improves the network stability of the hydrophobic polymer PVIm. Additionally, it acts as a co-factor, leveraging defective Zn sites to immobilize lipase through bonding with its amino acid moieties. This approach represents a typical two-birds-with-one-stone strategy. The optimal biocatalyst CalA@PVIm/ZIF-8(0.3) affords the highest yield of biodiesel of 82 % with a TON of 136.6 g (biodiesel) /g (CalA) from waste cooking oil under 30 °C and 24 h. Compared to CalA@PVIm/ZIF-8(0.3), the TON of free CalA is only 25 % of that value. Compared to the ZIF-8-free CalA@PVIm, CalA@PVIm/ZIF-8(0.3) exhibits near 1.2 folds enhancement of performance, further unveiling the co-factor role of ZIF-8 in the reaction. More importantly, this incorporation of ZIF-8 makes the resulted CalA@PVIm/ZIF-8(0.3) afford at least 44 days operation period and retains 83 % original activity after 16 running recycles, superior to almost all the reported immobilized lipase researches, far outperforming that (24.1 % activity after 16 cycles) of CalA@PVIm. The wide flexibility in various biodiesel synthesis can be further demonstrated, affording the practical application value of developed catalyst.