# Ionic Liquids for Development of Heterogeneous Catalysts Based on Nanomaterials for Biocatalysis
## 3 Supported Ionic Liquid Phases in Biocatalysis
The best PPL immobilization efficiency characterized silicas that were modified with ILs, thiol, amino, and phenyl groups. Moreover, PPL-SILLPs exhibited the best thermal stability, pH resistance, and stability among all of the examined biocatalysts. After five cycles, the activity of PPL-SILLP, functionalized with a carboxyl group, was above 62% [86]. A comparison of PLL adsorbed on SILLP, with PLL immobilized via enzyme aggregates, coating onto SBA-15 modified with IL, was also reported. The lipase immobilized as an enzyme aggregate coating demonstrated, after 25 days of storage, 74.25% of its original activity, when PLL-SILLP was only 48% [87]. Further investigations of enhanced enzyme activity led to the increased stability of immobilized PPL via physical adsorption onto SILLP, by embedding it with microspheres of sodium alginate gel. SILLP was obtained by grafting imidazolium-based IL with [BF4]\({}^{-}\) anion into SBA-15. Novel biocatalysts showed extremely higher thermal stability at 65 \({}^{\circ}\)C, almost no activity lost was observed [88]. Papain enzyme was immobilized on SILLP, based on SBA-15. Ionic liquid grafted to the support provided higher papain loading (261 mg/g) than for the enzyme on SBA-15 (185 mg/g). What is more, the papain-SILLP biocatalyst presented higher activity in the case of hydrolysis than papain-SBA-15 [89]. Periodic mesoporous organosilica (PMO) combined with IL was used as a carrier for \(\alpha\)-amylase from _Bacillus amyloliguefaciens_. PMO is an organic-inorganic material, where organic groups are ordered inside the silica's channel walls. Immobilized amylase on PMO-IL retained 88% of its initial activity after four reaction cycles, and showed two times better thermal stability at 70 \({}^{\circ}\)C and 80 \({}^{\circ}\)C compared with a native form [90]. The activity of CALB was examined in the glycerolysis of corn oil for diacylglycerol production. For that purpose, SBA-15 was modified by grafting onto a hydroxyl group of the imidazolium ring of IL, with two different anions ([BF4]\({}^{-}\), [PF6]\({}^{-}\)) and three different alkyl chain lengths (C1, C4, C8) in the cation. The best results were obtained for the CALB-SILLP consisting of a methyl group in the imidazolium ring and [BF\({}_{4}\)]\({}^{-}\) anion. The activity of CALB-SILLP, in comparison with CALB-SBA-15, increased from 1855 to 5044 U/g. Hence, the enzyme exhibited a greater selectivity towards diacylglycerols synthesis, with the diacylglycerols/monoacylglycerols ratio increasing from 3.72 to 11.99, and the content of the diacylglycerols improving from 53.6 to 67.2%. Also, a retained activity of 90%, after five reaction cycles, for the CALB-SILLP biocatalyst was observed [91]. Another approach uses silica aerogels combined with ILs. BCL lipase was immobilized on the mesoporous silica aerogels that were modified with PIL (PIL-N-methylmonoethanolamine pentanoate--C5) via physical adsorption, covalent bonding, and encapsulation. A comparison of the immobilization yield on PIL-modified support for the performed techniques showed the best results for physical adsorption (83%), and the longest stability presented an encapsulated enzyme (23 reuses) in olive oil hydrolysis as the tested reaction [92]. The same SILLP support was used for BCL immobilization, and applied in ethyl ester production from coconut oil. Further, a 70% conversion was achieved for oils after 144 h at 40 \({}^{\circ}\)C (coconut oil:ethanol, 1:7, molar ratio), when BCL-SILLP was used [93]. BCL lipase improved the activity of various phosphonium ILs. Selected trihexyltetradylphosphonium bis(trifluoromethylsulfonyl)amide [P666(14)][NTf\({}_{2}\)] allowed a relative activity up to 231% and immobilization yield of 98% to be achieved. The biocatalyst kept more than 50% of its initial activity after 26 cycles. It was reported that using [P666(14)][NTf\({}_{2}\)] during the silica support preparation and immobilization procedure significant influences the enzyme activity, stability, and immobilization yield [94].