Effect Of Polyvinylpyrrolidone On Mesoporous Silica Morphology And Esterification Of Butyl Laurate By Immobilized Enzyme Catalysis

Silicon-based materials, as a kind of mesoporous materials, have adjustable poresize from2to50nm, larger ratio surface aeeas, bigger pore volume, higherphysicochemical stability, and better biocompatility, which are widely used in drugcontrolled release, biosensor, protein separation and any other fields. With deepenedresearch of ordered mesoporous materials, more and more researches are inclined to thestudy of controllable morphology and pore size. Mesoporous materials with differentmorphologies (rod-shaped, spherical, vesicular, fiber-like, and layered) can besuccessfully synthesized by using different surfactants and changing the synthesiscondition. In this study, ordered mesoporous silica materials were successfullysynthesized using PVP and P123as co-template with tetraethoxysilane (TEOS) as silicasource through hydrothermal process under acidic condition, by varying differentreaction parameters such as mole ratio and molecular weight of PVP. Mesoporous silicamaterials with a range of morphology evolution, from curved rod-shaped mesoporoussilica (CRMS) to straight rod-shaped mesoporous silica (SRMS) were successfullyprepared. Then CRMS and SRMS were functionalized with(3-aminopropyl)triethoxysilane. SRMS-S2and functionalized SRMS-S2(NH-SRMS-S2) were evaluated as support for immobilization of Porcine pancreaticlipase (PPL) and the immobilized PPL (SRMS-S2-PPL, NH-SRMS-S2-PPL) wereevaluated in the esterification reaction of lauric acid with1-butanol at optimumconditions. We have investigated the optimum conditions, such as temperature and pH,of immobilized PPL employed to catalyze triacetin hydrolization. In addition, the effectsof NH-SRMS-S2-PPL content and immobilized PPL recycle numbers on lauric acidconversion rate were investigated.The obtained materials were characterized by Fourier transform infraredspectroscopy (FT-IR), small-angle X-ray powder diffraction (SAXRD), elementalanalysis (EA), N2adsorption desorption, transmission electron microscopy (TEM), andField emission scanning electron microscopy (FESEM). The results indicated thatmesoporous silica materials with2D mesostructure (p6mm) were successfully prepared,PVP molecular weight and concentration have important effects on mesoporous silicamorphologies and structure parameters. The results showed that surface area (SBET),pore diameter (D), and pore volume (V) decreased, wall thickness (Tp), particle size, interplanar spacing (d100), and cell parameter (a0) increased, with the addition of PVP,comparing to CRSM-S0. In addition, mesoporous silica tended to more regular withoutaggregation. As PVP concentration increased, d100and a0decreased continuously, D,SBET, and V decreased on the whole. With the increase of PVP molecular weight, SBETand V decreased continuously, D, Tp, d100, and a0first increased and than decreased. Theresults showed that SBETand V decreased continuously with the increase of PVPmolecular weight and SRMS-S3(K30) possessed bigger D, d100, and a0, compared withSRMS-S5(K15) and CRMS-S6(K90). In addition, as PVP concentration increased, d100and a0decreased continuously, D, SBET, and V decreased on the whole. SRMS-S2(K30)is uniform without aggregation which has better structure ordering than SRMS-S3(K30). It is found that the morphology of CRMS-S0, CRMS-S1, CRMS-S4, andCRMS-S6have a certain curvature, while SRMS-S2, SRMS-S3, and SRMS-S5presentstraight characteristic. Thus the molar ratio of1:0.058and PVP (K30) are the bestconditions. NH-CRMS and NH-SRMS were characterized by FT-IR, EA, SAXRD, andN2adsorption-desorption, indicating that the success of amino-functionalization and thehexagonal symmetry structure with no change after functionnalization with the decreaseof SBET, V, d100, and a0. SRMS-S2-PPL and NH-SRMS-S2-PPL were characterized byFT-IR, EA, SAXRD, and N2adsorption-desorption, indicating that PPL have beenlocated on the SRMS-S2and NH-SRMS-S2without destruction of mesoscopicstructure. It is noted that the optimum conditions of SRMS-S2-PPL are around308Kand pH=7.0, while NH-SRMS-S2-PPL are about313K and pH=8.0. SRMS-S2possesses good loading amounts and activities of45.2mg g1and1493.36U g1, whileNH-SRMS-S2with a loading amounts and activities of77.64mg g1and2337.71Ug1. The optimized amount of catalyst was60mg. It was found that NH-SRMS-S2-PPLmaintained50%of its esterification conversion rate even after5cycles of use with themaximum conversion rate about90.15%, while SRMS-S2-PPL maintained30%withmaximum conversion rate of76.85%.