Hydrophobicity Adjustment And Enhanced Local Water-repellent Effect Of Fluorous Acid Silica On Fructose Upgradation

The conversion of renewable biomass-derived hexoses to biofuels and bulkchemicals is imaged to be a ideal solution to diminishing fossil resources.It is a green synthetic strategy to realize the conversion of sugar catalyzed by solid acid catalysis.The acid strength and surface property of solid acids are thus very important.A series of mesoporous silica supporting-SO2NHSO2C4F9/CF3 was synthesized by two-step sol-gel method,incorporating 0-100 mol% of methyl group to regulate the surface property of the materials.The prepared solid acids were noted as SSFBI-MSMA15/Mex-SiO2 and SSFMI-MSMA15/Mex-SiO2,respectively.29The composition of solid acids were characterized by Si CP/MAS NMR and TEM-Mapping.The peak value of Si-C bond increases with the increase of-CH3 mole fraction(x),and the TEM-Mapping shows that the elements are distributed uniformly in the solid acid.The results of nitrogen adsorption desorption test showed that the two series solid acids were commonly rich in mesopores and micropores.In the SSFBI-type solid acid,the presence of C4F9 groups is helpful to formation of micropores.In this paper,we correlate the macroscopic hydrophobicity and microscopic surface polarity.Macroscopic hydrophobicity was obtained by measuring the static contact angle of water.The polarity of the chemically modified surface of the materials was investigated using fluorescence spectrometry to examine the absorbed pyrene molecules.For SO2NHSO2C4F9-functionalized silica,the macroscopic hydrophobicity was consistent with surface polarity.More incorporated-CH3 groups,higher surface nonpolarity,and better hydrophobicity suggested by increased contact angle;while difference happened to SO2NHSO2CF3-functionalized silica,which kept hydrophilic independently on the surface nonpolarity.The thermal stability of solid acid was characterized by TG,which indicated that the solid acid was stable at 210 oC,and the surface morphology was characterized by SEM and TEM.Solid acid load was 0.53-0.61 mmol/g.The catalytic dehydration of fructose was carried out in alcohol system with 0-20%water content.In nonaqueous system,the fructose conversion was 89-98% within 1 h.In10-20% aqueous alcohol,the addition of water apparently slowed down Fru dehydration.In 20% aqueous alcohol,the differences of yields of HMF between-CH3-deficient and-rich materials were 7% by-C4F9-series and 6% by-CF3-series,respectively,showing the similar water-repellent effect due to-CH3nonpolarity;while theyields by-C4F9-series was 10% higher than those by-CF3-series.-C4F9 group took effect to repel water superiorly to-CF3 group,especially around the adjacent acid site-NH.Additionally,the facial Si-OH contributed to hydrophilicity effect,facilitating fructose accessing and transforming.This should be interesting to promote the separation of water and watersensitiveproduct(HMF),concurrently at no expense of dehydration rate.