Preparation And Application Of Mesoporous Silica Via O/W Microemulsion Templating Strategy

Mesoporous silica nanoparticles with wrinkled surface having radially oriented mesochannels and hollow silica nanoparticles with wrinkled or smooth surface were successfully fabricated through a microemulsion templating strategy.In this method,oil-in-water microemulsion?composed of cyclohexane,water,ethanol,and cetyltrimethylammonium bromide?,and polyvinylpyrrolidone were utilized as template and capping agent,respectively.Characterization results indicated that we can well realize the morphological transformation of spheres with radially oriented mesochannels to hollow structures of silica nanoparticle only by regulating the hydrothermal temperature from 100°C to 200°C.Particle size and smoothness of silica varied simultaneously.Silica particle sizes increased firstly and then decreased when hydrothermal temperature increased.The range varied from 250 nm to 420 nm.At the same time,the wrinkle on surface of nanoparticles gradually disappear and surface become smooth as temperature increased to 200°C.The synthesized samples with different mesostructures were then used as supports to immobilize Candida rugosa lipase?CRL?in the pore channels or interior of hollow spheres by physical mixing.We investigated the CRL loading amounts onto the carriers and silica nanoparticles with radially oriented mesochannels possesses a good loading amount of 967.7 mg g^-1.The enzyme activities of free and immobilized CRL were evaluated by hydrolysis of triacetin.Likewise,silica with radially oriented mesochannels displays the highest hydrolysis activity of 77.5 U/g,whereas that of free CRL is only 33.7 U/g.ln addition,free and immobilized CRL were employed as new biocatalyst for biodiesel production through the esterification of heptanoic acid with ethanol.The conversion ratio of heptanoic acid was also measured.Notably,the maximum conversion ratio is 85.3%,which is obviously higher than that?39.4%?of free lipases.Furthermore,reusability studies were carried out to determine the stability of immobilized CRL during the reaction.Results of this study suggest that the prepared samples have potential applications in biocatalysis.When the hydrothermal temperature and time were fixed at 130°C and 24 h respectively,we found the amount of cyclohexane has huge effect on silica.Silica prepared with different amount of cyclohexane were denoted as MSNsT1V1,MSNsT1V2,MSNsT1V3,MSNsT1V4 and MSNsT1V5.The morphology of silica transform from spheres with radially oriented mesochannels to hollow structures by increasing the volume of cyclohexane.To some extent,particle size also varies with it.When added 2 or 3 mL cyclohexane into system,prepared silica presents novel yolk-shell structure.What is novel here is,the inner cores of MSNsT1V1 and MSNsT1V2 are flower-like and exist radially oriented mesochannels.The thickness of shell on MSNsT1V2 is about 20 nm.But the boundary between core and shell of MSNsT1V1 is not much clear.By increasing the volume of cyclohexane to 5 mL,silica with yolk-shell structure was displaced by silica with radially oriented mesochannels.The radially oriented mesochannels extend from center to the edge of sphere.As the volume of cyclohexane increased to 7 or 9 mL persistently,the structure of silica has no significant change.Silica particle sizes decreased firstly and then increased when the volume of cyclohexane increased.Partical size of MSNsT1V1 is 500 nm and that of MSNsT1V2 is 440 nm.MSNsT1V5 is the largest about 630 nm.We also fixed the hydrothermal temperature and time at 130°C and 24 h respectively,then similarly investigated the effect of cyclohexane on silica.The silica prepared with different amount of cyclohexane were denoted as MSNsT2V1,MSNsT2V2,MSNsT2V3,MSNsT2V4 and MSNsT2V5.When the amount of cyclohexane was minimum?2 m L?,silica exhibites clear hollow structure.Partical size ranged from 440 nm to 520 nm and thickness of shell is only 25 nm.The morphological transformation of spheres with hollow structures to yolk-shell structure occured while increasing the amount of cyclohexane to 3 mL.Nevertheless,the core is irregular sphere about 280 nm.The thickness of shell is similar to MSNsT2V1.Continue increasing the amount of cyclohexane,inner construction of silica remain unchanged.But the core presents flower-like structure.The size range varied from 540 nm to 620 nm.As 7 m L of cyclohexane was used,mean diameter of silica is 560 nm.The core is relatively small than others about 260 nm.The thickness of shell still does not changed.When the amount of cyclohexane was maximum?9 mL?,inner core becomes loose rather than dense.Mean diameter of MSNsT2V5 is 520 nm.In brief,we can well realize the morphological transformation of spheres with hollow structure to yolk-shell structure only by increasing the amount of cyclohexane from 2 m L to 9 m L.Particle size is adjustable within the range of 440 nm-620 nm.But the amount of cyclohexane has no effect on shell thickness of silica.