Fabrication And Application Of Mesoporous Silica Nanospheres With Radially Oriented Mesochannels

In this study, mesoporous silica nanospheres (MSNs) with radially oriented mesochannels were fabricated in cetyltrimethylammonium bromide (CTAB)-ethanol-cyclohexane-water oil-in-water microemulsion system at 35℃ under basic conditions, by regulating ethanol-to-cyclohexane volume ratio. In the oil-in-water microemulsion system, CTAB was used as the surfactant, ethanol as the cosurfactant, cyclohexane as the organic solvent, tetraethyl orthosilicate (TEOS) as the organic silicon source. The as-prepared silica samples were labeled as MSNsVl, MSNsV2, MSNsV3, and MSNsV4, respectively. The results indicated that nearly irregular spheroids with 400 nm-650nm mean diameter were obtained, revealing radially oriented pore structures. The pore size distribution was very narrow with only one peak centered at about 3.9 nm. These particles have high surface areas ranged from 1000 m2 g-1-1114 m2 g-1 and pore volumes ranged from 0.52 cm3 g-1-0.64 cm3 g-1. The application of the prepared MSNs in drug loading and release with aspirin as model drug was also investigated. MSNsV3 showed the biggest aspirin loading amount of 0.50 g aspirin/g MSNsV. The controlled release profiles of aspirin loaded samples were studied in phosphate buffered solution (pH=7.4). The results showed that MSNsV3-asp had the rapid aspirin release rate with approximately 92%maximum aspirin released after 7 h.In addition, MSNs were obtained by introducing polyvinylpyrrolidone (PVP) as stabilizing agent into the CTAB-ethanol-cyclohexane-water oil-in-water microemulsion system at 35℃ under basic conditions, TEOS as the organic silicon source. The as-prepared silica samples were labeled as MSNsMl, MSNsM2, MSNsM3, and MSNsM4, respectively. The results indicated that monodispersed spherical nanoparticles with 300 nm-450 nm mean diameter were obtained, revealing radially oriented pore structures. The pore size distribution was very narrow with only one peak centered at about 4.0 nm. These particles have high surface areas ranged from 975 m2 g-1-1052 m2g-1 and pore volumes ranged from 0.59 cm3 g-1-0.74 cm3 g-1. In addition, The MSNsM samples tended to more regular without aggregation compared with the MSNsV samples, and the radially oriented mesochannels structure was more ordered. Based on the experimental results, a possible mechanism for the structural regulation of MSNs with radially oriented mesochannels prepared with or without PVP O/W microemulsion was proposed. The application of the prepared MSNsM in drug loading and release with aspirin as model drug was also investigated. The results indicated that aspirin was successfully loaded into the MSNsM pores, and the aspirin loading amount increases with increasing amount of PVP. MSNsM4 showed the biggest aspirin loading amount of 0.57 g aspirin/g MSNsM, but the corresponding release time was shortened. Compared with MSNsV, the aspirin release rate of MSNsM was faster with nearly 40% of the aspirin released from the SiO2 after the first hour. Nearly complete release of aspirin was observed after 3 h for MSNsM4-asp. Compared with MSNsM1-4-asp, MSNsVl-4-asp exhibited better aspirin release effect. Therefore, MSNsVl-4 samples with radially oriented mesopores can be advantageous in simulated concentrative release of drugs.Mesoporous silica nanoparticles with radially oriented mesochannels were synthesized by a solvothermal method under basic conditions, in which a mixture of cyclohexane, ethanol and water were used as the solvent, TEOS as the source of organic silica. We report the solvothermal synthesis of MSNs by varying the ratios of CTAB to PVP. The formed materials MSNs-1 and MSNs-2 were spherical in shape with a wrinkle structure, while the coexistence of radial-orientated pore. The particles sizes varied from 240±10 nm to 480±10 nm. Remarkably, Silica particle sizes decreased when PVP was added. Using synthesized MSNs samples with radial-oriented mesochannels as the support, Candida rugosa lipase (CRL) was successfully immobilized into the channels of MSNs. The loading amount and enzymatic activity of MSNs samples were performed. The loading amount of MSNs-1 and MSNs-2 is 974 mgg-1 and 990 mgg-1, respectively. Immobilized CRL showed greater catalytic activity comparing with free lipase by hydrolysis of triacetin. We prepared immobilized CRL as a new biocatalyst for biodiesel production through the esterification of oleic acid with methanol. These results suggest that WSNs with highly ordered, radially oriented mesochannels have promising applications in biocatalysis.