| Recently,some of the pesticides have caused lots of environmental pollution problems for the short duration,repeated spraying and improper using.So it is necessary to develop the new sustained-release pesticides to extend the drug duration.In this thesis,the sustainedrelease systems which have different structure,morphology,pore structure and particle size had been established using the Avermectin with short duration as model drug,and the nanosilica as the sustained-release carrier.The sustained-release performance and process were studied.(1)Preparing different Sustained-release pesticide supports: the mesoporous silica(including mesoporous silica MSS,mesoporous silica nanorods MSR)and hollow mesoporous silica(including hollow mesoporous silica HMSS-W,worm-like mesoporous silica HMSS-O and hollow mesoporous silica HMSS-O with different particle sizes(160-550nm))were prepared,respectively,and the structure of the supports were characterized by scanning electron microscopy,transmission electron microscopy,specific surface analyzer and X-ray diffractometer.The MSS precursors were prepared at 25℃ and with the stirring speed was 1200 rpm The ammonia was added firstly and then was the TEOS..The concentration ratio of TEOS and CTAB was 1:0.09-1:0.12.The MSS used as the precursor exhibited monodisperse spherical morphology with a particle size of 550 nm and highly ordered radial mesoporous structure.The MSR prepared by dual template exhibited regular rod-like morphology,good monodispersity,large aspect ratio(>20)and wormlike mesoporous structure.Both of the two carrier materials which had narrow pore size distribution,large specific surface area and pore volume provided the better adsorption and diffusion conditions for the active components of the drugs.The HMSS prepared by water etching and HMSS-O and HMSS-W prepared by alkali etching were all the spherical materials with unique core-shell structure.The active components of the drugs can absorb and diffuse easily because of the narrow pore size distribution,large specific surface area and pore volume.The HMSS and HMSS-O shells owned highly ordered radial direct mesoporous channels,while the HMSS-W owned a unique worm-like mesoporous shell.(2)Different sustained-release systems of Avermectin had been prepared by loading Avermectin using ultrasonic impregnation.The analysis results of the infrared spectroscopy and ultraviolet spectrophotometer showed that Avermectin was loaded successfully.The drug loading and encapsulation efficiency increased with the particle size of the support materials increasing.For the same particle size carrier materials,the drug loading and encapsulation efficiency increased as the specific surface area became larger.The hollow structure had more advantages than the single mesoporous structure in drug loading and encapsulation efficiency.Hollow mesoporous silica(HMSS-O-550)with ordered straight channel structure prepared by alkali etching had relatively high drug loading and encapsulation efficiency,and which could reach 41.40% and 70.65%,respectively.The rodlike mesoporous silica MSR also owned larger drug loading and encapsulation efficiency due to its larger aspect ratio,and the value of which was 43.29% and 76.35%,respectively.(3)The results of slow-release performance of culture method showed that: Compared with the raw Avermectin,the sustained-release systems prepared by ultrasonic impregnation method had certain sustained-release effect.Sustained-release system which had been prepared by spherical materials with large particle size,ordered radial straight channels and hollow mesoporous structure performed the longer slow-release time and slower slowrelease rate.The cumulative release rate of Av@HMSS-O-550 was only 51.12% 160 hours later.The drug release process of the prepared sustained-release system was all diffusion process.The four-parameter Weibull model was fit the drug release process of different sustained-release systems better and the R-squaredis higher than 0.97. |
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