Adsorption of avermectin on porous hollow silica nanoparticles by supercritical technology.

Porous hollow silica nanoparticles with O.D. of approximately 100 nm and a wall thickness of approximately 10 nm were prepared by using inorganic CaCO3 templates. The produced PHSN were employed as a novel carrier to study the adsorption of avermectin in supercritical carbon dioxide by applying different adsorption pressure, adsorption temperature, adsorption time and volume of cosolvent. The results indicated that while increasing adsorption pressure and time always showed a positive effect on the avermectin adsorption until adsorption saturation is reached, both the adsorption temperature and volume of cosolvent require an optimal value for achieving the maximum adsorption. It was found that the optimal adsorption could be obtained at an adsorption pressure of 15 MPa and an adsorption temperature of 313 K for 90 minutes with 5 ml cosolvent. In addition, the desorption behavior of avermectin from the avermectin-loaded PHSN samples showed a sustained style: approximately 60% of avermectin was released in the first 20 minutes, while the other 40% followed a typical sustained desorption pattern and was dissolved out slowly for a time period of 3000 minutes, which is different from the quick and complete desorption from solid SiO2 carriers.