Isolation of Bio-Mesoporous Silica from Rice Husk

By using a simple and safe citric acid-hydrothermal treatment, bio-mesoporous silica with a high surface area (approximate to 200 m(2)g(-1)) and pore size of around 6.0 nm can be isolated from rice husk. We found that the surface area of the isolated porous silica is dependent on the pH value, hydrothermal temperature, and reaction time but independent on the water content. At pH around 2.0-2.5, the resulted bio-mesoporous silica possesses the highest surface area regardless to the acid sources. Increasing hydrothermal temperature can accelerate the removal rate of the metal impurity in the rice husk. From the data of the surface areas, the required reaction time to isolate the mesoporous silica of the largest surface area (approximate to 200 m(2)g(-1)) from rice husk increases with decreasing temperature. It takes only about 0.5 hour at 100 degrees C, 1.0 hour at 60 degrees C and 12.0 h at room temperature. This citric acid-hydrothermal treatment can also be applied to isolate bio-mesoporous silica from Equisetum grass.