By using a simple and safe citric acid-hydrothermal treatment, bio-mesoporous silica with a high surface area (≈200 m2g -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 (≈200 m 2g-1) from rice husk increases with decreasing temperature. It takes only about 0.5 hour at 100 °C, 1.0 hour at 60 °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. Bio-mesoporous silica with a high surface area (≈200 m2g -1) and pore size of around 6.0 nm can be isolated from rice husk by using a simple and safe citric acid-hydrothermal treatment. The effects of pH value, reaction time, temperature, and water content were studied to find a simple and energy-saving procedure to isolate the bio-mesoporous silica from rice husk.
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