Preparation of super-hydrophobic white carbon black from nano-rice husk ash

Nano-rice husk ashes were prepared by burning rice husk with a self-propagating method. The white carbon black with high purity was prepared by an alkali dissolving-acid reaction method from nano-husk ash. The super-hydrophobic SiO2 films were prepared by the sol-gel method using hexamethyldisilazane as a modifier. The effects of the pH and reaction time in the acid reaction process on the purity of the white carbon black, and the effect of the modifier on the hydrophobic property of SiO2 films were studied. The performances were characterized by XRD, BET, SEM, IR, and contact angle analyzer. The results showed that the purity of white carbon black reached 98.48 % when the NaOH solution with the rice husk ash was heated for 2 h at 90 A degrees C, then the pH of the solution was adjusted by sulfuric acid to 3, and the acid reaction time was 2 h. The contact angle of SiO2 films was more than 160A degrees when volume ratio of the modifier to silica-sodium hydroxide mixed solution was 0.15. The mechanism of the modifier on SiO2 surfaces is a graft copolymerization. The hydrophobic groups in the modifier replace the hydroxy groups on SiO2 surfaces and make SiO2 surfaces present super-hydrophobicity.