Preparation of SiO2 nanoparticles with adjustable size for fabrication of SiO2/PMHS ORMOSIL superhydrophobic surface on cellulose-based substrates

Silica (SiO2) nanoparticles with controlled particle size and poly(methylhydrogen)siloxane (PMHS) were applied to fabricate superhydrophobic SiO2/PMHS ORMOSIL (organically modified silicate) coating on cellulose-based substrates (wood, cotton and filter paper). The influence of weight ratio of ammonia to TEOS, H2O to TEOS and ethanol to TEOS on the particle size of SiO2 nanoparticles was evaluated by the response surface methodology. The results indicated that the particle size of SiO2 nanoparticles could be well-controlled between 25 nm and 100 nm. The effect of particle size on hydrophobicity of SiO2/PMHS ORMOSIL coated wood was investigated. The modified wood had the best hydrophobicity as the particle size of SiO2 was 75 nm, possessing a water contact angle of 158.2 degrees. After deposition of SiO2/PMHS ORMOSIL coating, the water resistance and anti-fouling property of wood increased obviously. The water absorption decreased significantly from 70.3% to 24.1%. In addition, SiO2/PMHS ORMOSIL was further applied to functionalize filter paper and cotton for oil/water separation. The separation efficiency of diesel from water was 96%-99% for modified filter paper after separation for 20 cycles, while the absorption capacity was 10.5 times of the modified cotton.