Superhydrophobic coating of silica with photoluminescence properties synthesized from rice husk ash

Water penetration into concrete can cause the degradation of concrete strength, leading into structure failure. Superhydrophobic coatings on concrete received tremendous attention in the recent years as these coatings repel water like lotus leaves. In this work, rice husk ash (RHA) was used to prepare the superhydrophobic coating. Rice husk was calcined at 550 °C and 650 °C to form silica particles with a small amount of carbon residue. RHA 550 sample showed slightly higher photoluminescence (PL) intensity than RHA 660 sample as shown in fluorescent images and PL spectra. Such difference could be related to the variation of carbon content measured using scanning electron microscope-energy-dispersive X-ray spectroscopy. The carbon residue in nano size was detected in transmission electron microscope images. RHA with PL properties was further mechanochemically modified using 1H,1H,2H,2H-perfluorodecyltriethoxysilane (HFDS) or stearic acid in ethanol. However, PL properties of RHA 550 was slightly reduced due the successful grafting of hydrophobic groups on silica particles. The modified RHA in ethanol was later spray coated on a layer of commercial adhesive to form superhyrophobic coatings on glass slides and concrete. The superhydrophobic coating on concrete with the water contact angle as high as 157.7° was recorded.