Abstract
Abstract Adsorption properties of Silica gel (commercial silica), rice husk ash (RHA) silica, and their hydrothermally treated products towards water molecules were studied in this work. RHA silica was prepared by heating rice husk to 650°C for 4 h after pretreatment with hydrochloric acid. Portions of the samples of silica were evacuated at 200℃ and then allowed to adsorb water molecules from the surrounding air at either 42 or 50% humidity. The near infrared spectra of these samples were measured at different time intervals during their adsorption of water molecules. The evolved near infrared spectra were analyzed using second derivative techniques. Adsorption properties of these samples were further studied by gravimetric analysis. Surface functionalities and adsorption evolution of water molecules on silica samples studied showed that the adsorption of water molecules on commercial silica gel sample and RHA silica Samples takes place readily with hydrogen-bonded silanol groups on the surfaces of the samples. This adsorption arising from the OH stretching and bending vibrations of these water molecules gives rise to a band at 5,270 cm−1 in the near infrared region. The adsorbed water molecules then continue at the free silanol groups which is indicated by the absorption around 5,314 cm−1. The results clearly show that the silica made from rice husk adsorb water in the same manner as the commercial silica, but the quantity of water molecules adsorbed is less compared to commercial silica used in this experiment. However, the study clearly shows that the rice husk silica can replace the commercial silica as a substitute for desiccant purposes in industry.
Highlights
Silica gel is produced by condensation polymerization of silicic acid (Si(OH)4)
Overtone –OH stretching Free silanol groups Vicinal silanol groups Water molecules hydrogen bonded to silanol group; water molecules hydrogen bonded to other water molecules Combination band OH stretching and bending water molecules hydrogen bonded to free silanol groups Water molecules hydrogen bonded to vicinal groups Water molecules hydrogen bonded to silanol group Combination band OH stretching free silanol and siloxane (Si–O–Si) Combination band silanol OH stretching and siloxane (Si–O–Si) bending
The spectra measured after evacuating show that the rice husk (RH) silica contains free and vicinal silanol groups
Summary
Silica gel is produced by condensation polymerization of silicic acid (Si(OH)). Silica gel produced by this method contains porous particles with cross-linked siloxane (Si–O–Si) structure in the bulk and silanol groups on the surface. Dry silica gel adsorbs water molecules when exposed to air. This quality of silica gel found its use in electronic industry as a desiccant. Christy [5] has studied several silica gel and silica gel-based samples and their water adsorption evolutions using gravimetry and near infrared reflectance spectroscopy with the help of second and fourth derivative techniques and showed that the hydrogen-bonded silanol groups adsorb water readily compared to free silanol groups. Water adsorption of rice husk silica and commercial silica 427 sharp bands in a peak relative to the broad band in the absorption spectrum of a sample. The aim of this work is to compare the water adsorption properties of silica produced from rice husk and commercial silica. Gravimetry was used for comparison of the mass of water adsorbed by these samples
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
