Preparation of mesoporous silica from rice husk ash: effect of depolymerizing agents on physico-chemical properties

The aim of this work was to prepare mesoporous silicas derived from rice husk ash (RHA) using three different depolymerizing agents; glycerol, 1,3 propanediol and 1,4 butanediol. The reaction of RI-TA with different depolymerizing agents was carried out between 200-250 degrees C for 2 hrs. The solution was then hydrolyzed with deionized water to obtain gels. After a few washing step, gels were oven-dried and calcined at 500 degrees C for 24 hrs. Prepared mesoporous silicas were then characterized using Nitrogen adsorption-desorption measurement, FTIR, TGA, SEM, XRD and XRF. The percent hydrophobicity was determined based on the amount of moisture absorbed using TGA. It was shown that RHA reacted with depolymerizing agents above 200 degrees C to form gels, which, after hydrolysis and calcination, still maintained the mesoporous characteristics. The BET and SEM results indicated that the RHA reacted with 1,3 propanediol had highest pore volume (0.95 cm(3)/g) and specific surface area (129.30 m(2)/g) compared to RHA reacted with glycerol and 1,4 butanediol. The distribution of pores computed from BJH desorption branch was also more uniform. FTIR indicated that there was no significant change in the chemical structure of RHA reacted with different depolymerizing agents. The residual C-H bands were found in FTIR spectra for all prepared mesoporous silicas. TGA thermograms confirmed the existence of organic residues (below 2 %wt), which might result from incomplete elimination even after calcination. This was found to be an important factor affecting the hydrophobic property of the reacted RHA. The hydrophobicity of RHA may be tailored by controlling depolymerizing agents and organic residues. Depolymerizing agents with longer carbon chains also favoured the hydrophobic characteristics.