Analysis of nitrogen and carbon tetrachloride adsorption isotherms and pore size distribution for siliceous MCM-41 synthesized from rice husk silica

RH-MCM-41 particles were synthesized using sodium silicate prepared from rice husk as a silica source and hexadecyltrimethylammonium bromide (CTAB) as a surfactant. The molar compositions were 1.0SiO2: 1.1NaOH: 0.13CTAB: 0.12H2O. This material was used for adsorption isotherm studies of carbon tetrachloride (CT) at 25 oC using a magnetically coupled microbalance, and compared with adsorption isotherms using nitrogen at 77 K. The CT isotherms were classified as reversible Type V isotherms, and the nitrogen adsorption isotherm was Type IVc. Capillary condensation was found in a very narrow pressure range, indicating the presence of nearly uniform pores in the RH-MCM-41 particles, which agrees very well with TEM results. The surface area estimated by using the BET method was (800 ± 8) m2 g-1. Pore size distributions (PSD) of nitrogen and CT adsorption isotherms for a series of MCM-41 were calculated by using method recommended by Naono and Hakuman (1997). The pore size distributions from the nitrogen isotherm using the BJH and Naono methods showed quite narrow pore diameter distributions, centered around 27 and 29 Å, respectively. Similarly, the peak pore diameters calculated from CT isotherms using the BJH and Naono methods were 24 and 28 Å. It was found that the PSDs analyzed by the BJH method were underestimated compared to that from Naono method.