Original Article Effect of pore size and surface chemistry of porous silica on CO 2 adsorption Thongthai Witoon 1,2* and Metta Chareonpanich 1,2 1 National Center of Excellence for Petroleum, Petrochemicals and Advance Material, Department of Chemical Engineering, Faculty of Engineering, 2 Center for Advanced Studies in Nanotechnology and Its Applications in Chemical Food and Agricultural Industries, Kasetsart University, Chatuchak, Bangkok, 10900 Thailand. Received 1 December 2011; Accepted 10 April 2012 Abstract In the present study, porous silica synthesized using sodium silicate as a low-cost raw material was selected as a CO 2 sorbent. The effects of pore size and amount of silanol content on CO 2 adsorption capacity were investigated. The physical properties and surface chemistry (silanol content) of the porous silica products were characterized by means of N 2 -physi- sorption, Fourier transform infrared spectroscopy and thermogravimetric analysis technique. The pore size of the porous silica materials did not affect the equilibrium CO 2 capacity; however the porous silica with large pore size could enhance the diffusion of CO 2 . The amount of silanol content was found to be a key factor for the CO 2 adsorption capacity. A greater CO 2 adsorption capacity would be obtained with an increase of the silanol concentration on the surface of the porous silica materials. Keywords: porous silica, sodium silicate, pore size, silanol content, CO 2 adsorption Songklanakarin J. Sci. Technol. 34 (4), 403-407, Jul. - Aug. 2012 1. Introduction The problem of global warming caused by CO 2 emis- sion, which is the main part of greenhouse gases, has raised serious concerns. The combustion of fossil fuels is one of the major sources of CO 2 emission to the atmosphere. However, due to the fact that these fossil fuels are essential as they supply more than 70% of the world’s energy consumption. It is therefore important to find novel technologies that can allow us to utilize fossil fuels with less CO 2 emission. Gener- ally, there are three steps for CO 2 management involving separation, transportation, and sequestration (Olajire, 2010). The key point of the CO 2 management is the separation of CO 2 from the flue gas because it contributes 75% to the over- all costs. Various technologies for CO 2 capture, such as absorp- tion, adsorption, cryogenic and membrane technologies, have been proposed and investigated (MacDowell et al., 2010). Among these techniques, adsorption is one of the most pro- mising approaches as it can reduce the cost associated with the capture step. Several porous materials such as zeolite, alumina, activated carbon, and porous silica, have been con- sidered for low temperature CO 2 separation. As the use of low-cost porous material can significantly reduce the cost of CO 2 management, porous silica is then becoming very com- petitive because of its economical potential and availability as it can be produced from the renewable resource such as rice husk ash. Recent research work has been devoted for the de- velopment of the synthesis of porous silica materials of vary- ing sizes in a controllable manner (Witoon et al., 2011), among the different routes are sol-gel process, precipitation, plasma, flame spray pyrolysis, and others. Sol-gel process, which is consisted of hydrolysis and polycondensation re- actions of a metal salt, is an effective method that is preferred * Corresponding author. Email address: fengttwi@ku.ac.th http://www.sjst.psu.ac.th