Synthesis and Performance of Nanostructure Templated Silica Membranes Surface-modified by Two Different Procedures

Uncontrolled population growth and increased consumption of fossil fuels have led to the emission of pollutants and greenhouse gases. This is mostly a concern for reducing emissions of greenhouse gases, such as carbon dioxide because of its impact on global climate change1,2. The presence of carbon dioxide in the natural gas mixture can lead to lower heating value of gas, corrosion of processing facilities and pipelines3–5. Thus, the separation of carbon dioxide from gas streams by a proper and highly efficient process is essential. Membrane processes, owing to their various advantages, are the interest of researchers in the field of gas separation. Meanwhile, the use of inorganic membranes has increased because of their chemical resistance in high temperatures and corrosive environments, appropriate selectivity, abrasion resistance and stable pore structure in carbon dioxide separation from flue gas6–8. The microporous silica membranes are the most important examples of non-crystalline or amorphous membranes9. These kinds of membranes have a thin separator layer (about 50–200 nm) with the molecular sieve property, resulting in high permeate flux and selectivity. Therefore, in comparison with other inorganic membranes, they are utilized for separation of acid gases10. The most common method to fabricate microporous silica membranes is the sol-gel method. The sol-gel method was firstly used by Leenaars et al.11 Controlling the pore size of the membrane, especially the smaller pores, the porosity control, simplicity and homogeneity of the layer are the main advantages of the sol-gel method11,12. The silica membranes modified by metal oxides or hydrophobic silanes with respect to pure silica membranes, show high stability in the presence of hot steam13–15. Thus, displacement of hydroxyl groups (–OH) with hydrophobic groups (–CH3) with a hydrophobic methyl template is an easy strategy to reduce water absorption and maintain the microporous structure of silica membranes16. In this case, the micropores were produced by using the thermal degradation of organic ligands (templates), which are covalently bonded to the silica network. The silica membranes with methyl template had high separation rates, and change in the carbon dioxide permeance with time was less observed17. It is notable that micropores created in this way, have controlled size (depending Synthesis and Performance of Nanostructure Templated Silica Membranes Surface-modified by Two Different Procedures