Revealing the pore characteristics and physicochemical properties of silica ionogels based on different sol-gel drying strategies

Highlights: • Monolithic silica ionogels were prepared by following sol-gel method. • Silica ionogels were dried by applying SCD, FD or APD. • Various drying procedure resulted in different morphology for the ionogels. • Monolithic structure was preserved in all methods, even after FD. • SCD leads ionogels to have more superior characteristics than other methods did. -- Abstract: In this study, an exhaustive investigation about the effect of drying methods on the physical properties and microstructures of silica ionogels was conducted. Silica ionogels were synthesized by following one-step sol-gel process and dried either by supercritical, ambient pressure or freeze-drying techniques. After drying periods, characterization studies of the ionogels were carried out by performing FTIR, SEM, BET and TGA analyses. Results have shown that, although they all appeared in a monolithic structure, their microstructural pattern were completely different. Supercritically dried silica ionogel resulted in mesoporous structure with superior properties such as low density (ρ = 0.21 kg/m³), high porosity (ϕ = 90%) and high surface area (646 m²/g). On the other hand, silica ionogel dried in ambient conditions comprised both micro-meso pores and the pores are mainly closed form and freeze dried ionogel had non-homogeneous pore distribution with relatively larger pores.