Selectively Tuned Pore Condensation and Hysteresis Behavior in Mesoporous SBA-15 Silica: Correlating Material Synthesis to Advanced Gas Adsorption Analysis

Regarding the design of SBA-15 silica, substantial efforts were deployed in the past decade in order to understand the mechanism of formation and the effects of the different synthesis conditions on the structure and porosity of the resulting materials. However, better insights into both the tailoring and the characterization of the pore structure of such mesoporous materials are still needed in order to enable the accurate control of adsorption and pore condensation properties in SBA-15. For this, the influence of the synthesis parameters on the properties of SBA-15 silica must be rationalized in terms of their implications for pore architecture, i.e., pore structure and network interconnectivity. Herein, it is demonstrated that pore condensation and hysteresis behavior of inert gases in subcritical conditions confined in ordered mesoporous SBA-15 silica can precisely be modulated as a function of the synthesis parameters. Synthesis conditions were found for generating SBA-15 samples that can be described entirely as a pseudo one-dimensional (1-D) pore system (i.e., pore condensation and hysteresis behavior are an intrinsic property of the liquid–vapor transition in a finite volume, in agreement with the independent open pore model). However, the data also revealed that distinct synthesis conditions allow for the preparation of SBA-15 with pore condensation properties affected by cooperative pore network effects, mimicking the behavior observed for materials with a pristine three-dimensional (3-D) interconnected pore network topology, such as KIT-6 silica. Therefore, this comprehensive study shows that SBA-15 should be best regarded as a family of solids with easily adjustable porosity, ranging from corrugated and/or distorted pore systems to highly interconnected networks of channels. The effect of each different synthesis parameter on the final pore size of SBA-15 was carefully monitored, and a threshold acid concentration range for optimal pore size variation was found. In addition to substantial progress in the SBA-15 synthesis, such in-depth characterization of a “model” ordered mesoporous material coupled with advanced application of state-of-the-art NLDFT methods is of prime importance both for the development of fundamental research on the topic and for the applications requiring tailored high surface area materials with selectively tuned pore structure.