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

Abstract

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.

Mesoporous Nanocast Electrocatalysts for Oxygen Reduction and Oxygen Evolution Reactions

“…It results in well-defined nanostructured (mixed) oxides that are of major interest for advanced investigations especially regarding the effect of the materials morphology, porosity and mesostructure on the electrocatalytic performances. For instance, using nanocasting, one may discriminate the role of the parent silica network dimensionality and its consequences on the nanocast, both from a structural and functional point of view, i.e., 2D vs 3D pore structure [34]. In the same way, the effect of the pore size and particle morphology might be systematically rationalized owing to the nanocasting process [35][36][37].…”

“…Inorganics 2019, 7, x FOR PEER REVIEW 6 of 21 characteristics of the nanocast oxides on the electrochemical properties of the samples will be discussed in the following sections in more detail. Images a, b, c [39] and d [34] were reprinted with a permission of © 2014 American Chemical Society.…”

“…Catalytic current measurements were performed in aqueous KOH electrolytes. The current density for ordered [39] and d [34] were reprinted with a permission of © 2014 American Chemical Society.…”

Recent Advances in the Separation of Rare Earth Elements Using Mesoporous Hybrid Materials

“…Based on their pore sizes, nanoporous materials can also be classified into four types: microporous (<2 nm), mesoporous (2–50 nm), macroporous (>50 nm), and hierarchically porous materials which combine two or three of the above pore size ranges . In the case of silica‐based mesoporous materials, some of the most interesting materials, both from the industrial and fundamental research points of view, are ordered mesoporous silica (OMS) materials with a well‐defined pore network such as MCM‐41 and SBA‐15 (OMS with hexagonal array of cylindrical pores, with pore size of 2–15 nm), KIT‐6 (OMS with highly interconnected 3‐D cubic structure),, and bimodal mesoporous‐macroporous silica with hierarchical architectural properties (Figure ) ,. Cooperative assembly between “soft” organic templates (e. g., triblock copolymers, quaternary cationic surfactants, C n H 2n+1 N(CH 3 ) 3 Br (n=8‐22)) and inorganic precursors (e. g., tetraethylorthosilicate (TEOS), tetramethylorthosilicate (TMOS)) in either acidic or basic media is generally involved, forming inorganic/organic mesostructured composites .…”

“…After template removal, the resulting nanoporosity of these materials ensures their particularly high specific surface area (typically >800–1000 m 2 g −1 ), which undoubtedly allows for a high degree of contact and functionalization. The pore size, pore shape, pore connectivity, and wall thickness of silica materials can be modulated precisely as a function of the synthesis parameters, such as choice of the template (e. g., surfactant molecule with different chain length), solution pH, hydrothermal treatment conditions (temperature and time), and addition of secondary structure‐directing agents such as co‐surfactant, swelling agents, and electrolytes ,,,. Another interesting aspect of these materials is the possibility to synthesize hierarchically structured silica‐based porous monoliths via sol‐gel processes allowing versatility both in terms of size and morphology (shape), which should be particularly beneficial for industrial applications ,.…”