Porous substrates play a major role in devices requiring the flow of fluids such as in filters and membranes. Porous substrates are also extensively used for the preparation of inorganic membranes for microfiltration, [1][2][3] desalination, [4][5][6][7] gas separation, [8][9][10][11] and percrystallization processes. [12,13] These inorganic membranes are known as asymmetric membranes as they are conventionally prepared by coating ceramic [14][15][16] or carbon [17][18][19] thin films as top layers on porous substrates. The importance of the porous substrate is to provide the mechanical strength otherwise not available in thin films. Many inorganic materials such as ceramics [20][21][22] and stainless steel [23][24][25] have been manufactured as porous substrates, though alumina is the most used material due to lower costs and processing versatility. Porous substrates come in several geometries such as tubes, [14,[26][27][28] hollow fibers, [29][30][31] and flat surfaces. [19,32] Traditionally, inorganic porous substrates are prepared from conventional ceramic processes such as slip-casting, [33,34] extrusion, [35,36] dry pressing, [37] tapecasting, [38][39][40] and phase inversion hollow fibers. [41,42] A relatively more recent method is the freeze-casting technique for processing porous ceramic substrates. [43][44][45][46] Due to the ability of forming an aligned pore structure, this technique can overcome problems associated with lower fluid fluxes conferred by conventional ceramic processing methods such as tortuous pore structure, constrictions, and dead-end and isolated pores. [47] Freeze-cast starts with the preparation of a stable ceramic suspension (or slurry) at normal conditions followed by controlled freezing of the solvent of the ceramic

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In the present report, Al-SBA mesoporous materials were investigated for use as water adsorbents. Different precursors for aluminum were investigated: aluminum sulfate and nitrate, boehmite, and aluminum tri-sec-butoxide. Furthermore, three different procedures for addition of the silica and alumina sources were tested. Samples were characterized by nitrogen adsorption to observe their textural characteristics and by thermogravimetric desorption of water to address their performance. The sample synthesized with aluminum tri-sec-butoxide as aluminum precursor and a pre-hydrolysis step of the silica source presented the highest adsorption capacity: 1057 g.kg -1 . It was also observed that water attaches more strongly to Al-containing samples than to pure silica, and that water adsorption capacity is more related to the pore volume of samples than to their surface area. This work has shown that functionalizing SBA-15 materials with aluminum is a promising strategy for producing water adsorbents with improved performance and potential for many applications.

Mesoporous silica materials have been widely investigated for their great potential as competitive adsorbents and catalysts in different areas, due to their ordered and uniform porous structures and high surface area. In order to increase the availability of these materials, the need to granulate them becomes vital for an efficient performance in industrial units. This study reports the production and characterization of clay-free granules of SBA-15 mesoporous silica, by applying the extrusion technique. The suggested methodology uses only methocel as the organic binder, which is removed after calcination. The granulation process was successfully achieved, producing pure granules of SBA-15 mesoporous silica, in size of millimeters, with 8.3 MPa of compacting pressure (by axial crushing test). The surface area and pore volume of SBA-15 mesoporous silica granules (calcined at 800 ºC) were around 392 m 2 /g and 0.53 cm 3 /g, respectively.

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Water vapor adsorption is a process of great importance for several industries. Because of that, new materials formed by mesoporous silica with metallic heteroatom functionalization have been studied for water adsorption. This functionalization process is still little studied in the literature, with many topics remaining to be evaluated. One of them is how each functionalization method (grafting and co-condensation) influences the generation of isomorphic substitution or extra-framework oxides. Another is which of these configurations is most interesting for water adsorption. This work aims to address both questions. For this, two groups of samples were synthesized using grafting and co-condensation for the insertion of Al, Ti, Zr and Li into mesoporous silica SBA-15. These samples were analyzed using nitrogen adsorption, high resolution scanning microscopy, energy dispersive X-ray spectroscopy, magic angle spinning nuclear magnetic resonance, Fourier transform infrared spectroscopy, pyridine adsorption and water adsorption. These techniques revealed that the co-condensation approach used in this work was most interesting for water adsorption at low partial pressures. This occurred because it generated a higher degree of isomorphic substitution, which was found to be the most active configuration of heteroatoms for this application.

Mesoporous silicas are known to be high-performing water adsorbents in high humidity levels due to their large pore volumes. However, for low humidity conditions, these materials typically present a less expressive performance, which is a drawback for many applications. In the present report, mesoporous silica SBA-15 was functionalized with Al, Ti, Zr and Li in order to improve their performance in this condition. The influence of functionalization in porosity, morphology and acidic sites was investigated. Samples with an increased number of acidic sites and with higher microporosity when compared to pure silica were produced. This was responsible for their enhanced performance for water adsorption in low moisture conditions. Sample functionalized with zirconium in SBA-15 synthesis improved the water adsorption capacity of pure silica by three times, reaching up to 127 g kg −1 at a relative pressure of 0.2 and 570 g kg −1 close to saturation pressure. This sample was found to be a promising material to be applied in processes which require high adsorption capacities in both low and high water partial pressure ranges. Moreover, the understanding of the mechanisms behind the heteroatom functionalization can be applied to any silica material in order to enhance its attractiveness towards any polar molecule. Supplementary Information The online version contains supplementary material available at 10.1007/s10450-021-00336-6.

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