Abstract
This work presents two easy ways for preparing nanostructured mesoporous composites by interconnecting and combining SBA-15 with mixed oxides derived from a calcined Mg–Al hydrotalcite. Two different Mg–Al hydrotalcite addition procedures were implemented, either after or during the SBA-15 synthesis (in situ method). The first procedure, i.e., the post-synthesis method, produces a composite material with Mg–Al mixed oxides homogeneously dispersed on the SBA-15 nanoporous surface. The resulting composites present textural properties similar to the SBA-15. On the other hand, with the second procedure (in situ method), Mg and Al mixed oxides occur on the porous composite, which displays a cauliflower morphology. This is an important microporosity contribution and micro and mesoporous surfaces coexist in almost the same proportion. Furthermore, the nanostructured mesoporous composites present an extraordinary water vapor sorption capacity. Such composites might be utilized as as acid-base catalysts, adsorbents, sensors or storage nanomaterials.
Highlights
Multifunctional nanomaterials are designed to satisfy specific ranged sets of performance requirements
Mg/Al m2/g cm3/g nm molar ratio aØp = average mesoporous diameter; d100 = interlaminar distance determined by X-ray diffraction; average wall thickness (AWT) = average wall-thickness [(2d100/√3 – Ø]; Smic = microporous surface; Smes = mesoporous surface; Sext = external surface, Vmic,Vmes = micro and mesopore volumes; SBET = Smic + Smes + Sext
The increasing water amount adsorbed is favored by the Mg–Al oxide nanocasting improving the water affinity on the composite surface. This can be more visualized by the results showed for sample (Mg/Al)/SBA prepared by the in situ method, which retains 14.5 mmol of H2O/gcomposite, almost three times more water than the calcined hydrotalcite
Summary
Multifunctional nanomaterials are designed to satisfy specific ranged sets of performance requirements. The 734 m2/g BET surface area of the post-synthesis composite, HT/SBA(NC), is higher than that of the calcined Mg–Al hydrotalcite (200 m2/g) and quite similar to the BET surface area of the SBA-15 (785 m2/g). It seems that the calcined hydrotalcite nanoparticles can cover the pores surface of the SBA-15.
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