Abstract
Heterostructures constructed with mesoporous silica and layered double hydroxides are interesting for catalytic and drug delivery applications. Different arrangements between these phases are possible. In this study, we prepared heterostructures by embedding layered double hydroxides phases [M4Al2(OH)12](CO3) (M = Mg2+ or Zn2+) within the MCM41 mesoporous silica type phase. According to our results, the most critical step of this preparation is the removal of the organic template used to create the mesopores in the silica phase, which can be done by calcination or extraction with solvent, normally a mixture of ethanol and a mineral acid. The results reported in this study demonstrate that both can cause structural changes in the components of the heterostructure at different extensions. Calcination promoted the collapse of the layered hydroxide phases. Attempts made for their reconstruction through rehydration, which is a quite known process, were not completely effective and also dependent on the chemical composition of the layered phase. The complete template removal with preservation of the layered phases was possible using the extraction method but by replacing the mineral acid with NH4Cl. However, some discrete structural changes were identified possibly due to a partial lixiviation of Al3+ from the double hydroxide layers.
Highlights
The first study about a heterostructure prepared by combining mesoporous silica (MS) with layered double hydroxide (LDH) was reported in 2008.1 This material was produced with the intention of improving the catalytic activity of the magnesium-aluminum LDH (Mg4Al2-LDH) by restricting the lateral growth of the hydroxide particles by preparing them directly inside the mesopores of the SBA15 silica
We evaluated if the modifications made in the synthetic procedure can facilitated the process of template removal and can influenced the porosity of the formed heterostructures
We evaluated the influence of the chemical composition of the layered double hydroxides on the structural stability and porosity of heterostructures produced with the LDH phases embedded within mesoporous silica
Summary
The first study about a heterostructure prepared by combining mesoporous silica (MS) with layered double hydroxide (LDH) was reported in 2008.1 This material was produced with the intention of improving the catalytic activity of the magnesium-aluminum LDH (Mg4Al2-LDH) by restricting the lateral growth of the hydroxide particles by preparing them directly inside the mesopores of the SBA15 silica. One of the critical steps in the preparation of heterostructures containing the layered phase embedded within the mesoporous silica matrix is the template removal
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