The existence of more than one functional entity is fundamental for materials, which are desired of fulfilling complementary or succeeding tasks. Whereas it is feasible to make materials with a homogeneous distribution of two different, functional groups, cases are extremely rare exhibiting a smooth transition from one property to the next along a defined distance. We present a new approach leading to high-surface area solids with functional gradients at the microstructural level. Periodically ordered mesoporous organosilicas (PMOs) and aerogel-like monolithic bodies with a maximum density of azide groups were prepared from a novel sol-gel precursor. The controlled and fast conversion of the azide into numerous functions by click chemistry is the prerequisite for the implementation of manifold gradient profiles. Herein we discuss materials with chemical, optical and structural gradients, which are interesting for all applications requiring directionality, for example, chromatography.

We used spatially and time-resolved electron paramagnetic resonance (EPR) spectroscopy to study diffusion of guest molecules within solvent filled aerogel monoliths. We experimentally obtained the time-dependent spin density of EPR active guest molecules ρ 1d (y,t), numerically solved the diffusion equation to simulate ρ 1d (y,t), and determined the macroscopic translational diffusion coefficients for different aerogels and guest molecules. Simultaneously, we determined the microscopic diffusion coefficient by spectral simulation. We show that diffusion in the aerogels under study is dominated by the tortuosity of the pore system but not by surface effects.

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The existence of more than one functional entity is fundamental for materials,w hich are desired of fulfilling complementary or succeeding tasks.W hereas it is feasible to make materials with ah omogeneous distribution of two different, functional groups,cases are extremely rare exhibiting as mooth transition from one property to the next along adefined distance.Wepresent anew approach leading to highsurface area solids with functional gradients at the microstructural level. Periodically ordered mesoporous organosilicas (PMOs) and aerogel-like monolithic bodies with am aximum density of azide groups were prepared from anovel solgel precursor.T he controlled and fast conversion of the azide into numerous functions by clickc hemistry is the prerequisite for the implementation of manifold gradient profiles.H erein we discuss materials with chemical, optical and structural gradients,w hicha re interesting for all applications requiring directionality,for example,chromatography.

Heterogeneous catalysis can be understood as a phenomenon which strongly relies on the occurrence of thermodynamically less favorable surface motifs like defects or high-energy planes. Because it is very difficult to control such parameters, an interesting approach is to explore metastable polymorphs of the respective solids. The latter is not an easy task as well because the emergence of polymorphs is dictated by kinetic control and materials with high surface area are required. Further, an inherent problem is that high temperatures required for many catalytic reactions can also induce the transformation to the thermodynamically stable modification. Alumina (AlO) was selected for the current study as it exists not only in the stable α-form but also as the metastable γ-polymorph. Kinetic control was realized by combining an aerosol-based synthesis approach and a highly reactive, volatile precursor (AlMe). Monolithic flakes of AlO with a highly porous, hierarchical structure (micro-, meso-, and macropores connected to each other) resemble so-called aerogels, which are normally known only from wet sol-gel routes. Monolothic aerogel flakes can be separated from the gas phase without supercritical drying, which in principle allows for a continuous preparation of the materials. Process parameters can be adjusted so the material is composed exclusively of the desired γ-modification. The γ-AlO aerogels were much more stable than they should be, and even after extended (80 h) high-temperature (1200 °C) treatment only an insignificant part has converted to the thermodynamically stable α-phase. The latter phenomenon was assigned to the extraordinary thermal insulation properties of aerogels. Finally, the material was tested concerning the catalytic dehydration of 1-hexanol. Comparison to other AlO materials with the same surface area demonstrates that the γ-AlO are superior in activity and selectivity regarding the formation of the desired product 1-hexene.