Cooperative effects for carbon dioxide capture in nanoporous, bifunctional organosilica materials

• Applicants: Professorin Dr. Karin Hauser; Professor Dr. Sebastian Polarz
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Analytical Chemistry ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 436399771

Atmospheric carbon dioxide (CO2) is an example for a plentifully available waste product. The chemical conversion of waste products into valuable compounds is highly desirable, in particular when no significant amounts of energy or other resources are consumed. The first necessary conversion step is the fixation of CO2 from the gas-phase. Sustainability is hardly realized considering the currently applied wet process, the so-called amine washing. Thus, numerous scientists became interested in developing solid adsorbents for carbon capture applications. The interplay between CO2 capture and release, the latter being required for succeeding process steps and the regeneration of the material, makes fine-tuning of the adsorption enthalpy desirable. Nanoporous silica materials with surfaces containing primary amines have already been demonstrated to be promising. However, the literature discusses almost exclusively mono-functional materials comprising only one single (amine) moiety. Here starts the current project. We want to understand, how the CO2 adsorption properties of a nanoporous material change, when an additional moiety is present on its surface in direct vicinity to the amine group. Such neighboring group effects have been described in only few papers, but a systematic, experimental study is missing. Half of the project is focused on materials synthesis providing bifunctional organosilica aerogels with monolithic shape. Close collaboration takes place with the physical chemistry part of the project, which analyzes the adsorption behavior using (T-dependent) volumetric methods as well as spectroscopic methods, most importantly infrared (IR)-spectroscopy including spatially resolved techniques. We expect that uptake capacities, adsorption enthalpies and kinetic data enable us to identify which neighboring group leads to strong interaction effects and why. After identification of promising combinations among amine- and neighboring groups, another parameter space opens up, namely the relative abundance of both moieties to each other. We will examine this parameter space by exploiting new materials characterized by chemical gradients, in which the density of one constituent systematically varies along one spatial coordinate. The anisotropic modification of the monoliths using click chemistry (azide-alkyne; thiol-alkene) will be applied for synthesizing the gradient materials. The uptake of CO2 can then be studied at different positions of the gradient materials using IR microscopy. The existence of a gradient material shall open new research possibilities, for instance for studying anisotropic and directional transport in the material.

• DFG Programme: Research Grants