Great Location: About Effects of Surface Bound Neighboring Groups for Passive and Active Fine-Tuning of CO2 Adsorption Properties in Carbon Capture Materials

Better carbon capture materials are crucial for managing today’s and the future CO₂ level in the atmosphere. The past focus was on increasing adsorption capacities. One knows by now that controlling the heat of adsorption (DH_ads) is equally important. Is it too low, CO₂ uptake takes place at unfavorable conditions far from ambient and with insufficient selectivity. Is it too high, chemisorption occurs, and the materials can hardly be regenerated. The conventional approach for influencing DH_ads is the modification of the adsorbing center. This paper proposes an alternative strategy. The hypothesis is that fine-tuning of the molecular environment in direct vicinity to the adsorbing center (primary amines) is a powerful tool for the adjustment of CO₂-binding properties. Via click chemistry, any desired neighboring group (NG) can be incorporated on the surfaces of the resulting bifunctional, nanoporous organosilica materials. Passive NGs induce a change of the polarity of the surface, whereas active NGs are capable of a direct interaction with the active-center/ CO₂pair. The effects on DH_ads and also on the selectivity are studied in detail. A situation can be realized on the surface which resembles frustrated Lewis acid-base pairs, and the investigation of the binding-species by ¹³C solid-state NMR indicate that the push-pull effects could play an essential role not only for CO₂ adsorption but also for its activation.