Environmentally friendly gas phase grafting of mesoporous silicas

Tumbling chemical vapour deposition (T-CVD) is presented as a novel methodology for the gas phase grafting (GPG) of a variety of alkoxy- and chloro-silanes on mesoporous silica. Compared to conventional solution grafting techniques, this method is sustainable, and cost- and time-effective. Although the method was successfully applied to a variety of silanes, application of the gas phase methodology to the preparation of propylamine-grafted CO2 adsorbents (AGA) is presented in depth, for illustration. A detailed comparative characterization of AGAs derived from GPG and solution grafting is discussed. Unprecedentedly high propylamine contents were achieved (up to 5.51 mmol/g), indicating enhanced accessibility of surface hydroxyl groups and more favorable packing of propylamine chains on the support surface, thereby enabling much higher surface density compared to traditional solution grafting procedures. The gas phase method achieves higher grafting efficiency, with less silane waste, necessitating recycling. Furthermore, not only higher CO2 uptake, but also higher amine efficiency (CO2/N) was obtained from GPG-derived adsorbents compared to those obtained by solution grafting. GPG was also found to be suitable for grafting granules and pellets with limited mechanical strength, which may otherwise be crushed while being stirred during grafting in solution.