Significantly enhancing CO2 adsorption on Amine-Grafted SBA-15 by boron doping and acid treatment for direct air capture

[Display omitted] •Boron-doped SBA-15 mesoporous silica was subjected to an acid treatment to remove boron.•The acid treatment forms “hydroxyl nests” that increase the surface silanol density.•The increased silanols led to higher amine grafting and consequently significantly increased CO2 capacities (by more than 100%).•This novel method was tested under DAC conditions with both dry and humid air feed. Among the most studied adsorbents for CO2 capture is amine-grafted mesoporous silica SBA-15. In this work, boron, a heteroatom, was incorporated into the SBA-15 framework and removed by acid treatment to increase the amount of surface hydroxyl groups. It was discovered that the removal of boron resulted in the formation of silanol nests, with four silanol groups in each nest. Compared with the common method of air calcination for SBA-15, acid-treated boron doped SBA-15, exhibited higher silanol density, as well as higher amine loading after amine grafting. This work is the first to study the use of the silanol nests to graft amines and interact with CO2 directly; the results show more than doubling of the CO2 adsorption capacity for direct air capture.