Method of capturing carbon dioxide from a gas mixture

A method of capturing CO2 from a gas mixture, comprising:

• contacting the gas mixture with an aminated siliceous adsorbent to adsorb at least a portion of the CO2 onto the aminated siliceous adsorbent, thereby forming a loaded aminated siliceous adsorbent and a gas stream depleted in CO2 compared to the gas mixture,
• wherein the aminated siliceous adsorbent has disordered mesopores and a carbon content of 24 to 30 wt. %, based on a total weight of the aminated siliceous adsorbent,
• wherein the aminated siliceous adsorbent is a reaction product of:
• dried acidified rice husk ash having disordered mesopores, an oxygen content of 40 to 46 wt. % and a silicon content of 34 to 40 wt %, each based on a total weight of the dried acidified rice husk ash;
• and
• an amino silane;
• and
• wherein amine functional groups are present on an external surface and within the mesopores of the dried acidified rice husk ash.