Tether loadings and CO2 adsorption capacities are typically reported on a mass or volume basis. However, to understand molecular level phenomena at the gas-solid interface, it is helpful to compare capacities on a surface area basis. Tether loadings and CO2 adsorption capacities were determined to substrates of varied morphology and levels of hydration. Materials prepared from high surface area HMS gave higher N contents and CO2 adsorption capacities per unit mass, yet lower loadings per square nanometer relative to materials prepared from the lower surface area silica gel 40. Longer reaction times led to improved capacities on a unit surface area basis. However, reducing the level of hydration or the average pore diameter of the substrate (within the range examined) did not affect loading capacity.