The impact of water co-adsorption on the removal of formaldehyde from the indoor air by oxygen-rich activated carbons: A theoretical and experimental study

Surface oxygen modification of activated carbon has been considered an effective sorbent to remove formaldehyde from indoor air, while the role of co-existing moisture on formaldehyde adsorption by oxygen-rich carbons is unclear. This study investigates the dynamic impact of water on formaldehyde adsorption from simulated indoor air was studied experimentally and theoretically. Among them, the improvement of formaldehyde adsorption on oxygen-rich activated carbon originated from forming stronger hydrogen bonds between oxygen functional groups and formaldehyde compared to conventional van der Waals force. However, the more vital interaction forces between water and oxygen functional groups by forming more hydrogen bonds and the pore blockage by accumulated water molecules around adsorption sites with the increasing adsorption time became the significant barriers of formaldehyde adsorption on carbon surface in a wet environment. Oxygen functional groups with pre-adsorbed water/formaldehyde can accommodate at least one more water while it can hardly adsorb another formaldehyde due to the weak interaction force that can easily be replaced by water molecules. Formaldehyde cannot form hydrogen bonds with the double bond O atom of the carboxyl group, but water can. The sustained adsorption capacity of water is much stronger than that of formaldehyde.