Formaldehyde interactions with oxygen- and nitrogen-functionalized carbonaceous surfaces in the presence of moisture: Computational approach vs experimental results

Theoretical studies of physical adsorption of formaldehyde and water (through a hydrogen bond formation), as well as chemisorption of formaldehyde (through a covalent CC bond formation) on the functionalized graphene surfaces were carried out. Various functional groups that are likely to exist at graphene surface edges, including hydroxyl, amine, carboxyl, amide, pyrrole, pyridine, lactam and imide groups were considered as interacting with HCHO. In the case of physical adsorption, hydroxyl, amine and amide groups showed the highest affinity towards formaldehyde, and lactam, carboxyl and hydroxyl groups towards water with stabilization energies in the range of 7.8-8.2 kcal mol- 1 and 8.2-9.9 kcal mol- 1 for formaldehyde and water, respectively. This effect was magnified when additional hydroxyl group(s), capable of forming hydrogen bonds with a specific target group, were present in its vicinity. For more than 50% configurations, physical adsorption favors water molecules. However, chemisorption of formaldehyde also occurred on surface functionalized with hydroxyl groups at room temperature since the electron rich graphene pi-electron system initiated CHCHO-Cgraphene bond formation. This process requires overstepping the energy barrier of merely ca. 2.5 kcal mol- 1 which means that it easily occurs at room temperature without an external catalyst. The opposite (desorption) reaction could not proceed as the energy barrier exceeded 30 kcal mol- 1. Similar reaction, less energetically favorable though, was shown to take place in the case of amine functionality.