Enhanced formaldehyde-vapor adsorption capacity of polymeric amine-incorporated aminosilicas

Airborne formaldehyde, which is a highly problematic volatile organic compound (VOC) pollutant, is adsorbed by polymeric amine-incorporated silicas (aminosilicas), and the factors that affect the adsorption performance are systematically investigated. Three different types of polymeric amines 1) poly(ethyleneimine) branched (PEIBR); 2) poly(ethyleneimine) linear (PEILI); and 3) poly(allylamine) (PAA) are impregnated into two types of porous silicas [SBA-15 and mesocellular foam (MCF) silicas] with systematic changes of the amine loadings. The adsorption results demonstrate that the adsorption capacity increases along with the amine loading until the polymeric amines completely fill the silica pores. This results in the MCF silica, which has a larger pore volume and hence can accommodate more polymeric amine before completely filling the pore, giving materials that adsorb more formaldehyde, with the largest adsorption capacity, q, of up to 5.7 mmolHCHO  g(-1) among the samples studied herein. Of the three different types of polymers, PAA, comprised of 100 % primary amines, showed the highest amine efficiency μ (mmolHCHO/mmolN) for capturing formaldehyde. The chemical structures of the adsorbed formaldehyde are analyzed by (13)C cross-polarization magic-angle spinning (CP-MAS) NMR, and it is demonstrated that the adsorbed formaldehyde is chemically attached to the aminosilica surface, forming hemiaminal and imine species. Because the chemical adsorption of formaldehyde forms covalent bonds, it is not desorbed from the aminosilicas below 130 °C based on temperature-programed-desorption (TPD) analysis. The high formaldehyde-adsorption capacity and stability of the trapped formaldehyde on the amine surface in this study reveal the potential utility of aminosilicas as formaldehyde abatement materials.