Unravelling synergetic removal of airborne carbonyls and inhibition of CO2 off-gas over robust amine-functionalised MnO2

Abstract Since the first standard available 2,4-dinitrophenylhydrazine (DNPH)-coated solid sorbents in the determination of carbonyls in the 1990s, studies of the ultrafast chemoselective reactions that form stable Schiff bases (C = N) in catalytic processes that remove airborne carbonyls have been scarce. Here, amine-functionalised MnO2 is engineered with a method involving freezing–thawing cycles, and interfacial structure and configuration of amino groups at the metal oxide surfaces that usually decay in nature are mechanically enhanced. Through molecular level characterisation and measurements, we find strong hydrogen bonds between robust amino groups and metal oxide sites in the well-ordered H5O2+ overlayer and the amino groups are negatively charged under environmental acidity. Compared with a DNPH control, we improve biocompatible amine-functionalised MnO2 to achieve the complete removal of sub-ppm formaldehyde, acetaldehyde and acetone synergically. Carbonyls and intermediate deprotonated hydrazones (–N = C(NH2)) are persistently chemosorbed and decomposed into recyclable bicarbonated amides (NH3+HCO3−), which are reservoirs or sinks of secondary aldehydes and routine CO2 off-gas.