Polyethylenimine-Functionalized Graphene Oxide Aerogel Microspheres Enabled the Synergistic Physical–Chemical Adsorption of Formaldehyde

The extensive hazards of formaldehyde (FA), as a typical carcinogenic compound present in daily life, necessitate the urgent development of effective removal strategies. Herein, graphene oxide aerogel microspheres (GOAMs) were initially fabricated via a high-pressure spraying and freeze-drying method. In the subsequent prethermal reduction process, partially reduced GOAMs (rGOAMs) were yielded to maintain the sphericity of the microspheres, while polyethylenimine (PEI) was further covalently grafted onto rGOAMs through an amidation reaction between the remaining carboxyl groups on rGOAMs and the amine groups of PEI to obtain PEI@rGAMs, accompanied by the formation of strong hydrogen bonding, resulting in enhanced reduction of rGOAMs with a relatively high carbon-to-oxygen (C/O) ratio, and mitigating restacking of graphene sheets. As the molecular weight and content of PEI increased, the sphericity, specific surface area, and pore volumes of the microspheres decreased, while bulk densities increased, attributed to mass increment and partially blocked pore channels induced by surface-grafted PEI. Compared with rGOAMs, a significant enhancement in mechanical strength (55.5% increase) was achieved for PEI@rGAMs, enabling structural stability under applied stress. Meanwhile, FA removal ratio/adsorption capacities exhibited remarkable improvement, increasing from 4.8%/10 mg·g –1 to 93.8%/153.8 mg·g –1, respectively. The FA adsorption behavior of PEI@rGAMs conformed to the pseudo-second-order kinetic model, while imine structures (−C═N−) formed via reaction between FA and −NH 2 on the microsphere confirmed that the adsorption process was primarily dominated by chemical interactions rather than solely physical adsorption mechanisms, contributing to a significantly synergistic physical–chemical adsorption effect. When PEI@rGAMs were utilized as fillers to prepare polyoxymethylene (POM) composites, they effectively reduced the formaldehyde emission amount (FEA) of POM.