It is of significant practical interest to develop high-performance air purifier (AP) for removing carcinogenic volatile organic compounds present ubiquitously in indoor air (e.g., formaldehyde (FA)). In this regard, a portable AP system was designed by loading honeycomb ceramic filters with diaminopropane (DAP)-appended activated carbon (AC). The maximum removal efficiencies (REs) of AP loaded with 10, 20, 30, and 50 %-DAP/AC were 26.2, 28, 88.3, and 89.4 %, respectively, against 5 ppm FA (at 160 L min⁻¹). Hence, the 30 % DAP unit was used mainly in this work. The removal efficiency of 30 %-DAP/AC (160 L min⁻¹), when tested against 2 ppm FA, decreased from 90.3 to 73.2 % with an increase in relative humidity from 0 to 60 %. The performance of the AP unit, when assessed kinetically in terms of the clean air delivery rate (CADR), reached as high as 10.2 L min⁻¹ at the flow rate of 160 L min⁻¹. Isotherm analysis further demonstrated the complex multilayered adsorption behavior of FA. Based on the density functional theory (DFT) simulation, the superiority of DAP/AC for FA adsorption can be attributed to the synergy of covalent (chemisorption) and non-covalent (pore filling and film diffusion) interactions.