<p>Effective removal of indoor formaldehyde (FA) pollution is essential for human health. This study aimed to enhance the FA adsorption performance of coal-based pellet activated carbon (AC) by developing a scalable modification method. A novel approach was introduced using negative pressure pretreatment followed by immersion in a 4-amino-1,2-butanediol (ABDO) solution. This combined method improves chemical functionality and scalability over conventional techniques. Adsorption isotherms followed the Langmuir–Freundlich model, which accounts for surface heterogeneity and mixed monolayer–multilayer adsorption, while kinetics conformed to the pseudo-second-order model, indicating chemisorption as the rate-limiting step–consistent with previous findings on FA removal by functionalized AC. Thermodynamic analysis confirmed that FA adsorption is exothermic and spontaneous. Dynamic tests showed a 32.5% increase in equilibrium adsorption capacity for AC pretreated at 0.011&#xa0;MPa, a pressure determined through preliminary experiments to enhance solvent penetration while preserving pore integrity. Adsorption performance was evaluated in 30 m³ and 3 m³ environmental chambers (21 ± 3°C; 50 ± 5% RH) at FA concentrations of 0.40 ~ 0.60 mg·m^-3. At 0.011&#xa0;MPa, the FA clean air delivery rate (FCADR) increased by 41.2%, and cumulative clean mass (FCCM) tripled versus atmospheric impregnation using an air cleaner at maximum flow. The relative humidity (RH) threshold for FCADR reduction was 65–75%, with pretreatment mitigating losses by 7.4% and 5.7% at 75% and 90% RH, respectively. Performance enhancement was attributed to increased ABDO loading and amino group formation that react with FA via Schiff base reactions. This method offers practical scalability for efficient indoor FA removal under realistic conditions.</p> Graphical Abstract <p></p>