Polyethyleneimine-modified activated biochar derived from rice husk ash: material development and preliminary formaldehyde adsorption study

Abstract This study developed polyethyleneimine (PEI)−modified activated biochar (ABC) as an efficient adsorbent for efficiently removing formaldehyde (HCHO) gas. The activated biochar was derived from rice husk ash (RHA) through chemical activation combined with ultrasonic treatment, effectively eliminating the need for high−temperature calcination, a common step in traditional methods. To better understand the structural and surface properties of this modified material, the Polyethyleneimine−modified activated biochar was meticulously characterized using advanced analytical techniques, including scanning electron microscopy (SEM), energy dispersive X–ray spectroscopy (EDS), X–ray diffraction (XRD), Fourier–transform infrared spectroscopy (FT–IR), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) surface area measurements, and Barrett–Joyner–Halenda (BJH) pore size distribution analysis. The PEI–modified ABC exhibited double the adsorption capacity of unmodified ABC, attributed to the increased density and diversity of active amine functional groups. Kinetic and isotherm studies confirmed that the adsorption process follows a first–order kinetic model and Langmuir isotherm. These results demonstrate the strong potential of biomass–derived adsorbents for cost–effective and sustainable indoor air purification, offering a promising approach to formaldehyde pollution control. Graphical Abstract