Synergistic modulation of in-plane N-doping and intrinsic vacancy defects in activated carbon for enhanced formaldehyde adsorption.

To address the inherent limitations of the nonpolar surface of activated carbon in polar formaldehyde adsorption, this study introduces a synergistic modulation strategy that combines in-plane nitrogen doping with intrinsic vacancy defects. Notably, the optimized co-doping material (NVAC-750) achieved a 1.65-fold increase in breakthrough time and a 4.80-fold improvement in adsorption capacity compared with pristine AC, demonstrating pronounced synergistic enhancements. Vacancy defect activated carbons (VACs), and N-doping vacancy defect activated carbons (NVACs) were successfully produced from pristine activated carbon (AC). Their nitrogen configurations and defect levels were comprehensively verified by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, respectively. The impacts of these defects on formaldehyde adsorption were systematically examined using a fixed-bed dynamic adsorption system combined with density functional theory (DFT) calculations. The results indicated that N-doping increases carbon surface polarity, with pyrrolic nitrogen specifically reinforcing electrostatic interactions with formaldehyde molecules. Intrinsic vacancy defects significantly boosted dispersion interactions by reshaping the van der Waals potential and improving surface charge redistribution. This substantial enhancement arises from the dual synergistic modulation of electrostatic and van der Waals potentials on the carbon planes. The study clarifies the quantum chemical mechanism governing the synergy between the two-defect types in the adsorption of polar molecules from an electron transfer perspective, thereby establishing a theoretical basis for designing advanced functional carbon-based adsorbents.