Simulation study of the effect of OGs on the adsorption of formaldehyde on modified activated carbon

Context To explore the impact of OGs (OGs) on formaldehyde (HCHO) adsorption by modified activated carbon, this paper studied the influence of OGs on HCHO adsorption characteristics, varying the groups including ester, carboxyl, and hydroxyl. Employing density functional theory (DFT), the effects of various OGs on the structure of N-doped activated carbon through GGA-PBE exchange-correlation functionals by Materials Studio combined with Gaussian software. The types of weak interactions during the adsorption process were calculated by RDG, elucidating the mechanism through which the three OGs affect HCHO adsorption on N-doped activated carbon. The dynamic adsorption process of HCHO was simulated by molecular dynamics (MD). The influence and proportion of OGs on HCHO adsorption were subsequently analyzed using van der Waals and electrostatic interactions, determining differences in formaldehyde adsorption effects across OG types. The carboxyl group exhibits the most robust synergistic adsorption effect on the modified activated carbon. There is a notable alteration in the position and distribution of electrostatic potential extremes observed following carboxyl modification. The calculation results show that the adsorption energy of hydroxyl groups on modified activated carbon is the highest, at −5.07 kcal/mol, with a transfer charge of 0.014 e. Following the introduction of carboxyl groups, the proportion of electrostatic interactions escalated from the initial 24% to 38%. This study will provide new ideas for guiding the design of activated carbon for efficient adsorption of formaldehyde. Methods The modified activated carbon fragments of three OGs were constructed by Materials Studio and Gaussian software, and the surface electrostatic potential polarity and area distribution, charge change, adsorption energy, and transferred charge of each molecular fragment were calculated. Moreover, cell models of OGs with the same dimensions were constructed to simulate the adsorption amount, heat of adsorption, interaction energy, radial distribution function, and hydrogen-bonding interactions for methane at room temperature and pressure. The results were consistent with the DFT simulations.