DFT Analysis of Short-Chain PFAS Absorption via Functionalized Biochar

Research into Per- and Polyfluoroalkyl Substances (PFAS) removal from aqueous solution has recently become a priority due to the toxicological dangers PFAS presents to humans and wildlife. This study has examined the absorbance of short-chain Perfluorobutanoic Acid (PFBA) on Biochar using a first principal computational tool known as Density Functional Theory (DFT). Biochar has shown promise as a cheap and easily scalable adsorption medium. However, Pristine Biochar has low rates of adsorption, requiring functional groups to increase its effectiveness. The computational nature of DFT means that the functionalized Biochar can be studied more quickly than in a lab setting. This helps narrow down the potential options for functional groups without needing to fully synthesize the molecules. This study examined the interaction of anionic PFBA with graphene-modeled Biochar at the atomic level. The graphene-modeled Biochar was functionalized with -NH₂, -N(CH₃)₃, and -CH₂N(CH₃)₃ groups. Five PFBA configurations were tested for each type of Biochar. Biochar functionalized with -N(CH₃)₃ or -CH₂N(CH₃)₃ was shown to be more effective at adsorbing anionic PFBA compared to Pristine and -NH₂ functionalized Biochar. Based on our results, the effectiveness of the trimethylamine group in adsorption was not hindered by the additional -CH₂. This was shown using Adsorption Energy, Minimum Interaction Length, and the Electrostatic Potential (ESP).