Orientation-Dependent Adsorption of Light Mercaptans on h‑BN Nanosheets: DFT Insights and Experimental Validation

Creating an adsorbent that is both high-performing and cost-effective is essential for enhancing the adsorption-based removal of sulfur from fuels. This study investigates the adsorption mechanisms of light mercaptans (ethyl, propyl, and butyl) on hexagonal boron nitride (h-BN) nanosheets using density functional theory (DFT), Quantum Theory of Atoms in Molecules (QTAIM), and Natural Bond Orbital (NBO) analyses. Energy minimization reveals the parallel configuration as the thermodynamically favored orientation, while the sideward arrangement demonstrates maximal adsorption affinity. The adsorption energy hierarchy (ethyl < propyl < butyl) correlates directly with molecular size, particularly hydrogen atom count, reflecting enhanced van der Waals interactions for larger alkyl chains. This insight is pivotal for optimizing h-BN gas sensors/filters targeting mercaptans, as ground-state molecular orientation dictates interfacial charge transfer and detection efficacy. AIM and NBO analyses confirm stronger bonding interactions in butyl mercaptan, attributed to its expanded contact surface area, which facilitates increased electron transfer events from mercaptan valence orbitals (S, C, and H) to h-BN's nonbonding states. Notably, experimental validation confirms exceptional agreement between calculated and empirical adsorption energies, underscoring the accuracy of the computational framework. These findings advance the design of h-BN-based adsorbents for the efficient removal of volatile sulfur contaminants in fuel purification systems.