Adsorption of naphthalene on nitrogen doped and Group 13 (B, Al, Ga) co-doped graphene surfaces with additional titanium decoration

Abstract This study investigates the influence of titanium decoration on nitrogen and Group 13 (B, Al, Ga) co-doped graphene surfaces for naphthalene adsorption using Density Functional Theory (DFT) at the wB97XD/GENECP–LANL2DZ/def2-SVP level. Geometry optimization showed that all systems preserved the graphene hexagonal framework with localized distortions around dopant and Ti sites, promoting enhanced orbital hybridization. Frontier molecular orbital (FMO) analysis revealed moderate band gaps for the undeco­rated adsorbed systems, 2.612 eV (NAP–B–N@GP) and 2.248 eV (NAP–Ga–N@GP), characteristic of weak π–π driven physisorption. Titanium incorporation significantly altered the electronic structure, increasing the band gaps after adsorption to 3.83 eV (NAP–Ti–Al–N@GP), 4.075 eV (NAP–Ti–B–N@GP), and 2.992 eV (NAP–Ti–Ga–N@GP). Density of states (DOS) analysis confirmed that these changes arise from Ti d-orbital contributions near the Fermi level, directly linking band gap variation to conductivity modulation relevant for sensing. Adsorption energy calculations (in eV) showed favourable adsorptions for all systems, with the strongest interaction observed for NAP–Ti–Ga–N@GP (− 9.551 eV), compared to the undeco­rated systems (− 3.401 to − 4.599 eV). NBO analysis demonstrated enhanced donor–acceptor interactions after Ti decoration, with a stabilization energy of 240.88 kcal/mol for Ti–Al–N@GP. QTAIM results confirmed that undeco­rated systems are governed by weak closed-shell interactions, whereas Ti incorporation induces greater electron density redistribution and partial covalent character. As naphthalene approaches the surface, its π-electrons donate charge to the doped graphene (ΔN > 0). After adsorption, significant back-donation from the dopant and Ti atoms to the π* orbitals of naphthalene occurs, with back-donation energies of 0.324 (Al), 0.327 (B), 0.281 (Ga) and higher values for Ti systems 0.479 (Ti–Al), 0.509 (Ti–B), 0.374 (Ti–Ga), characteristic of a Dewar–Chatt–Duncanson type metal–arene interaction. The large dipole moment observed for NAP–Al–N@GP (17.93 D) and strong polarization in Ti systems further confirm substantial electronic redistribution affecting graphene conductivity. Ti decoration markedly enhances adsorption strength, charge redistribution, and electronic sensitivity. Among all systems, Ti–Ga–N@GP provides the most favourable combination of strong adsorption and electronic response, while Ti–B–N@GP exhibits the strongest bidirectional charge transfer, indicating high sensing potential for naphthalene detection.