Single-Atom Adsorption on h-BN along the Periodic Table of Elements: From Pristine Surface to Vacancy-Engineered Sites

The adsorption of single atoms on pristine and defected hexagonal boron nitride (h-BN) was systematically investigated using density functional theory. Elements from the first three rows of the periodic table, together with selected transition and coinage metals, were examined on the pristine surface and at boron- and nitrogen-vacancy sites. On pristine h-BN, adsorption is generally weak and dominated by dispersion forces, with measurable chemisorption limited to highly electronegative atoms such as C, O, and F. The introduction of vacancies transforms h-BN into a chemically active material, increasing adsorption energies by one to two orders of magnitude. The boron vacancy strongly stabilizes metallic and electropositive species through coordination to undercoordinated nitrogen atoms, whereas the nitrogen vacancy selectively binds electronegative and covalent adsorbates. Scaling of adsorption energies with elemental cohesive energies distinguishes regimes of physisorption, chemisorption, and substitutional stabilization. These insights provide a unified description of adsorption trends across the periodic table and establish defect engineering as an effective strategy for tailoring the catalytic, sensing, and electronic properties of h-BN.

💡 Research Summary

This work presents a comprehensive density‑functional theory (DFT) investigation of single‑atom adsorption on both pristine and vacancy‑engineered hexagonal boron nitride (h‑BN). Using a 4 × 4 supercell (32 atoms) with a 20 Å vacuum, the authors performed spin‑polarized PBE‑GGA calculations supplemented by Grimme’s D3 dispersion correction. Adsorption energies were defined as E_b = E_h‑BN+ A − E_h‑BN − E_A, and Bader charge analysis together with density‑of‑states (DOS) calculations were employed to quantify charge transfer and electronic‑structure modifications.

On the defect‑free surface, h‑BN exhibits a wide band gap (~4.7 eV) and is chemically inert. Alkali (H, Li, Na, K, Rb) and alkaline‑earth (Be, Mg, Ca, Sr) atoms bind only weakly (‑0.05 to ‑0.33 eV) through dispersion forces, with negligible charge transfer and minimal impact on the band gap. Among p‑block elements, the highly electronegative O and F show the strongest chemisorption (‑2.08 eV and ‑1.94 eV, respectively), acting as electron acceptors and inducing pronounced band‑gap narrowing. Carbon and silicon bind at N‑top sites with moderate energies (‑0.94 to ‑1.31 eV) and donate a small amount of charge. Transition metals with partially filled d shells (Ni, Ru, Rh, Ir, Pt) display moderate‑to‑strong chemisorption (‑1.30 to ‑2.19 eV) driven by d‑p hybridization rather than charge transfer, whereas coinage metals (Cu, Ag, Au) interact only weakly (‑0.31 to ‑0.43 eV) and leave the electronic structure essentially unchanged. Noble gases bind via van‑der‑Waals forces with energies below 0.1 eV.

Introducing a boron vacancy (V_B) or a nitrogen vacancy (V_N) dramatically enhances reactivity. V_B creates under‑coordinated nitrogen atoms, yielding a magnetic moment of 3 μ_B and reducing the band gap to 0.11 eV. V_N generates under‑coordinated boron atoms, a 1 μ_B moment, and a 0.51 eV gap. At V_B, electropositive species (alkali, alkaline‑earth, many transition metals) are strongly anchored through coordination to the three neighboring N atoms; adsorption energies exceed 1 eV and often surpass the cohesive energy of the bulk element, indicating thermodynamic stabilization of single‑atom or substitution‑like configurations. At V_N, electronegative p‑block atoms (O, F, Cl, P, S) preferentially occupy B‑top sites, accepting up to ~0.9 e⁻ and creating deep defect states that further shrink the gap.

A scaling analysis of adsorption energies versus elemental cohesive energies reveals three distinct regimes: (i) physisorption where |E_b| ≪ cohesive energy, (ii) chemisorption where |E_b| ≈ cohesive energy, and (iii) substitutional stabilization where |E_b| > cohesive energy. This classification underscores that vacancy engineering does not merely amplify binding but fundamentally changes the bonding mechanism, enabling selective capture of either electropositive or electronegative atoms depending on vacancy type.

Electronic‑structure analysis shows that V_B‑bound transition metals introduce narrow d‑derived states near the Fermi level, partially metallizing the sheet and providing potential active sites for catalysis. V_N‑bound electronegative atoms generate localized states within the gap, which can be exploited for sensing applications due to their strong influence on charge transport. Charge‑transfer patterns (≈ 0.2–0.5 e⁻ from metals to V_B, ≈ ‑0.7 to ‑0.9 e⁻ from V_N to electronegative adsorbates) correlate with induced magnetic moments and band‑gap modifications.

Overall, the study delivers a unified, periodic‑table‑wide picture of single‑atom adsorption on h‑BN, demonstrating that pristine h‑BN is unsuitable for strong binding, while engineered B‑ and N‑vacancies provide complementary platforms for anchoring metals and non‑metals, respectively. These insights guide the rational design of h‑BN‑based single‑atom catalysts, gas sensors, and electronic devices, and they furnish a valuable dataset for training machine‑learning potentials aimed at rapid screening of 2‑D materials.