A Pd-functionalized β-ketoenamine COF for efficient hydrogen sensing under ambient conditions

Abstract

Hydrogen sensing materials are vital for energy and environmental safety, as hydrogen's high energy density and flammability demand rapid and reliable detection at low concentrations under ambient conditions. Here, we report a palladium nanoparticle-functionalized β-ketoenamine-linked covalent organic framework (Pd@TAPT-COF) that enables efficient room-temperature hydrogen sensing. Structural analyses (solid-state ¹³C CP-MAS NMR, FTIR, and XPS) confirm successful Pd incorporation into the TAPT-COF, with characteristic shifts in CO and CN peaks evidencing strong Pd–TAPT COF interactions. The ¹³C NMR spectra show a shift in the CO peak signal from 182 ppm to 190 ppm and the appearance of a new peak at 22 ppm, confirming Pd interactions with keto carbons. FTIR showed a CO stretching shift from 1622 cm⁻¹ to 1613 cm⁻¹ and a CN shift from 1497 to 1499 cm⁻¹ after Pd doping. XPS O1s spectra exhibited distinct peaks at ∼530.8 eV (CO) and ∼532.5 eV (Pd–O), providing further evidence of Pd coordination with oxygen-containing groups. The Pd@TAPT-COF exhibited exceptional chemiresistive performance toward H₂, attaining a response (R_a/R_g) of 10, with a fast response time (T_res) of 4 s and a recovery time (T_rec) of 3 s at 1 ppm, along with superior selectivity and stability. Density functional theory (DFT) calculations support these results, revealing strong H₂ binding energies (−484.57 kJ mol⁻¹), a narrowed HOMO–LUMO gap (∼2.82 eV), increased orbital hybridization near the Fermi level, and efficient charge transfer from Pd–H interactions. These results indicate that the integration of Pd catalytic sites within the pristine TAPT-COF facilitates rapid, selective, and reversible H₂ detection, making the Pd@TAPT-COF a strong sensing material for future energy and safety sensor applications.