Unveiling enhanced HCN sensing: a comparative DFT study on reactivity and sensitivity of X-doped biphenylene nanotubes (X = B, Al, and Ga)

Rational design of sensing materials is essential for developing high‑performance detectors for hazardous gases. In this work, density functional theory (DFT) is employed to assess B‑, Al‑, and Ga‑doped biphenylene nanotubes (BPNTs) for hydrogen cyanide (HCN) detection. Pristine BPNT shows minimal interaction with HCN, with an adsorption energy of - 0.12 eV, negligible charge transfer, and non‑spontaneous adsorption. Doping significantly strengthens the interaction, producing adsorption energies stronger than - 1 eV and markedly enhanced charge transfer, indicative of spontaneous and robust adsorption. The results from our systematic study indicate that the nitrogen lone pair and the C-N π bond in hydrogen cyanide are the dominant charge-donating electronic states toward the defective nanotubes. The doped systems also exhibit improved sensing characteristics, including an energy‑gap reduction of approximately 9% and short predicted recovery times. Complementary analyses-ELF, NBO, and IRI-were performed to further justify the interaction mechanisms and confirm the formation of active sites upon doping. Overall, the results identify defective BPNTs as promising candidates for next‑generation HCN gas sensors.