Gas Adsorption-Driven Electronic Modulation in WO₃@Cu₃(HHTP)₂ Heterostructure: Mechanistic Origin of Selective Drift Resistance Room-Temperature Formaldehyde Sensing

Formaldehyde is a ubiquitous indoor air pollutant whose carcinogenicity, high toxicity, and volatility pose severe health risks even at trace concentrations. Nevertheless, realizing ultra-low detection limits with high selectivity under ambient-temperature conditions using a single chemiresistive semiconductor remains an enduring challenge. A heterointerface-engineered WO₃@Cu₃(HHTP)₂ nanocomposite is developed, integrating the high surface reactivity of WO₃ with the intrinsic conductivity and ordered π-conjugated framework of the 2D conductive metal–organic framework (cMOF) Cu₃(HHTP)₂. Synergistic interfacial orbital hybridization between W 5d (WO₃) and O 2p π-orbitals (cMOF) induces pronounced electronic structure modulation, promoting enhanced charge transport and gas–solid interfacial reaction kinetics. DFT calculations reveal that HCHO preferentially adsorbs at phenolic O sites in the cMOF and O-vacancy sites on WO₃, inducing localized charge redistribution and suppressing mid-gap defect states. This adsorption-driven Fermi level shift correlates directly with the experimentally observed resistance drop under HCHO exposure. The WO₃@Cu₃(HHTP)₂ sensor exhibits an ultralow detection limit (∼48 ppb), rapid response/recovery, minimal baseline drift, and exceptional selectivity under mixed gas environments at room temperature. These findings establish a clear mechanistic link between interfacial electronic structure tuning and enhanced sensing performance, offering a generalizable strategy for designing next-generation VOC sensors via surface modification of metal oxides with cMOFs.