Tailored ZnCu Conductive MOF as a Floating-Gate in Carbon Nanotube Network FET NH₃ Sensors

Ammonia (NH₃) is a common and hazardous gas, and monitoring low concentrations of NH₃ is crucial for environmental protection and public health. This study reports a synergistically enhanced Zn/Cu bimetallic conductive metal-organic framework (MOF) for room-temperature gas sensing applications and its integration with carbon nanotube network field-effect transistors (CNTFETs). Zn/Cu-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene hydrate) with varying Zn/Cu ratios was synthesized via a solvothermal method and characterized in terms of its structure, morphology, and gas-sensing performance. Cu²⁺ facilitates efficient charge transfer during sensing, and Zn²⁺ provides active sites that enhance NH₃ adsorption. Gas sensing tests show that Zn₁Cu₂-HHTP achieves the highest chemiresistive response (|ΔR|/R₀ ≈ 4.48%) to 50 ppm of NH₃ with excellent selectivity. Kinetic analysis showed that Zn₁Cu₂-HHTP possessed a 3.45-10.46-fold faster adsorption kinetics rate relative to the monometallic systems. Density functional theory reveals that Zn-Cu synergy optimizes NH₃ adsorption at bimetallic sites by balancing adsorption strength. At a gate voltage of 1.0 V, the Zn₁Cu₂-HHTP floating-gate CNTFET exhibits a response of 91,202.25% to 1000 ppb NH₃ within 15 s at room temperature. Sensitivity has been greatly improved from 0.11%/ppm for chemiresistive sensors to 4168.69%/ppm for CNTFET sensors, an increase of nearly 37,500 times. This study presents a novel strategy for developing gas sensors with high performance, low power consumption, and excellent selectivity, offering broad application potential in complex environments for trace gas detection.