MOF-Derived NiO–SnO₂/Ti₃C₂T_<i>x</i> Composite Materials for Detection of ppb-Level NO₂ at Room Temperature

Achieving highly sensitive detection of ppb-level NO2 at room temperature remains a significant challenge for metal oxide semiconductors (MOS) due to their low chemical activity. Herein, a synergistic sensitization strategy is proposed, combining highly conductive MXene with high specific surface area mixed MOS. In this work, NiO–SnO2 is synthesized by thermal annealing using Ni–Sn–BTC (BTC: benzene-1,3,5-tricarboxylic) as a template. The mesoporous structure and high conductivity of NiO–SnO2/Ti3C2Tx provide a variety of channels for gas diffusion and carrier transfer. Gas sensor tests reveal that the fabricated NiO–SnO2/Ti3C2Tx sensor exhibits a 4.33-fold improvement in response (Rg/Ra = 70.86 to 200 ppb) to 200 ppb of NO2 at room temperature (RT, 25 °C) compared to NiO–SnO2. In addition, the sensor also maintains a low detection limit (50 ppb), superior selectivity (response ratio >30), good repeatability (RSD: 2.3%), and long-term stability at RT and 60% RH (RH: relative humidity). The outstanding sensing properties are mainly attributed to the functionalized surfaces and multiple-type heterojunctions formed by NiO, SnO2, and Ti3C2Tx phases, which significantly improve gas adsorption and electrical transduction function of the sensor.