Unveiling LiF-Engineered MXene: A Novel Ti3C2Tx/ZnO Hybrid Composite for Highly Selective and Sensitive Chemiresistive NH3 Detection via Schottky Barrier Modulation at Ambient Temperature

Abstract

The imperative for ammonia sensors to exhibit high selectivity and sensitivity, capable of detecting low ppm levels, is paramount for addressing toxicity risks, industrial hazards, and medical concerns. Nevertheless, MXene-based sensors often encounter performance constraints owing to residual Al impurities from the MAX phase, which hinder charge transport and surface reactivity. In this study, a LiF-HCl-assisted Minimally Intensive Layer Delamination (MILD) etching method was used to synthesize high-purity Ti3C2Tx MXene, obviating the need for HF. Optimization of the LiF concentration augmented the surface functionalization, creating numerous active sites for gas adsorption and redox reactions. A Ti3C2Tx/ZnO hybrid composite was produced via DC reactive magnetron sputtering and drop-casting, establishing a Schottky junction to promote charge transfer. The resultant L3-Ti3C2Tx/ZnO sensor demonstrated a 50-fold enhancement in NH₃ sensitivity, a 4.5-fold acceleration in response at 5 ppm compared to pristine ZnO, and an ultra-low detection threshold of 0.1 ppm (4.52 ± 1.1). It exhibited rapid response (44 s) and recovery (26 s) times, high selectivity, remarkable stability over 60 days, and resilience to humidity fluctuations at 300 K. The exceptional performance of the sensor was ascribed to the enhanced charge perturbation, expedited adsorption-desorption kinetics, and surface redox interactions at the interface. The proposed L3-Ti3C2Tx/ZnO hybrid Schottky junction represents a significant advancement in hazardous gas monitoring, industrial safety, and environmental protection applications.