Enhancing the Charge Carrier Separation and Transport via Nitrogen-Doped Graphene Quantum Dot-TiO₂ Nanoplate Hybrid Structure for an Efficient NO Gas Sensor

Abstract

Herein, we demonstrate the ultraviolet (UV) light activated high-performance room-temperature NO gas sensor based on nitrogen-doped graphene quantum dots (NGQDs)-decorated TiO₂ hybrid structure. TiO₂ employed in the form of {001} facets exposed rectangular nanoplate morphology, which is highly reactive for the adsorption of active oxygen species. NGQD layers are grown on TiO₂ nanoplates by graphitization of precursors via hydrothermal treatment. The decoration of NGQDs on the TiO₂ surface dramatically enhanced the efficiency of gas and carriers exchange, charge carrier separation and transportation, and oxygen vacancies, which eventually improved the sensing performance. At room temperature, the TiO₂@NGQDs hybrid structure exhibited a response of 12.0% to 100 ppm NO, which is 4.8 times higher compared to that of pristine TiO₂ nanoplates. The response of TiO₂@NGQDs hybrid structure is further upgraded by employing the ultraviolet light illumination and manipulating the operating temperature. Under the UV (λ = 365 nm) illumination at room temperature, the hybrid structure response escalated to ∼31.1% for 100 ppm NO. On the other hand, the tailoring of working temperature yielded a response of ∼223% at an optimum operating temperature of 250 °C. The NO gas-sensing mechanism of TiO₂@NGQDs nanoplate's hybrid structure sensors under UV illumination and different working temperatures is discussed.