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

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.