Hydrothermal Synthesis of Ag-Modified CuO/In₂O₃ Nanospheres for Rapidly Detecting Ppb-Level 2-Butanone

2-butanone has been identified as a volatile biomarker for a variety of diseases, and its rapid detection at ppb level is necessary for disease diagnosis. In2O3 is an ideal sensing material for the detection of trace volatile organic compounds (VOCs), achieving high sensitivity and fast detection of 2-butanone when heterojunctions and noble metals are present. In this work, spherical Ag/CuO/In2O3 composites are synthesized via mild hydrothermal method for the efficient detection of 2-butanone by modifying the amount of Ag (3%, 5%, 7%, 9%, and 15%). Characterization results show that CuO and Ag are evenly dispersed across In2O3 surfaces. The test results demonstrate that the 7% Ag-CuO/In2O3 sensor possesses the finest performance toward 2-butanone, achieving response value up to 151.5 (100 ppm) at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$250~^{\circ }$ </tex-math></inline-formula>C, which is far superior to several other sensors. In addition, it delivers 10-s response time, detects 50-ppb 2-butanone, and presents excellent repeatability and long-term stability. Finally, further mechanism analysis shows that the catalytic activity of CuO and active sites at the heterojunction interface enhance the selectivity for 2-butanone. Next, Ag produces spillover effect to accelerate the gas reaction, and the Ag2O-In2O3 interface and Ag-In2O3 interface interconvert to change the direction of electron movement and energy band structure. In addition, XPS shows that the Ag/CuO/In2O3 composites contain extensive oxygen vacancies and adsorbed oxygen species, which affect the electron depletion layer (EDL). Overall effect from the above factors dramatically improves the 2-butanone sensing performance of Ag/CuO/In2O3 composites. This work sheds fresh insight into the design of high-sensitivity 2-butanone gas sensors for rapid detection of ppb level.