Synthesis and characterization of rGO-CuO/ZnO nanocomposites for NO2 gas sensors

Abstract

Recently, the monitoring of toxic gases is becoming more important to human’s safety and environmental protection. Due to accelerated growth in urbanization and industries, the world is facing a big problem of severe air pollution. The name of some pollutant toxic gases such as NH3, CO, SO2, NO2, and H2S and Volatile Organic Compounds (VOCs) as example toluene, benzene, ethanol, acetone, formaldehyde, and acetaldehyde, etc. Currently, many types of gas sensors are developed for the detection of these gases based on different working principles like Optical gas sensors, Electrochemical gas sensors, Electrical sensors, Mass-sensitive sensors, Magnetic sensors, Metal oxide-based gas sensors, etc. Most of these techniques have some advantages and disadvantages. An ideal gas sensor is expected to be an economical portable device, highly sensitive, selective, and operated at ambient conditions like room temperature and also work in the presence of relative humidity. To fulfill these requirements, metal-oxide-semiconductor gas sensors have been the subject of immense research and development due to their reasonable cost, good chemical and thermal stabilities, compatibility with electronic devices, and ease of fabrication. In the present thesis, we synthesized CuO/ZnO nanocomposites in five different mole ratios like CZ10 (CuO: ZnO=1:0 i.e. CuO), CZ01(CuO: ZnO=0:1 i.e. ZnO), CZ11(CuO: ZnO=1:1), CZ21(CuO: ZnO=2:1), and CZ12(CuO: ZnO=1:2), respectively by using a facile hydrothermal method. A modified Hummer’s method is used for synthesizing the graphene oxide separately. The CZ12(CuO: ZnO=1:2) nanocomposites and the GO(GO=G) dispersion solution were then mixed together and sonicated for 2 hrs so that we can get a homogeneous solution. The obtained solution is named CZG12 (CuO: ZnO=1:2 and GO=G). By using the simple drop-casting method CZG12 thin films were fabricated on a glass substrate and for the complete transformation of GO to rGO, this film was annealed at 1500C for 3 hrs. In a similar way, we can synthesize the CZG10, CZG01, CZG11, and CZG21 thin films respectively. The synthesized films have more active sites and excellent electrical conductivity, which significantly enhanced the sensitivity and selectivity of the gas sensor and operated at room temperature. The sensors CZG10, CZG01, CZG11, CZG21, and CZG12 have percentage responses 30, 45, 56, 55, and 77 at 10 ppm NO2 gas. Among these sensors, CZG12 sensors have a superior percentage response and a response time is 13 sec. The gas sensing performance of the CZG12 ternary composites was thoroughly investigated, including the percentage response, response time, and recovery time. Moreover, the sensor CZG12 has remarkable sensitivity, reliable repeatability, and exceptional performance under moderate levels of relative humidity when it came to detecting NO2 gas. The remarkable gas sensing capabilities displayed by the CZG12 ternary composites strongly imply their immense promise as gas sensors for the purpose of environmental surveillance and regulation. This research offers fresh perspectives on the advancement of gas sensors with superior performance and holds the potential to pave the way for the creation of functional gas-sensing devices.