ZnO sensor modified with In2O3 obtained by the combination of the ultrasonic spray nozzle and hydrothermal assisted by microwave methods for detection of volatile organic compounds

Author(s)

Taís Nascimento Teixeira Oliveira

• Document type: Master's Dissertation
• Press: São José do Rio Preto. 2021-06-29.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências Letras e Ciências Exatas. São José do Rio Preto
• Defense date: 2021-06-11
• Advisor: Diogo Paschoalini Volanti

Abstract

Advances in the science and technology of volatile organic compounds (VOCs) sensors are important for the sustainable development of functional materials. Therefore, there is a need to improve the sensitivity, response time and lifetime of sensors. This work studies the influence of the ZnO-based sensor modification with In2O3, to detect VOCs. In this sense, the following syntheses were carried out: (i) synthesis of pure ZnO structures and (ii) synthesis of In2O3/ZnO heterostructures in the proportion of 1, 2 and 3% of In2O3 by mass in relation to ZnO. For the synthesis of materials, the ultrasonic spray nozzle was used in conjunction with hydrothermal method assisted by microwave. The synthesized materials were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Through the SEM images, it was found that the ZnO-based sensor presented a morphology called twin-rods. The VOCs detection tests were carried out under dry air and under a relative humidity between 26-98%. The VOC detection tests confirmed that the sensors based on ZnO and In2O3/ZnO heterostructures showed high selectivity to triethylamine (TEA), in comparison with the tested VOCs: acetone, butanone, benzene, isopropanol, ethanol, and methanol. It was found that the formation of the In2O3/ZnO heterostructure decreased the optimal operating temperature by 50 °C, compared to the sensor containing only ZnO. A sensitivity test was performed with the ZnO twin-rods and the In2O3/ZnO heterostructures, exposing them to different concentrations of TEA (1-200 ppm) in their respective optimal operating temperatures. For only 1 ppm, the responses achieved were 2.6; 3.1; 6.2 and 3.3 for sensors based on ZnO and 1% In2O3/ZnO, 2% In2O3/ZnO, and 3% In2O3/ZnO heterostructures, respectively, showing that the sample 2% In2O3/ZnO has improved sensitivity to TEA. The ZnO twin-rods and the In2O3/ZnO heterostructures exhibited a fast response to detect different concentrations of TEA by analyzing the response times. It was also found that the 2% In2O3/ZnO sample has good stability for detecting 20 ppm of TEA at 350 °C and a response equivalent to 21.2 for detecting 100 ppm of TEA in an atmosphere with relative humidity of 98%, confirming the improved TEA detection performance of the 2% In2O3/ZnO heterostructure. (AU)

• FAPESP's process: 19/12345-9 - ZnO sensors modified with Mn3O4 or In2O3 obtained by combining the ultrasonic spray and hydrothermal microwave assisted methods
• Grantee: Taís Nascimento Teixeira Oliveira
• Support Opportunities: Scholarships in Brazil - Master