Synthesis and Low-Concentration Acetone Sensing Properties of ZnFe2O4/Rgo Hollow Spheres Composites

Abstract

Introduction As a kind of synthetic raw material in industrial production, acetone is chemically active and extremely flammable. It also behaves toxic, a long-term exposure to acetone, if its concentration exceeds 173 ppm, will make a serious threat to human health [1-2]. Furthermore, acetone is also a fat metabolite in human’s body. According to the related literature, the concentration of acetone in the exhaled gas of healthy people is less than 0.8 ppm, while that in exhaled gas of diabetic patients is higher than 1.8 ppm [3-4]. In this view, it is possible to realize diagnosing diabetes with nondestructive testing. It is necessary to develop high performance gas sensor for practical application.With a unique spine structure and a narrow band gap width (~1.94 eV), zinc ferrite (ZnFe2O4) possesses several remarkable properties and shows a good potential in gas sensing filed. And our previous works had studied pure ZnFe2O4 hollow spheres and Ag-ZnFe2O4 gas sensing nanomaterials. Aiming at the high-performance acetone gas sensor, we prepared ZnFe2O4 hollow spheres/rGO composites via a facile solvothermal synthesis method followed with a high-temperature heat treatment process in an inert atmosphere. ZnFe2O4/rGO gas sensor The obtained pure ZnFe2O4 hollow spheres or ZnFe2O4/rGO powders were firstly dissolved into deionized water to form a homogeneous paste, which were then coated uniformly on the surface of Al2O3 ceramic plate with heating electrodes (Pt) and gold electrodes (Au) to fabricate a thin sensing films. Subsequently, the sensors were dried at 120℃ for 12 h, and after another aging for 24 h at 180℃, a series of gas sensors based ZnFe2O4/rGO (different mass contents of rGO: 0, 0.1, 0.25, 0.5 and 1 wt%) were obtained. The temperature of sensors was adjusted by aligning the applied voltage. Method Pure ZnFe2O4 hollow spheres and ZnFe2O4/rGO composites were prepared via a simple solvothermal method followed with a high-temperature heat treatment process in an inert atmosphere. Firstly, GO aqueous dispersion solution (0.5 mg/mL) was further ultrasonic treatment for 2 h, then various amounts of GO solution (0 mL, 0.242 mL, 0.602 mL, 1.205 mL, 2.410 mL) were added into the homogeneous solution of isopropanol (30 mL) and glycerol (8 mL) under slow stirring. Secondly, 0.1098g Zn(CH3COO)2·2H2O and 0.4042g Fe(NO3)3·9H2O were dissolved in the obtained homogeneous solution under magnetically stirring for 1 h. Subsequently, the mixed solutions were transferred into Teflon-lined stainless-steel autoclave (50 mL), and then maintained at 180oC for 12 h. After naturally cooling down to room temperature, the obtained suspensions were centrifuged using deionized water and anhydrous ethanol for 4 times and dried at 75 oC for 12 h. Ultimately, these as-prepared precursors were placed in an argon atmosphere, annealed at 400℃ for 2 h with a heating rate of 5oC/min to reduce GO to rGO, and five samples were obtained: pure ZnFe2O4 hollow spheres, 0.1 wt% ZnFe2O4/rGO, 0.25 wt% ZnFe2O4/rGO, 0.5 wt% ZnFe2O4/rGO and 1 wt% ZnFe2O4/rGO. Results and Conclusions In this work, the sensing properties of ZnFe2O4 sensors to low-ppm-level acetone were improved by compounding with reduced graphene oxide. As shown in Figure 1, as rGO was introduced, the sphere size and hollow structure were not affected while the surface morphology was modified and more regular. In Figure 2, 0.5 wt% ZnFe2O4/rGO sensor exhibited higher response, good selectivity and linear response to low concentration acetone at 200 oC. The response of 0.5 wt% ZnFe2O4/rGO to 10 ppm acetone was 8.18, which was about 2.5 times that of pure ZnFe2O4 gas sensor. Therefore, this sensor can be a promising material to detect low concentration (ppm) acetone, and it is expected to be a potential candidate to diagnose diabetes via nondestructive testing the exhaled acetone vapor if the sensitivity and response speed to ppb-level acetone are further improved.