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Humidity Sensing Behaviour of Lyophilized rGO/Fe2O3 Nanocomposite M. Morsy1   · M. M. Mokhtar1 · Sameh H. Ismail2 · Gehad G. Mohamed2,3 · M. Ibrahim4 Received: 10 March 2020 / Accepted: 29 April 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract For the purpose of humidity sensing, the rGO/Fe2O3 nanocomposite was synthesized through precipitation technique that is followed by lyophilization process to enhance the surface area of the prepared nanocomposite. In order to investigate the sensor preparation quality, its activity and efficiency, the prepared nanocomposite has undergone different characterization techniques such as; high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, thermo-gravimetric analysis (TGA), BET surface area and BJH pore diameter distribution. The study showed that ­Fe2O3 nanoparticles are densely and homogeneously loaded over rGO sheets. The porosity and surface area play an important role on humidity sensing property. In addition, the BET surface area and BJH pore radius of the rGO/Fe2O3 are found to be 2002.09 m ­ 2 ­g−1 and 1.68 nm, respectively. Furthermore, the humidity-sensing performances were investigated in a wide range of working humidity (11–97% RH) and frequency (100 Hz–100 kHz). The obtained results confirmed that the optimum measuring frequency is 1 kHz, due to in inability of water molecule to be polarized at higher frequency. The humidity sensing performance of rGO/Fe2O3 nanocomposite shows a parabola relationship with the RH value from 11 to 97%. The incorporation of F ­ e2O3 into rGO creates more active sites, such as vacancies and defects which promote the adsorption of water molecule thereby increasing the sensitivity of the sensor. Molecular models of graphene; graphene/2Fe2O3, graphene/2Fe2O3/2H2O were built. The model suggested that decorating the graphene with ­2Fe2O3 enable it to be sensitive for humidity. Keywords  Humidity sensor · Lyophilization · rGO/Fe2O3 nanocomposite · HRTEM · Thermal analysis

1 Introduction Humidity measuring and controlling are essential issue for numerous applications [1–4]. Different sensing mechanisms have been utilized to detect environmental humidity, including capacitance [5, 6], field-effect transistor [7], microbalance [8], microelectronic mechanical system (MEMS) [9] photonic crystal [10], quartz crystal micro balance (QCM) [11] and * M. Morsy [email protected] 1



Housing and Building National Research Center (HBRC), Building Physics Institute (BPI), 87 El‑Tahrir St., Dokki, P.O. Box 1770, Cairo, Egypt

2



Egypt Nanotechnology Center, Cairo University, El‑Sheikh Zayed, 6th October, Giza 12588, Egypt

3

Chemistry Department, Faculty of Science, Cairo University, Giza 12613, Egypt

4

Spectroscopy Department, National Research Centre, 33 El‑Bohouth Str., Dokki, Giza 12622, Egypt



resistance [12]. Among which resistive sensors are favorable due to their simple structure, mass production capabilities, high