Research Article 2018, 3(4), 193-198 Advanced Materials Proceedings Copyright © 2018 VBRI Press 193 Reduced graphene oxide-zinc oxide nano- composites for gas sensing applications Sitakshi Gupta, Chhaya Ravikant* Department of Applied Sciences & Humanities, Indira Gandhi Delhi Technical University for Women, Kashmere Gate, New Delhi-110006 *Corresponding author DOI: 10.5185/amp.2018/025 www.vbripress.com/amp Abstract Nowadays, gas sensors are fast becoming an imperative part of modern life with extensive applications in domestic safety, environmental monitoring, industrial process control, public security, medical applications and chemical warfare assessment amongst many others. The detection of minor gas leaks has been a challenging area of research, particularly in view of the hazards to human health and safety posed by toxic gases like NO2, NO, CO, NH3 etc and combustible gases like methane, hydrogen gas and some volatile organic compounds. Thus it is imperative to evolve and employ simple yet reliable gas sensing mechanisms with optimum response and selectivity towards even low concentration of analyte gas at room temperature. Most of the conventional gas sensors are based on metal-oxide semiconductors which are low-cost, exhibit good sensitivity and fast response/recovery. Zinc oxide is one such n-type semiconducting oxide, which has been widely studied for gas sensing response due to its ease of fabrication, high sensitivity and environment-friendly nature. However, the operating temperature of such sensors is usually high (>200°C) owing to the wide band-gap (3.37 eV) and high electrical resistance (kΩ-MΩ), which limits their practical utilization. In order to be used in hazard monitoring and home/workplace safety, the gas sensors need to be sensitive to gas exposure in mild operating conditions. As an alternative, more recently, graphene and its derivatives like pristine graphene (PG), reduced graphene oxide (rGO) etc. have been studied for sensing applications owing to their exceptional electronic and physical properties such as high carrier mobility at room temperature, good thermal stability, high mechanical strength, ballistic conductivity and large specific surface area. These sensors show high sensitivity at low operating temperatures (down to room temperature) towards low concentrations of analyte gas. However most of these rGO based sensors exhibit relatively longer response/recovery times than metal-oxide based gas sensors. Hence, nanocomposites formed by hybridizing graphene or its derivatives with metal-oxide nanoparticles are being explored as gas sensing materials. Combining reduced graphene oxide with zinc oxide to form hybrid nanostructures is particularly interesting because not only do they display the individual properties of the metal oxide NPs (faster response/recovery times) and of graphene (high electronic conductivity leading to efficient room temperature gas response), but may also have synergistic effects leading to better sensitivity as a gas sensing material. Here we present a review of the recent progress in rGO-ZnO nanocomposites based gas sensors. Copyright © 2018 VBRI Press. Keywords: Reduced graphene oxide, zinc oxide, gas sensor, grapheme. Introduction Gas sensors are fast becoming an imperative part of modern life with extensive applications in domestic safety, greenhouse gas monitoring for environmental studies, industrial process control such as methane detection in mines, in automotive industry for evaluating the exhaust of cars for pollution control check, public security, medical applications such as electronic noses simulating human olfactory system and chemical warfare assessment. They are being progressively employed in mass-market applications, such as in indoor air quality control as well as the more conventional areas of explosive and toxic gas detection. In view of the hazards to human health and safety posed by toxic gases like NO2, NO, CO, NH3 etc and combustible gases like methane, hydrogen gas, and some volatile organic compounds, it is imperative to evolve and employ simple yet reliable gas sensing mechanisms with optimum response and selectivity towards even low concentration of analyte gas at room temperature. An efficient gas sensing technique is characterized by certain performance parameters such as: (i) High sensitivity (ii) Low detection limit i.e. the minimum volume of target gas concentration at which response is generated should be low (iii) Good selectivity which means that the sensor should be able to detect a particular gas from a given gas mixture (iv) Faster response time (v) Short recovery time (vi) Operating Temperature should be ambient (vii) Reversibility i.e. the sensing material should return to its original state after detection is complete (viii) Good Adsorptive capacity (ix) Low Fabrication cost (x) Stability of Operation.