Ruma Ghosh

Chemically Reduced Graphene Oxide for Ammonia Detection at Room Temperature

Chemically reduced graphene oxide (RGO) has recently attracted growing interest in the area of chemical sensors because of its high electrical conductivity and chemically active defect sites. This paper reports the synthesis of chemically reduced GO using NaBH4 and its performance for ammonia detection at room temperature. The sensing layer was synthesized on a ceramic substrate containing platinum electrodes. The effect of the reduction time of graphene oxide (GO) was explored to optimize the response, recovery, and response time. The RGO film was characterized electrically and also with atomic force microscopy and X-ray photoelectron spectroscopy. The sensor response was found to lie between 5.5% at 200 ppm (parts per million) and 23% at 2800 ppm of ammonia, and also resistance recovered quickly without any application of heat (for lower concentrations of ammonia). The sensor was exposed to different vapors and found to be selective toward ammonia. We believe such chemically reduced GO could potentially be used to manufacture a new generation of low-power portable ammonia sensors.

Enhanced ammonia sensing at room temperature with reduced graphene oxide/tin oxide hybrid films

Sensitive and selective detection of ammonia at room temperature is required for proper environmental monitoring and also to avoid any health hazards in the industrial areas. The excellent electrical properties of reduced graphene oxide (RGO) and sensing capabilities of SnO2 were combined to achieve enhanced ammonia sensitivity. RGO–SnO2 films were synthesized hydrothermally as well as prepared by mixing different amounts of hydrothermally synthesized SnO2 nanoparticles with graphene oxide (GO). It was observed that the response of the hybrid sensing layer was considerably better than intrinsic RGO or SnO2. However, the best performance was observed in the 10 : 8 (RGO–SnO2) sample. The sample was exposed to nine different concentrations of ammonia in the presence of 20% RH at room temperature. The response of the sensor varied from 1.4 times (25 ppm) to 22 times (2800 ppm) with quick recovery after purging with air. The composite formation was verified by characterizing the samples using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). The results and their significance have been discussed in detail.

Highly proton conducting MoS2/graphene oxide nanocomposite based chemoresistive humidity sensor

This paper reports the development of MoS2/GO nanocomposite based sensing layers for resistive humidity sensors. The MoS2 nanoflakes were synthesized through liquid exfoliation and GO was synthesized using modified Hummers method. The nanocomposite was drop-cast on a Si/SiO2 substrate containing aluminium electrodes to fabricate the sensor device. The best performance was shown by the 1 : 4 (MoS2/GO) composite. Various characterization techniques like Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Fourier Transform Infrared Spectroscopy (FTIR) were used to verify the composite formation. The sensing response was found to lie between 55 times at 35% RH and 1600 times at 85% RH. Such a high response is believed to be because of proton conductivity in the water layer for both MoS2 and GO. The sensor performance was found to be repeatable even after three months of the first measurement with quick response and recovery. Thus the authors believe that the excellent sensitivity coupled with low cost synthesis and resistive sensing will make their work useful to develop new generation humidity sensors.

Humidity Sensor Based on High Proton Conductivity of Graphene Oxide

This paper explores the performance of graphene oxide (GO) as humidity sensor. GO was synthesized using modified Hummers and Offeman method, and the sensing layer was characterized using optical microscope, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The sensor devices were fabricated by drop-casting of GO on patterned gold electrodes on Si/SiO2 substrate. GO-based sensor was exposed to six different relative humidity (RH%), and the response of our sensor was found to be excellent due to large proton conduction. The sensor response varied from ~180 times (40% RH) to ~1200 times (88% RH). Our GO-based humidity sensor also showed ultrafast response and recovery times with extremely good repeatability. Also, the role of functional groups in humidity sensing was explored by fabricating the sensor devices by thermally reducing GO for different time durations. We believe GO could potentially be used to develop new-generation ultrasensitive humidity sensor.

Pt-functionalized reduced graphene oxide for excellent hydrogen sensing at room temperature

Cost effective and faster detection of H2 has always remained a challenge. We report synthesis of reduced graphene oxide (RGO)–Pt composite and its application as highly sensitive and selective H2 sensors at room temperature. Four samples by varying the ratio of RGO and Pt were prepared to test their sensing performance. The tests were carried out in inert (N2) ambience as well as air ambience. It was observed that the RGO:Pt (1:3) 1 h reduced sample demonstrated the best H2 sensing performance in terms of sensitivity, response time, and recovery time at room temperature. Its response varied from ∼19% (200 ppm) to 57% (5000 ppm) against H2 in air ambience. Also, the response time and recovery time of the RGO:Pt (1:3) sample were found to be as fast as 65 s and 230 s against 5000 ppm, respectively, in air ambience. In N2 ambience, the RGO:Pt (1:3) sample demonstrated the best response of −97% (500 ppm), but its recovery was found to be poor. The RGO–Pt composite formation was verified by high resolution tr...

Humidity Sensing by Chemically Reduced Graphene Oxide

Reduced Graphene Oxide (RGO) has been synthesized chemically by reducing micron-sized Graphene Oxide (GO) flakes using sodium borohydride solution. Indium Tin Oxide (ITO) coated glass was taken as the basic substrate for sensing layer deposition. Sensitivity tests for relative humidity (RH) measurements were carried out at five different concentrations of humid air at room temperature. The response of the sensor was found to vary between 3.8 for 10 % humid air and 20.4 for 100 % humid air. Characterizations of the sensing layer were carried out using Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FESEM).

Reduced graphene oxide–rose bengal hybrid film for improved ammonia detection with low humidity interference at room temperature

Development of chemoresistive ammonia sensor that does not suffer with humidity interference is highly desirable for practical environmental monitoring systems. We report enhanced ammonia sensing using chemically reduced graphene oxide (RGO) and rose bengal (RB) nanocomposite fabricated in a very simple and cost effective manner. The RGO–RB nanocomposites were synthesized using three different concentrations (2 mg mL−1, 5 mg mL−1 and 10 mg mL−1) of RB keeping the RGO concentration same. Ammonia and humidity sensing of these three different composites were explored. Interestingly, it was observed that with increasing concentration of RB, the sensitivity of the sensor towards ammonia was increased but the sensitivity towards humidity was decreased. The response of the nanocomposites varied from ~9–45% against 400−2800 ppm of ammonia whereas intrinsic RGO showed a response of merely 17% against 2800 ppm of ammonia. On the other hand the response of the nanocomposite based sensor was reduced from 18% to 7% against 100% relative humidity. Also, the sensor was found to be selective towards ammonia when tested against other toxic volatile organic compounds. The limit of detection of the RGO–RB based sensor was calculated to be as low as 0.9 ppm. Field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and UV–vis spectroscopy were carried out for the detailed structural characterizations of the sensing layer. These results are believed to be very useful for the cost effective fabrication of graphene based ammonia sensors which have reduced effects of humidity.

Enhanced Proton Conductivity of Graphene Oxide/Nafion Composite Material in Humidity Sensing Application

In this work, we report the performance of graphene oxide (GO) and Nafion composite as highly responsive humidity sensor. GO was synthesized using modified Hummers and Offeman method and was mixed with Nafion ionomer. The hybrid sensing layer was characterized using atomic force microscopy, field emission scanning electron microscopy, energy dispersive X-ray analysis and Fourier transform infrared spectroscopy. GO/Nafion composite solution was drop-casted on patterned gold electrodes on Si/SiO2 substrate to fabricate the sensor. GO/Nafion-based sensor was exposed to six different humidity level (40%-88%) and large response was obtained due to high proton conductivity of GO and Nafion. The sensor response varied from ~1400 times (40% RH) to ~18 000 times (88% RH). Our GO/Nafion based humidity sensor also exhibited very fast response and recovery times with excellent reproducibility and stability. The reported work shows that GO/Nafion is a promising candidate to be used in development of a modern highly sensitive humidity sensor.

Reduced Graphene Oxide-Based Piezoelectric Nanogenerator With Water Excitation

Generation of electrical power using mechanical energies that are readily available in the environment has become indispensible to provide source energy to all the electronic devices that are used in day-to-day lives. In this study, reduced graphene oxide (RGO)/poly methyl methacralyte (PMMA)-based hybrid film has been employed for nanogeneration. The thin films were characterized using atomic force microscopy, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. The mechanical force exerted due to falling water on the device has been converted to electrical current by the RGO/PMMA based nanogenerators. The magnitude of generated current varied with volume of water dropped on the device. The roles of amount of functional groups present in RGO, metal stripes as bottom electrode and the spacing between the fingers have been explored. It was demonstrated that the device can also operate in selfpowered mode, i.e., without applying any bias. It is believed that this study would help in development of highly efficient RGO-based nanogenerator in a cost effective manner.