Abstract
The work aims to develop a simple and low cost ammonia gas sensor based on reduced graphene oxide (rGO). Reduced graphene oxide doped with nickel sulfate (NiSO4/rGO) was used as a sensing material. The sensor was fabricated by a simple drop-cast and spin-coat technique. The performance of the nickel-doped reduce graphene oxide were studied in terms of electrical changes as well as chemical interactions. It was found that after the fabricated sensor was exposed to ammonia vapour for 10 min, the average resistivity was increased to 43% from initial resistance and retained about 8% resistance change upon ammonia removal. The mechanism of the sensor reaction with the ammonia gas is also studied using Fourier Transform Infrared Spectroscopy (FTIR) and is discussed. This preliminary work may help develop the highly sensitive ammonia gas sensor.
Highlights
Ammonia is extensively used in several fields of industries including fertilizers, food processing, automotive, rubber, refrigerator and medical diagnostics[1]
Fig. 4. displays the percent change of electrical resistance during exposure to the ammonia vapour which is allowed to flow in consecutive stages as follows: the burn-in period or the first time the sensor is exposed to ammonia vapour at 50% ratio for 10 min, followed by a recovery period by flowing airzero for 30 min
In the 3rd duty cycle, ammonia vapour is reduced to 25%, the resistance change is increased to about 38%, and the sensor can recover to about 8% above the baseline value within 30 min after the ammonia gas turned off
Summary
Ammonia is extensively used in several fields of industries including fertilizers, food processing, automotive, rubber, refrigerator and medical diagnostics[1]. High concentration of ammonia greater than 300 ppm can be harmful to human health[2]. It can cause suffocation, severe irritation to respiratory tract, eyes, and skin. When the graphite stack exfoliated by oxidation[4], the oxidized graphene oxide can be reduced back using chemical or thermal treatment to remove oxygenated functional group, producing materials with large surface area. This state is called reduced graphene oxide (rGO). Transformation of GO to rGO can be performed either by heat or by chemical treatment. rGO is studied in many applications such as biological engineering[5, 6], optical electronics, absorbent material[7], ultrafiltration, energy storage, and gas sensor[8,9,10]
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