Ammonia Gas Detection Using Fabricated Zinc Oxide Nanoparticles on Glass Tube Substrates

Abstract

INTRODUCTION

Ammonia (NH3) is useful to various fields especially in agriculture wherein 80% of it is used as fertilizer. Even so, its toxic nature along with its sharp and pungent smell may irritate the eyes, skin, and lungs; brief exposure to concentrations higher than 5000ppm may lead to death. This case brings a strong need to establish sensors that are capable of detecting ammonia. However, commercially available gas sensors are highly expensive and can only register NH3 in high concentrations. Thus, there is a demand for a reliable and cost-effective yet sensitive gas detector that requires inexpensive fabrication techniques.

METHODS

Substrates were prepared from glass tubes before being subjected to sonication in ethanol and in distilled water. Zinc oxide (ZnO) films were fabricated via successive ionic layer adsorption and reaction (SILAR), which involved alternate dipping of substrates in sodium zincate solution and hot water bath. The films were annealed at 250ºC, 300ºC, 350ºC, and 400ºC and were put inside a sealed container while being connected in a Wheatstone bridge circuit. Ammonium hydroxide (NH4OH) was used as a source of ammonia gas. Volumes of NH4OH yielded concentrations of 595ppm, 793ppm, 991ppm, 1189ppm, 2378ppm, and 3946ppm. All films were tested against ammonia with four trials per concentration.

RESULTS

The gas response was due to a change in film resistance, thus modifying the voltage output. When NH3 was introduced, the initial voltage went down rapidly, until it reached its lowest point. Upon gas release, the voltage went back to its initial reading. The concentrations were plotted against the average change in voltage. A linear trend was observed during 595ppm, 793ppm, 991ppm, and 1189ppm. However, no trend occurred in 2378ppm and 3946ppm due to film saturation, indicating an upper limit of 1189ppm. Consequently, films having R2 values closest to 1 were the most accurate. The films annealed at 250ºC, 300ºC, 350ºC, and 400ºC provided R2 of 0.997, 0.994, 0.904, and 0.999; sensitivity based on concentration increments tested (mV/200ppm) were 27, 10, 23, and 15, while the resolution (ppm/mV) were 3.7, 9.9,4.4, and 6.6, respectively.

DISCUSSIONS

Results showed that ZnO is a potential candidate for detecting ammonia due to high sensitivity and wide range of detection. The films also provided accurate readings. For further improvement of this study, parameters such as concentrations and film fabrication technique may be varied.