Abstract
Pure ZnO thick film, prepared by screen-printing technique, was almost insensitive to NH3. Pure ZnO thick films were surface modified with MnO2 by dipping them into 0.01 M aqueous solution of manganese chloride (MnCl2) for different intervals of time and fired at 500℃ for 12 h. The grains of MnO2 would disperse around the grains of ZnO base material. The MnO2 modified ZnO films dipped for 30 min were observed to be sensitive and highly selective to NH3 gas at room temperature. An exceptional sensitivity was found to low concentration (50 ppm) of NH3 gas at room temperature and no cross sensitivity was observed even to high concentrations of other hazardous and polluting gases. The effects of surface microstructure and MnO2 concentrations on the sensitivity, selectivity, response and recovery of the sensor in the presence of NH3and other gases were studied and discussed. The better performance could be attributed to an optimum number of surface misfits in terms of MnO2 on the ZnO films.
Highlights
Ammonia is produced and utilized extensively in many chemical industries, fertilizer factories, refrigeration systems, food processing, medical diagnosis, fire power plants etc
An exceptional sensitivity was found to low concentration (50 ppm) of NH3 gas at room temperature and no cross sensitivity was observed even to high concentrations of other hazardous and polluting gases
Response time (RST) was defined as the time required for a sensor to attain the 90% of the maximum increase in conductance after exposure of the sensor surface to a test gas, while recovery time (RCT) as the time taken to get back 90% of the maximum conductance [17] in air
Summary
Ammonia is produced and utilized extensively in many chemical industries, fertilizer factories, refrigeration systems, food processing, medical diagnosis, fire power plants etc. Efforts are made to develop the ZnO -based gas sensors, which should detect ammonia at room temperature. The electrolytic techniques using diaphragm electrodes are generally used for the detection of ammonia This method is expensive and does not have sufficient response and selectivity for ammonia [14,15]. Another technique utilizes a Pd-metal oxide semiconductor MOS device. The sensors operable at room temperature with low cost metal additives must be developed for large applicability. The efforts are made to develop a room temperature sensor with a low cost additive (MnO2) using dipping technique —a simplest method of modification.
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