In use of ammonium and nitrate electrodes to detect ammonia and nitrate mixed solution

Autor: Po-Zhi Chang, 張博智
Rok vydání: 2014
Druh dokumentu: 學位論文 ; thesis
Popis: 102
Ammonia and nitrate are essential elements for aquatic environments and aquatic animals. Ammonia is derived from chemical fertilizers and the decomposition of dead animal organs by saprophytes, and is used to produce ammonium (NH4+). Because NH4+ is poisonous to fish and causes fish to die, the NH4+concentration in wastewater that is discharged into rivers must be strictly monitored. To prevent the death of fish, NH4+ must undergo nitrification during the wastewater treatment process. During nitrification, nitrite bacteria convert NH4+ into nitrite ions (NO2-), which are then converted into nitrate ions (NO3-) by nitrifying bacteria. After heavy rain or excessive irrigation, NO3-and NO2- typically travel to groundwater or surface water. The increase of nitrate levels in groundwater influences the safety of drinking water. High NO3- concentration levels in drinking water leads to the generation of methemoglobin, which indicates that the oxidation state of iron in haemoglobin is the ferric state. Therefore, methemoglobin cannot bind to and transport oxygen, influencing the oxygen concentration in infant blood and resulting in methemoglobinaemia (or blue baby syndrome) and cancers. Moreover, the increase of nitric acid content in surface water may cause water eutrophication, inducing the considerable growth of algae, aquatic plants, and zooplankton in water, which further leads to the large difference in the amount of dissolved oxygen in water during the day and during the night because of photosynthesis and respiration. Thus, the water becomes an anoxic environment in which aquatic organisms cannot survive, leading to death, which causes water stench. This phenomenon is called the eutrophication of rivers or reservoirs. Consequently, the detection of ammonia and nitrate in the environment and agricultural fields is vital. This experiment uses extended ITO/PET gate field effect transistor in which NO3- and NH4+ selective electrodes are stabilized on the sensor zone to formulate nitrate and ammonia ion thin film that becomes 2 different detectors. According to the experimental results, when NH4Cl solution with pH 7 was selected as the electrode, the voltage response of NH4+ can be accurately measured in NH4Cl solution at various concentration levels (from 10-5 M to 100 M). When NaNO3 solution with pH 7 was selected as the electrode, the voltage response of nitric acid can be accurately measured in the NaNO3 solution at various concentration levels (from 10-4 M to 10-1 M). Based on these results, the optimal concentration range of the mixed solution of ammonia and nitrate was measured and evaluated using the 2 types of sensors. Bacteria were added into the mixed solution to change the concentration levels of ammonia and nitrate, and the voltage of NH4+ and that of NO3- in the mixed solution were then accurately measured. The developed sensing approach can accurately and rapidly evaluate the content of ammonia and nitratein water.
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