Ahmed Hasnain Jalal; A.G. Agwu Nnanna, Ph.D. Purdue University Calumet Water Institute Introduction
Results & Graphs
Principle & Methods 0.16
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Oxazine 170 per Chlorate used as a pH indicator for ammonia detection which changes its color from blue to yellow, then in red with the concentration whenever it exposes in ammonia solution and vice versa. This reversible property is an important feature of this sensor and therefore, it can be placed in a remote area. In our case, we detect ammonia at 1.4 ppm level in water. With the increase of concentration, light absorbance increases significantly, thus, the sensor can detect different concentration levels. In addition to these properties, the time response of the sensor is about 10 seconds. To provide real-time information about ammonia in water, the whole system is supported by an online monitoring system.
Preparation of Fiber Cable: The tips of the fiber are made plane and smooth. Around 3-5 cm cladding of the fiber is chosen to be stripped by Organic Solvent Etching Techni ue’.
0.14
Abs. 4.2 (Avg.)
0.1
Abs. 7 (Avg.) Abs. 14 (Avg.)
0.08
Abs. 28 (Avg.) 0.06 Abs. 70 (Avg.) 0.04
Abs. 112 (Avg.)
0.02
0.08 y = 0.0197ln(x) + 0.0032 R² = 0.9603 0.06 Absorbance Log. (Absorbance)
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0 350
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-0.02 -0.04
0 -0.06
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Concentration, ppm
Reversibility Test
Time
y = 0.0052x - 0.002 R² = 0.9222
16000
0.1 15000 0.08
0.06 Time Linear (Time)
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14000 Series1 13000
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11000
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500
Time, Minute
Discussion & Conclusion
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Time, Second
Power (µW)
10
Experimental Set-up
0.1
Abs. 5.6 (Avg.)
Coating of the pH Indicator : 0.0005 M Oxazine 170 per Chlorate is prepared for the coating purpose. The sensor part of the fiber is dipped in this solution around 50 – 60 minutes at 55°-70° C temperature. PDMS Formation on the pH sensing Material: Dip the fiber in the PDMS solution around 30 second. Hang vertically 24 hours for drying.
Absorbance
0.12
Abs. 2.8 (Avg.)
0.12
Absorbance
Due to large dynamic range, sensitivity, selectivity and cost-effectiveness the opto-chemical sensor is being preferred over other sensors for ammonia detection with pH sensitive dyes. In water environment, a thin layer of gas permeable membrane such as Poly Di-Methyl Siloxane (PDMS) is required to protect the pH sensitive dyes from water. The authors of this paper are trying to solve this problem by developing Plastic/Polymer Optical Fiber (POF) sensor instead of Glass Optical Fiber (GOF) sensor because of the fragility of GOF.
Principle: Light leaks out through the fiber due to the effects of Evanescent Field and bending. This light absorbs by the pH indicator and according to change the color of pH indicator, light intensity varies and this variation is monitored by the online monitoring system.
Power (µW)
10
y = -0.1528x + 9.3635 R² = 0.9693
9.5
9.5
9
9 Power (µW)
With the increase of the concentration, absorbance is increasing in blue region; but in yellow region, it is gradually decreasing with concentration. At 476.74 nm, Concentration vs. Absorbance’ follows logarithmic profile. At the same wavelength, absorbance is linearly increasing with time. This sensor shows almost 96% reversible property. At 490 nm, optical power is gradually decreasing with time in linear pattern. At 490 nm, optical power is exponentially decreasing with the concentration. From the above discussion and graphs, we can come to the conclusion that this sensor shows good reversible property. It can detect ammonia from 1.4 ppm but it shows better performance from 5.6 ppm. The response time is around 10 seconds of this sensor.
8.5
8.5
Power, µW
The Polymer Optical Fiber (POF) is connected with the LED Pulsed Light Source and compatible high-resolution spectrometer where the operating wavelength is 200-1100 nm. The sensor part of the fiber is placed in an air-tight container where it is filled with DI water and there is no over-head space. For the homogeneity of the ammonia solution in DI water after adding different concentrations, the container is kept in magnetic stirrer. By online monitoring system, we can monitor the light intensity before and after addition of ammonia solution.
Power, µW
In this work, Polymer Optical Fiber (POF) was used as an optical waveguide which was coated with a thin solid film of pH indicator on the etched part of the fiber. Cladding was removed from the fiber by using the Organic Solvent Etching Techni ue’. There was a thin layer of gas permeable membrane on the pH indicator which protect it from the water. When ammonia makes contact with the sensor, it changes its color from blue to yellow first, then in red with the increase of the concentration, and vice versa. Due to the change of the color of the pH indicator, intensity varies; we can monitor this variation on the end device screen as well as monitor the presence of ammonia in the air or water. This sensor has the capability to show the reversibility and sensitivity and has a short response time which is less than 10s.
The excess presence of ammonia causes diseases in the respiratory system of human beings. Oxidization of ammonia produces nitrite which is far more toxic. So, it is essentially necessary to detect contaminants such as ammonia in water by a highly sensitive, reliable and selective device with low production cost and which can monitor and detect ammonia on a real-time basis.
Absorbance
On-line detection of pollutants at parts per million or per billion levels is one of the major challenges of water quality and water security. Among the contaminants, ammonia is one of the common industrial pollutants. The excess presence of ammonia in the atmosphere is harmful for the respiratory system of human beings and ecosystems. This is why a continuous online monitoring system is required to detect ammonia for the safety issue.
Abs. 1.4 (Avg.)
Absorbance
ABSTRACT
Reversible Polymer Optical Fiber (POF) based Micro-sensor for Water Environment
Intensity, Count
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8 7.5
8 Power (µW) 7.5
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Time, Minute
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References 1. J. F. Giuliani, H. Wohltjen, and N. L. Jarvis, "Reversible optical waveguide sensor for ammonia vapors," Optical Letters, 8, 54-56 (1983) 2. Shiquan tao, Lina Xu and Fanguy oseph C., ― Optical fiber ammonia sensing probes using reagent immobilized porous silica coating as transducers.‖ Sensors and actuators. B, 115 (2006), 15 -163
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