Research On Optical Fiber Sensor For On-line Measurement Of 4-chlorophenol Concentration In Water

4-chlorophenol is a common chlorophenol compound in phenolic organic wastewater,which has the characteristics of high biological toxicity and stable chemical properties.4-chlorophenol can stay and enrich stably in the environment for a long time,and produce synergistic effect with other substances,which increases its toxicity and promotes carcinogenesis.Therefore,the ecological environment and human safety has threatened seriously by 4-chlorophenol.In order to ensure the safety of water environment and human health,it is very important to measure the concentration of4-chlorophenol in water online.At present,the main method for measuring the concentration of 4-chlorophenol is off-line measurement,which has the disadvantages of high measurement cost,unstable system,and difficulty in online and accurate detection.In order to overcome these shortcomings,a plastic optical fiber sensor based on selective adsorption membrane of 4-chlorophenol is proposed in this paper,which can accurately measure the concentration of 4-chlorophenol in water on line.In this paper,the optical fiber sensor for on-line accurate measurement of 4-chlorophenol concentration is taken as the research object,and the main research work is as follows:1)In order to accurately measure the concentration of 4-chlorophenol separated from multi-component wastewater,the 4-chlorophenol molecularly imprinted polymer was prepared by precipitation polymerization and its adsorption and desorption characteristics were studied.The experimental results show that the maximum adsorption capacity of molecularly imprinted polymer for 4-chlorophenol is 999.042 mg/g,and the adsorption process is highly fitted with the pseudo-second-order adsorption kinetic model.The fitting results of isotherm model show that the adsorption process of molecularly imprinted polymerization has a higher fitting degree with Langmuir isotherm model.When the p H of the adsorption solution is 4.0 and the adsorption temperature is 25℃,the adsorption performance of the polymer is the best.In order to improve the repeatability of molecularly imprinted polymer,its desorption conditions were optimized.When the composition of desorption solution is V_methanol:V_water:V_{acetic acid}=80:18:2,the desorption temperature is 55℃,and the desorption time is 90 min,the desorption efficiency of molecularly imprinted polymer is the highest,and the adsorption capacity can still reach more than 90%of the first adsorption capacity after repeated adsorption-desorption cycles for five times.2)In order to improve the sensitivity of plastic optical fiber sensor to 4-chlorophenol,the structural parameters of optical fiber sensor were studied.Firstly,the influence of D-shaped fiber with different grinding depth on the sensitivity and optical transmission characteristics of the fiber is studied.Then,different molecularly imprinted polymer sols were prepared and coated on the surface of D-shaped optical fiber,and the response characteristics of D-shaped optical fiber coated with different polymers to the same concentration of 4-chlorophenol were studied.Finally,the influence of different sensitive film thickness on the sensitivity of optical fiber sensor is studied.The experimental results show that when the diameter of D-shaped optical fiber is 1.2 mm,the surface of optical fiber sensing area is coated with molecularly imprinted polymer film,and the thickness of the coated molecularly imprinted polymer film is 6.8μm,the sensitivity of optical fiber sensor is the highest,reaching-0.56[（RIU）（μg/L）]^-1.3)In order to obtain the performance parameters of optical fiber sensor,a sensor measurement system was built,and the lower detection limit,response time,repeatability and selection sensitivity of the sensor were studied.The experimental results show that the relative variation of output light intensity（RCTLI）of optical fiber sensor is linearly related to low concentration 4-chlorophenol solution:RCTLI=-7E-07 c+1E-05（R2=0.994）,where c is 100-1000μg/L.The lower detection limit of the sensor is100μg/L;The response time of the optical fiber sensor is 15 min,and the sensitivity of the optical fiber sensor is kept constant when 4-chlorophenol solution with the same concentration is measured three times.