Research On Optical Fiber Sensor For Detecting Hydroxyl Radical Concentration

With the development of social economy,the problem of environmental pollution is becoming more and more serious,especially organic wastewater pollution.Organic pollutants in wastewater not only pose a threat to water resources,but also pose a threat to human health.In order to effectively remove organic pollutants in water,methods such as physical adsorption,biodegradation,advanced oxidation,and Fenton are widely used;among them,Fenton based on the reaction of hydrogen peroxide（H₂O₂）and Fe²⁺to generate hydroxyl radicals（·OH）The method can realize rapid mineralization of various organic pollutants and is widely used.In the Fenton reaction system,the·OH concentration directly determines the oxidation and mineralization ability of wastewater,and ultimately determines its degradation performance;therefore,accurate online detection of·OH concentration change information can reveal the mechanism and law of Fenton’s degradation of organic wastewater,and improve the Both wastewater degradation and mineralization capabilities are very important.However,the fast reaction rate of Fenton(the reaction process of H₂O₂and Fe²⁺is difficult to control)and the short lifetime of·OH have brought great challenges to the measurement of·OH concentration.In order to realize the on-line measurement of·OH concentration,this paper intends to use the ultraviolet radiation method which is easy to control the production of·OH of H₂O₂（H ₂O ₂（?）2·OH）to realize the production of·OH and the measurement of H2O2,so as to realize the indirect measurement of·OH concentration.In order to realize the measurement of·OH and H₂O₂concentration,two kinds of optical fiber sensors based on wavelength demodulation and intensity demodulation are constructed in this paper.The main research results are as follows:（1）The wavelength demodulation sensor of·OH fiber based on surface plasmon resonance was prepared.The effects of dopamine（DA）polymerization time and temperature on the fiber surface and the adsorption time of gold nanoparticles on the performance of the sensor were experimentally studied.The experimental results show that when the polymerization time of DA is 20 min,the polymerization temperature is 25℃,and the adsorption time of gold nanoparticles is 2 h,the resonant spectral transmittance of the sensor is the lowest,the full width at half maximum is the narrowest,and it is the most favorable for realizing the concentration of·OH and H₂O₂.Among them,after 100μmol/L H₂O₂is irradiated with ultraviolet rays for different times,the functional relationship between the sensor wavelength shift（y）and the time（t）of ultraviolet irradiation of H₂O₂within 0-120 min is y=0.075 t+10.183（R²=0.995）;in the concentration range of 20-100μmol/L H₂O₂,the sensor wavelength shift（x）has a good linear relationship with the H₂O₂concentration（c）x=0.105 c+3.791 E-4（R²=0.997）,the sensitivity is 0.105 nm/（μmol/L）,the response time is 180 s,the lower detection limit is 20μmol/L,and the sensor has good selection sensitivity and repeatability;·OH concentration（Z）and the sensor wavelength offset（y）have a linear response relationship Z=-20.140 y+203.904（R²=0.998）,the maximum relative error is 8.75%,and the linear detection range is 6-160μmol/L.（2）In order to reduce the cost of sensor analysis equipment,this paper further developed an intensity-demodulated fiber-optic evanescent wave sensor,and prepared a polydopamine-loaded enzyme-based·OH fiber-optic evanescent wave sensor.Effects of oxidase（HRP）fixation time and concentration and H₂O₂solution test temperature on sensor performance.The experimental results show that when the DA polymerization time is 30 min,the polymerization temperature is 15℃,the HRP fixation time is 2 h,the HRP concentration is 0.10 mg/m L,and the H₂O₂solution test temperature is 25℃,the sensor performance reaches the best;After 40μmol/L H₂O₂was irradiated with ultraviolet rays for different times,the functional relationship between the sensor output signal（r）and the H₂O₂light radiation time（t）within 0-150 min was expressed as r=8.826 E-5 t-0.016（R²=0.992）;in the range of 8-40μmol/L H₂O₂concentration,there is a good linear response relationship between the sensor output signal（RCTLI）and H₂O₂concentration（c）RCTLI=-4.295 E-4 c-2.947 E-7（R²=0.996）,the sensitivity is-4.295 E-4/（μmol/L）,the response time is 180 s,the lower detection limit is 8μmol/L,and the sensor has good selection sensitivity and repeatability;·OH concentration（Z）and the relationship between the sensor output signals（r）is Z=4731.228 r+79.693（R²=0.994）,the maximum relative error is 8.63%,and the linear detection range is 3-64μmol/L.（3）In order to further improve the sensitivity of the intensity-demodulated optical fiber sensor,a silane-loaded enzyme-based·OH optical fiber sensor was further developed.The concentration and cross-linking time of glutaraldehyde（GA）,the fixation time and concentration of HRP,and the test temperature of H₂O₂solution were experimentally studied.Influence on the performance of the sensor,the experimental study shows that when the GA concentration is 2%,the GA cross-linking time is 30 min,the HRP concentration is 0.10 mg/m L,the HRP fixing time is 3 h,and the H₂O₂solution test temperature is 30℃,the sensor can be improved.The sensitivity is optimal;after 20μmol/L H₂O₂is irradiated with ultraviolet rays for different times,the functional relationship between the sensor output signal（r）and the H₂O₂light irradiation time（t）within 0-170 min is expressed as r=4.255 E-5 t-0.009（R²=0.992）;in the range of 4-20μmol/L H₂O₂concentration,the linear response relationship between the sensor output signal（RCTLI）and H₂O₂concentration（c）is RCTLI=-5.034 E-4 c-1.921 E-5（R²=0.994）,the sensitivity was improved to-5.034 E-4/（μmol/L）,the response time was 180 s,and the detection limit was 4μmol/L,and the sensor has good selection sensitivity and repeatability;·OH concentration（Z）and the relationship between the sensor output signals（r）is Z=4795.094 r+44.156（R²=0.998）,the maximum relative error is 9.10%,and the linear detection range is 1-32μmol/L.