Fluorescence Characteristics Analysis And Application Of Typical Volatile Phenols In Water In Water

Volatile phenol（VPs）has a great impact on ecological environment and human production activities due to its toxicity,corrosiveness and carcinogenicity,so it is particularly important to carry out accurate detection of it.Therefore,it is urgent to establish an efficient,rapid and accurate method for VPs detection.Based on the three-dimensional fluorescence spectral characteristics of VPs,this study innovatively combined fluorescence lifetime（FLT）and fluorescence quantum yield（FQY）,two important luminescent characteristics parameters,to build a rapid detection method for VPs in water,so as to achieve accurate identification of volatile phenolic pollutants with similar spectral characteristics in water.The fluorescence characteristic parameters of 20 typical VPs in aqueous solution were determined,and the effects of the type,number and position of substituents on the fluorescence characteristic parameters of phenolic compounds were analyzed,and the influence mechanism was explored through quantum chemical calculation.The results show that methyl（-₃）,chlorine（-7）)and nitro（-₂）can reduce the fluorescence.The degree of inhibition of fluorescence by substituents was methyl（-₃）>chlorine（-7）)>nitro（-₂）,and the strength of the substituent effect was para-site>intersite>ortho.With the increase of the number of the three substituents,the fluorescence intensity and FQY would decrease until the fluorescence disappeared completely.The FTM of methyl（-₃）and chlorine（-7）)was shortened by ortho-substitution and para substitution.The FTM of chlorine（-7）)was shortened more easily than that of methyl（-₃）.The para substitution of methyl（-₃）and chlorine（-7）)atoms causes the excitation wavelengths（Ex）and emission wavelengths（Em）to redshift with respect to ortho-and meso-sites.The FQY of methyl（-₃）and chlorine（-7）)at different substituent positions are parapet>meso>ortho.There were only slight differences in the three-dimensional fluorescence spectra of the six DMPs.Except for 3,5-DMP,the other five DMPs showed a red shift of about 5 nm relative to the Ex and Em wavelength of PHE.The FQY and FTM of 3,5-DMP were the highest,and those of 2,6-DMP were the lowest.The fluorescence characteristic parameters of 20 typical VPs in aqueous solution were determined,and the effects of the type,number and position of substituents on the fluorescence characteristic parameters of phenolic compounds were analyzed,and the influence mechanism was explored through quantum chemical calculation.The results show that-₃,-7)and-₂ substitution can reduce fluorescence,and the degree of fluorescence inhibition of substituent groups was-₃>-7)>-₂.The ortho-substituent effect was small,the intersubstituent effect was large,and the para-substituent effect was the largest.The Ex and Em wavelengths were redshifted to different degrees by both the interposition and para substitution effects.With the increase of the number of substituents,the fluorescence intensity and FQY of the three substituents all decreased until the fluorescence disappeared completely.-₃ and-7)can shorten the FTM in both ortho and para substitution,and-₃ was more likely to shorten the FTM than-7)substitution.Molecular softness indicates that CHPs were more active than other substances in this group.The CHPs was easy to break,absorb excitation energy and transfer internal conversion energy due to the bond energy of VPs containing heavy atomic substituents（-Cl）was low,so affect the fluorescence emission spectra and fluorescence intensity of phenolic compounds.The molecular softness of alkyl substituted（-₃）VPs was lower than that of PHE only when substituted at para and intersite,resulting in a reduction in fluorescence intensity.The FQY of-₃ and-7)at different substituent positions were as follows:counterpoint substitution>interposition substitution>ortho substitution.-₃ and-7)have the highest FTM.The molecular hardness of 4-CRE was higher than 3-CRE and2-CRE,and that of 4-CHP was higher than 3-CHP and 2-CHP,indicating that the para-substituted electrons were more easily excited,and the fluorescence was more easily produced,and the fluorescence intensity was greater.There were only slight differences in the three-dimensional fluorescence spectra of the six DMPs.Except for3,5 DMP,the other five DMPs showed a red shift of about 5nm relative to the Ex and Em wavelength of PHE.The FQY and FTM of 3,5-DMP were the highest,and those of 2,6-DMP were the lowest.The effects of pH,ion and humic acid on the fluorescence characteristics of 3,4-DMP were investigated.The results showed that the fluorescence characteristics of3,4-DMP were not affected by p H values in the range of 2～8.The FTM of 3,4-DMP was shortened,and the fluorescence intensity and FQY of 3,4-DMP were reduced when the p H value of solution was about 8～14.The ions of0)³⁺、₃^-、₂^-、^-、^-、²⁺、2)²⁺、(7²⁺in water caused the fluorescence intensity of 3,4-DMP to decrease.With the increase of humic acid concentration,the fluorescence peak position of 3,4-DMP did not change,the fluorescence intensity and FQY gradually decreased,and the FTM remained unchanged.The FTM of 3,4-DMP with humic acid and without humic acid were equal,indicating that the fluorescence quenching of 3,4-DMP with humic acid was a static quenching,and non-radiation energy transfer occurred between 3,4-DMP and the quenching agent,which formed a complex and caused the fluorescence quenching.Freshwater lake water（TH）,reservoir water（MY）and sewage plant effluent（WC）were selected as the background,and a certain amount of PHE and 2-CHP were added to test the fluorescence characteristic parameters,respectively.The results showed that the fluorescence peaks of PHE and 2-CHP were produced in three kinds of water bodies.The fluorescence intensity of PHE and 2-CHP was within a certain concentration range and had a linear relationship with the concentration.The FQY of PHE decreases in the effluent（WC）,while the FTM remains unchanged,indicating that the reduction of PHE fluorescence was due to the static fluorescence quenching between PHE and other dissolved organic matter in the water.The p H value of reservoir water（MY）was the most basic,which indicates that the protonation of 2-CHP may lead to the reduction of FQY and the shortening of FTM.The increase of FQY and FTM of 2-CHP in sewage plant effluent（WC）may be due to the reaction of2-CHP with other compounds in sewage plant effluent（WC）to produce new fluorescent compounds.This paper summarized the law of the influence of the type,number and position of substituents on the fluorescence characteristic parameters of VPs,and explored the influence mechanism through quantum chemical calculation,obtained the fluorescence characteristic parameters of 20 typical VPs,and explained the influence mechanism of solution p H,ion,humic acid and actual water background on the fluorescence characteristics of typical VPs in water.It provides important basic data and theoretical basis for accurate tracing of VP pollutants in water,attempts to construct a new method for the detection of volatile phenols.Figure[22]table[33]reference[113]...