Qsar Study On The Degradation Of Kinetics Of Organic Compounds In UV-H₂O₂/UV/H₂O₂ Processes

UV-H2O2/UV/H2O2 methods have attracted more and more attention as three commonly used sewage treatment methods.In this paper,20 organic compounds were studied.The degradation of organic matter in UV-H2O2/UV/H2O2 system were studied from the perspective of quantum chemistry.The results showed that the degradation rate of the chromaticity and total organic carbon(TOC)at the initial stage of the two systems were consistent with the pseudo first-order reaction kinetics.Eighteen quantum chemical parameters were calculated by Gaussian 09 and Material Studio 7.0,and Quantitative structure-activity relationship(QSAR)of chromaticity and TOC degradation rate were established.The main research contents are as follows:(1)The removal rate and initial reaction rate based on chromaticity and TOC under UV-H2O2/UV/H2O2 systems were compared.It was found that the removal rate of chromaticity and TOC of most substances in the UV-H2O2 system were higher than those of the UV and H2O2 oxidation system.Moreover,the degradation rate of TOC is mostly less than 10%under the H2O2 oxidation system,and the combination of UV and H2O2 has a synergistic effect on the degradation of organic matter.The reaction rate of the UV-H2O2 system is also higher than that of the UV/H2O2 systems,indicating that the oxidation capacity of the composite system is more excellent.In addition,most organic compounds have a lower TOC removal rate than their chromaticity Because TOC represents the total organic carbon,while the removal rate based on chromaticity characterized by absorbance can not represents complete mineralization of the organic compounds.Some substances,such as 2-nitroaniline,have lower removal efficiency and degradation rate in both UV-H2O2/UV/H2O2 systems,indicating that the structure and physicochemical properties of the organic compounds are relatively stable,and the photocatalytic oxidation system can not achieve a good removal results.(2)By calculating 18 quantitative parameters of 20 organic compounds,the correlation between lnKcolor based on chrominance degradation rate(Kcolor)and lnKTOC based on TOC degradation rate(KTOC)and quantitative parameters were analyzed.The results show that in UV-H2O2 system,lnKcolor and lnKTOC have the most significant correlation with the q(C)max.q(C)max represents the maximum electric charge of the carbon atoms.The larger q(C)max is.the more uneven the density of the electron cloud is.It indicates that this part are more easier to attack by oxidants,and the oxidation reaction more easily occurs.In the UV system,lnKcolor has a strong correlation with BOx.BOx is the maximum value of the bond order,and the larger the bond level is,the more difficult it is to react at this part.However,lnKTOC has a strong correlation with EHOMO,and the correlation coefficient is 0.698.EHOMO represents the highest occupied orbital energy of the molecule.The higher the EHOMO is,the more unstable the electrons in the orbit are,and the more likely to start a oxidation reaction.In the H2O2 oxidation system,lnKcolor has a strong correlation with q(CH)max,which represents the distribution of atomic charges on organic molecules.However,lniKTOC has a strong correlation with q(C)max.(3)Four equations based on chromaticity degradation rate and TOC degradation rate under UV-H2O2 system and UV system were established by multiple linear regression(MLR)method.Established optimal models were obtained:the model based on chromacity degradation rate under UV-H2O2 process:lnKcolor=-4.837+12.996*EHOMO+5.655*q(C)max+28.764*f(-)min+39.293*q(CH)max-18.230*q(CH)min;and the model based on TOC degradation rate in UV-H2O2 process:lnKTOC=-0.224+3.115*q(C)max+6.915*EHOMO;then the Model based on chromaticity degradation rate:lnKcolor=-4.612+3.065*BOx+3.917*q(C)max+10.462*EHOMO+5.689*ELUMO;and the model based on TOC degradation rate under UV process:lnKTOC=2.149+16.405*EHOMO.The Model based on chromaticity degradation rate under H2O2 process:lnKcolor=-15.153+52.777*q(CH)max+0.207*?.All the models have passed internal and external tests,which have good robustness and predictive ability.It can be found that all the models in both systems contains parameters EHOMO,so it can be speculated that the electron loss ability of organic matter plays a key role on the degradation process of organic compounds under photocatalytic oxidation systems.