Study On The Influence Of Temperature And Oxidation Potential On The Degradation Rates Of Typical Organic Contaminants During Oxidation Process

The degradation of organic contaminants by oxidation process is one of the most important approaches for pollution control.Among various technologies,increasing reaction temperature and using strong oxidants are effective approaches to improve the degradation efficiency of organic contaminants.Though studies on the degradation experiments of organic contaminants under the effect of temperature and oxidatiom potential enhancement have been relatively mature,the relationship between molecular intrinsic quantum parameters and the removal rates of organic contaminants under the effect of temperature and oxidatiom potential enhancement is still lacking.Besides,the sensitivity of different molecular structures to the temperature and oxidation potential of oxidant is also diverse.Therefore,both experimental and theoretical approaches have been employed to figure out the influence of temperature and oxidation potential on the removal rates of organic contaminants in oxidation processes.Meanwhile,Quantitative-structure-activity-relationship(QSAR)has been used to reveal the internal quantum factors affecting the degradation of organic contaminants under the effect of temperature and oxidation potential enhancement from a micro perspective.The aim of this study is to provide the theoretical guidances for the pollution control of organic contaminants in water.The main contents and conclusions are as follows:(1)The degradation rates of organic contaminants during ozonation increase by an average of 1.070±0.025 times for every 10? rising(The minimum is 1.041±0.009 times for Metanil yellow,while the maximum is 1.120±0.055 times for Brilliant green)in the selected temperature range(25-60?).The developed model for degradation rates of selected organic contaminants during ozonation at different temperatures(lnkO3=4.102+0.007 T-3.419 BOn+1.765 f(+)x+5.698 ELUMO-4.016 EHOMO-0.241 On)shows that the number of oxygen atoms,bond order,Fukui indices and frontier orbital energies are the intrinsic factors for ozonation degradation rates.The optimal QSAR model of activation energies(Ea=18.840-295.644 f(+)x-28.949 Egap+0.001 EB3LYP)suggests that nucleophilic attacks,frontier orbital energies and molecular energies are the intrinsic factors affecting the degradation of organic contaminants under the effect of temperature enhancement during ozonation process.(2)The degradation rates of organic contaminants during Fenton oxidation increase by an average of 1.652±0.930 times for every 10? rising(The minimum is 1.032±0.035 times for Orange G,while the maximum is 5.439±4.665 times for Methyl orange)in the selected temperature range(25-60?).The developed model for degradation rates of selected organic contaminants during Fenton oxidation at different temperatures(lgk=-2.813+0.015 T-15.608 1/T-0.013 Cn+0.361(On:Cn)+7.392 q(CH+)x+1.181 q(C-)x-0.167 Egap+4.120E2gap-2.678 q(H+)+1.475 BOn-15.675 f(+)n+0.383 f(0)x)indicats that partial charge of carbon atoms,Fukui indices,as well as bond order are the intrinsic factors for Fenton degradation rates.The optimal QSAR model of activation energies(Ea=47.273+0.022 EB3LYP+967.312f(0)n-914.483 f(-)n)suggests that electrophilic and hydroxyl radical attacks,as well as molecular energies are the intrinsic factors affecting the degradation of organic contaminants under the effect of temperature enhancement during Fenton oxidation process.(3)The TOC degradation rates of organic contaminants during SCWO increase by an average of 1.915±0.234 times for every 50? rising(The minimum is 1.586±0.448 times for Nitrobenzene,while the maximum is 2.268±0.789 times for Alizarin Yellow GG)in the selected temperature range(350-550?).The optimal QSAR models of activation energies and pre-exponential factors for TOC removal are Ea=60.505+25.791 q(C)x+164.746 f(+)n-0.003 EB3LYP+99.507 EHOMO and A=-1.530-0.001 EB3LYP+9.849 q(C-)x+3.756 BOn+64.526 f(+)n,respectively,which indicate that partial charge of carbon atoms,Fukui indices,total energy of molecules,frontier orbital energies and bond order are the main intrinsic factors for the TOC removal during SCWO.Besides,two kinds of 3D-QSAR models indicate that steric field and hydrophobic field are two main factors for the TOC degradation rates of organic contaminants undergoing SCWO process.(4)The degradation of 30 organic compounds in different oxidation systems was evaluated,including oxygen(O2),hydrogen peroxide(H2O2),ozone(O3)and Fenton oxidation(·OH).Subsequently,two new indices,named potential slope constant ip-x(effect of oxidative ability of oxidant on the degradation rate of organic compound)and apparent working potential E1(i.e.,the working potential of oxidant when the degradation rate of organic contaminant is 1.0 min-1)are proposed based on the relationships between lnk values and oxidation potential of oxidants.Results show that the degradation rates increase by an average of 1.026±1.764 min-1 for every 1.0 V rising potential of oxidant.The average potential slope constant is 5.778±1.319 with the maximum value of 8.250±1.851 for o-Nitroaniline and minimum value of 2.735±0.694 for Methyl red.The average apparent working potential of 30 organic compounds is 2.703±2.696 V.Meanwhile,QSAR models for ip-k and E1 show that ?,q(H)+and q(CH)x+ are main factors influencing the potential slope constants,while q(C-)x,q(H)+and BOx are main factors influencing the apparent working potentials.(5)Effect of temperatuer and oxidation potential on the degradation of organic contaminants was compared by the relationships between activation energy,potential slope constant and structural parameters.QSAR study of activation energy further shows that f(+)n?Egap and EB3LYP are main intrinsic factors for the change of degradation rate in ozonation under the effect of temperature,f(0)n?f(-)n and EB3LYP are main intrinsic factors for the change of degradation rate in Fenton oxidation under the effect of temperature,which suggests that molecular and frontier orbital energies are the main factors influencing the temperature rising effect on degradation rates.While QSAR study of potential slope constant shows that ??q(H)+and q(CH)x+ are main intrinsic factors for the change of degradation rate under the effect of oxidation potential of oxidant,which indicates that the difference of charge distribution is the main factors influencing the oxidation potential rising effect on degradation rates.