Efficiency And Mechanism Of Phenolic Pollutants Photocatalytic Degradation By Co(Ⅱ)-BiOCl@Biochar

Phenolic pollutants can be detected in tap water,underground water,surface water,especially coal chemical wastewater,which has a certain impact on people’s production and life due to its own toxicity.However,owing to the limitations of traditional treatment technologies,the degradation of phenolic pollutants with different substituents in water bodies,especially the refractory ones,is still a hot spot in the field of environmental research.Ultraviolet radiation possesses high energy,easy operation and high efficiency,which result in the photocatalytic oxidation technology based on ultraviolet radiation has attracted much attention of researchers.However,the basic research on the photodegradation of phenolic pollutants with different substituents under ultraviolet light irradiation and the mechanism is still lacking.In this thesis,the degradation efficiency and kinetics of phenolic pollutants with different substituents were studied by using the main wavelength of UV（254 nm）and the mixed wavelength of VUV（185 nm and 254nm）as the light source.A modified bismuth oxychloride（BiOCl）catalyst was prepared with sludge biochar loading and cobalt metal doping.The photocatalytic performance and kinetics under VUV light were also evaluated.At the same time,based on density functional theory（DFT）calculation,the reaction characteristics of phenolic pollutants with different substituents and their degradation mechanism under VUV irradiation were further explored.Using UV and VUV ultraviolet light as the light source,the attenuation law in water under different wavelength ultraviolet light irradiation,the photodegradation efficiency and kinetics of phenolic pollutants with different substituents were investigated.Phenol,catechol,resorcinol,hydroquinone,and p-nitrophenol（PNP）were used as phenolic pollutants with different substituents.The degradation rates of the five phenolic pollutants under UV irradiation were 36.0%,38.3%,37.0%,39.1%,and 14.1%,and the average reaction rate constant was 0.042 min^-1.The degradation rates under VUV irradiation were 99.8%,96.9%,96.0%,97.8%and90.1%,respectively,and the average reaction rate constant was 0.340 min^-1.At the same concentration,the degradation rate of bisphenol A（BPA）under VUV irradiation for 90 min was 53.2%,which was 34.1%lower than that of PNP.The degradation rate under UV irradiation was 29.4%,which was 49.1%lower than that of PNP.The degradation efficiency of phenolic pollutants under VUV irradiation was better than UV irradiation.The degradation efficiency of the phenolic pollutants with electron-donating group is better than that with electron-withdrawing group and that with superconjugated system under ultraviolet light irradiation.The more complex the water quality,the worse the degradation efficiency of phenolic pollutants under ultraviolet light.For natural water bodies,the carboxyl group in humic acid was the main group that inhibited the photodegradation efficiency of phenolic pollutants,followed by the phenolic hydroxyl group.A modified BiOCl catalyst was prepared by one-step hydrothermal synthesis using sludge biochar loading and cobalt doping as modification means,which expected it could solve the problem of poor degradation of phenolic pollutants with electron-absorbing groups or superconjugated system under VUV irradiation.When the mass ratio of sludge biochar to BiOCl was 30%,the doping amount of cobalt was 5%,and the p H value of the solution was not adjusted,the degradation rate of20 mg/L PNP and BPA was 98.2%and 87.3%under VUV UV irradiation for 90 min with the addition of 0.4 g/L catalyst.After five cycles,the degradation rate of PNP was still above 85%,indicating that the Co（Ⅱ）-BiOCl@biochar catalyst had better catalytic performance.In order to explore the reaction characteristics of phenolic pollutants with different substituents and their degradation mechanism under VUV ultraviolet photocatalytic oxidation,quantitative calculations based on DFT theory were used for in-depth analysis.Results indicated that the presence of electron-donating groups would reduce the HOMO,I,μandωvalues of phenolic pollutants.The bond dissociation energies of phenol,catechol,resorcinol,hydroquinone,PNP and BPA were 90.71 kcal/mol,84.71 kcal/mol,90.42 kcal/mol,84.02 kcal/mol,97.03kcal/mol and 397.97 kcal/mol,respectively.Among them,the relationship between the reaction rate constant of phenolic pollutants and BDE isk（28）1.2209-0.0118BDE（10）2.2?10^-5BDE²,which can provide reference for the selection of later removal technology of phenolic pollutants.The degradation of phenol,hydroquinone and PNP under VUV irradiation was mainly photo-excited,·OH electrophilic addition,molecular rearrangement and ring-opening reactions.The main degradation pathway of phenol was pathway D,and the total energy required for degradation to products easily ring-opening was10.02 e V.Pathway C played a leading role in the degradation of hydroquinone,and the total energy required for degradation to products easily ring-opening was 8.4 e V.Pathway F played a leading role in the degradation process of PNP.The average total energy required for degradation to products easily ring-opening was 11.40 e V.Furthermore,·OH electrophilic addition reaction on C6 atom of ring A in BPA is the main reaction path,requiring a total energy of 2.84 e V.However,BPA can only absorb 254 nm light,which can excite the first three energy levels.The electron transition characteristics of BPA are n→π*from oxygen atom to benzene ring andπ→π*local excitation in benzene ring.In addition,the total required energy for photodegradation of BPA to products easily ring-opening was 4.86 e V.For the photocatalytic mechanism of Co（Ⅱ）-BiOCl@biochar under VUV irradiation,the wavelength of 185 nm was absorbed by water molecules to produce·OH.The light wavelength of 254 nm,part of which was absorbed by the pollutant and directly photolysis or produces e^-_aq,the other part excited BiOCl to produce·OH,e^-,h⁺and·O₂^-,which together participated in the degradation of the pollutants.The research results of this paper can enrich the photodegradation law and degradation mechanism of different substituted phenolic pollutants in water,and have important theoretical research significance for the removal of phenolic pollutants in water.