Study On Photocatalytic Degradation Of Nitrogen Heterocyclic Compounds In Coal Chemical Wastewater By ZnO And Its Composites

Coal chemical industry is an important strategic position in the national economy.But the composition of coal chemical wastewater is complex,containing tar,phenols,nitrogen-containing heterocyclic organics and other organic compounds,which are difficult to degrade effectively by conventional water treatment processes.Based on the above background,quinoline and pyridine,the typical nitrogen heterocyclic compounds were selected as the target pollutants in this thesis,and ZnO with advantages of stable performance and simple preparation was used as the catalyst to construct the photocatalytic system.In order to improve the photocatalytic performance of ZnO,on the one hand,the recombination of photogenerated electron-hole pairs was inhibited by the construction of heterojunction,and on the other hand,photocatalysis and persulfate advanced oxidation system were coupled to increase the active substance of the reaction.The main research contents and results are as follows:（1）High purity flake ZnO was prepared by hydrothermal method.ZnO was used as the catalyst to construct the photocatalytic system,and the effects of different process parameters on the photocatalytic degradation of quinoline by ZnO were explored.The results showed that when the pH of the solution was 7 and ZnO dosage was 0.5 g/L,the degradation efficiency of quinoline of 20 mg/L in 140 min was 76%.The degradation rate of quinoline decreased by only 6.5%after four cycles,which show excellent photocatalytic stability.Free radical quenching experiments show that·OH,h⁺and·O₂^-all affected the degradation of quinolone by ZnO.Among them,·OH played a major role.（2）LaFeO₃ was synthesized by solvothermal method,and a series of LFO-ZnO composites with different proportions of LaFeO₃ were synthesized by dehydration and shrinkage（LFO is an abbreviation for LaFeO₃）.The results of photocatalytic degradation of pyridine by different materials showed that 10%LFO ZnO showed the best photocatalytic performance.When the 10%LFO-ZnO dosage was 0.5 g/L,the concentration of pyridine was20 mg/L,and the pH of the solution was 7,the removal rate of pyridine can be increased to72%after 140min.The degradation rate of pyridine did not obviously decrease after four cycles of the composite photocatalyst,indicating that the composite material had good photocatalytic stability.Free radical quenching experiments show that·OH,·O^2-and h⁺were all involved in the photocatalytic degradation of pyridine,with·OH playing a leading role.（3）Coupling photocatalytic technology with SO₄^-·advanced oxidation technology,LFO-ZnO/PDS photocatalytic system was construct to strengthen the degradation effect of pyridine.The results show that when the 10%LFO-ZnO dosage was 0.5 g/L,the pH of the solution was 7,and the initial concentration of PDS was 0.5 mmol/L,the removal rate of 20mg/L pyridine in the composite system could reach 91%in 140 min.The degradation rate of pyridine decreased slightly to 83.9%after 4 cycle experiments,indicating that the10%LFO-ZnO composite was stable.The experimental results of free radical quenching experiments show that the active substances produced by LFO-ZnO/PDS photocatalytic system included SO₄^-·,·OH and·O^2-,where SO₄^-·played a leading role in the system.