Study On Degradation Of Organic Pollutants By Nano-cobalt-zinc Oxide Activated Peroxymonosulfate (PMS)

In recent years,the types and contents of toxic and harmful organic pollutants in water have increased rapidly,which has caused huge harm to the ecological environments and human health.Dye wastewater has become a difficult problem in the treatment of wastewater due to its high concentration and poor biodegradability.Carbamazepine also attracts the attention of many researchers because it is hard to degrade.The current treatment methods are not satisfactory for removing these two refractory organic pollutants,while the advanced oxidation technology based on sulfate radicals has shown the potential to be used for practical applications.However,the catalysts for the activation of peroxymonosulfate（PMS）still have disadvantages.It is urgent to develop new and efficient catalysts to activate PMS to degrade refractory organic pollutants in water.Using zinc-doped cobalt organic metal frames（MOFs）as a precursor,a new type of nano-cobalt zinc oxide material（N-Co₃O₄/ZnO）was prepared through high-temperature calcination,and an efficient and environmentally friendly N-Co₃O₄/ZnO/PMS system was developed to degrade organic pollutants in water.The preparation conditions of N-Co₃O₄/ZnO materials were optimized,and the materials were characterized.The degradation ability,reaction conditions and the reaction mechanism of N-Co₃O₄/ZnO/PMS system on typical organic pollutants（rhodamine B and carbamazepine）in water were discussed,the main research results are as follows:（1）The catalytic performance of nano-cobalt tetroxide（N-Co₃O₄）,nano-zinc oxide material（N-ZnO）and N-Co₃O₄/ZnO for activating PMS were compared.In the degradation of rhodamine B,the reaction rate constant of N-Co₃O₄/ZnO is 0.5380 min^-1.The reaction rates are 14.01 times higher than of N-Co₃O₄(0.0384 min^-1)and 15.37 times of N-ZnO(0.0350 min^-1),indicating that the catalytic performance of the nano-cobalt-zinc bimetal oxide is better than that of the two nano single metal oxides.The optimization experiment results of zinc doping show that the N-Co₃O₄/ZnO with the cobalt-zinc molar ratio of 1:1 presents the best catalytic ability for PMS activation.The N-Co₃O₄/ZnO material maintains the regular dodecahedral structure of the corresponding MOFs precursor.And the distribution of zinc and cobalt in the material is relatively uniform.XPS spectrum shows that zinc doping causes a large amount of oxygen vacancies on the surface of the material,and as the proportion of zinc doping increases,the content of oxygen vacancies also increases.（2）The effects of different factors on the degradation of Rhodamine B by N-Co₃O₄/ZnO/PMS system were discussed.The best reaction conditions were obtained:the solution pH is 7.00,the dosage of N-Co₃O₄/ZnO is 0.20 g/L,and the dosage of PMS is0.10 g/L.Under the condition of 25℃,the removal rate of rhodamine B in the solution reached 100%in 10 minutes.Radical quenching experiments and EPR test results show that·OH,SO₄^-·and ¹O₂ are produced in N-Co₃O₄/ZnO/PMS system.（3）The reaction process of N-Co₃O₄/ZnO/PMS system to degrade rhodamine B conforms to the first-order kinetic equation.Its activation energy is 31.517 kJ/mol.Compared with other catalysts,the catalytic ability of N-Co₃O₄/ZnO is superior.The result of repeated catalyst experiments shows that the removal rate of rhodamine B can be kept above 96%in the process of catalyst reuse in 4 times,indicating that the material has strong stability.The coexistence ion influence experiment shows that Cl^-had almost no effect on the reaction,while HCO₃^-and HPO₄^2-inhibited the degradation of rhodamine B,（4）The effects of different factors on the degradation of carbamazepine in N-Co₃O₄/ZnO/PMS system were discussed.The best reaction conditions were obtained:the solution pH is 7.00,the dosage of PMS is 0.05 g/L,and the dosage of N-Co₃O₄/ZnO is0.05 g/L.Under these conditions,the carbamazepine removal rate reached 100%in 7minutes,and the reaction rate was 0.5278 min^-1.（5）According to the high performance liquid chromatography-mass spectrometry technology,the intermediate product information of carbamazepine degradation was obtained.Combined with related research results,the reaction mechanism of carbamazepine degradation in N-Co₃O₄/ZnO/PMS system was analyzed,and the main degradation pathway of carbamazepine was speculated.