MgO-Based Composite Fenton-Like And Photocatalytic-Fenton-Like Degradation Of Organic Pollutants In Water

With the rapid development of industry,a large number organic wastewater is discharged into the water system,which is highly toxic,difficult to remove,and bringing a serious threat to human health and ecosystem.Therefore,a green solution is urgently requested.Among the methods,Fenton-like and photocatalytic methods attract attention for high efficiency,environmental friendliness,and ease to operate.However,the Fenton-like method is limited by narrow p H application range and the photocatalytic method is suffered by high photogenerated carrier complexation rate,leading to the limitation of their applications.Magnesium oxide（MgO）is considered as a Fenton-like and photocatalytic catalyst due to its abundant surface defects,large specific surface area,non-toxicity,and low cost.However,wide band gap（Eg=5.6 e V）of MgO induce results in a small light absorption range,easy complexation of photogenerated electron holes,and poor electrical conductivity.Thus,it is necessary to improve the catalytic performance of MgO.Here,MgO is compounded with other semiconductors（Zn Fe₂O₄,ZnO,g-C₃N₄）to form the heterojunctions.Meanwhile,oxygen vacancies are introduced to enhance the performance of Fenton-like catalytic and photocatalytic to achieve the efficient degradation of organic pollutants（Rhodamine Band and Tetracycline）.The details are as follows:（1）The MgO/Zn Fe₂O₄ with different ratios were prepared by sol-gel combined with high-temperature calcination method.and their Fenton-like degradation to Tetracycline and photocatalytic-Fenton-like synergistic degradation to Rhodamine B（Rh B）were investigated,respectively.The iron ions in Zn Fe₂O₄ assist the MgO/Zn Fe₂O₄ exhibiting a high Fenton-like（without light）degradation efficiency of Tetracycline（55.7%）and of Rh B（40%）.To further degrade Rh B,the photocatalytic-Fenton-like synergistic effect of MgO/Zn Fe₂O₄ was applied to increase the degradation efficiency to 69.6%.The conduction band and valence band positions of MgO and Zn Fe₂O₄ were measured.It was determined a type-Ⅱheterojunction was constructed by MgO and Zn Fe₂O₄.The electrons were transferred from the high conduction band（CB=-2.86 V）of MgO to the conduction band（CB=-0.19 V）of Zn Fe₂O₄,which effectively promoted the electron-hole separation and improved the degradation efficiency.Finally,the Fenton-like and photocatalytic-Fenton-like synergistic degradation mechanisms were obtained by quenching experiments,respectively.（2）Oxygen vacancies（OV）can accelerate the decomposition of H₂O₂,generate a large number of active species with redox function,and improve the catalytic efficiency.In this chapter,MgO/ZnO composites were prepared by high temperature calcination to obtain Fenton-like catalysts with different oxygen vacancy concentrations.The oxygen vacancy concentration of the composites was determined by EPR and XPS,and the degradation efficiency of MgO/ZnO on tetracycline was obtained as 82.3%after Fenton-like degradation experiments,and the experimental results showed that a certain concentration of oxygen vacancy has a certain influence on the Fenton-like degradation efficiency.Finally,the mechanism of Fenton-like degradation was obtained by quenching experiments.（3）S-type heterojunction of MgO/g-C₃N₄ with rich Oxygen vacancies were prepared.Mg-N bonds are formed between MgO and g-C₃N₄.Firstly,Oxygen vacancies can be generated by the completion between Mg-N and Mg-O bonds.Further,high-temperature calcination accelerates the generation of oxygen vacancies.It is confirmed that oxygen vacancies improve the efficiency of Fenton-like reactions.Secondly,the Mg-N bond connects MgO and g-C₃N₄ to form an S-type heterojunction,which hinder the recombination rate of electrons and holes to enhance the photocatalytic performance.The degradation efficiency of Rh B was detected to be 80%after photocatalytic-Fenton-like synergy experiments,1.5 and2.8 times more efficient than the degradation of MgO alone and g-C₃N₄ alone,respectively.Finally quenching experiments were conducted to obtain the mechanism of photocatalytic-Fenton-like synergistic degradation.