Study On The Adsorption Of Mofs And Photocatalytic Degradation Of Dyes By G-C₃N₄ Modified MOFs Composites

Graphite carbon nitride（g-C₃N₄）,as a low-cost and non-toxic semiconductor,has been widely used in the field of photocatalysis because of its suitable band gap,high chemical stability and visible light response.However,its shortcomings,such as small specific surface area,relatively narrow band gap and high recombination rate of photogenerated electron holes,limit its use.Metal-organic frameworks（MOFs）are characterized by large specific surface area and structural diversity,and can be composite with g-C₃N₄.The two materials can be constructed as heterojunction materials to make up for the shortcomings of g-C₃N₄ and improve the photocatalytic performance.The conclusions are as follows:（1）Two kinds of Zr-based MOFs,UiO-66 and UiO-66-NH₂,were prepared by hydrothermal method.By means of SEM,XRD,FTIR and BET,the results showed that the specific surface areas of UiO-66 and UiO-66-NH₂ were 1143.51 m²/g and 833.73 m²/g,respectively.The adsorption of methyl orange（MO）dye was studied.The adsorption isothermal process of UiO-66 and UiO-66-NH₂ was well fitted with the Langmuir model,and the maximum adsorption capacity of the material was 164.41 and 134.80 mg/g,respectively.The experimental results show that the adsorption capacity of UiO-66material fitted by Langmuir model decreases from 164.41mg/g to 127.05 mg/g when the temperature increases from 298K to 318K.With the increase of ion concentration,the adsorption capacity decreases,which may be due to the presence of chloride ion（Cl^-）,which reduces the electrostatic attraction between the dye molecule and the adsorbent surface.When the p H=4,the adsorption capacity of the material to methyl orange was the highest.When the p H value increased,the adsorption capacity of UiO-66 decreased,probably because the electrostatic repulsion between the dye and the material increased under high p H conditions.（2）Using simple grinding method,the prepared g-C₃N₄and UiO-66-NH₂ were composite,and the photocatalytic heterojunction composite CN-UN（X）was successfully prepared.Through the photocatalytic degradation experiment of methyl orange dye wastewater of 15mg/L and 100m L,the photocatalyst dosage of 1g/L,the removal efficiency of CN-UN（2）on methyl orange is the highest within 60min,which is96.1%.The composite material was characterized by a variety of characterization methods,and the results showed that g-C₃N₄ and UiO-66-NH₂ were successfully combined.The specific surface area of the composite is 289.88 m²/g,which is more than ten times that of g-C₃N₄,which is 28.51 m²/g.The large specific surface area provides more active sites for photocatalytic reaction.The experimental results show that the increase of the dosage of catalyst on the one hand will accelerate the rate of photocatalytic degradation of Mo,on the other hand,the excessive dosage will affect the photocatalytic degradation ability.The high initial concentration of Mo will reduce the photodegradation efficiency of photocatalyst,which may be the reaction rate of dye molecules and active substances is affected by the dye concentration.（3）Through free radical capture experiments,it was found that superoxide radical（·O₂^-）played a dominant role in the photocatalytic degradation process,followed by hole（h⁺）and hydroxyl radical（·OH）.The possible degradation mechanism was analyzed.In addition,the degradation intermediate products were detected during the degradation process,and the possible degradation path of MO was proposed.