Preparation Of Heterojunction Composite Based On Metal-organic Framework And Its Application In Photocatalytic Degradation Of Organic Pollutants

The rapid development of pharmaceutical industrialization and the increase of drug consumption have led to the accumulation of antibiotic organic pollutants in industrial wastewater.Photocatalytic oxidation has the advantages of innocuity,safety,low energy consumption,high efficiency and reusability,and is a good method to degrade organic pollutants in wastewater.Metal-organic frameworks(MOFs)are widely used in adsorption and photocatalytic degradation of organic pollutants because of their large specific surface area,high porosity,abundant active sites and easy modification.However,most MOFs have some shortcomings,such as low charge separation efficiency and poor visible light absorption ability.Therefore,people have explored various methods to improve the charge separation efficiency of MOFs,among which the construction of semiconductor/MOFs heterojunction is an effective method.According to the above research background,Z-scheme and p-n type composite photocatalysts based on MOFs were prepared in this paper,and a series of studies on their adsorption and photocatalytic degradation of tetracycline(TC)were carried out:(1)Through the strategy of surface site engineering,BiOBr nanoparticles were uniformly introduced into the channels of NU-1000,and three kinds of BiOBr@NU-1000-X(X=1,2 and 3)Z-Scheme heterojunction photocatalysts with different BiOBr loading were synthesized.XRD,XPS,UV-vis DRS,PL,SEM,TEM and other techniques were used to analyze its structure,morphology and optical properties.The results showed that the absorption area of NU-1000 was enlarged and the forbidden band width was reduced with the addition of BiOBr.Tetracycline(TC)was degraded under visible light irradiation to test the photocatalytic activity of BiOBr@NU-1000-X composite.BNU-X,as a porous composite photocatalyst,was superior to pure BiOBr nanosheets and NU-1000 in adsorption and photocatalytic degradation of TC.Especially,the photocatalytic rate constant k of BNU-2 was 2.2 times and 24.8 times of pure NU-1000 and BiOBr,respectively,and its structure had been maintained after four cyclic tests,which showed that BiOBr@NU-1000-X composite material has good photocatalytic activity and stability.In addition,the possible mechanism of photocatalytic degradation of tetracycline by composite materials was inferred from free radical capture experiment and electron spin resonance experiment(ESR).(2)Cu2O/PCN-222-X(X=10,20 and 30)composite photocatalysts with different Cu2O loadings were prepared by microwave-assisted method.XRD,XPS,SEM,PL and UV-vis were used to characterize the structure,composition and photoresponse of the prepared materials.The analysis showed that the visible light absorption of Cu2O/PCN-222-X composite was enhanced and the photo-generated electrons and holes were effectively separated.TC degradation experiments showed that Cu2O/PCN-222-X composite can effectively adsorb and photocatalytic degrade TC molecules,and the photocatalytic reaction rate constants k of Cu2O/PCN-222-20 was 1.7 times and 65 times of pure PCN-222 and Cu2O,respectively.According to Tauc curve and Mott-Schottky curve,the semiconductor types and energy band positions of Cu2O and PCN-222 were inferred,and then the p-n heterojunction photocatalytic mechanism of Cu2O/PCN-222-X composite was proposed.