Preparation,modification And Photocatalytic P Properties Of Hierarchical ZnO Microsphere Composites

ZnO is often used in the photocatalytic degradation of organic pollutants due to its non-toxicity,high stability and low cost.In this paper,a simple synthesis method was firstly used to prepare hierarchical ZnO nanospheres.And then ZnO is modified by the combination of doping Fe into ZnO lattic and loading Ag nanoparticles or carbon quantum dots on its surface to prepare the ZnO-based composites.Finally,using methyl orange solutionas the simulated dye wastewater,the photocatalytic performance of ZnO composites were evaluatedd.And the main researches are as follows:(1)Synergistic modification of ZnO through hierarchical assembly and noble metal loading.Firstly,the ZnO microspheres were prepared by chemical precipitation method,and then ZnO microspheres were modified by the uniform deposition of Ag nanoparticles on the surface of ZnO via the immersion of silver nitrate solution immersion followed by the reduction of sodium citrate(the obtained product was denoted as Ag/ZnO).Then characterized the morphology,composition,structure,specific surface area and spectral characteristics of the sample.The effect of Ag loading contents on the photocatalytic activity of Ag/ZnO was investigated in the degradation of methyl orange under visible light.The results show that Ag/ZnO are flake-shaped microspheres formed by the overlapping ZnO nanosheets,which could effectively avoid agglomeration of ZnO in the catalytic reaction process.Ag nanoparticles were uniformly loaded on the surface of ZnO by the method of immersion/reduction of silver nitrate.The generated plasmon resonance effect of Ag nanoparticles made the absorption band edge of ZnO red shift,and the visible light absorption of ZnO enhance.The photocatalytic activity of Ag/ZnO increased significantly with the increase of the Ag loading content,and the best photocatalytic efficiency of MO was 89.0% under the irradiation of ultraviolet light for 100 min when the feed weight ratio of Ag to ZnO was 8 wt%.(2)Synergistic modification of ZnO through hierarchical assembly,transition metal doping,and noble metal loading.First,a simple hydrothermal method was used to synthesize Fe-doped ZnO nanoflowers(denoted as ZnFeO),and then Ag nanoparticles were uniformly deposited on ZnFeO nanoflowers through the immersion of silver nitrate solution followed by the reduction silver nitrate with TCD.The obtained Ag-loaded ZnFeO nanoflowers were denoted as Ag/ZnFeO.Then characterized the morphology,composition,structure,specific surface area and spectral characteristics of the sample.The effects of the feed molar ratio of Fe to Zn and Ag loading content on the photocatalytic activity of Ag/ZnFeO were investigated in the degradation of MO under the irradiation of visible light The photoelectric properties of Ag/ZnFeO were tested.The results show that Ag/ZnFeO is a hierarchical nanoflower assembled by cypress-like ZnO leaves.Ag nanoparticles were uniformly loaded on the surface of ZnO.Fe doping increased the oxygen vacancies,and the generated plasmon resonance effect of Ag nanoparticles made the absorption band edge of ZnO red shift.The best photocatalytic efficiency of MO was 92.3% under the irradiation of visible light for 80 min when the mass ratio of Fe to Zn was 1.2% and the feed weight ratio of Ag to ZnO was 4 wt%.The morphology,structure and specific surface area of Ag/ZnFeO have not changed significantly after four cycles.(3)Carbon quantum dots(CQDs)after the preparation and modification was used to modify Fe-doped ZnO hierarchical structure and enhance its photocatalytic activity.First,using glucose solution as carbon source and CTAB as morphology control agent,CQDs were prepared by a simple hydrothermal method.Then,CQDs were modified with manganese carbonate to obtain Mn-CQDs.CQDs and Mn-CQDs were uniformly deposite on the hierarchical ZnFeO by a physical method,the obtained products weres denoted as CQDs/ZnFeO and Mn-CQDs/ZnFeO,respectively.Then characterized the morphology,composition,structure,specific surface area and spectral characteristics of the samples.By adjusting the glucose solution concentration and reaction time,the PL and UV-visible light absorption of CQDs and Mn-CQDs are investigated by the optimizing the hydrothermal temperature,hydrothermal time and Mn doping contents.The photoelectric properties of CQDs/ZnFeO and Mn-CQDs/ZnFeO were tested to decompose the influence of the photocatalytic activity of methyl orange.The results show that the particle width of CQDs and Mn-CQDs is about 2 to 3 nm which is larger than CQDs.The CQDs,Mn-CQDs and ZnO compounded to form a heterojunction,which makes the ZnO absorption band gap red shift and enhances the visible light absorption of ZnO.The best photocatalytic efficiency of MO was 82.2% and 91.4% under the irradiation of visible light for 80 min when the contents of CQDs and Mn-CQDs were both 0.4 g/L.The morphology,structure and specific surface area of CQDs/ZnFeO and Mn-CQDs/ZnFeO have not changed significantly after four cycles.