Photocatalytic Properties Of Metal-doped And Surface-modified ZnO Films

As a third-generation wide-bandgap semiconductor material,ZnO has good thermal stability,low thermal expansion coefficient and high saturation migration speed at room temperature,resulting in broad application prospects in the field of photocatalysis.In this paper,ZnO/PET-ITO and ZnO/PET-GR film samples were successfully prepared by ion sputtering assisted low-temperature hydrothermal method in which the flexible substrate polyethylene terephthalate covered with indium tin oxide(PET-ITO)or graphene(PET-GR)was employed as a growth substrate,Zn(NO₃)₂·6H₂O and C₆H₁₂N₄ were employed as the and a growth materials respectively,with sodium dodecyl benzene sulfonate employed as the surfactant.And through doping modification,ZnO nanorod arrays were prepared by using Ga(NO₃)₃·x H₂O,Cr(NO₃)₃·9H₂O and Li NO₃ as dopants.And then,the TiO₂/Cr-ZnO/PET-GR nanorod array composite structure was prepared in which the Cr-doped ZnO nanorod array was surface-modified with TiO₂.By analyzing the characters of the phase structure,microscopic morphology,species and chemical states of elements,optical properties,electrochemical impedance,(ultraviolet light and sunlight)photocatalytic properties of the film samples,the mechanism of doping modification and surface modification were studied to improve the photocatalytic performance of ZnO.The main research contents were involved as follows:(1)The process parameters for preparing ZnO rod array were optimized.The longer the sputtering time of the seed crystal layer was,the greater the density of the seed crystal layer.Correspondingly,the thickness of the seed crystal layer was also increased,resulting in an increase of the diameter of ZnO nanorods.With an increase of reaction time,the diameter of ZnO nanorods was firstly decreased,and then was increased.The photocatalytic performance of ZnO/PET-GR was better than that of ZnO/PET-ITO,which was up to 90.46%.(2)The growth and photocatalytic properties of ZnO films were modulated by doping modification with Ga,Cr,and Li element.It was shown the ZnO nanorods could be effectively refined by an appropriate doping concentration of the three elements resulting in better crystallinity and uniformity,and without other impurity elements entered the ZnO lattice.Cr element was doped into the ZnO lattice in the form of Cr³⁺and Cr²⁺,and the Cr²⁺concentration was increased with an increase of Cr doping concentration.When the Cr doping concentration was reached to 0.5 mmol/L,better photocatalytic performance was obtained with the degradation rate of MB was 99.26%in 60 min UV photocatalytic degradation,and degradation rate of MB was 29.57%in 120 min sunlight degradation.Based on the frontier orbital theory,it was found that the energy gap of Cr³⁺was lower than that in which Zn²⁺was replaced by Cr²⁺,indicating that Zn²⁺was more conducive to photoelectron generation after it was replaced by Cr³⁺.Doping element entered the ZnO lattice in the form of Ga³⁺.When the Ga doping concentration was reached to 0.03125 mmol/L,better photocatalytic performance would be obtained with the photocatalytic degradation of MB under UV light for 60 min reaching to99.12%.The doping element entered into the lattice of ZnO in the form of Li⁺.When the Li doping concentration was reached to 0.6 mmol/L,better photocatalytic performance would be obtained,with the photocatalytic degradation of MB under UV light for 60 min being up to93.13%.(3)Based on the ion sputtering method,Cr doped ZnO nanorod array was surface modified by TiO₂.Cr-ZnO/PET-GR nanorod array composites decorated with TiO₂ surface by using different sputtering time were prepared.After TiO₂ sputtered,the photocatalytic performance of UV light remained basically the same value,while the photocatalytic efficiency of sunlight was increased to 1.3 times that of the unmodified sample which reached to 38.78%.