Preparation And Photocatalytic Properties Of Graphene-Bi₂WO₆ Composite Photocatalyst

In recent years,environmental pollution and energy shortages have been intensified,environmentally-friendly semiconductor photocatalytic materials were paid more and more attentions because of their unique ability for environmental purification and energy conversion,especially Bi₂WO₆?BWO?photocatalysts with the visible-light-driven photocatalytic activity.However,the utilization efficiency of solar energy and photocatalytic activity of BWO need to be further improved.In this paper,the reduced graphene oxide-Bi₂WO₆?rGO-BWO?microspheres and the different ions doped hybrid photocatalyst of F-rGO-BWO,Ce-rGO-BWO,Ce-F-rGO-BWO,Eu-rGO-BWO,Eu-F-rGO-BWO and Fe₂O₃-rGO-BWO with different photocatalyst had been successfully synthesized via one-step hydrothermal method,which means the effective combination of three modification methods for BWO catalytic performance,such as ion doping,GO composite and morphology control,is realized.The morphology,crystal structure and visible-light photocatalytic performance and their evolution trend of different composite photocatalysts were systematically studied using X-ray diffractometer?XRD?,scanning electron microscope?FE-ESEM?,transmission electron microscope?TEM?,X-ray photoelectron spectroscopy?XPS?,microporous physical adsorption analyzer?BET?,Photoluminescence Spectroscopy?PL?,UV-visible spectrophotometer?Uv-vis?and other analytical instruments.The main conclusions are as follows:The morphology and structure of the rGO-BWO microspheres did not change significantly when the GO addition amount?R_M value?was 2‰-6%,and the addition of GO caused more mesopores to be formed in the microspheres and resulted in an increase in specific surface area.With the increase of GO content,the interplanar spacing of rGO-BWO gradually decreases,the introduction of GO does not change the bonding modes of Bi and WO₆ in BWO crystal,but makes the migration rate of photogenerated carriers faster,and the recombination of electron-hole pairs is effectively suppressed.The absorption wavelength of rGO-BWO firstly undergoes a significant red shift and then changes to a blue shift.The corresponding band gap decreases first and then increases,and its visible light photocatalytic activity first increases and then decreases.Among them,2%rGO-BWO has the largest absorption wavelength?468nm?,the smallest band gap?2.65eV?and the fastest RhB photocatalytic degradation rate,and its degradation rate reaches 95%.In the hydrothermal synthetic process of rGO-BWO microspheres,the F/Ce/Eu doped rGO-BWO and Ce/Eu-F codoped rGO-BWO samples had been synthesized according the different proportion ways and different doping sequences of the introduction of F,Ce and Eu elements.With the increase of F,Ce or Eu doping amount,the microspherical morphology of synthetic samples is gradually destroyed and becomes the disordered nanosheet or nanoparticle clusters,which leads to the final reduction of its specific surface area.On the basis of maintaining good microsphere morphology,the specific surface areas increased gradually and PL emission intensities weakened gradually in accordance with the sequences of rGO-BWO,F/Ce/Eu-rGO-BWO and Ce/Eu-F-rGO-BWO.The XRD diffraction peak of the single doping F/Ce/Eu-rGO-BWO sample showed the different changing regularity.When the small radius ions replaced large radius ions,it led to the interplanar spacing of the samples decresase so that the diffraction peak moved toward the larger angle;oppositely,the diffraction peak moved toward the smaller angle.The substitution of the ions with the same radius can not shift the location of diffraction peak.Ce/Eu ions had the double doping effects.The shift of the diffraction peak of the codoping Ce/Eu-F-rGO-BWO samples depended on the radius of ions and the synergistic effect of Ce/Eu and F ions cooping.The binding energy of the major element of the different single doping F/Ce/Eu-rGO-BWO samples exhibit the different change laws.When the more electronegative ions replaced the less electronegative ions,it made the peaks of the substituted element move slightly in the direction of larger binding energy.Oppositely,the peaks of the substituted element will move slightly in the direction of smaller binding energy.The final shift of the peak of the substituted element of the codoping Ce/Eu-F-rGO-BWO samples depended on the comprehensive results of the synergistic effect of Ce/F ions or Eu/F elements.With the increase of F,Ce or Eu doping amount,the absorption wavelength of the single doped F/Ce/Eu-rGO-BWO samples showed the same change law:the absorption wavelength was firstly increased and then reduced,that is to say,the absorption wavelength firstly undergoes red shift and then changes to obvious blue shift.Meanwhiles,the band gap correspondingly decreases first and then increases.With the increase of Ce/F,Eu/F doping amount,the absorption wavelength of the codoped Ce/Eu-F-rGO-BWO samples had a significant blue shift and band gap increased accordingly.Compared with the largest absorption wavelength of F/Ce/Eu-rGO-BWO sample,the codoped Ce/Eu-F-rGO-BWO samples had a larger absorption wavelength.On the basis of maintaining good microsphere morphology,band gap became smaller gradually in proper order according to the codoped samples,single doped smples,rGO-BWO.The different doped photocatalyst samples could degrade effectively RhB solution under visible light irradiation.The photocatalytic degradation velocity and rate of the codoped samples was faster and higher than that of the single doped smples.Furthermore,because of the double doping effects of Ce/Eu ions,Ce/Eu-rGO-BWO samples were faster photocatalytic degradation velocity than that of F-rGO-BWO sample.Finally,a Fe₂O₃-rGO-BWO heterojunction composite photocatalyst with complete microspherical morphology was successfully prepared by one-step hydrothermal method.On account of the synergistic effect of microspherical morphology,heterojunction and Fe³⁺ion doping,Fe₂O₃-rGO-BWO sample has bigger specific surface area,smaller band gap and faster photocatalytic degradation velocity than rGO-BWO.With the increase of Fe₂O₃ amount,PL emission intensity of Fe₂O₃-rGO-BWO heterojunction decreases first and then increases,the absorption wavelength firstly undergoes a red shift and then changes to a blue shift,the band gap correspondingly decreases first and then increases,and its visible light photocatalytic activity first increases and then decreases.