Study On The Activity Of Solar Driven Z-scheme:Photocatalysts With Noble Metal Surface Plasma Effect

At present,the problems of global resource shortage and environmental pollution are becoming more and more serious in the world.Hydrogen,as a promising energy carrier,has attracted more and more attentions because of its characteristics such as cleanliness,economy and high calorific value.Therefore,it may be widely used to alleviate the global energy crisis in the future.Since the pioneering work of Fujishima and Honda in 1972,photocatalytic hydrogen production has been aroused great interests to researchers.The applications of single component semiconductor photocatalyst for photocatalytic hydrogen production have been reported many times.However,it still has some limitations,such as only responding to the ultraviolet light,rapid recombination of photo-generated carriers and so on.Therefore,the photocatalytic efficiency of semiconductor photocatalysts is still far from ideal in practical application.In this case,a large number of studies have shown that Z-scheme photocatalytic system has many advantages in practical application because it retains stronger redox potential and significantly widens the light response range.However,in order to further improve the photocatalytic efficiency of Z-scheme photocatalytic system,we introduced metal nanoparticles with surface plasmonic resonance（SPR）effect,which can significantly accelerate the transfer of photo-generated electrons and inhibit the recombination of electron-hole pairs.In addition,in this study,we also introduced up-conversion luminescent materials to effectively utilize the near-infrared light in the sunlight.The Z-scheme photocatalytic system can efficiently degrade organic pollutants and produce clean energy-hydrogen.In the first part of the study,a novel Z-scheme Ca F₂:Yb³⁺,Er³⁺@ZnTiO₃/Au/Cd S photocatalyst was prepared.In this system,we introduced an excellent up-conversion luminescence agent CaF₂:Yb³⁺,Er³⁺to broaden the light response range.And also,the efficient charge transfer was achieved using Au with SPR effect.The photocatalytic activity of Z-scheme CaF₂:Yb³⁺,Er³⁺@ZnTiO₃/Au/Cd S photocatalyst was assessed by photocatalytic degradation of norfloxacin and hydrogen production.The effects of sunlight irradiation time,sacrificial agent concentration and cycle times on the performance of the photocatalyst were also discussed.The emission spectrum and energy conversion mechanism of CaF₂:Yb³⁺,Er³⁺were studied.The degradation ratio of norfloxacin reached to 92.05%and the hydrogen production amount reached to513.39μmol/g after 5.0 h sunlight irradiation.The photocatalyst still showed high stability within five cycles.In addition,a possible photocatalytic mechanism of Z-scheme CaF₂:Yb³⁺,Er³⁺@ZnTiO₃/Au/Cd S photocatalyst for the degradation of norfloxacin with simultaneous hydrogen generation was also proposed.In the second part of the study,the WO₃:Yb³⁺,Er³⁺/Ag/Ag₃VO₄/Ag photocatalyst was successfully prepared by hydrothermal and calcination methods.In this system,the introduction of WO₃:Yb³⁺,Er³⁺as excellent up-conversion fluorescence agent and highly active photocatalyst significantly broadened the light response range.The Ag nanoparticles with SPR effect can be used as electron channel and co-catalyst to accelerate electron transfer and increase hydrogen production amount.The photocatalytic performance of WO₃:Yb³⁺,Er³⁺/Ag/Ag₃VO₄/Ag photocatalyst was evaluated by levofloxacin degradation with simultaneous hydrogen production.The effects of sunlight irradiation time,concentration of sacrificial agent and cycle times of catalyst on photocatalytic performance were discussed.The emission spectrum and energy conversion mechanism of WO₃:Yb³⁺,Er³⁺excited at 980 nm were also studied.The degradation ratio of levofloxacin attained to 90.44%and the hydrogen production amount reached to 489.02μmol/g under sunlight irradiation for 180 min.The photocatalyst showed high stability and good reusability within five cycles.We also proposed a possible photocatalytic mechanism of WO₃:Yb³⁺,Er³⁺/Ag/Ag₃VO₄/Ag photocatalyst for LEV degradation with simultaneous hydrogen production.This work provides a new idea for designing high efficiency Z-scheme photocatalytic system.