Ru Doped Tungsten Oxide With Different Morphologies And Their Photocatalytic Performance For Nitrogen Fixation

"Haber-Bosch"nitrogen fixation method,as the most widely used ammonia synthesis process in industry,has made great contributions to social development as well as scientific&technological progress.However,this process not only requires a large number of energy input,but also release an amount of greenhouse gas（CO ₂）which is not environmental friendly.Therefore,it has become a research hotspot in recent years to improve the traditional industrial nitrogen fixation technology and to seek efficient,low consumption and clean nitrogen fixation synthesis method.Visible-light-driven reduction of dinitrogen（N₂）to ammonia（NH₃）has been regarded as one of the most challenging process aroused tremendous attention among scientists.However,there exist some main drawbacks,including lack of efficient photocatalysts,low visible light utilization,weak adsorption and activation capacity for inert N ₂ of the developed photocatalysts prevent their applications.Over the past years,W₁₈O₄₉ has been intensively investigated in N₂ photocatalysis and photoelectrocatalysis because of the defect structure and great visible light absorption performance.However,the single W₁₈O₄₉has the disadvantages of single morphology,high band gap,low defect concentration and rapid el ectron-hole recombination.Herein,W₁₈O₄₉with different morphologies were synthesized by simple solvothermal methods and the photocatalytic performance was enhanced through Ru doping,which would be applied in N₂photofixation reaction process under visible light irradiation.The physical and chemical properties of the as-prepared samples were characterized by various techniques such as SEM,TEM,XRD,XPS,ESR,UV-vis and so on and the relationship between structures and catalytic performances was investigated.Furthermore,we explore the underlying reaction mechanism,and the main research contents and innovative results of the paper are summarized as follows:At first,a series of Ru doped W₁₈O₄₉ bulk catalysts with different doping amounts were prepared by simple solvothermal method in the presence of CTAB.It was found that the photocatalytic nitrogen fixation activity of the prepared bulk W₁₈O₄₉ was enhanced after Ru doping.Under the condition of pure water without sacrificial agent,the 3mol%Ru-doped W₁₈O₄₉ showed the highest activity under visible light irradiation with the ammonia production rate up to 25.8μmol g_cat^-1h^-1,which is 128 times higher than the original W₁₈O₄₉(0.2μmol g_cat^-1h^-1).In addition,the prepared composite photocatalyst showed good recycle property.Secondly,a series of Ru-doped W₁₈O₄₉microspheres photocatalysts were synthesized via a facile solvothermal process without any additives.The morphology and size of the catalysts were adjusted by changing the amount of raw materials,reaction temperature and reaction time.Compared with the large size W ₁₈O₄₉ in bulk morphology,the microsphere catalyst with small size showed better photocatalytic activity.Under the condition of pure water without sacrificial agent,the 3%Ru-doped W₁₈O₄₉microspheres performed the best with an ammonia production rate of 66.4μmol g_cat^-1h^-1,which is 133 times higher than that of pristine W₁₈O₄₉(0.5μmol g_cat^-1h^-1)under visible light irradiation.Moreover,at the same Ru doping amount,its activity is about 2.6 times as high as the bulk one.It was found that the Ru-doping could not only effectively increase the number of defects of semiconductor,but also reduce the bandgap energy of W₁₈O₄₉,which makes the photoexcited electrons transfer to N₂molecule efficiently and better impel the N≡N bond dissociation and N₂ reduction.