Photocatalysis Process Of Mesoporous Nb₂O₅ Nanowire And N Doped Ta Oxide

As a emerging green technology,photo-catalysis technology has so many advantages,such as environmental-friendly,energy-saving and non-toxic,etc.and thus is potentially applied in waste water and air purification,water splitting,CO₂ recycling in atmosphere,antivirus sterilization,etc.Therefore,it has gradually become one of hot topic in fields of functional materials and condensed matter physics.Among many photo-catalysts,those traditional metal oxide semiconductors,such as TiO₂ etc.have been most widely studied because of their innocuityc,good stability,and low cost.The traditional photo-catalysts from metal oxide semiconductor only can response to the light with high frequency in a narrow spectrum band due to its wide energy gap,and have relative high recombination between photo-generated electrons and holes,thereby leading to a restrictions on natural light to use and a low efficiency in photo-catalytic process.Therefore,it is very important to increase quantum efficiency and photo-catalytic activity through modifying traditional photo-catalysts and designing novel photo-catalysts of low energy gap.They are summarized in this paper for basic principle on photo-catalysis,main factors affecting the photo-catalytic activity of the photo-catalysts,popular methods to modify semiconductor-based photo-catalysts and some emerging applications of photo-catalysts.In our work,Nb₂O₅ nanowires were prepared by hydrothermal method,and then mesoporous Nb₂O₅ nanowires were obtained through treating Nb₂O₅ nanowires with NH₃ annealing and air re-oxidation respectively;the perovskite type NaTaO₃ with monoclinic structure was synthesized by hydrothermal method as well,and the N-doped NaTaO₃ was obtained through NH₃ annealing treatment of NaTaO₃.The structures of Nb₂O₅ nanowires and N-doped NaTaO₃ were characterized by X ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and X photoelectron spectroscopy（XPS）respectively.In order to simulate process of degrading organic pollutants in water,rhodamine B and methylthionine chloride were chosen as the target dye to evaluate their photocatalytic activity and photostability of Nb₂O₅ nanowires and N-doped NaTaO₃ under exposure of UV-light and visible light repectively.The main conclusions are concluded as follows:（1）Niobic acid was obtained through hydrothermal process of Nb powder and Na OH solution and subsequent ion exchange,then Nb₄N₅ was obtained by nitridation of niobic acid and porous Nb₂O₅ was obtained through re-oxidation of Nb₄N₅.The temperature of oxidation affected formation of Nb₂O₅: When annealing temperature is below 450℃,the crystal of Nb₂O₅ was incomplete in crystallization.（2）Nb₂O₅ nanowires prepared through the 750℃annealing process of niobic acid in Ar have smooth and compact surface,however,these nanowires appear porous morphologic structure on their surface after Nb₂O₅ treated by NH₃ annealing.The pore is in meso-pore size range,and the pore structure is still remained after re-oxidation in air and at a high temperature.It shows that the specific surface area of the porous niobium oxide is about 3 times over that of the non-porous niobium oxide;（3）The XPS spectrum analysis of the porous Nb₂O₅ shows that the chemical state of Nb t in the sample is +5 valence metal oxide;（4）Under the UV irradiation for 2 hours,the degradation proportion of rhodamine B can be up to 94% in the presence of porous Nb₂O₅ nano-wires as a photo-catalyst.Compared with these reported oxide semiconductor photo-catalysts,it shows the better performance to segregate organic compounds under the UV irradiation;（5）A monoclinic crystal NaTaO₃ was fabricated through hydrothermal method of tantalum powder.When it was annealed in NH₃ atmosphere,NaTaO₃ remained monoclinic crystal phase;when annealing temperature was below 650℃,N hardly enter the monoclinic NaTaO₃ lattice;the influence of annealing temperature on crystal structure of the products is not obvious;when the annealing temperature increased to 750℃,new phase of Ta3N5 appeared;the content of doped N increased with temperature;（6）When the annealing temperature is lower than 750℃,NaTaO₃ crystal remains cubic geometrical shape,and its morphology gradually becomes irregular and split into a granular structure once the temperature over 750℃;in addition,annealing temperature obviously affect the N content in N-doped NaTaO₃ corresponding to the color change of N-doped NaTaO₃ from white to dark red increasing with temperature and the annealing time;（7）Comparing with NaTaO₃,N-doped NaTaO₃ shows significant response to a spectrum band with wider frequency region,which is benefit for improving photo-catalytic properties.In the scope of our experiment,doped-N content in N-doped NaTaO₃ photo-catalyst has a optimal value,namely,0.0597,which can be achieved by 650℃ annealing in NH₃ for 3h,and its photo-catalytic power is the strongest ether under UV light or visible light among all samples.20 mg N-doped NaTaO₃ photo-catalyst sample can make 50 ml Rh B aqueous（20mg/L）to degraded 95% under UV-light for 1.5 hour,this value is over nearly 10 times than that of NaTaO₃ in the same condition.