| BiVO4 crystal band gap of monoclinic scheelite structure is 2.4eV,which can respond to visible light.It is considered as a new photocatalytic material,which has attracted researchers'attention.In this paper,BiVO4 crystals were synthesized by three preparation methods:the first way is non-polar solvent thermal method with toluene as solvent;the second way is mixed solvent thermal method with toluene-water-ethanol and toluene-ethanol reaction systems;the third way is microwave hydrothermal method with fluorine reaction systems.Using XRD,FESEM and EDS,and the UV-vis characterization methods of BiVO4 crystal phase,microstructure,were characterized visible light response performance analysis,and use the photocatalytic degradation of methylene blue solution experiments,analysis the photocatalytic performance of the sample,the process parameters on the crystal morphology of regulation and control in the process of the experiment effect and the influence of light catalytic properties.The experimental results are as follows:1.Using toluene as solvent of nonpolar solvent hot method,the monoclinic scheelite phase BiVO4 crystals was synthesized from Bi?NO3?3·5H2O and NaVO3 as Bi source and V source,amine as surfactant,reaction temperature as 180?,changed the reaction time.The reaction time increased from 10 h to 20 h,crystal morphology is nanosheet into a stack of nanosheet.When the reaction time was 16h,the nanosheet structure had better dispersion and higher photocatalytic performance.2.Monoclinic scheelite BiVO4 crystals were synthesized by mixed solvent thermal method.The Bi and V sources is Bi?NO3?3·5H2O and NaVO3.?1?The mixed solvent hot method of the three components of toluene-water-ethyl alcohol,controlled the reaction temperature is 180?,reaction time is 20 h,change the amount of ethanol,making the ratio of water alcohol is W/E 30/0,25/5,15/15,10/20,crystal morphology by the accumulation of flower into a dispersed nanosheet.When W/E=15/15,the dispersed nanosheet crystals showed good photocatalytic activity.?2?The mixture of oleamine and oleic acid?OM/OA?was changed by the mixed solvent thermal method of toluene-ethanol two components reaction medium.When only oleamine existed,the crystal morphology was spherical.With the increase of the ratio from 5/1 and 1/1 to 1/2,the crystal morphology changed from nano-flake,flower-like,rod-like to jujube nucleus-like to micron-scale flower clusters.When OM/OA=5/1,the prepared nanoparticles exhibited good photocatalytic activity.3.BiVO4 crystal with monoclinic scheelite phase was synthesized in a reaction system containing fluorine ion by microwave hydrothermal method.The Bi and V sources is Bi?NO3?3·5H2O and NH4VO3?1?The reaction temperature is T=160?,the holding time is t=2h,solution pH is adjusted to 0.52,the amount of fluoride ion is changed.So that[Bi3+]:[F-]is increased from 1:4 to 8:1,the sample microstructure is with high exposure?040?the truncation octahedral structure.When[Bi3+]:[F-]is 1:4,the truncated octahedral side changes from two congruent isosceles trapezoids to an isosceles trapezoid and a parallelogram.When[Bi3+]:[F-]=1:1,the visible light photocatalytic decomposition of water produced oxygen reached 2457?mol/h.?2?We controlled[Bi3+]:[F-]=1:1,T=160?,t=2h,changed the solution pH.when the pH is 6.5and 8.5,there are impurity phases,and the morphology is irregular small particles.BiVO4 crystal of pure monoclinic scheelite phase can be synthesized under the acid condition of pH=0.52 and 3.58,and the morphology is truncated octahedron.?3?We controlled[Bi3+]:[F-]=3:4,t=2h,pH=0.52,changed the reaction temperature from100?,130?,160?to 190?.When the reaction temperature is 100?,synthetic crystals as tetragonal phase.At 130?,the crystal has a mixed crystal phase,which is the tetragonal phase and the monoclinic phase.When the reaction temperature is 160?,there are many grain surface level off is smooth,crystal unified truncation octahedral shape.High temperature to 190?,the?040?crystal plane decreases.?4?We controlled[Bi3+]:[F-]=1:1,T=160?,pH=0.52,change the holding time.When the time is less than40min,the tetragonal phase and the monoclinic phase coexist.When the time is longer than 80min,the crystal is pure monoclinic phase.With the extension of time,the crystal morphology changes from the stage octahedron to the regular tetrahedron which is"cut off"at the top.The degradation rate of the methylene blue solution was up to 83%for the sample with a holding time of 2h. |
PDF Full Text Request