Preparation And Photocatalytic Performance Of NaYF₄:Yb,RE@Bi₂WO₆ Composites

In this thesis,hydrothermal method was used to synthesize NaYF₄:Yb,Er/Ho@Bi₂WO₆ up-conversion composites,and each sample was characterized by means of XRD,SEM,XPS,specific surface area analyzer,etc.The ore dressing agent ammonium dibutyl dithiophosphate was used as the target pollution to investigate photocatalytic activities of prepare composites.The effects of synthesis conditions on the adsorption and photodegradability of bismuth tungstate were also investigated.?1?NaYF₄:Yb,RE?Er/Ho?materials were prepared by hydrothermal synthesis.The characterization results show that the prepared samples are hexagonal phase NaYF₄when NaF:Y³⁺=12.5:1.As the pH increases,the smoothness of the crystal changes from rough to smooth,and finally the hexagonal prism NaYF₄ nanomaterials with uniform size and morphology are obtained.After exciting by 980nm light,NaYF₄:Yb,Er emits green light of 522nm?541nm and red light of 655nm,NaYF₄:Yb,Ho emits green light of 542nm and red light of 644nm.NaYF₄:Yb,Er/Ho materials were prepared under the condition of pH=9 have the strongest luminous intensity,and the luminous performance of NaYF₄:Yb/Er is better than that of NaYF₄:Yb/Ho.?2?The physical and chemical properties of different doping ratios?pH=9?and different pH conditions?molar doping ratio is 0.15%?on x%NaYF₄:Yb,Er@Bi₂WO₆composites materials were investigated,and the photodegradation effect improved by up-conversion was tested.The results show that all the prepared samples are orthogonal Bi₂WO₆.In the doping ratio range of 0.00%to 1.00%,the specific surface area increases,the crystal size and maximum absorption wavelength of the composite material doped with NaYF₄:Yb,Er decrese compared with pure Bi₂WO₆.As the pH increases from 1 to 11,the crystal size and maximum absorption wavelength of the composite material increase,and the specific surface area decreases.When pH=9 and doping ratio is 0.15%,the crystal particle size,maximum absorption wavelength,and specific surface area of NaYF₄:Yb,Er@Bi₂WO₆ are 22.5nm,429nm,4.63m²/g,respectively.Under the irradiation of infrared lamp,the photocatalytic acitivity of Bi₂WO₆ to rhodamine B was improved after the doping with NaYF₄:Yb,Er.?3?The physical and chemical properties of different doping ratios?pH=9?and different pH conditions?molar doping ratio is 0.15%?on x%NaYF₄:Yb,Ho@Bi₂WO₆composites materials were investigated,and the photodegradation effect improved by up-conversion was tested.The results show that all the prepared samples are orthogonal Bi₂WO₆.In the doping ratio range of 0.00%to 1.00%,the specific surface area increases,the crystal size and maximum absorption wavelength of the composite material doped with NaYF₄:Yb,Ho decrese compared with pure Bi₂WO₆.As the pH increases from 1 to 11,the crystal particle size,maximum absorption wavelength,and specific surface area of NaYF₄:Yb,Ho@Bi₂WO₆ are 21.9nm,449nm,8.59m²/g,respectively.Under the irradiation of infrared lamp,the photocatalytic acitivity of Bi₂WO₆ to rhodamine B was improved after the doping with NaYF₄:Yb,Ho.?4?NaYF₄:Yb,Er/Ho doping ratio and pH value both have significant effect on the grain size,maximum absorption wavelength,and specific surface area of Bi₂WO₆.And then affect the photocatalytic performance of Bi₂WO₆.The photocatalytic properties of the 0.15%NaYF₄:Yb,Er@Bi₂WO₆ and 0.15%NaYF₄:Yb,Ho@Bi₂WO₆upconversion composites synthesized at pH=9 were demonstrated as the optimal photocatalysts to ammonium dibutyl dithiophosphate,and the degradation rates were76%and 77%.Besides,the adsorption process and photocatalytic process of ammonium dibutyl dithiophosphate conform to the quasi-second-order kinetic equation and the first-order kinetic equation,respectively.The equilibrium adsorption amounts are 4.53mg/g and 4.06mg/g,and the degradation rate constants are 0.0087min^-1.0.0090min^-1.As above,that the doping of the up-conversion luminescent materials change the surface properties of Bi₂WO₆ and initiate the usability of infrared light,which might support the theory to the application in the pollution treatment of environment.