Photosensitized Mechanism And Photocatalytic Performance Of Phthalocyanines On Polyoxometalates

Due to Polyoxometalate's?POM's?similar chemical composition and electronic properties with TiO₂ semiconductors,and containing a transition metal atom and an oxygen atom in the d⁰configuration,it has a good photochemical activity and has been widely used in energy photocatalysis,environmental photocatalysis,and industrial photocatalysis.However,it is that only ultraviolet light can be used for POM with the large bandgap,while ultraviolet light in the sunlight only accounts for 4%-6%,and visible light reaches 43%-46%.In the process of application,the electrons and holes generated by light excitation are very easy to recombine,which makes the quantum efficiency of light very low and greatly affects the utilization of solar energy and the photocatalytic efficiency.This article addresses the issue of high bandgap of POM and low energy conversion efficiency visible light.The phthalocyanine dye was used to photosensitize POM in order to combine the strong absorption of phthalocyanine towards solar light with the good redox ability and photoelectrochemical properties of POM by using.Not only can it broaden the light absorption range of the photocatalyst,but also greatly increase its photocatalytic efficiency.At the same time,using POM as an excellent electron acceptor can quickly transfer the electrons of dye-excited species,so can effectively prevent the degradation of the dye sensitizer,and construct an efficient,highly stable dye-sensitized POM photocatalyst or system.First of all,cationized zinc phthalocyanine?Y-ZnPc?was obtained by cationizing 8-hydroxyquinoline zinc phthalocyanine?ZnPc?with iodomethane as a quaternizing agent,Then it was electrostatically combined with Keggin-type phosphotungstic acid(H₃PW₁₂O₄₀)to form a water-insoluble association complex ZnPc/PW₁₂,and their structures and morphologies were characterized by Fourier transform infrared?FT-IR?spectrometry,X-Ray Diffraction?XRD?and transmission electron microscopy?TEM?.The ratio of ZnPc and PW₁₂ in the association complex was determined to be approximately 1.1:1 by conductometric titration and TG,and the thermal stability of ZnPc/PW₁₂ was good;The results of UV-Vis absorption spectra,fluorescence emission spectra and cyclic voltammetry showed that ZnPc could makes PW₁₂photosensitized,and the light absorption range of PW₁₂ could be extended to the visible light region.The photoinduced electrons of ZnPc could be transferred to the lowest unoccupied molecular orbit?LUMO?of PW₁₂,which leaded to fluorescence quenching of ZnPc and the enhancement of fluorescence emission intensity of PW₁₂.In addition,the photocatalytic activity of ZnPc/PW₁₂ for the degradation of methylene blue?MB?was studied.The effect of ZnPc/PW₁₂ catalyst on the photocatalytic degradation activity of MB was investigated by changing catalyst dosages and pH and other factors,and the mechanism of its photocatalytic degradation of MB was discussed.The results showed that the formed ZnPc/PW₁₂ composite photocatalyst has visible light absorption and has good visible light catalytic activity for MB.When the amount of ZnPc/PW₁₂ was 0.7 g L^-1,the degradation rate of MB was as high as 97%;The degradation rate of MB increased with the increase of p H ranged from3 to 10,and it was the highest when the solution was at pH=10.Next,zinc phthalocyanine?ZnPc?was combined with Dawson-type phosphotungstate(K₆[?P₂W₁₈O₆₂·14H₂O])and(K₁₀[?-P₂W₁₇O₆₁]·20H₂O)respectively by means of electrostatic interaction to form ZnPc/P₂W₁₈ and ZnPc/P₂W₁₇ association complex and the structures of the two association complexes were characterized by FT-IR.The combination ratio of ZnPc with P₂W₁₈ and P₂W₁₇ in the two association complex were determined to be 1:0.63 and 1:0.34respectively by TG,and the thermal stabilities of them were good;The results of UV-Vis absorption spectra,fluorescence emission spectra and cyclic voltammetry showed that ZnPc has visible light photosensitization on both P₂W₁₈8 and P₂W₁₇,and the light absorption ranges of P₂W₁₈8 and P₂W₁₇ could be both extended to the visible light region.Meanwhile,the photo-induced electrons of ZnPc induced by visible light could be transferred to P₂W₁₈ and P₂W₁₇,resulting in the quenching of ZnPc fluorescence.The energy level of ZnPc could match and with that of P₂W₁₈ and P₂W₁₇ respectively,and the electronic migration between them could process well.The photocatalytic activity of ZnPc/P₂W₁₇ towards the degradation of methylene blue?MB?under visible light was studied,and the effect of dosages of ZnPc/P₂W₁₇ on the photocatalytic degradation of MB was investigated.The results showed that the degredation rate of MB was 98%when the amount of ZnPc/P₂W₁₇ was 0.5 g·L^-1,which proved that ZnPc/P₂W₁₇ association complex had good visible light photocatalytic activity,The photocatalytic activity of P₂W₁₈ for degredation of MB was lower than P₂W₁₇.The photocatalytic activity of P₂W₁₈ for the catalytic decomposition of aquatic hydrogen were studied under visible light in the presences of ZnPc and electron sacrificial agent.The effect of the concentration of P₂W₁₈ on the visible light photocatalytic activity of hydrogen production was investigated.The results showed that in the presence of ZnPc and electron sacrificial agent,P₂W₁₈ exhibited better photocatalytic activity for hydrogen production decomposed by water.With the concentration of ZnPc was 5×10^-4 M and the concentration of P₂W₁₈ was 2.5×10^-8 M,the turn over number reach to 194 under visible light at 9.33 h,...