Controllable synthesis,characterization and catalytic performance of a divacant Keggin-type tungstosilicate dimer-estertin derivative
A lacunary Keggin-type tungstosilicate dimer-estertin derivative,(C(NH2)3)7H3.5[K⊂Ni(H2O)2(SnCH2CH2COO)((Ni(H2O))0.75(WO)0.25)(Si2W18O67)]·6H2 O(abbreviated as Si2W18-Ni-SnR-COO,R=CH2CH2),was synthesized by using the conventional aqueous solution method,and character-ized by a series of physical and spectral methods.Single crystal X-ray structural analysis revealed that the polyoxometalate(POM)was a dimeric tungstosilicate-based organic-inorganic hybrid compound,which contained two Ni ions and a cyclic carboxyltin group(SnRCOO).Unexpectedly,the carboxyl-oxygen at-om of SnRCOO acted as a bridging oxygen atom belonged to the POM skeleton and connected to NiO6 oc-tahedron.The thermal and photocatalytic activities of Si2W18-Ni-SnRCOO were studied.As a homogene-ous catalyst,the conversion of cyclohexanol to cyclohexanone was as high as 98％,and the degradation ef-ficiency of 20 mg·L-1 RhB reached 88％.The experimental results showed that the introduction of the carboxyethyltin group significantly enhanced the catalytic activity of this type of POM-based catalyst.Ad-ditionally,the composite of Si2W18-Ni-SnRCOO and TiO2 enabled the catalyst to be recycled,and the pho-tocatalytic efficiency of Si2W18-Ni-SnRCOO/TiO2 remained almost unchanged after five cycles.
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