Keggin-based Nanomaterials:Synthesis And Adsorption Of Organic Dyes And Photocatalytic Activity Of O₂ Evolution From Water

At present,organic dye has become one of the environmental pollutants,in which the industrial waste organic dye has become a ubiquitous environmental pollutant.More importantly,most of these dyes contain halogenated,nitro,amino and other toxic and harmful compounds,which will cause serious harm to the water environment.The use of nanomaterials to treat pollutants is being highly valued by experts at home and abroad,which has characteristics of relatively simple,efficient,environmental protection,economic and been expected to play an important role in environmental pollution treatment.Because of the different physical properties of nanomaterials,such as light,heat,electricity and magnetism,there are many novel properties.In contrast,the synthesis method of polyoxometallates(POMs)nanometer materials is relatively unitary,and there is great exploration space in both the preparation method and the application of materials.But the size of POMs limits its practical use.Therefore,the modification and improvement of the POMs to widen spectrum absorption range and reduce the nanometer size,and the development of a new efficient and stable visible light catalyst have become the focus of research in the field of photocatalysis.Therefore,it is of great significance to find a low-cost and highly efficient nanometer sized POMs catalyst to adsorb organic dyes.In this paper,we synthesized 8 kinds of different morphologies of the POMs nanomaterials,which are based on the Keggin type POMs as the basic building blocks and transition metal Ag in the conventional aqueous solution combining soft-chemistry method and micellar directional methods.Further,we obtained two Ag-doped WO3 and MoO3 nanomaterials for the first time through the sintering of the POMs nanomaterials.The effects of different reaction conditions on the structure and properties of the POMs nanomaterials were discussed,and the properties of the adsorbed organic dyes and visible light photocatalytic water oxidation were studied.1.Four Keggin-based nanomaterials(nanomaterials 1,2,3 and 4)were controllably prepared.Further investigations showed that four Keggin-based nanomaterials exhibited fast adsorption rate towards dye molecules.The adsorption efficiency of those compounds(100 mg)towards MB(100 mL of 20 mg/L)could reach up to 96.3%in the initial 5 min under dark condition,the adsorption efficiency sequence is nanomaterials 2>1>4>3.And also,the adsorption efficiency towards RhB(100 mL of 20 mg/L)could reach up to 96.1%in 30 min under the same conditions,the adsorption efficiency sequence is nanomaterials 1>2>3>4.All the investigations indicated that the four kinds of POMs-nanomaterials presented excellent adsorption properties of the organic dyes.2.A large-scale synthesis of Polyoxometalates(POMs)materialse nano-cube(nanomaterials 5),-rectangular(nanomaterials 6),-five sides(nanomaterials 7)and-ball(nanomaterials 8)nanomaterials was performed by a solution-phase route using surfactant(OP-10)as structure modifier.The results suggested that the morphology of the product is largely dependent on the assembly structure of the different amounts of surfactant(OP-10)and coordination between the surfactant(OP-10)and the reactant.3.In this paper,an Ag-doped WO3(nanomaterials 9)and Ag-doped MoO3(nanomaterials 10)composite was prepared by a simple micelle directed method and high temperature sintering route.Nanomaterials 9(nanomaterials 10)also showed excellent adsorption property for RhB and MB in aqueous solution,and the maximum Qt towards RhB and MB were 822 and 820 mg/g for nanomaterials 9(642 and 805 mg/g for nanomaterials 10),respectively.Moreover,the photocatalytic experiments revealed that their oxygen production rates increased to 95.43 μmol/(L,h)for nanomaterials 9(75.45 μmol/(L,h)for nanomaterials 10),which is 9.5 times higher than that of pure WO3:9.012 μmol/(L,h)(7.3 times higher than MoO3:9.00 μmol/(L,h))under visible light illumination(λ≥ 420 nm),respectively.The improvement of photocatalytic activities are attributed to the enhancement of their visible-light absorption and the separation efficiency of photogenerated carriers by Ag doping.The research provides some new ideas for the development of other novel composite photocatalysts.