Synthesis And Characterization Of Hierarchical Magnesium Borate Nanomaterials And Their Luminescence Properties

The hierarchical nanostructures exhibit not only the initial properties of the nanounits,but also more excellent synergistic effects,which enriches the properties of the nanomaterials and is important for the success of“bottom-up”approaches toward future nanodevices.Consequently,synthesis of the lower dimensional(OD,ID and 2D)nanoscale building blocks into complex architectures has been the focus of significant interest in materials chemistry.Metal borates as host lattices for the luminescent materials have triggered more and more research enthusiasm owing to their convenient fabrication,low synthesis temperature,strong luminescence intensity,high chemical stability and so on.The investigation of the metal borates as host lattices for the luminescent materials is significative both from scientific research and practical points of view.The hierarchical magnesium borate and europium-doped magnesium borate nanomaterials were successfully fabricated by the precipitation process and using poly(vinyl pyrrolidone)(PVP)and 1-ethylpyridinium ethyl sulfate([Epy]EtOS03)as the templates.The as-prepared products were charcterized by XRD,SEM,TEM,FT-IR,PL,etc.The main points can be summarized as follows:(1)The hierarchical flower-like architectures of Mg7B4O13·7H2O have been successfully synthesized via PVP-assisted precipitation process at 80 °C using Mg(N03)2·6H20 and Na2B4O7·l10H2O as the raw materials.The nanostructures with diameters of 0.8-1.2 ?m are built from numerous poly crystalline nanosheets with thickness of about 10 nm.On the basis of a series of time-dependent experiments,the probable growth mechanism of the flower-like nanostructures was proposed.The influence of calcination temperature on the crystal structure and morphology of the products was also investigated.The transformations of the phases can be observed during the calcination process.The overall appearance of flower-shaped sphere was successfully kept after calcination at 550 °C and 650 °C.The adsorption-desorption experiments indicate the products exhibit high specific surface of 111.57 m2/g and large pore volume of 0.37 cm3/g.In addition,the products before and after calcination have mesopores,while a few macropores also exist.(2)The hierarchical Mg3B206:Eu3+ flower-like microsphere phosphors have been successfully synthesized via PVP-assisted precipitation process at 80? and a subsequent calcination using Mg(NO3)2-6H20 and Na2B4O7·l0H2O as the raw materials.After calcination at 650 °C,the precursor was completely converted to Mg3B206:Eu3+ flower-like microsphere with diameters of 2.0-2.5 ?m.And the microsphere is composed of large numbers of nanosheets with thicknesses of 40-60 nm.The excitation spectra of the products monitored at 612 nm show a broad band and a series of sharp bands.And the strongest one is at 393 nm.The products present the strong characteristic emission at 612 nm corresponding to 5D0?7F2 of the Eu3+ transition under 393 nm excitation.Both the Eu3+concentration and the calcination temperature have great effects on the luminescence properties of the products.(3)The core-shell Mg7B4O13·7H2O microspheres have been successfully synthesized via a facile precipitation process at 80 ?,using an ionic liquid[Epy]EtOS03 as an assisted agent and Mg(N03)2·6H20 and Na2B4O7· l0H2O as the raw materials.The diameters of the core-shell Mg7B4O13·7H2O microspheres are 2.0-2.5 ?m.And the core diameter is 1.2?m and the shell width is 400 nm.The microspheres are made up of large numbers of nanosheets with thickness of about 10 nm.The BET specific surface area of the core-shell Mg7B4O13·7H20 microspheres is found to be as high as 214.40 m2/g and the pore volume is 0.80 cm3/g,the average pore diameter is 202 nm.The influences of the ionic liquid adding amounts,reaction time on the morphologies of the final products were investigated.Based on the results,the growth mechanism of the core-shell Mg7B4O13·7H2O microspheres was proposed.The core-shell Mg3B2O6 microspheres with diameters of 2.0-2.5 ?m have been successfully synthesized by thermal decomposition of the as-synthesized Mg7B4O13·7H20 microspheres at 650 °C.The hierarchical Mg3B2O6:Eu3+ core-shell microsphere phosphors have been successfully obtained via the similar synthetic process.The excitation spectrum of the product monitored at 614 nm shows a series of sharp bands.And the strongest one is at 394 nm.The product presents the strong characteristic emission at 614 nm corresponding to 5D0?7F2 of the Eu3+ transition under 394 nm excitation.