Microwave And Hydrothermal Synthesis And Characterization Of Rare-earth Compounds And Molybdenum Disulfide Nanomaterials

It is known that the size and shape of inorganic nanomaterials have great influence on their physical and chemical properties.Thus,the synthesis and propertycharacterization of inorganic nanomaterials with special morphologies andmicrostructures are of great importance for the basical and applied research of new inorganic functional materials.Rare earth compounds have been widely used in high performance luminescent devices,magnets,catalysts,and other functional materials owing to the numerous well-defined transition modes involving the 4f shell of their ions.It is expected that in nanosized rare earth compounds the luminescent quantum effciency and displayresolution could be improved.Layered transition metal sulfides such as MoS₂ withsandwich structures continue to generate considerable interest because of theirpotential applications in catalyst,potential hydrogen storage media,electrodematerials for Mg ion and Li ion batteries and solid superlubricants.In this dissertation,the rapid microwave heating method and the mild hydrothermal method were employed to prepare a series of rare earth compounds nanomaterials with differentmorphologies,such as Pr(OH)₃ and Pr₆O₇ nanorods,PrF₃ hollow nanoparticles,rareearth ions such as Ce³⁺,Eu³⁺ and Tb³⁺ doped LaF₃ nanoparticles and LaPO₄ nanorods,CeF₃ nanostructures with different morphologies,CePO₄ and Tb³⁺ doped CePO₄ nanorods aggregates with different morphologies,shuttle-like CeOHCO₃ and CeO₂and their corresponding formation mechanisms were discussed;MoS₂ microspheres constructed by nanosheets were successfully synthesized by a mild hydrothermal route with room temperature ionic liquid as an additive.In addition,C/MoS₂composite microspheres have been successfully synthesized via a facile hydrothermal route with glucose as carbon source.The microstructures of the MoS₂ microspheres and the C/MoS₂ composite microspheres were characterized and their formation mechanisms were discussed.In this dissertation,the obtained innovative results are as follows:1)Uniform Pr(OH)₃ nanorods with hexagonal phase were prepared by a facileand rapid microwave heating method and uniform Pr₆O₇ nanorods with cubic phase were also obtained by calcination of Pr(OH)₃ nanorods precursors at 500℃in air.Itwas found that the KOH concentration and microwave heating time had greatinfluences on the size and morphologies of Pr(OH)₃ nanorods.The mechanism for theformation of Pr(OH)₃ nanorods under microwave heating process was preliminarilyproposed;Uniform PrF₃ hollow nanoparticles with hexagonal phase and lanthanideions such as Ce³⁺,Eu³⁺ and Tb³⁺ doped LaF₃ nanoparticles were synthesized by amicrowave heating method.It was found that the PrF₃ nanoparticles had obvious hollow structures and the photoluminescene emission spectra of lanthanide ionsdoped LaF₃ nanoparticles exhibited their characteristic spectra,which indicated thatthe lanthanide ions had been successfully doped in LaF₃ nanoparticles;Lanthanide ions such as Ce³⁺,Eu³⁺ and Tb³⁺ doped LaPO₄ nanorods with hexagonal phase were synthesized by a microwave heating method.It was found that the products had obvious one-dimensional structures and the photoluminescene emission spectra oflanthanide ions doped LaPO₄ nanorods exhibited their characteristic spectra,which indicated that the lanthanide ions had been successfully doped in LaPO₄ nanorods;Shuttle-like CeOHCO₃ with orthorhombic phase were prepared by a microwaveheating method with cetyltrimethyl ammonium bromide(CTAB)as surfacant.Shuttle-like CeO₂ with cubic phase were also obtained by calcination of CeOHCO₃precursors at 500℃in air.It was found that compared with the CeO₂ products prepared without CTAB,the CeO₂ products prepared with CTAB had more smooth surfaces and their UV-vis obsorption bands showed an obvious red shift. 2) CeF₃ nanostructures with hexagonal phase and different morphologies such as disks,walnuts,and particles had been successfully synthesized via a rapid microwave heating method with ethylenediamine tetraacetic acid disodium salt(Na₂H₂EDTA)as complexing reagent.Experimental results showed that some reaction parameters suchas the molar ratio of EDTA/Ce³⁺,reaction time and different fluorides had greatinfluences on the morphologies and sizes of the final products.The possible growthmechanism for CeF₃ nanostructures was presented.The optical properties of thedifferent CeF₃ nanostructures obtained from different fluorides,such as UV-vis obsorption spectra and photoluminescene emission spectra,were also characterized;Uniform CePO₄ and Ce_0.9Tb_0.1 PO₄ nanorods aggregates with monoclinic phase weresuccessfully synthesized by a mild hydrothermal route with ethylenediaminetetraacetic acid disodium salt(Na₂H₂EDTA)as complexing reagent.It was found thatthe CePO₄ aggregates were constructed with many nearly parallel aligned nanorods.The molar ratio of EDTA/Ce³⁺,solution pH and reaction time had great influences on the morphologies and sizes of the final products.The formation mechanism of CePO₄aggregates was investigated.The photoluminescene emission spectra of theCe_0.9Tb_0.1PO₄ aggregates with different morphologies were also invetigated.3) Uniform MoS₂ microspheres with hexagonal phase were successfullysynthesized by a mild ionic liquid-assisted hydrothermal route with sodium molybdate and thioacetamide as precursors and room temperature ionic liquid named1-butyl-3-methylimidazolium tetrafiuoroborate([BMIM][BF₄])or 1-butyl-3-methyli-midazolium hexafluorophosphate([BMIM][PF₆])as an additive.By calcination of thehydrothermal products at 800℃in the atmosphere of N₂ and H₂ for 2h,the MoS₂microspheres with good crystallinity and well-stacked layered structure could be obtained.It was found that the obtained MoS₂ microspheres were constructed with sheet-like structures.The amount and species of the ionic liquid had great influences on the morphologies and sizes of the final products.Ionic liquid played a crucial roleas a templating reagent on formation of MoS₂ microspheres in our experiments.Apossible formation mechanism of MoS₂ microspheres was preliminarily presented.4)Uniform C/MoS₂ composite microspheres have been successfully synthesized via a facile one-pot hydrothermal route with sodium molybdate,sulfocarbamide and glucose as precursors.By calcination of the hydrothermal products at 800℃in theatmosphere of N₂ and H₂,the obtained C/MoS₂ microspheres were still basicallyamorphous.Our studies showed that the appropriate amount of glucose was favourable to formation of uniform C/MoS₂ microspheres and the carbonaceousmicrospheres produced by dehydration of glucose under hydrothermal conditionsprevented the development of layered structures of sheet-like MoS₂ and interactedwith MoS₂ to form the C/MoS₂ microspheres.In the following calcination process,the carbon materials prevented the crystal growth of MoS₂.A possible formationmechanism of C/MoS₂ composite microspheres was preliminarily presented.