Rare Earth Fluoride Nanomaterials:Fabrication, Self-assembly, Properties And Application As A Matrix For MALDI-TOF-MS Analysis Of Small Molecules And Polyethylene Glycols

Rare-earth fluorides with controllable shapes and sizes attracted considerable attention as they are widely used in luminescence, biochemical probes, and medical diagnostics for their unique luminescence properties arising from the transitions of 4f electrons. Self-assembly is an effective approach to fabricate the special nanostructures and nanodevices and a key step to put nanodevices into applications. Rare-earth fluorides with hollow structures fabricated by self-assembling method have attracted fascinating interest owing to their higher specific surface area, lower density and better permeation, and widespread potential applications in chemical reactors, drug delivery, catalysis, sensors, and various new application fields. This dissertation mainly researches the fabrication of rare-earth fluorides such as EuF3, SmF3 and EuLnF3 (Ln= Y, Gd, Tb, Dy, Ho, Er, Tm) hollow architectures, and NaTbF4 mesoporous structures prepared by self-assembling methods. We explored a simply and one-pot template-free method to fabricate EuF3 hollow sub-microspheres, hollow hexagonal sub-microdisks and single-crystal hexagonal sub-microdisks; we successfully fabricated single-crystalline SmF3 sub-micropumpkins with a rattle-type structure via a facile aqueous synthetic process; we explored a large-scale and simple approach for the spontaneous assembly of EuLnF3 (Ln= Y, Gd, Tb, Dy, Ho, Er, Tm) alloyed nanocrystals into hexagonal sub-microdisks and hollow sub-microspheres; we established a fabrication method of single-crystalline mesoporous NaTbF4 nano-rice by an EDTA-directed assembly process accompanied by the localized Ostwald ripening. We also employed EuF3 hollow hexagonal microdisks as a background-free matrix for MALDI-TOF-MS characterization of small molecules and PEGs. This dissertation mainly includes the five parts as follows:(1) Hexagonal phase EuF3 hollow sub-microspheres and single-crystal hexagonal sub-microdisks with controllable sizes were fabricated by reaction of aqueous Eu3+ with ammonium fluoride in the presence of ethylenediaminetetraacetic acid (EDTA) and oleic acid. The diameters of EuF3 hollow sub-microspheres and hexagonal sub-microdisks are effectively adjusted by the concentration of Eu3+ ions. Detailed investigations on samples at different preparation stages revealed that the hollow sub-microspheres were formed via a self-transformation process within the same aggregated particles accompanied by the localized Ostwald ripening. Subsequently, hexagonal sub-microdisks were achieved at the consumption of the hollow sub-microspheres, which were attributed to oriented attachment mechanism. Also, single-crystalline EuF3 hexagonal sub-microdisks with hollow interior were fabricated via a facile aqueous synthetic process, which is virtually a cooperation of oriented aggregation process and Ostwald ripening. The luminescent properties of EuF3 hierarchical architectures were studied in detail.(2) Single-crystalline SmF3 sub-micropumpkins with a rattle-type structure have been successfully synthesized in large scale by reaction of aqueous Sm3+ with ammonium fluoride in the presence of EDTA at 110 ℃ for 16 h, which were confirmed by X-ray powder diffraction, energy dispersive X-ray analysis, transmission electron microscopy, and scanning electron microscopy. The EDTA and reaction time have been shown to play important roles in the formation of rattle-structured sub-microcrystals. A mechanism for the formation of the rattle-structured sub-micropumpkins by a cooperation of an oriented aggregation process and Ostwald ripening has been proposed based on observations of time-dependent experiments. In addition, this crystal growth mode could be expanded to the synthesized Eu-doped SmF3 rattle-structured sub-microcrystals.(3) We presented a facile approach for the spontaneous assembly of EuLnF3 (Ln= Y, Gd, Tb, Dy, Ho, Er, Tm) alloyed nanocrystals into hexagonal sub-microdisks and hollow sub-microspheres. By adjusting the Eu/Ln feed ratio in the starting solution, the crystal phases and compositions of the alloyed crystallites can be defined, then the self-assembly process and final morphology would be controlled. The possible formation mechanisms for EuLnF3 alloyed sub-microcrystals with diverse morphologies have been discussed in detail. Our XRD and XPS analyses indicate that EuLnF3 alloyed nanocrystals were formed by nucleation-directed epitaxial growth. Also, the studies illustrate that the luminescence properties of Eu3+ can be improved by doping appropriate Ln3+ ions.(4) Single-crystalline mesoporous NaTbF4 nano-rice have been successfully synthesized in large scale by reaction of aqueous Tb3+ with sodium fluoride in the presence of EDTA at 110 ℃ for 12 h, which were confirmed by X-ray powder diffraction, energy dispersive X-ray analysis, transmission electron microscopy, scanning electron microscopy, and nitrogen adsorption-desorption isotherms. A mechanism for the formation of the mesoporous nano-rice by an EDTA-directed assembly process accompanied by the localized Ostwald ripening has been proposed based on the observations of time-dependent experiments. In addition, this novel nano-rice can be used as an excellent host lattices for Eu3+ ions, in which the luminescence properties of Eu3+would be improved significantly. Our study indicates that the maximum quantum efficiency of NaTbF4:Eu nano-rice is as high as 69.9%.(5) We reported the use of EuF3 hollow hexagonal sub-microdisks for MALDI-TOF-MS characterization of small molecules and PEGs. The long-lived excited state of europium ions can transfer energy to high-energy vibrations of organic molecules, which provides the potential technological application in MALDI-TOF-MS analysis of small molecules and PEGs. The efficiency of the hollow sub-microdisks as a novel matrix of low molecular weight compounds was verified by analysis of small peptide, amino acid, organic compounds, fullerene, and hydroxypropyl β-cyclodextrin (HP-β-CD). The advantage of this matrix in comparison with a-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB) was demonstrated by MALDI-TOF-MS analysis of an amino acid mixture and a peptide mixture. This matrix is successfully used for analysis of PEGs (PEG 2000, PEG 4000, PEG 8000, PEG 15000 and PEG 30000), suggesting a potential for monitoring reactions and for synthetic polymers quality control. The upper limit of detectable mass range was ～35000 Da (PEG 30000).