Font Size: a A A

Titanium-/Carbon-based Core-shell Nanomaterials: Synthesis And Applications

Posted on:2014-11-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:W LiFull Text:PDF
GTID:1221330464964393Subject:Inorganic Chemistry
Abstract/Summary:PDF Full Text Request
The rational design and controllable synthesis of multifunctional hybrid nanomaterials is the driving force for the continuous development of current material science and human society. Core-shell nanomaterials are a new class of hybrid nanomaterials, in which different component or functional compositions are uniformly and controllably assembled in different space but in one unit. They not only possess the properties of single composition, but also exhibit some new or synergistic effects between the core and shell. Therefore, core-shell nanomaterials are of great interest in a wide range of fields from optics, electronics, sensors, catalysis to energy storage and conversion. So far, a large number of core-shell nanomaterials have been created with a high degree of control over the compositions and properties. However, for practical applications, how to rationally design and controllably synthesize novel functional core-shell nanomaterials and to explore the formation mechanisms is still a great challenge.Through rational consideration of the research frontiers and possible requirements in practical applications of core-shell nanomaterials, this thesis mainly focuses on two aspects:(1) A systematic study on core@TiO2 nanomaterials, including the rational design, controllable synthesis, structure manipulation, function regulation, formation mechanism and their applications; (2) Owing to the excellent properties of carbon, some functional carbon nanomaterials are prepared and used in biomedicine and electrochemical energy storage.In Chapter 2, we devise a versatile kinetics-controlled coating method to synthesize uniform core@TiO2 shell nanomaterials. In this case, the preferential and exclusive heterogeneous nucleation and growth of TiO2 on the surface of cores are realized by precisely controlling the reaction kinetics of TBOT in pure ethanol. To our knowledge, this is the first report on extending the classical Stober method to construct uniform porous TiO2 shells for multifunctional core-shell structures. This method is very simple and reproducible, yet importantly, which is general for diverse cores such as a-Fe203@TiO2, Fe3O4@TiO2, SiO2@TiO2, GO@TiO2, C@TiO2, Fe3O4@SiO2@TiO2, NaYF4:Yb,Er@Si02@Ti02, and so on. The thickness of Ti02 shells can be easily adjusted from 0 to-70 nm by tuning the ammonia content in the system. The resultant α-Fe2O3@TiO2 nanoparticles possess a large surface area of 404 m2/g and a uniform pore size of~2.5 nm, and can be easily crystallized into anatase phase without changing the uniform core-shell structures, which can be used as a high-performance anode material for lithium ion batteries.In Chapter 3, we study the initial molecular structure of the TiO2 shell via the kinetics-controlled coating method proposed in Chapter 2. The XPS and FTIR results show that there are plentiful organic OR moieties in the matrix of the TiO2 shell, suggesting the incompletely hydrolyzed nature of TBOT under the low content of ammonia in this system. As such, we employ an ultrasonic water treatment process to further hydrolyze the TiO2 shell’s frameworks. Using a-Fe2O3 as a typical core precursor, monodispersed mesoprous a-Fe203@mTi02 core-shell nanoparticles with a high surface area of 365.5 m2/g and a large pore size of 2.6 nm can be obtained. After a thermal treatment and a reduction with H2, Fe3O4@mTiO2 mesoporous magnetic core-shell nanoparticles are present with a high surface area (116.2 m2/g) and a large saturation magnetization value (-18 emu/g). The resultant mesoporous magnetic core-shell nanoparticles show a high-performance for effective enrichment of phosphorylated peptides and magnetic separation. The adsorption capacity is up to 300 mg/g.In Chapter 4, we develop a facile "hydrothermal etching assisted crystallization" route to produce titanium-based yolk-shell microspheres with nanosheets-assembled double shells. Using the kinetics-controlled coating method proposed in Chapter 2, a typical sandwich structure (Fe3O4@SiO2@TiO2) can be first synthesized and used as the precursor. During hydrothermal treatment in an alkaline solution, the SiO2 interlayer was first etched, resulting in two discrete interfaces of T1O2 shell for alkaline solution. Followed by concurrent but separate TiO2 layer-etching and epitaxial titanate nanosheets-growth, the yolk-shell structure with nanosheets assembled double shells is achieved. The obtained Fe3O4@titanate microspheres possess a uniform size (~560 nm), good structural stability, versatile ion-exchange capability, a high surface area (150 m2/g), and a large magnetization (17.7 emu/g). The corresponding Fe3O4@s-TiO2 derivatives show excellent photocatalytic activity. More importantly, the shell nanostructure can be easily tailored from single to double one, and the building blocks can also be tuned from 0D nanoparticle,2D nanosheet to ID nanotube.In Chapter 5, we report a simple sol-gel design method for the synthesis of ultra-dispersed TiO2 nanoparticles on graphene. The unprecedented control of the hybrid materials is achieved by the rational separation and precise manipulation over the synthetic processes of a system (involving TiO2 nanoparticles nucleated, grown, anchored and crystallized on GO sheets, the individual separation and reduction of GO sheets). In this case, a slow, uniform, selectively controlled nucleation and growth of amorphous TiO2 nanoparticles on GO sheets over free growth in solution can be first driven by precisely manipulating the rate of hydrolysis and condensation of tetrabutyltitanate (TBOT) via the kinetics-controlled coating method. Owing to the strong covalent bond between them, the amorphous TiO2 nanoparticles can undergo a localized crystallization process to well-defined uniform, small, ultra-dispersed anatase nanoparticles via a thermal annealing approach; and simultaneously, the GO sheets could be easily restored into graphenes. The resultant TiO2 nanocrystals/graphene sheets not only possess ultra-dispersed anatase nanoparticles (-5 nm), ultra-thin thickness and a high surface area of 229 m2/g, but also exhibit a high specific capacity of~94 mAhg-1 at~59 C even if only 52 wt% of the active ingredient, which is twice as that of mechanically mixed composites (41 mAhg-1).In Chapter 6, we have developed a simple and green route to synthesize water-soluble and fluorescent carbon nanospheres via the hydrothermal treatment of cocoon silk in water, without any additives, such as salts, acids, or bases. The obtained carbon nanospheres possess a uniform size of ca.70 nm, a large content of nitrogen (~12.3 wt%) and a high QY of ca.38%. Optical property characterization and cytotoxicity studies indicate that these CNSs display excellent photoluminescent properties and low cytotoxicity, which have been successfully used in imaging living cells and MCF-7 cell tissues at a depth of 60-120 μm. Moreover, the CNSs can be applied as a fluorescent probe for the selective detection of Hg2+ and Fe3+ ions. Most importantly, we have demonstrated that this method features an integrated top-down and bottom-up growth mechanism for the CNSs, which we believe can be extended to high-throughput design and can be used to synthesize functional carbon nanomaterials from abundant natural biomass materials.In Chapter 7, we have demonstrated a simple self-template and shell-protected strategy for the synthesis of mesoporous carbon nanofibers based on a solution-growth pathway. In which, the ethylene glycol (EG) and Zn(CH3COO)2 were used as the carbon precursor and the structural constructor, respectively. The initially formed zinc glycolate fibers can be converted into C@ZnO core-shell nanofibers during the subsequent carbonization process. The formation of ZnO shell is critical for the carbonization of organic materials. After the removal of ZnO with HCl, mesoporous carbon nanofibers can be achived with a high surface area of 1725 m 2/g, a 3D interconnected pore texture, a large pore size of 3.4 nm, and finely developed oxygenated surface functionalities (~9 wt%). The obtained fibers show excellent supercapacitance performance in both aqueous (~280 Fg-1) and organic electrolytes (168 Fg-1) at a current density of 0.5 A/g, and a good cyclic stability.
Keywords/Search Tags:core-shell, yolk-shell, TiO2, carbon materials, graphene, porous materials, bioimaging, photocatalysis, energy storage and conversion
PDF Full Text Request
Related items