Synthesis And Applications Of Metal-Organic Framework Hollow Nanospheres

Porous metal-organic frameworks (MOFs) consisting of multiple metal ions and polyfunctional organic ligands have received tremendous attention in recent years, due to their fascinating structures, chemical diversity and the myriad potential applications, such as gas storage, adsorption and separations, drug delivery and selectively sensing. More recently, there has been considerable interest in the rational design of sophisticated structures. To date, significant progress has been made in the design and fabrication of MOF-based nanocomposites, core-shell structures, however, the number of reports on hollow MOF nanospheres is significantly limited. Hollow spheres, a very fascinating class of materials with good permeation and low density, have increasingly attracted interest in the last several years because of their wide range of potential applications in photocatalysis, energy storage, controlled delivery, and sensing.In this paper, highly monodisperse metal-organic framework hollow nanospheres have been rationally synthesized using monodisperse polystyrene (PS) nanoparticles as templates through a versatile step-by-step self-assembly strategy. As a result, the as-obtained hollow nanospheres showed well performance in controlled delivery and catalytic activity. The main contents of this thesis are as follows:1. At first, PS@MIL-100(Fe) core-shell nanospheres were prepared using a step-by-step assembly strategy at room tempreture. Then, through immersing the as-prepared core-shell nanospheres into N,N-dimethylformamide (DMF) to remove the PS cores, monodisperse hollow MIL-100(Fe) nanospheres with narrow size distribution were successfully prepared. The shell thickness of the hollow structures presents linear growth with the number of increasing growth cycles, so it is obvious that the shell thickness can be controlled by altering the number of growth cycles during the stepwise MIL-100(Fe) growth process. The Brunauer-Emmett-Teller (BET) surface area of hollow MIL-100(Fe)(25℃,90cycles) nanospheres is determined to be448.22m2/g, which is larger than those made of other materials. The material of MIL-100(Fe) is suitable for the application of drug delivery due to their non-toxicity and good biocompatibility. The hollow MIL-100(Fe) nanospheres adsorbed0.31g of Nimesulide/gram of dehydrated sample by elemental analysis, and it took as long as23d to the complete drug release in physiological saline at37℃.2. In order to further prove the general stepwise strategy providing a feasible path for the fabrication of other hollow MOF spheres, hollow Cu-BTC nanospheres were synthesized under the same reaction conditions. The SEM and TEM images clearly show that the shell thickness of hollow Cu-BTC nanospheres can be easily controlled by altering the number of growth cycles. Compared with hollow MIL-100(Fe) nanospheres, hollow Cu-BTC nanospheres with the same growth cycle number have thicker shells, which is due to the different cell lattice parameters of the two MOFs. Because of the presence of coordinatively unsaturated Cu(Ⅱ) centers in Cu-BTC, we have used hollow Cu-BTC nanospheres as heterogeneous catalyst to effect the aerobic oxidation of benzylic alcohols to the corresponding benzaldehydes. The opposite experiment of Cu-BTC prepared by hydro-thermal method clearly indicates that hollow Cu-BTC nanospheres are better catalyst for the aerobic oxidation of benzylic alcohols. The recyclability of the hollow Cu-BTC nanospheres catalyst was also examined in the aerobic oxidation of benzylic alcohols. The results demonstrate that catalyst possesses long-term stability.3. On the based of hollow MIL-100(Fe) nanospheres, we synthesized Ag/MIL-100(Fe) hollow nanospheres by direct-reduction process and microwave-assisted synthesis. Synthesized by direct-reduction process, Ag/MIL-100(Fe) hollow nanospheres with free-standing Ag cores can be used as selective catalyst. With the help of microwave-assisted synthesis, highly dispersed Ag nanoparticles were load onto MOF hollow nanospheres. Microwave-assisted synthesis is a very effective method, which is not only timesaving and environmental protection, but also solving the problem of aggregation for Ag nanoparticles. Up to now, there is no paper published about Ag/MOFs hollow nanospheres, so it is of some scientific research value.