Synthesis Of Hierarchical Cyanide-based Coordination Polymers And Their Applications

Modifying the properties of materials by hierarchical structuring has emerged as one important research field. Hierarchical structure contains multi-levels structure self-assembled from single component nanocrystals and multi-components heterostructure. It has been demonstrated that hierarchical structuring not only makes materials show highly enhanced intrinsic properties, but also endows them multifunctionality and even new properties due to the synergistic and coupling interactions of their building blocks. Cyanide-based coordination polymers are one kind of inorganic-organic hybrid materials self-assembled from metal ions and cyanide ion, which have promising applications in many fields, such as adsorption, sensing, catalysis, energy storage and conversion, and biomedicine. In addition, they are ideal precursors for the fabrication of porous metal oxides, carbon and carbon-based composites. Even through large amounts of hierarchical inorganic materials have been prepared, rare attentions have been paid to cyanide-based coordination polymers due to the lack of their crystallization knowledge. Thus it is urgent and significant task to develop some reaction systems that can synthesize hierarchical cyanide-based coordination polymers, and to reveal the formation mechanisms of these materials. This will not only deepens our understanding of their crystallization knowledge, but also opens up new ways for the synthesis of other coordination polymers and paves the way for the future exploration of their properties.In order to create hierarchical cyanide-based coordination polymers with excellent performances, we develop reverse microemulsion systems, mixed solvents systems and etching-assisted heterogeneous nucleation systems and reveal the formation mechanisms of these hierarchical cyanide-based coordination polymers and investigate their applications. The compositions, morphologies, stucture, the porosity, optical properties and magnetic properties of the obtained products were characterized by X-ray diffraction analysis, Fourier transform infrared spectra, Mossbauer spectrum analysis, electron microscope, surface area analyzer, ultraviolet and visible spectrophotometer, vibrating sample magnetometer. The concentrations of methylene blue were analysized by ultraviolet and visible spectrophotometer and the concentrations of Cs+were determined by atom adsorption spectra. The optothermal properties and magnetothemal properties of the products were measured by a continuous-wave diode NIR (T808D2W) and RF generator (SP-15A). The electrochemical performances of the electrode materials were evaluated by a battery tester. The main results and conclusions are listed as follows:1. One-Pot Synthesis of Prussian Blue Superparticles from Reverse MicroemulsionPrussian blue superparticles (SPs), one kind of highly ordered hierarchical Prussian blue, assembled from monodisperse Prussian blue nanocubes were synthesized by hydrothermal reverse microemulsion method, which employs acidic K3Fe(CN)6 solution as water phase hexadecyltrimethyl-ammonium bromide (CTAB) as surfactant, isopropanol as cosurfactant and cyclohexane as oil phase. These quasi-cubic Prussian blue SPs have an average size of 0.9 μm and they were composed of Prussian blue nanocubes with an average size about 41.36 nm. Various Prussian blue SPs composed of different sizes can be prepared by simply changing the related reaction parameters, such as temperature, concentration of K3Fe(CN)6 and water/CTAB ratio. Time-dependent experiments demonstrated that Prussian blue SPs are formed by self-assembly of in-situ formed Prussian blue nanocubes in reverse microemulsion. It is to be noted that the formation of SPs involved in spontaneous size selection. In addition to hydrophobic interaction of surfactants, geometric complementation factor was firstly suggested to play important role in the self-assembly of Prussian blue nanocubes. This kind of self-assembly is closely related to the morphology of nanocrystals and may loosen the size distribution requirement for nanocrystals self-assembly. The formation process of Prussian blue SPs can be considered as a clear demonstration of detailed formation process of mesocrystals and can deepen our understanding for mesocrystals. Due to unique organization style of nanocubes, these SPs have many voids and show large specific area, and also demonstrate interesting optical property.2. Synthesis of Hollow Prussian White Mesocrystal and Their Enhanced Catalytic PropertyHollow hierarchical Prussian white (PW) self-assembled from nanoparticles were synthesized by hydrothermal reaction in mixed water/ethanol solvents containing K4Fe(CN)6 and benzoic acid. This hierarchical PW possess quasi-cubic framework with a pit and step-like surfaces in each of the six faces, and the size of which ranges from 500 nm to 2 um. In combination of the single-crystal-like electron diffraction behavior as well as the rough surfaces, the hierarchical PW crystals belong to mesocrystals. Time-dependent experiments demonstrated that the formation process of hollow PW mesocrytsals underwent the synthesis and self-assembly of nanoparticles and the following etching processes, along with the morphology change from spherical nanoparticles aggregations, cubic nanoparticles aggregations to the resulted hollow hierarchical strcucture. High supersaturation degree was proved to be essential for the formation of hollow mesocrystals, which is strongly influenced by the concentration of reagents and the polarity of solvents. Increasing the concentration of K4Fe(CN)6 and decrease water/ethanol ratio is favorable for the formation of hollow PW mesocrystals. The Fenton-like catalytic properties of hollow PW mesocrystals in the degradation of methylene blue (MB) was evaluated. Compared to cubic PW crystals (less than 24% MB was decolorized after 5 min), more than three times of methylene blue (MB) (73.9%) was decolorized within 5 min for hollow PW mesocrystals. Moreover, all MB was removed in the presence of hollow PW mesocrystal after 25 min while only less than 43% MB was degraded by cubic PW crystals. The possible reasons for the high performance of hollow PW mesocrystals can be described as two points. Firstly, the hierarchical architecture can provide more active surface sites, such as steps, kinks, corners and edges. Secondly, the nanoscale size of its building blocks and hollow structure enlarges the specific surface area of the hollow PW mesocrystals, and facilitates the mass exchange and catalysis process.3. Synthesis of Three-dimensional Hierarchical Prussian Blue Composed of Nanosheets and Their Enhanced Catalytic and Adsorption PropertiesThe hierarchical Prussian blue composed of nanosheets (HPBNs) were prepared by solvothermal treatment of potassium ferricyanide and hydrochloric acid in the mixture of water/ N,N-dimethylformamide (DMF). The HPBNs was constructed by numerous interconnected nanosheets with thickness about 5 nm, and the size of which ranges from 500 nm to 1.5μm. Time-dependent experiments demonstrated that the formation process of HPBNs experienced the formation and self-aggregation of nanoparticles and the following growth of nanosheets on the previously formed nanoparticles aggregations. The nanosheets were self-assembled from amorphous nanoparticles, which crystallized and attached with each other in crystallographically ordered manner in the following reaction process. It was discovered that species and content of solvent played an important role in the formation of HPBNs. When DMF was changed into dimethylacetamide, ethanol and formamide, it was found that only reaction system using dimethylacetamide produced HPBNs. While, cubic Prussian blue were prepared by employing ethanol and formamide. In addition, increasing the volume ratio of water/DMF from 5/25 to 10/20 and 15/15 lead to irregular cube aggregations. N2 adsorption-desorption analysis exhibited that HPBNs have a high specific surface area (246 m2 g-1) and large amount intrinsic micropores and constricted mesopores originated from the organization of nanosheets. This HPBNs show remarkable catalytic performance in degradation of MB, about 13 and 140 times faster than commercial Prussian blue (CoPB) and micro-scale Prussian blue cube aggregations (MPB). The reason can be ascribed as the following two points:Firstly, the HPBNs provide higher BET surface area and thus more FeⅡ reactive sites. Secondly, the hierarchical structure could effectively prevent the loss of FeⅡ reactive sites caused by agglomeration of particles and large amount of mesopores in the hierarchical structure could more effectively promote the transport of MB and degradation products. Simultaneously, the HPBNs possess enhanced adsorption property of Cs+, about 1.5 and 2 times more than MPB and CoPB. Even though increasing exposed micropores and crystal lattice vacancy of Prussian blue are both effective routes to improve adsorption capacity of Cs+on Prussian blue. However, due to exposure of more surface lattice, HPBNs with the least vacancies still displayed the highest Cs+ adsorption capacity.4. Thermal Transformation of Hierarchical Prussian BlueHierarchical porous Prussian blue (HPPB) composed of ultrathin nanosheets were synthesized by treating sodium ferrocyanide in hydrochloric acid/water/N,N-dimethylformamide mixed solution for 72 h. HPPB show irregular spherical and square-like morphology with size varing from 300 nm to 2 μm. Those particles with large sizes in the resulted products, especially square-like microparticles, are hollow, while other particles with small sizes are often not hollow. Time-dependent experiments demonstrated that those hollow particles were formed based on Ostwald ripening mechanism. In order to reveal the influence of hierarchical structure of Prussian blue on the structure and properties of Prussian blue derived iron oxides, we firstly transformed the above HPPB into iron oxides unde air condition by thermal treatment and examined the transformation process. We found that the resulted products obtained at different temperature were all pure-phase hematites. When the heat treatment temperature was set at 350 C, porous hematites (Fe2O3-Hp35o) that maintained the morphology of HPPB were obtained. When the temperature was increased to 550 ~C, open hollow porous hematites (Fe2O3-HP550) were fabricated. With the further increase of temperature, the whole structure would collapse and seriously aggregated irregular nanoparticles (Fe2O3-HP75o) appeared. Then we prepared irregular Fe2O3 nanoparticles (Fe2O3-N550) and porous microcubic Fe2O3 (Fe2O3-M550) by using non-hierarchical irregular commercial Prussian blue nanoparticles and Prussian blue microcubes as precursors. When evaluated as anode materials for lithium ion battery, Fe2O3-HP550 exhibited superior cycling stability and rate capacity to Fe2O3-N550 andFe2O3-HP550. Fe2O3-HP550 possessed a discharge capacity of 1143 mAh g-1 at 200 mA g-1 in the 40th cycle and also delivered high discharge capacity of 920, 758, 553 mAh g-1 at 500, 1000 and 2000 mA g-15. Synthesis of Metal Oxide@ Cyanide-based Coordination Polymer Heterostrutures and Their MultifunctionalityOne novel and simple spatially confined self-assembly strategy to integrate metal oxides (MOs) with cyanide-based coordination polymer (CCPs) into well-defined hierarchical core@shell heterostructures have been developed. This strategy is based on the simultaneous dissolution of MOs and the formation and self-assembly of CCPs on the surface of MOs in acidic solutions. By controlling the acidity, the dissolution rate of MOs could be easily tailored to regulate the release rate of metal ions. At low H+ concentration, the amount of metal ions released is modest, the cyanometallate ions can terminate them at the moment they are released, leading to the formation of core@shell heterostructures; at high H~ concentration, a large amount of metal ions are released, the cyanometallate ions would be retarded at the surface of the MOs and yolk@shell heterostructures would be obtained. Using truncatedoctahedral Cu2O as core, we obtained well-dispersed core@shell and yolk@shell structured Cu2O@copper ferrocyanide heterostructures. Then using core@shell heterostructure as model,we synthesize various MO@CCP heterostructures, including core@shell Cu2O@[Cu(H2O)2Ni(CN)4], Cu2O@ copper ferrocyanide with different morphologies and spherical Fe3O4@ Prussian blue with different sizes, by changing the compositions of MOs and cyanometallate ions, the size and morphology of MOs. For different reaction systems, the key to obtain well-defined core@shell MO@CCP heterostructures is choosing appropriate acids and controlling their concentration. The obtained Fe3O4@ Prussian blue heterostructures not only exhibit response to magnetic field but also NIR laser irradiation. When examined as hyperthermia agent, they show excellent photothermal and magnetothermal properties, indicating that they can be used as potential multiple-responses thermal ablation agent for cancer therapy.