Le Xin Song

Formation, structure and physical properties of a series of α-MoO3 nanocrystals: from 3D to 1D and 2D

A variety of α-MoO3 nanostructures, including 1D nanobelts, 2D nanolayers and 3D nanoparticles, were prepared via three methods: sintering AMT, sintering aggregates of AMT with PEGs, and oxidating MoO2. Our results suggested that the surface structures of the α-MoO3 crystals obtained can be controlled by preparation conditions, including sintering temperatures, sintering times and starting materials. Several rough rules were given to explain the influence of the preparation conditions. Also, this work provided a paradigm for the structural regulation of α-MoO3 crystals from 3D to 1D to 2D. Furthermore, the electron structures, photoluminescence performances and photocatalytic properties of the α-MoO3 crystals were investigated. It was found that they were highly dependent on surface features of the α-MoO3 crystals. For instance, the binding energies of Mo 3d3/2 and Mo 3d5/2 increased corresponding to a decrease in surface area of particles, induced by a structural transformation from 3D to 2D. Also, their photoluminescence intensity was greatly enhanced compared to that of commercial α-MoO3. More importantly, fascinating photocatalytic properties of the as-obtained α-MoO3 crystals were also associated with their morphologies and surface areas, for example, the smaller nanoparticles and larger surface areas of the catalysts and the higher photodegradation percentage of methylene blue. Interestingly, the photocatalytic efficiency of all the as-obtained α-MoO3 crystals was much better than commercial α-MoO3. A possible photocatalytic degradation mechanism was proposed. Overall, these results not only enhance our understanding of the relationship between structures and properties of inorganic nanomaterials but also could be potentially useful for new crystal design and growth of inorganic nanomaterials.

Molecule-ion interaction and its effect on electrostatic interaction in the system of copper chloride and β-cyclodextrin.

The present work was devoted to an experimental investigation of the molecule-ion interaction between copper chloride (CuCl(2)) and β-cyclodextrin (CD) and its effect on the electrostatic interaction between Cu(2+) and Cl(-) ions. Our results gave an explicit description of the mutual effect between the interactions. First, the molecular arrangement and surface feature of β-CD experienced a fundamental structural change after interaction with Cu(2+) and Cl(-) ions, which was ascribed to a good separation of Cu(2+) from Cl(-) ions in β-CD matrix. Second, arguments based on electronic structural analysis provided a direct indication of the change in charge density distributions of Cu(2+) and Cl(-) ions in the presence of β-CD. Third, the actual occurrence of a second signal in the course of water release at a higher temperature suggested that the Cu(2+) ions were trapped in the form of hydrates in the crystal interstice of β-CD molecules. Fourth, comparison of the mass spectra indicated that the thermal decomposition of β-CD in the presence of CuCl(2) produced a series of interesting molecular ions: C(3)H(2)OH(+), C(4)H(3)OH(+), C(5)H(4)OH(+), and C(7)H(6)OH(+). We consider that this study is helpful in providing a new approach to the evaluation of the extent of the mutual effect between an inorganic salt and an organic molecule.

Meaningful Differences in Spectral Performance, Thermal Behavior, and Heterogeneous Catalysis between Ammonium Molybdate Tetrahydrate and Its Adduct of β-Cyclodextrin

A novel molecule-ion adduct of ammonium molybdate tetrahydrate (AMT) with beta-cyclodextrin (CD) was prepared in this work. Significant differences in spectral properties between AMT and the adduct AMT-beta-CD were observed by a series of experimental probes, such as powder X-ray diffraction, Fourier transformation infrared spectroscopy, and Raman spectroscopy. Field emission scanning electron microscopy showed that, although the crystal growth of AMT-beta-CD was dominated by the molecular stacking of AMT, the size and morphology of the adduct were rather different from those seen in free AMT. The difference in stacking forms was attributed to the contribution of the molecule-ion interaction between AMT and beta-CD. A drastic improvement in thermal stability of AMT and beta-CD after adduct formation was observed by thermogravimetry analysis, which was confirmed by controlled sintering measurements. This revealed that the adduct interaction between them played an important role in mediating the thermal decomposition process of the adducted components. Furthermore, our results indicated that AMT and its adduct had a different performance in the catalytic desulfurization of thiophene and its derivatives. The fact that the catalytic efficiency of AMT was decreased after adduct formation implied there was a complexation between AMT and beta-CD. Besides, several unusual molecular ions--NH(3)(+), NH(2)(+), and NH(+)--were simultaneously found with gas chromatography coupled to time-of-flight mass spectrometry of free AMT.

Molecule-ion interaction and its effect on coordination interaction.

The present work revealed the presence of the molecule-ion interaction between ethylenediaminetetraacetic acid disodium salt (Na(2)H(2)EDTA) and β-cyclodextrin (CD) on the basis of observable changes in crystal patterns and thermal behaviors before and after interaction. Results from electric conductivity measurements confirmed this presence and showed that the extent of the molecule-ion interaction was associated with the concentration of β-CD. More importantly, the molecule-ion interaction led to a decreased coordination interaction of Na(2)H(2)EDTA and copper chloride, and this decrease exhibited a concentration dependence of β-CD. Similar phenomena were also observed in the case of several analogs of Na(2)H(2)EDTA by UV-vis spectroscopy. A possible explanation was proposed on the basis of the hypothesis that there was a competitive relationship between the molecule-ion interaction and the coordination interaction. Further, nuclear magnetic resonance measurements provided important information on the difference in interaction modes of β-CD with H(2)EDTA(2-) and [Cu(EDTA)](2-). We are of the opinion that the results would provide a significant bridge between coordination chemistry and supramolecular chemistry and help us further understand factors related to different interactions in multicomponent systems.

Important effects of lithium carbonate on stoichiometry and property of the inclusion complexes of polypropylene glycol and β-cyclodextrin.

The present work reveals a significant influence of lithium carbonate (Li(2)CO(3)) on stoichiometry, yield, spectral property, and thermal behavior of the inclusion complex formed by polypropylene glycol (PPG) and β-cyclodextrin (CD). First, the presence of Li(2)CO(3) in aqueous solution leads to the formation of an inclusion complex PPG-(β-CD)(6), which is completely different from that precipitated from pure water. This finding is supported by the result of a similar experiment in the case of lithium chloride, demonstrating that the self-assembling behavior of PPG, a flexible oligomer, and β-CD, a rigid oligomer, in solution can be mediated by additions of the lithium salts. Second, powder X-ray diffraction patterns indicate that the lithium salts in solution play a considerable role in fabricating three-dimensional structures of the complex. Third, the difference in stoichiometry and microstructure of the complexes precipitated from different media is reflected by the difference of their thermal properties. Finally, the results of viscosity, surface tension, and conductivity measurements provide positive support on the effect of the lithium salts on the physical property of PPG solution. Taken together, these observations provide a novel framework for understanding functions of inorganic salts in designing and constructing supramolecules.

Low-temperature carbonization and more effective degradation of carbohydrates induced by ferric trichloride.

The present work is devoted to an attempt to understand the effect of an inorganic salt such as ferric trichloride (FeCl(3)) on the carbonization and degradation of carbohydrates such as β-cyclodextrin (CD), amylose, and cellulose. Our data revealed two important observations. First, the presence of FeCl(3) led to the occurrence of a low carbonization temperature of 373 K. This is a rare phenomenon, in which carbonization improvement is present even if a small amount of FeCl(3) was added. Experimental results had provided evidence for the fact that a redox process was started during the low-temperature carbonization of β-CD, causing the reduction of FeCl(3) to ferrous chloride (FeCl(2)) by carbon materials formed in the carbonization process in air. However, the reduction process of FeCl(3) produced the in situ composite nanomaterial of Fe-FeCl(2) combination in nitrogen. Second, a molecule-ion interaction emerged between FeCl(3) and the carbohydrates in aqueous solution, resulting in a more effective degradation of the carbohydrates. Moreover, our results demonstrated that FeCl(3) played the role of a catalyst during the degradation of the carbohydrates in solution. We believe that the current work not only has a significant potential application in disposal of waste carbohydrates but also could be helpful in many fields such as environmental protection, biomass energy development, and inorganic composite nanomaterials.

Fc-content dependence of composition, structure and degradation degree in supramolecular aggregates of polypropylene glycol, ferrocene and β-cyclodextrin

The present work provides a framework to understand a key question of supramolecular chemistry: how the composition of supramolecular aggregates in multicomponent systems is associated with the initial stoichiometries of aggregated components. In this regard, the presentation and discussion on the importance of the content of ferrocene (Fc) in regulating the composition, structure and degradation degree of a series of ternary aggregates formed by polypropylene glycol (PPG), Fc and β-cyclodextrin (β-CD) reveal several significant findings. First, the higher the initial concentration of Fc, the higher the Fc-content in the aggregates precipitated, the higher the complexation ratio (CR) of β-CD to Fc, the lower the CR of β-CD to PPG. Not only does this significant finding open a window to the design and synthesis of multicomponent aggregates, but also it provides us with a new insight on our understanding of supramolecular stoichiometry. Second, the influence of Fc-content dependences was further supported by differences in microstructure and electronic structure of the aggregates. Third, a positive effect of Fc in improving degradation degrees of organic oligomers aggregated was demonstrated by the facts that the degradation degrees strongly depended on the amount of Fc, and that even in the presence of a little amount of Fc, the positive effect was still apparent. Finally, a further research indicates that the Fe component plays a key role in dominating the thermal degradation process of aggregates compared to the cyclopentadienyl rings. Taken together, these observations provide a scientific basis for the development of new multicomponent aggregates.

Controlled growth and magnetic properties of α-Fe2O3 nanocrystals: Octahedra, cuboctahedra and truncated cubes

A series of α-Fe2O3 crystalline materials with fascinating polyhedral morphologies, such as octahedral, cuboctahedral and truncated cubic structures, were prepared through a novel solid-phase sintering process. Our results demonstrated that the structural transformations among the polyhedra were easily controlled by the sintering times. This suggested that the Wulff polyhedra transformation could occur in a hexagonal crystal system. Furthermore, we found that the magnetic properties of the α-Fe2O3 crystals were associated with their size and shape.

Significant roles of Fe nanoparticles in mediating the thermal properties of polymers

In this work, we make efforts to understand how the stability of a polymer is influenced by the presence of metal nanoparticles. Experimental results from binary systems of Fe nanoparticles with polyethylene glycol (PEG), polypropylene glycol (PPG) and polytetrafluoroethylene (PTFE) revealed several novel and unexpected findings. First, the addition of Fe nanoparticles to PEG elicited a moderate increase in thermal stability and a large change in the degradation mechanism of PEG. Such a mechanism transformation was explained by two factors: 1) the atom-molecule interaction between Fe atoms and O atoms in the PEG molecules and 2) the catalytic effect of Fe nanoparticles. Second, there was a structural rearrangement of fragments from PPG chains during heating in the presence of Fe nanoparticles. This provides important information for material recycling. Third, we found that the use of Fe nanoparticles led to a more complete degradation (99.9%) of PTFE, the appearance of the monomer fragment C2F4+ and an impairment of the etching effect on the quartz injection chamber. We consider that these findings are significant for basic and applied research on polymer materials.

Distinctive electronic structure, unusual magnetic properties and large enhancement in SERS of 1D gallium nanoribbons achieved by doping calix[6]arene

The present work provides a novel route for forming one-dimensional (1D) gallium (Ga) nanoribbon materials with a host molecule calix[6]arene (CA-6) as a template by a facile, one-step and low temperature chemical bath method. Field-emission scanning electron microscopy and transmission electron microscopy showed that the uniform 1D Ga nanoribbon material (Ga-a) can be constructed only in the presence of CA-6, and the formation of ribbon structures is highly dependent on doping ratios and deposition times. Our data indicate that the unusual effect of CA-6 is due to a combination of two factors: a high density of OH groups in the outer surface of its cavity and an appropriate cavity diameter. Especially, the uniform 1D Ga nanoribbon material exhibits a distinct electronic structure and very rare magnetic behaviour when compared to those 3D Ga materials obtained by means of other host molecules: calix[4]arene, γ-cyclodextrin and 18-crown-6. For example, of all the Ga materials, the uniform 1D nanoribbon material has the lowest electron density of Ga core levels in light of X-ray photoelectron spectroscopy analysis. This result suggests that there is a stronger molecule–atom interaction between Ga atoms and CA-6 molecules compared with those in other host–guest systems. More importantly, the uniform 1D Ga nanoribbon material exhibits a magnetic transformation from a diamagnetic to a paramagnetic state under the influence of an applied field, which is completely different from those of all the 3D Ga materials and all the irregular Ga nanoribbon materials. Such a transformation is novel in metals and particularly useful in the chemistry of materials since it allows dramatic modifications of magnetic properties of metal nanocrystals. Finally, a strong surface-enhanced Raman scattering of the uniform 1D Ga nanoribbon material has been observed for organic molecules adsorbed on their surface. Taken together, we believe this work opens a new channel for development of 1D metal-based nanomaterials.