Jiqing Jiao

Facile synthesis of FeS2 nanocrystals and their magnetic and electrochemical properties

Metal sulfides have received growing attention as electrode materials for lithium ion batteries. However, large volume changes often cause a sharp decrease in capacity and thus leads to poor cycling performance. Here, we developed a facile hydrothermal process for preparation of FeS2 nanocrystals (NCs) with diameter ranging from 10 to 35 nm and tested them as anode materials for lithium-ion batteries. In comparison with FeS2 micro-particles, these FeS2 NCs show higher capacity, a more stable discharge plateau and better cycling performance. Moreover, we studied the magnetic properties of these FeS2 NCs in detail for the first time. The two as-prepared FeS2 NCs have completely different magnetic properties. FeS2 NCs prepared from Fe(acac)3 show antiferromagnetism at room temperature and exhibit weak paramagnetism at low temperature. However, when nano-Fe3O4 was used as the iron source, the synthesized products show ferromagnetic and paramagnetic behaviors which is due to the formation of a trace amount of pyrrhotite in the main phase. Our results indicate that detection of the trace amount of impurity in the main FeS2 phase by traditional methods such as XRD, EDS, XPS and even room-temperature Mossbauer spectroscopy is ineffective, and that magnetic measurements alone are reliable.

Synthesis of FeS2 and Co-doped FeS2 films with the aid of supercritical carbon dioxide and their photoelectrochemical properties

The prepared FeS2 and Co-doped FeS2 films revealed better properties in photocurrent response and photocatalysis of water photolysis under simulated sunlight. The films were synthesized on iron substrates with the aid of supercritical carbon dioxide. The experimental results demonstrated that the supercritical carbon dioxide could play an important role in evolution of phases and morphologies during the reaction process. Moreover, the prepared films were characterized by XRD, SEM, TEM and EDS. The UV-vis absorption spectroscopy indicated that the absorption edge has obvious blue shift compared with bulk FeS2. Interestingly, characteristics of photoelectric response and water photolysis were shown by photoelectrochemical experiments under sunlight. Therefore, the prepared films would have an advantage in water photolysis utilizing sunlight.

Two-step synthesis flowerlike calcium carbonate/biopolymer composite materials

The CaCO3/biopolymer composite materials have been prepared by a two-step synthesis. The biopolymer was synthesized from chitosan and acrylic acid in supercritical carbon dioxide, then a large scale of novel flowerlike structured calcite CaCO3 on the biopolymer has been synthesized for the first time by the following process of mineralization. The well-defined flowerlike morphology consisting of orderly and regular petals could be tailored by controlling the reaction time. The morphology evolution of CaCO3 was investigated by the XRD, FTIR and SEM. Moreover, the prepared CaCO3/biopolymer composite materials were further characterized by 1H NMR, HRTEM, SAED and XPS, respectively. The experimental results show that the petal possessed a single crystal structure and consisted of stackings of (18). Interestingly, the product is sensitive to the lower laser power by Raman spectra. Based on experimental results, the growth process of formation of a special shape for CaCO3 was also speculated, which indicates that acrylic acid and chitosan played an important role in forming substrates and in following further mineralization of CaCO3.

Natures of benzene-water and pyrrole-water interactions in the forms of σ and π types: theoretical studies from clusters to liquid mixture

AbstractA combined and sequential use of quantum mechanical (QM) calculations and classical molecular dynamics (MD) simulations was made to investigate the σ and π types of hydrogen bond (HB) in benzene-water and pyrrole-water as clusters and as their liquid mixture, respectively. This paper aims at analyzing similarities and differences of these HBs resulted from QM and MD on an equal footing. Based on the optimized geometry at ωb97xD/aug-cc-pVTZ level of theory, the nature and property of σ and π types of HBs are unveiled by means of atoms in molecules (AIM), natural bond orbital (NBO) and energy decomposition analysis (EDA). In light of the above findings, MD simulation with OPLS-AA and SPC model was applied to study the liquid mixture at different temperatures. The MD results further characterize the behavior and structural properties of σ and π types HBs, which are somewhat different but reasonable for the clusters by QM. Finally, we provide a reasonable explanation for the different solubility between benzene/water and pyrrole/water. FigureThe σ and π types of hydrogen bond as benzene-water and pyrrole-water clusters in gas; Snapshot of benzene/water and pyrrole/water as 1:1 liquid mixture extracted from the MD simulations

From clusters to liquid: what are the preferred ways for benzene and pyrrole to interact?

The various interactions occurring between pyrrole and benzene are a particularly appropriate model, as they are viewed as better X–H···π examples. A combined and sequential use of Quantum Mechanical (QM) calculations and Molecular Dynamics (MD) simulations was applied to investigate the different intermolecular interactions for benzene and pyrrole as clusters and its liquid mixture. All the cluster structures were fully optimized by the B2PLYP-D methods (including dispersion correction) with jun-cc-pVTZ (a revised aug-cc-pVTZ basis set). MD simulation with OPLS-AA force field was used to study the liquid mixture of benzene/pyrrole at different temperatures. Two types of N–H···π hydrogen bonds are preferred interactions compared with C–H···π interactions, either as clusters or as its liquid mixture. Based on the QM results, we clarify the difference in red-shifts of N–H bond of N–H···π hydrogen bonds observed by Jet FT-IR (Phys Chem Chem Phys 10: 2827, 2008). Meanwhile, the nature of various X–H···π interactions is unveiled by atoms in molecules (AIM), natural bond orbital and energy decomposition analysis (EDA). Furthermore, in light of QM results, MD simulation results further characterize the behavior and structural properties of these interactions. Finally, we proposed an original idea to explain the strength variation of different N–H···π hydrogen bond in liquid mixture based on AIM and EDA analysis.Graphical Abstract