J.X. Zhong

The Structure and Optical Properties of the [Au18(SR)14] Nanocluster

Decreasing the core size is one of the best ways to study the evolution from Au(I) complexes into Au nanoclusters. Toward this goal, we successfully synthesized the [Au18(SC6H11)14] nanocluster using the [Au18(SG)14] (SG=L-glutathione) nanocluster as the starting material to react with cyclohexylthiol, and determined the X-ray structure of the cyclohexylthiol-protected [Au18(C6H11S)14] nanocluster. The [Au18(SR)14] cluster has a Au9 bi-octahedral kernel (or inner core). This Au9 inner core is built by two octahedral Au6 cores sharing one triangular face. One transitional gold atom is found in the Au9 core, which can also be considered as part of the Au4(SR)5 staple motif. These findings offer new insight in terms of understanding the evolution from [Au(I)(SR)] complexes into Au nanoclusters.

Crystal Structure and Optical Properties of the [Ag62S12(SBut)32]2+ Nanocluster with a Complete Face-Centered Cubic Kernel

The crystal structure of the [Ag62S12(SBu(t))32](2+) nanocluster (denoted as NC-I) has been successfully determined, and it shows a complete face-centered-cubic (FCC) Ag14 core structure with a Ag48(SBu(t))32 shell configuration interconnected by 12 sulfide ions, which is similar to the [Ag62S13(SBu(t))32](4+) structure (denoted as NC-II for short) reported by Wang. Interestingly, NC-I exhibits prominent differences in the optical properties in comparison with the case of the NC-II nanocluster. We employed femtosecond transient absorption spectroscopy to further identify the differences between the two nanoclusters. The results show that the quenching of photoluminescence in NC-I in comparison to that of NC-II is caused by the free valence electrons, which dramatically change the ligand to metal charge transfer (LMCT, S 3p → Ag 5s). To get further insight into these, we carried out time-dependent density functional theory (TDDFT) calculations on the electronic structure and optical absorption spectra of NC-I and NC-II. These findings offer a new insight into the structure and property evolution of silver cluster materials.

Mesoporous anatase TiO2 submicrospheres embedded in self-assembled three-dimensional reduced graphene oxide networks for enhanced lithium storage

A novel composite of mesoporous TiO2 submicrospheres embedded in three-dimensional (3D) reduced graphene oxide networks (denoted as MTO/3D-GN) as an electrode material for Li-ion batteries (LIBs) was prepared via a facile hydrothermal self-assembly strategy. The as prepared MTO/3D-GN composite shows monolithic 3D interconnected networks of reduced graphene oxide sheets with well-dispersed mesoporous submicrospheres composed of small-size anatase TiO2 nanocrystals. The novel composite integrates the advantages of mesoporous structure, submicrometer-sized spherical morphology and reduced graphene oxide, thereby providing a high contact area between the electrolyte and electrode, favorable diffusion kinetics for both electrons and lithium ions, and double protection against the volume changes of electroactive TiO2 materials and excellent electrical conductivity of the overall electrode during electrochemical processes. The evaluation of its electrochemical performance for lithium storage demonstrates that the prepared MTO/3D-GN composite has greatly improved lithium storage properties. In particular, the unique hybrid material has the ability to deliver high reversible capacities with superlative cyclic capacity retention at different current rates for prolonged cycling, and exhibit excellent high-rate performance at a current rate as high as 20 C. The embedded reduced graphene oxide composite with designed mesoporous structure and advanced chemical composition can be used for high-performance LIB negative-electrode materials and other important applications such as solar cells and photocatalysis.

Non-covalent doping of graphitic carbon nitride with ultrathin graphene oxide and molybdenum disulfide nanosheets: An effective binary heterojunction photocatalyst under visible light irradiation

A proof of concept integrating binary p-n heterojunctions into a semiconductor hybrid photocatalyst is demonstrated by non-covalent doping of graphite-like carbon nitride (g-C3N4) with ultrathin GO and MoS2 nanosheets using a facile sonochemical method. In this unique ternary hybrid, the layered MoS2 and GO nanosheets with a large surface area enhance light absorption to generate more photoelectrons. On account of the coupling between MoS2 and GO with g-C3N4, the ternary hybrid possesses binary p-n heterojunctions at the g-C3N4/MoS2 and g-C3N4/GO interfaces. The space charge layers created by the p-n heterojunctions not only enhance photogeneration, but also promote charge separation and transfer of electron-hole pairs. In addition, the ultrathin MoS2 and GO with high mobility act as electron mediators to facilitate separation of photogenerated electron-hole pairs at each p-n heterojunction. As a result, the ternary hybrid photocatalyst exhibits improved photoelectrochemical and photocatalytic activity under visible light irradiation compared to other reference materials. The results provide new insights into the large-scale production of semiconductor photocatalysts.

Quasi-seeded growth, phase transformation, and size tuning of multifunctional hexagonal NaLnF4 (Ln = Y, Gd, Yb) nanocrystalsvia in situ cation-exchange reaction

In situ cation exchange between alkali ions in ternary alkali lanthanide (Ln3+) fluoride on the nanoscale is reported. Experimental results reveal that the differences in the solubility constants and thermodynamic stability of the reactants and products affect the irreversible cation exchange between potassium and sodium, resulting in the phase transformation of cubic KLnF4 to hexagonal NaLnF4. The unusual cation-exchange reaction can be used as an efficient tool to produce seed nuclei and control the nucleation and final size of hexagonal NaLnF4 nanocrystals (NCs). During the in situ cation exchange between potassium and sodium and corresponding cubic to hexagonal phase transformation, the stable hexagonal NaLnF4 particles serving as the seed nuclei play a key role in the final size of the NCs. The in situ cation exchange approach provides not only valuable insights into the growth dynamics of Ln3+ doping-induced size tuning and phase transformation in NaYF4 and alkaline-earth fluoride NCs, but also a method to prepare high-quality multifunctional NaLnF4 NCs with tunable paramagnetism and multi-color upconversion emission.

Hetero-assembly of a Li4Ti5O12 nanosheet and multi-walled carbon nanotube nanocomposite for high-performance lithium and sodium ion batteries

A nanocomposite composed of crystalline Li4Ti5O12 (LTO) nanosheets and multi-walled carbon nanotubes (denoted as LTO/MWCNTs) is prepared for lithium/sodium storage via a facile hetero-assembly process driven by the screening effect of electrostatic repulsion and following thermal treatment. The morphology and microstructure characterizations reveal that LTO nanosheets are embedded in a highly porous and electrically conductive MWCNT network, thereby producing robust inner-connected architectures. Owing to improved electron and ion transportation during electrochemical reaction rendered by a unique integrated architecture of two-dimensional LTO nanosheets and MWCNTs, the nanocomposite exhibits excellent lithium and sodium storage performances. For lithium ion batteries, the anode delivers reversible capacity of 149.7 mA h g−1 at 10C after 500 cycles. As anode for sodium ion batteries, it has reversible capacity of 82 mA h g−1 at 5C. The prepared LTO/MWCNT nanocomposite has great potential as a high-performance anode material for dual storage applications in lithium and sodium ion batteries.