Ligand Modification of Au25 Nanoclusters for Near-Infrared Photocatalytic Oxidative Functionalization.

The inorganic-organic interface between metal catalysts and their substrates greatly influences reaction processes, but few studies of this interface have been conducted for a detailed understanding of its structure. Herein, we describe the synthesis and structural determination of an arylthiolated Au25(F-Ph)18- nanocluster and characterize in detail the key roles of its ligands in photocatalyzed oxidative functionalization reactions. The most significant findings are that (i) interactions are established between ligands to avoid distortion of the geometric structure, limit the Jahn-Teller effect, and protect the nanocluster from oxidization and (ii) the low energy gap (HOMO-LUMO) of the synthetic clusters enables three types of photocatalytic oxidative functionalization reactions by near-infrared light (850 nm).

Two-photon saturable absorption properties and laser Q-switch application of carbon quantum dots.

In this Letter, high-quality carbon quantum dots (C-QDs) with an average size of 15 nm are synthesized by using a solvothermal method. A C-QD saturable absorber mirror (SAM) was prepared, characterized, and employed as an ultrafast optical switch successfully in a 1.0 µm solid-state laser. The saturable absorption effect (at 1 µm) far away from the linear absorption band of the C-QDs could be attributed to two-photon saturable absorption, which has a native characteristic of wavelength selectivity. The modulation depth (ΔT) and saturable energy intensity (ϕs) of the C-QD-SA was measured to be about 4% and 15.34 W/mm2, respectively. By using this SA, a Q-switched Nd:GdVO4 laser at 1 µm were first realized with the shortest pulse width of 66.8 ns and a maximum repetition rate of 1.13 MHz, respectively. The results indicate that C-QDs may found to be a decent carbon SA material for the high-repetition-rate pulsed laser applications.

Understanding the decomposition process of the Pt1Ag24(SPhCl2)18 nanocluster at the atomic level.

We report the decomposition of the Pt1Ag24(SPhCl2)18 nanocluster into a crown-like Pt1Ag4(SR)8 (SR = 2,4-SPhCl2 and 4-SPhBr) complex. UV-vis spectra and single crystal X-ray diffraction were used to track the structure-conversion process. Based on the total structure, the differences in ligand exchange rates at different sites and the effects on the stability were mapped out. This work can not only help us understand the ligand exchange behavior of the clusters, but also provide experimental support for the design of stable metal clusters.

Light transmission enhancement from hybrid ZnO micro-mesh and nanorod arrays with application to GaN-based light-emitting diodes.

A hybrid ZnO micro-mesh and nanorod arrays (MMNR) was fabricated as a light output window for GaN-based light-emitting diodes (LEDs) to enhance the light extraction efficiency. The light output power of GaN-based LEDs with the ZnO MMNR is improved by 95% compared to the original planar LEDs. The ZnO MMNR is manufactured by photolithography techniques and a two-step wet chemical growth process. The incident angle-resolved light transmission of the ZnO MMNR beyond the critical angle of total internal reflection is greatly enhanced. The light diffraction pattern of the ZnO MMNR shows that it possesses both the two-dimensional diffraction grating effect of a ZnO micro-mesh and the light scattering effect of a ZnO nanorod array. LEDs with the ZnO MMNR have greater light extraction efficiency than those with only a ZnO micro-mesh or a ZnO nanorod array. The local optical field patterns of the ZnO micro-mesh and the ZnO MMNR are investigated using confocal scanning electroluminescence microscopy. The microscopic light extraction mechanism of the ZnO MMNR is analyzed in-depth.

The smallest superatom Au4(PPh3)4I2 with two free electrons: synthesis, structure analysis, and electrocatalytic conversion of CO2 to CO.

Atomically precise metal nanoclusters (NCs) have emerged as a new class of ultrasmall nanoparticles with both free valence electrons and precise structures (from the metal core to the organic ligand shell) and provide great opportunities to understand the relationship between their structures and properties, such as electrocatalytic CO2 reduction reaction (eCO2RR) performance, at the atomic level. Herein, we report the synthesis and the overall structure of the phosphine and iodine co-protected Au4(PPh3)4I2 (Au4) NC, which is the smallest multinuclear Au superatom with two free e- reported so far. Single-crystal X-ray diffraction reveals a tetrahedral Au4 core stabilized by four phosphines and two iodides. Interestingly, the Au4 NC exhibits much higher catalytic selectivity for CO (FECO: > 60%) at more positive potentials (from -0.6 to -0.7 V vs. RHE) than Au11(PPh3)7I3 (FECO: < 60%), a larger 8 e- superatom, and Au(i)PPh3Cl complex; whereas the hydrogen evolution reaction (HER) dominates the electrocatalysis when the potential becomes more negative (FEH2 of Au4 = 85.8% at -1.2 V vs. RHE). Structural and electronic analyses reveal that the Au4 tetrahedron becomes unstable at more negative reduction potentials, resulting in decomposition and aggregation, and consequently the decay in catalytic performance of Au based catalysts towards the eCO2RR.

Enhancement of light extraction in GaN-based light-emitting diodes using rough beveled ZnO nanocone arrays.

A remarkable enhancement of light extraction efficiency in GaN-based blue light-emitting diodes (LEDs) with rough beveled ZnO nanocone arrays grown on the planar indium tin oxide (ITO) layer is reported. The light output power of LEDs with rough beveled ZnO nanocone arrays was increased by about 110% at 20 mA compared with conventional LEDs with planar ITO. The light extraction efficiency of GaN-based LEDs with rough-beveled ZnO nanocones is measured much greater than with smooth-surface hexagonal ZnO nanorods. The light-ray tracing analysis showed that ZnO nanocones with rough surfaces enlarge the light escape cone of GaN-based LEDs and have a greater advantage for extracting light compared with ZnO nanorods.

Understanding a ligand's effects on intra-cluster and inter-cluster assembly.

Ligands play an essential role in cluster assembly; however, understanding this behavior at the atomic level is far off. In this work, Cd12Ag32(S-PhOMe)36(PPh)4@Cd6Ag2(S-PhOMe)6Cl6(PPh3)8@Ag6(S-PhOMe)6Cl2 (Abbrev. Cd12Ag32-1) and Cd12Ag32(S-c-C6H11)36 (Abbrev. Cd12Ag32-2) were synthesized and structurally determined by single-crystal X-ray diffraction. An important finding is the selective adsorption of phosphine ligands that is caused by the different types of thiol ligands. In addition, Cd12Ag32-1 follows a unique stacking pattern in a superlattice with multiple inter-cluster channels. Overall, this study is helpful for an in-depth understanding of the effect of mixed ligands on nanocluster formation and the correlation between structure and properties in the nanocluster range.

Conjugating AIE-featured AuAg nanoclusters with highly luminescent carbon dots for improved visible-light-driven antibacterial activity.

Metal nanoclusters (NCs) have emerged as novel antibacterial agents featuring broad-spectrum antibacterial activity without drug resistance for bacteria, but suffer from fast antibacterial invalidation due to their consumption by bacteria. Herein we report the design of a visible-light-driven photodynamic antibacterial agent based on conjugating aggregation-induced emission (AIE)-featured AuAg NCs with highly luminescent carbon dots (CDs). The conjugation of CDs with AuAg NCs could not only enhance the visible-light harvest, but also promote charge carrier generation/separation via charge/energy transfer, leading to the production of abundant reactive oxygen species (ROS) for bacterial killing under visible-light irradiation. Consequently, the as-obtained CDs@AuAg NCs display excellent photodynamic antibacterial activity against both Gram-positive and Gram-negative bacteria with 4-5 orders of magnitude reduction in colony forming units, which is different from the conventional metal NC-based analogue relying on self-consumption for bacterial killing. In addition, the CDs@AuAg NCs are found to be free of cytotoxicity; the ROS capture experiments indicate that the photoproduced H2O2 by CDs@AuAg NCs is the main active species for bacterial killing, accounting for nearly 48% of the total antibacterial efficacy. This study provides a paradigm for the design of metal NC-based photodynamic antibacterial agents for diverse bactericidal applications.

Marrying luminescent Au nanoclusters to TiO2 for visible-light-driven antibacterial application.

Long-lasting yet visible-light-driven bacterial inhibition is highly desired for environmental protection and public health maintenance. However, conventional semiconductors such as titanium dioxide (TiO2) are impotent for such antibacterial application due to their low utilization rate for visible light. Herein we report the design of a long-lasting yet visible-light-driven antibacterial agent based on marrying luminescent Au nanoclusters (Au NCs for short) to TiO2 (TiO2-NH2@Au NCs). The as-obtained TiO2-NH2@Au NC antibacterial agent not only possesses superior utilization for visible light due to the participation of Au NCs as a good photosensitizer, but also has excellent separation efficacy of photogenerated carriers, thereby efficiently enhancing the generation of reactive oxygen species (ROS) for killing bacteria. Consequently, the TiO2-NH2@Au NCs display excellent antibacterial activity with good durability against both Gram-positive and Gram-negative bacteria such as Staphylococcus aureus (99.37%) and Escherichia coli (99.92%) under visible-light irradiation (λ ≥ 400 nm). This study is interesting because it provides a paradigm change in the design of long-lasting yet visible-light-driven NC-based antibacterial agents for diversified bactericidal applications.

Molecular engineering towards efficientwhite-light-emitting perovskite.

Low-dimensional hybrid perovskites have demonstrated excellent performance as white-light emitters. The broadband white emission originates from self-trapped excitons (STEs). Since the mechanism of STEs formation in perovskites is still not clear, preparing new low-dimensional white perovskites relies mostly on screening lots of intercalated organic molecules rather than rational design. Here, we report an atom-substituting strategy to trigger STEs formation in layered perovskites. Halogen-substituted phenyl molecules are applied to synthesize perovskite crystals. The halogen-substituents will withdraw electrons from the branched chain (-R-NH3+) of the phenyl molecule. This will result in positive charge accumulation on -R-NH3+, and thus stronger Coulomb force of bond (-R-NH3+)-(PbBr42-), which facilitates excitons self-trapping. Our designed white perovskites exhibit photoluminescence quantum yield of 32%, color-rendering index of near 90 and chromaticity coordinates close to standard white-light. Our joint experiment-theory study provides insights into the STEs formation in perovskites and will benefit tailoring white perovskites with boosting performance.

Enhanced oxygen and hydrogen evolution performance by carbon-coated CoS2-FeS2 nanosheets.

It is vital to tailor the surface structure and composition of nanocatalysts, which greatly affect the catalytic activity through the exposure of specific atom coordination environment. To date, less progress has been made in tuning the interface structures of pyrite for promoting the catalytic activity towards overall water splitting. Herein, we developed a facile one-spot strategy to make carbon-layer-coated CoS2-FeS2 heterojunction nanosheets. The carbon layer and interface structures between Co-S and Fe-S were characterized via high resolution transmission electron microscopy. It exhibited a high OER activity with 1.47 V at 10 mA cm-2, which was superior to that of the commercial RuO2. Meanwhile, the carbon-layer-coated CoS2-FeS2 heterojunction nanosheets with the overpotential of 210 mV at 10 mA cm-2 was more active than FeS2 nanosheets with 240 mV in the hydrogen evolution reaction. Notably, it enhanced the catalytic activity towards the overall water splitting with the voltage of 1.66 V at 10 mA cm-2 using a two-electrode system. The remarkable long-term stability was verified by a slight change in the current density of 6 mA cm-2 for 26 h. The prominent catalytic activity could be related to the exposure of the carbon layer and interface structures. This work demonstrates that engineering the interface structure is essential for boosting the overall water splitting activity.

A Robust Strategy for Engineering Fe7S8/C Hybrid Nanocages Reinforced by Defect-Rich MoS2 Nanosheets for Superior Potassium-Ion Storage.

Metal sulfides have attracted tremendous research interest for developing high-performance electrodes for potassium-ion batteries (PIBs) for their high theoretical capacities. Nevertheless, the practical application of metal sulfides in PIBs is still unaddressed due to their intrinsic shortcomings of low conductivity and severe volume changes during the potassiation/depotassiation process. Herein, robust Fe7S8/C hybrid nanocages reinforced by defect-rich MoS2 nanosheets (Fe7S8/C@d-MoS2) were designed, which possess abundant multichannel and active sites for potassium-ion transportation and storage. Kinetic analysis and theoretical calculation verify that the introduction of defect-rich MoS2 nanosheets dramatically promotes the potassium-ion diffusion coefficient. The ex-situ measurements revealed the potassium-ion storage mechanism in the Fe7S8/C@d-MoS2 composite. Benefitting from the tailored structural design, the Fe7S8/C@d-MoS2 hybrid nanocages show high reversible capacity, exceptional rate property, and superior cyclability.

White Light-Emitting Diodes Based on Individual Polymerized Carbon Nanodots.

A search for new phosphor materials that exhibit high light-emission, spectral purity, long-time stability and processability capture particular attention to modern solid-state lighting. Here, polymerizable silane pre-functionalized carbon dot (SiCD) fluids were dripped and co-polymerized or completely bulk polymerized to build color conversion and encapsulation coatings of commercially available GaN blue LEDs. Most parameters of SiCD-based white LEDs were similar to or even better than those of phosphor-based white LEDs, particularly the insensitivity to excitation wavelength and working current. Thus, SiCDs were superior to those phosphors in terms of broadband properties, high transparency (no light blocking and leaking), as well as arbitrary doping of its content as color conversion and encapsulation layers simultaneously, unique solubility, flexible chemical, optical and mechanical processability. Thus, designing new CD-based white LEDs, instead of inorganic rare earth phosphor-based LEDs, is possible for better performance solid state lighting devices.

Polysiloxane Functionalized Carbon Dots and Their Cross-Linked Flexible Silicone Rubbers for Color Conversion and Encapsulation of White LEDs.

In this work, aminopropylmethylpolysiloxane (AMS) functionalized luminescent carbon dots (AMS-CDs) were prepared via a one-step solvothermal method. AMS-CDs could be self- or co-cross-linking with AMS to form 3D flexible transparent silicone rubbers (SRs) where CDs acted as cross-linking points, so the loading fraction of AMS-CDs could be adjusted from 10 to 100 wt %, thus modulating fluorescence properties and flexibility of silicone rubbers. Because of the self-curing property and high thermal stability, AMS-CDs were also studied in white LEDs (WLEDs), serving as a color conversion and encapsulation layer of GaN based blue LEDs simultaneously that would avoid the traditional problem of poor compatibility between emitting and packaging materials. And the color coordinate of AMS-CDs based WLEDs (0.33, 0.28) was very close to the pure white light. In addition, the obtained CDs cross-linked SRs had good transparency (T > 80%) at 510-1400 nm and high refractive indexes (1.33-1.54) that could meet the need of commercial packaging materials and optical application. AMS-CDs were also promising to be used in the UV LEDs based WLEDs according to their wide wavelength emission and flexible optoelectronic device.

Improving the quality of GaN crystals by using graphene or hexagonal boron nitride nanosheets substrate.

The progress in nitrides technology is widely believed to be limited and hampered by the lack of high-quality gallium nitride wafers. Though various epitaxial techniques like epitaxial lateral overgrowth and its derivatives have been used to reduce defect density, there is still plenty of room for the improvement of gallium nitride crystal. Here, we report graphene or hexagonal boron nitride nanosheets can be used to improve the quality of GaN crystal using hydride vapor phase epitaxy methods. These nanosheets were directly deposited on the substrate that is used for the epitaxial growth of GaN crystal. Systematic characterizations of the as-obtained crystal show that quality of GaN crystal is greatly improved. The fabricated light-emitting diodes using the as-obtained GaN crystals emit strong electroluminescence under room illumination. This simple yet effective technique is believed to be applicable in metal-organic chemical vapor deposition systems and will find wide applications on other crystal growth.