We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

The controlled synthesis of nanohybrids composed of noble metals (Au, Ag, Pt and Pd, as well as AuAg alloy) and metal oxides (ZnO, TiO2, Cu2O and CeO2) have received considerable attention for applications in photocatalysis, solar cells, drug delivery, surface enhanced Raman spectroscopy and many other important areas. The overall architecture of nanocomposites is one of the most important factors dictating the physical properties of nanohybrids. Noble metals can be coupled to metal oxides to yield diversified nanostructures, including noble metal decorated-metal oxide nanoparticles (NPs), nanoarrays, noble metal/metal oxide core/shell, noble metal/metal oxide yolk/shell and Janus noble metal–metal oxide nanostructures. In this review, we focus on the significant advances in tailored nanostructures of noble metal–metal oxide nanohybrids. The improvement in performance in the representative solar energy conversion applications including photocatalytic degradation of organic pollutants, photocatalytic hydrogen generation, photocatalytic CO2 reduction, dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are discussed. Finally, we conclude with a perspective on the future direction and prospects of these controllable nanohybrid materials.

Noble metal–metal oxide nanohybrids with tailored nanostructures for efficient solar energy conversion, photocatalysis and environmental remediation

Polymeric carbon nitride (C3N4) has emerged as the most promising candidate for metal-free photocatalysts but is plagued by low activity due to the poor quantum efficiency and low specific surface area. Exfoliation of bulk crystals into ultrathin nanosheets has proven to be an effective and widely used strategy for enabling high photocatalytic performances; however, this process is complicated, time-consuming, and costly. Here, we report a simple bottom-up method to synthesize porous few-layer C3N4, which involves molecule self-assembly into layered precursors, alcohol molecules intercalation, and subsequent thermal-induced exfoliation and polycondensation. The as-prepared few-layer C3N4 expose more active sites and greatly enhance the separation of charge carriers, thus exhibiting a 26-fold higher hydrogen evolution activity than bulk counterpart. Furthermore, we find that both the high activity and selectivity for the oxidative coupling of amines to imines can be obtained under visible light that surpass those of other metal-free photocatalysts so far.

Molecule Self-Assembly Synthesis of Porous Few-Layer Carbon Nitride for Highly Efficient Photoredox Catalysis.

ZnO is a material which is of great interest for a variety of applications due to its unique properties and the availability of a variety of growth methods resulting in a number of different morphologies and a wide range of material properties of synthesized nanostructures. In this review, we will discuss recent advances in important and/or controversial issues concerning ZnO properties and its applications. We will also discuss areas where further improvements are needed, and in particular discuss the issues related to the environmental stability of ZnO and its implications on reproducibility of measurements and the toxicity of ZnO nanomaterials.

ZnO nanostructures: growth, properties and applications

ZnO tetrapod materials for functional applications

Photocatalytic hydrogen evolution from water has triggered an intensive search for metal-free semiconducting photocatalysts. However, traditional semiconducting materials suffer from limited hydrogen evolution efficiency owing to low intrinsic electron transfer, rapid recombination of photogenerated carriers, and lack of artificial microstructure. Herein, we report a metal-free half-metallic carbon nitride for highly efficient photocatalytic hydrogen evolution. The introduced half-metallic features not only effectively facilitate carrier transfer but also provide more active sites for hydrogen evolution reaction. The nanosheets incorporated into a micro grid mode resonance structure via in situ pyrolysis of ionic liquid, which show further enhanced photoelectronic coupling and entire solar energy exploitation, boosts the hydrogen evolution rate reach up to 1009 μmol g−1 h−1. Our findings propose a strategy for micro-structural regulations of half-metallic carbon nitride material, and meanwhile the fundamentals provide inspirations for the steering of electron transfer and solar energy absorption in electrocatalysis, photoelectrocatalysis, and photovoltaic cells.

/pdf/half-metallic-carbon-nitride-nanosheets-with-micro-grid-mode-3ijtnge33a.pdf

Half-metallic carbon nitride nanosheets with micro grid mode resonance structure for efficient photocatalytic hydrogen evolution

We report the intrinsic room-temperature ferromagnetism in undoped ZnO nanoparticles with different sizes synthesized by a wet chemical method at different temperatures. Electron paramagnetic resonance, X-ray photoelectron spectroscopy, and photoluminescence measurements demonstrate clearly the singly charged oxygen vacancies are the main defects, and the relative occupancy of that decreases with increasing sizes and annealing temperatures. Importantly, a direct correlation between the ferromagnetism and the relative concentration of the singly charged oxygen vacancies is established, which suggests that the singly charged oxygen vacancies play a crucial role in modulating ferromagnetic behaviors. Moreover, the size-dependent ferromagnetism can be manipulated conveniently by changing of the surface–volume ratio, which is in favor of future electronic and spintronic application.

Size Dependence of Defect-Induced Room Temperature Ferromagnetism in Undoped ZnO Nanoparticles

IO N As a direct wide bandgap (3.3 eV) semiconductor material with a large exciton binding energy (60 meV) at room temperature (RT), ZnO acts as an important candidate for ultraviolet optoelectronic devices, especially for microand nanolasers. [ 1 , 2 ] So far, the optically pumped lasing has been successfully demonstrated in various ZnO microand nanostructures. The lasing actions can be classifi ed as random, [ 1 ] Fabry–Perot (F–P), [ 2 ]

ZnO-microrod/p-GaN heterostructured whispering-gallery-mode microlaser diodes.

In this study, localized surface plasmon resonance mediated by aluminium nanoparticles (Al NPs) was employed to enhance the ultraviolet (UV) response of ZnO nanorod array (NRA) photodetectors grown vertically on a Quartz substrate using a simple vapor transport method. The responsivity of the ZnO NRA photodetector decorated with Al NPs was enhanced from 0.12 to 1.59 A W−1 and the sensitivity and response rate have been improved greatly compared with those of the bare one. The measurement results in the transmittance spectra and time-resolved photoluminescence spectra suggest that the improved photoresponse and the enhanced spontaneous emission of the ZnO NRA photodetector with Al NP decoration are both attributed to resonant coupling between the excitons in ZnO and the localized surface plasmons (LSPs) in the Al NPs. Our results demonstrated that the plasmon-enhanced ZnO NRA photodetector has a great potential for application in building sensors with a fast response and reset time, high sensitivity, and good signal-to-noise ratio for photoelectric sensing.

Improved UV photoresponse of ZnO nanorod arrays by resonant coupling with surface plasmons of Al nanoparticles

Zinc oxide (ZnO) is considered as an ideal candidate for ultraviolet (UV) lasers due to its unique advantages of wide direct bandgap and large exciton binding energy. Recently, whispering-gallery mode (WGM) lasing has attracted considerable attention for its high quality factor and low lasing threshold. The corresponding investigations have very important significance not only for fundamental scientific research but also for the potential applications in short-wavelength optoelectronic devices. In this paper, progress in ZnO microlasers is reviewed systematically. The fabrication methods for ZnO WGM microcavities are introduced first. Then the characteristics of single-photon and multiphoton pumped WGM lasing are presented. The lasing mechanisms on excitonic, electron–hole plasma and exciton–polariton lasing are reviewed in detail. Finally, recent advances in ZnO-based microlaser devices such as heterojunction laser diodes are explored. The further research challenges and some strategies are also indicated for the promising applications.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/lpor.201300127

Jun Dai

Papers

Half-metallic carbon nitride nanosheets with micro grid mode resonance structure for efficient photocatalytic hydrogen evolution

Size Dependence of Defect-Induced Room Temperature Ferromagnetism in Undoped ZnO Nanoparticles

ZnO-microrod/p-GaN heterostructured whispering-gallery-mode microlaser diodes.

Improved UV photoresponse of ZnO nanorod arrays by resonant coupling with surface plasmons of Al nanoparticles

Whispering‐gallery mode lasing in ZnO microcavities