Jiancang Shen

High-Efficiency Electrochemical Hydrogen Evolution Based on Surface Autocatalytic Effect of Ultrathin 3C-SiC Nanocrystals

Good understanding of the reaction mechanism in the electrochemical reduction of water to hydrogen is crucial to renewable energy technologies. Although previous studies have revealed that the surface properties of materials affect the catalytic reactivity, the effects of a catalytic surface on the hydrogen evolution reaction (HER) on the molecular level are still not well understood. Contrary to general belief, water molecules do not adsorb onto the surfaces of 3C-SiC nanocrystals (NCs), but rather spontaneously dissociate via a surface autocatalytic process forming a complex consisting of -H and -OH fragments. In this study, we show that ultrathin 3C-SiC NCs possess superior electrocatalytic activity in the HER. This arises from the large reduction in the activation barrier on the NC surface enabling efficient dissociation of H(2)O molecules. Furthermore, the ultrathin 3C-SiC NCs show enhanced HER activity in photoelectrochemical cells and are very promising to the water splitting based on the synergistic electrocatalytic and photoelectrochemical actions. This study provides a molecular-level understanding of the HER mechanism and reveals that NCs with surface autocatalytic effects can be used to split water with high efficiency thereby enabling renewable and economical production of hydrogen.

Light‐Induced Ferroelectricity in Bioinspired Self‐Assembled Diphenylalanine Nanotubes/Microtubes

The switchable SP together withthe unique properties of ferroelectric materials can lead toPNTs/PMTs that have a wide range of applications butexperimental verification of the predicted FE is imperative.In FF PNTs/PMTs, direct experimental demonstration ofthe hysteresis loop is rather difficult because of the highcoercive field of the PMTs. A change of the SP under anapplied external field is an important experimental indicatortoidentifythepossiblepresenceofFE.Inthiswork,theoriginof the SP based on the structure of the PNTs is studied. Byobserving the photoluminescence (PL) spectral shift and itssplitting with increasing intensity of the excitation light, wedisclose the photoinduced reduction of the PNT intrinsicpolarization field which implies that SP occurs at the nano-scale.Thesaturatedpolarization–electricfield(P-E)loopsareobtained by the action of light during the hysteresis loopmeasurements.Figure 1a depicts the optical microscopy image ofa cleaved PMT prepared by immersing the as-made FFPMTs in ethanol for several hours. The optical microscopicimage of some PNTs stripped from the PMTs is shown inFigure 1b. The remarkable stepwise surface of the cleavedPMT confirms that the PMTs are composed of multi-NTsproduced by a self-assembly process (inset),

In situ probing of intracellular pH by fluorescence from inorganic nanoparticles

Intracellular pH (pHi) plays a critical role in the physiological processes of cells. Nanoscale sensors based on pH-sensitive fluorescent proteins attached on nanoparticles (NPs) have been designed but inorganic NP-dependent fluorescent nanosensors have not yet been explored. Herein we describe a pH sensitive inorganic semiconductor fluorescent probe based on ultrathin 3C-SiC NPs which can effectively monitor pH in the range of 5.6-7.4 by taking advantage of the linear dependence between the fluorescent intensity ratio of the surface OH(-) and H(+) bonding states to band-to-band recombination and pH. Detection of pHi is demonstrated in living HeLa cells. In particular, pHi measurements during apoptosis confirm the validity and sensitivity of this technique in monitoring real-time changes in the intracellular environment. Toxicity assessment and confocal laser scanning microscopy indicate that the 3C-SiC NPs have low cytotoxicity and are compatible with living cells.

Low-frequency Raman scattering of bioinspired self-assembled diphenylalanine nanotubes/microtubes

Low-frequency Raman scattering from self-assembled bioinspired diphenylalanine (FF) nanotubes/microtubes (NTs/MTs) has been observed for the first time. Four double peaks are identified as the three-dimensional localized collective (acoustic phonon) vibrations of FF molecules in the subnanometer crystalline structure (biological building block) forming the FF NTs/MTs. The increased energy separations between two subpeaks caused by the loss of water in the nanochannel cores are due to the enhancement of vibrational couplings between the FF molecules as a result of the reduction of the influence from water on the coupling. The results provide experimental evidence of localized but still weakly coupled vibrations in organic crystalline nanostructures in the low-frequency region.

Brianyoungite/Graphene Oxide Coordination Composites for High-Performance Cu2+ Adsorption and Tunable Deep-Red Photoluminescence.

Graphene oxide (GO) is a good adsorbent for heavy-metal ions because the oxygen functional groups offer active adsorption sites, but a small-size GO with dense oxygen-containing groups has high water solubility causing difficulty in separation. Herein, GO is bound to large brianyoungite (BY) by Zn-O coordination via a hydrothermal reaction that produces BY-GO composites with hollow spherical and flakelike morphologies that are easy to remove. By producing abundant oxygen-containing groups on GO, the Cu(2+) adsorption capacity increases to 1724.1 mg/g, which is the highest value in graphene-related materials. The experimental and theoretical analysis clearly shows that the infrared spectral shifts toward the low-frequency side of C-O-H and O═C-O bending vibrations in the BY-GO composites stem from the Zn(2+) (or Cu(2+)) coordination with O atoms in GO. The BY-GO also exhibits tunable deep-red photoluminescence up to 750 nm with a quantum yield of about 1%, which may be useful in infrared optoelectronic devices and solar energy exploitation. The photoluminescence which is different from that previously reported from chemically derived GO can be attributed to the optical transition in the disorder-induced localized states of the carbon-oxygen functional groups.

Ultrahigh quantum efficiency photodetector and ultrafast reversible surface wettability transition of square In2O3 nanowires

Due to a large surface-to-volume ratio, the optoelectronic performance of lowdimensional semiconductor nanostructure-based photodetectors depends in principle on chemisorption/photodesorption at the exposed surface, but practical examples that show such an effect are still unavailable. Some theoretical calculations have predicted that the {001} facets of In2O3 can effectively accumulate photogenerated holes under irradiation, providing a model material to examine whether the facet cutting of nanowires (NWs) can boost their optoelectronic performance. Herein, we present the design and construction of a novel nanowire-based photodetector using square In2O3 NWs with four exposed {001} crystal facets. The photodetector delivers excellent optoelectronic performance with excellent repeatability, fast response speed, high spectral responsivity (Rλ), and high external quantum efficiency (EQE). The Rλ and EQE values are as high as 4.8 × 106 A/W and 1.46 × 109%, respectively, which are larger than those of other popular semiconductor photodetectors. In addition, the square In2O3 NWs show hydrophobic wettability as manifested by a contact angle of 118° and a fast photoinduced reversible switching behavior is observed.

Phase-Engineering-Induced Generation and Control of Highly Anisotropic and Robust Excitons in Few-Layer ReS2

The anisotropic exciton behavior in two-dimensional materials induced by spin-orbit coupling or anisotropic spatial confinement has been exploited in imaging applications. Herein, we propose a new strategy to generate high-energy and robust anisotropic excitons in few-layer ReS2 nanosheets by phase engineering. This approach overcomes the limitation imposed by the layer thickness, enabling production of visible polarized photoluminescence at room temperature. Ultrasonic chemical exfoliation is implemented to introduce the metallic T phase of ReS2 into the few-layer semiconducting Td nanosheets. In this configuration, light excitation can readily produce hot electrons to tunnel to the Td phase via the metal-semiconductor interface to enhance the overlap between the wave functions and screened Coulomb interactions. Owing to the strong electron-hole interaction, significant increase in the optical band gap is observed. Highly anisotropic and tightly bound excitons with visible light emission (1.5-2.25 eV) are produced and can be controlled by tailoring the T phase concentration. This novel strategy allows manipulation of polarized optical information and has great potential in optoelectronic devices.

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

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 1009u2009μmolu2009g−1u2009h−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.The “storage” of sunlight as a chemical fuel can provide renewable on-demand energy, although current earth-abundant materials usually show low activities. Here, authors construct a carbon nitride material whose half-metallicity and micro grid resonance structure boost light-driven H2 evolution.