Porous 2D Catalyst Covers Improve Photoelectrochemical Water-Oxidation Performance.

Confined catalysis under the cover of 2D materials has emerged as a promising approach for achieving highly effective catalysts in various essential reactions. In this work, a porous cover structure is designed to boost the interfacial charge and mass transfer kinetics of 2D-covered catalysts. The improvement in catalytic performance is confirmed by the photoelectrochemical oxidation evolution reaction (OER) on a photoanode based on an n-Si substrate modified with a NiOx thin-film model electrocatalyst covered with a porous graphene (pGr) monolayer. Experimental results demonstrate that the pGr cover enhances the OER kinetics by balancing the charge and mass transfer at the photoanode and electrolyte interface compared to the intrinsic graphene cover and cover-free control samples. Theoretical investigations further corroborate that the pore edges of the pGr cover boost the intrinsic catalytic activity of active sites on NiOx by reducing the reaction overpotential. Furthermore, the optimized pores, which can be easily controlled by plasma bombardment, allow oxygen molecules produced in the OER to pass through without peeling off the pGr cover, thus ensuring the structural stability of the catalyst. This study highlights the significant role of the porous cover structure in 2D-covered catalysts and provides new insight into the design of high-performance catalysts.

A facile covalent strategy for ultrafast negative photoconductance hybrid graphene/porphyrin-based photodetector.

As a powerful complement to positive photoconductance (PPC), negative photoconductance (NPC) holds great potential for photodetector. However, the slow response of NPC relative to PPC devices limits their integration. Here, we propose a facile covalent strategy for an ultrafast NPC hybrid 2D photodetector. Our transistor-based graphene/porphyrin model device with a rise time of 0.2 ms and decay time of 0.3 ms has the fastest response time in the so far reported NPC hybrid photodetectors, which is attributed to efficient photogenerated charge transport and transfer. Both the photosensitive porphyrin with an electron-rich and large rigid structure and the built-in graphene frame with high carrier mobility are prone to the photogenerated charge transport. Especially, the intramolecular donor-acceptor system formed by graphene and porphyrin through covalent bonding promotes photoinduced charge transfer. This covalent strategy can be applied to other nanosystems for high-performance NPC hybrid photodetector.

Modification of interface and electronic transport in van der Waals heterojunctions by UV/O3.

Two-dimensional (2D) van der Waals heterojunctions have many unique properties, and energy band modulation is central to applying these properties to electronic devices. Taking the 2D graphene/MoS2heterojunction as a model system, we demonstrate that the band structure can be finely tuned by changing the graphene structure of the 2D heterojunction via ultraviolet/ozone (UV/O3). With increasing UV/O3exposure time, graphene in the heterojunction has more defect structures. The varied defect levels in graphene modulate the interfacial charge transfer, accordingly the band structure of the heterojunction. And the corresponding performance change of the graphene/MoS2field effect transistor indicates the shift of the Schottky barrier height after UV/O3treatment. The result further proves the effective band structure modulation of the graphene/MoS2heterojunction by UV/O3. This work will be beneficial to both fundamental research and practical applications of 2D van der Waals heterojunction in electronic devices.

Nanoarray Structures for Artificial Photosynthesis.

Conversion and storage of solar energy into fuels and chemicals by artificial photosynthesis has been considered as one of the promising methods to address the global energy crisis. However, it is still far from the practical applications on a large scale. Nanoarray structures that combine the advantages of nanosize and array alignment have demonstrated great potential to improve solar energy conversion efficiency, stability, and selectivity. This article provides a comprehensive review on the utilization of nanoarray structures in artificial photosynthesis of renewable fuels and high value-added chemicals. First, basic principles of solar energy conversion and superiorities of using nanoarray structures in this field are described. Recent research progress on nanoarray structures in both abiotic and abiotic-biotic hybrid systems is then outlined, highlighting contributions to light absorption, charge transport and transfer, and catalytic reactions (including kinetics and selectivity). Finally, conclusions and outlooks on future research directions of nanoarray structures for artificial photosynthesis are presented.

Preparation of blue- and green-emissive nitrogen-doped graphene quantum dots from graphite and their application in bioimaging.

Owing to the superior photoluminescence property, low toxicity and good biocompatibility, nitrogen-doped graphene quantum dots (NGQDs) have been regarded as promising nanomaterials for biological applications such as bioimaging. However, many of the preparation methods are complicated, high cost, eco-unfriendly, and with a low product yield. Here, we demonstrate a novel top-down approach for NGQDs preparation, in which the low cost graphite was used as a precursor, ammonium persulfate as an oxidative molecule and nitrogen source, and H2O2 as an oxidative agent, N-methyl-2-pyrrolidone as a solvent and potential functionalizer. Meanwhile, the solvent extraction was applied for the first time to purify NGQDs. The separated NGQDs display green and blue fluorescence, deriving from the difference sizes and nitrogen doped types. The total product yield of NGQDs is calculated to be about 52%, containing 88% of green-emissive NGQDs and 12% of blue-emissive NGQDs. Meanwhile, our NGQDs own low cytotoxicity, and display a good bioimaging performance in the in vitro and in vivo investigation. The synthesis idea in our work might be also applicable to obtain other kinds of quantum dots from the readily obtainable bulk materials.

Selective Growth of Stacking Fault Free ⟨100⟩ Nanowires on a Polycrystalline Substrate for Energy Conversion Application.

Cubic semiconductor nanowires grown along ⟨100⟩ directions have been reported to be promising for optoelectronics and energy conversion applications, owing to their pure zinc-blende structure without any stacking fault. But, until date, only limited success has been achieved in growing ⟨100⟩ oriented nanowires. Here we report the selective growth of stacking fault free ⟨100⟩ nanowires on a commercial transparent conductive polycrystalline fluorine-doped SnO2 (FTO) glass substrate via a simple and cost-effective chemical vapor deposition (CVD) method. By means of crystallographic analysis and density functional theory calculation, we prove that the orientation relationship between the Au catalyst and the FTO substrate play a vital role in inducing the selective growth of ⟨100⟩ nanowires, which opens a new pathway for controlling the growth directions of nanowires via the elaborate selection of the catalyst and substrate couples during the vapor-solid-liquid (VLS) growth process. The ZnSe nanowires grown on the FTO substrate are further applied as a photoanode in photoelectrochemical (PEC) water splitting. It exhibits a higher photocurrent than the ZnSe nanowires do without preferential orientations on a Sn-doped In2O3 (ITO) glass substrate, which we believe to be correlated with the smooth transport of charge carriers in ZnSe ⟨100⟩ nanowires with pure zinc-blende structures, in distinct contrast with the severe electron scattering happened at the stacking faults in ZnSe nanowires on the ITO substrate, as well as the efficient charge transfer across the intensively interacting nanowire-substrate interfaces.

Two-Dimensional Covalent Organic Framework-Graphene Photodetectors: Insight into the Relationship between the Microscopic Interfacial Structure and Performance.

Graphene is an attractive material for photodetection and optoelectronic applications because it offers a broad spectral bandwidth and ultrafast response speed. However, because of the broad light absorption characteristic, graphene has a lack of selectivity to the wavelength, which limits the performance of graphene-based photodetectors. Here, we demonstrate a novel hybrid photodetector with monolayer graphene covered with an ultrathin film of surface covalent organic frameworks (COFs) with variable structures as the light-harvesting materials. Photodetectors based on surface COF-G show enhanced responsivity in comparison with unmodified graphene and graphene modified with monomers. The submolecular resolution of scanning tunneling microscopy allows us to get a direct insight into the relationship between the microscopic interfacial structure and the performance of the device. We prove that the enhancement in the device performance is directly related with the orderliness of surface COFs, which influences the interfacial charge transfer by tuning π-π stacking between surface COF and graphene.

Improving the Water Oxidation Efficiency with a Light-Induced Electric Field in Nanograting Photoanodes.

Severe charge recombination in solar water-splitting devices significantly limits their performance. To address this issue, we design a frustum of a cone nanograting configuration by taking the hematite and Au-based thin-film photoanode as a model system, which greatly improves the photoelectrochemical water oxidation activity, affording an approximately 10-fold increase in the photocurrent density at 1.23 V versus the reversible hydrogen electrode compared to the planar counterpart. The surface plasmon polariton-induced electric field in hematite plays a dominant role in efficiency enhancement by facilitating charge separation, thus dramatically increasing the incident photon-to-current efficiency (IPCE) by more than 2 orders of magnitude in the near band gap of hematite. And the relatively weak electric field caused by light scattering in the nanograting structure is responsible for the approximate maximum 20-fold increase in IPCE within a broadband wavelength range. Our scalable strategy can be generalized to other solar energy conversion systems.

Interaction-Dependent Interfacial Charge-Transfer Behavior in Solar Water-Splitting Systems.

Dual-band-gap systems are promising for solar water splitting due to their excellent light-harvesting capability and high charge-separation efficiency. However, a fundamental understanding of interfacial charge-transfer behavior in the dual-band-gap configuration is still incomplete. Taking CdS/reduced graphene oxide (CdS/RGO) nanoheterojunctions as a model solar water splitting system, we attempt here to highlight the interaction-dependent interfacial charge-transfer behavior based on both experimental observations and theoretical calculations. Experimental evidence points to charge transfer at the CdS-RGO interface playing a dominant role in the photocatalytic hydrogen production activity. By tuning the degree of reduction of RGO, the interfacial interaction, and, thereby, the charge transfer can be controlled at the CdS-RGO interface. This observation is supported by theoretical analysis, where we find that the interfacial charge transfer is a balance between the effective single-electron- and hole-transfer probability and the surface free electron and hole concentration, both of which are related to the surface potential and tailored by interfacial interaction. This mechanism is applicable to all systems for solar water splitting, providing a useful guidance for the design and study of heterointerfaces for high-efficiency energy conversion.

A new nanowire-based lithium hexaoxotungstate anode for lithium-ion batteries.

This study reports one dimensional lithium hexaoxotungstate (Li6WO6), with a diameter in the range of 200-500 nm, as a novel anode material for lithium-ion batteries. The electrochemical performance of lithium hexaoxotungstate was investigated and a discharge capacity of 705 mA h g-1 was achieved after 50 cycles, along with an excellent rate capability. The 1D morphology of the material is believed to provide excellent transport properties, resulting in a high rate capability. The remarkable electrochemical performance of the Li6WO6 nanowires indicates that this new class of anode holds a lot of promise for future deployment in energy storage devices.

Antibacterial Carbon-Based Nanomaterials.

The emergence and global spread of bacterial resistance to currently available antibiotics underscore the urgent need for new alternative antibacterial agents. Recent studies on the application of nanomaterials as antibacterial agents have demonstrated their great potential for management of infectious diseases. Among these antibacterial nanomaterials, carbon-based nanomaterials (CNMs) have attracted much attention due to their unique physicochemical properties and relatively higher biosafety. Here, a comprehensive review of the recent research progress on antibacterial CNMs is provided, starting with a brief description of the different kinds of CNMs with respect to their physicochemical characteristics. Then, a detailed introduction to the various mechanisms underlying antibacterial activity in these materials is given, including physical/mechanical damage, oxidative stress, photothermal/photocatalytic effect, lipid extraction, inhibition of bacterial metabolism, isolation by wrapping, and the synergistic effect when CNMs are used in combination with other antibacterial materials, followed by a summary of the influence of the physicochemical properties of CNMs on their antibacterial activity. Finally, the current challenges and an outlook for the development of more effective and safer antibacterial CNMs are discussed.

Vertically Aligned Porous Organic Semiconductor Nanorod Array Photoanodes for Efficient Charge Utilization.

Because of inefficient charge utilization caused by localized π-electron conjugation and large exciton binding energy, the photoelectrochemical water-splitting efficiency of organic polymers is seriously limited. Taking the graphitic carbon nitride (g-CN) polymer as an example, we report a novel photoanode based on a vertically aligned g-CN porous nanorod (PNR) array prepared in situ, using a thermal polycondensation approach, with anodic aluminum oxide as the template. The g-CN PNR array exhibits an excellent photocurrent density of 120.5 µA cm-2 at 1.23 VRHE under one sun illumination, the highest reported incident photon-to-current efficiency of ∼15% at 360 nm, and an outstanding oxygen evolution reaction stability in 0.1 M Na2SO4 aqueous solution, which constitutes a benchmark performance among the reported g-CN-based polymer photoanodes without any sacrificial reagents. When compared with its planar counterpart, the enhanced performance of the PNR array results principally from its unique structure that enables a high degree of aromatic ring π-electron conjugation for higher mobility of charge carriers, provides a direct pathway for the electron transport to the substrate, produces a large portion of hole-accepting defect sites and space charge region to promote exciton dissociation, and also withstands more strain at the interface to ensure intimate contact with the substrate. This work opens a new avenue to develop nanostructured organic semiconductors for large-scale application of solar energy conversion devices.

Low-Temperature and Fast Kinetics for CO2 Sorption Using Li6WO6 Nanowires.

In this paper, lithium hexaoxotungstate (Li6WO6) nanowires were synthesized via facile solid-state reaction and were tested for CO2 capture applications at both low (<100 °C) and high temperatures (>700 °C). Under dry conditions, the nanowire materials were able to capture CO2 with a weight increment of 12% in only 60 s at an operating temperature of 710 °C. By contrast, under humidified ambience, Li6WO6 nanowires capture CO2 with weight increment of 7.6% at temperatures as low as 30-40 °C within a time-scale of 1 min. It was observed that the CO2 chemisorption in Li6WO6 is favored in the oxygen ambience at higher temperatures and in the presence of water vapor at lower temperatures. Nanowire morphology favors the swift lithium supply to the surface of lithium-rich Li6WO6, thereby enhancing the reaction kinetics and lowering time scales for high capacity adsorption. Overall, high chemisorption capacities, superfast reaction kinetics, wide range of operating temperatures, and reasonably good recyclability make 1-D Li6WO6 materials highly suitable for various CO2 capture applications.

Facile Integration between Si and Catalyst for High-Performance Photoanodes by a Multifunctional Bridging Layer.

Designing high-quality interfaces is crucial for high-performance photoelectrochemical (PEC) water-splitting devices. Here, we demonstrate a facile integration between polycrystalline n+p-Si and NiFe-layered double hydroxide (LDH) nanosheet array by a partially activated Ni (Ni/NiOx) bridging layer for the excellent PEC water oxidation. In this model system, the thermally deposited Ni interlayer protects Si against corrosion and makes good contact with Si, and NiOx has a high capacity of hole accumulation and strong bonding with the electrodeposited NiFe-LDH due to the similarity in material composition and structure, facilitating transfer of accumulated holes to the catalyst. In addition, the back illumination configuration makes NiFe-LDH sufficiently thick for more catalytically active sites without compromising Si light absorption. This earth-abundant multicomponent photoanode affords the PEC performance with an onset potential of ∼0.78 V versus reversible hydrogen electrode (RHE), a photocurrent density of ∼37 mA cm-2 at 1.23 V versus RHE, and retains good stability in 1.0 M KOH, the highest water oxidation activity so far reported for the crystalline Si-based photoanodes. This bridging layer strategy is efficient and simple to smooth charge transfer and make robust contact at the semiconductor/electrocatalyst interface in the solar water-splitting systems.

Nitrogen-doped graphene quantum dots coupled with photosensitizers for one-/two-photon activated photodynamic therapy based on a FRET mechanism.

A novel material with a large two-photon absorption cross-section was conjugated with a typical photosensitizer for inducing a FRET process. The photosensitizer can be excited by a one-/two-photon laser and then induced photo-toxicity in vitro and in vivo. The system presents great potential for improving treatment depth and the precision of traditional photodynamic therapy.

Sacrificial Interlayer for Promoting Charge Transport in Hematite Photoanode.

The semiconductor/electrolyte interface plays a crucial role in photoelectrochemical (PEC) water-splitting devices as it determines both thermodynamic and kinetic properties of the photoelectrode. Interfacial engineering is central for the device performance improvement. Taking the cheap and stable hematite (α-Fe2O3) wormlike nanostructure photoanode as a model system, we design a facile sacrificial interlayer approach to suppress the crystal overgrowth and realize Ti doping into the crystal lattice of α-Fe2O3 in one annealing step as well as to avoid the consequent anodic shift of the photocurrent onset potential, ultimately achieving five times increase in its water oxidation photocurrent compared to the bare hematite by promoting the transport of charge carriers, including both separation of photogenerated charge carriers within the bulk semiconductor and transfer of holes across the semiconductor-electrolyte interface. Our research indicates that understanding the semiconductor/electrolyte interfacial engineering mechanism is pivotal for reconciling various strategies in a beneficial way, and this simple and cost-effective method can be generalized into other systems aiming for efficient and scalable solar energy conversion.

Electron spin resonance and fluorescence imaging assisted electrochemical approach for accurate and comprehensive monitoring of cellular hydrogen peroxide dynamics.

Dynamic alteration in the levels of cellular hydrogen peroxide (H2O2) is closely related to a variety of human diseases, as well as signal transduction pathways that regulate cell survival and death. Although qualitative or quantitative methods are available for measuring either intra- or extra-cellular H2O2 levels, accurate and comprehensive in situ detection of the real-time H2O2 dynamics of living cells remains a significant challenge. To solve this problem, a novel multi-dimensional in situ cell assay platform combining electrochemistry, electron spin resonance (ESR) and optical imaging is designed. In this platform, the real-time concentration of extracellular H2O2 released from stimulated cells can be accurately detected by ESR assisted chronoamperometry, while the level of intracellular H2O2 is simultaneously monitored via the incorporated fluorescence imaging. Accurately and simultaneously analyzing the level variations of extra- and intra-cellular reactive oxygen species based on our assay platform can complement each other for further precise and in-depth investigation of their membrane transport and related cellular signaling, which will benefit disease diagnosis and treatment.

Chiral Nanoparticle as a New Efficient Antimicrobial Nanoagent.

d-type functionalized nanoparticles (NPs) can bind to MurD ligase with high affinity and inhibit its peptidoglycan synthetic enzyme activity, and finally cause bacterial killing. In contrast, its L-type counterpart displays a negligible effect, indicating that the chiral structure of the functionalized NPs plays an essential role in their binding interaction with MurD and therefore the antibacterial activity.

Extracellular Biocoordinated Zinc Nanofibers Inhibit Malignant Characteristics of Cancer Cell.

Inhibition of the heat shock proteins (HSPs) has been considered to be one of the promising strategies for cancer treatment. However, developing highly effective HSP inhibitors remains a challenge. Recent studies on the evolutionarily distinct functions between intracellular and extracellular HSPs (eHSPs) trigger a new direction with eHSPs as chemotherapeutic targets. Herein, the first engineered eHSP nanoinhibitor with high effectiveness is reported. The zinc-aspartic acid nanofibers have specific binding ability to eHSP90, which induces a decrease in the level of the tumor marker-gelatinases, consequently resulting in downregulation of the tumor-promoting inflammation nuclear factor-kappa B signaling, and finally inhibiting cancer cell proliferation, migration, and invasion; while they are harmless to normal cells. Our findings highlight the potential for cancer treatment by altering the key determinants that shape its ability to adapt and evolve using novel nanomaterials.

One-pot microbial method to synthesize dual-doped graphene and its use as high-performance electrocatalyst.

A novel strategy to synthesize nitrogen (N) and sulfur (S)-doped graphene (G) is developed through sulfate-reducing bacteria treating graphene oxide (GO). The N, S-doped G demonstrates significantly improved electrocatalytic properties and electrochemical sensing performances in comparison with single-doped graphene due to the synergistic effects of dual dopants on the properties of graphene.