Showing papers by "Nanjing Tech University published in 2016"

Recent progress in the development of fluorescent, luminescent and colorimetric probes for detection of reactive oxygen and nitrogen species

Abstract: Reactive oxygen (ROS) and nitrogen (RNS) species cause oxidative and nitrosative stresses, respectively. These stresses are implicated not only in diverse physiological processes but also in various pathological processes, including cancer and neurodegenerative disorders. In addition, some ROS and RNS in the environment are pollutants that threaten human health. As a consequence of these effects, sensitive methods, which can be employed to selectively monitor ROS and RNS in live cells, tissues and organisms as well as in environmental samples, are needed so that their biological roles can be understood and their concentrations in environmental samples can be determined. In this review, fluorescent, luminescent and colorimetric ROS and RNS probes, which have been developed since 2011, are comprehensively discussed.

Enhancing Electrocatalytic Activity of Perovskite Oxides by Tuning Cation Deficiency for Oxygen Reduction and Evolution Reactions

Abstract: Development of cost-effective and efficient electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of prime importance to emerging renewable energy technologies. Here, we report a simple and effective strategy for enhancing ORR and OER electrocatalytic activity in alkaline solution by introducing A-site cation deficiency in LaFeO3 perovskite; the enhancement effect is more pronounced for the OER than the ORR. Among the A-site cation deficient perovskites studied, La0.95FeO3-δ (L0.95F) demonstrates the highest ORR and OER activity and, hence, the best bifunctionality. The dramatic enhancement is attributed to the creation of surface oxygen vacancies and a small amount of Fe4+ species. This work highlights the importance of tuning cation deficiency in perovskites as an effective strategy for enhancing ORR and OER activity for applications in various oxygen-based energy storage and conversion processes.

Two-Dimensional-Material Membranes: A New Family of High-Performance Separation Membranes.

Abstract: Two-dimensional (2D) materials of atomic thickness have emerged as nano-building blocks to develop high-performance separation membranes that feature unique nanopores and/or nanochannels. These 2D-material membranes exhibit extraordinary permeation properties, opening a new avenue to ultra-fast and highly selective membranes for water and gas separation. Summarized in this Minireview are the latest ground-breaking studies in 2D-material membranes as nanosheet and laminar membranes, with a focus on starting materials, nanostructures, and transport properties. Challenges and future directions of 2D-material membranes for wide implementation are discussed briefly.

Excited State Modulation for Organic Afterglow: Materials and Applications

Abstract: Organic afterglow materials, developed recently by breaking through the difficulties in modulating ultrafast-decayed excited states, exhibit ultralong-lived emission for persistent luminescence with lifetimes of several orders of magnitude longer than traditional fluorescent and phosphorescent emissions at room temperature. Their exceptional properties, namely ultralong luminescent lifetime, large Stokes shifts, facile excited state transformation, and environmentally sensitive emission, have led to a diverse range of advanced optoelectronic applications. Here, the organic afterglow is reviewed from the perspective of fundamental concepts on both phenomenon and mechanism, examining the technical challenges in relation to excited state tuning and lifetime elongation. In particular, the advances in material design strategies that afford a large variety of organic afterglow materials for a broad utility in optoelectronics including lighting and displays, anti-counterfeiting, optical recording, chemical sensors and bio-imaging are highlighted.

An Aqueous Rechargeable Zn//Co3 O4 Battery with High Energy Density and Good Cycling Behavior.

Abstract: An aqueous rechargeable Zn//Co3 O4 battery is demonstrated with Zn@carbon fibers and Co3 O4 @Ni foam as the negative and positive electrodes, respectively, using an electrolyte of 1 m KOH and 10 × 10(-3) m Zn(Ac)2 . It can operate at a cell voltage as high as 1.78 V with an energy density of 241 W h kg(-1) and presents excellent cycling. The battery is also assembled into a flexible shape, which can be applied in flexible or wearable devices requiring high energy.

Advances in non-enzymatic glucose sensors based on metal oxides.

Abstract: Glucose sensors have been extensively developed because of their broad applications, especially in diabetes diagnosis. Up to date, electrochemical enzymatic glucose sensors are commonly used in daily life for glucose detection and commercially successful as glucose-meters because they exhibit excellent selectivity, high reliability, and could be handled under physiological pH conditions. However, considering some intrinsic disadvantages of enzymes, such as high fabrication cost and poor stability, non-enzymatic glucose sensors have attracted increasing research interest in recent years due to their low cost, high stability, prompt response, and low detection limit. Furthermore, the development of nanotechnology has also offered new opportunities to construct nanostructured electrodes for glucose sensing applications. With distinguished advantages, metal oxides have garnered extensive effort in the development of cost-effective sensors with high stability, sensitivity and quick response for the determination of glucose via electrochemical oxidation. Hence, this review summarizes the advances in non-enzymatic glucose sensors based on different metal oxides (such as ZnO, CuO/Cu2O, NiO, Co3O4, MnO2, etc.) and their nanocomposites. Additionally, a brief prospective is presented on metal oxides for glucose sensors.

Subnanometer Two-Dimensional Graphene Oxide Channels for Ultrafast Gas Sieving

Abstract: Two-dimensional (2D) materials with atomic thickness and extraordinary physicochemical properties exhibit unique mass transport behaviors, enabling them as emerging nanobuilding blocks for separation membranes. Engineering 2D materials into membrane with subnanometer apertures for precise molecular sieving remains a great challenge. Here, we report rational-designing external forces to precisely manipulate nanoarchitecture of graphene oxide (GO)-assembled 2D channels with interlayer height of ∼0.4 nm for fast transporting and selective sieving gases. The external forces are synergistic to direct the GO nanosheets stacking so as to realize delicate size-tailoring of in-plane slit-like pores and plane-to-plane interlayer-galleries. The 2D channels endow GO membrane with excellent molecular-sieving characteristics that offer 2–3 orders of magnitude higher H2 permeability and 3-fold enhancement in H2/CO2 selectivity compared with commercial membranes. Formation mechanism of 2D channels is proposed on the basi...

Instantaneous ballistic velocity of suspended Brownian nanocrystals measured by upconversion nanothermometry

Abstract: Luminescence spectroscopy can be employed to investigate the Brownian motion of upconversion nanocrystals with high spatial resolution and thermal sensitivity.

Co-doping Strategy for Developing Perovskite Oxides as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction

Abstract: A synergistic co-doping strategy is proposed to identify a series of BaCo0.9-x Fe x Sn0.1O3-δ perovskites with tunable electrocatalytic activity for the oxygen evolution reaction (OER). Simply through tailoring the relative concentrations of less OER-active tin and iron dopants, a cubic perovskite structure (BaCo0.7Fe0.2Sn0.1O3-δ) is stabilized, showing intrinsic OER activity >1 order of magnitude larger than IrO2 and a Tafel slope of 69 mV dec-1.

Large Spin-Valley Polarization in Monolayer MoTe2 on Top of EuO(111)

Abstract: The electronic properties of monolayer MoTe2 on top of EuO(111) are studied by first-principles calculations. Strong spin polarization is induced in MoTe2 , which results in a large valley polarization. In a longitudinal electric field this will result in a valley and spin-polarized charge Hall effect. The direction of the Hall current as well as the valley and spin polarizations can be tuned by an external magnetic field.

Nanostructured positive electrode materials for post-lithium ion batteries

Abstract: Nanotechnology has opened up new frontiers in materials science and engineering in the past several decades. Considerable efforts on nanostructured electrode materials have been made in recent years to fulfill the future requirements of electrochemical energy storage. Compared to bulk materials, most of these nanostructured electrode materials improve the thermodynamic and kinetic properties of electrochemical reactions for achieving high energy and power densities. Here we briefly review the state-of-the-art research activities in the area of nanostructured positive electrode materials for post-lithium ion batteries, including Li–S batteries, Li–Se batteries, aqueous rechargeable lithium batteries, Li–O2 batteries, Na-ion batteries, Mg-ion batteries and Al-ion batteries. These future rechargeable battery systems may offer increased energy densities, reduced cost, and more environmental benignity. A particular focus is directed to the design principles of these nanostructured positive electrode materials and how nanostructuring influences electrochemical performance. Moreover, the recent achievements in nanostructured positive electrode materials for some of the latest emerging rechargeable batteries are also summarized, such as Zn-ion batteries, F- and Cl-ion batteries, Na–, K– and Al–S batteries, Na– and K–O2 batteries, Li–CO2 batteries, novel Zn–air batteries, and hybrid redox flow batteries. To facilitate further research and development, some future research trends and directions are finally discussed.

A reduced graphene oxide nanofiltration membrane intercalated by well-dispersed carbon nanotubes for drinking water purification

Abstract: In this study, we report a promising rGO–CNT hybrid nanofiltration (NF) membrane that was fabricated by loading reduced graphene oxide that was intercalated with carbon nanotubes (rGO–CNTs) onto an anodic aluminum oxide (AAO) microfiltration membrane via a facile vacuum-assisted filtration process. To create this NF membrane, the CNTs were first dispersed using block copolymers (BCPs); the effects of the types and contents of BCPs used on the dispersion of CNTs have been investigated. The as-prepared rGO–CNT hybrid NF membranes were then used for drinking water purification to retain the nanoparticles, dyes, proteins, organophosphates, sugars, and particularly humic acid. Experimentally, it is shown that the rGO–CNT hybrid NF membranes have high retention efficiency, good permeability and good anti-fouling properties. The retention was above 97.3% even for methyl orange (327 Da); for other objects, the retention was above 99%. The membrane's permeability was found to be as high as 20–30 L m−2 h−1 bar−1. Based on these results, we can conclude that (i) the use of BCPs as a surfactant can enhance steric repulsion and thus disperse CNTs effectively; (ii) placing well-dispersed 1D CNTs within 2D graphene sheets allows an uniform network to form, which can provide many mass transfer channels through the continuous 3D nanostructure, resulting in the high permeability and separation performance of the rGO–CNT hybrid NF membranes.

Two-Dimensional Nb-Based M4C3 Solid Solutions (MXenes)

Abstract: Herein, two new two-dimensional Nb4C3-based solid solutions (MXenes), (Nb-0.8,Ti-0.2)(4)C3Tx and (Nb-0.8,Zr-0.2)(4)C3Tx (where T is a surface termination) were synthesizedas confirmed by X-ray diff ...

Promotion of Oxygen Reduction by Exsolved Silver Nanoparticles on a Perovskite Scaffold for Low-Temperature Solid Oxide Fuel Cells

Abstract: Solid oxide fuel cells (SOFCs) have potential to be the cleanest and most efficient electrochemical energy conversion devices with excellent fuel flexibility. To make SOFC systems more durable and economically competitive, however, the operation temperature must be significantly reduced, which depends sensitively on the development of highly active electrocatalysts for oxygen reduction reaction (ORR) at low temperatures. Here we report a novel silver nanoparticle-decorated perovskite oxide, prepared via a facile exsolution process from a Sr0.95Ag0.05Nb0.1Co0.9O3-δ (SANC) perovskite precursor, as a highly active and robust ORR electrocatalyst for low-temperature SOFCs. The exsolved Sr0.95Ag0.05Nb0.1Co0.9O3-δ (denoted as e-SANC) electrode is very active for ORR, achieving a very low area specific resistance (∼0.214 Ω cm2 at 500 °C). An anode-supported cell with the new heterostructured cathode demonstrates very high peak power density (1116 mW cm–2 at 500 °C) and stable operation for 140 h at a current dens...

Electrically Tunable Valley-Light Emitting Diode (vLED) Based on CVD-Grown Monolayer WS2

Abstract: Owing to direct band gap and strong spin–orbit coupling, monolayer transition-metal dichalcogenides (TMDs) exhibit rich new physics and great applicable potentials. The remarkable valley contrast and light emission promise such two-dimensional (2D) semiconductors a bright future of valleytronics and light-emitting diodes (LEDs). Though the electroluminescence (EL) has been observed in mechanically exfoliated small flakes of TMDs, considering real applications, a strategy that could offer mass-product and high compatibility is greatly demanded. Large-area and high-quality samples prepared by chemical vapor deposition (CVD) are perfect candidates toward such goal. Here, we report the first demonstration of electrically tunable chiral EL from CVD-grown monolayer WS2 by constructing a p–i–n heterojunction. The chirality contrast of the overall EL reaches as high as 81% and can be effectively modulated by forward current. The success of fabricating valley LEDs based on CVD WS2 opens up many opportunities for d...

Palladium Nanoparticles Supported on Nitrogen and Sulfur Dual-Doped Graphene as Highly Active Electrocatalysts for Formic Acid and Methanol Oxidation

Abstract: Optimized designing of highly active electrocatalysts has been regarded as a critical point to the development of portable fuel cell systems with high power density. Here we report a facile and cost-effective strategy to synthesis of ultrafine Pd nanoparticles (NPs) supported on N and S dual-doped graphene (NS-G) nanosheets as multifunctional electrocatalysts for both direct formic acid fuel cell and direct methanol fuel cell. The incorporation of N and S atoms into graphene frameworks is achieved by a thermal treatment process, followed by the controlled growth of Pd NPs via a solvothermal approach. Owning to the unique structural features as well as the strong synergistic effects, the resulting Pd/NS-G hybrid exhibits outstanding electrocatalytic performance toward both formic acid and methanol electro-oxidation, such as higher anodic peak current densities and more exceptional catalytic stability than those of Pd/Vulcan XC-72R and Pd/undoped graphene catalysts. These findings open up new possibility in the construction of advanced Pd-based catalysts, which is conducive to solving the current bottlenecks of fuel cell technologies.

A minimalist fluorescent probe for differentiating Cys, Hcy and GSH in live cells

Abstract: A simple molecule, tetrafluoroterephthalonitrile (4F-2CN), was discovered to be an efficient fluorescent probe for detecting biological thiol species. The probe responded to Cys and emitted strong green fluorescence, whereas it reacted with Hcy/GSH and generated blue fluorescence. Addition of CTAB (cetyl trimethylammonium bromide) was observed to alter the fluorescence color of the reaction product of 4F-2CN and Hcy (from blue to green), but no alteration of the fluorescence color occurred for Cys and GSH. For the very first time, cell imaging experiments showed that the three commonly occurring thiols (Cys/Hcy/GSH) could be differentiated using a single fluorescent probe. In addition, the reaction product of 4F-2CN and Cys exhibits two-photon properties, offering a potentially useful tool for tissue imaging studies. To the best of our knowledge, 4F-2CN is currently the smallest fluorescent probe for thiol detection. We envision that this new and versatile probe will be a useful tool for further elucidating the roles of thiols in biology.

Proton-pump inhibitors and risk of fractures: an update meta-analysis

Abstract: To identify the relationship between proton-pump inhibitors (PPIs) and the risk of fracture, we conducted an update meta-analysis of observational studies. Results showed that PPI use was associated with a modestly increased risk of hip, spine, and any-site fracture. Many studies have investigated the association of proton-pump inhibitors (PPIs) with fracture risk, but the results have been inconsistent. To evaluate this question, we performed a meta-analysis of relevant observational studies. A systematic literature search up to February 2015 was performed in PubMed. We combined relative risks (RRs) for fractures using random-effects models and conducted subgroup and stratified analyses. Eighteen studies involving a total of 244,109 fracture cases were included in this meta-analysis. Pooled analysis showed that PPI use could moderately increase the risk of hip fracture [RR = 1.26, 95 % confidence intervals (CIs) 1.16–1.36]. There was statistically significant heterogeneity among studies (p < 0.001; I 2 = 71.9 %). After limiting to cohort studies, there was also a moderate increase in hip fracture risk without evidence of study heterogeneity. Pooling revealed that short-term use ( 1 year) were similarly associated with increased risk of hip fracture. Furthermore, a moderately increased risk of spine (RR = 1.58, 95 % CI 1.38–1.82) and any-site fracture (RR = 1.33, 95 % CI 1.15–1.54) was also found among PPI users. In this update meta-analysis of observational studies, PPI use modestly increased the risk of hip, spine, and any-site fracture, but no evidence of duration effect in subgroup analysis.

Advancements in the stability of perovskite solar cells: degradation mechanisms and improvement approaches

Abstract: Recently, organic metal halide perovskites have emerged as one of the most promising photoactive materials in the field of photovoltaics. Over the past six years, the efficiency of perovskite solar cells (PSCs) has increased from initially 3.8% to 20.8% through the optimization of perovskite film fabrication and device architecture. However, perovskites suffer inherent instability and degrade rapidly under different exposures (water, oxygen, UV-light irradiation and high temperature), limiting their further application to commercialization. Herein, several studies have been carried out to resolve this problem to some extent. In this paper, possible degradation mechanisms are summarized in order to help us understand the process of perovskite decomposition. Moreover, we also systematically outline and classify the approaches to improve the long-term stability of perovskite devices.

In-Situ Fabrication of Graphene Oxide Hybrid Ni-Based Metal-Organic Framework (Ni-MOFs@GO) with Ultrahigh Capacitance as Electrochemical Pseudocapacitor Materials.

Abstract: This paper reports a series of novel Ni-based metal–organic framework (Ni–MOFs) prepared by a facile solvothermal process. The synthetic conditions have great effects on the Ni–MOFs morphologies, porous textures, and their electrochemical performance. Improved capacitance performance was successfully realized by the in-situ hybrid of Ni–MOFs with graphene oxide (GO) nanosheets (Ni–MOFs@GO). The pseudocapacitance of ca. 1457.7 F/g for Ni–MOFs obtained at 180 °C with HCl as the modulator was elevated to ca. 2192.4 F/g at a current density of 1 A/g for the Ni–MOFs@GO with GO contents of 3 wt %. Additionally, the capacitance retention was also promoted from ca. 83.5% to 85.1% of its original capacitance at 10 A/g even after 3000 cycles accordingly. These outstanding electrochemical properties of Ni-based MOF materials may be related to their inherent characteristics, such as the unique flower-like architecture and fascinating synergetic effect between the Ni–MOFs and the GO nanosheets.

Multicolour synthesis in lanthanide-doped nanocrystals through cation exchange in water.

Abstract: Meeting the high demand for lanthanide-doped luminescent nanocrystals across a broad range of fields hinges upon the development of a robust synthetic protocol that provides rapid, just-in-time nanocrystal preparation. However, to date, almost all lanthanide-doped luminescent nanomaterials have relied on direct synthesis requiring stringent controls over crystal nucleation and growth at elevated temperatures. Here we demonstrate the use of a cation exchange strategy for expeditiously accessing large classes of such nanocrystals. By combining the process of cation exchange with energy migration, the luminescence properties of the nanocrystals can be easily tuned while preserving the size, morphology and crystal phase of the initial nanocrystal template. This post-synthesis strategy enables us to achieve upconversion luminescence in Ce3+ and Mn2+-activated hexagonal-phased nanocrystals, opening a gateway towards applications ranging from chemical sensing to anti-counterfeiting.