Search

The self-dissipation and attenuation capacity of materials play an important role in realizing efficient electromagnetic absorption, in this case, the roles of macroscopic composition and micro-structure should be emphasized simultaneously in the reasonable design of microwave absorbent. Given that, Fe3N alloy embedded in two-dimensional porous carbon composites were fabricated via facile sol-gel and sacrificial template methods. Satisfactorily, the magnetic/dielectric materials combination and porous structure introduction are conductive to the optimization of impedance matching property, as result of the enhancement of microwave absorption capacity. In addition, sufficient magnetic loss capacity, strong conductivity as well as polarization attenuation bring about the outstanding microwave absorbing performance with an effective absorption bandwidth of 6.76 GHz and a minimum reflection loss value of -65.6 dB. It is believed that this work not only lay a foundation to achieve microwave response materials in a wide frequency range, but also emphasize the significant role of the component selection and structural design.

Here, we report a unique core-shell nanocomposite of Fe2N@N-doped carbon that coats dopamine-derived carbon shells on porous Fe2N nanoparticles via a facile and effective soft chemical method. The feasibility of preparing core-shell structure in the process of polymerization is realized by utilizing the fact that affluent amino and hydroxyl groups in dopamine endow the formidable chelation ability with metal ions. Temperature-dependent volume shrinkage effect of Fe2N originates from the lattice transformation in nitridation process, which is the key factor to control the void space inside carbon nanocubes and optimize the electromagnetic performance. Consequently, the as-prepared samples achieve excellent reflection loss (RL) values and effective absorption bandwidth at an even thin thickness of 1.4 mm. The balance between the temperature-dependent conduction loss and the optimization of hole structure impedance matching may be responsible for the excellent microwave behaviors. This work offers an attractive core-shell Fe2N@carbon with controllable void space as a promising candidate to handle the electromagnetic interface (EMI) issues.

Ascorbic acid (AA) is one of the most important vitamins and serves many physiological activities in the body. In this work, we propose a simple colorimetric sensor for the rapid detection of AA through the redox reaction between CoOOH nanoflakes and ascorbic acid with the 2, 2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) as a colorimetric signal indicator. CoOOH nanoflakes could catalytically oxidize colorless ABTS to produce green oxidized ABTS (ox ABTS) with an absorption band at 412 nm in UV–vis spectra. The presence of AA could induce the oxidation of ABTS, resulting in a significant color fading and decrease of the absorbance at 412 nm. Thus quantitative detection of AA is realized. Under the optimal experimental conditions, the linear range is obtained from 0.5 to 15 μM with a lower detection limit of 0.16 μM (S/N = 3). Particularly, this colorimetric assay is capable of detecting AA in different vitamins C tablet and fresh kiwi fruit samples. Hence, the fast response, high sensitivity and easy operation of the proposed colorimetric sensor make it suitable for further application in bioassay.

The aim of this study was to develop carbonaceous materials hybridized with anatase TiO2 composed of Activated Carbon-TiO2 (AC-TiO2), Olive Pits-TiO2 (OP-TiO2) and Wood Shaving-TiO2 (WS-TiO2) by ultrasonic-assisted sol-gel process for the photocatalytic Cr(VI) reduction under UV and narrow visible light. The morphology, crystal structure, surface chemistry and optical properties of the as-prepared and bare-TiO2 were investigated by SEM-EDS, XRD, FTIR, BET, UV-DRS, XPS and photo-current measurements. Unlike bare-TiO2, these composite photocatalysts exhibited an enhanced absorption in visible-light. The band gap energies were found to be 3.20 eV, 2.89 eV, 2.81 eV and 2.95 eV for bare-TiO2, AC-TiO2, OP-TiO2 and WS-TiO2, respectively. On the other hand, as-prepared photocatalysts showed significantly improved photocatalytic Cr(VI) reduction performances under UV and visible light illumination compared to bare-TiO2. A total reduction of 10 ppm of Cr(VI) was obtained after 30 min, 50 min and 130 min under visible light (>420) for AC-TiO2, OP-TiO2 and WS-TiO2, respectively at pH: 3 and in the presence of 10 ppm tartaric acid as hole scavenger, while no reduction was detected for bare-TiO2 under visible light (>420). The efficient photocatalytic reduction of Cr(VI) under visible light by AC-TiO2, OP-TiO2 and WS-TiO2 was mainly due to (i): the narrow band gap of TiO2 nanoparticle deposited in carbonaceous materials, (ii): self-photo-sensitizer role of carbonaceous materials via Ti O C bonds and (iii): the electron transfer from TiO2 to carbonaceous materials.

A simple and economical colorimetric probe for the detection of uric acid (UA) based on redox reaction of 3,3ʹ,5,5ʹ-tetramethylbenzidine (TMB) with HAuCl4 was designed. A novel chromogenic reaction was primarily demonstrated based on the reaction between HAuCl4 and TMB, which produces many color responses from red to blue in the resulting solutions. In this method, the colorless TMB can be oxidized by HAuCl4 to generate oxidized TMB (oxTMB) and induce a blue color solution which corresponding to the absorption peak at 652 nm. However, HAuCl4 would be reduced in the presence of UA, which inducing a blue color diminishing of HAuCl4-TMB system and decrease of the absorbance at 652 nm because the content of HAuCl4 was declined in the solution. Based on this phenomenon, we proposed a method to detect UA which does not require nanomaterials or organic probes. The detection conditions, pH value, incubation time and the concentration of HAuCl4 and TMB were optimized. The probe displayed a linear response in the range of 0.001–8.0 μM and 8.0–80.0 μM, with a detection limit of 0.67 nM (S/N = 3). This method has been successfully applied to the determination of uric acid in human urine samples.

A highly sensitive and selective colorimetric assay is proposed for the detection of mercury ions (Hg2+), cadmium ions (Cd2+) and ascorbic acid (AA) using trithiocyanuric acid (TMT) functionalized gold nanoparticles (TMT-AuNPs). TMT-AuNPs are dispersed in 40 mM NaCl solution, while the presence of Hg2+ and Cd2+ can induce TMT-AuNPs aggregate due to the strong interaction of Hg2+ and Cd2+ with TMT. Then the quantitative detection of Hg2+ and Cd2+can be realized in the linear range from 5 × 10−9 to 1 × 10−6 M and 1 × 10−8 to 3 × 10−7 M, with a lower detection limit of 2.8 nM for Hg2+ and 3.5 nM for Cd2+ (S/N = 3), respectively. To distinguish Hg2+ from Cd2+, a reductive biological small molecule ascorbic acid (AA) was used based on the different redox interaction of AA with Hg2+ and Cd2+. When the mixture of AA and Hg2+ was added into TMT-AuNPs solution, the state of TMT-AuNPs was still dispersed because Hg2+ was reduced by AA. On the contrary, when the mixture of AA and Cd2+ was added into TMT-AuNPs solution, the TMT-AuNPs was aggregated and the color of the solution has no obvious change compared to the system of Cd2+-TMT-AuNPs since the weak interaction between AA and Cd2+. Thus, AA could be detected. A linear correlation exists between the ratio of A640/A520 and the concentration of AA in the range from 1 × 10−8 to 1 × 10−6 M with a detection limit of 4.8 nM (S/N = 3). Importantly, it has been successfully applied to determine Hg2+, Cd2+ in lake water and AA in vitamins C tablet.

In the present work, 2­-aminobenzothiazole and 2-­amino­-4-­thiazoleacetic acid functionalized graphene decorated with fluorine, chlorine and iodine@SnO2 nanoparticles were prepared by hydrothermal synthesis method, respectively. The morphology and structure of these obtained nanocomposites were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray diffraction analysis and X-ray photoelectron spectrum (XPS). Results of cyclic voltammetry (CV) demonstrated that thiazole derivatives functionalized graphene decorated with fluorine@SnO2 had superior performance for detection of Cu2+ than others. Electrochemical sensor based on this nanocomposite was constructed for detection of Cu2+ and a wider linear range was obtained from 2 to 1000 nM with a detection limit of 0.3 nM (S/N = 3). Moreover, simultaneous detection of Cd2+, Cu2+ and Hg2+ was realized with high sensitivity and selectivity by the sensor owing to synergetic effects of thiazole derivatives, fluorine@SnO2 and graphene. Finally, the sensor was applied to real sample analysis with a satisfactory result.

Light-absorbing impurities (LAIs), such as organic carbon (OC), black carbon (BC), and mineral dust (MD), deposited on the surface snow of glacier can reduce the surface albedo. As there exists insufficient knowledge to completely characterize LAIs variations and difference in LAIs distributions, it is essential to investigate the behaviors of LAIs and their influence on the glaciers across the Tibetan Plateau (TP). Therefore, surface snow and snowpit samples were collected during September 2014 to September 2015 from Zhadang (ZD) glacier in the southern TP to investigate the role of LAIs in the glacier. LAIs concentrations were observed to be higher in surface aged snow than in the fresh snow possibly due to post-depositional processes such as melting or sublimation. The LAIs concentrations showed a significant spatial distribution and marked negative relationship with elevation. Impurity concentrations varied significantly with depth in the vertical profile of the snowpit, with maximum LAIs concentrations frequently occurred in the distinct dust layers which were deposited in non-monsoon, and the bottom of snowpit due to the eluviation in monsoon. Major ions in snowpit and backward trajectory analysis indicated that regional activities and South Asian emissions were the major sources. According to the SNow ICe Aerosol Radiative (SNICAR) model, the average simulated albedo caused by MD and BC in aged snow collected on 31 May 2015 accounts for about 13% ± 3% and 46% ± 2% of the albedo reduction. Furthermore, we also found that instantaneous RF caused by MD and BC in aged snow collected on 31 May 2015 varied between 4–16 W m − 2 and 7–64 W m − 2 , respectively. The effect of BC exceeds that of MD on albedo reduction and instantaneous RF in the study area, indicating that BC played a major role on the surface of the ZD glacier.

The nanocomposite of polyamidoamine (PAMAM) modified gold nanoparticles (pAuNPs)/SnO 2 /graphene sheets (GNs) was prepared by a new method. That is, the well dispersed AuNPs were prepared in the presence of PAMAM and resembled on the surface of 5,10,15,20-tetrakis (4-sulonatophenyl) porphyrin (H 4 TPPS 2– ) modified graphite oxide (GO) by electrostatic interaction. Then the well-distributed SnO 2 was obtained from SnCl 2 with the aid of GO and GO was reduced to graphene by hydrazine hydrate. The synthesized nanocomposite was characterized by Raman spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction analysis (XRD). Cyclic voltammetry (CV) experiment demonstrated that the nanocomposite exhibited excellent electrochemical performance for the detection of dopamine (DA). Then the quantitative detection of DA was carried out by differential pulse voltammetry (DPV) in the presence of ascorbic acid (AA). A linear range of 0.03–10 μM was obtained with a correlation coefficient of 0.9970. The detection limit was as low as 8 nM (S/N = 3). Moreover, the proposed method was applied for the determination of DA in real serum samples.

It's a major challenge to explore highly active and stable electrocatalysts for efficient hydrogen evolution reactions (HER) and oxygen evolution reactions (OER). In this work, we report a new hybrid electrocatalyst: iron-cobalt decorated nitrogen doped carbon/reduced graphene oxide-700 °C (Fe-Co-CN/rGO-700). The catalyst shows an excellent electrocatalytic performance toward HER and OER in alkaline solution, which has lower overpotentials of 0.215 V and 0.308 V at the current density 10 mA cm−2, respectively, and this catalyst has an outstanding durability (after 45 h). The excellent activity mainly benefit from the highly dispersed iron/cobalt species, sheet structure with high porosity, the improvement of electronic structures with nitrogen-doped carbon and high conductivity of rGO. Combined with the density function theory (DFT) calculations, the improvement of the HER and OER performance were also attributed to the balance of adsorption/desorption of the hydrogen and oxygen-containing intermediates, and the increased electronic states density near the Fermi level. The proposed work provides a novel and simple strategy to synthesize a porous carbon electrocatalyst material using metal-organic frameworks (MOFs) as precursor with high activity and strong stability for HER and OER.

In this paper, a sensitive and selective electrochemical sensor was constructed for nickel (II) detection by employing the electrode material of zeolitic imidazolate framework-8@dimethylglyoxime/β-cyclodextrin/reduced graphene oxide (ZIF-8@DMG/β-CD/RGO). The material was characterized and analyzed by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Nitrogen adsorption-desorption isotherms in detail. In these composite, ZIF-8 served as the supporting material of DMG which was the selective complexing agent to Ni (II), RGO employed conductivity while β-CD prevented the aggregation of RGO sheets. With these features, the sensor showed a wide linear range of 0.01–1.0 μM and a low detection limit of 0.005 μM (S/N = 3). Interferences of diethanol, citric acid, humic acid, Triton X-100 and some common metal ions can be ignored to some extent. Finally, the sensor was applied to Ni (II) detection in real water sample.

Synthetic customized heterostructure via optimizing structure as well as designing components is considered as an effective strategy to endow materials with specific functional applications. Here, we reported a facile and green process to obtain one dimensional (1D) Fe3N@C heterogeneous structures by using organic amines as nitrogen and carbon sources. Multiple processes including nitridation, formation of Fe3N nanoparticles and encapsulation of the produced Fe3N nanoparticles are simultaneously achieved. It is well known that microwave absorbers with stability and excellent performance are very important for the practical application. In this work, the as-prepared Fe3N@C composites can maintain excellent microwave absorbing performance when the samples are exposed to the open air for 3 months. Wide effective absorption bandwidths and strong absorption can be gained with the thickness less than 2 mm. In particular, an effective absorption bandwidth as wide as 5.92 GHz was obtained with thickness of 1.8 mm. Furthermore, the vector network analyzer (VNA) tests after 9 months of exposure to air provide more favorable evidence for its excellent and stable absorbing properties. The strong stability should be attributed to the covalent bonds after nitriding and the air-barrier provided by the outer carbon base. This study may provide new insights into the design and development of high-performance electromagnetic wave absorbers with excellent stability.

Excessive fertilization in rice paddy fields leads to surface water eutrophication, groundwater contamination and air pollution. Determining optimum nitrogen (N) management is essential for maintaining rice yield while reducing the environmental risk caused by N loss. A two-year field experiment (2017–2018) was carried out in a typical paddy field in the middle reaches of the Yangtze River. The WHCNS (soil Water Heat Carbon Nitrogen Simulator) model was calibrated and evaluated for simulations of measured ponding water depth, evapotranspiration, aboveground dry matter, yield, runoff and crop N. The model was then used to evaluate the effects of different N fertilizer rates and split-N application ratios (SNR) practices on crop growth and N losses. Results showed that the model performed well in simulating rice growth and N losses in the region. Ammonia volatilization and denitrification were the mainly pathways of N loss in paddy field, and their two-year average losses were 34% and 38% of the total N loss, respectively. N leaching accounted for 23%, and runoff N loss accounted for 5% of total N loss. N losses were evaluated for two different scenarios and simulated ratios of ammonia volatilization, denitrification, N leaching, and runoff to total N loss under different N management scenarios were 15%–53%, 33%–55%, 6%–30%, and 4%–8%, respectively. Ammonia volatilization and N runoff exponentially increased with an increase of N fertilizer rate, whereas denitrification and N leaching showed an increasing and then a decreasing trend. Yield increased by 36 kg ha−1, and the total N loss decreased by 32.6 kg N ha−1 when the N fertilizer rate was reduced from 231 kg N ha−1 to 155 kg N ha−1 and the SNR was changed from 5:3:1 to 1:1:4. Therefore, reducing the N fertilizer rate and increasing the SNR in the late rice growing season can significantly reduce N loss and effectively improve N use efficiency.

Residues of norfloxacin (NF) in environment caused public concerns for its side effects and the presence of bacteria resistance. Developing novel method for selective and sensitive determination of NF is important. In the present work, an electrochemical sensing method was proposed by employing the electrode material composed of graphitized carbon supported Ni/NiO clusters (Ni/NiO/C) and β-Cyclodextrin modified reduced graphene oxide (β-CD/RGO). These materials were characterized and analyzed by Fourier transform infrared (FT-IR), Raman, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Transmission electron microscopy (TEM) in detail. β-CD/RGO as electrode modification material with the ability to adsorb more guest molecules and promote electron transfer had been reported. Herein, electrochemical test demonstrated that Ni/NiO/C can catalyze NF oxidation and showed similar conductivity with β-CD/RGO. Benefited from the synergy effect between Ni/NiO/C and β-CD/RGO, the proposed method showed a wide linear range of 0.4 to 80 μM and a low detection limit of 0.01 μM (S/N = 3) for NF detection. Additionally, the proposed method was also applied to detect NF added in water sample with good recoveries obtained.

Based on a 20.12 m shallow ice core drilled at the Laohugou Glacier No. 12 (39 degrees 25.7'N, 96 degrees 33.4'E, 5040 m a.s.l.), north slope of Qilian Mountains in the northeastern Qinghai-Tibetan Plateau in June 2006, the changes of atmospheric environment over the Qilian Mountains and northwestern China recorded by ice chemistry and its possible connection with atmospheric circulation and the winter North Atlantic Oscillation (NAO) are investigated. A total of 606 samples were analyzed for major ions (Ca2+, Na+, K+, Mg2+, NH4+, Cl-, SO42- and NO3-) and stable oxygen isotope ratios (delta O-18). The ion chemistry of the ice core, covering the past 47 years, is mainly characterized by mineral dust species (Ca2+, Na+, Mg2+, SO42-, Cl- and K+), and anthropogenic species (SO42-, NH4+ and NO3-). Ca2+ is the dominant cation in the ice core with a medium value of 2815.5 mu eg L-1, accounting for 65.8% of the total cations, and SO42- is the predominant anion with a medium value of 1500.4 mu eg L-1, accounting for 45.8% of the total anions. Compared with ice core records from Altai and Himalayas, at the northern and southern margin of western China, respectively, dust-related species concentrations in the Laohugou ice core are much higher due to pronounced regional crustal dust aerosol inputs from surrounding arid and semiarid deserts. The results show that dust species concentrations decreased during 1960-2006 A.D., while non-dust species (SO42-, NH4+ and NO3-, anthropogenic species) concentrations increased, which indicating that the ice core record of dust storm activity over Qilian Mountains exhibits a significant decreasing trend during the past 47 years. This change of dust species may be caused by decrease in wind speed and increase in precipitation over the Laohugou surrounding areas in Qilian Mountains and northwestern China, and wind speed decrease is probably caused by spatial differences of inter-decadal air temperature change of the 600 hPa in central Asia. The normalized time series of the winter NAO index shows a significant inverse correlation with the annual flux of Ca2+ in dust, implying a possible connection between the winter NAO and the dust storm activity over the Qilian Mountains. (C) 2013 Elsevier Ltd and INQUA. All rights reserved.