纳米碳中的微观缺陷结构特征

测定了定向石墨和纳米碳的正电子寿命谱,结果表明,热解法制备的纳米碳存在开空间小于单空位的自由体积以及开宽间相当于约１０个空位聚集体全的微孔洞,比较了热解法制备的纳米碳,ＵＦＰ冷压法制备的纳米Ｆｅ和纳米ＴｉＯ２以有非晶晶化法制备的纳米ＮｉＰ的缺陷结构特征,结果为纳米ＮｉＰ中缺陷的电子密度最高,纳米Ｆｅ和纲米ＴｉＯ２次之,纳米碳的最低,纳米碳中的缺陷浓度最高,纳米Ｆｅ和纳米ＴｉＯ２的次之,纳米ＮｉＰ的     

Forest carbon densities and uncertainties from Lidar, QuickBird, and field measurements in California

Greenhouse gas inventories and emissions reduction programs require robust methods to quantify carbon sequestration in forests. We compare forest carbon estimates from Light Detection and Ranging (Lidar) data and QuickBird high-resolution satellite images, calibrated and validated by field measurements of individual trees. We conducted the tests at two sites in California: (1) 59 km² of secondary and old-growth coast redwood (Sequoia sempervirens) forest (Garcia-Mailliard area) and (2) 58 km² of old-growth Sierra Nevada forest (North Yuba area). Regression of aboveground live tree carbon density, calculated from field measurements, against Lidar height metrics and against QuickBird-derived tree crown diameter generated equations of carbon density as a function of the remote sensing parameters. Employing Monte Carlo methods, we quantified uncertainties of forest carbon estimates from uncertainties in field measurements, remote sensing accuracy, biomass regression equations, and spatial autocorrelation. Validation of QuickBird crown diameters against field measurements of the same trees showed significant correlation (r = 0.82, P < 0.05). Comparison of stand-level Lidar height metrics with field-derived Lorey's mean height showed significant correlation (Garcia-Mailliard r = 0.94, P < 0.0001; North Yuba R = 0.89, P < 0.0001). Field measurements of five aboveground carbon pools (live trees, dead trees, shrubs, coarse woody debris, and litter) yielded aboveground carbon densities (mean ± standard error without Monte Carlo) as high as 320 ± 35 Mg ha^− 1 (old-growth coast redwood) and 510 ± 120 Mg ha^− 1 (red fir [Abies magnifica] forest), as great or greater than tropical rainforest. Lidar and QuickBird detected aboveground carbon in live trees, 70-97% of the total. Large sample sizes in the Monte Carlo analyses of remote sensing data generated low estimates of uncertainty. Lidar showed lower uncertainty and higher accuracy than QuickBird, due to high correlation of biomass to height and undercounting of trees by the crown detection algorithm. Lidar achieved uncertainties of < 1%, providing estimates of aboveground live tree carbon density (mean ± 95% confidence interval with Monte Carlo) of 82 ± 0.7 Mg ha^− 1 in Garcia-Mailliard and 140 ± 0.9 Mg ha^− 1 in North Yuba. The method that we tested, combining field measurements, Lidar, and Monte Carlo, can produce robust wall-to-wall spatial data on forest carbon.     

Remote sensing of photosynthetic light-use efficiency across two forested biomes: Spatial scaling

Eddy covariance (EC) measurements have greatly advanced our knowledge of carbon exchange in terrestrial ecosystems. However, appropriate techniques are required to upscale these spatially discrete findings globally. Satellite remote sensing provides unique opportunities in this respect, but remote sensing of the photosynthetic light-use efficiency (ε), one of the key components of Gross Primary Production, is challenging. Some progress has been made in recent years using the photochemical reflectance index, a narrow waveband index centered at 531 and 570 nm. The high sensitivity of this index to various extraneous effects such as canopy structure, and the view observer geometry has so far prevented its use at landscape and global scales. One critical aspect of upscaling PRI is the development of generic algorithms to account for structural differences in vegetation. Building on previous work, this study compares the differences in the PRI: ? relationship between a coastal Douglas-fir forest located on Vancouver Island, British Columbia, and a mature Aspen stand located in central Saskatchewan, Canada. Using continuous, tower-based observations acquired from an automated multi-angular spectro-radiometer (AMSPEC II) installed at each site, we demonstrate that PRI can be used to measure ? throughout the vegetation season at the DF-49 stand (r² = 0.91, p < 0.00) as well as the deciduous site (r² = 0.88, p < 0.00). It is further shown that this PRI signal can be also observed from space at both sites using daily observations from the Moderate Resolution Imaging Spectro-radiometer (MODIS) and a multi-angular implementation of atmospheric correction (MAIAC) (r² = 0.54 DF-49; r² = 0.63 SOA; p < 0.00). By implementing a simple hillshade model derived from airborne light detection and ranging (LiDAR) to approximate canopy shadow fractions (α_s), it is further demonstrated that the differences observed in the relationship between PRI and ε at DF-49 and SOA can be attributed largely to differences in α_s. The findings of this study suggest that algorithms used to separate physiological from extraneous effects in PRI reflectance may be more broadly applicable and portable across these two climatically and structurally different biome types, when the differences in canopy structure are known.     

Electrochemical determination of imidacloprid using nanosilver Nafion/nanoTiO2 Nafion composite modified glassy carbon electrode

A novel biocompatible environment friendly nanosilver Nafion^®/nanoTiO₂ Nafion^® modified glassy carbon electrode was prepared by a simple procedure and characterized. This modified electrode was used as a sensing electrode for the detection of imidacloprid. Cyclic voltammetry, differential pulse voltammetry and amperometry were used in this work. The reduction potential of imidacloprid on this electrode is lower compared to other electrodes reported in the literature. The LOD and LOQ values obtained for the sensing of imidacloprid on this modified electrode are comparable to the values reported in the literature.     

Controlling the initial phase of PECVD growth of vertically aligned carbon nanofibers on TiN

We explore the growth of vertically aligned carbon nanofibers by plasma enhanced chemical vapor deposition, using lithographically defined Ni catalyst seeds on TiN. TiN is selected for being an electrically conducting diffusion barrier suitable for the realization of electronic devices. We show that the rate of Ni diffusion correlates to both the level of oxygen content in the TiN film and to the film resistivity. The synthesis of the nanofibers was characterized using electron microscopy with an emphasis on three growth parameters: substrate temperature, plasma power, and chamber pressure. We propose that a catalyst surface free from carbon deposits throughout the process will induce diffusion-limited growth. The growth will shift towards a supply-limited process when the balance between acetylene, as the effective carbon bearing gas, and atomic hydrogen, as the main etching agent, is skewed in favor of acetylene. This determines whether the dominating growth mode will be vertically aligned ‘tip-type’ or disordered ‘base-type’, by affecting the competition between the formation of the first graphitic sheets on the catalyst surface and at the catalyst-substrate interface.     

Room temperature hydrogen gas sensor nanocomposite based on Pd-decorated multi-walled carbon nanotubes thin films

Multi-walled carbon nanotubes (MWCNTs) are successfully processed in the form of thin films (buckypapers), and their morphology and electrical behaviour are characterized. The MWCNTs are synthesized by the floating catalyst chemical vapour deposition process. The effects of a sequence of treatments applied for MWCNTs purification on the buckypapers electrical behaviour are also examined. Nanocomposite thin films constituted of pristine and purified MWCNTs and Pd nanoparticles are prepared in order to evaluate their viability as H₂ sensors at room temperature. For this purpose, the electrical resistance of the nanocomposite films in atmospheres with different H₂ concentrations, is determined. Scanning electron microscopy (SEM) images show that the buckypapers and the nanocomposite films are 2D structures constituted by randomly oriented MWCNTs. The buckypapers present a semiconductor-like electrical behaviour as determined by the standard four point method. Room temperature resistivity values of around 10⁻³ Ω m are assessed. Nanocomposite films show different electrical behaviour depending on the purification treatment applied to the MWCNTs employed. Furthermore, the electrical resistance of the nanocomposite films is found to increase when the measurements are performed in H₂ atmosphere. Values of H₂ sensitivity at room temperature of the nanocomposite films up to 2.15% are determined for H₂ average concentration higher than 350 ppm with short recovery time.     

Poly(brilliant cresyl blue) electrogenerated on single-walled carbon nanotubes modified electrode and its application in mediated biosensing system

Single-walled carbon nanotubes (SWCNTs) functionalized with carboxylic acid groups were cast to glassy carbon electrode (GCE) to construct a three-dimensional nano-micro structured scaffold. Brilliant cresyl blue (BCB) was electropolymerized on the above-mentioned SWCNTs/GCE using continuous cycling between −0.7 and 0.9 V vs. SCE. PolyBCB yielded on SWCNTs/GCE exhibited the enhanced electrochemical redox behavior compared with that electrogenerated on bare GCE. The apparent surface coverage of PolyBCB obtained by SWCNTs/GCE was at least 10 times higher than that obtained by bare GCE, namely 4.8 × 10⁻⁹ and 3.6 × 10⁻¹⁰ mol cm⁻². The cyclic voltammograms recorded by PolyBCB/SWCNTs/GCE exhibited well-defined two peaks located at −0.25 V and −0.06 V, respectively, with a surface-controlled mechanism. In addition, morphologies of PolyBCB electrogenerated on GCE and SWCNTS/GCE were characterized by atomic force microscopy. Finally, this proposed PolyBCB/SWCNTs/GCE was used in the construction of the second-generation biosensors to hydrogen peroxide and glucose, with the enhanced analytical performance.     

Preparation and performance of IPMC actuators with electrospun Nafion-MWNT composite electrodes

A new ionic polymer actuator was prepared with Nafion^®-117 membrane and electrodes made of an electrospun Nafion^®/multiwalled carbon nanotube (MWNT) web. The surfaces of composite electrodes were ion-beam coated with gold layers of 2-3 μm thickness to reduce the surface resistance. The composite electrodes offer several advantages over conventional platinum electrodes prepared via electroless plating process, i.e. flexibility, simple processability in large scales, and batch-to-batch reproducibility. The new ionic polymer-metal composite (IPMC) actuators showed a rapid and large bending motion. Under an applied potential of 3 V dc, the maximum horizontal displacement (δ_max) measured at the tip of IPMC strip (cantilever length: 20 mm) was 16.7 mm, the tip velocity in the initial linear region was 10.5 mm/s, 88% of the δ_max was reached within initial 5 s, and the generated strain% was 0.79 (13.6 mm, 7.2 mm/s, 85%, and 0.88, respectively for a conventional Nafion^®-IPMC made via the electroless plating of platinum). It was noted that the energy efficiency of strain was over 10 times higher than that of the conventional Nafion^®-IPMC. And the crack formation of metal electrode after repeated bending deformation significantly reduced with the introduction of relatively flexible electrode assembly into the IPMC architecture. The remarkable improvements in its performance were considered to be due to the efficient quantum chemical and double-layer electrostatic effects in a charge injection model, induced by the good dispersion of MWNTs through a typical electrospinning technique.     

A label-free amperometric immunosensor based on horseradish peroxidase functionalized carbon nanotubes and bilayer gold nanoparticles

In this work, a novel label-free amperometric immunosensor has been constructed for detecting α-1-fetoprotein (AFP) based on nanocomposite of horseradish peroxidase (HRP) labeled carbon nanotubes (CNTs). First, the gold nanoparticles (AuNPs) were electrodeposited on the surface of the glass carbon electrode by electrochemical reduction of gold chloride tetrahydrate (HAuCl₄) to immobilize horseradish peroxidase labeled carbon nanotubes (HRP-CNTs). Then HRP-CNTs bioconjugate was immobilized on the surface of the electrodeposited AuNPs layer by the combination of forces (coordination and electrostatic force). Subsequently, it was immersed into gold colloidal nanoparticles (GNPs) solution, which was used to immobilize antibody biomolecules (anti-AFP). Enhanced sensitivity was obtained by using bioconjugates featuring HRP labeled (HRP-CNTs), which had lager specific surface area and good electronic catalysis (current response signal) compared to carbon nanotubes. Under optimized conditions, the linear ranges were from 0.2 to 200 ng mL⁻¹ with a detection limit of 0.067 ng mL⁻¹ (at an S/N of 3). The proposed immunosenor showed good precision, acceptable stability and reproducibility and could be used for the detection AFP in normal human serum, which provided a potential alternative tool for the detection of protein in clinical diagnosis.     

Effect of soft-hard segment structure on vapor responsiveness of polyurethane conducting composite thin films loaded with multi-walled carbon nanotubes

A series of multi-walled carbon nanotubes/polyurethane (MWNTs/PU) composite conducting dispersoids were prepared via an in situ coupling reaction among linear hydroxyl-terminated polymer diols, 1,6-hexamethylene diisocyanate (HDI) and various chain extenders. The composite conducting thin films were formed by spin-coating and depositing the dispersoids onto comb-like electrode substrates. The resulting structure and the dispersion quality of MWNTs in the dispersoids were examined by means of FTIR, XRD, TEM, SEM and UV-vis analyses. The response of the as-prepared films toward some volatile organic solvent vapors such as benzene, anhydrous ether, acetone and chloroform was evaluated. The experimental results indicated that the composite conducting films constructed by hydroxyl-terminated poly(butadiene-co-acrylonitrile), trimethylolpropane, and MWNTs-OH bear better vapor responsiveness. The dispersion behavior of MWNTs in the dispersoids, types of MWNTs and soft-hard segmental compositions are believed to be closely related with the sensing properties of the films. In particular, the chemical linkage of MWNT-OH with HDI in the PU matrix is expected to improve the dispersivity and further to enhance the sensing properties of the composite sensors. The vapor sensing properties well reveal that these materials have a possibility as a candidate of volatile organic solvent vapor sensors.