scholarly journals Investigation of L-Tryptophan Electrochemical Oxidation with a Graphene-Modified Electrode

Biosensors ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 36
Author(s):  
Florina Pogacean ◽  
Codruta Varodi ◽  
Maria Coros ◽  
Irina Kacso ◽  
Teodora Radu ◽  
...  
Keyword(s):  
Structural Investigation ◽  
Oxidation Potential ◽  
Electrochemical Exfoliation ◽  
Considerable Decrease ◽  
X Ray ◽  
Lower Detection Limit ◽  
Graphene Sample ◽  
Lower Detection ◽  
Graphite Rods ◽  
Higher Sensitivity

A graphene sample (EGr) was prepared by electrochemical exfoliation of graphite rods in solution containing 0.05 M (NH4)2SO4 + 0.1 M H3BO3 + 0.05 M NaCl. The exfoliation was performed by applying a constant voltage (12 V) between the graphite rods, while the temperature was kept constant (18 °C) with a temperature-controlled cryostat. The structural investigation of the graphene sample, performed by X-ray powder diffraction (XRD), revealed that the sample consists of a mixture of few-layer (69%), multi-layer graphene (14%) and graphene oxide (17%). In addition, XPS analysis proved that the sample was triple-doped with heteroatoms such as nitrogen (1.7 at%), sulfur (2.5 at%), and boron (3 at%). The sample was deposited onto the surface of a clean, glassy carbon electrode (GC) and investigated for the non-enzymatic electrochemical detection of L-tryptophan (TRP). The electrocatalytic properties of the EGr/GC electrode led to a considerable decrease in the oxidation potential from +0.9 V (bare GC) to +0.72 V. In addition, the EGr/GC electrode has higher sensitivity (two times) and a lower detection limit (ten times) in comparison with the bare GC electrode.

Facet-dependent nonenzymatic glucose sensing properties of Cu2O cubes and octahedra

2016 ◽  
Vol 40 (8) ◽  
pp. 6573-6576 ◽  
Author(s):  
Linli Tang ◽  
Jian Lv ◽  
Chuncai Kong ◽  
Zhimao Yang ◽  
Jianhui Li
Keyword(s):  
Detection Limit ◽  
Modified Electrode ◽  
Glucose Sensing ◽  
Glucose Sensors ◽  
Linear Range ◽  
Sensing Properties ◽  
Lower Detection Limit ◽  
Lower Detection ◽  
Crystallographic Facets ◽  
Higher Sensitivity

Cu2O cubes and octahedra which have different crystallographic facets have been used for the nonenzymatic glucose sensors. A Cu2O octahedra modified electrode shows higher sensitivity, lower detection limit, and wider linear range than that of the cubes.

Quantitative Analysis of Fluorine and Oxygen by X-ray Fluorescence Spectrometry Using a Layered Structure Analyzer

1988 ◽  
Vol 32 ◽  
pp. 185-190
Author(s):  
Momoko Takemura ◽  
Hirobumi Ohmori
Keyword(s):  
Quantitative Analysis ◽  
Layered Structure ◽  
Wave Length ◽  
Light Element ◽  
Light Elements ◽  
X Ray ◽  
Lower Detection Limit ◽  
Lower Detection ◽  
Structure Analyzer ◽  
Synthetic Microstructures

Recently, layered structure analyzers (called LSA for short) or layered synthetic microstructures (called LSM) with d spacing of several tens of Å, have been developed for use as X-ray analyzing devices in wave-length dispersive spectrometers. The lower detection limit for light elements of atomic numbers lower than 13 , such as aluminum, sodium, fluorine, oxygen, carbon and so on, has been greatly improved.There have been several reports published regarding LSA (or LSM) applications to light element analyses.

Impurity Analysis on Si Wafer Using Monochro-Trex

1990 ◽  
Vol 34 ◽  
pp. 81-89 ◽  
Author(s):  
Kazuo Nishihagi ◽  
Noboru Yamashita ◽  
Kobukatsu Fujino ◽  
Kazuo Taniguchi ◽  
Shigero Ikeda
Keyword(s):  
Fluorescence Analysis ◽  
Analytical Sensitivity ◽  
Si Substrate ◽  
Surface Impurity ◽  
X Ray ◽  
Lower Detection Limit ◽  
Impurity Analysis ◽  
Lower Detection ◽  
Non Destructive ◽  
Si Wafer

Recently, semiconductors have been integrated and densified to much higher levels. Under this circumstance, control of surface impurity on the Si substrate has become more important. We have attempted to increase analytical sensitivity of the transition metals, which have the greatest influence on productivity.For the last few years, x-ray fluorescence analysis, using total reflection as a non-destructive and speedy method, has been applied for surface impurity analysis of Si wafers. However, this method is insufficiently sensitive (to the level required for surface impurity analysis) and the lower detection limit is still 1011 to 1012 atoms/cm2 order because the continuous x-ray excitation causes lots of scattering which makes the background higher.

Preparation and Investigation of Toluene-Sensing Properties of Polymer/Inorganic Composite and Multi-Layer Films

2012 ◽  
Vol 531-532 ◽  
pp. 570-573
Author(s):  
Jian Liao ◽  
Guang Zhong Xie ◽  
Ya Dong Jiang ◽  
Tao Zhu ◽  
Wei Zhi Li ◽  
...  
Keyword(s):  
Composite Film ◽  
Recovery Time ◽  
Room Temperature ◽  
Film Sensor ◽  
Sensing Properties ◽  
Multi Wall Carbon Nanotubes ◽  
Lower Detection Limit ◽  
Toluene Vapor ◽  
Lower Detection ◽  
Higher Sensitivity

In this paper, poly 4-vinylphenol (P4VP)/multi-wall carbon nanotubes (MWNTs) composite film, P4VP/ carbon black (CB) composite film and P4VP/MWNTs multi-layer sensitive films prepared using airbrush technology were deposited on interdigitated electrodes to detect tolunene vapor at room temperature. The surface of the composite film was observed under a scanning electron microscope (SEM). It was found that the resistance of the sensor increased after the exposure to toluene vapor and the increased magnitude of the changes had a good linearity with concentrations of toluene. Meanwhile, the P4VP/MWNTs composite film sensor also has a higher sensitivity than P4VP/CB composite film sensor. P4VP/MWNTs three-layer film sensor was fabricated as well. It was estimated that the response time and recovery time of P4VP/MWNTs three-layer films sensor were about 15 s and 20 s, respectively. The sensor responses of S=0.12% at 10mg/m3 toluene vapor for P4VP/MWNTs three-layer films. The results showed that the multi-layer films sensor exhibited a lower detection limit and better sensing properties compared with the sensors based composite film.

scholarly journals One-step Synthesis of Molybdenum Oxide/graphene Composites

2021 ◽  
Vol 37 (1) ◽  
Author(s):  
Minh Nhat Dang ◽  
Do Nhat Minh ◽  
Le Ngoc Trung ◽  
Nguyen Thanh Hai ◽  
Le Trong Lu ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
X Ray Diffraction ◽  
Electrochemical Exfoliation ◽  
New Approach ◽  
Dc Voltage ◽  
X Ray ◽  
Transmission Electron ◽  
Experimental Parameters ◽  
One Step ◽  
Graphite Rods

We herein introduce a new approach to synthesize MoO2/graphene composites via plasma-enhanced electrochemical exfoliation process. Our samples were prepared by electrifying graphite rods in (NH4)2Mo7O24 solution under a DC voltage of 70V. By controlling the experimental parameters such as the initial ratio of [Mo7O24]2– precursor, the current and time, we can modify the size and the size distribution of MoO2 nanoparticles on graphene sheets. The composites were characterized with Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray Diffraction and Raman Spectroscopy.  

Xanthine sensor development based on ZnO–CNT, ZnO–CB, ZnO–GO and ZnO nanoparticles: an electrochemical approach

2017 ◽  
Vol 41 (14) ◽  
pp. 6262-6271 ◽  
Author(s):  
Mohammed M. Rahman ◽  
Hadi M. Marwani ◽  
Faisal K. Algethami ◽  
Abdullah M. Asiri
Keyword(s):  
Zno Nanoparticles ◽  
Dynamic Range ◽  
Linear Dynamic Range ◽  
Wet Chemical Method ◽  
Linear Dynamic ◽  
Lower Detection Limit ◽  
Electrochemical Approach ◽  
Lower Detection ◽  
Wet Chemical ◽  
Higher Sensitivity

The wet-chemical method was used to prepare the various ZnO–CNT, ZnO–CB, ZnO–GO nanocomposites, and ZnO nanoparticles in higher pH medium, which were finally utilized with 5% nafion to produce a thin film of NCs/Nafion/GCE sensor that has a faster response towards selected xanthine with higher sensitivity, lower detection limit, and large linear dynamic range by electrochemical approach.

Development of a method for multielemental determination in water by EDXRF with radioisotopic source of 238Pu.

2019 ◽  
Vol 7 (2A) ◽  
Author(s):  
Camilo Fuentes Serrano ◽  
Juan Reinaldo Estevez Alvares ◽  
Alfredo Montero Alvarez ◽  
Ivan Pupo Gonzales ◽  
Zahily Herrero Fernandez ◽  
...  
Keyword(s):  
Thin Layer ◽  
Expanded Uncertainty ◽  
Considerable Decrease ◽  
X Ray ◽  
Precipitation Efficiency ◽  
Method Of Determination ◽  
Sensitivity Curves ◽  
Order Of Magnitude ◽  
Metrological Parameters

A method for determination of Cr, Fe, Co, Ni, Cu, Zn, Hg and Pb in waters by Energy Dispersive X Ray Fluorescence (EDXRF) was implemented, using a radioisotopic source of 238Pu. For previous concentration was employed a procedure including a coprecipitation step with ammonium pyrrolidinedithiocarbamate (APDC) as quelant agent, the separation of the phases by filtration, the measurement of filter by EDXRF and quantification by a thin layer absolute method. Sensitivity curves for K and L lines were obtained respectively. The sensitivity for most elements was greater by an order of magnitude in the case of measurement with a source of 238Pu instead of 109Cd, which means a considerable decrease in measurement times. The influence of the concentration in the precipitation efficiency was evaluated for each element. In all cases the recoveries are close to 100%, for this reason it can be affirmed that the method of determination of the studied elements is quantitative. Metrological parameters of the method such as trueness, precision, detection limit and uncertainty were calculated. A procedure to calculate the uncertainty of the method was elaborated; the most significant source of uncertainty for the thin layer EDXRF method is associated with the determination of instrumental sensitivities. The error associated with the determination, expressed as expanded uncertainty (in %), varied from 15.4% for low element concentrations (2.5-5 μg/L) to 5.4% for the higher concentration range (20-25 μg/L).

scholarly journals Photocatalytic Reduction of CO2 to Methanol Using a Copper-Zirconia Imidazolate Framework

Catalysts ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 346
Author(s):  
Sonam Goyal ◽  
Maizatul Shima Shaharun ◽  
Ganaga Suriya Jayabal ◽  
Chong Fai Kait ◽  
Bawadi Abdullah ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Catalyst Support ◽  
Oxidation Potential ◽  
Molar Ratio ◽  
X Ray Diffraction ◽  
X Ray ◽  
Molar Ratios ◽  
Optimum Parameters ◽  
Reduction Of Co2 ◽  
Enhanced Yield

A set of novel photocatalysts, i.e., copper-zirconia imidazolate (CuZrIm) frameworks, were synthesized using different zirconia molar ratios (i.e., 0.5, 1, and 1.5 mmol). The photoreduction process of CO2 to methanol in a continuous-flow stirred photoreactor at pressure and temperature of 1 atm and 25 °C, respectively, was studied. The physicochemical properties of the synthesized catalysts were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. The highest methanol activity of 818.59 µmol/L.g was recorded when the CuZrIm1 catalyst with Cu/Zr/Im/NH4OH molar ratio of 2:1:4:2 (mmol/mmol/mmol/M) was employed. The enhanced yield is attributed to the presence of Cu2+ oxidation state and the uniformly dispersed active metals. The response surface methodology (RSM) was used to optimize the reaction parameters. The predicted results agreed well with the experimental ones with the correlation coefficient (R2) of 0.99. The optimization results showed that the highest methanol activity of 1054 µmol/L.g was recorded when the optimum parameters were employed, i.e., stirring rate (540 rpm), intensity of light (275 W/m2) and photocatalyst loading (1.3 g/L). The redox potential value for the CuZrIm1 shows that the reduction potential is −1.70 V and the oxidation potential is +1.28 V for the photoreduction of CO2 to methanol. The current work has established the potential utilization of the imidazolate framework as catalyst support for the photoreduction of CO2 to methanol.

scholarly journals Molecular Dynamics Simulation of the Influence of RDX Internal Defects on Sensitivity

Crystals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 329
Author(s):  
Pengmin Yan ◽  
Xue Zhao ◽  
Jiuhou Rui ◽  
Juan Zhao ◽  
Min Xu ◽  
...  
Keyword(s):  
Energetic Materials ◽  
Low Cost ◽  
Relative Sensitivity ◽  
Dynamics Simulation ◽  
Safety Properties ◽  
Internal Defects ◽  
X Ray ◽  
X Ray Computed ◽  
Low Sensitivity ◽  
Higher Sensitivity

The internal defect is an important factor that could influence the energy and safety properties of energetic materials. RDX samples of two qualities were characterized and simulated to reveal the influence of different defects on sensitivity. The internal defects were characterized with optical microscopy, Raman spectroscopy and microfocus X-ray computed tomography technology. The results show that high-density RDX has fewer defects and a more uniform distribution. Based on the characterization results, defect models with different defect rates and distribution were established. The simulation results show that the models with fewer internal defects lead to shorter N-NO2 maximum bond lengths and greater cohesive energy density (CED). The maximum bond length and CED can be used as the criterion for the relative sensitivity of RDX, and therefore defect models doped with different solvents are established. The results show that the models doped with propylene carbonate and acetone lead to higher sensitivity. This may help to select the solvent to prepare low-sensitivity RDX. The results reported in this paper are aiming at the development of a more convenient and low-cost method for studying the influence of internal defects on the sensitivity of energetic materials.

Structural investigation of spherical hollow excipient Mannit Q by X-ray microtomography

2015 ◽  
Vol 495 (1) ◽  
pp. 140-143 ◽  
Author(s):  
Ryusuke Kajihara ◽  
Shuji Noguchi ◽  
Yasunori Iwao ◽  
Yuki Yasuda ◽  
Megumi Segawa ◽  
...  
Keyword(s):  
Structural Investigation ◽  
X Ray ◽  
Spherical Hollow
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