scholarly journals Wavelength-Dependent Solar N2 Fixation into Ammonia and Nitrate in Pure Water

Research ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Wenju Ren ◽  
Zongwei Mei ◽  
Shisheng Zheng ◽  
Shunning Li ◽  
Yuanmin Zhu ◽  
...  
Keyword(s):  
Oxygen Vacancies ◽  
Surface Defects ◽  
Environmental Concern ◽  
Pure Water ◽  
Molar Fraction ◽  
Underlying Mechanism ◽  
Equilibrium Potential ◽  
Simultaneous Formation ◽  
Promising Alternative ◽  
Simulated Solar Light

Solar-driven N2 fixation using a photocatalyst in water presents a promising alternative to the traditional Haber-Bosch process in terms of both energy efficiency and environmental concern. At present, the product of solar N2 fixation is either NH4+ or NO3-. Few reports described the simultaneous formation of ammonia (NH4+) and nitrate (NO3-) by a photocatalytic reaction and the related mechanism. In this work, we report a strategy to photocatalytically fix nitrogen through simultaneous reduction and oxidation to produce NH4+ and NO3- by W18O49 nanowires in pure water. The underlying mechanism of wavelength-dependent N2 fixation in the presence of surface defects is proposed, with an emphasis on oxygen vacancies that not only facilitate the activation and dissociation of N2 but also improve light absorption and the separation of the photoexcited carriers. Both NH4+ and NO3- can be produced in pure water under a simulated solar light and even till the wavelength reaching 730 nm. The maximum quantum efficiency reaches 9% at 365 nm. Theoretical calculation reveals that disproportionation reaction of the N2 molecule is more energetically favorable than either reduction or oxidation alone. It is worth noting that the molar fraction of NH4+ in the total product (NH4+ plus NO3-) shows an inverted volcano shape from 365 nm to 730 nm. The increased fraction of NO3- from 365 nm to around 427 nm results from the competition between the oxygen evolution reaction (OER) at W sites without oxygen vacancies and the N2 oxidation reaction (NOR) at oxygen vacancy sites, which is driven by the intrinsically delocalized photoexcited holes. From 427 nm to 730 nm, NOR is energetically restricted due to its higher equilibrium potential than that of OER, accompanied by the localized photoexcited holes on oxygen vacancies. Full disproportionation of N2 is achieved within a range of wavelength from ~427 nm to ~515 nm. This work presents a rational strategy to efficiently utilize the photoexcited carriers and optimize the photocatalyst for practical nitrogen fixation.

Experimental and Numerical Study of Methanol-Water Mixture Single-Phase Heat Transfer in a Micro-Channel Heat Sink

2012 ◽  
Author(s):  
Chun K. Kwok ◽  
Matthew M. Asada ◽  
Jonathan R. Mita ◽  
Weilin Qu
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Sink ◽  
Single Phase ◽  
Numerical Study ◽  
Pure Water ◽  
Molar Fraction ◽  
Water Mixture ◽  
Micro Channel ◽  
Numerical Predictions

This paper presents an experimental study of single-phase heat transfer characteristics of binary methanol-water mixtures in a micro-channel heat sink containing an array of 22 microchannels with 240μm × 630μm cross-section. Pure water, pure methanol, and five methanol-water mixtures with methanol molar fraction of 16%, 36%, 50%, 63% and 82% were tested. Key parametric trends were identified and discussed. The experimental study was complemented by a three-dimensional numerical simulation. Numerical predictions and experimental data are in good agreement with a mean absolute error (MAE) of 0.87%.

EFFECT OF NANO PARTICLE SIZES ON HIGH PRESSURE RAMAN SCATTERING IN NANOCRYSTALLINE CERIUM DIOXIDE

2011 ◽  
Vol 25 (31) ◽  
pp. 2399-2405 ◽  
Author(s):  
P. JIMLIM ◽  
T. BOVORNRATANARAKS ◽  
W. CHAIMAYO ◽  
S. PRATONTEP
Keyword(s):  
Particle Size ◽  
High Pressure ◽  
Oxygen Vacancies ◽  
Molar Fraction ◽  
Raman Frequency ◽  
Particle Sizes ◽  
Nano Particle ◽  
First Order ◽  
Nanocrystalline Cerium Dioxide ◽  
Diamond Anvil

Nanocrystalline CeO 2 with different particle sizes has been studied under high pressure using Raman spectroscopy techniques and diamond anvil cell at room temperature. The pressure shift of the first-order Raman frequency for each particle sizes was measured. Linear dependence of the first order Raman frequency on pressure for each particle sizes has been observed. We found that the first order Raman frequency decreases with the decreasing particle sizes under ambient condition and the lattice constant increases with the decreasing particle size. The increasing molar fraction of oxygen vacancies with the decreasing particle size is responsible for the lattice expansion.

scholarly journals Marrying Medicine and Materials: Artemisinin (Qinghaosu) Particle is Soft Enough for Scratching Hard SiC Wafer in Water

2016 ◽  
Author(s):  
Yu-rong Zhu ◽  
Dan Zhang ◽  
Yang Gan ◽  
Fei-hu Zhang
Keyword(s):  
Pure Water ◽  
High Hardness ◽  
Underlying Mechanism ◽  
Molecular Solids ◽  
High Brightness ◽  
Force Microscopy ◽  
Atomic Force ◽  
Chemical Inertness ◽  
Sic Wafer ◽  
First Time

<p>Silicon carbide (SiC) single crystals, along with sapphire and silicon, are one of most important substrates for high-brightness LED fabrications. Owing to extremely high hardness (Mohs&rsquo; scale of 9.5) and chemical inertness, the polishing rate of SiC with conventional chemical mechanical polishing (CMP) methods is not high, and surface scratches are also inevitable because of using slurry containing hard abrasives such as silica particles. Here artemisinin (Qinghaosu) crystals, very soft molecular solids, were found, for the first time to the best of our knowledge, to effectively polish SiC wafers even in pure water as demonstrated by proof-of-concept scratching experiments using atomic force microscopy (AFM). The underlying mechanism is attributed to activated oxidation of SiC by mechanically released reactive &middot;OH free radicals from the endoperoxide bridges. The preliminary results reported here have important implications for developing novel alternative green and scratch-free polishing methods for hard-brittle substrates including SiC and others.</p>

scholarly journals Precise Control of Surface Oxygen Vacancies in ZnO Nanoparticles for Extremely High Acetone Sensing Response

2021 ◽  
Author(s):  
Jihyun Lee ◽  
Youngmoon Choi ◽  
Byoung Joon Park ◽  
Jeong Woo Han ◽  
Hyun-Sook Lee ◽  
...  
Keyword(s):  
Zno Nanoparticles ◽  
Oxygen Vacancies ◽  
Surface Defects ◽  
High Sensitivity ◽  
Fast Response ◽  
Oxide Semiconductor ◽  
Surface Oxygen ◽  
Zno Nps ◽  
Precise Control ◽  
Optimal Surface

Abstract ZnO has been studied intensely for chemical sensors due to its high sensitivity and fast response. Here, we present a simple approach to precisely control oxygen vacancy contents to provide significantly enhanced acetone sensing performance of commercial ZnO nanopowders. A combination of H2O2 treatment and thermal annealing produces optimal surface defects with oxygen vacancies on the ZnO nanoparticles (NPs). The highest response of ~27,562 was achieved for 10 ppm acetone in 0.125 M H2O2 treated/annealed ZnO NPs at the optimal working temperature of 400 ℃, which is significantly higher than that of reported so far in various acetone sensors based on metal-oxide-semiconductor (MOS). Furthermore, first-principles calculations indicate that pre-adsorbed O formed on the surface of H2O2-treated ZnO NPs can provide a favorable adsorption energy, especially for acetone detection, due to strong bidentate bonding between carbonyl C atom of acetone molecules and pre-adsorbed O on the ZnO surface. Our study demonstrates that controlling surface oxygen vacancies by H2O2 treatment and re-annealing at optimal temperature is an effective method to improve the sensing properties of commercial MOS materials.

Electrocatalytic Fixation of N2 into NO3-: Electron Transfer between Oxygen Vacancies and Loaded Au in Nb2O5-x Nanobelts to Promote Ambient Nitrogen Oxidation

2021 ◽  
Author(s):  
Yintong Zhang ◽  
Feng Du ◽  
Ruyi Wang ◽  
Xintong Ling ◽  
Xiaoyong Wang ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Oxidation Reaction ◽  
Oxygen Vacancies ◽  
Promising Alternative ◽  
Industrial Synthesis ◽  
Nitrogen Oxidation

The electrocatalytic nitrogen oxidation reaction (NOR) is a promising alternative to the industrial synthesis of nitrate. However, with the enhancement of the NOR activity by modification methods, the competitive oxygen...

Size Dependent Dielectric Properties of TiO2 Nanoparticles

2020 ◽  
Vol 833 ◽  
pp. 147-151
Author(s):  
K.K. Anjali ◽  
A. Uma Maheswari ◽  
Manickam Sivakumar
Keyword(s):  
Dielectric Properties ◽  
Oxygen Vacancies ◽  
Surface Defects ◽  
Peak Shift ◽  
Chemical Precipitation ◽  
Space Charge Polarization ◽  
Precipitation Method ◽  
Bandgap Energy ◽  
Size Dependent ◽  
Mobility Of Charge Carriers

In this study, influence of nanoparticles size on optical and dielectric properties of TiO2 nanoparticles is investigated through thermal treatment of hydrous amorphous titania synthesized by chemical precipitation method at temperatures 300 °C and 600 °C. The average sizes of nanoparticles estimated respectively are ~ 8 nm and ~ 22 nm. Although the optical bandgap energy of both samples remains the same the Eg Raman mode observed at 144 cm-1 for bulk TiO2 is shifted to 150 cm-1 only for nanoparticles calcined at 300 °C. The shift is ascribed to the size as well as higher density of surface defects. Moreover, the presence of surface defects like oxygen vacancies which provide effective sites for catalytic reaction are confirmed by EPR and photoluminescence studies. The oxygen vacancies enhances space charge polarization and consequently results in higher dielectric constant. In addition, the peak shift of loss tangent which determines the mobility of charge carriers is found to be size dependent. Hence calcination temperature has significant influence on defect levels which in turn determine the optical and dielectric properties of TiO2 nanoparticles.

scholarly journals A New Metaheuristic Inspired by the Vapour-Liquid Equilibrium for Continuous Optimization

2018 ◽  
Vol 8 (11) ◽  
pp. 2080 ◽  
Author(s):  
Enrique Cortés-Toro ◽  
Broderick Crawford ◽  
Juan Gómez-Pulido ◽  
Ricardo Soto ◽  
José Lanza-Gutiérrez
Keyword(s):  
Equilibrium State ◽  
Optimization Problem ◽  
Optimization Problems ◽  
Molar Fraction ◽  
Chemical System ◽  
Decision Variable ◽  
Liquid Equilibrium ◽  
Acceptance Probability ◽  
Promising Alternative ◽  
Highly Nonlinear

In this article, a novel optimization metaheuristic based on the vapour-liquid equilibrium is described to solve highly nonlinear optimization problems in continuous domains. During the search for the optimum, the procedure truly simulates the vapour-liquid equilibrium state of multiple binary chemical systems. Each decision variable of the optimization problem behaves as the molar fraction of the lightest component of a binary chemical system. The equilibrium state of each system is modified several times, independently and gradually, in two opposite directions and at different rates. The best thermodynamic conditions of equilibrium for each system are searched and evaluated to identify the following step towards the solution of the optimization problem. While the search is carried out, the algorithm randomly accepts inadequate solutions. This process is done in a controlled way by setting a minimum acceptance probability to restart the exploration in other areas to prevent becoming trapped in local optimal solutions. Moreover, the range of each decision variable is reduced autonomously during the search. The algorithm reaches competitive results with those obtained by other stochastic algorithms when testing several benchmark functions, which allows us to conclude that our metaheuristic is a promising alternative in the optimization field.

scholarly journals Rapid evaluation of oxygen vacancies-enhanced photogeneration of the superoxide radical in nano-TiO2 suspensions

RSC Advances ◽  
2020 ◽  
Vol 10 (49) ◽  
pp. 29082-29089
Author(s):  
Wanchao Yu ◽  
Fengjie Chen ◽  
Yarui Wang ◽  
Lixia Zhao
Keyword(s):  
Reactive Oxygen Species ◽  
Photocatalytic Degradation ◽  
Oxygen Vacancies ◽  
Superoxide Radical ◽  
Surface Defects ◽  
Reactive Oxygen ◽  
Rapid Evaluation ◽  
Oxygen Species ◽  
Nano Tio2 ◽  
Degradation Of Pollutants

Reactive oxygen species (ROS) play an important role in the photocatalytic degradation of pollutants and are closely related to the surface defects of a semiconductor.

MOLECULAR DYNAMICS SIMULATION ON THE STRUCTURE AND DYNAMICS OF WATER IN THE 1-BUTYL-3-METHYLIMIDAZOLIUM TETRAFLUOROBORATE/WATER MIXTURE

2010 ◽  
Vol 09 (03) ◽  
pp. 573-584 ◽  
Author(s):  
GUOCAI TIAN ◽  
JIAN LI
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Pure Water ◽  
Molar Fraction ◽  
Blue Shift ◽  
Dynamics Simulation ◽  
Water Molecules ◽  
Water Mixture ◽  
Structure And Dynamics ◽  
Hydrogen Bond Interactions

The micro-structure, and IR spectrum of water molecules in 1-butyl-3-methylimi- dazolium tetrafluoroborate( [Bmim]BF4 )/water mixture with different concentrations (x1 = 25.0%, 50.0%, 75.0%, and 90.0%) were studied with molecular dynamics simulation at room temperature. It was shown that water molecules tend to be isolated from each other in mixtures with more ions than water molecules in pure water. With the increase of the molar fraction of water in the mixture, the rotation bands and the bending bands of water display red shift from 566.2 to 651.4 cm-1 and from 1638.4 to 1683.2 cm-1 respectively, whereas the O–H stretch bands show blue shift from 3519.8 to 3452 cm-1, which agree well with the experimental results. This suggests that the molecules are hindered and their motions are difficult and slow, due to the hydrogen-bond interactions and the inharmonic interactions between the inter- or intra-molecular modes of water molecules.

Understanding Metal Oxide Surfaces at the Atomic Scale: STM Investigations of Bulk-defect Dependent Surface Processes

2000 ◽  
Vol 654 ◽  
Author(s):  
Ulrike Diebold
Keyword(s):  
Oxygen Vacancies ◽  
Science Studies ◽  
Elevated Temperatures ◽  
Surface Defects ◽  
Surface Reactivity ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Oxide Surface ◽  
Tunneling Microscopy ◽  
Adsorption Sites

AbstractSurface defects are important in oxide surface chemistry, because they change not only the surface geometric structure, but also affect the local electronic structure. Scanning Tunneling Microscopy (STM) images with atomic-scale resolution, in combination with area-averaging surface spectroscopies, is an ideal tool to study local surface defects and their relationship to surface reactivity. We report STM results onTiO2(110) surfaces which show the surprising influence of bulk defects on surface properties. Thereduced crystals used in this and other surface science studies contain Ti interstitials and oxygen vacancies. Re-oxidation at elevated temperatures results in the growth of additional TiO2 layers with Ti coming from the bulk of the crystal and O from the gas phase. This often result in partially incomplete surface structures with many undercoordinated atoms. The esorption behavior of elemental S, dosed at room temperature, depends on the reduction state of the sample. This is explained by a mechanism where desorption froma weaklybound precursor state competes with the availability of new adsorption sites in the form of oxygen vacancies which migrate from the bulk to the surface.

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