scholarly journals Defective Grey TiO2 with Minuscule Anatase–Rutile Heterophase Junctions for Hydroxyl Radicals Formation in a Visible Light-Triggered Photocatalysis

Catalysts ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1500
Author(s):  
Sanjay Gopal Ullattil ◽  
Janez Zavašnik ◽  
Ksenija Maver ◽  
Matjaž Finšgar ◽  
Nataša Novak Tušar ◽  
...  
Keyword(s):  
Hydroxyl Radical ◽  
Hydroxyl Radicals ◽  
High Surface ◽  
High Surface Area ◽  
Reaction Rates ◽  
Trace Quantity ◽  
Absorption Of Light ◽  
Photocatalytic Reactions ◽  
Tio2 Nanostructures ◽  
High Calcination Temperature

The novelty of this work was to prepare a series of defect-rich colored TiO2 nanostructures, using a peroxo solvothermal-assisted, high-pressure nitrogenation method. Among these solids, certain TiO2 materials possessed a trace quantity of anatase–rutile heterojunctions, which are beneficial in obtaining high reaction rates in photocatalytic reactions. In addition, high surface area (above 100 m2/g), even when utilizing a high calcination temperature (500 °C), and absorption of light at higher wavelengths, due to the grey color of the synthesized titania, were observed as an added advantage for photocatalytic hydroxyl radical formation. In this work, we adopted a photoluminescent probe method to monitor the temporal evolution of hydroxyl radicals. As a result, promising hydroxyl radical formations were observed for all the colored samples synthesized at 400 and 500 °C, irrespective of the duration of calcination.

scholarly journals A Potential–dependent Thiele Modulus to Quantify the Effectiveness of Porous Electrocatalysts

2021 ◽  
Author(s):  
Charles Wan ◽  
Katharine Greco ◽  
Amira Alazmi ◽  
Robert Darling ◽  
Yet- Ming Chiang ◽  
...  
Keyword(s):  
High Surface ◽  
High Surface Area ◽  
Reaction Rates ◽  
Effectiveness Factor ◽  
Mathematical Framework ◽  
Electrochemical Reactors ◽  
Thiele Modulus ◽  
Thermochemical Processes ◽  
Increase Productivity ◽  
Catalyst Utilization

<p>Electrochemical reactors often employ high surface area electrocatalysts to accelerate volumetric reaction rates and increase productivity. While electrocatalysts can alleviate kinetic overpotentials, diffusional resistances at the pore-scale often prevent full catalyst utilization. The effect of intraparticle diffusion on the overall reaction rate can be quantified through an effectiveness factor expression governed by the Thiele modulus parameter. This analytical approach is integral to the development of catalytic structures for thermochemical processes and can be extended to electrochemical processes provided the relationship between reaction kinetics and electrode overpotential is incorporated. Here, we derive a potential-dependent Thiele modulus to quantify the effectiveness factor for porous electrocatalytic structures. We apply this mathematical framework to spherical microparticles as a function of applied overpotential across catalyst properties and reactant characteristics. The relative effects of kinetics and mass transport are related to overall reaction rates, revealing markedly lower catalyst utilization at increasing overpotential. Subsequently, we generalize the analysis to alternative catalyst shapes and provide guidance on the design of porous catalytic materials for use in electrochemical reactors.</p>

scholarly journals Enzymatic microreactors in biocatalysis: history, features, and future perspectives

Biocatalysis ◽  
2016 ◽  
Vol 1 (1) ◽  
Author(s):  
Enzo Laurenti ◽  
Ardson dos Santos Vianna Jr.
Keyword(s):  
High Surface ◽  
High Surface Area ◽  
Volume Ratio ◽  
Immobilized Enzymes ◽  
Reaction Rates ◽  
Chemical Processes ◽  
Biochemical Processes ◽  
Enzymatic Microreactors ◽  
Materials Used ◽  
Broad Overview

AbstractMicrofluidic reaction devices are a very promising technology for chemical and biochemical processes. In microreactors, the micro dimensions, coupled with a high surface area/volume ratio, permit rapid heat exchange and mass transfer, resulting in higher reaction yields and reaction rates than in conventional reactors. Moreover, the lower energy consumption and easier separation of products permit these systems to have a lower environmental impact compared to macroscale, conventional reactors. Due to these benefits, the use of microreactors is increasing in the biocatalysis field, both by using enzymes in solution and their immobilized counterparts. Following an introduction to the most common applications of microreactors in chemical processes, a broad overview will be given of the latest applications in biocatalytic processes performed in microreactors with free or immobilized enzymes. In particular, attention is given to the nature of the materials used as a support for the enzymes and the strategies employed for their immobilization. Mathematical and engineering aspects concerning fluid dynamics in microreactors were also taken into account as fundamental factors for the optimization of these systems.

Radionuclide Decay Effects on Waste Glass Corrosion

1993 ◽  
Vol 333 ◽  
Author(s):  
D. J. Wronkiewicz
Keyword(s):  
Radiation Damage ◽  
High Surface ◽  
High Surface Area ◽  
Reaction Rates ◽  
Water Dissociation ◽  
Corrosion Rates ◽  
Atomic Displacements ◽  
Glass Corrosion ◽  
Solid Glass ◽  
Solution Volume

ABSTRACTThe release of glass components into solution, including radionuclides, may be influenced by the presence of radiolytically produced nitric acid, carboxylic acid, and transient water dissociation products such as ·OH and O2-. Under batch test conditions, glass corrosion has been shown to increase up to a maximum of three-to five-fold in irradiated tests relative to nonirradiated tests, while in other studies the presence of radiolytic products has actually decreased glass corrosion rates. Bicarbonate groundwaters will buffer against pH decreases and changes in corrosion rates. Under high surface area-to-solution volume (S/V) conditions, the bicarbonate buffering reservoir may be quickly overwhelmed by radiolytic acids that are concentrated in the thin films of water contacting the samples. Glass reaction rates have been shown to increase up to 10-to-15-fold due to radiation exposure under high S/V conditions.Radiation damage to solid glass materials results in bond damage and atomic displacements. This type of damage has been shown to increase the release rates of glass components up to four-fold during subsequent corrosion tests, although under actual disposal conditions, glass annealing processes may negate the solid radiation damage effects.

scholarly journals A Potential–dependent Thiele Modulus to Quantify the Effectiveness of Porous Electrocatalysts

2021 ◽  
Author(s):  
Charles Wan ◽  
Katharine Greco ◽  
Amira Alazmi ◽  
Robert Darling ◽  
Yet- Ming Chiang ◽  
...  
Keyword(s):  
High Surface ◽  
High Surface Area ◽  
Reaction Rates ◽  
Effectiveness Factor ◽  
Mathematical Framework ◽  
Electrochemical Reactors ◽  
Thiele Modulus ◽  
Thermochemical Processes ◽  
Increase Productivity ◽  
Catalyst Utilization

<p>Electrochemical reactors often employ high surface area electrocatalysts to accelerate volumetric reaction rates and increase productivity. While electrocatalysts can alleviate kinetic overpotentials, diffusional resistances at the pore-scale often prevent full catalyst utilization. The effect of intraparticle diffusion on the overall reaction rate can be quantified through an effectiveness factor expression governed by the Thiele modulus parameter. This analytical approach is integral to the development of catalytic structures for thermochemical processes and can be extended to electrochemical processes provided the relationship between reaction kinetics and electrode overpotential is incorporated. Here, we derive a potential-dependent Thiele modulus to quantify the effectiveness factor for porous electrocatalytic structures. We apply this mathematical framework to spherical microparticles as a function of applied overpotential across catalyst properties and reactant characteristics. The relative effects of kinetics and mass transport are related to overall reaction rates, revealing markedly lower catalyst utilization at increasing overpotential. Subsequently, we generalize the analysis to alternative catalyst shapes and provide guidance on the design of porous catalytic materials for use in electrochemical reactors.</p>

A facile approach for high surface area electrospun TiO2 nanostructures for photovoltaic and photocatalytic applications

2014 ◽  
Vol 43 (12) ◽  
pp. 4830 ◽  
Author(s):  
T. A. Arun ◽  
Asha Anish Madhavan ◽  
Daya K. Chacko ◽  
G. S. Anjusree ◽  
T. G. Deepak ◽  
...  
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Photocatalytic Applications ◽  
Tio2 Nanostructures

scholarly journals Evaluating the photocatalytic efficiency of the BiVO4/rGO photocatalyst

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Sukon Phanichphant ◽  
Auppatham Nakaruk ◽  
Kantapat Chansaenpak ◽  
Duangdao Channei
Keyword(s):  
Photocatalytic Activity ◽  
Hydroxyl Radical ◽  
Photocatalytic Degradation ◽  
Degradation Mechanism ◽  
High Surface ◽  
High Surface Area ◽  
Active Species ◽  
Precipitation Method ◽  
Integrating Sphere ◽  
Photocatalytic Efficiency

Abstract The present study reported the preparation of BiVO4 by co-precipitation method. The as-prepared BiVO4 photocatalyst were deposited on rGO sheets to form BiVO4/rGO via the hydrothermal method. The crystalline structure, morphological, optical properties, and surface properties of the synthesized pure BiVO4 compared to BiVO4/rGO composite were studied using X-ray diffraction (XRD), scanning electronmicroscopy (SEM), photoluminescence (PL) spectrophotoscopy, UV–vis spectrophotometer with an integrating sphere, and N2 adsorption-desorption isotherm based on BET theory. The photocatalytic activity of the prepared samples were evaluated by the degradation of MB dye in aqueous medium under visible light irradiation. The result showed that the BiVO4/rGO composite exhibited greater photocatalytic efficiency compared to pure BiVO4 with the photocatalytic degradation efficiency remains stable up to fifth cycle. The improved activity of the BiVO4/rGO composite might be attributed to the high surface area available to adsorb more MB molecules, and efficient charge separation of BiVO4 through π electron on the rGO structure. According to experimental results, the possible photocatalytic mechanism of the BiVO4/rGO composite were determined and the active species hydroxyl radical were reported. Based on photocatalytic activity inhibition in the presence of both h+ (VB) and O2•− (CB) scavengers over the BiVO4 photocatalyst, it can be proposed that the hydroxyl radical generated during the photocatalytic degradation mechanism is mainly responsible by the main active species of h+ and O2•− at VB and CB positions, respectively.

Fractal Reactor in Micro-Scale for Process Intensification

2018 ◽  
Vol 17 (1) ◽  
Author(s):  
Yue Lu ◽  
Gang Wang ◽  
Zhuangdian Liang ◽  
Jian Sun ◽  
Yu Gu ◽  
...  
Keyword(s):  
Fractal Theory ◽  
High Surface ◽  
High Surface Area ◽  
Process Intensification ◽  
Volume Ratio ◽  
Reactor Design ◽  
Precise Control ◽  
Photocatalytic Reactions ◽  
Micro Reactors ◽  
Micro Reactor

AbstractFractal theory, with its novel architectures inspired by nature, provides some novel concepts for smart reactor design. Here, researches on the applications of fractal theory to micro-reactor design are reviewed, in term of its high surface area-to-volume ratio, rapid and direct numbering-up, safety, and precise control. In addition, two designs of fractal micro-reactor are introduced as typical examples. First, the H-type fractal structure is considered in the context of the design of a double-plate micro-reactor, which is used for photocatalytic reactions of CO2. Second, applications of fractal Hilbert curves are considered in the design of channel structures for gas-liquid reactions. These two fractal micro-reactors can be fabricated via 3D printing technology and used for CO2conversion under mild conditions.

In Situ microscopy of the anodic etching of silicon

1995 ◽  
Vol 53 ◽  
pp. 232-233
Author(s):  
Frances M. Ross ◽  
Peter C. Searson
Keyword(s):  
Composite Structures ◽  
High Surface ◽  
High Surface Area ◽  
Chemical Properties ◽  
Selective Etching ◽  
Silicon On Insulator ◽  
Second Phase ◽  
Porous Layers ◽  
New Class ◽  
Porous Semiconductors

Porous semiconductors represent a relatively new class of materials formed by the selective etching of a single or polycrystalline substrate. Although porous silicon has received considerable attention due to its novel optical properties1, porous layers can be formed in other semiconductors such as GaAs and GaP. These materials are characterised by very high surface area and by electrical, optical and chemical properties that may differ considerably from bulk. The properties depend on the pore morphology, which can be controlled by adjusting the processing conditions and the dopant concentration. A number of novel structures can be fabricated using selective etching. For example, self-supporting membranes can be made by growing pores through a wafer, films with modulated pore structure can be fabricated by varying the applied potential during growth, composite structures can be prepared by depositing a second phase into the pores and silicon-on-insulator structures can be formed by oxidising a buried porous layer. In all these applications the ability to grow nanostructures controllably is critical.

Electron holography of catalysts

1995 ◽  
Vol 53 ◽  
pp. 416-417
Author(s):  
A. K. Datye ◽  
D. S. Kalakkad ◽  
L. F. Allard ◽  
E. Völkl
Keyword(s):  
Heterogeneous Catalysts ◽  
High Surface ◽  
High Surface Area ◽  
Atomic Scale ◽  
Nano Particles ◽  
Phase Image ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Phase Information ◽  
Particle Structure

The active phase in heterogeneous catalysts consists of nanometer-sized metal or oxide particles dispersed within the tortuous pore structure of a high surface area matrix. Such catalysts are extensively used for controlling emissions from automobile exhausts or in industrial processes such as the refining of crude oil to produce gasoline. The morphology of these nano-particles is of great interest to catalytic chemists since it affects the activity and selectivity for a class of reactions known as structure-sensitive reactions. In this paper, we describe some of the challenges in the study of heterogeneous catalysts, and provide examples of how electron holography can help in extracting details of particle structure and morphology on an atomic scale.Conventional high-resolution TEM imaging methods permit the image intensity to be recorded, but the phase information in the complex image wave is lost. However, it is the phase information which is sensitive at the atomic scale to changes in specimen thickness and composition, and thus analysis of the phase image can yield important information on morphological details at the nanometer level.

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