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Kinetics of Photocatalyzed Reactions: Five Lessons Learned

Elucidation of kinetics of photocatalyzed chemical mechanisms occurring at interfaces (gas-solid, liquid-solid) has been challenging. We summarize here five lessons learned over five decades. 1. An assumed reaction network leads to a single kinetic model, but a common model, the Langmuir–Hinshelwood...

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Autor principal: Ollis, David F.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Frontiers Media S.A. 2018
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6127272/
https://www.ncbi.nlm.nih.gov/pubmed/30234100
http://dx.doi.org/10.3389/fchem.2018.00378
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author Ollis, David F.
author_facet Ollis, David F.
author_sort Ollis, David F.
collection PubMed
description Elucidation of kinetics of photocatalyzed chemical mechanisms occurring at interfaces (gas-solid, liquid-solid) has been challenging. We summarize here five lessons learned over five decades. 1. An assumed reaction network leads to a single kinetic model, but a common model, the Langmuir–Hinshelwood rate equation, r = k(cat) K C/ [1 +KC], arises from multiple mechanisms, hence models alone do not reveal unique mechanisms. 2. The Langmuir–Hinshelwood model parameter k(cat) represents the slow step at a catalyst surface, and in thermal catalysis, depends upon the reactant structure. However, early photocatalysis work with light chlorinated hydrocarbons in aqueous solutions showed a single k(cat) value, independent of reactant structure. 3. The dependence of the Langmuir-Hinshelwood parameters, k(cat) and K, upon intensity indicates that a pseudo-steady state approach is more fundamental than the presumed equilibrated adsorption of the LH model. 4. Dyes and phenols are commonly studied, and claimed as first order reactions, despite often exhibiting rate constants which diminish with increasing contaminant concentration. We show that such studies are the result of intrinsic zero order data plotted on a semilog graph, and involve zero order rate limitation by reactant saturation, electron transfer to O(2), oxygen mass transfer, or light supply. 5. The apparent kinetics for contaminant removal from photocatalytic self-cleaning surfaces depends upon multiple circumstances, including the geometry of reactant deposit, catalyst porosity, and reactant light absorption. A single decision table suffices to indicate the apparent reaction order, n, to assume when fitting photocatalytic kinetic data from self-cleaning surfaces to a power law rate form, rate = k C(n).
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spelling pubmed-61272722018-09-19 Kinetics of Photocatalyzed Reactions: Five Lessons Learned Ollis, David F. Front Chem Chemistry Elucidation of kinetics of photocatalyzed chemical mechanisms occurring at interfaces (gas-solid, liquid-solid) has been challenging. We summarize here five lessons learned over five decades. 1. An assumed reaction network leads to a single kinetic model, but a common model, the Langmuir–Hinshelwood rate equation, r = k(cat) K C/ [1 +KC], arises from multiple mechanisms, hence models alone do not reveal unique mechanisms. 2. The Langmuir–Hinshelwood model parameter k(cat) represents the slow step at a catalyst surface, and in thermal catalysis, depends upon the reactant structure. However, early photocatalysis work with light chlorinated hydrocarbons in aqueous solutions showed a single k(cat) value, independent of reactant structure. 3. The dependence of the Langmuir-Hinshelwood parameters, k(cat) and K, upon intensity indicates that a pseudo-steady state approach is more fundamental than the presumed equilibrated adsorption of the LH model. 4. Dyes and phenols are commonly studied, and claimed as first order reactions, despite often exhibiting rate constants which diminish with increasing contaminant concentration. We show that such studies are the result of intrinsic zero order data plotted on a semilog graph, and involve zero order rate limitation by reactant saturation, electron transfer to O(2), oxygen mass transfer, or light supply. 5. The apparent kinetics for contaminant removal from photocatalytic self-cleaning surfaces depends upon multiple circumstances, including the geometry of reactant deposit, catalyst porosity, and reactant light absorption. A single decision table suffices to indicate the apparent reaction order, n, to assume when fitting photocatalytic kinetic data from self-cleaning surfaces to a power law rate form, rate = k C(n). Frontiers Media S.A. 2018-08-31 /pmc/articles/PMC6127272/ /pubmed/30234100 http://dx.doi.org/10.3389/fchem.2018.00378 Text en Copyright © 2018 Ollis. http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
spellingShingle Chemistry
Ollis, David F.
Kinetics of Photocatalyzed Reactions: Five Lessons Learned
title Kinetics of Photocatalyzed Reactions: Five Lessons Learned
title_full Kinetics of Photocatalyzed Reactions: Five Lessons Learned
title_fullStr Kinetics of Photocatalyzed Reactions: Five Lessons Learned
title_full_unstemmed Kinetics of Photocatalyzed Reactions: Five Lessons Learned
title_short Kinetics of Photocatalyzed Reactions: Five Lessons Learned
title_sort kinetics of photocatalyzed reactions: five lessons learned
topic Chemistry
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6127272/
https://www.ncbi.nlm.nih.gov/pubmed/30234100
http://dx.doi.org/10.3389/fchem.2018.00378
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