On the Problem of Comparing Rates or Apparent Quantum Yields in Heterogeneous Photocatalysis

2010 ◽  
Vol 122 (50) ◽  
pp. 9782-9783 ◽  
Author(s):  
Horst Kisch
Keyword(s):  
Heterogeneous Photocatalysis ◽  
Quantum Yields

scholarly journals Photocatalytic Activity: Experimental Features to Report in Heterogeneous Photocatalysis

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1990 ◽  
Author(s):  
Md. Hoque ◽  
Marcelo Guzman
Keyword(s):  
Reaction Rate ◽  
Monochromatic Light ◽  
Heterogeneous Photocatalysis ◽  
Research Articles ◽  
Quantum Yields ◽  
Characterization Methods ◽  
Valuable Data ◽  
Photocatalytic Activities ◽  
Scientific Papers

Heterogeneous photocatalysis is a prominent area of research with major applications in solar energy conversion, air pollution mitigation, and removal of contaminants from water. A large number of scientific papers related to the photocatalysis field and its environmental applications are published in different journals specializing in materials and nanomaterials. However, many problems exist in the conception of papers by authors unfamiliar with standard characterization methods of photocatalysts as well as with the procedures needed to determine photocatalytic activities based on the determination of “apparent quantum efficiencies” within a wavelength interval or “apparent quantum yields” in the case of using monochromatic light. In this regard, an astonishing number of recent research articles include claims of highly efficient (photo)catalysts or similar terms about materials with superior or enhanced efficiency for a given reaction without proper experimental support. Consequently, the comparison of the efficiencies of photocatalysts may result as being meaningless, especially when reports are only based on expressions determining (1) a reaction rate per weight of catalyst or its surface area, (2) quantum efficiencies or quantum yields, and (3) turnover frequencies or turnover numbers. Herein, we summarize the standards needed for reporting valuable data in photocatalysis and highlight some common discrepancies found in the literature. This work should inform researchers interested in reporting photocatalysis projects about the correct procedures for collecting experimental data and properly characterizing the materials by providing examples and key supporting literature.

Terminology, relative photonic efficiencies and quantum yields in heterogeneous photocatalysis. Part II: Experimental determination of quantum yields

1999 ◽  
Vol 71 (2) ◽  
pp. 321-335 ◽  
Author(s):  
Angela Salinaro ◽  
Alexei V. Emeline ◽  
Jincai Zhao ◽  
Hisao Hidaka ◽  
Vladimir K. Ryabchuk ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Visible Region ◽  
Heterogeneous Photocatalysis ◽  
Quantum Yields ◽  
Yield Data ◽  
Normal Absorption ◽  
The One ◽  
Solid Liquid ◽  
Photonic Efficiency

In the preceding article [Serpone and Salinaro, Pure Appl. Chem., 71(2), 303-320 (1999)] we examined two principal features of heterogeneous photocatalysis that demanded scrutiny: (i) description of photocatalysis and (ii) description of process efficiencies. For the latter we proposed a protocol relative photonic efficiency which could subsequently be converted to quantum yields. A difficulty in expressing a quantum yield in heterogeneous photochemistry is the very nature of the system, either solid/liquid or solid/gas, which places severe restrictions on measurement of the photon flow absorbed by the light harvesting component, herein the photocatalyst TiO2, owing to non-negligible scattering by the particulates. It was imperative therefore to examine the extent of this problem. Extinction and absorption spectra of TiO2 dispersions were determined at low titania loadings by normal absorption spectroscopy and by an integrated sphere method, respectively, to assess the extent of light scattering. The method is compared to the one reported by Grela et al. [J. Phys. Chem., 100, 16940 (1996)] who used a polynomial extrapolation of the light scattered in the visible region into the UV region where TiO2 absorbs significantly. This extrapolation underestimates the scattering component present in the extinction spectra, and will no doubt affect the accuracy of the quantum yield data. Further, we report additional details in assessing limiting photonic efficiencies and quantum yields in heterogeneous photocatalysis.

Terminology, relative photonic efficiencies and quantum yields in heterogeneous photocatalysis. Part I: Suggested protocol

1999 ◽  
Vol 71 (2) ◽  
pp. 303-320 ◽  
Author(s):  
Nick Serpone ◽  
Angela Salinaro
Keyword(s):  
Quantum Yield ◽  
Heterogeneous Photocatalysis ◽  
Standard Test ◽  
Process Efficiency ◽  
Quantum Yields ◽  
Light Sources ◽  
Experimental Conditions ◽  
Simple Description ◽  
Broadband Radiation ◽  
Test Molecule

The term photocatalysis is one amongst several in a quagmire of labels used to describe a photon-driven catalytic process; a simple description of photocatalysis is proposed herein. Other labels such as quantum yield and/or quantum efficiency used in solid/liquid and solid/gas hetero-geneous photocatalytic systems to express process efficiencies have come to refer (incorrectly) to the ratio of the rate of a given event to the rate of incident photons impinging on the reactor walls and typically for broadband radiation. There is no accord on the expression for process efficiency. At times quantum yield is defined; often, it is ill-defined and more frequently how it was assessed is not described. This has led to much confusion in the literature, not only because of its different meaning from homogeneous photochemistry, but also because the description of photon efficiency precludes comparison of results from different laboratories owing to variations in light sources, reactor geometries, and overall experimental conditions. The previously reported quantum yields are in fact apparent quantum yields, i.e. lower limits of the true quantum yields. We address this issue and argue that any reference to quantum yields or quantum efficiencies in a heterogeneous medium is inadvisable until the number of photons absorbed by the light harvester (the photocatalyst) is known. A practical and simple alternative is proposed for general use and in particular for processes employing complex reactor geometries: the concept of relative photonic efficiency (xr) is useful to compare process efficiencies using a given photocatalyst material and a given standard test molecule. A quantum yield can subsequently be calculated since f= xrfphenol, where fphenol denotes the quantum yield for the photocatalyzed oxidative transformation of phenol used as the standard secondary actinometer and Degussa P-25 TiO2 as the standard photocatalyst. For heterogeneous suspensions (only), an additional method to determine quantum yields f is also proposed.

On the usage of turnover numbers and quantum yields in heterogeneous photocatalysis

1993 ◽  
Vol 73 (1) ◽  
pp. 11-16 ◽  
Author(s):  
Nick Serpone ◽  
Rita Terzian ◽  
Darren Lawless ◽  
Pierre Kennepohl ◽  
Geneviève Sauvé
Keyword(s):  
Heterogeneous Photocatalysis ◽  
Quantum Yields

Relative Photonic Efficiencies and Quantum Yields in Heterogeneous Photocatalysis

1997 ◽  
Vol 2 (1) ◽  
Author(s):  
Nick Serpone
Keyword(s):  
Quantum Yield ◽  
Heterogeneous Medium ◽  
Heterogeneous Photocatalysis ◽  
Process Efficiency ◽  
Quantum Yields ◽  
Light Sources ◽  
Apparent Quantum Yield ◽  
Experimental Conditions ◽  
Broadband Radiation ◽  
Solid Liquid

AbstractQuantum yield and quantum efficiency (QY) as used in heterogeneous photocatalysis (solid/liquid or solid/gas systems) have too often been used incorrectly to mean the ratio of the rate of a given event to the rate of incident photons impinging on the (external) reactor walls, typicallyfor broadband radiation. There is little accord on how to express process efficiency. At times QY is defined, often ill-defined, and more frequently workers fail to describe how it was assessed. This has led to much confusion in the literature, not only because of its different meaning from homogeneous photochemistry but also because this method of describing photon efficiency precludes a comparison of results from different laboratories owing to variations in light sources, reactor geometries, and overall experimental conditions. It cannot be overemphasized that the reported QY is an apparent quantum yield, indeed a lower limit of the true quantum yield. This position paper addresses this issue and argues that any reference to quantum yields or quantum efficiencies in a heterogeneous medium is ill-advised unless the actual number of photons absorbed by the light harvester (the photocatalyst) has been determined. The extent of light scattering in a solid/liquid heterogeneous medium is significant. A practical and simple alternative to compare process efficiencies was recently (Serpone et al., J Photochem. Photobiol. A.Chem., 94 (1996) 191-203) suggested by defining a relative photonic efficiency (ζ

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