Application Limits of the Ferrioxalate Actinometer**

Abstract

Evaluating the efficiency of newly designed photoreactors is crucial for systematic development and optimization of photochemical processes. A suitable tool is actinometry, prominently represented by the most widely studied and applied ferrioxalate system. However, such measurements show reproducibility problems in the data consistency. This study scrutinizes these issues and approaches an experimental elucidation. An application limit for the ferrioxalate actinometer under intense irradiation was identified and experimentally validated. A drop of the quantum yield at high incident photon fluxes, generating high local concentrations of carboxyl radicals, leads to systematically wrong measurements. For reliable measurements with the ferrioxalate actinometry, a continuous operation mode or extensive mixing should be ensured.

Comparative Evaluation of Light‐Driven Catalysis: A Framework for Standardized Reporting of Data**

“…[76] Note that actinometry is time-consuming, experimentally tedious, and has to be performed for each individual reaction vessel and experimental setup. [77][78][79][80] As a practical alternative to improve evaluation and reproducibility, we recommend the following minimum information to be reported: the geometric arrangement and relative positioning of light source and photoreactor, as well as the emission characteristics of the light source, and the overall reactor design and the reactor materials. [81,82] The use of well-characterized or standardized reactor setups represents another approach to ensure reproducibility.…”

“…The absorbed photon flux forms a basis for photonic efficiency determinations, and therefore requires quantitative determination (see below). However, determining photon fluxes is error prone and requires careful experimentation [77, 78, 88] . This can be addressed by establishing a thorough understanding of the radiation field around a photoreactor by multidimensional radiometric measurements combined with numerical methods; e.g., ray tracing [89] …”

Making Photocatalysis Comparable Using a Modular and Characterized Open‐Source Photoreactor**

“…Chemical actinometry was performed using the ferrioxalate actinometer based on the method of Hatchard and Parker and following the procedure presented by Wriedt et al [28,46,47] Actinometric experiments were performed in 4 mL GC vials under constant stirring. The vials were each filled with 3 mL of a 0.016 M K 3 Fe(C 2 O 4 ) 3 solution in 0.05 M H 2 SO 4 .…”

“…Raw data of the characterization can be found on Zenodo https://doi.org/10.5281/10.5281/ 10.5281/zenodo.5614942 and evaluated with the tools published on GitHub. [32] Experimental Section Actinometry Chemical actinometry was performed using the ferrioxalate actinometer based on the method of Hatchard and Parker and following the procedure of Wriedt et al [27,46,47] Actinometric experiments were performed in 4 mL GC vials under constant stirring. The vials were each filled with 3 mL of a 0.016 M K3Fe(C2O4)3 solution in 0.05 M H2SO4.…”

Vergleichende Evaluierung lichtgetriebener Katalyse: Ein Rahmenkonzept für das standardisierte Berichten von Daten**

“…Die Bestimmung des Photonenstromes ist jedoch fehleranfällig und erfordert sorgfältige Experimente. [77,78,88] Dies kann durch ein gründliches Verständnis des Strahlungsfeldes um einen Photoreaktor durch mehrdimensionale radiometrische Messungen in Kombination mit numerischen Methoden, z. B. Raytracing, erreicht werden.…”