Leveraging chemical actinometry and optical radiometry to reduce uncertainty in photochemical research

Subtle aspects of illumination sources and their characterization methods can introduce significant uncertainty into the data gathered from light-activated experiments, limiting their reproducibility and technology transition. Degradation kinetics of methyl orange (MO) and carbamazepine (CM) under illumination with TiO₂ were used as a case study for investigating the role of incident photon flux on photocatalytic degradation rates. Valerophenone and ferrioxalate actinometry were paired with optical radiometry in three different illumination systems: xenon arc (XE), tungsten halogen (W-H), and UV fluorescent (UV-F). Degradation rate constants for MO and CM varied similarly among the three light systems as k W-H < kiv-F < kXE, implying the same relative photon flux emission by each light. However, the apparent relative photon flux emitted by the different lights varied depending on the light characterization method. This discrepancy is shown to be caused by the spectral distribution present in light emission profiles, as well as absorption behavior of chemical actinometers and optical sensors. Data and calculations for the determination of photon flux from chemical and calibrated optical light characterization is presented, allowing us to interpret photo-degradation rate constants as a function of incident photon flux. This approach enabled the derivation of a calibrated ‘rate-flux’ metric for evaluating and translating data from photocatalysis studies.

Photoconductivity kinetics of indium sulfofluoride thin films

Indium sulfofluoride is an amorphous wide-gap semiconductor exhibiting high sensitivity to UV radiation. This work reports on the kinetics of photoconductivity in indium sulfofluoride thin films along with their electrical and optical properties. The films were deposited by radio-frequency plasma-enhanced reactive thermal evaporation. The film characterization includes electrical, optical, and photoconductivity measurements. The films are highly transparent in the visible-infrared range due to an indirect bandgap of 2.8 eV. The spectral response measurements have revealed existence of the band tail states. The synthesized compound is highly resistive (∼200 MΩ-cm at 300 K) and exhibits extremely slow photocurrent relaxations. Photoconductivity kinetics was studied under various excitation conditions. A dependence of the photocurrent on the incident photon flux was also determined.

Photocatalytic Activity of TiO2 Thin Films: Kinetic and Efficiency Study

The aim of this work was to evaluate the photocatalytic activity of two distinct anatase thin films. Films were prepared following the sol-gel procedure from titanium (IV) isopropoxide (TF-1) and from commercial TiO2 P25 as a starting material (TF-2). The films were compared based on the salicylic acid (2-dihydroxybenzoic acid, 2-HBA) photocatalytic degradation in reactors of different geometry and under different irradiation conditions. Experiments were performed in (i) an annular photoreactors operated under turbulent flow (TAR1 and TAR2) and (ii) semi-annular reactor operated under laminar flow (LFR). The TF-1 and TF-2 were immobilized on the inner side of outer wall of TAR1 and TAR2 and on the bottom of LFR. Experimental study included sorption study and four consecutive photocatalytic runs (tirr= 8 h) using TF-1 and TF-2 in each reactor. Obtained results confirmed the stability and the similar photocatalytic activity of the both films. The 2,5-dihydroxybenzoic acid (2,5-DHBA) and 2,3-dihydroxybenzoic acid (2,3-DHBA) were identified as main 2-HBA degradation by-products. Kinetic models were developed accordingly. Incident photon flux was determined along the inner reactor wall in annular reactors and on the bottom of LFR, i. e. on the thin film surface (Itf, W m−2) using ESSDE radiation emission model. The irradiation factor, i. e. the product of absorption coefficient and incident photon flux at film surface (μItf(z))m was introduced into the kinetic models. Resulting reaction rate constants ki (min−1W−0.5 m1.5) were independent of reactor geometry, hydrodynamics, irradiation condition and the optical properties of thin films. Efficiencies of TF-1 and TF-2 in studied reactors were given on the basis of quantum yields (QY) for 2-HBA oxidation and overall mineralization toward CO2.

Chemical actinometry (IUPAC Technical Report)

This document updates the first version of the IUPAC technical report on “Chemical actinometers” published in Pure Appl. Chem. 61 ,187-210 (1989). Since then, some methods have been improved, procedures have been modified, and new substances have been proposed as chemical actinometers. An actinometer is a chemical system or a physical device by which the number of photons in a beam absorbed into the defined space of a chemical reactor can be determined integrally or per time. This compilation includes chemical actinometers for the gas, solid, microheterogeneous, and liquid phases, as well as for the use with pulsed lasers for the measurement of transient absorbances, including the quantum yield of phototransformation, as well as the literature for each of the actinometers. The actinometers listed are for the use in the wavelength range from the UV to the red region of the spectrum. A set of recommended standard procedures is also given. Advantages and disadvantages are discussed regarding the use of chemical actinometers vs. electronic devices for the measurement of the number of photons absorbed. Procedures for the absolute measurement of incident photon flux by means of photodiodes are also discussed.

Kinetics of Radiative Melting of Si

ABSTRACTDuring radiative melting, a silicon surface breaks up into coexisting solid and liquid regions with spacing dependent on incident flux, thermal parameters, and crystalline properties of the sample. The space-averaged reflectivity becomes a function of the incident photon flux, profoundly affecting the transfer of energy and the rate of melting.We explain time evolution of the molten surface morphology and present data relating depth of melting to the incident photon flux for bulk Si and Si with buried oxide. The data prove the existence of a steady state transition region in which meltingis only superficial and time-independent.