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Defect-engineering of TiO2 can have a major impact on its photocatalytic properties for the degradation of persisting and non-biodegradable pollutants. Herein, a series of intrinsic and extrinsic defects are induced by post annealing of crystalline TiO2 under different reducing atmospheres. A detailed optoelectronic characterization sheds light on the key characteristics of the defect-engineered TiO2 nanopowders that are linked to the photocatalytic performance of the prepared photocatalysts. The photodegradation of a model dye, malachite green, as well as the inactivation of bacterial endospores of the Geobacillus stearothermophilus species were studied in the presence of the developed catalysts under visible light illumination. Our results indicate that a combination of certain defects is necessary for the improvement of the photocatalytic process for water purification and disinfection under visible light.

The simple amino acid l-alpha-alanine (ala) in polycrystalline form was among the first substances to be proposed and subsequently developed for Electron Paramagnetic Resonance (EPR)-based solid state radiation dosimetry. One disadvantage with ala is a relatively low sensitivity for doses below a few gray (Gy) which is a dose range of particular interest in medical, accident and environmental applications. A number of other compounds have been screened and some of these have shown a better sensitivity to radiation exposure than ala, in some cases up to a factor of 7-8. In particular ammonium tartrate (AT) and lithium formate (LiFo) have been taken into practical use. The present work was initially aimed to investigate the low-temperature radical products in AT, and the reactions leading to the product of dosimetric interest at room temperature. As a part of these studies, the previously characterized major room temperature radical product was re-investigated using single crystal electron magnetic resonance (EMR) techniques combined with periodic density functional theory (DFT) -type quantum chemical calculations. Surprisingly, this study showed that the molecular structure of the dominant radical at room temperature is somewhat different from that previously proposed. Furthermore, a second room temperature radical, previously not well characterized, was carefully investigated and three hyperfine coupling tensors were determined. These three tensors were sufficient to simulate all experimental observations for the second radical but not alone sufficient to permit an unambiguous molecular structure of the defect to be determined. It appears that the EPR resonance from this radical does not influence the dosimetric potential of AT.

The analysis of single crystal electron magnetic resonance (EMR) data has traditionally been performed using software in programming languages that are difficult to update, are not easily available, or are obsolete. By using a modern script-language with tools for the analysis and graphical display of the data, three MatLab (R) codes were prepared to compute the g, zero-field splitting (zfs) and hyperfine coupling (hfc) tensors from roadmaps obtained by EPR or ENDOR measurements in three crystal planes. Schonlands original method was used to compute the g- and hfc-tensors by a least-squares fit to the experimental data in each plane. The modifications required for the analysis of the zfs of radical pairs with S = 1 were accounted for. A non-linear fit was employed in a second code to obtain the hfc-tensor from EPR measurements, taking the nuclear Zeeman interaction of an I = 1/2 nucleus into account. A previously developed method to calculate the g- and hfc -tensors by a simultaneous linear fit to all data was used in the third code. The validity of the methods was examined by comparison with results obtained experimentally, and by roadmaps computed by exact diagonalization. The probable errors were estimated using functions for regression analysis available in MatLab. The software will be published at https://doi.org/10.17632/ps24sw95gz.1, Input and output examples presented in this work can also be downloaded from https://old.liu.se/simarc/downloads?l=en. (C) 2021 The Author(s). Published by Elsevier Inc. Funding Agencies|Linkoping University; Ghent UniversityGhent University; University of Oslo

In the present study, the degradation of methylene blue in non-irradiated TiO2-H2O2 suspensions was investigated. Five commercially available catalysts were characterized (BET surface area, zeta potential, hydrodynamic diameter) and their oxidative power was assessed by means of the degradation of methylene blue. A subsequent EPR study was made to verify and identify potential oxidative radicals. The results showed that all suspensions could degrade methylene blue significantly stronger compared to hydrogen peroxide alone. A broad variation between the different catalysts in their capability to adsorb dye molecules was found which was essential for decomposition of methylene blue in darkness. The highest degradation rate of all samples was found for Degussa P25 at neutral pH. EPR studies of this sample verified the presence of oxygen centred radicals namely hydroxyl ( OH) and superoxide radicals (O2− / OOH). Non-irradiated TiO2-H2O2 systems show great potential not only in dye removal applications but also in the field of disinfection where low concentrations of hydrogen peroxide are required and irradiation may not be feasible.

The amino acid L-α-alanine is the most commonly used material for solidstate electron paramagnetic resonance (EPR) dosimetry, due to the formation of highly stable radicals upon irradiation, with yields proportional to the radiation dose. Two major alanine radical components designated R1 and R2 have previously been uniquely characterized from EPR and electron−nuclear double resonance (ENDOR) studies as well as from quantum chemical calculations. There is also convincing experimental evidence of a third minor radical component R3, and a tentative radical structure has been suggested, even though no well-defined spectral signature has been observed experimentally. In the present study, temperature dependent EPR spectra of X-ray irradiated polycrystalline alanine were analyzed using five multivariate methods in further attempts to understand the composite nature of the alanine dosimeter EPR spectrum. Principal component analysis (PCA), maximum likelihood common factor analysis (MLCFA), independent component analysis (ICA), self-modeling mixture analysis (SMA), and multivariate curve resolution (MCR) were used to extract pure radical spectra and their fractional contributions from the experimental EPR spectra. All methods yielded spectral estimates resembling the established R1 spectrum. Furthermore, SMA and MCR consistently predicted both the established R2 spectrum and the shape of the R3 spectrum. The predicted shape of the R3 spectrum corresponded well with the proposed tentative spectrum derived from spectrum simulations. Thus, results from two independent multivariate data analysis techniques strongly support the previous evidence that three radicals are indeed present in irradiated alanine samples. This research was first published in the Journal of Physical Chemistry A. © 2017 American Chemical Society

Identification of radiation-induced radicals in relatively simple molecules is a prerequisite for the understanding of reaction pathways of the radiation chemistry of complex systems. Sucrose presents an additional practical interest as a versatile radiation dosimetric system. In this work, we present a periodic density functional theory study aimed to identify the fourth stable radical species in this carbohydrate. The proposed model is a fragment suspended in the lattice by hydrogen bonds with an unpaired electron at the original C5’ carbon of the fructose unit. It requires a double scission of the ring accompanied by substantial chemical and geometric reorganization.

Radical formation and trapping of radicals in X-irradiated crystals of rhamnose at 6 K were investigated using electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR) and ENDOR-induced EPR (EIE) techniques, complemented with periodic density functional theory (DFT) calculations. The two major radical species at 6 K were the O4-centered alkoxy radical and the intermolecularly trapped electron (IMTE), previously also detected by other authors. The current experimental results provided hyperfine coupling constants for these two species in good agreement with the previous data, thus providing a consistency check that improves their credibility. In addition to the O4-centered alkoxy radical and the IMTE, the C3-centered and C5-centered hydroxyalkyl radicals are the most prominent primary species at 6 K. The C3-centered radical appears in two slightly different conformations at 6 K, designated C and D. The C5-centered radical exhibits a coupling to a methyl group with tunneling rotation at 6 K, and analysis of one of the rotational substates (A) of the spin system yielded an understanding of the structure of this radical. Visible light bleaching of the IMTE at 6 K led to the C3-centered radical C, and thermal annealing above 6 K resulted in a conversion of the C to the D conformation. In addition, thermal annealing releases the IMTE, apparently resulting in the formation of the C2-centered radical. It is possible that the thermal decay of the IMTE also contributes to a small part of the C3-centered radical (D) population at 85 K. There are several other products trapped in rhamnose crystals directly after irradiation at 6 K, among which are resonance lines due to the C2 H-abstraction product. However, these other products are minority species and were not fully characterized in the current work.

The secondary radiation-induced radicals in lithium formate monohydrate were studied using electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and ENDOR-induced EPR (EIE) techniques complemented with periodic density functional theory (DFT) calculations. Single crystals of lithium formate monohydrate were X irradiated at 77 K and at room temperature. The main radicals present after irradiation at 77 K are the CO(2)(•-) radical (R1), the recently identified protonated electron-gain product, HCOOH(•-) (R2) (Krivokapić et al., Radiat Res 2014: 181:503-11), and a different geometrical conformation of this latter radical, a species that, up until now, has remained unidentified (R3). The successful quantum chemical modeling of R3 confirmed its structure and also provided a possible mechanism for its formation. After irradiation at 295 K, the crystals were investigated both shortly after irradiation and after storage for eight months at room temperature in ambient environments. After long-term storage the CO(2)(•-) radical had significantly decayed and the EPR spectra were dominated by two minority radicals. Both of these radicals are most likely formate-centered π-radicals, and based on the observed EPR parameters (g- and hyperfine coupling tensors) tentative candidates are the CO(•-) radical and the dimer formed by the CO(2)(•-) radical and a neighboring formate molecule yielding the radical (-)O(2)C·O·(•)CH·O(-).