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Highlights • The validity of Weissler, Fricke and terephthalic acid dosimetry methods is reported. • Weissler and Fricke dosimetries provided comparable OH radical yields. • Terephthalic acid dosimetry provided very low OH radical yield. • Possible reasons and recommendations are discussed. • Opinion Paper may initiate further discussion among researchers working in sonochemistry., Acoustic cavitation and sonochemical reactions play a significant role in various applications of ultrasound. A number of dosimetry methods are in practice to quantify the amount of radicals generated by acoustic cavitation. In this study, hydroxyl radical (OH•) yields measured by Weissler, Fricke and terephthalic acid dosimetry methods have been compared to evaluate the validities of these methods using a 490 kHz high frequency sonochemical reactor. The OH• yields obtained after 5 min sonication at 490 kHz from Weissler and Fricke dosimetries were 200 µM and 289 µM, respectively. Whereas, the OH• yield was found to be very low (8 µM) when terephthalic acid dosimetry was used under similar experimental conditions. While the results agree with those reported by Iida et al. (Microchem. J., 80 (2005) 159), further mechanistic details and interfering reactions have been discussed in this study. For example, the amount of OH• determined by the Weissler and Fricke methods may have some uncertainty due to the formation of HO2• in the presence of oxygen. In order to account for the major discrepancy observed with the terephthalic acid dosimetry method, high performance liquid chromatography (HPLC) analysis was performed, where two additional products other than 2-hydroxy terephthalic acid were observed. Electrospray ionization mass spectrometry (ESI-MS) analysis showed the formation of 2,5-dihydroxyterephthalic acid as one of the by-products along with other unidentified by-products. Despite the formation of additional products consuming OH•, the reason for a very low OH• yield obtained by this dosimetry could not be justified, questioning the applicability of this method, which has been used to quantify OH• yields generated not only by acoustic cavitation, but also by other processes such as γ-radiolysis. The authors are hoping that this Opinion Paper may initiate further discussion among researchers working in sonochemistry area that could help resolve the uncertainties around using these dosimetry methods.

Dispersion of petite quantity (Mg1−xCexZryO3) of cerium dopant in the lattice of magnesium zirconate (MgZrO3) is an efficient strategy to stimulate solar light photocatalytic activity of the material and achieve superior charge carrier separation. In this research, we demonstrate the tailoring of MgZrO3 to become a solar light sensitive material for the degradation of methyl orange (MO) dye and hydrogen evolution from water. Cerium doped MgZrO3 nanocubes (Mg1−xCexZryO3NCs) showed 93% efficiency for the degradation of MO and was able to show a maximum hydrogen evolution rate of 13,318 µmol h−1 g−1. It was found that, concentration of cerium plays a key role in the overall performance of the photocatalyst. A systematic characterization by Brunauer–Emmett–Teller (BET), Scavenger experiments, Electron Spin Resonance Spectroscopy (ESR), Photoluminescence (PL) and photocurrent measurements of the Mg1−xCexZryO3 NCs showed that, it possesses high surface area, promotes transfer of photo-stimulated electrons and provides rich photo-active centers for the enhanced photocatalytic redox activity. Retention of structure and morphology even after rigorous cycling of the catalyst with respect to MO degradation and hydrogen evolution makes Mg1−xCexZryO3 NCs a robust photocatalytic material.