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Abstract The enhanced compositional flexibility to incorporate multiple-principal cations in high entropy oxides (HEOs) offers the opportunity to expand boundaries for accessible compositions and unconventional properties in oxides. Attractive functionalities have been reported in some bulk HEOs, which are attributed to the long-range compositional homogeneity, lattice distortion, and local chemical bonding characteristics in materials. However, the intricate details of local composition fluctuation, metal-oxygen bond distortion and covalency are difficult to visualize experimentally, especially on the atomic scale. Here, we study the atomic structure-chemical bonding-property correlations in a series of perovskite-HEOs utilizing the recently developed four-dimensional scanning transmission electron microscopy techniques which enables to determine the structure, chemical bonding, electric field, and charge density on the atomic scale. The existence of compositional fluctuations along with significant composition-dependent distortion of metal-oxygen bonds is observed. Consequently, distinct variations of metal-oxygen bonding covalency are shown by the real-space charge-density distribution maps with sub-ångström resolution. The observed atomic features not only provide a realistic picture of the local physico-chemistry of chemically complex HEOs but can also be directly correlated to their distinctive magneto-electronic properties. 

Peracetic acid (PAA) is being considered as a disinfectant in membrane-based wastewater reuse systems, but its compatibility with polyamide membranes has not been thoroughly investigated. In this work, we showed that PAA induced much less change in the performance and material characteristics of NF90 membranes than the traditional disinfectant free chlorine (NaOCl). The change in membrane water flux and the rejection of salt and neutral organic compounds after PAA exposure (1–180 g h L −1 ) is significantly less than that resulting from NaOCl exposure at levels as low as 1 g h L −1 . The presence of two wastewater constituents, chloride or Fe( ii ), did not significantly impact membrane performance upon exposure to PAA. Surface characterization showed that oxygen was incorporated into polyamide by PAA, some of which was attributed to the formation of carboxylic acid groups. Experiments using a model aromatic amide, benzanilide, indicated an unexpected role of PAA in protecting the membrane from radicals formed by Fe( ii ) and the H 2 O 2 present in commercial PAA formulations. Furthermore, product identification suggests that both amide bond breakage and ring oxidation are possible reaction mechanisms for PAA. Our findings support that PAA is a viable disinfectant candidate for wastewater reuse and warrants further evaluation. 

Pesticides are commonly applied on foliage, forming dry deposits on the leaf cuticular wax. However, their photochemical transformation in this lipophilic environment is much less understood compared with that in surface water. In this work, sunlight photolysis of six chlorinated phenoxyacetic acid herbicides ( i.e. , 2,4-D and structural analogues) was evaluated in four organic solvents, on quartz, and on paraffin wax. In solvents of low polarity ( i.e. , n -heptane and 2-propanol), direct photolysis of 2,4-D herbicides was enhanced due to the relatively high quantum yields in these solvents. Photolysis on paraffin wax was slower than photolysis on quartz by a factor of 3–9, but was comparable with that in solvents of low polarity. With environmentally relevant irradiation and surface loading, the half-lives of 2,4-D herbicides on paraffin wax were 27–159 h, which are within the same range reported for biodegradation, the dominant dissipation pathway in the current 2,4-D fate model. Product analyses showed that photoreductive dechlorination is the dominant pathway in organic solvents, accounting for 68–100% of parent compound decay. On quartz and paraffin wax surfaces, however, photoreductive dechlorination products accounted for <60% of parent compound decay. Combining kinetic modeling and product analyses, it was shown that neither could the two additional putative pathways (photosubstitution of chlorine by hydroxyl group and cleavage of the ether bond) fully account for the total phototransformation on surfaces. These results suggest that rapid photolysis on surfaces can be attributed to unique pathways that are absent in the organic solvent phase.