Peracetic acid (PAA) is increasingly used as an alternative disinfectant and its advanced oxidation processes (AOPs) could be useful for pollutant degradation. Co­(II) or Co­(III) can activate PAA to produce acetyloxyl (CH3C­(O)­O•) and acetylperoxyl (CH3C­(O)­OO•) radicals with little •OH radical formation, and Co­(II)/Co­(III) is cycled. For the first time, this study determined the reaction rates of PAA with Co­(II) (k PAA,Co(II) = 1.70 × 101 to 6.67 × 102 M–1·s–1) and Co­(III) (k PAA,Co(III) = 3.91 × 100 to 4.57 × 102 M–1·s–1) ions over the initial pH 3.0–8.2 and evaluated 30 different aromatic organic compounds for degradation by Co/PAA. In-depth investigation confirmed that CH3C­(O)­OO• is the key reactive species under Co/PAA for compound degradation. Assessing the structure–activity relationship between compounds’ molecular descriptors and pseudo-first-order degradation rate constants (k′PAA• in s–1) by Co/PAA showed the number of ring atoms, E HOMO, softness, and ionization potential to be the most influential, strongly suggesting the electron transfer mechanism from aromatic compounds to the acetylperoxyl radical. The radical production and compound degradation in Co/PAA are most efficient in the intermediate pH range and can be influenced by water matrix constituents of bicarbonate, phosphate, and humic acids. These results significantly improve the knowledge regarding the acetylperoxyl radical from PAA and will be useful for further development and applications of PAA-based AOPs.

Heterogeneous catalytic ozonation (HCO) processes have been widely studied for water purification. The reaction mechanisms of these processes are very complicated because of the simultaneous involvement of gas, solid, and liquid phases. Although typical reaction mechanisms have been established for HCO, some of them are only appropriate for specific systems. The divergence and deficiency in mechanisms hinders the development of novel active catalysts. This critical review compares the various existing mechanisms and categorizes the catalytic oxidation of HCO into radical-based oxidation and nonradical oxidation processes with an in-depth discussion. The catalytic active sites and adsorption behaviors of O 3 molecules on the catalyst surface are regarded as the key clues for further elucidating the O 3 activation processes, evolution of reactive oxygen species (ROS) or organic oxidation pathways. Moreover, the detection methods of the ROS produced in both types of oxidations and their roles in the destruction of organics are reviewed with discussion of some specific problems among them, including the scavengers selection, experiment results analysis as well as some questionable conclusions. Finally, alternative strategies for the systematic investigation of the HCO mechanism and the prospects for future studies are envisaged.

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Peracetic acid (PAA) is a sanitizer with increasing use in food, medical and water treatment industries. Amino acids are important components in targeted foods for PAA treatment and ubiquitous in natural waterbodies and wastewater effluents as the primary form of dissolved organic nitrogen. To better understand the possible reactions, this work investigated the reaction kinetics and transformation pathways of selected amino acids towards PAA. Experimental results demonstrated that most amino acids showed sluggish reactivity to PAA except cysteine (CYS), methionine (MET), and histidine (HIS). CYS showed the highest reactivity with a very rapid reaction rate. Reactions of MET and HIS with PAA followed second-order kinetics with rate constants of 4.6 ± 0.2, and 1.8 ± 0.1 M −1 ⋅s −1 at pH 7, respectively. The reactions were faster at pH 5 and 7 than at pH 9 due to PAA speciation. Low concentrations of H 2 O 2 coexistent with PAA contributed little to the oxidation of amino acids. The primary oxidation products of amino acids with PAA were [O] addition compounds on the reactive sites at thiol, thioether and imidazole groups. Theoretical calculations were applied to predict the reactivity and regioselectivity of PAA electrophilic attacks on amino acids and improved mechanistic understanding. As an oxidative disinfectant, the reaction of PAA with organics to form byproducts is inevitable; however, this study shows that PAA exhibits lower and more selective reactivity towards biomolecules such as amino acids than other common disinfectants, causing less concern of toxic disinfection byproducts. This attribute may allow greater stability and more targeted actions of PAA in various applications.

It is challenging to selectively upgrade phenolic compounds to aromatics because of much weaker adsorption of hydroxyl compared to that of phenyl upon Ni catalysts. With 10% Ni loading in theory, three Ni catalysts with different Ni nanoparticle sizes were prepared with the wet impregnation method on SiO 2 and Silicalite-1 and with the in situ encapsulation method (Silicalite-1). On the basis of the results, we proposed a general rule concerning temperaturedependent selectivity control on phenol hydroconversion over Ni catalysts. As well as benzene saturation in consecutive mode, hydrogenation of phenyl ring was more dramatically inhibited at elevated temperature via decreased adsorption of benzene rings than that of hydroxyl to selectively favor hydrogenolysis over hydrogenation in parallel mode. Among three Ni catalysts, Ni@Silicalite-1 with 3−5 nm Ni nanoparticle sizes encapsulated imposed the restricted adsorption conformation of phenol via end-up mode within channels of Silicalite-1 zeolite to further improve benzene selectivity. Because of the restriction of channels and smaller Ni nanoparticle sizes, better activity and stability were simultaneously achieved over Ni@Silicalite-1 catalyst, as well as superior benzene selectivity at higher temperature via thermodynamic hindrance on phenyl adsorption to facilitate benzene formation in kinetics rather than hydrogenation of phenyl without further saturation of benzene via hindrance on benzene adsorption.