Cl• and Cl2 •– radicals contribute to the degradation of trace organic contaminants (TrOCs) such as pharmaceutical and personal care products and endocrine-disrupting chemicals. However, little is known about their reaction rate constants and mechanisms. In this study, the reaction rate constants of Cl• and Cl2 •– with 88 target compounds were determined using laser flash photolysis. Decay kinetics, product buildup kinetics, and competition kinetics were applied to track the changes in their transient spectra. Cl• exhibited quite high reactivity toward TrOCs with reaction rate constants ranging from 3.10 × 109 to 4.08 × 1010 M–1 s–1. Cl2 •– was less reactive but more selective, with reaction rate constants varying from <1 × 106 to 2.78 × 109 M–1 s–1. Three QSAR models were developed, which were capable of predicting the reaction rate constants of Cl2 •– with TrOCs bearing phenol, alkoxy benzene, and aniline groups. The detection of Cl•-adducts of many TrOCs suggested that Cl• addition was an important reaction mechanism. Single electron transfer (SET) predominated in reactions of Cl• with TrOCs bearing electron-rich moieties (e.g., sulfonamides), and their cation radicals were observed. Cl• might also abstract hydrogen atoms from phenolic compounds to generate phenoxyl radicals. Moreover, Cl• could react with TrOCs through multiple pathways since more than one transient intermediate was detected simultaneously. SET was the major reaction mechanism of Cl2 •– reactions with TrOCs bearing phenols, alkoxy benzenes, and anilines groups. Cl2 •– was found to play an important role in TrOC degradation, though it has been often neglected in previous studies. The results improve the understanding of halogen radical-involved chemistry in TrOC degradation.

Bromine radicals can pose great impacts on the photochemical transformation of trace organic contaminants in natural and engineered waters. However, the reaction kinetics and mechanisms involved are barely known. In this work, second-order reaction rate constants with Br• and Br2 •– were determined for 70 common trace organic contaminants and for 17 model compounds using laser flash photolysis and steady-state competition kinetics. The k Br• values ranged from <108 to (2.86 ± 0.31) × 1010 M–1 s–1 and the k Br2 •– values from <105 to (1.18 ± 0.09) × 109 M–1 s–1 at pH 7.0. Six quantitative structure–activity relationships were developed, which allow predicting additional unknown k Br• and k Br2 •– values. Single-electron transfer was shown to be a favored pathway for the reactions of Br• and Br2 •– with trace organic contaminants, and this was supported by transient spectroscopy and quantum chemical calculations. This study is essential in advancing the scientific understanding of halogen radical-involved chemistry in contaminant transformation.

This study investigated the role of bromide ions in the degradation of nine pharmaceuticals and personal care products (PPCPs) during the UV/chlorine treatment of simulated drinking water containing 2.5 mgC L natural organic matter (NOM). The kinetics of contributions from UV irradiation and from oxidation by free chlorine, free bromine, hydroxyl radical and reactive halogen species were evaluated. The observed loss rate constants of PPCPs in the presence of 10 μM bromide were 1.6-23 times of those observed in the absence of bromide (except for iopromide and ibuprofen). Bromide was shown to play multiple roles in PPCP degradation. It reacts rapidly with free chlorine to produce a trace amount of free bromine, which then contributes to up to 55% of the degradation of some PPCPs during 15 min of UV/chlorine treatment. Bromide was also shown to reduce the level of HO and to change the reactive chlorine species to bromine-containing species, which resulted in decreases in ibuprofen degradation and enhancement in carbamazepine and caffeine degradation, respectively. Reactive halogen species contributed to between 37 and 96% of the degradation of the studied PPCPs except ibuprofen in the presence of 10 μM bromide ion. The effect of bromide is non-negligible during the UV/chlorine treatment.

Nowadays the development of machine vision is oriented toward real-time applications such as autonomous driving. This demands a hardware solution with low latency, high energy efficiency, and good reliability. Here, we demonstrate a robust and self-powered in-sensor computing paradigm with a ferroelectric photosensor network (FE-PS-NET). The FE-PS-NET, constituted by ferroelectric photosensors (FE-PSs) with tunable photoresponsivities, is capable of simultaneously capturing and processing images. In each FE-PS, self-powered photovoltaic responses, modulated by remanent polarization of an epitaxial ferroelectric Pb(Zr0.2Ti0.8)O3 layer, show not only multiple nonvolatile levels but also sign reversibility, enabling the representation of a signed weight in a single device and hence reducing the hardware overhead for network construction. With multiple FE-PSs wired together, the FE-PS-NET acts on its own as an artificial neural network. In situ multiply-accumulate operation between an input image and a stored photoresponsivity matrix is demonstrated in the FE-PS-NET. Moreover, the FE-PS-NET is faultlessly competent for real-time image processing functionalities, including binary classification between ‘X’ and ‘T’ patterns with 100% accuracy and edge detection for an arrow sign with an F-Measure of 1 (under 365 nm ultraviolet light). This study highlights the great potential of ferroelectric photovoltaics as the hardware basis of real-time machine vision.

Dissolved organic matter (DOM) is a major scavenger of bromine radicals (e.g., Br• and Br2 •–) in sunlit surface waters and during oxidative processes used in water treatment. However, the literature lacks quantitative measurements of reaction rate constants between bromine radicals and DOM and lacks information on the extent to which these reactions form brominated organic byproducts. Based on transient kinetic analysis with different fractions and sources of DOM, we determined reaction rate constants for DOM with Br• ranging from <5.0 × 107 to (4.2 ± 1.3) × 108 MC –1 s–1, which are comparable with those of HO• but higher than those with Br2 •– (k = (9.0 ± 2.0) × 104 to (12.4 ± 2.1) × 105 MC –1 s–1). Br• and Br2 •– attack the aromatic and antioxidant moieties of DOM via the electron transfer mechanism, resulting in Br– release with minimal substitution of bromine into DOM. For example, the total organic bromine was less than 0.25 μM (as Br) at environmentally relevant bromine radicals’ exposures of ∼10–9 M·s. The results give robust evidence that the scavenging of bromine radicals by DOM is a crucial step to prevent inorganic bromine radical chemistry from producing free bromine (HOBr/OBr–) and subsequent brominated byproducts.