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1. Rapid Disinfection by Peracetic Acid Combined with UV Irradiation

   https://doi.org/https://doi.org/10.1021/acs.estlett.8b00249  

   Sun, P.; Zhang, T.; Mejia-Tickner, B.; Zhang, R.; Cai, M.; Huang, C.-H. (January 2018, Environmental science & technology letters)

   This study proposes a novel disinfection process by sequential application of peracetic acid (PAA) and ultra-violet light (UV), on the basis of elucidation of disinfection mechanisms under UV/PAA. Results show that hydroxyl radicals, generated by UV-activated PAA, contribute to the enhanced inactivation of Escherichia coli under UV/PAA compared to PAA alone or UV alone. Furthermore, the location of hydroxyl radical generation is a critical factor. Unlike UV/H2O2, which generates hydroxyl radicals mainly in the bulk solution, the hydroxyl radicals under UV/PAA are produced close to or inside E. coli cells, due to PAA diffusion. Therefore, hydroxyl radicals exert significantly stronger disinfection power under UV/PAA than under UV/H2O2 conditions. Pre-exposing E. coli to PAA in the dark followed by application of UV (i.e., a PAA-UV/PAA process) promotes diffusion of PAA to the cells and achieves excellent disinfection efficiency while saving more than half of the energy cost associated with UV compared to simultaneous application of UV and PAA. The effectiveness of this new disinfection strategy has been demonstrated not only in lab water but also in wastewater matrices. 

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2. Unveiling the environmental significance of acetylperoxyl radical: Reactivity quantification and kinetic modeling

   https://doi.org/10.1093/pnasnexus/pgae330  

   Wang, Junyue; Schaefer, Thomas; Lisouskaya, Aliaksandra; Firak, Daniele_S; Xin, Xiaoyue; Meng, Lingjun; Herrmann, Hartmut; Sharma, Virender_K; Huang, Ching-Hua; Xu, ed., Yi-Jun (August 2024, PNAS Nexus)

   Abstract Acetylperoxyl radical (CH3C(O)OO•) is among highly reactive organic radicals which are known to play crucial roles in atmospheric chemistry, aqueous chemistry and, most recently, peracetic acid (PAA)-based advanced oxidation processes. However, fundamental knowledge for its reactivity is scarce and severely hampers the understanding of relevant environmental processes. Herein, three independent experimental approaches were exploited for revelation and quantification of the reaction rates of acetylperoxyl radical. First, we developed and verified laser flash photolysis of biacetyl, ultraviolet (UV) photolysis of biacetyl, and pulse radiolysis of acetaldehyde, each as a clean source of CH3C(O)OO•. Then, using competition kinetics and selection of suitable probe and competitor compounds, the rate constants between CH3C(O)OO• and compounds of diverse structures were determined. The three experimental approaches complemented in reaction time scale and ease of operation, and provided cross-validation of the rate constants. Moreover, the formation of CH3C(O)OO• was verified by spin-trapped electron paramagnetic resonance, and potential influence of other reactive species in the systems was assessed. Overall, CH3C(O)OO• displays distinctively high reactivity and selectivity, reacting especially favorably with naphthyl and diene compounds (k ∼ 107–108 M−1 s−1) but sluggishly with N- and S-containing groups. Significantly, we demonstrated that incorporating acetylperoxyl radical-oxidation reactions significantly improved the accuracy in modeling the degradation of environmental micropollutants by UV/PAA treatment. This study is among the most comprehensive investigation for peroxyl radical reactivity to date, and establishes a robust methodology for investigating organic radical chemistry. The determined rate constants strengthen kinetic databases and improve modeling accuracy for natural and engineered systems. 

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3. Photolysis Products of Fluorinated Pharmaceuticals: A Combined Fluorine Nuclear Magnetic Resonance Spectroscopy and Mass Spectrometry Approach

   https://doi.org/10.1002/etc.5773  

   Mundhenke, Thomas F.; Bhat, Akash P.; Pomerantz, William C. K.; Arnold, William A. (November 2023, Environmental Toxicology and Chemistry)

   Abstract The aqueous photolysis of four pharmaceuticals with varying fluorinated functional groups was assessed under neutral, alkaline, advanced oxidation, and advanced reduction conditions with varying light sources. Solar simulator quantum yields were 2.21 × 10⁻¹ mol Ei⁻¹for enrofloxacin, 9.36 × 10⁻³ mol Ei⁻¹for voriconazole, and 1.49 × 10⁻² mol Ei⁻¹for flecainide. Florfenicol direct photolysis was slow, taking 150 h for three degradation half‐lives. Bimolecular rate constants between pharmaceuticals and hydroxyl radicals were 10⁹to 10¹⁰ M⁻¹ s⁻¹. Using a combined quantitative fluorine nuclear magnetic resonance spectroscopy (¹⁹F‐NMR) and mass spectrometry approach, fluorine mass balances and photolysis product structures were elucidated. Enrofloxacin formed a variety of short‐lived fluorinated intermediates that retained the aryl F motif. Extended photolysis time led to complete aryl F mineralization to fluoride. The aliphatic F moiety on florfenicol was also mineralized to fluoride, but the resulting product was a known antibiotic (thiamphenicol). For voriconazole, the two aryl Fs contributed more to fluoride production compared with the heteroaromatic F, indicating higher stability of the heteroaromatic F motif. The two aliphatic CF₃moieties in the flecainide structure remained intact under all conditions, further supporting the stability of these moieties found in per‐ and polyfluoroalkyl substances under a variety of conditions. The advanced treatment conditions generating hydroxyl radicals or hydrated electrons accelerated the degradation, but not the defluorination, of flecainide. The combination of¹⁹F‐NMR and mass spectrometry proved powerful in allowing identification of fluorinated products and verifying the functional groups present in the intermediates and products. The results found in the present study will aid in the understanding of which fluorinated functional groups should be incorporated into pharmaceuticals to ensure organofluorine byproducts are not formed in the environment and help determine the water‐treatment processes that effectively remove specific pharmaceuticals and more generally fluorinated motifs.Environ Toxicol Chem2023;00:1–12. © 2023 The Authors.Environmental Toxicology and Chemistrypublished by Wiley Periodicals LLC on behalf of SETAC. 

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4. Emerging investigators series: the efficacy of chlorine photolysis as an advanced oxidation process for drinking water treatment

   https://doi.org/10.1039/C6EW00029K  

   Remucal, C. K.; Manley, D. (January 2016, Environmental Science: Water Research & Technology)

   null (Ed.)

   The photolysis of hypochlorous acid (HOCl) and hypochlorite (OCl − ) produces a suite of reactive oxidants, including hydroxyl radical (˙OH), chlorine radical (Cl˙), and ozone (O 3 ). Therefore, the addition of light to chlorine disinfection units could effectively convert existing drinking water treatment systems into advanced oxidation processes. This review critically examines existing studies on chlorine photolysis as a water treatment process. After describing the fundamental chemistry of chlorine photolysis, we evaluate the ability of chlorine photolysis to transform model probe compounds, target organic contaminants, and chlorine-resistant microorganisms. The efficacy of chlorine photolysis to produce reactive oxidants is dependent on solution and irradiation conditions ( e.g. , pH and irradiation wavelengths). For example, lower pH values result in higher steady-state concentrations of ˙OH and Cl˙, resulting in enhanced contaminant removal. We also present the current state of knowledge on the alteration of dissolved organic matter and subsequent formation of disinfection by-products (DBPs) during chlorine photolysis. Although the relative yields of DBPs during chlorine photolysis are also dependent on solution conditions ( e.g. , higher organic DBP yields at low pH values), there is conflicting evidence on whether chlorine photolysis increases or decreases DBP production compared to thermal reactions between chlorine and dissolved organic matter in the dark. We conclude the review by identifying knowledge gaps in the current body of literature. 

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5. Carbon–titanium dioxide (C/TiO ₂ ) nanofiber composites for chemical oxidation of emerging organic contaminants in reactive filtration applications

   https://doi.org/10.1039/D0EN00975J  

   Greenstein, Katherine E.; Nagorzanski, Matthew R.; Kelsay, Bailey; Verdugo, Edgard M.; Myung, Nosang V.; Parkin, Gene F.; Cwiertny, David M. (March 2021, Environmental Science: Nano)

   null (Ed.)

   The recalcitrance of some emerging organic contaminants through conventional water treatment systems may necessitate advanced technologies that use highly reactive, non-specific hydroxyl radicals. Here, polyacrylonitrile (PAN) nanofibers with embedded titanium dioxide (TiO 2 ) nanoparticles were synthesized via electrospinning and subsequently carbonized to produce mechanically stable carbon/TiO 2 (C/TiO 2 ) nanofiber composite filters. Nanofiber composites were optimized for reactivity in flow through treatment systems by varying their mass loading of TiO 2 , adding phthalic acid (PTA) as a dispersing agent for nanoparticles in electrospinning sol gels, comparing different types of commercially available TiO 2 nanoparticles (Aeroxide® P25 and 5 nm anatase nanoparticles) and through functionalization with gold (Au/TiO 2 ) as a co-catalyst. High bulk and surface TiO 2 concentrations correspond with enhanced nanofiber reactivity, while PTA as a dispersant makes it possible to fabricate materials at very high P25 loadings (∼80% wt%). The optimal composite formulation (50 wt% P25 with 2.5 wt% PTA) combining high reactivity and material stability was then tested across a range of variables relevant to filtration applications including filter thickness (300–1800 μm), permeate flux (from 540–2700 L m −2 h), incident light energy (UV-254 and simulated sunlight), flow configuration (dead-end and cross-flow filtration), presence of potentially interfering co-solutes (dissolved organic matter and carbonate alkalinity), and across a suite of eight organic micropollutants (atrazine, benzotriazole, caffeine, carbamazepine, DEET, metoprolol, naproxen, and sulfamethoxazole). During cross-flow recirculation under UV-irradiation, 300 μm thick filters (30 mg total mass) produced micropollutant half-lives ∼45 min, with 40–90% removal (from an initial 0.5 μM concentration) in a single pass through the filter. The initial reaction rate coefficients of micropollutant transformation did not clearly correlate with reported second order rate coefficients for reaction with hydroxyl radical ( k OH ), implying that processes other than reaction with photogenerated hydroxyl radical ( e.g. , surface sorption) may control the overall rate of transformation. The materials developed herein represent a promising next-generation filtration technology that integrates photocatalytic activity in a robust platform for nanomaterial-enabled water treatment. 

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