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The urgency of water remediation and the conversion of toxic pollutants into non-toxic compounds is increasingly crucial in our industrialized world. Heterogeneous catalysts based on metal nanoparticles, which are cost-effective, non-toxic, and readily available, have garnered significant attention in the market due to their unique catalytic properties. This study presents sol–gel-based hybrid silica matrices that encapsulate nickel, designed for the efficient reductive de-halogenation of tri-bromoacetic acid (TBAA), di-bromoacetic acid (DBAA), mono-bromoacetic acid (MBAA), tri-chloroacetic acid (TCAA), mono-chloroacetic acid (MCAA), and Chloroacetanilide (CAA). A detailed study of the product distribution from each halo-acetic acid (HAA) is presented. The study points out that other products are formed from Ni-catalyzed reduction reactions of HAAs, breaking the conventional rules of stepwise reduction mechanisms. The plausible mechanisms of the catalytic processes are discussed. [ABSTRACT FROM AUTHOR]

The kinetics of the reactions of H2 with rhodium and iridium nanoparticles (NPs), in aqueous suspensions, were studied by following their catalytic reduction of PW12O403−, POM. The reaction of H2 with the same size (∼2.5 nm) of two different nanoparticles was carried out to check how the nature of the nanoparticles affects the reaction kinetics. Herein we report the first kinetic measurement of H2 + Rh0 and Ir0 NPs in the absence of an electric field. A comparison of the apparent rate constants of the reactions Rh0-NPs and Ir0-NPs + H2 to the previously reported Pt0-NPs + H2 indicates that the rates decrease along the series k(Pt) > k(Rh) > k(Ir), though they are of the same order of magnitude. The adsorption of hydrogen and/or H atom can affect the structure of the M0-NPs. [ABSTRACT FROM AUTHOR]

Photocatalytic hydrogen production is proposed as a sustainable energy source. Simultaneous reduction and oxidation of water is a complex multistep reaction with high overpotential. Photocatalytic processes involving semiconductors transfer electrons from the valence band to the conduction band. Sacrificial substrates that react with the photochemically formed holes in the valence band are often used to study the mechanism of H2 production, as they scavenge the holes and hinder charge carrier recombination (electron‐hole pairs). Here, we show that the desired sacrificial agent is one forming a radical that is a fairly strong reducing agent, and whose oxidized form is not a good electron acceptor that might suppress the hydrogen evolution reaction (HER). In an acidic medium, methanol was found to fulfill both these requirements better than ethanol and propan‐2‐ol in the TiO2‐(M0‐NPs) (M=Au or Pt) system, whereas in an alkaline medium, the alcohols exhibit a reverse order of activity. Moreover, we report that CH2(OH)2 is by far the most efficient sacrificial agent in a nontrivial mechanism in acidic media. Our study provides general guidelines for choosing an appropriate sacrificial substrate and helps to explain the variance in the performance of alcohol scavenger‐based photocatalytic systems. [ABSTRACT FROM AUTHOR]

Acetone, hydrogen evolution reaction, radicals, reaction mechanism, sacrificial agents Keywords: acetone; hydrogen evolution reaction; radicals; reaction mechanism; sacrificial agents EN acetone hydrogen evolution reaction radicals reaction mechanism sacrificial agents 15826 15826 1 11/19/21 20211117 NES 211117 B HER photocatalysis: Choosing the right sacrificial agent b ! Our work aims to deepen understanding of the reaction mechanism and guidelines for selecting the best sacrificial agent. [Extracted from the article]

Many advanced oxidation processes (AOPs) use Fenton-like reactions to degrade organic pollutants by activating peroxymonosulfate (HSO 5 - , PMS) or peroxydisulfate (S 2 O 8 2- , PDS) with Fe(H 2 O) 6 2+ (Fe aq II ). This paper presents results on the kinetics and mechanisms of reactions between Fe aq II and PMS or PDS in the absence and presence of bicarbonate (HCO 3 - ) at different pH. In the absence of HCO 3 - , Fe aq IV , rather than the commonly assumed SO 4 •- , is the dominant oxidizing species. Multianalytical methods verified the selective conversion of dimethyl sulfoxide (DMSO) and phenyl methyl sulfoxide (PMSO) to dimethyl sulfone (DMSO 2 ) and phenyl methyl sulfone (PMSO 2 ), respectively, confirming the generation of Fe aq IV by the Fe aq II -PMS/PDS systems without HCO 3 - . Significantly, in the presence of environmentally relevant concentrations of HCO 3 - , a carbonate radical anion (CO 3 •- ) becomes the dominant reactive species as confirmed by the electron paramagnetic resonance (EPR) analysis. The new findings suggest that the mechanisms of the persulfate-based Fenton-like reactions in natural environments might differ remarkably from those obtained in ideal conditions. Using sulfonamide antibiotics (sulfamethoxazole (SMX) and sulfadimethoxine (SDM)) as model contaminants, our study further demonstrated the different reactivities of Fe aq IV and CO 3 •- in the Fe aq II -PMS/PDS systems. The results shed significant light on advancing the persulfate-based AOPs to oxidize pollutants in natural water.

Photocatalytic hydrogen production is proposed as a sustainable energy source. Simultaneous reduction and oxidation of water is a complex multistep reaction with high overpotential. Photocatalytic processes involving semiconductors transfer electrons from the valence band to the conduction band. Sacrificial substrates that react with the photochemically formed holes in the valence band are often used to study the mechanism of H 2 production, as they scavenge the holes and hinder charge carrier recombination (electron-hole pairs). Here, we show that the desired sacrificial agent is one forming a radical that is a fairly strong reducing agent, and whose oxidized form is not a good electron acceptor that might suppress the hydrogen evolution reaction (HER). In an acidic medium, methanol was found to fulfill both these requirements better than ethanol and propan-2-ol in the TiO 2 -(M 0 -NPs) (M=Au or Pt) system, whereas in an alkaline medium, the alcohols exhibit a reverse order of activity. Moreover, we report that CH 2 (OH) 2 is by far the most efficient sacrificial agent in a nontrivial mechanism in acidic media. Our study provides general guidelines for choosing an appropriate sacrificial substrate and helps to explain the variance in the performance of alcohol scavenger-based photocatalytic systems., (© 2021 Wiley-VCH GmbH.)