Fenton-like reactions are broadly employed in advanced oxidation processes (AOPs) for the degradation of organic pollutants through catalytic peroxide activation. In this study, NiO was precipitated on a wrinkled SiO2 to improve catalytic performance. The kinetics and reaction mechanism between the catalyst and S2O82- were studied via following the degradation of methylene blue as a model organic pollutant. The findings indicate that the excellent catalytic activity of Ni/SiO2 and highly active sulfate radicals enhanced the degradation of methylene blue for environmental remediation. Moreover, the cost-effectiveness, and eco-friendly characteristics of the prepared Ni@SiO2-persulfate system represents a substantial advancement in the field of catalytic oxidation, contributing valuable knowledge to the development of next-generation catalytic systems.

Organic water pollution is calling for advanced remediation methods such as the Fenton process, yet actual procedures involve transition metals at acidic pH, and generate only one oxidant, the hydroxyl radical. Here we used a solution of magnesium ions, bicarbonate ions, and hydrogen peroxide at pH 7.4 to generate reactive oxygen species for degrading dimethyl sulfoxide and acetamidophenol, as models of water pollutants. The performance and the identification of degradation products were assessed by nuclear magnetic resonance and high-performance liquid chromatography. Results show the generation of several oxidizing agents such as hydroxyl radical, carbonate anion radical, and superoxide. The novel aspect is that the Fenton-like process can be achieved with Mg2⁺ serving only as a template to facilitate redox reactions rather than participating directly. The mechanisms for generating oxidizing radicals suggests potential applications in both environmental cleanup and biological processes.

Ce-IV(DOTA) (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) was produced both radiolytically and electrochemically in the presence of halides and azide anions. Only fluoride, the hardest Lewis base studied, ligates to both [Ce-III(DOTA)(H2O)](-) and Ce-IV(DOTA), stabilizing the high oxidation state by two orders of magnitude versus [Ce-IV/III(DOTA)](0/-) in its absence. The Ce-IV(DOTA) complexes are long-lived in the dark (decompose photochemically). The tetravalent complexes decompose mainly via kinetics which obeys a first order rate law. The first step is de-carboxylation of the DOTA ligand followed by the formation of CH2O. The kinetics of oxidation of [Ce-III(DOTA)(H2O)](-) by Cl-2(-), Br-2(-) and N-3 were studied. Cl-2(-), the strongest oxidizing agent studied, reacts mainly via H atom abstraction from the DOTA ligand. Br-2(-) at both acidic and neutral pH oxidizes [Ce-III(DOTA)(H2O)](-) with rate constants of <3 x 10(6) M(-1)s(-1), as measured by pulse radiolysis, via an inner sphere mechanism. N-3 oxidizes [Ce-III(DOTA)(H2O)](-) to its tetravalent analogue as well, as proved by UV-vis data after steady-state radiolysis. The presence of F- increased the yield of the Ce-IV(DOTA) formed. The oxidation rate by N-3 is probably lower than that measured for Br-2(-).

The reactions of methyl radicals with noble metal nanoparticles, M0-NPs, M = Ru, Os, and Ir, were studied. The M0-NPs were prepared by reduction of the corresponding salts with NaBH4. HR-TEM, XPS, and Raman analysis of the M0-NPs thus formed point out that the Ru0-NPs and Os0-NPs formed are covered with an oxide/hydroxide layer. The Ir0-NPs are only partially covered by such a layer. The methyl radicals oxidize all of the M0-NPs studied herein. Thus, the mechanism differs from the mechanisms of reaction with M0-NPs, M = Ag, Au, and Pt. This phenomenon is attributed to the differences in the reduction potentials of these metals. The rate constant of the reaction of methyl radicals with Ir0-NP is very high, similar to that reported for other M0-NPs, M = Ag, Au, and Pt. This is attributed to the interaction of the radicals with the electrons in the conduction bands of the metals. On the other hand, the rate constants of the reactions of methyl radicals with M0-NPs, M = Ru and Os, are considerably lower and similar to those reported for titania. The total yield of methyl radicals, the yield of methane + twice the yield of ethane, observed in the presence of the M0-NPs, is somewhat smaller than expected. This is attributed to either the formation of a mixture of side products, at concentrations below the limit of observation under our experimental conditions, or some energy absorption by the M0-NPs.

Silver nanoparticles (Ag0-NPs) prepared via the Creighton procedure (chemical reduction by BH4-) from the Ag2SO4 and AgNO3 precursors exhibit significant differences in sizes, crystal structures, and catalytic properties, even though neither sulfate nor nitrate is a good ligand for Ag+. Furthermore, the addition of NH3 before the reduction of silver ions into Ag0 nanoparticles leads to a marked increase in nanoparticle size and alters both their crystallographic features and catalytic performance. These results highlight that even seemingly minor modifications in solution composition, such as the nature of the counterion or the presence of simple ligands like ammonia, can profoundly affect the nucleation and growth processes of Ag0 nanoparticles. Such simple solution-phase components, often overlooked, significantly influence the final size, morphology, and properties of metal nanoparticles.

The results reported herein indicate that solutions containing Mg(H2O)62+ + HCO3- + H2O2 can replace Fe(H2O)62+ + H2O2, or the use of other transition metal complexes, as catalysts of the Fenton-like processes. The reactive oxidizing intermediate formed in this system is the CO3˙- anion radical. Detailed experimental and density functional theory (DFT) calculations point out that CO3˙- is formed via the decomposition of [(H2O)4MgII(CO32-)(H2O2)]. Implications of this new and green, advanced oxidation process are briefly discussed.

Radicals are highly reactive species that undergo fast reactions on metal surfaces, exhibiting charge transfer to/from the surface upon adsorption. Organic acids, including weak ones, are reported to undergo deprotonation on metal surfaces. Computational studies are used to study the surface reactions of hydroxy methyl radicals, which have a high aqueous pKa (10.7) on the (111) surface of Ag, Au, and Pt. The study shows that the hydroxymethyl radical undergoes faster deprotonation on the metal surfaces than in the homogeneous media. Deprotonation on Ag and Au surfaces leads to the formation of charged NPs along with the formation of formaldehyde in accordance with the mechanism proposed by Henglein. However, on Pt(111), only partial charge transfer from the radical to the surface is observed. These results are in accordance with reported experimental results.

[This corrects the article DOI: 10.1021/acs.jpcc.4c06554.].

The DFT method was used to evaluate the adsorption of methyl radicals and the evolution of ethane on the M(111) (M = Co, Ni, Pd, Pt) surfaces, eight metal atoms, in aqueous medium. A maximum of five and four radicals can be adsorbed on Co(111) and Ni(111), respectively, and six on Pd(111) and Pt(111) (top site). The ethane evolution occurs via the Langmuir–Hinshelwood (LH) or Eley–Rideal (ER) mechanisms. The production of ethane through the interaction of two adsorbed radicals is thermodynamically feasible for high coverage ratios on the four surfaces; however, kinetically, it is feasible at room temperature only on Co(111) at a coverage of (5/5) and on Pd(111) at a coverage ratio of 4/6, 5/6, and 6/6. Ethane production occurs via the ER mechanism: a collision with solvated methyl radical produces either C2H6 or CH2∗+CH4(aq). On Pd(111) the product is only C2H6, on Pt(111), both products (C2H6 or CH2∗) are plausible, and on Co(111) and Ni(111), only CH2∗+CH4(aq) is produced. Further reactions of CH2∗ with CH2∗ or CH3∗ to give C2H4∗ or C2H5∗ are thermodynamically plausible only on Pt(111); however, they are very slow due to high energy barriers, 1.48 and 1.36 eV, respectively.

Reactions of ferrous iron (Fe(II)) with oxidants (O2, H2O2, and persulfate) in the presence of bicarbonate affect the Fenton and Fenton-like reactions in water treatment at neutral pH through the formation of the carbonate radical anion (CO3•-) rather than only the usually accepted hydroxyl radical (HO•) or sulfate radical anion (SO4•-). Mechanisms of such a direct formation of CO3•- in reactions of low-valent iron with oxidants are presented. The reactivity of ferrate (Fe(VI)) enhanced the oxidation of pollutants in carbonate-rich water, and herein, the role of carbonate in high-valent iron-based oxidations is discussed. Advanced oxidation methods, based on HO• treatments and reactions occurring in natural waters and water-containing aerosol particles, should consider these overlooked reactions in inorganic carbon-containing environments.

Polyoxometalates (POMs) have been well studied and explored in electro/photochemical water oxidation catalysis for over a decade. The high solubility of POMs in water has limited its use in homogeneous conditions. Over the last decade, different approaches have been used for the heterogenization of POMs to exploit their catalytic properties. This study focused on a Keggin POM, K6[CoW12O40], which was entrapped in a sol-gel matrix for heterogeneous electrochemical water oxidation. Its entrapment in the sol-gel matrix enables it to catalyze the oxygen evolution reaction at acidic pH, pH 2.0. Heterogenization of POMs using the sol-gel method aids in POM's recyclability and structural stability under electrochemical conditions. The prepared sol-gel electrode is robust and stable. It achieved electrochemical water oxidation at a current density of 2 mA/cm2 at a low overpotential of 300 mV with a high turnover frequency (TOF) of 1.76 [mol O2 (mol Co)-1s-1]. A plausible mechanism of the electrocatalytic process is presented.

The de-halogenation of highly concentrated halo-organic compounds using Zero Valent Iron entrapped in silica matrices as a catalyst was investigated. This study aimed to evaluate the effectiveness of the Zero Valent Iron-entrapped organically modified silica matrices in transforming highly concentrated hazardous halogenated compounds into environmentally benign materials in the presence of BH4−. The Zero Valent Iron-entrapped silica gel matrices were synthesized using the sol–gel method. The de-halogenation products were analyzed using high-performance liquid chromatography. The results suggest that the Zero Valent Iron-entrapped silica matrices are effective catalysts in the de-halogenation reaction of halo-organics by BH4− with 100% efficiency. The current work also highlights the complete de-bromination of harmful wastewater generated by the bromoacetic acid manufacturing industry using Zero Valent Iron-entrapped silica matrices. Therefore, Zero Valent Iron-entrapped silica matrices can be considered potential candidates for the catalytic removal of highly concentrated halo-organic compounds from contaminated water. This technology can play a crucial role in reducing the environmental impact of hazardous substances.

Heterogeneous catalysts hold immense potential applicability in batch-advanced oxidation technologies. The present study examined LaFeO3 Fenton-like catalyzed oxidation of EtOH and DMSO. LaFeO3 is used to catalyze many processes, including an advanced oxidation process (AOP). Less is known about its role in Fenton-like reactions for AOPs. The results point out that two short-lived oxidizing intermediates are formed. Based on oxidation products analysis, it is tentatively proposed that the two short-lived oxidizing intermediates are [((LaFeIIIO3)n)n((LaFeIIIO2(OH)m-2)(LaFeIV(O)O2)2] and [(LaFeIVO3)2(LaFeIIIO3)n-2]2+. Both substrates are oxidized by [((LaFeIIIO3)n)n((LaFeIIIO2(OH)m-2)(LaFeIV(O)O2)2], the oxidation of DMSO by this intermediate is considerably faster than that of ethanol. [(LaFeIVO3)2(LaFeIIIO3)n-2]2+ oxidizes only EtOH. The yield of [((LaFeIIIO3)n)n((LaFeIIIO2(OH)m-2)(LaFeIV(O)O2)2] is larger than that of [(LaFeIVO3)2(LaFeIIIO3)n-2]2+. The knowledge gained in this study will help elucidate the detailed mechanisms of perovskite catalyzed Fenton-like processes and thus facilitate the development of efficient AOPs. The involvement of two short-lived intermediates was shown only by studying the oxidation of two very different substrates, a novel approach whose groundbreaking results are important for catalytic processes that will advance environmental strategies.

FeIV =Oaq is a key intermediate in many advanced oxidation processes and probably in biological systems. It is usually referred to as FeIV =O2+ . The pKa's of FeIV =Oaq as derived by DFT are: pKa1=2.37 M06 L/6-311++G(d,p) (SDD for Fe) and pKa2=7.79 M06 L/6-311++G(d,p) (SDD for Fe). This means that in neutral solutions, FeIV =Oaq is a mixture of (H2 O)4 (OH)FeIV =O+ and (H2 O)2 (OH)2 FeIV =O. The oxidation potential of FeIV =Oaq in an acidic solution, E0 {(H2 O)5 FeIV =O2+ /FeIII (H2 O)63+ , pH 0.0} is calculated with and without a second solvation sphere and the recommended value is between 2.86 V (B3LYP/Def2-TZVP, with a second solvation sphere) and 2.23 V (M06 L/Def2-TZVP without a second solvation sphere). This means that FeIV =Oaq is the strongest oxidizing agent formed in systems involving FeVI O42- even in neutral media.

Correction for ‘Nickel carbonate (Ni 2 (CO 3 ) 3 ) as an electrocatalyst and photo-electrocatalyst for methanol electro-oxidation’ by Iranna Udachyan et al. , J. Mater. Chem. A , 2023, 11 , 17769–17778, https://doi.org/10.1039/D3TA02713A.

Iron(II), (Fe(H 2 O) 6 2+ , (Fe II ) participates in many reactions of natural and biological importance. It is critically important to understand the rates and the mechanism of Fe II oxidation by dissolved molecular oxygen, O 2 , under environmental conditions containing bicarbonate (HCO 3 − ), which exists up to millimolar concentrations. In the absence and presence of HCO 3 − , the formation of reactive oxygen species (O 2 ⋅ − , H 2 O 2 , and HO⋅) in Fe II oxidation by O 2 has been suggested. In contrast, our study demonstrates for the first time the rapid generation of carbonate radical anions (CO 3 ⋅ − ) in the oxidation of Fe II by O 2 in the presence of bicarbonate, HCO 3 − . The rate of the formation of CO 3 ⋅ − may be expressed as d[CO 3 ⋅ − ]/dt=[Fe II [[O 2 ][HCO 3 − ] 2 . The formation of reactive species was investigated using 1 H nuclear magnetic resonance ( 1 H NMR) and gas chromatographic techniques. The study presented herein provides new insights into the reaction mechanism of Fe II oxidation by O 2 in the presence of bicarbonate and highlights the importance of considering the formation of CO 3 ⋅ − in the geochemical cycling of iron and carbon.

Assessing competitive environmental catalytic reduction processes via NaBH4 is essential, as BH4− is both an energy carrier (as H2) and a reducing agent. A comprehensive catalytic study of the competition between the borohydride hydrolysis reaction (BHR, releasing H2) and 4-nitrophenol reduction via BH4− on M0- and M/M′ (alloy)-nanoparticle catalysts is reported. The results reveal an inverse correlation between the catalytic efficiency for BH4− hydrolysis and 4-nitrophenol reduction, indicating that catalysts performing well in one process exhibit lower activity in the other. Plausible catalytic mechanisms are discussed, focusing on the impact of reaction products such as 4-aminophenol and borate on the rate and yield of BH4− hydrolysis. The investigated catalysts were Ag0, Au0, Pt0, and Ag/Pt-alloy nanoparticles synthesized without any added stabilizer. Notably, the observed rate constants for the 4-nitrophenol reduction on Ag0, Ag-Pt (9:1), and Au0 are significantly higher than the corresponding rate constants for BH4− hydrolysis, suggesting that most reductions do not proceed through surface-adsorbed hydrogen atoms, as observed for Pt0 nanoparticles. This research emphasizes the conflicting nature of BH4− hydrolysis and reduction processes, provides insights for designing improved catalysts for competitive reactions, and sheds light on the catalyst properties required for each specific process.

The CuI/IIATP react with methyl radicals to form methane and methanol, where CuIATP reacts with •CH3 in a process that is surprisingly slow. The low-rate constant of this process is attributed to the significant rearrangement of the chelating ligand required for the transient's formation. These results were corroborated by DFT calculations of the relevant compounds.

Advanced oxidation technologies often use peroxymonosulfate in the presence of Co-aq(II). It is commonly assumed that the reaction of Co(H2O)(6)(2+) with HSO5- yields Co-aq(III) and SO4.-. DFT results point out that first Co-II(SO5)(H2O)(2) is formed. The homolysis of Co-II(SO5)(H2O)(2) to yield (H2O)Co-II(SO5)OH.+SO4.-, is exothermic but has a large activation energy. However the cobalt is not oxidized in this reaction. Co-II(SO5)(H2O)(2) reacts with a second HSO5- to form Co-II(SO5)(2)(H2O)(2-) that decomposes via disproportionation of the monoperoxysulfate ions without oxidation of the central cobalt ion. Surprisingly even in the presence of ligands, L, that stabilize Co-III, i. e., pyrophosphate; tri-polyphosphate and ATP, the experimentally observed reaction mechanism involves the formation of LCoII-OOSO3aq which then reacts with another HSO5- to form LCoII-(OOSO32-)(2). The latter complex decomposes via disproportionation of the monoperoxysulfate ligands followed by oxidation of the central cobalt cation. Alternatively, in the presence of excess (CoLaq)-L-II, LCoII-OOSO3aq reacts with (CoLaq)-L-II to form 2Co(III)L(aq). These results point out that the mechanism of advanced oxidation processes initiated by a mixture of Co(H2O)(6)(2+) and HSO5- must be re-considered.