Primary Oxidant Research Articles

Cu Anchored Carbon Nitride (Cu/CN) Catalyzes Selective Oxidation of Thiol by Controlling Reactive Oxygen Species Generation.

Production of H2O2 using heterogeneous semiconductor photocatalysts has emerged as an ecofriendly and practical approach across various applications, ranging from environmental detoxification to fuel cells and chemical synthesis. Extensive efforts have been devoted to engineering semiconductors to enhance their catalytic capabilities for H2O2 production. However, in chemical synthesis, the utilization of the potent oxidant H2O2 can present challenges in selectively oxidizing organic compounds. In this study, we introduce copper atoms into carbon nitride (Cu/CN), facilitating the generation of hydroperoxyl radicals (·OOH) as primary reactive oxidants and offering reaction conditions entirely devoid of H2O2 via the Fenton reaction. Cu/CN demonstrates selective oxidation of thiols to disulfides, in contrast to other current heterogeneous photocatalysts that yield undesired overoxidized side products, such as thiosulfinate and thiosulfonate. Cu/CN's controllable capacity for specific ROS generation, broad substrate scopes, and recyclability empower greener and highly selective photooxidation of organic compounds.

Scale-up of Sodium Persulfate Mediated, Nitroxide Catalyzed Oxidative Functionalization Reactions.

Oxidation is a valuable tool in preparative organic chemistry. Oxoammonium salts and nitroxides have proven valuable as reagents and catalysts in this endeavor. The objective of this study is to scale up the oxidative amidation, ester formation, and nitrile formation using nitroxide as an organocatalyst. Oxidative functionalization reactions were scaled from the 1 mmol to the 1 mole level. Sodium persulfate was used as the primary oxidant, and a nitroxide was employed as a catalyst. The products of the reactions were isolated in analytically pure form by extraction with no need for column chromatography. The oxidative amidation and esterification of aldehydes can be scaled up from 1 mmol to 1 mole effectively, with comparable product yields being obtained at each increment. This work shows that conditions developed on a small scale can be transferred to a larger scale without reoptimization. The oxidative functionalization of aldehydes to prepare nitriles is not amenable to direct scale-up due to the concomitant formation of significant quantities of the corresponding carboxylic acid, thereby compromising the product yield. Two of the three oxidative transformations studied here can be scaled up successfully from the 1 mmol to the 1 mole level.

Electrochemically activated calcium sulfite for atrazine degradation: Performance, mechanism and kinetics

The conventional use of Na2SO3 in advanced oxidation processes leads to excessive dissolved SO32−, limiting the utilization of oxysulfur species. This study introduced an electrochemically activated CaSO3 (EC-CaSO3) process that exploited the slow-release property of CaSO3. The results showed that the removal ratios of several micropollutants were over 90 % within 10 min, with SO4•− as the primary oxidant. A mathematic model was further developed to simulate the radical conversion, analyze the degradation kinetics and optimize the operational parameters, using atrazine (ATZ) as the target pollutant. The continuous low concentration of SO32− promoted O2 evolution for oxysulfur species transformation and reduced SO4•− quenching. This resulted in 74 % of SO3•− converting to SO5•− and 84 % of SO32− contributing to SO4•− formation. In the initial 2 min, the matched electro-generation of SO3•− and O2 remarkably accelerated SO4•− generation, leading to 82 % removal of ATZ. As electrolysis continued, the reduced release rate of SO32− prevented excessive accumulation of SO32− and maintained high O2 evolution rate to drive SO4•− generation. Consequently, complete degradation of ATZ was achieved within 5 min, with the contribution of SO4•− exceeding 99 %. By investigating the influence of operational parameters on ATZ degradation and energy consumption, the cost-effective conditions (EE/O values < 2.2 kWh/m3/order) occurred at pH above 7, current densities of 60 to 90 A/m2 and initial CaSO3 dosages of 2 to 4 mM. Additionally, density functional calculation and LC-MS analysis confirmed the formation of less toxic intermediates through dealkylation and dechlorination-hydroxylation. These findings suggested that EC-CaSO3 process was a promising technology for oxidizing micropollutants.

Effective removal of organic compounds by g-C3N4-AQ/Fe(III) via photocatalytic oxidation and photochemical cycling of iron

Anthraquinone-anchored graphitic carbon nitride (denoted as g-C3N4-AQ), which has been reported in the photochemical production of H2O2, demonstrated significant visible light photocatalytic activity with Fe(III) for the degradation of organic compounds. The synthesized g-C3N4-AQ exhibited a light absorption spectrum and crystallinity comparable to that of pristine g-C3N4. FT-IR and XPS analyses confirmed the covalent bonding between AQ and g-C3N4. The synthesized g-C3N4-AQ generated 12 μM of H2O2 within 2 h under visible light illumination, a quantity negligible for the degradation of organic compounds. However, in the combination with Fe(III), the system successfully degraded organic compounds, achieving degradation of 88 – 99 % in the presence of dissolved oxygen. It was also observed that the photochemical activity of g-C3N4-AQ/Fe(III) was non-selective towards the target organic compounds. Intriguingly, the visible light-illuminated g-C3N4-AQ/Fe(III) selectively degraded target organic compounds in the absence of dissolved oxygen. Experimental work employing reactive oxidant scavengers and oxidant probes revealed that •OH is the main reactive species responsible for the degradation of organic compounds in the presence of dissolved oxygen, whereas in its absence, the hole acts as the primary oxidant in the selective degradation of organic compounds. This finding provides important insights into the application of the g-C3N4-AQ/Fe(III) system for effective micropollutant removal.

Oxyanion-Sensitive Catalytic Activity of Ni(II)/Oxyanion Systems for Heterogeneous Organic Degradation: Differential Oxidizing Capacity of Ni(III) and Ni(IV) as High-Valent Intermediates.

This study demonstrated that NiO and Ni(OH)2 as Ni(II) catalysts exhibited significant activity for organic oxidation in the presence of various oxyanions, such as hypochlorous acid (HOCl), peroxymonosulfate (PMS), and peroxydisulfate (PDS), which markedly contrasted with Co-based counterparts exclusively activating PMS to yield sulfate radicals. The oxidizing capacity of the Ni catalyst/oxyanion varied depending on the oxyanion type. Ni catalyst/PMS (or HOCl) degraded a broad spectrum of organics, whereas PDS enabled selective phenol oxidation. This stemmed from the differential reactivity of two high-valent Ni intermediates, Ni(III) and Ni(IV). A high similarity with Ni(III)OOH in a substrate-specific reactivity indicated the role of Ni(III) as the primary oxidant of Ni-activated PDS. With the minor progress of redox reactions with radical probes and multiple spectroscopic evidence on moderate Ni(III) accumulation, the significant elimination of non-phenolic contaminants by NiOOH/PMS (or HOCl) suggested the involvement of Ni(IV) in the substrate-insensitive treatment capability of Ni catalyst/PMS (or HOCl). Since the electron-transfer oxidation of organics by high-valent Ni species involved Ni(II) regeneration, the loss of the treatment efficiency of Ni/oxyanion was marginal over multiple catalytic cycles.

Enhanced removal of malachite green from wastewater using nonthermal plasma gliding arc discharge combined with ferrate oxidation

The rapid and complete removal of Malachite Green (MG) dye was effectively achieved by combining potassium ferrate (Fe(VI)) treatment with nonthermal plasma discharge in both deionized water (DIW) and tap water (TW). This study evaluated the decolorization and mineralization efficiencies under varying MG concentrations, Fe(VI) dosages, and pH levels, as well as the impact of radical scavengers on the process. Fe(VI) alone resulted in moderate decolorization (35.01 %) and low mineralization (21.46 %) at an MG concentration of 50 mg/L in DIW. Plasma discharge alone achieved mineralization rates of 20.6 % in TW and 24.16 % in DIW. While complete decolorization was observed for all initial MG concentrations, it required significantly longer treatment times (>30 min). However, the combination of Fe(VI) with plasma (Fe(VI)-Plasma) demonstrated significant synergistic effects, achieving total decolorization and high mineralization rates -up to 92.5 % in DIW and 88.7 % in TW for 20 mg/L MG- at much shorter treatment times. Radical scavenger tests revealed that hydroxyl radicals (OH) were the primary oxidants in MG degradation, followed by superoxide radicals and electrons. These findings suggest that the combined Fe(VI)-Plasma technology is a promising and efficient solution for dye removal, reducing both chemical usage and treatment time.

Facet exposed-dependent surface bonding patterns between CuO and peroxymonosulfate vary activation mechanism: Reactive species and degradation pathways

The elusive factors determining peroxymonosulfate (PMS) activation lead to the “trial-and-error” method when developing efficient catalysts. Herein, we demonstrate that the suitable bonding pattern between PMS and exposed facets of CuO is the key parameter in catalysis. The kobs of ibuprofen removal by CuO with (110) facet (p-CuO) was 1.67 times higher than that of CuO with (001) facet (c-CuO). Simultaneously, Cu(III) was confirmed to be the primary intermediate oxidant among multiple reactive species (Cu(III), •OH, and 1O2 in both CuO/PMS systems, whereas O2•− only in c-CuO/PMS system). Furthermore, density functional theory calculations unveiled that compared to chaise longue connection between p-CuO and PMS, the higher adsorption energy (Eads) of bridge-like connection between c-CuO and PMS leads to a more stable intermediate (−5.56 eV vs −3.76 eV), thus hindering the formation of Cu(III). This work provides new opportunities for fabricating diverse metal oxides with new interfaces as PMS catalysts.

Pyrogenic HONO seen from space: insights from global IASI observations

Abstract. Nitrous acid (HONO) is a key atmospheric component, acting as a major source of the hydroxyl radical (OH), the primary oxidant in the Earth's atmosphere. However, understanding its spatial and temporal variability remains a significant challenge. Recent TROPOspheric Monitoring Instrument (TROPOMI)/Sentinel-5 Precursor (S5P) ultraviolet–visible (UV–Vis) measurements of fresh fire plumes shed light on the impact of global pyrogenic HONO emissions. Here, we leverage Infrared Atmospheric Sounding Interferometer (IASI)/MetOp's global infrared satellite measurements, complementing midday TROPOMI observations with morning and evening overpasses, to detect and retrieve pyrogenic HONO in 2007–2023. Employing a sensitive detection method, we identify HONO enhancements within concentrated fire plumes worldwide. Most detections are in the Northern Hemisphere (NH) mid- and high latitudes, where intense wildfires and high injection heights favour HONO detection. IASI's nighttime measurements yield 10-fold more HONO detections than daytime measurements, emphasizing HONO's extended lifetime in the absence of photolysis during the night. The annual detection count increases by at least 3–4 times throughout the IASI time series, mirroring the recent surge in intense wildfires at these latitudes. Additionally, we employ a neural-network-based algorithm for retrieving pyrogenic HONO total columns from IASI and compare them with TROPOMI in the same fire plumes. The results demonstrate TROPOMI's efficacy in capturing HONO enhancements in smaller fire plumes and in proximity to fire sources, while IASI's morning and evening overpasses enable HONO measurements further downwind, highlighting the survival of HONO or its secondary formation along long-range transport in smoke plumes.

Enhanced dewaterability of waste activated sludge via peroxymonosulfate activation process initiated by magnetic biochar derived from iron-rich sludge

The reduction of water content (WC) in waste activated sludge (WAS) is crucial for the recycling and environmentally-friendly treatment sludge in wastewater treatment plants. A new process of combined conditioning of iron-rich sludge biochar (Fe-BC) and peroxymonosulfate (PMS) was proposed and verified to enhance the dewaterability of WAS. The WC of sludge cake decreased significantly from 85.76% to 76.29% after Fe-BC/PMS treatment. For sludge extracellular polymeric substances (EPS) in sludge, the content of protein and polysaccharide in both TB-EPS and LB-EPS exhibited a decrease after Fe-BC/PMS treatment, whereas the S-EPS demonstrated an increase. Three-dimensional fluorescence (3D-EEM) showed that the fluorescence regions of protein-like and soluble microorganisms in both LB-EPS and TB-EPS were weakened. Through the experiment of free radical quenching, it has been demonstrated that the SO4•− and •OH as the primary oxidant in the Fe-BC/PMS system, effectively degrade proteinaceous components and humic substances present in sludge. The variation of particle size showed that the damaged EPS appeared reflocculation and achieved deep dehydration with Fe-BC as the skeleton. Consequently, a four-step mechanism was proposed for Fe-BC/PMS process, namely, oxidation cracking-sludge biochar flocculation-skeleton support – Fe2+ and Fe3+ reflocculation, which demonstrated the combined process with superior sludge dewatering effect and application potential.

Recent advances on the role of high-valent metals formed during persulfate activation

Over the past years, persulfate-based advanced oxidation processes have been widely employed in scientific research and practical application because of their outstanding oxidizing capability for decontamination and sterilization. In contrast to SO4•− and •OH radicals that are commonly considered to be the primary reactive oxidants, high-valent metals, such as Fe(IV), Co(IV), Cu(III), and Mn(V), formed during persulfate activation have only been observed in recent years. The advantages of high-valent metals over radicals lie in the better tolerance of background ions and the selective reaction towards compounds containing electron-rich groups. In this review, current research progress on high-valent metals generated during persulfate activation is outlined, and the formation mechanism, oxidation performance, and practical application are discussed. Specifically, the formation of high-valent metals has been observed via 18O-labeled water combined with chemical probes and in situ spectroscopy; compared to radicals, the formation of these metals was more thermodynamically favorable. Unlike •OH and SO4•−, which exhibit strong and nonselective reactivity, high-valent metals possess moderate oxidation power and selectively react with compounds containing electron-rich groups; these reactions are affected by several parameters, such as pH, temperature, activator/persulfate dosage, and ligand. The applications of high-valent metal-mediated oxidation processes and challenges encountered are discussed. Overall, potential applications of high-valent metal-mediated oxidation based on persulfate could be extended for practical wastewater treatment.

Mn-TiO2 catalyst collaborates with trace O3 to enhance the removal of mercury in ESP environment

Ozone, known for its strong oxidizing properties, is commonly utilized in water pollution control. However, the catalytic ozonation of gaseous pollutants also shows potential as an emission reduction technology. The challenge lies in the high concentrations of ozone required in the catalytic process, which increases costs and complexity, hindering widespread adoption. Industrial electrostatic precipitators (ESPs) powered by high-voltage sources can produce ozone during operation, potentially causing environmental pollution if not managed. This study suggests utilizing a catalyst in the low-concentration ozone environment generated by an ESP for the catalytic oxidation of Hg0 in flue gas. The removal efficiency of Hg0 by either the catalyst alone or ozone alone (O3: 10 ppm) is modest at 43 % and 8 % respectively. However, when combined, the catalyst and ozone demonstrate a remarkable removal efficiency of over 98 %, significantly outperforming their individual capabilities. Furthermore, this process exhibits consistent high efficiency in a wide temperature range of 50–150 ℃. The study reveals that in the absence of O3, adsorbed oxygen acts as the primary oxidant, limiting the oxidation of Hg0. The introduction of O3 enhances electron transfer within the Mn-Ti catalyst, optimizing the electronic structure of oxygen and enhancing the oxidizing capacity of lattice oxygen, resulting in superior Hg0 removal efficiency. These findings offer valuable insights for the catalytic ozonation of Hg0.

Oxalate-enhanced degradation of ranitidine in the TiO2/H2O2 system under dark conditions

The effect of oxalate on the degradation of ranitidine was investigated in the titanium dioxide (TiO2)/hydrogen peroxide (H2O2) system. The degradation of ranitidine proceeded more rapidly, with a 5.7-fold increase in the presence of oxalate. The oxalate-enhanced degradation is attributed to the higher production of hydroperoxyl radicals (HO2 ●) through the complexation of oxalate on the &gt;TiIII (&gt;TiIII(oxalate)n (2n−3)−), generated from inner-sphere electron transfer in the peroxo metal complexes (&gt;TiIV−OOH). This was confirmed by measuring the time-dependent concentrations of HO2 ●, hydroxyl radicals (●OH), and H2O2 both with and without oxalate. The results of reactive oxygen species (ROS)-quenching experiments show that both HO2 ● and singlet oxygen (1O2) are primary oxidants in the TiO2/H2O2/oxalate system. The pseudo-first-order degradation rate constants (k) for ranitidine were higher with increasing TiO2 dosage (up to [TiO2] = 1.0 g/L) and H2O2 concentration but were optimal at [oxalate] = 1 mM. Although other chelating agents, such as citrate, acetate, and malonate, also showed a positive effect on the degradation of ranitidine in the TiO2/H2O2 system, oxalate exhibited the best performance. In addition, the extent of positive effect of oxalate in the TiO2/H2O2 system was much higher than that in the tungsten oxide (WO3)/H2O2 system.

Spontaneous Oxidation in Aqueous Microdroplets: Water Radical Cation as Primary Oxidizing Agent

AbstractExploration of the unique chemical properties of interfaces can unlock new understanding. A striking example is the finding of accelerated reactions, particularly spontaneous oxidation reactions, that occur without assistance of catalysts or external oxidants at the air interface of both aqueous and organic solutions (provided they contain some water). This finding opened a new area of interfacial chemistry but also caused heated debate regarding the primary chemical species responsible for the observed oxidation. An overview of the literature covering oxidation in microdroplets with air interfaces is provided, together with a critical examination of previous findings and hypotheses. The water radical cation/radical anion pair, formed spontaneously and responsible for the electric field at or near the droplet/air interface, is suggested to constitute the primary redox species. Mechanisms of accelerated microdroplet reactions are critically discussed and it is shown that hydroxyl radical/hydrogen peroxide formation in microdroplets does not require that these species be the primary oxidant. Instead, we suggest that hydroxyl radical and hydrogen peroxide are the products of water radical cation decay in water. The importance of microdroplet chemistry in the prebiotic environment is sketched briefly and the role of partial solvation in reaction acceleration is noted.

Spontaneous Oxidation in Aqueous Microdroplets: Water Radical Cation as Primary Oxidizing Agent.

Exploration of the unique chemical properties of interfaces can unlock new understanding. A striking example is the finding of accelerated reactions, particularly spontaneous oxidation reactions, that occur without assistance of catalysts or external oxidants at the air interface of both aqueous and organic solutions (provided they contain some water). This finding opened a new area of interfacial chemistry but also caused heated debate regarding the primary chemical species responsible for the observed oxidation. An overview of the literature covering oxidation in microdroplets with air interfaces is provided, together with a critical examination of previous findings and hypotheses. The water radical cation/radical anion pair, formed spontaneously and responsible for the electric field at or near the droplet/air interface, is suggested to constitute the primary redox species. Mechanisms of accelerated microdroplet reactions are critically discussed and it is shown that hydroxyl radical/hydrogen peroxide formation in microdroplets does not require that these species be the primary oxidant. Instead, we suggest that hydroxyl radical and hydrogen peroxide are the products of water radical cation decay in water. The importance of microdroplet chemistry in the prebiotic environment is sketched briefly and the role of partial solvation in reaction acceleration is noted.

Modeling the Role in pH on Contaminant Sequestration by Zerovalent Metals: Chromate Reduction by Zerovalent Magnesium.

The role of pH in sequestration of Cr(VI) by zerovalent magnesium (ZVMg) was characterized by global fitting of a kinetic model to time-series data from unbuffered batch experiments with varying initial pH values. At initial pH values ranging from 2.0 to 6.8, ZVMg (0.5 g/L) completely reduced Cr(VI) (18.1 μM) within 24 h, during which time pH rapidly increased to a plateau value of ∼10. Time-series correlation analysis of the pH and aqueous Cr(VI), Cr(III), and Mg(II) concentration data suggested that these conditions are controlled by combinations of reactions (involving Mg0 oxidative dissolution and Cr(VI) sequestration) that evolve over the time course of each experiment. Since this is also likely to occur during any engineering applications of ZVMg for remediation, we developed a kinetic model for dynamic pH changes coupled with ZVMg corrosion processes. Using this model, the synchronous changes in Cr(VI) and Mg(II) concentrations were fully predicted based on the Langmuir-Hinshelwood kinetics and transition-state theory, respectively. The reactivity of ZVMg was different in two pH regimes that were pH-dependent at pH < 4 and pH-independent at the higher pH. This contrasting pH effect could be ascribed to the shift of the primary oxidant of ZVMg from H+ to H2O at the lower and higher pH regimes, respectively.

Ozonation of dioxolanes in water: Kinetics, transformation mechanism, and toxicity

Dioxolanes, which are structural analogs to dioxane, are emerging persistent mobile organic contaminants. These compounds are frequently detected in water and wastewater, but their removal has been rarely addressed in the literature. This work systematically investigated the ozonation of two representative dioxolanes, i.e., 1,3-dioxolane (1,3-D) and 2-methyl-1,3-dioxolane (2-M-1,3-D). The degradation rates of two dioxolanes exhibited a positive correlation with both ozone dosage and solution pH increment. Specifically, direct ozone oxidation dominates the degradation of dioxolanes at slightly acidic pH, while hydroxyl radical (•OH) becomes the primary oxidant under weak alkaline condition. The second-order reaction rate constants of ozone with 1,3-D and 2-M-1,3-D were determined to be 5.48 and 8.00 M−1s−1, respectively. The reaction rate constants with •OH were 9 orders of magnitude higher, reaching (3.75-8.18) × 109 and (2.65-5.78) × 109 M−1s−1 for 1,3-D and 2-M-1,3-D, respectively. A kinetic model involving 112 reactions well simulated the degradation of 1,3-D and 2-M-1,3-D under various conditions accordingly. Eight transformation products were identified totally, and seven of them (i.e., formic acid, acetic acid, oxalic acid, formaldehyde, acetaldehyde, glyoxylic acid, and 1,2-ethanediol monoacetate) were quantified. The observed evolution of these identified degradation products concludes that the degradation of 1,3-D and 2-M-1,3-D during ozonation mainly involves H-abstraction, dimerization, ring opening, disproportionation, and hydrolysis. This work not only provides essential kinetic data of dioxolanes, but also sheds light on their potential transformation mechanisms and aquatic environment risks during ozonation process.

Polyglucuronic acids prepared from α-(1 → 3)-glucan by TEMPO-catalytic oxidation

2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO)-catalytic oxidation was applied to a water-insoluble α-(1 → 3)-glucan in water at pH 10 and room temperature (∼24 °C), with solid NaOCl·5H2O as the primary oxidant. Oxidation with NaOCl at 15 mmol/g gave a water-soluble TEMPO-oxidized product at a mass recovery ratio of 97 %. The carboxy content of the TEMPO-oxidized product was 5.3 mmol/g, which corresponds to a degree of C6-oxidation (DO) of 93 %. A new water-soluble α-(1 → 3)-polyglucuronic acid with a nearly homogeneous chemical structure was therefore quantitatively obtained. X-ray diffraction and solid-state 13C NMR spectroscopic analyses showed that the original α-(1 → 3)-glucan and its TEMPO-oxidized product with a carboxy content of 5.3 mmol/g had crystalline structures, whereas the oxidized products with DOs of 50 % and 66 % had almost disordered structures. The carboxy groups in the oxidized products were regioselectively methyl esterified with trimethylsilyl diazomethane, and analyzed by using size-exclusion chromatography with multi-angle laser-light scattering and refractive index detections. The results show that the original α-(1 → 3)-glucan and its oxidized products with DOs of 50 %, 66 %, and 93 % had weight-average degrees of polymerization of 671, 288, 54, and 45, respectively. Substantial depolymerization of the α-(1 → 3)-glucan molecules therefore occurred during catalytic oxidation, irrespective of the oxidation pH.

Degradation of humic acid by UV/PMS: process comparison, influencing factors, and degradation mechanism.

In natural water bodies, humic acid (HA), generated during the chlorination disinfection process at water treatment plants, can produce halogenated disinfection by-products, increasing the risk to drinking water safety and posing a threat to human health. Effectively removing HA from natural waters is a critical focus of environmental research. This study established a synergistic ultraviolet/peroxymonosulfate (UV/PMS) system to remove HA from water. It compared the efficacy of various UV/advanced oxidation processes (AOPs) on HA degradation, and assessed the influence of different water sources, initial pH, oxidant concentration, and anions (HCO3 -, Cl-, NO3 -) on HA degradation. The degradation mechanism of HA by the UV/PMS process was also investigated. Results showed that under the conditions of 3 mmol L-1 PMS concentration, 10 mg L-1 HA concentration, initial solution pH of 7, and a reaction time of 240 minutes, the mineralization rate of HA by UV/PMS reached 94.15%. The pseudo-first-order kinetic constant (k obs) was 0.01034 and the single-electric energy (EE/O) was 0.0157 kW h m-3, indicating superior HA removal efficiency compared to other systems. Common anions (HCO3 -, Cl-, NO3 -) in water were found to inhibit the degradation of HA, and acidic conditions were more conducive to HA removal, with the optimal pH being 3. Free radical quenching experiments showed that both sulfate radical (SO4 -˙) and hydroxyl radical (˙OH) radicals were involved in HA degradation, with SO4 -˙ being the primary oxidant and ˙OH as the auxiliary species. Analyses using 3D-excitation-emission matrix (EEM), parallel factor analysis (PARAFAC), specific fluorescence index, and absorbance demonstrated that UV/PMS technology could effectively degrade HA in water. This study provides theoretical references for further research on the removal of HA and other organic substances using UV/PMS technology.

Aerobic self-photooxidation of arylphosphines studied by steady state and laser flash photolyses

Arylphosphines (ArP) undergo UV-photodecomposition with quantum yields of 2 in aerated acetonitrile to form the corresponding oxides (ArPO). Laser flash photolysis studies showed that triplet ArP was quenched by the dissolved oxygen. Based on these results, it was concluded that singlet oxygen produced by triplet energy transfer from triplet ArP is involved as the primary oxidant in the formation of ArPO upon photolysis of ArP. We discuss the mechanism for forming ArPO upon photolysis of ArP with the over-unity quantum yield by considering phosphadioxiranes of ArP as the secondary oxidant.

Oxidation of organic pollutants over MnO2 in cold water assisted by peroxydisulfate

MnO2 can be used in advanced oxidation processes to activate peroxydisulfate (PS) and generate reactive species such as sulfate radicals (SO4•-), hydroxyl radicals (•OH) and singlet oxygen (1O2) for the abatement of organic water contaminants. Alternatively, one can use MnO2 as particulate oxidant which, in contrast to PS, is active already at low temperatures. This low-temperature activity is particularly attractive for in situ groundwater treatment. The roles of PS and MnO2 as oxidant and catalyst, respectively, may invert: MnO2 functions as primary oxidant and PS works as re-oxidant of reduced Mn-oxides. In this way, the limited oxidation capacity of particulate MnO2 can be overcome. So far, such reaction systems have not been extensively explored.In the present study, the degradation of 4-hydroxybenzoic acid (HBA) by PS + MnO2 was studied under various experimental conditions, by varying reaction temperature (15–45 °C), reagent concentrations, and water matrix. Both PS and MnO2 alone have the ability to effect the oxidation of HBA. In the co-presence of PS and MnO2, a fast removal of HBA from water was achieved even at low temperatures (half-life of HBA about 0.5 h with 2.4 g L-1 MnO2 at 25 °C), owing to a synergic effect between the two components.Quenching experiments indicate that the primary HBA oxidation step is a heterogeneous reaction on the MnO2 surface rather than a homogeneous reaction driven by SO4•- or 1O2, as frequently reported in literature. This is in line with results from the PS driven oxidation of perfluorooctanoic acid which is not significantly enhanced in the presence of MnO2.