Search

Recently, graphitized carbon nitride (g-C 3 N 4) is widely used as a metal-free photocatalyst for photocatalytic hydrogen peroxide (H 2 O 2) generation. However, its photocatalytic activity still suffers from the poor separation efficiency of charge carrier and weak adsorption ability towards dioxygen. Herein, a series of polydopamine (PDA) surface-modified g-C 3 N 4 composites (CNPX) are successfully fabricated through a self-assembled method. The optimum material, i.e. CNP40, produced H 2 O 2 of 69.0 μM/L under visible-light irradiation for 3 h, demonstrating 4.6-fold higher activity in comparison with the pristine g-C 3 N 4. Meanwhile, the apparent quantum yield (AQY) reached as high as 1.91% over CNP40 under monochromatic irradiation of 420 nm, which is 6.2-fold higher than CN. It is identified that the remarkably increased photocatalytic activity is contributed to the significantly promoted charge separation and dioxygen adsorption. This present work could provide a novel environmental-friendly material for the efficient photocatalytic H 2 O 2 production. • Loading PDA with various thickness on the surface of g-C 3 N 4 through simply adjusting the polymerization time of DA. • PDA's loading introduces rich hydroxyl group on the surface of CN/PDA-X catalyst. • The introduced hydroxyl group simultaneously promote charge-carriers separation and dioxygen adsorption. • The AQY over CN/PDA-40 reach as high as 1.91% at 420 nm, being 6.2 times higher than the pristine g-C 3 N 4. [ABSTRACT FROM AUTHOR]

In order to enhance the Fenton oxidation of 2,4,6-trichlorophenol, copper ion was introduced to the Fenton reaction. The results show that, differing from ferrous ion, the copper ion exhibits no capability to decompose hydrogen peroxide to degrade the organic substrates; however, it can accelerate the degradation rate of 2,4,6-trichlorophenol by Fenton reaction, enhance the decomposition of hydrogen peroxide, increase the removal efficiency of TOC and release of chloride ion. Even lower copper ion dosage have significant enhancement on the degradation. The result of complete inhibition of the reaction by methanol and tert-Butanol suggests that hydroxyl radical is the most important reactive species in the Cu2+ enhanced Fenton reaction. [ABSTRACT FROM AUTHOR]

Removal of phosphate in secondary effluents was investigated in presence of Fe2+/H2O2. The effect of H2O2-dose, Fe-dose and initial phosphate concentration were assessed. The results indicated that Fe2+/H2O2 could greatly increase the removal of phosphate compared with those achieved by Fe2+ alone. For initial phosphate concentration of 0.97–3.75mg P/L, phosphate removal rates of 50–60% were observed at 1:1 molar addition of Fe(II). However, a 125% excess of Fe-dose was necessary for complete phosphate removal. The experimental data demonstrated that removal of phosphate with Fe2+/H2O2 was higher than that observed with ferric coagulation alone. This fact suggested that in situ formed Fe(III) having much affinity for ligand phosphate. Chemical co-precipitation was considered as the dominant mechanism about phosphate removal in presence of Fe2+/H2O2. The electron paramagnetic resonance (EPR) spectra tests in secondary effluents showed that Fe2+/H2O2 could produce an increasing hydroxyl radical concentration with a decrease in both H2O2 dosage and phosphate concentration. Fe2+/H2O2 had the potential to be utilized for removal of phosphate due to the lower cost and the higher phosphate removal capability. [Copyright &y& Elsevier]

To better predict the elimination of highly ozone-refractory organic micro-pollutants from wastewater in ozonation and peroxone (O 3 /H 2 O 2 ) processes, it is important to understand the OH formation therein. Nevertheless, the contribution of the propagation reactions (in brief, OH + DOM (Dissolved Organic Matter) + O 2 → O 2 − , O 3 + O 2 − → O 3 − → OH ) to the OH yields ( Ф ) in these two processes has not received great attention so far. In this study, >25% of O 3 was estimated to be consumed via the propagation reactions in ozonation of wastewater effluents. The competition method (taking the OH exposure and scavenging capacity of water matrix into account) was recommended to determine the Ф values, and thus the relatively higher values (i.e., 33–58% vs. 6–24%) in ozonation were obtained as compared with the “ tert- Butanol ( t BuOH) assay” (with excess t BuOH to scavenge OH producing stoichiometric formaldehyde), where the contribution of the propagation reactions was otherwise neglected when excess t BuOH completely scavenged OH . In peroxone of wastewater effluents, the rate constant of O 3 consumption increased significantly with the increase of H 2 O 2 concentration ([H 2 O 2 ]:[O 3 ] = 0.1–0.35). However, compared to ozonation alone, the improvement of the Ф values was negligible over a wide range of [H 2 O 2 ]:[O 3 ] = 0.1–2.0. This discrepancy was mainly ascribed to the fact that substantial O 3 consumption via the propagation reactions resulted in comparable Ф values in peroxone vs. ozonation processes. [ABSTRACT FROM AUTHOR]

The use of vacuum-ultraviolet (VUV) photolysis in water treatment has been gaining significant interest due to its efficacy in degrading refractory organic contaminants and eliminating oxyanions. In recent years, the reactive species driving pollutant decomposition in VUV-based advanced oxidation and reduction processes (VUV-AOPs and VUV-ARPs) have been identified. This review aims to provide a concise overview of VUV photolysis and its advancements in water treatment. We begin with an introduction to VUV irradiation, followed by a summary of the primary reactive species in both VUV-AOPs and VUV-ARPs. We then explore the factors influencing VUV-photolysis in water treatment, including VUV irradiation dose, catalysts or activators, dissolved gases, water matrix components (e.g., DOM and inorganic anions), and solution pH. In VUV-AOPs, the predominant reactive species are hydroxyl radicals (˙OH), hydrogen peroxide (H 2 O 2), and ozone (O 3). Conversely, in VUV-ARPs, the main reactive species are the hydrated electron (e aq −) and hydrogen atom (˙H). It is worth noting that VUV-based advanced oxidation/reduction processes (VUV-AORPs) can transit between VUV-AOPs and VUV-ARPs based on the externally added chemicals and dissolved gases in the solution. Increase of the VUV irradiation dose and the concentration of catalysts/activators enhances the degradation of contaminants, whereas DOM and inorganic anions inhibit the reaction. The pH influences the redox potential of ˙OH, the speciation of contaminants and activators, and thus the overall performance of the VUV-AOPs. Conversely, an alkaline pH is favored in VUV-ARPs because e aq − predominates at higher pH. [Display omitted] • VUV photolysis includes AOP driven by ˙OH, H 2 O 2 , and O 3 , and ARP driven by e aq − /˙H. • Irradiation dose, catalysts, gas, water matrix, and pH influences VUV efficacy. • VUV-AOP cost is lower than ultrasound, UV, electric AOP, plasma, and photo-Fenton. • Shallow penetration depth of VUV in water leads to full-scale treatment unworkable. • Optimizing the VUV reactor is a good way to overcome its limitations. [ABSTRACT FROM AUTHOR]

[Display omitted] • A bifunctional core–shell V O -LCO@CeO x nanoreactor was designed for H 2 O 2 activation. • Heterostructure boosted V O levels via the removal of oxygen atoms to interface. • Direct electron transfer between ≡Cu and ≡Ce achieved efficient ROS production. • The catalytic mechanism had been further confirmed through DFT calculations. Double oxygen vacancies (V O) tuned core–shell La V CuO δ @CeO x (V O -LCO@CeO x) nanoreactors with direct electron transfer (DET) structure was synthesized as an effective heterogeneous Fenton-like catalyst for the quinoline removal. The DET structure was constructed by electron-rich ≡Cu center of V O -LCO core and electron-capture center of CeO x shell for electrons supplying and consuming. This structure elevated total V O levels of catalyst through the removal of oxygen atoms in CeO 2 from attice to interface sites. Meanwhile, the ≡Ce(III) acted as reactive sites for the adsorption of hydrogen peroxide (H 2 O 2) to form surface peroxide species, and then the electron-rich ≡Cu center was further provided electrons to surface peroxide species by DET to produce hydroxyl radical. Moreover, the newly formed surface V O would also be further promote hydroxyl radical production through self-activation of H 2 O 2. This catalyst displayed excellent catalytic activity and stability. The density functional theory (DFT) results further pointed out that this structure had excellent adsorption energy, and generable electron transfer from V O -LCO to CeO x. This work provided a novel approach for the development of heterogeneous Fenton-like catalysts to degrade quinoline wastewater. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • UV/PDS is proposed to be unsuitable for treatment of bromophenols compared to UV/H 2 O 2. • Brominated polymeric products can be formed in UV-based oxidation process. • BrO 3 − evolution in the degradation of 2,4-DBP by UV/PDS exhibited biphasic kinetics. Abstract The sustained massive use of bromophenols in industrial products leads to their especially pernicious in aquatic environments. This study explored the oxidation kinetics of 2,4-bromophenol (2,4-DBP) and formation potential of bromate (BrO 3 −) and brominated polymeric products of concern during water treatment by UV/persulfate (PDS) and UV/hydrogen peroxide (H 2 O 2). 2,4-DBP exhibited appreciable reactivity toward sulfate radical (SO 4 −) and hydroxyl radical (HO). The second-order rate constants of SO 4 − and/or HO with 2,4-DBP at pH 9 were higher than those at pH 5 and 7. It is mainly due to the deprotonation of the hydroxyl group in 2,4-DBP when pH > pKa (pKa = 7.79). The chloride ions (Cl−) significantly inhibited 2,4-DBP degradation in UV/PDS process, which showed little inhibition in the UV/H 2 O 2 process. Carbonate/bicarbonate (CO 3 2−/HCO 3 −) and natural organic matters (NOM) significantly retarded 2,4-DBP degradation in both processes. BrO 3 − formation in UV/PDS process in the presence of 2,4-DBP (as organic carbon model compound) exhibited biphasic kinetics, i.e., BrO 3 − was undetectable in the lag phase and rapid generated in the secondary rapid phase. However, BrO 3 − was not detected throughout UV/H 2 O 2 process. According to the analysis by electrospray ionization-triple quadruple mass spectrometry, tentative oxidation pathway was proposed. The results showed that brominated polymeric products in the reaction of 2,4-DBP with SO 4 − and/or HO were readily produced by electrophilic addition and coupling reactions. Given the enhanced toxicological effects of these BrO 3 − and brominated polymeric products compared with the bromophenols precursors, it is important to better understand their reactivities and fates when UV/PDS or UV/H 2 O 2 is applied for the oxidative treatment of bromophenols-containing waters. [ABSTRACT FROM AUTHOR]

Abstract The frequent detection of propranolol, a widely used β-blocker, in wastewater effluents and surface waters has raised serious concern, due to its adverse effects on organisms. UV/hydrogen peroxide (UV/H 2 O 2) and UV/persulfate (UV/PDS) processes are efficient in eliminating propranolol in various waters, but the formation of oxidation products in these processes, as well as the assessment of their toxicity, has not been systematically addressed. In this study, we identified and compared transformation products of propranolol produced by hydroxyl radical (•OH) and sulfate radical (SO 4 •-). The electrostatic attraction enhances the reaction between SO 4 •- and the protonated form of propranolol, while •OH shows non-selectivity toward both protonated and neutral propranolol species. The hydroxylation of propranolol by •OH occurs at either amine moiety or naphthalene group while SO 4 •- favors the oxidation of the electron-rich naphthalene group. Further oxidation by •OH and SO 4 •- results in ring-opening products. Bicarbonate and chloride exert no effect on propranolol degradation. The generation of CO 3 •- and Cl-containing radicals is favorable to oxidizing naphthalene group. The acute toxicity assay of Vibrio fischeri suggests that SO 4 •- generates more toxic products than •OH, while CO 3 •- and Cl-containing radicals produce similar toxicity as SO 4 •-. High concentrations of bicarbonate in UV/H 2 O 2 increase the toxicity of treated solution. Graphical abstract Image 1 Highlights • Propranolol degradation is comparatively studied in UV/H 2 O 2 and UV/PDS. • CO 3.•- and Cl-containing radicals react with propranolol •.•OH induces hydroxylation of propranolol at either amine or naphthalene group • SO 4.•-, CO 3 •- and Cl-containing radicals attack the naphthalene group • SO 4.•-, CO 3 •- and Cl-containing radicals generate more toxic products than •OH [ABSTRACT FROM AUTHOR]

Enhanced ozonation degradation of para -chlorobenzoic acid ( p CBA) with the addition of peroxymonosulfate (PMS) was investigated in aqueous solution. The results demonstrated that the addition of PMS could accelerate the decomposition of O 3 by 50 times compared to that of O 3 alone, and the effect was comparable to that of hydrogen peroxide. The degradation of a typical organic contaminant p CBA, was significantly enhanced by the addition of O 3 /PMS. The mechanism behind the synergistic effect was preliminarily explored by the addition of hydroxyl and sulfate radical ( SO 4 - ) scavengers. The degradation of p CBA by O 3 /PMS could not be completely inhibited by tert -butanol, whereas it was inhibited by the addition of methanol, indicating that the effect of O 3 /PMS was primarily due to the production of a greater amount of SO 4 - . The addition of O 3 /PMS had a selective effect on various contaminants. The enhanced degradation of p CBA by O 3 /PMS was also observed in actual water samples, and provided some impetus for practical applications of the developed system. [ABSTRACT FROM AUTHOR]

• Fe(II)/NH 2 OH/PDS and Fe(II)/NH 2 OH/H 2 O 2 systems followed different kinetic rules. • Cl− had opposite effects on BA degradation in Fe(II)/NH 2 OH/PDS and Fe(II)/NH 2 OH/H 2 O 2 systems. • Cl− changed relative contents of ·OH, SO 4 ·− and Fe(IV) in Fe(II)/NH 2 OH/PDS system. • Cl− competitively consumed ·OH with target pollutants in Fe(II)/NH 2 OH/H 2 O 2 system. Hydroxylamine (NH 2 OH) has been verified to efficiently strengthen pollutants oxidation in Fe(II)/peroxydisulfate (PDS) and Fe(II)/H 2 O 2 systems. However, the different effects of hydroxylamine salts types were rarely recognized. Herein, the effects of two commonly used hydroxylamine salts (i.e. NH 2 OH·HCl and (NH 2 OH) 2 ·H 2 SO 4) on oxidation kinetics and reactive species composition were compared in Fe(II)/PDS and Fe(II)/H 2 O 2 systems for the first time. Pseudo first order kinetics could only describe benzoic acid (BA) oxidation well in Fe(II)/NH 2 OH/H 2 O 2 system, which was related to the different concentration changes of Fe(III) determined by [ Oxidant ] [ N H 3 O H + ] 2. Hydroxylamine salts types influenced not kinetic rules, but reaction rates of target compounds. The empirical reaction rate constant of BA in Fe(II)/NH 2 OH·HCl/PDS system was 141.5% of that in Fe(II)/(NH 2 OH) 2 ·H 2 SO 4 /PDS system under the same concentration of NH 2 OH (1.4 mM), while the apparent reaction rate constant in Fe(II)/NH 2 OH·HCl/H 2 O 2 system was 68% of that in Fe(II)/(NH 2 OH) 2 ·H 2 SO 4 /H 2 O 2 system. This opposite effect resulted from the differences in primary reactive species compositions and their interactions with Cl−. Reactive species identification indicated that Cl− would decrease the contribution of ferryl ion (Fe(IV)) and transform sulfate radical (SO 4 ·−) to hydroxyl radical (·OH) in Fe(II)/NH 2 OH/PDS system, while it competitively consumed the only reactive species ·OH in Fe(II)/NH 2 OH/H 2 O 2 system. This study highlights the importance of reductants types on strengthening Fenton oxidation and offers a reference for reasonable construction of the relevant systems. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: In this study, two Fenton (Fe2+/H2O2) and Fenton-like (Fe3+/H2O2) reactions were compared to clarify their roles in phenol degradation under varying H2O2 concentrations, iron dosages and pHs, as well as in the presence of radical scavenger. The results of this study showed that a Fenton-like reaction must proceed concurrently with a classic Fenton reaction, and the concurrent Fenton reaction played a major role in the degradation of pollutants. For the Fenton-like reaction, some oxidation intermediates of phenolic compounds may promote the conversion of Fe(III) to Fe(II) in addition to the uni-molecular decomposition of the Fe(III)–hydroperoxy complexes. The results also showed that varying H2O2 concentrations exerted identical effects on the two reactions, and that phenol degradation in both reactions could be correlated to the decomposition of H2O2. At low levels of iron concentration, the Fenton reaction appeared to be more efficient than the Fenton-like reaction in terms of the phenol degradation and H2O2 decomposition. Additionally, the Fenton reaction had an effective pH range of 2.5–6.0, while the Fenton-like reaction was limited to a narrow pH range of 2.8–3.8. Although the Fenton-like reaction was much slower than that of the Fenton reaction, the overall extent of phenol degradation and H2O2 decomposition at the optimal conditions was equivalent. [Copyright &y& Elsevier]

Understanding ultraviolet photolysis induced by low pressure mercury lamp that emits both 254 nm ultraviolet (UV 254) and 185 nm vacuum UV (VUV 185) is currently challenging due to the copresence of multiple direct and indirect photochemical processes involving a series of highly-reactive radicals. Herein we examined the formation and transformation of H 2 O 2 in water, which is both a precursor and a product of radicals, under various pH and dissolved oxygen (DO) conditions. The trends show that H 2 O 2 increased rapidly at early stage and then remained steady in DO-rich water or declined somewhat in DO-poor water, ultimately leading to higher steady-state H 2 O 2 in DO-rich water. The maximum H 2 O 2 contents nonetheless were similar among waters with different DO, suggesting that H 2 O 2 in this system was mostly generated by hydroxyl radical (OH) recombination, which is an oxygen-independent H 2 O 2 formation pathway, rather than by reduced oxygen via hydrogen atom (H) or hydrated electron (e aq −), which is an oxygen-dependent pathway. Increasing pH (from 6.3 to 10.0) or bicarbonate dosage dramatically decreased H 2 O 2 formation too. Mathematically, the fates of H 2 O 2 as a function of pH, DO, and time were well modeled (R2 ≥ 0.92), in which the rates of H 2 O 2 formation and destruction were greater in DO-poor water than those in DO-rich water. In addition, we found that the steady-state concentrations of OH used for degradation of p-chlorobenzoic acid, an OH probe, correlated well with the OH levels used for H 2 O 2 formation (R2 = 0.98). These results hence may help better understand the UV/VUV process via H 2 O 2 evolutions. Image 1 • The H 2 O 2 formation were found to be mainly attributed to OH recombination. • A mathematical model was established that simulates the H 2 O 2 kinetics well. • Increasing pH from 6.3 to 10.0 decreased the H 2 O 2 formation dramatically. • The steady-state H 2 O 2 in DO-rich water was greater than that in DO-poor water. • OH] degrading p-CBA matched well with [.•OH] yielding H 2 O 2 (R2 = 0.98). [ABSTRACT FROM AUTHOR]