PS Oxidation Research Articles

The regulating mechanisms of Triton X-100 affected oxidation of PAHs in site soil aggregates using sodium citrate assisted Fe2+-persulfate

Here, we present a first investigation of the inhibition mechanism of surfactant Triton X-100 (TX-100) on the oxidation degradation of polycyclic aromatic hydrocarbons (PAHs) in site soil aggregates using sodium citrate assisted Fe2+-activated persulfate (SC/Fe2+/PS). First, TX-100 was not only competed the adsorption sites of soil aggregates with PS, but also consumed PS, which inhibit the PAHs remediation rate in the TX-100 elution followed by the SC/Fe2+/PS oxidation system from 55.6 % in the oxidation system to 50.3 %. Furthermore, in the oxidation followed by elution system, PAHs was adsorbed on the iron minerals produced during the oxidation, which would be form a bound PAHs that was difficult to react with PS, and then re-eluted to the soil by the TX-100. Additionally, it was found that the oxidative and the elution efficiency of PAHs exhibited negative correlations with aggregate particle sizes. Finally, soil microorganism communities were more strongly changed by SC/Fe2+/PS oxidation and PAHs concentration than that of TX-100 elution, with obvious alterations bacteria than fungi, the effects of SC/Fe2+/PS and PAHs concentration on microorganism communities were opposite. This study provided a proof of regulating mechanisms for the site soil remediation using surfactants combined with the iron-PS system.

Synthesis of CaCO3 supported nano zero-valent iron-nickel nanocomposite (nZVI-Ni@CaCO3) and its application for trichloroethylene removal in persulfate activated system

Nano zero-valent (nZVI) based composite have been widely utilized in environmental remediation. However, the rapid agglomeration and quick deactivation of nZVI limited its application on large scale. In this work, CaCO3 supported nZVI-Ni catalyst, namely nZVI-Ni@CaCO3 was prepared and used for the efficient removal of trichloroethylene (TCE) in PS oxidation process. The successful disbursement of nZVI-Ni on CaCO3 support material not only increased the surface area of nZVI-Ni@CaCO3 (69.45 m2/g) with respect to CaCO3 (5.92 m2/g) and bare nZVI (13.29 m2/g) but also improved the catalytic activity. XRD, XPS and FTIR analysis confirmed the successful formation of nZVI-Ni@CaCO3 nanoparticles. The nZVI-Ni@CaCO3 nanoparticles combined with PS had achieved complete removal of TCE (99.8%) with dosage of 36 mg/L and 1.34 mM respectively. These results showed that the use of CaCO3 as support material for nZVI-Ni could have significant influence on contaminant removal process. Scavenging and EPR tests validated the existence of SO4•–, OH• and O2•– radicals in PS/nZVI-Ni@CaCO3 system and highlighted the dominant role of SO4•– radicals in TCE removal process. HCO3ˉ ions and humic acid have shown adverse effect on TCE removal due to radical scavenging and buffering effect. Owing to improved catalytic activity and easy preparation, the nZVI-Ni@CaCO3 nanoparticles could be served as an alternative strategy for environmental remediation.

Carbonized eggshell membranes as highly active co-catalyst with Fe3+/persulfate for boosting degradation of carbamazepine by accelerating Fe3+/Fe2+ cycle

The sluggish Fe3+/Fe2+ cycle greatly limits the effectiveness of the Fe3+-induced persulfate (Fe3+/PS) system for degrading refractory organic pollutants. Coupling Fe3+/PS system with a co-catalyst is a promising strategy to solve this issue. Herein, we report a carbonized eggshell membrane (CESM) as a potential co-catalyst to efficiently drive Fe3+/PS oxidation. The promotion effect of the CESM on the Fe3+/Fe2+ cycle resulted in the improvement in the activity of the Fe3+/PS system to degrade carbamazepine (CBZ), with ∼100 % CBZ removal achieved with low doses of Fe3+ (1.0 mg/L) and PS (100 mg/L). Crucially, a pseudo-first-order rate constant of CESM/Fe3+/PS system was 18- and 28-times that of the Fe3+/PS and CESM/PS systems. Experimental and theoretical findings reveal that the phenolic –OH groups and carbon--center persistent free radicals in CESM are electron donors, while the nitrogen sites function as favorable Fe3+-adsorption sites. The electron transfer in CESM/Fe3+/PS system occurred between a CESM and an attached Fe3+, facilitating the generation of Fe2+ and thus contributing to the continuous activation of PS. The quenching and electron paramagnetic resonance results indicate that active oxygen radicals (O2•−,•OH and SO4•−) and Fe(IV) acted together to realize the efficient CBZ degradation. Moreover, this system exhibited good reusability and environmental adaptability in various real water matrices. The co-catalyst effect of CESM is expected to inspire the exploration of utilization of different waste-biomass-derived organic materials as co-catalysts in the Fe3+/PS system for water purification.

Comparative Stability Study of Polysorbate 20 and Polysorbate 80 Related to Oxidative Degradation.

The surfactants polysorbate 20 (PS20) and polysorbate 80 (PS80) are utilized to stabilize protein drugs. However, concerns have been raised regarding the degradation of PSs in biologics and the potential impact on product quality. Oxidation has been identified as a prevalent degradation mechanism under pharmaceutically relevant conditions. So far, a systematic stability comparison of both PSs under pharmaceutically relevant conditions has not been conducted and little is known about the dependence of oxidation on PS concentration. Here, we conducted a comparative stability study to investigate (i) the different oxidative degradation propensities between PS20 and PS80 and (ii) the impact of PS concentration on oxidative degradation. PS20 and PS80 in concentrations ranging from 0.1 mg⋅mL-1 to raw material were stored at 5, 25, and 40 °C for 48 weeks in acetate buffer pH 5.5 and water, respectively. We observed a temperature-dependent oxidative degradation of the PSs with strong (40 °C), moderate (25 °C), and weak/no degradation (5 °C). Especially at elevated temperatures such as 40 °C, fast oxidative PS degradation processes were detected. In this case study, a stronger degradation and earlier onset of oxidation was observed for PS80 in comparison to PS20, detected via the fluorescence micelle assay. Additionally, degradation was found to be strongly dependent on PS concentration, with significantly less oxidative processes at higher PS concentrations. Iron impurities, oxygen in the vial headspaces, and the pH values of the formulations were identified as the main contributing factors to accelerate PS oxidation.

Hydrodynamic cavitation degradation of hydroquinone using swirl-type micro-nano bubble reactor

ABSTRACT This study reports the degradation of hydroquinone using lab-scale hydrodynamic cavitation approach (aswirl-type micro-nano bubble reactor), which is considered a green and effective method. The effects of inlet pressure, gas flow rate, pH and initial hydroquinone concentration on hydroquinone degradation were analysed based on experimental research. After experiments investigation, it was concluded that with pH 7.38, hydroquinone concentration of 50 mg/L, and int pressure of 0.2 MPa, the degradation efficiency of hydroquinone reached 91.25% in wastewater. Furthermore, this study also investigated the degradation effect of hydroquinone wastewater by hydrodynamic cavitation combined with persulfate oxidation (HC + PS). The kinetics of hydroquinone degradation by HC or PS oxidation alone and HC + PS oxidation were also examined. Compared with the degradation method alone, the degradation of hydroquinone by HC + PS was more pronounced, and the enhancement factor was 4.55, which indicates that HC greatly enhances the oxidation capacity of PS. In additon, from viewpoint of energy consumption and operating cost, the synergy of HC + PS (1.05 mM) is also the most promising combination. Based on the detection results of the Gas chromatography-mass spectrometry (GC-MS) the possible degradation pathways of hydroquinone were analysed: under the action of ·OH and the high temperature and pressure by cavitation process, the hydroquinone molecule undergoes dehydrogenation and ring-opening reaction, demethylation and decarboxylation reaction to produce intermediate products, which are finally converted into CO2 and H2O in micro-nano bubble cavitation process.

Roles of soil active constituents in the degradation of sulfamethoxazole by biochar/persulfate: Contrasting effects of iron minerals and organic matter

The biochar/persulfate (BC/PS) has been extensively applied in the degradation of organic contaminants in the aqueous solutions. However, much less work has been done on the degradation of organic contaminants in soil by BC/PS, especially on the unclear roles of soil active constituents in the degradation. This study was conducted to investigate the degradation of sulfamethoxazole (SMX) in two soils through PS oxidation activated by biochar. Biochar was produced via the pyrolysis of peanut shell at 400 °C and 700 °C, which was denoted as BC400 and BC700, respectively. Two soils used were red soil and paddy soil, mainly differing in iron minerals and organic matter. Both biochar promoted SMX degradation (42.6 %–90.7 %) in two soils, compared to PS alone (20.9 %–41.7 %). In BC400/PS system, the free radicals were the dominant reactive species for SMX degradation, while the electron transfer pathway played a vital role in the SMX degradation by BC700/PS. Higher SMX degradation was observed in red soil (41.7 %–97.8 %) than that in paddy soil (20.3 %–94.8 %), which was ascribed to the promotion of iron minerals in red soil yet the inhibition of organic matter in paddy soil. Specifically, the reaction between ≡Fe(III)/≡Fe(II) and PS on the surface of iron minerals in red soil generated more SO4•− and •OH, resulting in the enhanced SMX degradation. However, the consumption of free radicals and suppression of electron transfer pathway by organic matter in paddy soil inhibited SMX degradation. As the comparative carbonaceous materials to biochar, graphite exerted no obvious degradation effect, whereas activated carbon exhibited the comparable promoting efficacy to BC700. Both biochar, especially BC700, significantly (p < 0.05) alleviated the adverse effects of PS treatment on wheat (Triticum aestivum L.) growth. Overall, this study demonstrates that biochar/persulfate was effective in SMX degradation in soil and the degradation was affected by soil iron minerals and organic matter, which should be paid more attention in the persulfate remediation of organic contaminated soils at a specific site.

Enhancement of synergistic effect photocatalytic/persulfate activation for degradation of antibiotics by the combination of photo-induced electrons and carbon dots

• CDs in the CDs-ZIS improves visible-light response and separation of photoinduced charges. • The electron transmission “bridge” and “reservoir” of CDs promote PS for capturing electron. • The introduction of CDs boosts the synergistic effect between photocatalysis and PS oxidation. • The Vis/CDs-ZIS/PS system exhibits the outstanding photocatalytic degradation activity of TC. Photocatalytic/persulfate-oxidation hybrid (PPSOH) system is considered as a feasible method for antibiotic degradation owing to it contains affluent active species. Herein, the flower-shaped ZnIn 2 S 4 (ZIS) nanosheets modified by carbon dots (CDs) to form CDs-ZIS composite was selected as a catalyst for degradation of tetracycline (TC) in PPOH system. The degradation experimental results reveal that the optimal photocatalytic performance of 1% Vis/CDs-ZIS/persulfate (PS) system was achieved with TC (50 mg/L) removal rate of 83% within 120 min, which is attributed to the successful introduction of CDs that can effectively combine photo-induced electrons of ZIS to co-activate PS for enhancing photocatalytic degradation of TC. The active species capturing experiments exhibit that with the unique electron transfer property of CDs, the synergistic effect between photocatalytic and persulfate-oxidation was realized, in which persulfate was captured by electrons and generated plentiful sulfate radicals (SO 4 • - ) and hydroxyl radicals (•OH). This work provides a new idea and strategy for CDs-based composite photocatalysts for the combination of photocatalysis and advanced oxidation.

A dandelion-like NiCo2O4 microsphere with superior catalytic activity as the mediator of persulfate activation for high-efficiency degradation of emerging contaminants

Nowadays efficient treatment of emerging organic contaminants is still a complex task with a big challenge. Herein, a novel dandelion-like NiCo2O4 microsphere was synthesized by a simple step-by-step self-assembly strategy, and obtained NiCo2O4 was then as an efficient heterogeneous catalyst to activate PS for rapid degradation of emerging organic pollutants. Importantly, as-prepared NiCo2O4-300 microsphere not only exhibited great catalytic activity, but also possessed excellent performance stability and structural stability. More significantly, developed NiCo2O4-300/PS oxidation system displayed strong degradation ability toward typical contaminants, including TC, IBP, SMX, BPA, DFC as well as OFX. TOC analyses revealed that these organic pollutants could eventually be degraded into H2O, CO2 and other byproducts, and wherein degradation byproducts were low toxicity or no toxicity. During the process of PS activation over NiCo2O4-300, the redox couples of Co3+/Co2+ and Ni3+/Ni2+ provided major catalytic sites, and the redox couples of Ni3+/Ni2+ played a bigger role. Furthermore, it was also found that both SO4−• and •OH were main active species in the reaction system. Even in actual water samples, proposed NiCo2O4-300/PS oxidation system still showed great performance for removing pollutants. In short, current work would provide valuable references for further research.

One-step synthesis of biochar supported nZVI composites for highly efficient activating persulfate to oxidatively degrade atrazine

• nZVI@BC composites were successfully prepared by a simple one-pot method via oxygen-limited high-temperature co-pyrolysis of the mixture of soybean straw and Fe 2 O 3 . • The as-prepared nZVI@BC effectively promotes the oxidative degradation of atrazine. • SO 4 ̇ - , ·OH, PFRs and 1 O 2 are jointly contribute to the efficient degradation of atrazine. • The oxidative degradation of atrazine is incomplete, but the toxicity is significantly reduced. Biochar supported nZVI composites (nZVI@BC) have received extensive attention due to their important application potential in the field of environmental pollution remediation. However, one-pot synthesis of nZVI@BC faces challenges. In this study, a type of nZVI@BC was successfully prepared by a simple one-pot method via oxygen-limited high-temperature co-pyrolysis of the mixture of soybean straw powder and Fe 2 O 3 . The XRD results showed that in the absence of biomass, Fe 2 O 3 is transformed into Fe 3 O 4 instead of Fe 0 . Interestingly, in the presence of biomass, a large amount of Fe 0 and a small amount of Fe 3 C are formed. Moreover, the as-designed composites could effectively activate Na 2 S 2 O 8 (PS) promoting the oxidative degradation of atrazine. A series of reaction kinetics in different systems were carried out to explore the effect of synthesis conditions, and reaction parameters on the degradation process of atrazine. And we have obtained a representative catalyst, which was produced by pyrolysis of a mixture of soybean straw and Fe 2 O 3 (mass ratio = 7:1) at 800 °C. In the representative catalyst-PS system, the atrazine removal rate was up to 93.8%, and the apparent activation energy ( E ) was calculated as 83.34 kJ/mol that is lower than that reported previously in heat-activated PS oxidation system of atrazine, demonstrating that nZVI@BC as a catalyst can effectively reduce the reaction activation energy to promote the degradation of atrazine. SO 4 ̇ - , ·OH, PFRs and 1 O 2 are jointly contribute to the degradation efficiency of atrazine. The oxidation mechanism of atrazine mainly includes 1) alkyl-oxidation, 2) de-alkylation, 3) dehydrogenation, 4) dechlorination hydroxylation, and 5) olefination.

Products distribution and contribution of (de)chlorination, hydroxylation and coupling reactions to 2,4-dichlorophenol removal in seven oxidation systems

We systemically investigated the transformation behavior of 2,4-dichlorophenol (24-DCP) in seven different reaction systems including KMnO4, heat/PS, O3, UV, Fenton, NaClO and K2FeO4 treatment. The results revealed that complete removal of 24-DCP could be reached in minutes, especially for Fe(VI), KMnO4, NaClO, Fenton and O3 system. A total of 41 products were identified by LC-MS, and 10 of them were validated using commercial and self-synthesized standards. Hydroxyl substitution and coupling reactions were commonly observed in the studied systems. Meanwhile, extra routes such as sulfate substitution, (de)chlorination and direct oxidation were also involved for certain oxidation methods. Comparisons showed that a high degree of chlorination (>90%) occurred for NaClO system, while coupling products accounted for ~45% of the removed 24-DCP under PS oxidation. Moreover, low mineralization degree together with high aquatic toxicity was attributed to the occurrence of coupling reaction, which was possibly related to the redox potential of the main oxidative species. Considering the low abundance of coupling products and the gentle reaction condition, UV irradiation is a better option for 24-DCP removal in water and wastewaters. These findings can deepen our understanding on the transformation process of 24-DCP and provide some useful information for the environmental elimination of substituted phenols.

Ferrous-activated persulfate oxidation of triclosan in soil and groundwater: The roles of natural mineral and organic matter

Contamination of antimicrobial agents such as Triclosan (TCS) in soil and groundwater possess high risk to human health and ecological systems. Present study systematically studied the degradation of TCS in soil and groundwater by Fe2+ activated persulfate (Fe2+/PS) oxidation process and special attention was paid on revealing the influence of remediation process on soil physicochemical and microbial characteristics. Experimental results demonstrated that TCS was readily degraded in soil upon Fe2+/PS oxidation system. Higher Fe2+/PS concentration and lower pH value may promote the TCS degradation. Besides added Fe2+, the naturally present Fe (III)-O and dissolved Fe from iron containing minerals may also activate PS for TCS degradation. SO4•−, HO•, R• and 1O2 were identified to be involved in the reaction system while addition of Fe2+-chelating agents, e.g., oxalic acid and ethylene diamine tetraacetic acid (EDTA) may slightly promote the degradation. Low concentration of Cl− facilitated TCS degradation and high concentration of Cl− slowed down the degradation. The presence of HCO3− may inhibit the degradation. Fe2+/PS oxidation process may partly reduce the soil organic matter content and diversely affect the composition of various C functional groups on soil. It also induced the breakdown of large soil aggregates and reduced the soil porosity, especially at macroporosity region. Phospholipid Fatty Acid test indicated that soil microbial community structure has been altered and the actinomycetes, fungi and Gram-negative bacteria decreased largely. The feasibility of remediation of TCS using Fe2+/PS oxidation in various natural groundwater samples was evaluated. Finally, five degradation intermediates of TCS by Fe2+/PS oxidation in soil were enriched by solid phase extraction and were identified by liquid chromatography-triple quadrupole mass spectrometry for proposing detailed transformation pathways.

Persulfate-mediated Photocatalytic Degradation of Ciprofloxacin in Water Using Ultraviolet Light and Zero-valent Aluminum

Aims: The study aimed at assessing the effectiveness of the PS/UV-C, PS/ZVA and PS/ZVA/UV-C processes in terms of ciprofloxacin, a fluoroquinolone type commercially important antibiotic, and toxicity abatements in raw surface water (RSW) and distilled water (DW). Background: The occurrence of ciprofloxacin (CIP), the most widely prescribed second-generation fluoroquinolone antibiotic, even at trace level (ng/L) gives rise to antibiotic resistant bacteria and resistance genes, which can further impair the selection of genetic variants of microorganisms and impose adverse effect on human health. Objective: The degradation and detoxification of ciprofloxacin with UV-C (PS/UV-C) and ZVA (PS/ZVA) activated PS oxidation systems were investigated in distilled water (DW) and raw (untreated) surface water (RSW) samples. Moreover, CIP degradation with the PS/ZVA/UV-C heterogeneous photochemical treatment combination was also studied. Methods: The process performances of the investigated treatment systems were evaluated in terms of CIP abatement and PS consumption rates as well as dissolved organic carbon (DOC) removal efficiencies. The influence of common inorganic ions and natural organic matter (NOM) on CIP degradation was evaluated. Radical quenching experiments were conducted using probe compounds in order to elucidate the dominant reaction mechanism. In addition, acute toxicity of the original CIP and its degradation products were questioned by employing Vibrio fischeri (V. fischeri), the marine photobacterium, under optimized treatment conditions. Results: CIP was completely degraded in distilled water (DW) and raw (untreated) surface water (RSW) samples after 15 min of treatment with the PS/UV-C process (PS=0.25mM; pH=3; UVC= 2.7W/m2). PS/UV-C experiments conducted with RSW at its natural pH (=8.5) resulted in 98% CIP and practically no DOC removal whereas 56% DOC was removed at pH 3 after 120 min. Radical quenching studies revealed that sulfate radicals prevailed over hydroxyl radicals. CIP degradation was significantly inhibited by the presence of humic acid due to the effect of UV absorption and free radical quenching. Acute toxicity tests with V. fischeri exhibited fluctuating trends throughout the investigated processes and did not change appreciably after 120 min of oxidation. Conclusion: The results of this study demonstrated that PS/UV-C is superior to the PS/ZVA and PS/ZVA/UV-C treatment systems for both DW and RSW samples in terms of CIP removal rates. No additional positive effect was evident for simultaneous catalytic and photochemical PS activation (PS/ZVA/UV-C treatment system). It could be also demonstrated that the selected oxidation processes conducted in pure water might give an idea about the advanced treatment systems but realistic conditions with actual water/wastewater matrices still need to be further investigated to verify their feasibility and ecotoxicological safety.

Paper mill wastewater treatment by Fe2+ and heat‐activated persulfate oxidation: Process modeling and optimization

AbstractThis study investigated Chemical Oxygen Demand (COD) and turbidity removal from paper mill industry wastewater via Fe2+/heat‐activated persulfate oxidation. A mathematical model was developed, and the process variables (pH, reaction time, PS/COD, Fe2+ concentration for Fe2+‐activated PS, and temperature for heat‐activated PS) were optimized using the Response Surface Methodology and Central Composite Design methods. Under the optimum conditions, respectively, 70.9 and 99.4% COD and turbidity removal efficiencies were obtained for Fe2+‐activated PS oxidation, while 56.1 and 98.9% COD and turbidity removal efficiencies were determined for heat‐activated PS oxidation. The results indicated that both processes are efficient for paper mill industry wastewater treatment, and central composite design is an appropriate method for designing and optimizing process parameters.

Fe (II)-activated persulfate oxidation effectively degrades iodoform in water: Influential factors and kinetics analysis

Iodoform (CHI3) is one of the disinfection by-products (DBPs) that is formed in the pre-oxidation and disinfection processes of drinking water treatment. In this study, Fe(II)-activated persulfate oxidation (Fe2+/PS) was employed to degrade iodoform, the effects of initial reactants concentration, reaction parameters, kinetics model were investigated, and the underlying mechanisms of CHI3 degradation in Fe2+/PS oxidation process was unveiled. The results showed that the mole ratio Fe2+/PS of 1:5, initial PS concentration of 15 μmmol/L, and pH of 3.0 were identified as the optimum operating parameters. In addition, a relatively higher temperature could enhance CHI3 removal and deiodination. The kinetic model has two different reaction steps: a fast one during the first ten minutes of reaction; then followed by a much slower one. Suppression of the reaction by TBA and MeOH showed that the combined effects of SO4−· and ·OH contributed to the degradation of CHI3, but ·OH played a dominant role. The degradation pathways and the products of total liberated iodine species demonstrate that the applicability of the Fe2+/PS oxidation process for CHI3 degradation. These results indicated that the Fe2+/PS oxidation process is an effective advanced oxidation process for CHI3 removal in water treatment.

Sulfur-centered hemi-bond radicals as active intermediates in S-DNA phosphorothioate oxidation.

Phosphorothioate (PS) modifications naturally appear in bacteria and archaea genome and are widely used as antisense strategy in gene therapy. But the chemical effects of PS introduction as a redox active site into DNA (S-DNA) is still poorly understood. Herein, we perform time-resolved spectroscopy to examine the underlying mechanisms and dynamics of the PS oxidation by potent radicals in free model, in dinucleotide, and in S-oligomer. The crucial sulphur-centered hemi-bonded intermediates -P–S∴S–P- were observed and found to play critical roles leading to the stable adducts of -P–S–S–P-, which are backbone DNA lesion products. Moreover, the oxidation of the PS moiety in dinucleotides d[GPSG], d[APSA], d[GPSA], d[APSG] and in S-oligomers was monitored in real-time, showing that PS oxidation can compete with adenine but not with guanine. Significantly, hole transfer process from A+• to PS and concomitant -P–S∴S–P- formation was observed, demonstrating the base-to-backbone hole transfer unique to S-DNA, which is different from the normally adopted backbone-to-base hole transfer in native DNA. These findings reveal the distinct backbone lesion pathway brought by the PS modification and also imply an alternative -P–S∴S–P-/-P–S–S–P- pathway accounting for the interesting protective role of PS as an oxidation sacrifice in bacterial genome.

Degradation of diatrizoate in water by Fe(II)-activated persulfate oxidation

As a type of iodinated contrast medium (ICM), the diatrizoate (DTZ) found in aquatic systems has posed a serious threat to the ecosystem and to human health. In this study, Fe(II)-activated persulfate (Fe2+/PS) oxidation was employed to degrade DTZ, and the optimal operating conditions were determined. Electron paramagnetic resonance (EPR) spectra and density functional theory (DFT) calculations were adopted to determine the dominant radicals and analyze the degradation paths, respectively. It was found that a PS concentration of 10 mmol/L, an n(Fe2+)/n(PS) ratio of 1:10, an initial pH of 3.0, and a high temperature increased the degradation efficiency of DTZ. After suppression of the oxidation process by tertiary butyl alcohol (TBA) and methanol (MtOH), the EPR spectra demonstrated that DTZ degradation was attributed to the combined effects of SO4− and OH and that OH played a more important role. Based on the theoretical calculation and comparison of the reduction energies of possible degradation products, the path from DTZ to TP630 and then to TP628 and finally to TP602 was recognized as the main DTZ degradation pathway during the Fe2+/PS oxidation process. These findings validated and demonstrated that DTZ could be effectively degraded by Fe2+/PS oxidation, which is a promising approach to remove DTZ from water.

Degradation of the flame retardant triphenyl phosphate by ferrous ion-activated hydrogen peroxide and persulfate: Kinetics, pathways, and mechanisms

The efficacies of ferrous ion-activated hydrogen peroxide (Fe2+/H2O2, Fenton) and persulfate (Fe2+/S2O82−, Fe2+/PS) processes for degrading triphenyl phosphate (TPhP) in aqueous solutions were systemically investigated and compared. Both Fenton and Fe2+/PS processes can effectively degrade TPhP in water. A fast TPhP degradation was achieved in 5 min by Fenton oxidation, while TPhP was gradually degraded with prolonging reaction time via Fe2+/PS oxidation. The effects of operating parameters, including oxidant and Fe2+ dosage, pH, and water constitutes, on TPhP degradation were systemically evaluated. TPhP removal was increased as the oxidant and Fe2+ dosage increase, while TPhP degradation was not greatly changed under the examined pH (4.0–9.0). Water constitutes, humic acid, and anions (Cl− and NO3−) did not obviously influence TPhP degradation for both processes. However, HCO3− significantly inhibited TPhP oxidation, and the inhibition was inversely related to HCO3− concentrations. Radical quenching experiments and electron paramagnetic resonance spectrometry revealed that HO was the dominant radical in Fenton process whereas SO4− played a dominant role in Fe2+/PS process for TPhP degradation. Moreover, TPhP removal in various natural water matrices was examined to better understand the feasibility of AOPs on the elimination of TPhP from natural waters. The lower removal of TPhP indicates that both of high oxidant dosage and/or long reaction time were required to achieve high removal efficiency and high mineralization. Furthermore, TPhP degradation products were identified through LC-MS/MS technology. Similar products were observed in both oxidation processes, and the degradation pathways mainly involved hydroxylation and phenoxy bond cleavage. The results of this study indicates that it is technically feasible for applying HO and SO4− based AOPs to treat TPhP contamination in water/wastewater.

Treatment of dinitrodiazophenol industrial wastewater in heat-activated persulfate system.

Heat-activated persulfate oxidation process was investigated as the treatment of dinitrodiazophenol industrial wastewater to degrade refractory pollutants and improve biodegradability. By studying the effects of 4 factors and carrying out orthogonal tests and scale-up experiments, optimal treatment conditions (temperature 90 °C, reaction time 75 min, PS dosage 20.0 g L−1 and initial pH ∼2.0) were obtained. The results showed that under these conditions, COD and color removal efficiencies were 99.22% and 99.99%, respectively. Moreover, an increase in BOD5/COD ratio (from 0 to 0.31) indicates significantly improved biodegradability. Dinitrodiazophenol dosage was measured by high performance liquid chromatography, which showed that dinitrodiazophenol removal efficiency reached 99.99%. Furthermore, the degradation process was analyzed by ultraviolet-visible spectra and Fourier transform infrared spectra. The former demonstrated that aromatic compounds in the system were destroyed during mineralization and the latter indicated that nitro groups on the benzene ring could be oxidized to nitrate. After verification test of the free radicals, mechanism of heat-activated persulfate system was assumed to be that SO4˙− and ·OH function together and SO4˙− predominate. To conclude, the heat-activated PS oxidation technology performs effectively in treatment of DDNP wastewater and expands applications of sulfate-radical-based advanced oxidation technology in industrial-wastewater treatment.

Transformation of iodide and formation of iodinated by-products in heat activated persulfate oxidation process

Formation of halogenated disinfection by-products (DBPs) in sulfate radical-based advanced oxidation processes (SR-AOPs) have attracted considerable concerns recently. Previous studies have focused on the formation of chlorinated and brominated DBPs. This research examined the transformation of I− in heat activated PS oxidation process. Phenol was employed as a model compound to mimic the reactivity of dissolved natural organic matter (NOM) toward halogenation. It was found that I− was transformed to free iodine which attacked phenol subsequently leading to iodinated DBPs such as iodoform and iodoacetic acids. Iodophenols were detected as the intermediates during the formation of the iodoform and triiodoacetic acid (TIAA). However, diiodoacetic acid (DIAA) was formed almost concomitantly with iodophenols. In addition, the yield of DIAA was significantly higher than that of TIAA, which is distinct from conventional halogenation process. Both the facts suggest that different pathway might be involved during DIAA formation in SR-AOPs. Temperature and persulfate dose were the key factors governing the transformation process. The iodinated by-products can be further degraded by excessive SO4− and transformed to iodate. This study elucidated the transformation pathway of I− in SR-AOPs, which should be taken into consideration when persulfate was applied in environmental matrices containing iodine.

Ultrafast, Light-Induced Electron Transfer in a Perylene Diimide Chromophore-Donor Assembly on TiO2.

Surface-bound, perylenediimide (PDI)-based molecular assemblies have been synthesized on nanocrystalline TiO2 by reaction of a dianhydride with a surface-bound aniline and succinimide bonding. In a second step, the Fe(II) polypyridyl complex [Fe(II)(tpy-PhNH2)2](2+) was added to the outside of the film, also by succinimide bonding. Ultrafast transient absorption measurements in 0.1 M HClO4 reveal that electron injection into TiO2 by (1)PDI* does not occur, but rather leads to the ultrafast formation of the redox-separated pair PDI(•+),PDI(•-), which decays with complex kinetics (τ1 = 0.8 ps, τ2 = 15 ps, and τ3 = 1500 ps). With the added Fe(II) polypyridyl complex, rapid (<25 ps) oxidation of Fe(II) by the PDI(•+),PDI(•-) redox pair occurs to give Fe(III),PDI(•-) persisting for >400 μs in the film environment.