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Few researches have focused on the role of nanoscale zero‐valent iron (nZVI) in Fenton‐like process for polycyclic aromatic hydrocarbons (PAHs) removal. In this study, the naphthalene (NAP) degradation tests in ultrapure water showed that nZVI addition could enhance NAP degradation from 79.7% to 99.0% in hydrogen peroxide (H2O2)/Fe (II)/nZVI/NAP system at the molar ratio of 10/5/3/1, showing the excellent role of nZVI in promoting NAP removal. Multiple linear regression analysis found that the correlation coefficient between H2O2 consumption and NAP degradation was converted from −9.17 to 0.48 with nZVI and 1‐mM H2O2, indicating that nZVI could decompose H2O2 more beneficially for NAP degradation. Multiple Fe (II)‐dosing and iron leaching tests revealed that nZVI could gently liberate Fe (II) and promote Fe (II)/Fe (III) redox cycle to enhance the NAP degradation. When the H2O2/Fe (II)/nZVI/NAP molar ratios of 10/5/3/1 and 50/25/15/1 were applied in the simulated NAP contaminated actual groundwater and soil slurry, respectively, 75.0% and 82.9% of NAP removals were achieved. Based on the major degradation intermediates detected by GC/MS, such as 1,4‐naphthalenedione, cinnamaldehyde, and o‐phthalaldehyde, three possible NAP degradation pathways were proposed. This study provided the applicable potential of nZVI in Fenton process for PAHs contaminated groundwater and soil remediation. Practitioner Points: nZVI enhanced the NAP degradation in Fenton‐like process.Three schemes of NAP degradation pathway were proposed.nZVI performed well in the remediation of the simulated NAP contamination. [ABSTRACT FROM AUTHOR]

[Display omitted] • ZVI and B-assisted nCP/Fe(III) systems could achieve efficient decontamination. • The dominant active species in the enhanced nCP/Fe(III) systems were identified. • Fe(II) was generated simultaneously by Fe(III) reduction and ZVI corrosion. • B continuously supplied electrons to Fe(III) to ensure fast Fe(II) generation. • Efficient NAP degradation in various water matrixes was achieved. Nano calcium peroxide (nCP) has attracted attention as an alternative for liquid H 2 O 2 -mediated advanced oxidation processes. However, the slow reduction kinetics of Fe(III) still significantly limit its application. Here, zero valent iron (ZVI) and amorphous boron (B) could remarkably promote the Fe(III)/Fe(II) cycle in nCP/Fe(III) system to generate various active species (HO•, O 2 −•, and 1O 2) with HO• acting as the predominant role in naphthalene (NAP) degradation. nCP/Fe(III)/ZVI process could achieve 98.2% NAP degradation and 70.6% TOC removal, compared with 97.5% NAP degradation and 56.3% TOC removal in nCP/Fe(III)/B process. ZVI could donate electrons to Fe(III) to generate Fe(II) and itself could also be corroded to release Fe(II). B was stepwise oxidized (B0 to B(I)/B(II) to B 2 O 3) and continuously supplied electrons to Fe(III) to ensure fast and long-lasting Fe(II) generation. Moreover, B 2 O 3 was dissolved as H 3 BO 3 in aqueous solution, which kept the B surface reactive for the continuous reduction of Fe(III). Although the two co-activators showed different promotion mechanisms in nCP/Fe(III) system, both systems exhibited excellent NAP degradation performance in different experimental conditions and various water matrixes. Overall, this study provided the strategies to overcome the limitation of nCP/Fe(III) system and extended its application potential in contaminants remediation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Over 90% NAP could be removed in PDS/Fe(II)/CaSO 3 and PMS/Fe(II)/CaSO 3 systems. • The enhancement mechanism of CaSO 3 on the removal of NAP was illuminated. • SO 4 − was the dominant ROS for NAP degradation in CaSO 3 -enhanced systems. • NAP degradation intermediates and pathways were elucidated. • The applicability of CaSO 3 -enhanced systems in various water matrixes was assessed. Na 2 SO 3 and NaHSO 3 have been widely used as the source of SO 3 2− to participate in the reproduction of Fe(II) in iron-based advanced oxidation processes. In this work, CaSO 3 with low solubility was innovatively introduced and compared with Na 2 SO 3 and NaHSO 3 to investigate their effects on naphthalene (NAP) degradation in Fe(II)-activated peroxydisulfate (PDS) and peroxymonosulfate (PMS) processes. The results showed that CaSO 3 displayed a better performance due to its sustained-release of SO 3 2−, and NAP removal increased from 57.6% and 77.7% to 91.4% and 98.5% in PDS/Fe(II) and PMS/Fe(II) processes, respectively, with the addition of CaSO 3. The enhancement mechanisms of CaSO 3 were illustrated by measuring the variation of iron and SO 3 2− concentrations and by quantitatively determining the production of reactive oxygen species (ROS). The dominant ROS generated in CaSO 3 -enhanced systems was confirmed by scavenging tests. Moreover, NAP degradation intermediates and pathways, as well as the toxicological properties of intermediates, were accordingly elucidated. Finally, CaSO 3 -enhanced systems had a wide application range of pH, and exhibited a great performance on the tolerance of various water matrixes. The significant removal of various contaminants in CaSO 3 -enhanced processes confirmed that these techniques are suitable for the remediation of organic contaminated groundwater. [ABSTRACT FROM AUTHOR]

• nCP/FeS 2 /CA system could degrade over 90% NAP at a wide pH range of 3–9. • Reductive sulfur species and citric acid played a vital role in Fe(II) regeneration. • nCP/FeS 2 /CA system achieved over 90% of NAP removal in various water matrixes. • Mechanisms of NAP degradation in nCP/FeS 2 /CA system were explored in detail. • NAP degradation intermediates were successfully detoxified. In this research, pyrite was applied in synergy with citric acid for the activation of homemade nano-calcium peroxide to degrade naphthalene in aqueous solution. Results showed that over 90% of naphthalene could be removed within 180 min at a pH range of 3–9 due to the proton-releasing ability of pyrite. Hydroxyl radical, alkyl radical, and singlet oxygen were all detected by electron paramagnetic resonance spectra, with hydroxyl radical playing a dominant role in naphthalene degradation. The nano-calcium peroxide was mainly activated by Fe(II) leached from pyrite in homogeneous ways and the vital role of Fe(III) was also revealed. The superior naphthalene degradation in this system was attributed to the excellent electron-donating capacity of reductive sulfur species in Fe(II)/Fe(III) cycle and the increased concentration of available iron species by the chelating effect of citric acid. Meanwhile, the system showed high tolerance to complex water matrixes and excellent degradation performance for other polycyclic aromatic hydrocarbons and chlorinated olefins. In addition, the naphthalene degradation pathways and the toxicity of detected intermediates were investigated. This research revealed the mechanism of nano-calcium peroxide activation by pyrite coupled with citric acid and demonstrated the great application potential of this system in the treatment of polluted groundwater. [ABSTRACT FROM AUTHOR]

[Display omitted] • The homogeneous reaction played a dominant role in H 2 O 2 /FeS 2 /NAP system. • FeS 2 performed best compared with S-nZVI and FeS. • Sulfur intermediates from FeS 2 facilitated the iron redox cycle. • FeS 2 performed well in complex environment conditions. Fe-containing natural minerals, such as pyrite, have been conducted an extensive study in Fenton-like processes, however, answers for the role of homogeneous and heterogeneous reactions and their application potentials need to be theoretically demonstrated. In this study, the performance and mechanism of Fenton-like process catalyzed by pyrite were investigated by surface characterizations and degradation experiments using naphthalene as a target contaminant. First, the major role of homogeneous reaction in the naphthalene degradation in H 2 O 2 /pyrite system was confirmed by iron determination and iron quenching tests, where 2,2′-bipyridine was used as the iron quencher. Second, it was clarified that sulfur species including polysulfides, elemental sulfur, and thiosulfate facilitated the Iron redox cycle and the yield of reactive oxygen species, thus enhanced the degradation of naphthalene. Moreover, compared with sulfidated nanoscale zero valent iron and ferrous sulfide, pyrite exhibited superiority in naphthalene degradation due to higher reaction stoichiometry efficiency (0.31) and lower running cost (77 RMB (kg naphthalene)−1). Finally, pyrite showed excellent performance for various pollutants removal and in multiple water environments. This work provides the underlying mechanisms of H 2 O 2 /pyrite process and a solid step forward to pyrite application in the remediation of naphthalene contaminated water. [ABSTRACT FROM AUTHOR]

In this work, the effect of different desorbents (low molecular weight organic acids (LMWOAs), surfactants, and inorganic salts) on naphthalene (NAP) desorption in soil was investigated, and the results showed that NAP desorption pattern fitted the pseudo-second-order kinetics. The addition of LMWOAs, especially citric acid (CA), could stimulate the reactive oxygen species (ROS) generation and NAP degradation in Fe(II) activated persulfate (PS) system, while the presence of surfactants and CaCl 2 could inhibit the NAP removal due to the competitive consumption of ROS. The maximum removal of NAP was 97.5% within 120 min at the PS/Fe(II)/CA/NAP molar ratio of 15/5/1/1, and the pseudo-first-order kinetic constant of NAP removal increased from 0.0110 min−1 to 0.0783 min−1 with the addition of CA. Compared with surfactants and inorganic salts, LMWOAs, especially CA, were more suitable as desorbent in soil washing coupled with in situ chemical oxidation technique. Moreover, 1.86 mg L−1 desorbed amount and 36.1% removal of NAP from soil could be obtained with the presence of 1 mM CA. Finally, the significant removal of NAP and other contaminants (phenanthrene, fluoranthene, and benzene series) in actual groundwater could provide theoretical basis and technical support for the remediation of organic contaminated sites with desorbents. [Display omitted] This study systematically reported the performance and mechanisms of NAP desorption and degradation in the presence of three different kinds of desorbents. The kinetics of NAP desorption and degradation with desorbents were elucidated. The effect of different desorbents on NAP removal was compared and LMWOAs, especially CA, were evaluated to be the optimal desorbents in the soil washing coupled with ISCO process. The enhancement of LMWOAs for NAP degradation was further illuminated. The significant removal of NAP in actual groundwater and other contaminants (PHE, FLT, and BTEX) could provide technical support for the remediation of organic contaminated sites with desorbents. • Effect of different desorbents on NAP desorption and degradation was investigated. • The kinetics of NAP desorption and degradation with desorbents was elucidated. • SO 4 −• and HO• contributed to NAP degradation in PS/Fe(II) system with desorbents. • Effective removal of NAP in actual groundwater containing desorbents was achieved. [ABSTRACT FROM AUTHOR]

Naphthalene (NAP) has received increasing concern due to frequent detection in groundwater and harm to humans. In this study, FeS 2 was selected as a novel catalyst to activate nano calcium peroxide (nCP) for NAP degradation. Batch experiments were conducted in a 250 mL glass reactor containing 0.1 mM NAP solution to investigate the effect of reagents dosage, pH, air conditions (with or without N 2 purge), and different solution matrixes on NAP degradation. Scavenging tests, electron paramagnetic resonance (EPR) spectrum, and radical probe tests were conducted to identify the main radicals. Results indicated that over 96% NAP was removed in a wide pH range (3.0–9.0) within 180 min at optimal dosage of nCP = 1.0 mM and FeS 2 = 5.0 g L−1 in nCP/FeS 2 system. Aerobic condition was more beneficial to NAP degradation and the system could tolerate complex solution conditions. Moreover, HO• was determined to be responsible for NAP degradation. NAP degradation intermediates were detected by gas chromatography-mass spectrometry (GC-MS) and the possible degradation pathways were revealed. Finally, the efficient degradation of other organic pollutants confirmed the broad-spectrum reactivity of the nCP/FeS 2 system. Overall, these findings strongly demonstrated the potential applicability of nCP/FeS 2 system in remediating organic contaminated groundwater. [Display omitted] • nCP/FeS 2 system could degrade NAP efficiently at a wide pH range of 3.0–9.0. • FeS 2 played a significant role in Fe(II)/Fe(III) cycle. • Mechanisms of NAP degradation in nCP/FeS 2 system were revealed. • Performance of NAP degradation in different solution matrixes was investigated. • Excellent reactivity for other organic pollutants in nCP/FeS 2 system was achieved. [ABSTRACT FROM AUTHOR]

The performance of naphthalene (NAP) degradation in peroxodisulfate (PDS) and peroxymonosulfate (PMS) oxidation systems by nano zero valent iron (nZVI) combined with citric acid (CA) activation was reported in aqueous solution and soil slurry medium. The results in aqueous solution tests indicated that 98.1% and 98.9% of NAP were individually degraded in PDS/nZVI/CA and PMS/nZVI/CA systems within 2 h when the dosages of PDS, PMS, nZVI and CA were 1.0 mM, 0.1 mM, 0.2 mM and 0.1 mM, respectively. The consequences of scavenging tests and electron paramagnetic resonance detection demonstrated that HO• and SO 4 −• were the key factors on NAP removal. The presence of surfactants could consume ROSs and inhibit NAP removal. In addition, GC-MS was applied for the determination of NAP degradation intermediates, and three possible NAP degradation pathways were proposed in PDS oxidation process and two pathways in PMS oxidation process, respectively. The results in soil slurry medium showed that the presence of CA could promote the dissolution of soil minerals and the desorption of NAP from soil medium. 93.5% and 96.8% degradation of NAP were obtained in PDS/nZVI/CA and PMS/nZVI/CA systems within 24 h. Besides, the existence of DOM in soil could promote Fe(II)/Fe(III) cycle and NAP degradation through electron transfer. Based on the NAP degradation performance in the actual groundwater and soil medium, the above findings could provide basis and strong support for the potential application of PDS/nZVI/CA and PMS/nZVI/CA systems in the remediation of NAP contaminated sites. [Display omitted] • NAP degradation in actual groundwater and soil slurry medium was investigated. • HO.• and SO 4 −• were the key factors in PDS and PMS oxidation systems. • The possible degradation pathways of NAP were proposed. • The enhancement of citric acid for NAP removal was illuminated. • The mechanism of NAP degradation influenced by DOM in soil was clarified. [ABSTRACT FROM AUTHOR]

The presence of polycyclic aromatic hydrocarbons (PAHs) in groundwater is making a great threat to human health in the world which has received an increasing environmental concern. Among various Fenton oxidation processes, 97.6%, 92.1% and 89.4% naphthalene (NaP) removals were observed using hydrogen peroxide (H 2 O 2), sodium percarbonate (SPC) and calcium peroxide (CP) as oxidants activated by Fe(II) in ultrapure water tests, respectively. While, the inhibitory effect on NaP degradation caused by the weak alkaline solution pH and the presence of HCO 3 − in actual groundwater could be compensated by doubling dosages of oxidants and Fe(II) to different extent. 98.0%, 49.8% and 11.5% of NaP were degraded by using H 2 O 2 , SPC and CP, respectively, strongly suggesting the best H 2 O 2 performance among them. It was observed that 83.3% and 9.6% inhibition on NaP degradation in H 2 O 2 /Fe(II)/NaP system occurred in the presence of isopropyl alcohol and chloroform, confirming that both hydroxyl radical (HO) and superoxide anion radical (▪) contributed to NaP degradation in Fenton process and HO was the prominent radical. The presence of HO was further demonstrated by electro-spin resonance spectrometer analysis. The identification of transformation products of NaP revealed that hydroxylation and ring rupture were the main NaP degradation pathways. [Display omitted] • H 2 O 2 performed best among H 2 O 2 , SPC and CP for NaP degradation. • HO was the dominant ROSs in H 2 O 2 (SPC or CP)/Fe(II)/NaP system. • HCO 3 — had significant inhibitory influence on NaP degradation. • Hydroxylation and ring rupture were the main NaP degradation pathways. [ABSTRACT FROM AUTHOR]

[Display omitted] • 98.7% removal of NAP was achieved in actual groundwater. • The strengthening effect of CA on NAP degradation was investigated. • HO• was the predominant ROSs in PS/Fe(II)/CA system for NAP degradation. • The effects of TW-80 and SDS on NAP degradation were investigated. • The possible degradation pathways of NAP were proposed. More and more attention has been paid to polycyclic aromatic hydrocarbons (PAHs) contaminated sites caused by coking industries and chemical manufactures. In this study, the degradation performance of naphthalene (NAP), one of the typical pollutants in PAHs contaminated sites, in persulfate (PS) oxidation system activated by Fe(II) coupled with citric acid (CA) was investigated. The effects of PS, CA, and Fe(II) dosages on NAP were evaluated. 97.5% removal of NAP was obtained at the molar ratio of 15/5/1/1 of PS/Fe(II)/CA/NAP within 120 min, demonstrating that the addition of CA could significantly strengthen NAP degradation. The results of probe tests, EPR detection and scavenging experiments suggested that HO• played a predominant role in the degradation of NAP. The effect of surfactants including tween-80 (TW-80) and sodium dodecyl sulfate (SDS) on NAP degradation was explored. Moreover, the major degradation intermediates of NAP were determined by GC–MS and the possible degradation pathways of NAP were proposed. Finally, the effectiveness of PS/Fe(II)/CA process for NAP degradation in the actual groundwater demonstrated that this technique has a remarkable preponderance and prospect in NAP contaminated groundwater remediation. [ABSTRACT FROM AUTHOR]