In this study, nano‐CaO2 (nCaO2) was successfully synthesized and constituted the nCaO2/Fe(II) system applying to remediate BTEX, which are typical mixed pollutants in contaminated groundwater. The particle size of the synthesized nCaO2 was 108.91 nm, and it displayed better BTEX remediation performance than that of commercial CaO2. The innovative generation pattern of hydroxyl radicals (HO·) in the nCaO2/Fe(II) system has been investigated using benzoic acid as the HO· probe, and the proper molar ratio of nCaO2/Fe(II) was optimized as 1/1. Over 90% of BTEX was removed in 180 min with the nCaO2/Fe(II)/BTEX molar ratio of 40/40/1. Further experiments evaluated the influence of co‐existence of mixed pollutants chlorinated hydrocarbon compounds (CHCs) or surfactant constituents on BTEX remediation performance. The experimental results suggested that CHCs have limited influence on BTEX removal rate and surfactants have negative effects on BTEX remediation performance in the experimental conditions. In conclusion, the findings in this study could give some inspirations to apply the nCaO2/Fe(II) process in remediating co‐existing pollutants in contaminated groundwater. Practitioner points nCaO2/Fe(II) system applied to remediate mixed contaminants. HO· generation pattern of the nCaO2/Fe(II) system has been investigated. The influence of chloride hydrocarbon compounds have been studied. The effects of surfactants were evaluated.

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Benzene, toluene, ethylbenzene and xylene (BTEX) possess a negative impact on the environment and human being due to their highly toxic and carcinogenic properties. In this study, persulfate (PS) activated by nano zero-valent iron (nZVI) coupled with chelated L-cysteine (L-cys) process was investigated for BTEX degradation in contaminated groundwater. BTEX degradation had a significant acceleration and improvement with the removal from 62.7 to 100% along with the increasing dosage of L-cys from 0.12 to 0.27 M in 24 h. Further, the compact nZVI catalytic cylinder and nZVI encapsulated L-cys catalytic cylinder were successfully manufactured by encapsulating nZVI, and nZVI and L-cys together with additives of cement, river sand, stearic acid (SA) and zeolite. The SEM image, XRD patterns and FTIR spectra showed that the manufactured catalytic cylinder had a porous structure and encapsulated nZVI and L-cys successfully. Six successive cycles of BTEX degradation were completed and the degradation rate decreased gradually in each cycle. The catalytic activity of nZVI encapsulated L-cys catalytic cylinder was superior to nZVI catalytic cylinder in each cycle. The electron paramagnetic resonance (EPR) results indicated that HO• was the dominant active species in the BTEX degradation process. Benzoic acid (BA) scavenge experiments showed that L-cys could increase the yield of HO• in the PS/nZVI system. The HO• yields of PS/nZVI encapsulated L-cys catalytic cylinder system were 3.2 to 4.8 folds higher than those of PS/nZVI catalytic cylinder system. The possible mechanisms of PS activation by nZVI encapsulated L-cys catalytic cylinder were supposed. Homogeneous Fenton reaction and heterogeneous catalysis on the nZVI surface are two co-existence mechanisms in the PS/nZVI encapsulated L-cys catalytic cylinder system. The findings of this study provide new insights into the mechanism of nZVI encapsulated L-cys catalytic cylinder activating PS, showing its potential applications for the remediation of groundwater.

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The chlorobenzene (CB) degradation performances by various oxidants, including hydrogen peroxide (H2O2), nanoscale calcium peroxide (nCaO2) and sodium percarbonate (SPC), activated with ferrous iron (Fe(II)) were investigated and thoroughly compared. The results showed that all tested systems had strong abilities to degrade CB. The CB removal rate increased with increasing dosages of oxidants or Fe(II) because the generation of reactive oxygen species could be promoted with the chemical dosages' increase. Response surface and contour plots showed that CB could achieve a better removal performance at the same H2O2 and Fe(II) molar content, but the Fe(II) dosage was higher than that of oxidants in the nCaO2 and SPC systems. The optimal molar ratios of H2O2/Fe(II)/CB, nCaO2/Fe(II)/CB and SPC /Fe(II)/CB were 5.2/7.6/1, 8/8/1, and 4.5/8/1, respectively, in which 98.1%, 98%, and 96.4% CB removals could be obtained in 30 min reaction. The optimal pH condition was around 3, while CB removal rates were less than 20% in all three systems when the initial pH was adjusted to 9. The oxidative hydroxyl radicals (HO•) and singlet oxygen (1O2) had been detected by the electron paramagnetic resonance test. Based upon the results of liquid chromatograph-mass spectrometer analysis, the pathways of CB degradation were proposed, in which 1O2 roles were elaborated innovatively in the CB degradation mechanism. The CB degradation performance was significantly affected in actual groundwater, while increasing the molar ratio of oxidant/Fe(II)/CB was an effective way to overcome the adverse effects caused by the complex of actual groundwater matrix.

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.

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l‐cysteine‐modified Fe3O4 nanoparticles (l‐cys@nFe3O4) were synthesized successfully and used as catalyst to activate persulfate (PS) for benzene, toluene, ethylbenzene, and xylenes (BTEX) degradation. The composite was fully characterized, and the l‐cys@nFe3O4 had more protrusions and l‐cys was combined on the surface of nFe3O4. The removals of BTEX were 78.2%, 85.1%, 85.3%, 81.2%, respectively, in PS/l‐cys@nFe3O4 system, while only 52.7% 57.8%, 60.8%, and 56.3% of BTEX removals reached under the same condition for nFe3O4 chelated with l‐cys in 48 h. Four successive cycles of BTEX degradation were completed in PS/l‐cys@nFe3O4 system. The synergistic mechanisms of BTEX degradation in PS/l‐cys@nFe3O4 system were investigated by electron paramagnetic resonance (EPR), benzoic acid (BA) probe and X‐ray photoelectron spectroscopy (XPS) tests. SFe bond in l‐cys‐Fe complexes promoted the electron transfer between nFe3O4 core and the solution, iron and iron at the interface, thereby promoting the Fe3+/Fe2+ cycle and the catalytic capacity of nFe3O4. The optimal pH of PS/l‐cys@nFe3O4 system was 3, while HCO3− and Cl− exhibited negative influences on BTEX degradation. Only 14.2%, 15.5%, 15.9%, and 15.6% BTEX had been removed in the presence of 0.12‐M PS and 8.0 g/L l‐cys@nFe3O4 under the actual groundwater condition. However, expanding the dosage of PS and l‐cys@nFe3O4 was an effective strategy to overcome the adverse effect. Practitioner Points L‐cys@nFe3O4 were synthesized successfully and used as catalyst to activate PS for BTEX degradation. Four successive cycles of BTEX degradation were completed in PS/L‐cys@nFe3O4 system. lS―Fe bond in L‐cys@nFe3O4 promoted the electron transfer between PS and nFe3O4 core.