Efficient naphthalene degradation in FeS2-activated nano calcium peroxide system: Performance and mechanisms

Mechanistic insights into fluoranthene degradation: Activation of peroxymonosulfate by mackinawite and pyrite in aqueous solution and soil slurry

The slow regeneration of Fe(II) in conventional Fenton and Fenton-like systems poses significant limitations for sustained and continuous generation of reactive oxygen species (ROS), which is critical for effective pollutant degradation. This study investigates the use of iron sulfide minerals-specifically, mackinawite (FeS) and pyrite (FeS2)-as both activators and reductants in peroxymonosulfate (PMS)-based Fenton-like systems to enhance Fe(II) regeneration and improve pollutant degradation efficiency. Results demonstrate that over 90 % of fluoranthene (FLT) was degraded within 60 min using the PMS/FeS and PMS/FeS2 systems. Reactive species including SO4-•, HO•, and 1O2 were generated in both systems, with SO4-• playing a primary role in FLT degradation, while 1O2 contributed partially to the process. Both FeS and FeS2 maintained structural stability during PMS activation, with surface Fe(II) oxidized to Fe(III) and reductive sulfur species (S2- in FeS and S22- in FeS2) facilitating the Fe(III)/Fe(II) cycle before ultimately converting to SO42-. These systems demonstrated robust performance across diverse water matrices, achieving excellent FLT degradation in actual groundwater and soil slurry, underscoring the promising application potential of PMS/FeS and PMS/FeS2 systems for remediating FLT-contaminated environments.

Synthesis of ZIF-67 composite lignin hydrogel and its catalytic degradation of naphthalene by PMS in wastewater

The incorporation of ZIF-67 into hydrogels for wastewater pollutant remediation has been widely studied, but the synthesis often requires organic solvents such as methanol or ethanol, which can result in the generation of toxic liquid waste. In this study, a novel hydrogel (ZIF-67@SL) was synthesized by integrating ZIF-67 into a dual-network system of sodium lignosulfonate (SL) and acrylamide (AM) using an in situ precipitation method in water. The material was characterized by XRD, FTIR, XPS, SEM, TEM, BET, and TGA analyses. ZIF-67@SL was used to activate peroxymonosulfate (PMS) for degrading naphthalene (NAP) in aqueous solutions. Results showed that ZIF-67@SL effectively activated PMS, achieving an 85.43 % removal rate of NAP within 60 min at 30 °C, with an initial NAP concentration of 10 mg·L-1, ZIF-67@SL dosage of 800 mg·L-1, PMS concentration of 1000 mg·L-1, and pH 7.0. The catalytic efficiency remained high after five recycling cycles. Quenching experiments and EPR spectra revealed that the degradation of NAP in the ZIF-67@SL/PMS system occurred through both free radical pathways (SO4•-, •OH, and O2•-) and a non-radical pathway (1O2). XPS analysis indicated that the activation of PMS and generation of radicals were influenced by Co2+, Co3+, Co0, nitrogen elements, and adsorbed oxygen in the ZIF-67@SL composite. Furthermore, the ZIF-67@SL/PMS system demonstrated strong resistance to low-concentration anions and humic acid (HA) interference and effectively removed multiple polycyclic aromatic hydrocarbons (PAHs) in mixed wastewater. Maximum removal rates for NAP, ACN, ACT, PHE, and FLU were 95.26 %, 99.9 %, 99.79 %, 99.04 %, and 75.69 %, respectively. This study provides an environmentally friendly strategy for wastewater treatment by synthesizing ZIF-67 hydrogel in water and utilizing it as an efficient catalyst.

Slow-release of hydrogen peroxide from PDA-coated calcium peroxide for enhanced dye wastewater decolourisation removal

In Fenton-like systems, a slow-release of hydrogen peroxide (H2O2) is of great value in improving the sustainable treatment of pollutants. In this study, calcium peroxide (CaO2) was first synthesized by different methods, and its slow-release performance of H2O2 was evaluated. Then CaO2@PDA composites (referred to as CP-X, X represent the mass ratio of Polydopamine (PDA) to CaO2 were prepared by using a simple precipitation method. And the H2O2 slow-release experimental result indicates that the average release rate of the prepared CP-1.0 is 0.19 mmol g-1·min-1 within 130 min. The release of H2O2 from CP-1.0 is consistent with the biexponential biphasic kinetic model, where water molecules and H2O2 osmotic diffusion are the main factors affecting the rate of H2O2 release. Decolourisation removal of crystalline violet (CV) solution was carried out using CP-1.0 as oxidants. Under the conditions of 0.02 g CP-1.0, pH = 6.5, and 20 °C, more than 98.0% of CV solution (30 mg/L) was removaled within 30 min. Then, possible degradation pathways were postulated using a combination of density functional theory (DFT) and liquid chromatography mass spectrometry (LC-MS). Finally, the decolourisation degradation mechanism was proposed according to the active species quenching experiments and Electron Paramagnetic Resonance (EPR) analysis. This study presents novel insights into the removal of emerging pollutants in aqueous media by CaO2-based Fenton-like systems.

Enhanced removal of 1,2-dichloroethane by nanoscale calcium peroxide activation with Fe(III) coupled with different iron sulfides

Fe(II) is of great importance in iron-based advanced oxidation processes. However, traditional methods to maintain Fe(II) concentration, such as the addition of chelating agents or reducing agents, may lead to an increase in chemical oxygen demand of secondary pollution. Therefore, in this study, iron sulfides, namely ferrous sulfide (FeS), pyrite (FeS2), and sulfidated nanoscale zero-valent iron (S-nZVI), were applied for not only the regeneration of Fe(II) but also the direct dissolution of Fe(II). Nanoscale calcium peroxide (nCaO2) was synthesized and used as the oxidant. The removal of 1,2-dichloroethane (1,2-DCA) were significantly promoted from 8.8 to 98.2, 79.2, and 80.8% with the aid of FeS, FeS2, and S-nZVI within 180 min, respectively. The dominant reactive oxygen species were demonstrated and their steady-state concentrations were quantified. Besides, the dechlorination of 1,2-DCA reached 90.4, 69.5, and 83.9% in nCaO2/Fe(III) systems coupled with FeS, FeS2, and S-nZVI, respectively. All three systems had high tolerance to the complex water conditions, of which FeS-enhanced nCaO2/Fe(III) system displayed the best performance, which could be recommended to put into practice for the remediation of 1,2-DCA contaminated groundwater.

A novel 3D nitrogen-doped porous carbon supported Fe-Cu bimetallic nanoparticles composite derived from lignin: an efficient peroxymonosulfate activator for naphthalene degradation

A novel 3D nitrogen-doped porous carbon supported Fe-Cu bimetallic nanoparticles composite (Fe-Cu-N-PC) was prepared via direct pyrolysis by employing black liquor lignin as a main precursor, and it was utilized as a novel catalyst for PMS activation in degrading naphthalene. Under the optimum experimental conditions, the naphthalene degradation rate was up to 93.2% within 60 min in the Fe-Cu-N-PC/PMS system. The porous carbon framework of Fe-Cu-N-PC could facilitate the quick molecule diffusion of reactants towards the inner bimetallic nanoparticles and enriched naphthalene molecules from the solution by a specific adsorption, which increased the odds of contact between naphthalene and reactive oxygen species and improved the reaction efficiency. The quenching reaction proved that the non-free radical pathway dominated by 1O2 was the main way in naphthalene degradation, while the free radical pathway involving SO4·- and ·OH only played a secondary role. Moreover, owing to its high magnetization performance, Fe-Cu-N-PC could be magnetically recovered and maintained excellent naphthalene degradation rate after four degradation cycles. This research will offer a theoretical basis for the construction of facile, efficient, and green technologies to remediate persistent organic pollutants in the environment.

FeS as excellent co-activator driving nano calcium peroxide oxidation for contaminants degradation: Performance and mechanisms

In this study, ferrous sulfide (FeS) was introduced to nano calcium peroxide (nCP)/Fe(III) system to facilitate the generation of Fe(II), more than 90% of naphthalene (NAP) could be removed at a wide pH range of 3-9. As a heterogeneous reductant, FeS could mitigate competitive reactions with reactive oxygen species (ROS), which favored the NAP degradation. As evidenced by scavenging experiments, HO• was the major ROS contributing to NAP degradation. The role of sulfur species (S2-, SO32-, and S2O32-) in nCP/Fe(III) system was investigated with S2O32- showing the preferable reactivity in Fe(III) reduction. In addition, the surface-bound HO• and surface Fe(II) were detected and the role of them on NAP degradation was revealed and concluded that both dissolved and surface Fe(II) contributed to NAP degradation, whereas surface-bound HO• was not superior to solution HO• in degrading NAP. Furthermore, nCP/Fe(III)/FeS system showed high feasibility to different solution matrixes and various types of water as well as the broad-spectrum reactivity to other toxic organic pollutants, exhibiting promise for practical application to remediate complex contaminants.

A novel aminated lignin/geopolymer supported with Fe nanoparticles for removing Cr(VI) and naphthalene: Intermediates promoting the reduction of Cr(VI)

A novel, inexpensive and eco-friendly aminated lignin/geopolymer supported with Fe nanoparticles (Fe@N-L-GM) composite was successfully synthesized using kaolin and lignin as the major precursors. The prepared Fe@N-L-GM had larger specific surface area, rich oxygen-containing and nitrogen-containing functional groups, greater electron transfer ability and interconnective porous structure. The Fe@N-L-GM could be employed as the adsorbent of Cr(VI) and the activator of potassium peroxymonosulfate (PMS) for treatment of Cr(VI) and naphthalene (NAP) in wastewater. The adsorption and degradation results indicated that the maximum adsorption capacity of Cr(VI) could reach 65.83 mg g^-1, whereas the maximum NAP degradation efficiency could reach 97.81 %. The adsorbed Cr(VI) was mostly converted to the low toxic Cr(III) through the reduction of electron donors such as Fe(II), amino and hydroxyl groups. The quenching experiment results confirmed that ·OH might be the crucial ROSs in mediating NAP degradation. In the simultaneous removal experiment of Cr(VI) and NAP, the Cr(VI) removal rate was significantly improved in the presence of NAP, while phenol as the degradation intermediate of NAP might be the main substance for promoting the reduction of Cr(VI). This work provided the theoretical foundation and a new type of material for the simultaneous removal of heavy metal and persistent organic pollutants (POPs).