Core-shell structural nitrogen-doped carbon foam loaded with nano zero-valent iron for simultaneous remediation of Cd (II) and NAP in water and soil: Kinetics, mechanism, and environmental evaluation

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.

Mechanism and ecological environmental risk assessment of peroxymonosulfate for the treatment of heavy metals in soil

Oxidation technologies based on peroxymonosulfate (PMS) have been effectively used for the remediation of soil organic pollutants due to their high efficiency. However, the effects of advanced PMS-based oxidation technologies on other soil pollutants, such as heavy metals, remain unknown. In this study, changes in the form of heavy metals in soil after using PMS and the risk of pollution to the ecological environment were investigated. Furthermore, two risk assessment methods, the mung bean germination toxicity test and groundwater leaching soil column test, were employed to evaluate the soil before and after PMS treatment. The results showed that PMS has a strong ability to degrade complex compounds, enabling the transformation of heavy metals, such as Cd, Pb, and Zn, from stable to active states in the soil. The risk assessments showed that PMS treatment activated heavy metals in the soil, which delayed the growth of plants, increased heavy metal content in plant tissues and the risk of groundwater pollution. These findings provide a new perspective for understanding the effects of PMS on soil, thus facilitating the sustained and reliable development of future research in the field of advanced oxidation applied to soil treatment.

High performance self-assembled sulfidized nanoscale zero-valent iron for the immobilization of cadmium in contaminated sediments: Optimization, microbial response, and mechanisms

Sulfidized nanoscale zero-valent iron (S-nZVI) showed excellent removal capacity for cadmium (Cd) in aqueous phase. However, the remediation effects of S-nZVI on Cd-contaminated sediment and its interactions with microorganisms in relation to Cd fate remain unclear. The complexity of the external environment posed a challenge for Cd remediation. This study synthesized S-nZVI with different S and Fe precursors to investigate the effect of precursors and applied the optimal material to immobilize Cd in sediments. Characterization analysis revealed that the precursor affected the morphology, Fe0 crystallinity, and the degree of oxidation of the material. Incubation experiments demonstrated that the immobilization efficiency of Cd using S-nZVIFe3++S2- (S/Fe = 0.14) reached the peak value of 99.54%. 1% and 5% dosages of S-nZVI significantly reduced Cd concentration in the overlying water, DTPA-extractable Cd content, and exchangeable (EX) Cd speciation (P < 0.05). Cd leaching in sediment and total iron in the overlying water remained at low levels during 90 d of incubation. Notably, each treatment maintained a high Cd immobilization efficiency under different pH, water/sediment ratio, organic acid, and coexisting ion conditions. Sediment physicochemical properties, functional bacteria, and a range of adsorption, complexation and precipitation of CdS effects dominated Cd immobilization.

Degradation and mechanism of PFOA by peroxymonosulfate activated by nitrogen-doped carbon foam-anchored nZVI in aqueous solutions

Perfluorooctanoic acid (PFOA) is an emerging pollutant that is non-biodegradable and presents severe environmental and human health risks. In this study, we present an effective and mild approach for PFOA degradation that involves the use of nitrogen-doped carbon foam anchored with nanoscale zero-valent iron (nZVI@NCF) to activate low concentration peroxymonosulfate (PMS) for the treatment. The nZVI@NCF/PMS system efficiently removed 84.4% of PFOA (2.4 μM). The active sites of nZVI@NCF including Fe0 (110) and graphitic nitrogen played crucial roles in the degradation. Electrochemical analyses and density functional theory calculations revealed that nZVI@NCF acted as an electronic donor, transferring electrons to both PMS and PFOA during the reaction. By further analyzing the electron paramagnetic resonance and byproducts, it was determined that electron transfer and singlet oxygen were responsible for PFOA degradation. Three degradation pathways involving decarboxylation and surface reduction of PFOA in the nZVI@NCF/PMS system were determined. Finding from this study indicate that nZVI@NCF/PMS systems are effective in degrading PFOA and thus present a promising persulfate-advanced oxidation process technology for PFAS treatment.

Transport of nZVI/copper synthesized by green tea extract in Cr(IV)-contaminated soil: modeling study and reduced toxicity

In this study, nano-zero-valent iron/copper was synthesized by green tea extracts (GT-nZVI/Cu) and produced a stable suspension than nano-zero-valent iron synthesized by green tea extracts (GT-nZVI) injected into Cr(VI)-containing soil column. The equilibrium 1D-CDE model was successfully used to fit the penetration curves of Fe(tot), Fe(aq), and Fe(0) in order to determine the relevant parameters. The hydrodynamic dispersion coefficient of chromium-contaminated soil was 0.401 cm2·h-1, and the pore flow rate was 0.144 cm·h-1. The stable C/C0 of Fe(tot), Fe(aq), and Fe(0) in the effluent were retarded to 0.39, 0.79, and 0.11, respectively, compared to a ratio of 1 for the concentration of the tracer Cl- in the effluent to the concentration in the influent. Additionally, the 1D-CDE model describes the migration behavior of Cr(VI) with a high R2 (> 0.97). The obtained blocking coefficients declined gradually with increasing concentration of GT-nZVI/Cu suspension and decreasing concentration of Cr(VI). The content of reduced chromium in the soil decreased from 2.986 to 1.121 after remediation, while the content of more stable oxidizable chromium and residual chromium increased from 2.975 and 20.021 to 16.471 and 27.612. The phytotoxicity test showed that mung bean seeds still had a germination rate of 90% (control of 100%), root length of 29.63 mm (control of 35.25 mm), and stem length of 17.9 cm (control of 18.96 cm) after remediation with GT-nZVI/Cu. These indicated that GT-nZVI/Cu was effective in immobilizing Cr(VI) in the soil column and reduced the ecological threat. This study provides an analytical basis and theoretical model for the migration of chromium-contaminated soil in practical application.

The influence of various microplastics on PBDEs contaminated soil remediation by nZVI and sulfide-nZVI: Impedance, electron-accepting/-donating capacity and aging

The microplastics (MPs) existed in the environment widely has resulted in novel thinking about in-situ remediation techniques, such as nano-zero-valent iron (nZVI) and sulfided nZVI (S-nZVI), which were often compromised by various environmental factors. In this study, three common MPs such as polyvinyl chloride (PVC), polystyrene (PS), and polypropylene (PP) in soil were found to inhibit the degradation rate of decabromodiphenyl ether (BDE209) by nZVI and S-nZVI to different degrees due to MPs inhibiting of electron transfer which is the main way to degrade BDE209. The inhibition strength was related to its impedance (Z) and electron-accepting (EAC)/-donating capacity (EDC). Based on the explanation of the inhibition mechanism, the reason for different aging degrees of nZVI and S-nZVI in different MPs was illustrated, especially in PVC systems. Furthermore, the aging of reacted MPs, functionalization and fragmentation in particular, indicated that they were involved in the degradation process. Moreover, this work provided new insights into the field application of nZVI-based materials for removing persistent organic pollutants (POPs).

Chitosan-Grafted Carbon Oxynitride Nanoparticles: Investigation of Photocatalytic Degradation and Antibacterial Activity

In this work, a series of chitosan (CS)-grafted carbon oxynitride (OCN) nanoparticles (denoted as CS-OCN) were successfully synthesized for the first time by thermal polycondensation and subsequent esterification. The structure and photocatalytic performance of CS-OCN nanoparticles were investigated. The XPS spectra of CS-OCN-3 showed the presence of amino bonds. The optimal photocatalytic degradation efficiency of the synthesized CS-OCN-3 could reach 94.3% within 390 min, while the photocurrent response intensity was about 150% more than that of pure OCN. The improved photocatalytic performance may be mainly attributed to the enhanced photogenerated carrier's separation and transportation and stronger visible light response after CS grafting. In addition, the inhibition diameter of CS-OCN-3 reached 23 mm against E. coli within 24 h under visible light irradiation, exhibiting excellent photocatalytic bactericidal ability. The results of bacterial inhibition were supported by absorbance measurements (OD600) studies of E. coli. In a word, this work provided a rational design of an efficient novel metal-free photocatalyst to remove bacterial contamination and accelerate the degradation of organic dyes.

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).

Morphology regulation of zero-valent iron nanosheets supported on microsilica for promoting peroxymonosulfate activation

Combing the assisted dispersion strategy of support with the wet chemical reduction method, a novel nano-zero valent iron/microsilica (nZVI/M) composite was successfully fabricated, where the 2D nZVI nanosheets were uniformly anchored and covered on the surface of microsilica. The introduction of microsilica notably relieved the agglomeration effect of nZVI nanosheets, which induced the improvement of specific surface area (45.68 m²/g) and pore volume (0.172 cm³/g), and thereby exposing more active sites for bisphenol A (BPA) removal. The optimized nZVI/M-0.6 displayed the superior catalytic performance in the presence of peroxymonosulfate (PMS) with the degradation rate of BPA reached above 97% within 3 min and a higher constant rate of 0.659 min^-1, which was approximately 3.9 times as high as that of nZVI/PMS system. The homogeneously dispersion of nZVI nanosheets on microsilica benefited for the assembly of the pollutants and boosting the kinetics of the catalytic degradation process. As a highly efficient PMS activator, it could well maintain the catalytic activity in different real water samples. The quenching experiments verified that SO₄^•- played the dominate role for BPA removal. This work offered novel insights for designing and preparing iron-based persulfate activator for wastewater treatment.

Sulfurized bimetallic biochar as adsorbent and catalyst for selective co-removal of cadmium and PAHs from soil washing effluents

Although biosurfactant enhanced soil washing is effective to remediate Polycyclic Aromatic Hydrocarbons (PAHs)-Heavy metals (HMs) co-contaminated soil, the treatment of soil washing effluents containing pollutant and biosurfactant remains a critical challenge. In this study, the sulfurized Fe-Mn bimetallic biochar, named FMSBC was prepared, which exhibited excellent performance in activating sodium percarbonate (SPC) to degrade phenanthrene and the good adsorption capacity of cadmium. A simple system using FMSBC adsorption and SPC oxidation (FMSBC/SPC) is thus developed to remove phenanthrene and cadmium from soil washing effluents. Although there was antagonistic behavior between PAHs and HMs in the FMSBC/SPC system, over 80% phenanthrene and cadmium can be simultaneously removed from soil washing effluents. Adsorption of cadmium was mainly driven by complexation and precipitation. Free radical quenching studies and electron paramagnetic resonance (EPR) analyses verified that the dominant radical in the FMSBC/SPC system was hydroxyl radical (·OH). The performances of adsorption and catalyst were stable across a wide pH range and in the presence of competitive metal ions or natural organic matters. The recovered biosurfactants could be further reused for three washing cycles. This study has suggested biosurfactant enhanced soil washing coupled with FMSBC/SPC system is a promising method for remediation of HMs-PAHs co-contaminated soil.

Kinetics of zero-valent iron-activated persulfate for methylparaben degradation and the promotion of Cl. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2022;321:115973. [PMID: 36104884 DOI: 10.1016/j.jenvman.2022.115973]

Methylparaben (MP) is an emerging pollutant, and the optimal conditions and kinetics of MP degradation using nano-zero-valent iron-activated persulfate (nZVI/PDS) need to be further investigated. This paper firstly investigated the response surface methodology (RSM) analysis of MP degradation by the heterogeneous system nZVI/PDS and concluded that the initial pH had the most significant effect on MP degradation. The optimal experimental conditions predicted by the RSM were as follows: initial pH 2.75, [nZVI]₀ = 2.87 mM, [PDS]₀ = 2.18 mM (MP degradation level of 95.30%). First- and second-order kinetic fits were performed for different initial pH levels and different concentrations of MP, nZVI, and PDS. It was determined that k = 0.0365 min^-1 (R² = 0.984) when the initial pH was 3, [PDS]₀ = 2 mM, [MP]₀ = 20 mg L^-1, and [nZVI]₀ = 3 mM (MP degradation level of 94.25%). The rest of the conditions were more closely fitted to the second-order reactions. The effects of different concentrations of anions and humic acid (HA) on the MP degradation level and k were examined, and it was found that Cl^- could promote MP degradation to 97.69% (increased by 3.65%) and increase the k in accordance with the first-order reaction kinetics (0.0780 min^-1, R² = 0.991). Finally, the analysis of intermediates revealed 5 reaction pathways and 7 reaction intermediates, which inferred a possible reaction mechanism with the recycling performance of nZVI. In this paper, the superiority of nZVI/PDS for the purposes of activating MP degradation was affirmed. The presence of Cl^- can enhance the level of MP degradation was confirmed, which provides a new direction for future practical engineering applications.

A low-cost and eco-friendly powder catalyst: Iron and copper nanoparticles supported on biochar/geopolymer for activating potassium peroxymonosulfate to degrade naphthalene in water and soil

A low-cost and environment-friendly biochar/geopolymer composite loaded with Fe and Cu nanoparticles (Fe-Cu@BC-GM) was prepared by impregnation-calcination using lignin and kaolin as precursors. SEM, FTIR and XRD analysis suggested that the Fe-Cu@BC-GM had a certain pore structure, rich functional groups and stable crystal structure. The obtained Fe-Cu@BC-GM was used as the catalyst of potassium peroxymonosulfate (PMS) for remediation of wastewater and soil polluted by naphthalene (NAP). Experimental results indicated that Fe-Cu@BC-GM exhibited outstanding catalytic performance, and the maximum degradation rate of NAP in water and soil reached 98.35% and 67.98% within 120 min, respectively. The XPS measurement confirmed the presence of successive Fe (Ⅲ)/Fe (Ⅱ) and Cu(Ⅱ)/Cu(Ⅰ) redox pairs cycles on the surface of Fe-Cu@BC-GM, which made Fe (Ⅲ) and Cu(Ⅰ) continuously generated Fe (Ⅱ) activating PMS to produce SO₄^·- and ·OH for the degradation of NAP. The effects of Fe-Cu@BC-GM/PMS system on plant toxicity were evaluated by analyzing the degradation intermediates and bioassay of mung bean. It was proved that the Fe-Cu@BC-GM/PMS system could degrade NAP into less toxic intermediates, and the seed germination rate, root and stem length of mung bean after soil remediation were not notably different from those of the uncontaminated soil. This work opened new prospect for the application of geopolymer in degradation of persistent organic pollutants (POPs) and provided a cost-effective option for the remediation of the persistent organic pollutants contaminated water and soil.

Phase transformation of nanosized zero-valent iron modulated by As(III) determines heavy metal passivation

Nanoscale zero-valent iron (nZVI) has been extensively used for the passivation of cadmium (Cd) or arsenic (As) from wastewaters, while the underlying mechanisms of nZVI reaction with coexisting Cd and As are largely overlooked. Herein, the interactions of Cd and As during the course of nZVI transformation and the corresponding effects on respective pollutant removal have been systematically investigated. Batch experiments results show that As(III) addition significantly promotes the passivation of Cd(II) by nZVI, and the removal capacity increases by 7.8 times compared to that of Cd(II) alone. However, the adsorption and oxidative transformation of As(III) are barely affected under a relatively low Cd(II) concentration. It is conducive to the adsorption of Cd(II) and As(III) using nZVI under neutral conditions. The transformation of nZVI to lepidocrocite dominates in the Cd(II) single system, while it mainly converts to amorphous Fe oxyhydroxide with the addition of As(III). As(III) notably reduces the surface charge of Fe oxyhydroxide intermediates and to form the ternary complexes with Cd (Fe-As-Cd), which is the predominant mechanism for the promoted Cd(II) passivation. This work provides new understanding of nZVI transformation coupled to Cd(II) and As(III) passivation, which are likely contributing to the heavy metalloids regulation in waters and subsurface environments.

One-Step Synthesis of High-Performance N/S Co-Doped Porous Carbon Material for Environmental Remediation

Potassium thiocyanate (KSCN), a highly efficient “three birds with one stone” activator, might work with inorganic activators to produce excellent N/S co-doped porous carbon (NSC) materials for environmental remediation. However, the effects of inorganic activators on cooperative activation are unclear. As a result, the influence of inorganic activators on the synthesis of NSC materials was investigated further. This study shows that the surface areas of the NSC materials acquired through cooperative activation by potassium salts (KOH or K2CO3) were considerably higher than those acquired through KSCN activation alone (1403 m2/g). Furthermore, KSCN could cooperate with K2CO3 to prepare samples with excellent specific surface area (2900 m2/g) or N/S content. The as-prepared NSC materials demonstrated higher adsorption capability for chloramphenicol (833 mg/g) and Pb2+ (303 mg/g) (pore fitting, complexation). The research provides critical insights into the one-step synthesis of NSC materials with a vast application potential.