Degradation of chlorinated organic solvents in aqueous percarbonate system using zeolite supported nano zero valent iron (Z-nZVI) composite

Transport of nanoscale zero-valent iron in the presence of rhamnolipid

Nanoscale zero-valent iron (nZVI) particles have gained widespread use for in-situ treatment of various chlorinated hydrocarbons. Their non-toxic nature, affordability, and minimal maintenance requirements have made them a favored material for nanoremediation. The treatment typically involves the injection of nZVI particles into contaminated sites using direct-push well injection systems. However, their small size leads to high surface energy, causing aggregation that alters their physiochemical properties, reactivity, and transport behavior. To counteract aggregation, nZVI suspension can be stabilized with different surfactants, reducing the surface energy during subsurface soil transport. This study investigates the impact of rhamnolipid, a biosurfactant produced by Pseudomonas aeruginosa during the late growth phase, on the aggregation and mobility of nZVI particles. The retardation factor of nZVI in the model media of zeolite, ZK406H, decreased from 1.66 in the absence of rhamnolipid to 1.03, 0.98, 0.93, and 0.87, corresponding to the presence of rhamnolipid at concentrations of 20, 50, 80, and 100 mg/L. The deposition coefficient also decreased from 2.39 in the absence of rhamnolipid to 0.459, 0.279, 0.217, and 0.0966, corresponding to the presence of rhamnolipid at concentrations of 20, 50, 80, and 100 mg/L. The transport parameters of nZVI in ZK406H were linked to the interactions of nZVI particles with ZK406H by the DLVO theory.

A systematic review on percarbonate-based advanced oxidation processes in wastewater remediation: From theoretical understandings to practical applications

Percarbonate encompasses sodium percarbonate (SPC) and composite in-situ generated peroxymonocarbonate (PMC). SPC emerges as a promising alternative to hydrogen peroxide (H2O2), hailed for its superior transportation safety, stability, cost-effectiveness, and eco-friendliness, thereby becoming a staple in advanced oxidation processes for mitigating water pollution. Yet, scholarly literature scarcely explores the deployment of percarbonate-AOPs in eradicating organic contaminants from aquatic systems. Consequently, this review endeavors to demystify the formation mechanisms and challenges associated with reactive oxygen species (ROS) in percarbonate-AOPs, alongside highlighting directions for future inquiry and development. The genesis of ROS encompasses the in situ chemical oxidation of activated SPC (including iron-based activation, discharge plasma, ozone activation, photon activation, and metal-free materials activation) and composite in situ chemical oxidation via PMC (namely, H2O2/NaHCO3/Na2CO3, peroxymonosulfate/NaHCO3/Na2CO3 systems). Moreover, the ROS generated by percarbonate-AOPs, such as •OH, O2•-, CO3•-, HO2•-, 1O2, and HCO4-, can work individually or synergistically to disintegrate target pollutants. Concurrently, this review systematically addresses conceivable obstacles posing percarbonate-AOPs in real-world application from the angle of environmental conditions (pH, temperature, coexisting substances), and potential ecological toxicity. Considering the outlined challenges and advantages, we posit future research directions to amplify the applicability and efficacy of percarbonate-AOPs in tangible settings. It is anticipated that the insights provided in this review will catalyze the progression of percarbonate-AOPs in water purification endeavors and bridge the existing knowledge void.

Activity and recyclability enhancement of pH-dependent Fe0@BC-mediated heterogeneous sodium percarbonate (SPC)-reducing agents (RA) system

Dyes pose great threats to the aquatic environment and human health. Fe0-based Fenton-like systems have been widely employed for the degradation of organic dyes. However, the regulation of degradability and recyclability was still unclear. In this study, Rhodamine B (RhB) was served as the model pollutant, hydroxylamine hydrochloride was selected as the RA, the natural photocatalysis system demonstrated stable operation. RA, as performance enhancement agent, was firstly reported in micro/nano-Zero-Valent Iron@Biochar (m/nZVI@BC) based SPC-RA system. Carrier size-fractionated m/nZVI@BC was fabricated by one-step carbothermal method. As a result, RA synergistically interacted with SPC, and the reaction time reduced from 15 min to 4 min. In the 0.010 g m/nZVI@BC-mediated SPC-RA system, over 95% of RhB (100 mg·L-1, 1041.667 mg·g-1) was successfully degraded. The maximum degradation ability could still exceed 1g·g-1 via 5 times repeated applications. Meanwhile, the loss of degradability, caused by halving SPC concentration could be compensated by RA dosage measurement. The entire degradation process was predominantly dominated by free radicals (•OH> 1O2> •O2-> •CO3-). Reactive oxidizing species (ROSs) were primarily excited by α-Fe0, Fe3C and N sites of biochar (BC). Light and BC carrier dedicated slight influence. These discoveries shed a light on the activity and recyclability regulation of catalytic material, aligning with the principles of green chemistry and cleaner production. This study demonstrates a novel approach to efficient management of solid waste disposal, reuse of waste biomass, advanced treatment of dye-containing wastewater, pollution control in aquatic environments.

The performance and mechanism of iron-mediated chemical oxidation: Advances in hydrogen peroxide, persulfate and percarbonate oxidation

Many studies have successfully built iron-mediated materials to activate or catalyze Fenton-like reactions, with applications in water and wastewater treatment being investigated. However, the developed materials are rarely compared with each other regarding their performance of organic contaminant removal. In this review, the recent advances of Fenton-like processes in homogeneous and heterogeneous ways are summarized, especially the performance and mechanism of activators including ferrous iron, zero valent iron, iron oxides, iron-loaded carbon, zeolite, and metal organic framework materials. Also, this work mainly compares three O-O bond containing oxidants including hydrogen dioxide, persulfate, and percarbonate, which are environmental-friendly oxidants and feasible for in-situ chemical oxidation. The influence of reaction conditions, catalyst properties and benefits are analyzed and compared. In addition, the challenges and strategies of these oxidants in applications and the major mechanisms of the oxidation process have been discussed. This work can help understand the mechanistic insights of variable Fenton-like reactions, the role of emerging iron-based materials, and provide guidance for choosing appropriate technologies when facing real-world water and wastewater applications.

Advanced oxidation processes for water purification using percarbonate: Insights into oxidation mechanisms, challenges, and enhancing strategies

Percarbonate (SPC) has drawn considerable attention due to its merits in the safety of handling and transport, stability, and price as well as environmental friendliness, which has been extensively applied in advanced oxidation processes (AOPs) for water decontamination. Nevertheless, comprehensive information on the application of SPC-AOPs for the treatment of organic compounds in aquatic media is scarce. Hence, the focus of this review is to shed light on the mechanisms of reactive oxygen species (ROS) evolution in typical SPC-AOPs (i.e., Fenton-like oxidation, photo-assisted oxidation, and discharge plasma-involved oxidation processes). These SPC-AOPs enable the formation of multiple reactive species like hydroxyl radical (^•OH), superoxide radical (O₂^•-), singlet oxygen (¹O₂), carbonate radicals (CO₃^•-), and peroxymonocarbonate (HCO₄^-), which together or solely contribute to the degradation of target pollutants. Simultaneously, the potential challenges in practical applications of SPC-AOPs are systematically discussed, which include the influence of water quality parameters, cost-effectiveness, available active sites, feasible activation approaches, and ecotoxicity. Subsequently, enhancing strategies to improve the feasibility of SPC-AOPs in the practical implementation are tentatively proposed, which can be achieved by introducing reducing and chelating agents, developing novel activation approaches, designing multiple integrated oxidation processes, as well as alleviating the toxicity after SPC-AOPs treatment. Accordingly, future perspectives and research gaps in SPC-AOPs are elucidated. This review will hopefully offer valuable viewpoints and promote the future development of SPC-AOPs for actual water purification.

Removal of organic compounds by nanoscale zero-valent iron and its composites

During the latest several decades, the continuous development of the economy and industry has brought more and more serious organic pollutants to the natural environment, which have inevitably aroused severe menace to human health and the environmental system. The nano zero-valent iron (NZVI) particles and NZVI-based materials have widely applied to remove organic pollutants. This article reviews the key advancements of different methods for the synthesis of NZVI and NZVI-based materials. Different modification methods (e.g., doped NZVI, encapsulated NZVI and supported NZVI) are also introduced detailedly for overcoming the defects of NZVI such as aggregation and easy oxidation. The removal of different organic pollutants including dyes, halogenated organic compounds, nitro-organic compounds, phenolic compounds, pesticides, and antibiotics are summarized. The interaction mechanisms, including adsorption, reduction, and active oxidation of organic pollutants by NZVI/NZVI-based composites, are discussed. The dyes are mainly removed by destroying their chromogenic group according to the reduction or the Fenton-like reaction with NZVI. The removal of halogenated organic compounds (HOCs) is realized by the dehalogenation process, including reductive elimination, hydrogenolysis, and hydrogenation. As for the nitro-organic compounds, three different reduction pathways as nitro-reduction (into amino), cleavage at the carbon‑nitrogen bond or denitration of the NO₂ group may take effect. The phenolic compounds can be mineralized into inorganic molecules, including CO₂ and H₂O, by Fenton oxidation. This review might provide the basis for future studies on developing more effective NZVI-based materials for the treatment of wastewaters contaminated by organic pollutants.

Application of percarbonate and peroxymonocarbonate in decontamination technologies

Sodium percarbonate (SPC) and peroxymonocarbonate (PMC) have been widely used in modified Fenton reactions because of their multiple superior features, such as a wide pH range and environmental friendliness. This broad review is intended to provide the fundamental information, status and progress of SPC and PMC based decontamination technologies according to the peer-reviewed papers in the last two decades. Both SPC and PMC can directly decompose various pollutants. The degradation efficiency will be enhanced and the target contaminants will be expanded after the activation of SPC and PMC. The most commonly used catalysts for SPC activation are iron compounds while cobalt compositions are applied to activate PMC in homogenous and heterogeneous catalytical systems. The generation and participation of hydroxyl, superoxide and/or carbonate radicals are involved in the activated SPC and PMC system. The reductive radicals, such as carbon dioxide and hydroxyethyl radicals, can be generated when formic acid or methanol is added in the Fe(II)/SPC system, which can reduce target contaminants. SPC can also be activated by energy, tetraacetylethylenediamine, ozone and buffered alkaline to generate different reactive radicals for pollutant decomposition. The SPC and activated SPC have been assessed for application in-situ chemical oxidation and sludge dewatering treatment. The challenges and prospects of SPC and PMC based decontamination technologies are also addressed in the last section.

Mechanism of Stability and Transport of Chitosan-Stabilized Nano Zero-Valent Iron in Saturated Porous Media

Chitosan-stabilized nano zero-valent iron (CTS-nZVI) prepared by the liquid-phase reduction method has been shown to achieve a good dispersion effect. However, there has been little analysis on the mechanism affecting its stability and transport in saturated porous media. In this paper, settling experiments were conducted to study the stabilization of CTS-nZVI. The transport of CTS-nZVI in saturated porous media at different influencing factors was studied by sand column experiments. The stability mechanism of CTS-nZVI was analyzed from the point of view of colloidal stability by settling experiments and a zeta potential test. The theoretical model of colloidal filtration was applied for the calculation of transport coefficients on the basis of the column experiments data. Considering attachment–detachment effects, a particle transport model was built using HYDRUS-1D software to analyze the transport and spatial distribution of CTS-nZVI in a sand column.

Persulfate activation by natural zeolite supported nanoscale zero-valent iron for trichloroethylene degradation in groundwater

In the advanced oxidation processes, using persulfate (PS) as a radical precursor for pollutant degradation in groundwater has received increasing attention. In this study, zeolite supported nZVI composites (Z/nZVI) were synthesized through an ion exchange and borohydride reduction method to investigate their ability to activate PS for the TCE degradation. Based on preliminary screening of the PS activation by the Z/nZVI (PS-Z/nZVI) system in terms of TCE degradation, Z/nZVI composite with a zeolite to nZVI mass ratio of 1:1 (Z/nZVI (1)) was optimized as the best composition and chosen for further characterization and examination. Especially, for this PS-Z/nZVI system, PS concentration, solution matrix effects (i.e., solution pH, coexisting anions and natural organic matter) were studied. Characterization results revealed that the aggregation of nZVI particles was alleviated and they were good dispersed on the zeolite sheet with a large SSA (159.49 m²/g) compared to the unsupported nZVI (8.77 m²/g). The synthesized Z/nZVI (1) composite exhibited excellent activated ability towards PS (1.5 mM) and effectively degraded 98.8% of TCE at pH 7 within 120 min. The PS-Z/nZVI system was observed to operate effectively over a wide range of pH (i.e., 4-7) for TCE degradation. Moreover, the presence of nitrates (1 mM) and bicarbonates (10 mM) decreased the TCE degradation efficiency to 91.5% and 59.6%, respectively. Scavenger tests demonstrated that both sulfate and hydroxyl radicals participated in the TCE degradation. The ion chromatography analysis suggested the formation of oxalic acid and formic acid as the reaction intermediates during the TCE degradation process in the PS-Z/nZVI system.

The impact of surface properties and dominant ions on the effectiveness of G-nZVI heterogeneous catalyst for environmental remediation

The surface properties of nanocomposites are influenced by the existence of inorganic species that may affect its performance for specific catalytic applications. The impact of different ionic species on particular catalytic activity had not been investigated to date. In this study, the surface charge (zeta potential) of graphene-oxide-supported nano zero valent iron (G-nZVI) was tested in definitive cationic (Na⁺, K⁺, Ca²⁺ and Mg²⁺) and anionic (Br^-, Cl^-, NO₃^-, SO₄^2-, and HCO₃^-) environments. The efficiency of G-nZVI catalyst was inspected by measuring the generation of reactive oxygen species (ROS) for the degradation of 1,1,1-trichloroethane (TCA) in sodium percarbonate (SPC) system. Tests conducted using probe compounds confirmed the generation of OH and O₂^- radicals in the system. In addition, the experiments performed using scavenging agents certified that O₂^- were primary radicals responsible for TCA removal, along with prominent contribution from OH radicals. The study confirmed that G-nZVI catalytic capability for TCA degradation is notably affected by various cationic species. The presence of Ni²⁺ and Cu²⁺ significantly enhanced (94%), whereas Na⁺ and K⁺ had minor effects on TCA removal. Overall, the results indicated that groundwater ionic composition may have low impact on the effectiveness of G-nZVI-catalyzed peroxide TCA treatment.

Remediation of contaminated soils by enhanced nanoscale zero valent iron

The use of nanoscale zero valent iron (nZVI) for in situ remediation of soil contamination caused by heavy metals and organic pollutants has drawn great concern, primarily owing to its potential for excellent activity, low cost and low toxicity. This reviews considers recent advances in our understanding of the role of nZVI and enhanced nZVI strategy in the remediation of heavy metals and persistent organic contaminants polluted soil. The performance, the migration and transformation of nZVI affected by the soil physical and chemical conditions are summarized. However, the addition of nZVI inevitably disturbs the soil ecosystem, thus the impacts of nZVI on soil organisms are discussed. In order to further investigate the remediation effect of nZVI, physical, chemical and biological method combination with nZVI was developed to enhance the performance of nZVI. From a high efficient and environmentally friendly perspective, biological method enhanced nZVI technology will be future research needs. Possible improvement of nZVI-based materials and potential areas for further applications in soil remediation are also proposed.

Removal of chlorinated organic solvents from hydraulic fracturing wastewater by bare and entrapped nanoscale zero-valent iron

With the increasing application of hydraulic fracturing, it is urgent to develop an effective and economically feasible method to treat the large volumes of fracturing wastewater. In this study, bare and entrapped nanoscale zero-valent iron (nZVI) were introduced for the removal of carbon tetrachloride (CT) and 1,1,2-trichloroethane (TCA) in model high-salinity fracturing wastewater. With increasing ionic strength (I) from Day-1 (I = 0.35 M) to Day-90 (I = 4.10 M) wastewaters, bare nZVI presented significantly lower removal efficiency of CT (from 53.5% to 38.7%) and 1,1,2-TCA (from 71.1% to 21.7%) and underwent more serious Fe dissolution from 1.31 ± 1.19% in Day-1 to 5.79 ± 0.32% in Day-90 wastewater. Particle aggregation induced by high ionic strength was primarily responsible for the lowered performance of nZVI due to less available reactive sites on nZVI surface. The immobilization of nZVI in alginate with/without polyvinyl alcohol provided resistance to particle aggregation and contributed to the superior performance of entrapped nZVI in Day-90 wastewater for 1,1,2-TCA removal (62.6-72.3%), which also mitigated Fe dissolution (4.00-4.69%). Both adsorption (by polymer matrix) and reduction (by immobilized nZVI) were involved in the 1,1,2-TCA removal by entrapped nZVI. However, after 1-month immersion in synthetic fracturing wastewater, a marked drop in the reactivity of entrapped nZVI for 1,1,2-TCA removal from Day-90 wastewater was observed with significant release of Na and total organic carbon. In summary, bare nZVI was sensitive to the nature of the fracturing wastewater, while the use of environmentally benign entrapped nZVI was more promising for wastewater treatment.

Efficient transformation in characteristics of cations supported-reduced graphene oxide nanocomposites for the destruction of trichloroethane

Experiments were conducted to investigate the use of graphene-oxide supported metallic nanocomposites for improving the degradation of trichloroethane (TCA) by sodium percarbonate (SPC). Two methods of production, chemical reduction (CR) and solvo-thermal (ST), were tested for preparation of single (Fe) and binary (Fe-Cu) nanocomposites supported by reduced graphene oxide (rGO). A variety of analytical techniques including N2 adsorption Brunauer-Emmett-Teller (BET), x-ray diffraction (XRD), fourier-transfrom infrared spectroscopy (FTIR), and transmisison electron microscopy (TEM) were applied to characterize the physicochemical and microstructural properties of the synthesized nanocomposites. The characterization indicated that the CR method produced nanocomposites that comprised only mesoporous structure. Conversely, both micro and mesoporous structures were present for samples produced with the ST method. The synthesized single and bimetallic composites produced from the ST method showed higher surface areas, i.e. 93.6 m²/g and 119.2 m²/g as compared to the ones synthesized via the CR method, i.e. 13.8 m²/g and 38.0 m²/g respectively. The results of FTIR and XRD analyses confirmed that the ST method produced highly crystalline nanocomposites. SEM and TEM analysis validated that metallic particles with definite morphology well distributed on the surface of rGO. X-ray photoelectron spectroscopy (XPS) analysis confirmed the homogeneity nanocomposites and occurrence of variation in copper oxidation states during degradation process. EDS mapping validate the homogeneous distribution of Cu and Fe at reduced graphene oxide surface. The Fe-Cu/rGO (ST) activated SPC system effectively degraded TCA (92%) in 2.5 h at low nanocomposite dose compared to the Fe-Cu/rGO (CR) and only Fe, for which the maximum degradation efficiencies achieved were 81% and 34%. In conclusion, excellent catalytic characteristics were observed for the ST-synthesized single and bimetallic (Fe/rGO, Fe-Cu/rGO) catalysts. These catalysts were successful in improving the degradation of TCA via activated SPC.

An efficient catalytic degradation of trichloroethene in a percarbonate system catalyzed by ultra-fine heterogeneous zeolite supported zero valent iron-nickel bimetallic composite

Zeolite supported nano iron-nickel bimetallic composite (Z-nZVI-Ni) was prepared using a liquid-phase reduction process. The corresponding surface morphologies and physico-chemical properties of the Z-nZVI-Ni composite were determined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Energy dispersive X-ray spectra (EDS), Brunauer Emmett Teller (BET) adsorption, wide angle X-ray diffractometry (WA-XRD), and Fourier transform infrared spectroscopy (FTIR). The results indicated high dispersion of iron and nickel nano particles on the zeolite sheet with an enhanced surface area. Complete destruction of trichloroethene (TCE) and efficient removal of total organic carbon (TOC) were observed by using Z-nZVI-Ni as a heterogeneous catalyst for a Fenton-like oxidation process employing sodium percarbonate (SPC) as an oxidant. The electron spin resonance (ESR) of Z-nZVI-Ni verified the generation and intensity of hydroxyl radicals (OH•). The quantification of OH• elucidated by using p-chlorobenzoic acid, a probe indicator, confirmed the higher intensity of OH•. The transformation products were identified using GC-MS. The slow iron and nickel leaching offered higher stability and better catalytic activity of Z-nZVI-Ni, demonstrating its prospective long term applications in groundwater for TCE degradation.

Nanoscale zerovalent iron (nZVI) supported by natural and acid-activated sepiolites: the effect of the nZVI/support ratio on the composite properties and Cd2+ adsorption

Natural (SEP) and partially acid-activated (AAS) sepiolites were used to prepare composites with nanoscale zerovalent iron (nZVI) at different (SEP or AAS)/nZVI ratios in order to achieve the best nZVI dispersibility and the highest adsorption capacity for Cd²⁺. Despite the higher surface area and pore volume of AAS, better nZVI dispersibility was achieved by using SEP as the support. On the other hand, a lower oxidation degree was achieved during the synthesis using AAS. X-ray photoelectron spectroscopy (XPS) analysis of the composite with the best nZVI dispersibility, before and after Cd²⁺ adsorption, confirmed that the surface of the nZVI was composed of oxidized iron species. Metallic iron was not present on the surface, but it was detected in the subsurface region after sputtering. The content of zerovalent iron decreased after Cd²⁺ adsorption as a result of iron oxidation during Cd²⁺ adsorption. The XPS depth profile showed that cadmium was present not only at the surface of the composite but also in the subsurface region. The adsorption isotherms for Cd²⁺ confirmed that the presence of SEP and AAS decreased the agglomeration of the nZVI particles in comparison to the pure nZVI, which provided a higher adsorption capacity. The results showed that the prevention of both aggregation and oxidation during the synthesis was necessary for obtaining an SEP/AAS-nZVI composite with a high adsorption capacity, but oxidation during adsorption was beneficial for Cd²⁺ removal. The formation of strong bonds between Cd²⁺ and the adsorbents sites of different energy until monolayer formation was proposed according to modeling of the adsorption isotherms.

Unveiling the mechanism of electron transfer facilitated regeneration of active Fe2+ by nano-dispersed iron/graphene catalyst for phenol removal

Unveiling the mechanism of electron transfer-facilitated regeneration of active Fe²⁺ by nano-dispersed iron/graphene catalyst for phenol removal.

Dehalogenation of diatrizoate using nanoscale zero-valent iron: impacts of various parameters and assessment of aerobic biological post-treatment

The potential of nanoscale zero-valent iron for dehalogenation of iodinated contrast media was demonstrated.