Degradation of trichloroethylene in aqueous solution by persulfate activated with Fe(III)–EDDS complex

Electrochemical/Peroxymonosulfate/NrGO-MnFe2O4 for Advanced Treatment of Landfill Leachate Nanofiltration Concentrate

A simple one-pot method was used to successfully embed manganese ferrite (MnFe2O4) nanoparticles on the nitrogen-doped reduced graphene oxide matrix (NrGO), which was used to activate peroxymonosulfate to treat the landfill leachate nanofiltration concentration (LLNC) with electrochemical enhancement. NrGO-MnFe2O4 and rGO-MnFe2O4 were characterized by various means. This indicates that nitrogen-doped could induce more graphene oxide (GO) spall and reduction to produce more active centers, and was favorable for uniformly loading MnFe2O4 particles. The comparison between electrochemical/peroxymonosulfate/NrGO-MnFe2O4 (EC/PMS/NrGO-MnFe2O4) system and different catalytic systems shows that electrochemical reaction, NrGO and MnFe2O4 can produce synergies, and the chemical oxygen demand (COD) removal rate of LLNC can reach 72.89% under the optimal conditions. The three-dimensional (3D-EEM) fluorescence spectrum shows that the system has a strong treatment effect on the macromolecules with intense fluorescence emission in LLNC, such as humic acid, and degrades into substances with weak or no fluorescence characteristics. Gas chromatography-mass spectrometry (GC-MS) indicates that the complex structure of refractory organic compounds can be simplified, while the simple small molecular organic compounds can be directly mineralized. The mechanism of catalytic degradation of the system was preliminarily discussed by the free radical quenching experiment. Therefore, the EC/PMS/NrGO-MnFe2O4 system has significant application potential in the treatment of refractory wastewater.

Nano-magnetite supported by biochar pyrolyzed at different temperatures as hydrogen peroxide activator: Synthesis mechanism and the effects on ethylbenzene removal

Nano-magnetite supported by biochar (nFe₃O₄/BC) pyrolyzed at temperatures of 300 °C-600 °C was developed to activate hydrogen peroxide (H₂O₂) for the efficient degradation of ethylbenzene in aqueous solution. It was revealed that the degradation efficiency of ethylbenzene and TOC removal were 96.9% and 36.2% respectively after the reaction for 40 min in the presence of initial concentration of 0.1 mmol L^-1 ethylbenzene, 2.76 g L^-1 nFe₃O₄/BC₅₀₀ with the mass ratio of nFe₃O₄ to BC₅₀₀ of 4:1 and 2.0 mmol L^-1 H₂O₂ at pH 7.0. Based on electron paramagnetic resonance (EPR), quenching experiment and X-ray photoelectron spectroscopy (XPS) data, both OH and O₂^- radicals were generated in the nFe₃O₄/BC₅₀₀ activated H₂O₂ system, and the OH radicals were the predominant species for the degradation of ethylbenzene. Through electron transfer process, mechanisms of Fe(II), phenolic hydroxyl group and persistent free radicals (PFRs) on BC surfaces accounted for the generation of OH radicals, and Fe(III) in nFe₃O₄ and formed from Fe(II) oxidation responsible for the generation of O₂^- radicals in the nFe₃O₄/BC activated H₂O₂ system were proposed.

Oxidation of flumequine in aqueous solution by UV-activated peroxymonosulfate: Kinetics, water matrix effects, degradation products and reaction pathways

The degradation of flumequine (FLU) in aqueous solution by ultraviolet (UV)-activated peroxymonosulfate (PMS) was investigated in this work. Under the conditions of [PMS]₀:[FLU]₀ = 1:1, T = 25 ± 2 °C, pH = 7.0 ± 0.1, nearly complete removal of FLU was achieved after 60 min. The effects of various operating parameters, including oxidant doses, pH, the presence of typical ions (NH₄⁺、Mg²⁺、Fe³⁺、Cl^-、NO₃^-、HCO₃^-) and humic acid were evaluated. It was found that the pseudo-first-order rate constants of FLU degradation increased with increasing PMS dosage and decreasing solution pH. The presence of Mg²⁺ could accelerate FLU removal, while Fe³⁺, HCO₃^-, NO₃^- and HA inhibited the reaction. Moreover, the degradation of FLU in different water matrices were also explored, and the removal followed the order of Tap water > Ultrapure water > River water > Secondary clarifier effluent. According to the control and radical quenching experiment results, direct photolysis and reactive radicals (SO₄^- and HO) contributed mainly to FLU degradation in the UV/PMS system. Initial FLU molecule underwent reactions such as hydroxylation, hydroxyl substitution, demethylation, decarboxylation/decarbonylation and ring opening, leading to the formation of nineteen oxidation products. The effective degradation by UV/PMS suggests a feasible technology for treating FLU in waters and wastewaters.

In Situ Persulfate Oxidation of 1,2,3-Trichloropropane in Groundwater of North China Plain

In situ injection of Fe(II)-activated persulfate was carried out to oxidize chlorinated hydrocarbons and benzene, toluene, ethylbenzene, and xylene (BTEX) in groundwater in a contaminated site in North China Plain. To confirm the degradation of contaminants, an oxidant mixture of persulfate, ferrous sulfate, and citric acid was mixed with the main contaminants including 1,2,3-trichloropropane (TCP) and benzene before field demonstration. Then the mixed oxidant solution of 6 m³ was injected into an aquifer with two different depths of 8 and 15 m to oxidize a high concentration of TCP, other kinds of chlorinated hydrocarbons, and BTEX. In laboratory tests, the removal efficiency of TCP reached 61.4% in 24 h without other contaminants but the removal rate was decreased by the presence of benzene. Organic matter also reduced the TCP degradation rate and the removal efficiency was only 8.3% in 24 h. In the field test, as the solution was injected, the oxidation reaction occurred immediately, accompanied by a sharp increase of oxidation–reduction potential (ORP) and a decrease in pH. Though the concentration of pollutants increased due to the dissolution of non-aqueous phase liquid (NAPL) at the initial stage, BTEX could still be effectively degraded in subsequent time by persulfate in both aquifers, and their removal efficiency approached 100%. However, chlorinated hydrocarbon was relatively difficult to degrade, especially TCP, which had a relatively higher initial concentration, only had a removal efficiency of 30%–45% at different aquifers and monitoring wells. These finding are important for the development of injection technology for chlorinated hydrocarbon and BTEX contaminated site remediation.

Structural evolution of calcia during calcium deoxidation in Fe-O-Ca melt

The crystallization process of CaO in iron melt begins with nucleation, which determines the structure and size of the CaO inclusions; thus, it is important to investigate the mechanism of inclusion modification by calcium treatment. In this study, a two-step nucleation method was used to investigate the behavior during the early stages of CaO inclusion crystallization. The first principles method was applied to calculate the structures and properties of CaO crystals and CaO clusters. Then, the nucleation mechanism of CaO in the Fe-O-Ca melt has been discussed. The numerical results show that CaO clusters with cubic structures and appropriate variations are the lowest energy structures and are more stable than other isomers. The stability of the cubic (CaO)_n clusters increases with the increase in size and gradually approaches that of the CaO crystal. CaO clusters can form spontaneously in the Fe-O-Ca melt, while the transformation reaction of the CaO clusters in the Fe-O-Ca melt deeply depends on the supersaturation ratio of [Ca] and [O]. CaO clusters may remain as suspended CaO inclusions in the iron melt for a long time, and these suspensions of CaO clusters are the source of excess oxygen in the iron melt.

Zero-valent iron (ZVI) Activation of Persulfate (PS) for Degradation of Para-Chloronitrobenzene in Soil

Para-chloronitrobenzene (p-CNB) in soil has posed significant health risks because of its persistence and high toxicity. The efficacy of catalyzed Zero-Valent Iron (ZVI), activated persulfate, and ZVI-persulfate processes for the degradation of p-CNB in soil was investigated. The p-CNB removal rate significantly increased from 10.8 to 90.1% with increased ZVI dosage from 0.1 mmol g^-1 to 1.0 mmol g^-1. The p-CNB removal increased with the decrease of initial pH and a removal efficiency of 85.3% was obtained at an initial pH value of 6.8 in combined system. The p-CNB removal rate in the single persulfate system and ZVI system was 36.5% and 60.2%, while the ZVI-persulfate system showed more sufficient p-CNB removal capacity and the removal rate of p-CNB was 88.7%. Scanning electron microscopy (SEM) and Electron paramagnetic resonance (EPR) was adopted in order to explore the degradation mechanism by ZVI-Persulfate system in soil.

EDDS as complexing agent for enhancing solar advanced oxidation processes in natural water: Effect of iron species and different oxidants

The main purpose of this pilot plant study was to compare degradation of five microcontaminants (MCs) (antipyrine, carbamazepine, caffeine, ciprofloxacin and sulfamethoxazole at 100 μg/L) by solar photo-Fenton mediated by EDDS and solar/Fe:EDDS/S₂O₈^2-. The effects of the Fe:EDDS ratio (1:1 and 1:2), initial iron species (Fe(II) or Fe(III) at 0.1 mM) and oxidizing agent (S₂O₈^2- or H₂O₂ at 0.25-1.5 mM) were evaluated. The higher the S₂O₈^2- concentration, the faster MC degradation was, with S₂O₈^2- consumption always below 0.6 mM and similar degradation rates with Fe(II) and Fe(III). Under the best conditions (Fe 0.1 mM, Fe:EDDS 1:1, S₂O₈^2- 1 mM) antipyrine, carbamazepine, caffeine, ciprofloxacin and sulfamethoxazole at 100 μg/L where 90% eliminated applying a solar energy of 2 kJ/L (13 min at 30 W/m² solar radiation <400 nm). Therefore, S₂O₈^2- promotes lower consumption of EDDS as Fe:EDDS 1:1 was better than Fe:EDDS 1:2. In photo-Fenton-like processes at circumneutral pH, EDDS with S₂O₈^2- is an alternative to H₂O₂ as an oxidizing agent.

Nucleation and growth for magnesia inclusion in Fe-O-Mg melt

The crystallization process of magnesia in iron melt begins with nucleation, which determines the structure and size of magnesia inclusions. Thus, it is necessary to have a deep insight into the crystallization of magnesia by two-step nucleation mechanisms. In this work, the two-step nucleation method was used to investigate the behavior during the early stages of magnesia inclusions crystallization. A first principles method was applied to calculate the thermodynamic properties of magnesia crystal from various cluster structures for the formation of magnesia inclusions. Based on the numerical results, the nucleation mechanism of magnesia in liquid iron has been discussed. The magnesia clusters appear as the structural units for Mg-deoxidation reaction in the liquid iron, and the residual magnesia clusters are the reason for the supersaturation ratio or the excess oxygen for MgO formation in the liquid iron. Based on the comparison between Mg-deoxidation equilibrium experiments and numerical results, the previous experiments may be in a different thermodynamic state. The equilibrium reaction product should be not only magnesia clusters but also bulk-magnesia in those equilibrium experiments.

The crystallization process of magnesia involves two steps.

One-step fabrication of carbonaceous solid acid derived from lignosulfonate for the synthesis of biobased furan derivatives

An eco-friendly and low-cost lignosulfonate-based acidic carbonaceous catalyst (LS-SO₃H) was effectively fabricated using the sulfite pulping by-product of sodium lignosulfonate as a precursor by facile one-step simultaneous carbonization and sulfonation, and employed for the synthesis of promising biofuel furan derivatives from biorenewable feedstocks. The catalyst preparation conditions significantly affected the preparation and properties of LS-SO₃H. A relatively high catalyst preparation yield (40.4%) with strong –SO₃H density (1.33 mmol g⁻¹) were achieved when the lignosulfonate was treated in concentrated H₂SO₄ solution at 120 °C for 6 h. The preparation yield of LS-SO₃H was nearly twice as much as that of one-step prepared catalyst using alkaline lignin (another technical lignin from pulping) as a precursor. The as-prepared LS-SO₃H had similar textural characteristics to the frequently-used two-step prepared carbonaceous catalyst involving pyrolysis carbonization and sulfonation. LS-SO₃H was found to show good catalytic activity for the synthesis of 5-ethoxymethylfurfural (EMF) in ethanol medium, affording around 86%, 57% and 47% yields from 5-hydroxymethylfurfural (HMF), fructose and inulin, respectively. Also, a high HMF yield of 83% could be obtained from fructose when DMSO was replaced as reaction medium. The used LS-SO₃H was readily recovered by filtration, and remained active in recycle runs.

An easy-prepared and bio-supported lignosulfonate-based acidic carbonaceous catalyst was developed for the synthesis of promising furan biofuels from biorenewable feedstocks.

Metal- and catalyst-free, one-pot, three-component synthesis of propargylamines in magnetized water: experimental aspects and molecular dynamics simulation

Multi-component reactions of aldehydes, amines, and alkynes in magnetized water as a green-promoting medium.