Persulfate activation by MnCuS nanocomposites for degradation of organic pollutants

Ball-milled layer double hydroxide as persulfate activator for efficient degradation of organic: Alkaline sites-triggered non-radical mechanism

Considerable efforts have been put into enhancing the activation performance of peroxydisulfate (PDS) by catalysts toward oxidative degradation of organic pollutants, while the oxidative selectivity is somehow overlooked. Here, we reported an enhanced non-radical oxidation pathway of PDS, activated by ball-milled Mg/Al-layered double hydroxide (BM-LDH), to reconcile the selectivity and reactivity. EPR and quenching experiments suggested that 1O2 dominated the oxidative pathway for phenol degradation without generating carcinogenic halide by-products. Multiple interfacial characterizations and density functional theory (DFT) calculations revealed that BM-LDH played dual roles in PDS activation: (1) the interlaminar BM-LDH allowed PDS intercalation to form complexed PDS, resulting in decreases in the activation barrier of PDS; (2) abundant terminal hydroxyls in the layers of BM-LDH acted as alkaline-activation sites that can efficiently activate PDS to generate 1O2 toward phenol degradation. Ball-milling treatment of LDH refined the structural hierarchy of LDH to create pore volumes, which greatly enhanced the diffusion of phenol to the intercalated PDS, resulting in more than twice the reaction rate for phenol degradation. This study provided a promising approach to simultaneously control over the reactivity and selectivity toward PDS activation that are critical for the degradation of organic pollutants particularly in drinking water treatment.

Engineering active heterojunction architecture with oxygenated-Co, Mo bimetallic sulfide heteronanosheet and graphene oxide for peroxymonosulfate activation

Bimetallic sulfides have distinctive catalytic property in activating peroxymonosulfate (PMS) for water remediation. Polyoxometalates as potential precursors have rarely been reported for the catalytic degradation of refractory organic pollutants. Herein, a composite catalyst of Co-Mo bimetallic sulfides supported onto graphene oxide (O-CoMoS/GO) with a heterojunction architecture was synthesized through a hydrothermal strategy with polyoxometalates ((NH₄)₄[Co^IIMo₆O₂₄H₆]·6H₂O) as the precursor and applied in the PMS activation. This material showed a superior performance for the catalytic degradation of the model organic pollutant, 4-chlorophenol (rapidly removed within 10 min with an apparent reaction rate constant of 0.5458 min^-1). O-CoMoS/GO outperformed most of the reported catalysts in terms of activity and had a strong tolerance towards common organic and inorganic compounds in water, and could perform well in different real water systems. Experimental and theoretical results indicated that the introduction of GO could achieve the enrichment of electrons on the metals and reduce the d band center (ε_d) of Co close to the Fermi level (ε_F), thereby facilitating the interfacial electron transfer process. The activation mechanism was due to the as-prepared bimetallic sulfides and the formation of heterojunction structure with GO, where Co(II) as the active center could be regenerated by the adjacent Mo element (as co-catalyst) and by gathering electrons from GO through the Co/Mo-O-C coupling. This work provides insights into the design of bimetallic sulfide catalysts in activating PMS for water remediation.

A review of advanced oxidation process towards organic pollutants and its potential application in fracturing flowback fluid

Fracturing flowback fluid (FFF) including various kinds of organic pollutants that do harms to people and new treatments are urgently needed. Advanced oxidation processes (AOPs) are suitable methods in consideration with molecular weight, removal cost and efficiency. Here, we summarize the recent studies about AOP treatments towards organic pollutants and discuss the application prospects in treatment of FFF. Immobilization and loading methods of catalysts, evaluation method of degradation of FFF, and continuous treatment process flow are discussed in this review. In conclusion, further studies are urgently needed in aspects of catalyst loading methods, macromolecule organic evaluation methods, industrial process, and pathways of macromolecule organics' decomposition.

Sensitive fluorescent detection and micromechanism of Mn-doped CuS probe for oxytetracycline hydrochloride

The novel CuMnS nanoflower fluorescent probe based on Mn-doped CuS was developed to achieve the fluorescence detection of oxytetracycline hydrochloride (OTC), the fluorescent sensor has good selectivity and stability. The doping of Mn significantly increased the fluorescence intensity of CuS, which was above 10 times that of CuS. When the predominant species of OTC molecule was zwitterionic OTC^+/-at the solution pH of about 5.00, the fluorescence quenching efficiency of CuMnS by OTC reached the highest. Through fluorescence lifetime and UV absorption, the sensing mechanism between CuMnS and OTC was found to be static quenching. Moreover, Multiwfn wavefunction analysis program based on density function theory (DFT) calculation was applied to compare the interactions between different OTC species and CuMnS at different pH, to reveal the micromechanism of fluorescence quenching of CuMnS by OTC from the views of atoms. The molecular surface quantitative analysis and basin analysis of different OTC species demonstrated that the N atom and O atoms of tricarbonylamide moiety of zwitterionic OTC^+/- can provide lone pair electrons to form a non-fluorescent ground state complex with CuMnS. Meanwhile, the electrostatic attraction of OTC^+/- with negatively charged CuMnS was also beneficial to the interaction, resulting in the effective fluorescence quenching of CuMnS. This work offers a convenient method for sensitively detecting OTC and broadens the application of CuMnS in the field of fluorescence detection.

Natural coal gangue as a stable catalyst to activate persulfate: tetracycline hydrochloride degradation and its explored mechanism

The surface-bonded hydroxyl groups on CG play the dominant role in PS activation and TC removal.

Synergistic effect of novel Co-modified micro/nano geopolymers in a photo-PDS system

Persulfate activation is an efficient advanced oxidation process for water treatment. However, many catalyst materials make their preparation methods and raw materials very complicated and expensive while pursuing high-efficiency catalytic effects. In this research, a novel Co-modified micro/nano geopolymer (Co-MNG) material was prepared from solid waste using a mechanochemical method. The whole preparation process of Co-MNG is simple and time-saving, and most of its raw materials are solid waste. In addition, it has few adverse effects on the environment during preparation and use and has a good effect on PDS activation. Under dark conditions, 1 mg L^-1 of unloaded Co metal MNG material could degrade 20 mg L^-1 Rhodamine B solution by 79% in 60 min with 15 mM PDS, but the application of visible light could not enhance its effect. However, after adding 4 wt% of different Co-containing compounds, the prepared Co-MNG materials could improve their degradation effect under the same conditions, and it is more obvious under the condition of applying visible light. Among them, MNG-Co(NO₃)₂ could completely degrade RhB within 40 min under the application of visible light. ESR (electron spin resonance) tests showed that the MNG-Co(NO₃)₂ material could generate a variety of active radicals in a photo-PDS system, such as h⁺, ·OH, ·O₂^- and SO₄^-. Mechanistic research experiments showed that both visible light and Co-MNG materials can activate PDS to a certain extent, but when both exist at the same time, the material could effectively couple visible light and Co activation of PDS in a photo-PDS activation system to achieve synergistic degradation of pollutants in water.

Efficient Adsorption-Photocatalytic Removal of Tetracycline Hydrochloride over Octahedral MnS

To disclose the effect of crystal plane on the adsorption-photocatalytic activity of MnS, octahedral MnS was prepared via the hydrothermal route to enhance the adsorption and photocatalytic efficiencies of tetracycline hydrochloride (TCH) in visible light region. The optimal MnS treated at 433 K for 16 h could remove 94.83% TCH solution of 260 mg L⁻¹ within 180 min, and its adsorption-photocatalytic efficiency declined to 89.68% after five cycles. Its excellent adsorption-photocatalytic activity and durability were ascribed to the sufficient vacant sites of octahedral structure for TCH adsorption and the feasible band-gap structure for visible-light response. In addition, the band gap structure (1.37 eV) of MnS with a conduction band value of −0.58 eV and a valence band value of 0.79 eV was favorable for the generation of O²⁻, while unsuitable for the formation of OH. Hence, octahedral MnS was a potential material for the removal of antibiotics from wastewater.

Novel combination of bioleaching and persulfate for the removal of heavy metals from metallurgical industry sludge

The objective of this study was to remove heavy metals from metallurgical industry sludge by bioleaching alone and bioleaching combined with persulfate (PDS). The results showed that the removal of Cu, Zn, Pb, and Mn reached 70%, 83.8%, 25.2%, and 76.9% by bioleaching alone after 18 days, respectively. The experiment of bioleaching combined with PDS was carried out in which the optimal additive dosage of K₂S₂O₈, 8 g/L, was added to bioleaching after 6 d. After 1 h, the removal of four heavy metals reached 75.1, 84.3, 36.7, and 81.6%, respectively. Compared with bioleaching alone, although the increase in removal efficiency was only slightly increased, the treatment cycle was distinctly shortened from 18 to 6 days + 1 h. The scanning electron microscopy (SEM) results showed that the surface morphology of the sludge was changed significantly by the combined treatment. The content of heavy metals was significantly reduced after bioleaching combined with PDS by energy dispersive X-ray spectroscopy (EDX). Through electron paramagnetic resonance (EPR) and free radical quenching experiments, it was indicated that sulfate radicals [Formula: see text] plays a leading role in the combined treatment. The treated sludge mainly existed in a stable form, and the bioavailability was reduced with European Community Bureau of Reference (BCR) morphology analysis. This study proved that the combination of bioleaching and PDS could not only shorten the treatment cycle but also further improve the efficiency of heavy metal leaching. It provides a novel treatment method for the removal of heavy metals from metallurgical industry sludge.

Heterogeneous activation of persulfate by Bi2MoO6-CuS composite for efficient degradation of orange II under visible light

Here in, a special catalytic system of potassium persulfate (K₂S₂O₈, PS) activated by Bi₂MoO₆-CuS composite was established for the orange II (OII) degradation under visible light. The Bi₂MoO₆-CuS composite was synthesized by a two-step hydrothermal and solvothermal methods. The structure, morphology, light absorption and photocatalytic properties of the composite were respectively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible diffuse reflectance spectroscopy (UV-vis DRS). The removal efficiency of OII degradation in the Bi₂MoO₆-CuS/PS/vis system reached to 98% within 80 min, which was much higher than that of either Bi₂MoO₆ or CuS alone. A feasible mechanism analysis of OII degradation was proposed and validated by simple classical quenching experiments and electron spin resonance (ESR) spectroscopy. The high removal efficiency by the nanocomposite could be attributed to highly active species of O₂^·-, ·OH and SO₄^•- radicals in the Bi₂MoO₆-CuS photocatalytic oxidation system. Moreover, the composite material retained its activation performance even after 5 degradation cycles, which suggested its high stability.

Modified nanoscale zero-valent iron in persulfate activation for organic pollution remediation: a review

Under the action of different activators, persulfate can produce sulfate radicals (SO₄·^-) with strong oxidizing ability, which can destruct many organic compounds. Meanwhile, persulfate is widely used in groundwater and soil remediation because of its fast reaction and wide application. With the high specific surface area and reactivity of nanoscale zero-valent iron (nZVI), it can enhance the degradation efficiency of the persulfate system on organic pollutants in soil and water as a persulfate activator. However, nZVI is easy to get oxidized and has a tendency to aggregation. To solve these problems, a variety of nZVI modification methods have been put forward and put into to applications in the activation of persulfate. This article will give a systematic introduction of the background and problems of nZVI-activated persulfate in the remediation of organic pollution. In addition, the modification methods and mechanisms of nZVI are summarized, and the applications and progress of modified nZVI-activated persulfate are reviewed. The factors that affect the removal of organic compounds by the activation system are discussed as well. Worldwide, the field studies and full-scale remediation using modified nZVI in persulfate activation are yet limited. However, the already known cases reveal the good prospect of applying modified nZVI in persulfate activation to organic pollution remediation.