Removal of NO in flue gas simulated by the Fe2+/Cu2+-activated double oxidant system

⋅ O H The wet denitrification technology has a good development prospect due to its simple system and mild reaction conditions, and related research has become a hot topic in the field of flue gas purification. In this work, a novel simultaneous removal technology of NO from flue gas using Fe2+/Cu2+-catalytic H2O2/(NH4)2S2O8 system was developed for the first time. The feasibility of this new flue gas cleaning technology was explored through a series of experiments and performance analyses. The mechanism of oxidation products, free radicals and simultaneous removal of NO was revealed. The effects of the main process parameters on the removal of NO were investigated. Relevant results demonstrated that the removal efficiency of NO was elevated when the concentration of (NH4)2S2O8 or reacting temperature increased, while it was decreased after increasing the raising of Fe2+, Cu2+ and H2O2 concentrations. The main radicals were and·S O 4 - , using the electron spin resonance technique in the solution, and played a very important role in NO removal. The main products were carried out by ion chromatography and elemental N material accountancy, and the results showed that it was sulfate and nitrate in the solution, which provided theoretical guidance for the subsequent treatment and resource utilization of the absorption solution. The results of the study provided a theoretical basis for the industrial application of wet denitrification.Highlights A new green process of NO removal by a wet process with Fe2+/Cu2+ activated (NH4)2S2O8 system is proposed in this paper;Elimination mechanisms and paths of NO are elucidated;The synergistic role produced by Cu2+ and Fe2+ is beneficial to the purification of NO;The synergistic role produced by (NH4)2S2O8 and H2O2 increased the concentration of free radicals in the solution;This process jointly considers the enhanced removal of NO and recycling of transition metal ions.

Alternative treatment of olive mill wastewater by combined sulfate radical-based advanced electrocoagulation processes

The aim of this study is to investigate the performance of advanced electrocoagulation (EC) process for the treatment of olive mill wastewater. In EC process, iron plates were used as electrodes, and peroxydisulfate (PS) and peroxymonosulfate (PMS) were added as oxidants. The effects of the initial pH value, current density, oxidant dose, and electrolysis time were optimized for pollutant removal from olive mill wastewater by EC-PS and EC-PMS processes. Control experiments showed that addition of oxidants to the conventional EC process increased the pollutant removal efficiency. Classical optimization method was used to determine optimum conditions, which were initial pH 4, current density 40 mA/cm2 , oxidant dose 5 g/L, and electrolysis time 30 min for both processes. Under these conditions, EC-PS and EC-PMS processes achieved 50.5% and 48.9% chemical oxygen demand (COD), 93.8% and 89.3% total phenol, 87.7% and 83% UV254 , and 74.5% and 64.1% total suspended solid removal efficiencies. Quenching experiments were performed to determine the dominant radical species participating in the processes. It was observed that hydroxyl and sulfate radicals were involved in both processes but hydroxyl radicals were more active. Specific energy consumption was calculated as 5.90 kWh/kg COD for EC process, 4.95 kWh/kg COD for EC-PS process, and 5.20 kWh/kg COD for EC-PMS process. The organic removal/sludge ratio of EC-PS process was found to be higher with 17.5 g/L value. Although the application of EC-PS and EC-PMS processes alone is insufficient to meet the discharge limits, they have been found to be effective in olive mill wastewater treatment. PRACTITIONER POINTS: Peroxydisulfate (PS) and peroxymonosulfate (PMS)-based advanced electrocoagulation (EC) was used in olive mill wastewater treatment. 50.5% chemical oxygen demand (COD), 93.8% TP, 87.7% UV254 , and 74.5% TSS removals were achieved by EC-PS. 48.9% COD, 89.3% TP, 83% UV254 , and 64.1% TSS removals were obtained by EC-PMS. Hydroxyl and sulfate radicals were involved in both processes.

H2O2 activation and contaminants removal in heterogeneous Fenton-like systems

Emerging contaminants can be removed effectively in heterogeneous Fenton-like systems. Currently, catalyst activity and contaminant removal mechanisms have been studied extensively in Fenton-like systems. However, a systematic summary was lacking. This review summarized: 1) The effects of various heterogeneous catalysts on emerging contaminants degradation by activating H₂O₂; 2) The role of active sites in different catalysts during the activation of H₂O₂ and their contribution to the generation of active species; 3) The modulation of degradation pathways of emerging contaminants. This paper will help scholars to advance the controlled construction of active sites in heterogeneous Fenton-like systems. Suitable heterogeneous Fenton catalysts can be selected in practical water treatment processes.

Efficient degradation of Congo red by persulfate activated with different particle sizes of zero-valent copper: performance and mechanism

In this study, Congo red (CR) was degraded by different particle sizes of zero-valent copper (ZVC) activated persulfate (PS) under mild temperature. The CR removal by 50 nm, 500 nm, 15 μm of ZVC activated PS was 97%, 72%, and 16%, respectively. The co-existence of SO₄^2- and Cl^- promoted the degradation of CR, and HCO₃^- and H₂PO₄^- were detrimental to the degradation. With the reduction of ZVC particle size, the effect of coexisting anions on degradation grew stronger. The high degradation efficiency of 50 nm and 500 nm ZVC was achieved at pH=7.0, while the high degradation of 15 μm ZVC was achieved at pH=3.0. It was more favorable to leach copper ions for activating PS to generate reactive oxygen species (ROS) with the smaller particle size of ZVC. The radical quenching experiment and electron paramagnetic resonance (EPR) analysis indicated that SO₄^-•, •OH and •O₂^- existed in the reaction. The mineralization of CR reached 80% and three possible paths were suggested for the degradation. Moreover, the degradation of 50 nm ZVC can still reach 96% in the 5th cycle, indicating promising application potential in dyeing wastewater treatment.

Activated persulfate by iron-carbon micro electrolysis used for refractory organics degradation in wastewater: a review

With the rapid economic development, the discharge of industrial wastewater and municipal wastewater containing many refractory organic pollutants is increasing, so there is an urgent need for processes that can treat refractory organics in wastewater. Iron-carbon micro electrolysis and advanced oxidation based on persulfate radicals (SO₄^-·) have received much attention in the field of organic wastewater treatment. Iron-carbon micro electrolysis activated persulfate (Fe-C/PS) treatment of wastewater is characterized by high oxidation efficiency and no secondary pollution. This paper reviews the mechanism and process of Fe-C/PS, degradation of organics in different wastewater, and the influencing factors. In addition, the degradation efficiency and optimal reaction conditions (oxidant concentration, catalyst concentration, iron-carbon material, and pH) of Fe-C/PS in the treatment of refractory organics in wastewater are summarized. Moreover, the important factors affecting the degradation of organics by Fe-C/PS are presented. Finally, we analyzed the challenges and the prospects for the future of Fe-C/PS in application, and concluded that the main future directions are to improve the degradation efficiency and cost by synthesizing stable and efficient catalysts, optimizing process parameters, and expanding the application scope.

Zero-Valent Copper-Mediated Peroxymonosulfate Activation for Efficient Degradation of Azo Dye Orange G

Zero-valent metal (ZVMs)-based persulfate activation systems are extensively applied for the elimination of organic pollutants in aqueous environments. In this study, for the first time, zero-valent copper (ZVC) was employed as the peroxymonosulfate (PMS) activator for the efficient degradation of Orange G (OG). The physicochemical properties of ZVC were systematically characterized by FESEM, EDX, TEM, XRD and XPS measurements. Furthermore, the effects of catalyst loading, PMS dosage, OG concentration and inorganic anions on the ZVC/PMS system were, respectively, investigated and explicated. The formation of •OH and SO4•− in the system was verified by quenching experiments and then the possible reaction mechanism was proposed. This work can provide insight into water treatment technology based on ZVMs.

A review on efficient removal of phthalic acid esters via biochars and transition metals-activated persulfate systems

As emerging contaminants, PAEs (Phthalic Acid Esters or Phthalate Esters) have been extensively utilized in industrial production to soften the rigid plastics (plasticizers), and their related products are widely distributed in our daily life. The PAEs can readily transfer from the products to the surrounding environment due to not being chemically bound to the products. In this study, we analyzed the PAEs' properties, usage, and consumption in the world, as well as toxicity to human beings. As endocrine-disrupting chemicals (EDCs), PAEs can disturb the normal hormones reactions, resulting in developmental and reproductive problems. Thus, we have to concern the removal strategies of PAEs. We summarized two novel approaches, including biochars and persulfate (PS) oxidation for effectively removing PAEs in the literature. Their characteristics, removal mechanisms, and the main impact factors on the removal of PAEs were highlighted. Moreover, transition metal-activated PS showed good performance on PAEs degradation. Furthermore, the synergy of biochars and transition metals-PS can overcome the disadvantages of a single approach, and show better performance on the removal of PAEs. Finally, we put forward vital strategies to update two approaches (including the combined) for enhancing the removal of PAEs. It is expected that the researchers or scientists can get a hint on effectively remediating PAEs-contaminated sites via the biochars' sorption/transition metals-PS or the combined two from this review paper.

A comparison study of applying natural iron minerals and zero-valent metals as Fenton-like catalysts for the removal of imidacloprid

Natural iron minerals and zero-valent metals have been widely tested as catalysts for the Fenton-like process, but the systematical comparison study about their catalytic performance was rarely conducted, and the risk of the secondary pollution of toxic heavy metals was still not uncertain. In this paper, a comparison study of applying pyrite, ilmenite, vanadium titano-magnetite (VTM), zero-valent iron (ZVI), and zero-valent copper (ZVC) as Fenton-like catalysts for the removal of imidacloprid was performed. The results showed that ZVI exhibited the highest activity among the recyclable solid catalysts with a removal rate of 96.8% at initial pH 3 using 10.78 mmol/L H₂O₂, due to iron corrosive dissolution. Vanadium titano-magnetite (VTM) exhibited the best activity at first use among tested minerals but with low reusability. Pyrite with stable morphology showed a medium but sustainable ability to degrade imidacloprid, achieving a removal rate of 10.5% in the fifth use. The reaction much favored the acidic condition of initial pH around 2 or 3. Meanwhile, there was a significant positive correlation between removal efficiency and dissolved Fe or Cu concentration. Pyrite was considered to be a promising catalyst in Fenton-like reaction. It was suggested that the system proceeded predominantly through a homogeneous route via dissolved Fe or Cu ions. Except ZVC and VTM, other tested catalysts showed the low possibility of causing secondary pollution of toxic metals in the application of Fenton-like process.

Cu2+/Cu+ cycle promoted PMS decomposition with the assistance of Mo for the degradation of organic pollutant

The limited production of Cu⁺ in the Cu²⁺/PMS processes constrained its large-scan application for the elimination of organic pollutants. In this study, molybdenum powder (Mo) was applied as the co-catalyst to improve the degradation of 2,4-dichlorophenol (2,4-DCP) in Cu²⁺/PMS system at pH 5.6. By the assistance of Mo, Cu²⁺ was rapidly reduced to Cu⁺ which exhibited super activity for the peroxymonosulfate (PMS) activation. Compared with Cu²⁺/PMS processes, the PMS decomposition rate and 2,4-DCP degradation efficiency respectively increased by 62.1% and 83.6% in the Mo co-catalytic Cu²⁺/PMS system after reaction for 20 min. The degradation of 2,4-DCP was completed via both the free radical and non-radical pathways and the free radicals rather than Cu³⁺ contributed most to the reaction. In contrast to fresh Mo, the ratio of Mo⁴⁺ increased and Mo⁶⁺ decreased in the used Mo powder, due to the oxidation of Mo⁰ by Cu²⁺ and/or ∙OH and the reduction of Mo⁶⁺ by O₂∙^-. Additionally, the coexistence of Cl^- and humic acid with low concentrations showed little effects on the Mo/Cu²⁺/PMS system while HCO₃^- presented an obvious depression for 2,4-DCP degradation. During five cycling runs, all the degradation rates were higher than 92.8%, indicating the good stability of Mo/Cu²⁺/PMS system.

A novel biodegradable injectable chitosan hydrogel for overcoming postoperative trauma and combating multiple tumors

Wound bacterial infections and tumor recurrence are the main reasons for the poor prognosis after primary tumor resection. Here, we fabricated a novel therapeutic nanocomposite using chitosan (CS) hydrogel combined with black phosphate nanosheets (BPNSs) and in situ grown copper nanoparticles (CuNPs). The obtained hydrogel (CS@BPNSs@CuNPs), possessing a remarkable temperature-sensitive spongy-like state, offered 24.98 % blood clotting index. The released BPNSs@CuNPs could produce reactive oxygen species (ROS) to kill infected invasive bacteria (98.1 %) and inhibit local residual tumor cell regeneration (11.3 %). Moreover, by coupling the photothermal properties of BPNSs, the BPNSs@CuNPs showed 19.6 % penetration rate to cross the blood tumor barrier (BTB) for treating brain tumors. The hydrogel platform was further combined with aPD-L1-based immunotherapy to employ its synergetic therapeutic effect in the prevention of tumors. The in vivo studies showed that biodegradable hydrogel could hold a great potential as a novel strategy for improving postoperative therapy and multi-tumor treatments.

The efficient degradation of organic pollutants in an aqueous environment under visible light irradiation by persulfate catalytically activated with kaolin-Fe2O3

Characterizations and properties of catalysts.

Activation of peroxymonosulfate system by copper-based catalyst for degradation of naproxen: Mechanisms and pathways

Organic degradation by zero-valent metal (ZVM)-activated peroxymonosulfate (PMS) systems has drawn great attention in water treatment. Among various types of ZVM, zero-valent copper (ZVC) showed greatest activating capacity. However, the disadvantages of the released Cu²⁺ limit the practical utilization of ZVC. In this study, the activation capacity of four normal-sized copper catalysts, namely, copper sheet, graphene-copper sheet, copper foam, and graphene-copper foam, for PMS was investigated using Naproxen (NPX) as the probe compound. Results showed that the degradation efficiency of NPX increased by 10%, while the release of Cu²⁺ decreased by 30% by coating the copper with graphene. Stability tests showed that all of the four catalysts exhibited considerable stability in PMS activation. Furthermore, we found for the first time that the hydroxyl radical was the dominant species in the degradation of NPX rather than the sulfate radical, which was proved by ESR and radical scavenging experiments. Finally, six intermediates were identified by HPLC-MS/MS, and the degradation pathways were proposed. This study confirmed the feasibility of graphene coating on metals to achieve the enhancement of PMS activation.

Tetracycline degradation by persulfate activated with magnetic Cu/CuFe2O4 composite: Efficiency, stability, mechanism and degradation pathway

Magnetically separable Cu/CuFe₂O₄ composite obtained by a solvothermal method was used to active persulfate (PS) for the removal of tetracycline (TC). Under different pH conditions, Cu/CuFe₂O₄ catalyst exhibited a higher catalytic activity for PS activation to degrade TC than that of CuFe₂O₄. The effects of some key parameters including initial pH value, PS concentration, catalyst dosage, reaction temperature and coexisting ions on TC degradation were investigated in Cu/CuFe₂O₄/PS system. The reuse of Cu/CuFe₂O₄ catalyst at pH 3.50, 7.00 and 11.00 indicated that the catalyst showed a low stability due to the corrosion of metallic copper (Cu°), but bicarbonate ions could enhance the stability and recyclability of this catalyst through the suppression of copper leaching. Both sulfate and hydroxyl radicals were the main reactive species in Cu/CuFe₂O₄/PS system. Cu° can not only work as electron donor to active PS to produce the reactive radicals but also act as an electron bridge to facilitate the fast electron transfer between PS and catalyst. The structural cuprous and ferrous ions on the surface of CuFe₂O₄ participated in the PS activation process through the redox reactions, as confirmed by XPS analysis. The possible degradation pathways of TC were proposed based on the identified intermediates.

Environmental remediation processes by zero valence copper: reaction mechanisms

Recent studies have shown Cu(0) as a promising material for the removal of organic and inorganic pollutants. However, there is no review addressing the studies performed. This fact may be related to the toxicity of the particles and the copper released in solution that has not motivated researchers, which entails in a reduced number of publications. However, studies point out how to solve the problem of Cu deposition in support materials. In this work, a detailed review of Cu(0) applications was performed. The specific focus was the reaction mechanisms related to adsorption, oxidation, and reduction processes. Initially, the resources that allow the understanding of the reaction mechanism, such as characterization techniques and the experimental conditions for investigation of the species involved in the process, were presented. The studies were evaluated separately, showing the mechanisms involved only with the application of Cu(0) in pure and isolated form and in association with oxidizing or reductive agents, combined with irradiation sources and ultrasonic waves and in the form supported in polymer matrices. It was verified that by the proposed reaction mechanisms, the exclusive participation of Cu(0), being the removal process, explained only by the redox behavior of copper. Therefore, the review showed the need for future research regarding the redox behavior of the contaminants.

Three-dimensional macroporous graphene-wrapped zero-valent copper nanoparticles as efficient micro-electrolysis-promoted Fenton-like catalysts for metronidazole removal

Three-dimensional macroporous graphene-wrapped zero-valent copper nanoparticles (3D-GN@Cu⁰) were synthesized using a self-assembly process of liquid-phase reduction and characterized by field emission scanning electron microscopy, nitrogen adsorption/desorption isotherms, X-ray diffraction, Raman spectrum analysis, and X-ray photoelectron spectroscopy. The catalytic activity of 3D-GN@Cu⁰ was evaluated in view of the effects of various systems, the pH value, catalyst dosage, initial metronidazole concentration and temperature, and it showed a high efficiency for removing metronidazole with saturated dissolved oxygen (without adding extra H₂O₂) in a wide range of pH value from 3.2 to 9.8. Combined with the results of dissolved oxygen activation, determination of reactive oxidizing species, and X-ray photoelectron spectroscopy (XPS) analysis, the surface-bounded ·OH_ads formed by the reaction of the in situ generation H₂O₂ with 3D-GN@Cu⁰ was mainly responsible for the removal of metronidazole. The charge distribution and electrostatic potential (ESP) of 3D-GN@Cu⁰ further illustrated the distribution and transfer of electrons on the catalyst surface, which predicted a micro-electrolysis-promoted Fenton-like reaction mechanism.