Removal of multi-pollutant from flue gas utilizing ammonium persulfate solution catalyzed by Fe/ZSM-5

Advancement in nanomaterials for environmental pollutants remediation: a systematic review on bibliometrics analysis, material types, synthesis pathways, and related mechanisms

Environmental pollution is a major issue that requires effective solutions. Nanomaterials (NMs) have emerged as promising candidates for pollution remediation due to their unique properties. This review paper provides a systematic analysis of the potential of NMs for environmental pollution remediation compared to conventional techniques. It elaborates on several aspects, including conventional and advanced techniques for removing pollutants, classification of NMs (organic, inorganic, and composite base). The efficiency of NMs in remediation of pollutants depends on their dispersion and retention, with each type of NM having different advantages and disadvantages. Various synthesis pathways for NMs, including traditional synthesis (chemical and physical) and biological synthesis pathways, mechanisms of reaction for pollutants removal using NMs, such as adsorption, filtration, disinfection, photocatalysis, and oxidation, also are evaluated. Additionally, this review presents suggestions for future investigation strategies to improve the efficacy of NMs in environmental remediation. The research so far provides strong evidence that NMs could effectively remove contaminants and may be valuable assets for various industrial purposes. However, further research and development are necessary to fully realize this potential, such as exploring new synthesis pathways and improving the dispersion and retention of NMs in the environment. Furthermore, there is a need to compare the efficacy of different types of NMs for remediating specific pollutants. Overall, this review highlights the immense potential of NMs for mitigating environmental pollutants and calls for more research in this direction.

Advances in air pollution control for key industries in China during the 13th five-year plan

Industrial development is an essential foundation of the national economy, but the industry is also the largest source of air pollution, of which power plants, iron and steel, building materials, and other industries emit large amounts of pollutants. Therefore, the Chinese government has promulgated a series of stringent emission regulations, and it is against this backdrop that research into air pollution control technologies for key industrial sectors is in full swing. In particular, during the 13th Five-Year Plan, breakthroughs have been made in pollution control technology for key industrial sectors. A multi-pollutant treatment technology system of desulfurization, denitrification, and dust collection, which applies to key industries such as power plants, steel, and building materials, has been developed. High-performance materials for the treatment of different pollutants, such as denitrification catalysts and desulfurization absorbers, were developed. At the same time, multi-pollutant synergistic removal technologies for flue gas in various industries have also become a hot research topic, with important breakthroughs in the synergistic removal of NO_x, SO_x, and Hg. Due to the increasingly stringent emission standards and regulations in China, there is still a need to work on the development of multi-pollutant synergistic technologies and further research and development of synergistic abatement technologies for CO₂ to meet the requirements of ultra-low emissions in industrial sectors.

A critical review on the technique and mechanism of microwave-based denitrification in flue gas

Microwave radiation has received extensive attention due to its significant thermal and non-thermal effects, and the development of MW-based denitrification in flue gas has become one of the most promising methods to avoid the defects of ammonia escape, high temperature and cost in traditional SCR. This review introduces the thermal and non-thermal effects of microwaves and divides MW-based denitrification methods into MW reduction and oxidation denitrification, systematically summarizes these denitrification methods, including MW discharge reduction, MW-induced catalytic reduction using active carbon, molecular sieves, metal oxides (transition metals, perovskites, etc.), MW-induced oxidation denitrification with and without additional oxidant, and discusses their removal pathway and mechanism. Finally, several research prospects and directions regarding the development of microwave-based denitrification methods are provided.

Novel sodalite stabilized zero-valent iron for super stable and outstanding efficiency in activating persulfate for organic pollutants fast removal

In this study, novel porous sodalite (SOD) was synthesized through Reactive Oxidation Species (ROS) route from industrial waste lithium silicon fume (LSF) to stabilize nZVI (SOD@nZVI), and used as an outstanding persulfate (PS) activator for efficient organic degradation. Characterization results revealed nZVI evenly distributed on SOD via ion-exchange, and the fabricated SOD@nZVI exhibited high stability and superior reactivity over a wide pH range of 2-12 during oxidation reaction. The mechanism responsible for fast organic degradation in the SOD@nZVI+PS system was carefully investigated, and weak magnetic field (WMF) and friction were found to contribute to improved SOD@nZVI performance. The fast redox cycle of Fe²⁺/Fe³⁺ on SOD@nZVI can be stimulated by changing the mixing condition and altering the friction layer to harvest mechanical energy during the reaction, which can maximum persulfate activation to generate more reactive radicals for organic fast degradation. This study is of great significance, as it offers a practical route turning waste into excellent PS activator for in-situ organic pollution remediation, as well as proposing a new idea to maximum PS activation performance by manipulating the inner lining of reactor.

LaOx modified MnOx loaded biomass activated carbon and its enhanced performance for simultaneous abatement of NO and Hg0

A battery of agricultural straw derived biomass activated carbons supported LaO_x modified MnO_x (LaMn/BACs) was prepared by a facile impregnation method and then tested for simultaneous abatement of NO and Hg⁰. 15%LaMn/BAC manifested excellent removal efficiency of Hg⁰ (100%) and NO (86.7%) at 180 °C, which also exhibited splendid resistance to SO₂ and H₂O. The interaction between Hg⁰ removal and NO removal was explored; thereinto, Hg⁰ removal had no influence on NO removal, while NO removal preponderated over Hg⁰ removal. The inhibitory effect of NH₃ was greater than the accelerative effect of NO and O₂ on Hg⁰ removal. The physicochemical characterization of related samples was characterized by SEM, XRD, BET, H₂-TPR, NH₃-TPD, and XPS. After incorporating suitable LaO_x into 15%Mn/BAC, the synergistic effect between LaO_x and MnO_x contributed to the improvement of BET surface area and total pore volume, the promotion of redox ability, surface active oxygen species, and acid sites, inhibiting the crystallization of MnO_x. 15%LaMn/BAC has the best catalytic oxidation activity at low temperature. That might be answerable for superior performance and preferable tolerance to SO₂ and H₂O. The results indicated that 15%LaMn/BAC was a promising catalyst for simultaneous abatement of Hg⁰ and NO at low temperature.

Recent advances in hybrid wet scrubbing techniques for NOx and SO2 removal: State of the art and future research

Recently, the discharge of flue gas has become a global issue due to the rapid development in industrial and anthropogenic activities. Various dry and wet treatment approaches including conventional and hybrid hybrid wet scrubbing have been employing to combat against these toxic exhaust emissions. However, certain issues i.e., large energy consumption, generation of secondary pollutants, low regeneration of scrubbing liquid and high efficieny are hindering their practical applications on industrial level. Despite this, the hybrid wet scrubbing technique (advanced oxidation, ionic-liquids and solid engineered interface hybrid materials based techniques) is gaining great attention because of its low installation costs, simultaneous removal of multi-air pollutants and low energy requirements. However, the lack of understanding about the basic principles and fundamental requirements are great hurdles for its commercial scale application, which is aim of this review article. This review article highlights the recent developments, minimization of GHG, sustainable improvements for the regeneration of used catalyst via green and electron rich donors. It explains, various hybrid wet scrubbing techniques can perform well under mild condition with possible improvements such as development of stable, heterogeneous catalysts, fast and in-situ regeneration for large scale applications. Finally, it discussed recovery of resources i.e., N₂O, NH₃ and N₂, the key challenges about several competitive side products and loss of catalytic activity over time to treat toxic gases via feasible solutions by hybrid wet scrubbing techniques.

Synergistically enhanced heterogeneous activation of persulfate for aqueous carbamazepine degradation using Fe3O4@SBA-15

The exploration of low-cost, high-performance and stable catalytic materials for sulfate radical-based advanced oxidation processes (SR-AOPs) is of great importance. This study presents Fe₃O₄-wrapped SBA-15 mesoporous silica catalyst (Fe₃O₄@SBA-15) for persulfate (PS) activation. The Fe₃O₄@SBA-15 with an Fe₃O₄ to SBA-15 weight ratio of 3:1 exhibited an impressive carbamazepine (CBZ) removal efficiency of ~100% after 30 min of SR-AOP at an initial pH of 3.0, a temperature of 25 °C, an initial PS concentration of 300 mg L^-1 and a catalyst concentration of 0.50 g L^-1. The primary oxidizing species produced in the system were identified as SO₄^- and HO by electron paramagnetic resonance spectra and radical quenching experiments. Benefiting from the synergetic effects of improved Fe₃O₄ dispersion and enhanced adsorption of CBZ and PS by SBA-15, the as-obtained heterogeneous Fe₃O₄@SBA-15 catalysts offer large numbers of active sites for free radical generation and high surface concentrations of CBZ and PS for SR-AOPs, as verified by physicochemical characterization and Langmuir-Hinshelwood model analysis. In addition, the activity of Fe₃O₄@SBA-15 was maintained throughout six successive cycling tests. Various inorganic anions, including Cl^-, NO₃^-, HCO₃^-, and CO₃^2-, as well as organic material in natural water, exert a negative impact on the Fe₃O₄@SBA-15 catalyzed SR-AOPs and deserve special attention.

Utilization of electrochemical treatment and surface reconstruction to achieve long lasting catalyst for NOx removal

The development of catalysts has seen tremendous growth recently but most strategies only report utilization of catalysts for a few initial cycles without taking into account the influence of oxygen poisoning. Here, the magnetic Fe₃O₄@EDTA-Fe (MEFe, having a core Fe₃O₄ particle with EDTA-Fe coating) was investigated as a model catalyst for long-term recycling for the removal of nitrogen oxide (NO_x) from NO/O₂ mixture, followed by N₂O recovery. The concentration of oxygen in the flue gas was found to have a strong impact on NO_x absorption and catalytic response. To circumvent the oxygen poisoning, the MEFe was subjected to electrochemical treatment in the presence of neutral red (N.R.) and NO removal efficiency was ∼95 % noted. Furthermore, the surface of the catalyst degraded significantly (p < 0.05) after 6-7 repetitive cycling due to surface catalytic reactions, surface poisoning, oxidation of metallic species as well as residual stresses. The MEFe surface was reconstructed after 7 cycles using EDTA solution and Fe source to achieve similar surface coating as the fresh MEFe catalyst. The reconstructed MEFe exhibited similar NO_x absorption capability as the fresh MEFe and the reconstruction loop was repeated several times to achieve long term cycling, which make the catalyst cost-effective. Hence, it is proposed that a successful regeneration process can be employed for promising, sustainable and long-lasting catalytic treatment of air pollutants.

Ethylene glycol assisted synthesis of hierarchical Fe-ZSM-5 nanorods assembled microsphere for adsorption Fenton degradation of chlorobenzene

A unique zeolite catalyst, Fe doped ZSM-5 microsphere assembled by uniform nanorod-like crystals with hierarchical pore structure, was successfully synthesized and applied for the adsorption and degradation of trace chlorobenzene (CB) in the presence of H₂O₂. The organic ferric salts as the precursors, ethylene glycol as a chelating/reducing agent and the dynamic two-stage temperature-varied hydrothermal technique, together made the synthesized hierarchical Fe-ZSM-5 nanorods assembled microspheres (FZ-CA-5EG) to be characterized by abundant highly dispersed and valency-controlled framework Fe^3+/2+ species. As a result of these features, the FZ-CA-5EG showed excellent ability of adsorption and degradation efficiency of CB, and enhanced durability due to negligible leaching of framework Fe species. Moreover, the hydroxyl radicals were determined as the main the reactive oxygen species of CB oxidation degradation, and a possible adsorption-oxidation degradation pathway was proposed.

Simultaneous desulfurization and denitrification from flue gas by catalytic ozonation combined with NH3/(NH4)2S2O8 absorption: Mechanisms and recovery of compound fertilizer

An integrated method of simultaneous desulfurization and denitrification from flue gas by catalytic ozonation combined with NH₃/(NH₄)₂S₂O₈ absorption was developed for the first time. It consisted of two parts: (1) the catalytic ozonation of NO over FeO_x/SAPO-34 to study the effects of the various influencing factors, and (2) the absorption-oxidation of NO_x and SO₂ induced by ozone combined with a NH₃/(NH₄)₂S₂O₈ solution in a bubble column reactor. In Part 1, results showed that under the optimal condition of a molar ratio of 0.5 for O₃/NO, a residence time of 3 s, a water vapor volume fraction of 4%, a NO initial concentration of 536 mg/m³, and a SO₂ initial concentration of 343 mg/m³, the oxidation rate of NO was 55%. The characterizations of poisoned catalyst are briefly discussed. In Part 2, as the gas passed sequentially through the ozonizing reactor and the absorber (NH₃/(NH₄)₂S₂O₈ solution of 0.8% ammonia and 0.2 mol/L (NH₄)₂S₂O₈), a NO conversion rate of approximately 92.6% and SO₂ conversion rate of 100% were obtained. The pH of the NH₃/(NH₄)₂S₂O₈ solution had a significant impact on the NO conversion. According to the analysis of the composition of products under different pHs, a mechanism of desulfurization and denitrification based on NH₃/(NH₄)₂S₂O₈ solutions was proposed. The reaction product as a compound fertilizer contained up to 24.5% nitrogen.

Synergistic coupling Co3Fe7 alloy and CoFe2O4 spinel for highly efficient removal of 2,4-dichlorophenol by activating peroxymonosulfate

Efficient wastewater restoration depends on the robustness and capability of the catalyst to promote sophisticated decontamination technologies. In this study, Co₃Fe₇-CoFe₂O₄ nanoparticles (NPs) prepared by facile pyrolysis were completely characterized and used to decompose 2,4-dichlorophenol (2,4-DCP). Furthermore, the catalytic performance and relevant mechanisms involved in the activation of peroxymonosulfate (PMS) were also investigated. The optimal conditions were achieved at the catalyst loading of 0.05 g L^-1, PMS dosage of 1.26 g L^-1, and pH of 7.7 through the response surface methodology by using the Box-Behnken design model. Under optimal conditions, 97.1% efficiency of 2,4-DCP removal was obtained within 30 min. Moreover, the quenching experiments and electron paramagnetic resonance result indicated that sulfate (SO₄^•-) and hydroxyl (HO^•) radicals were considered as the dominant reactive oxygen species, which resulted in the effective removal of 2,4-DCP in the Co₃Fe₇-CoFe₂O₄/PMS system. Moreover, Co₃Fe₇-CoFe₂O₄ showed efficient catalytic performance in continuous five runs and exhibited less metal leaching of 0.052 and 0.036 mg L^-1 for Co and Fe species, respectively. Furthermore, no considerable change was observed in the structural characteristics of the fresh and used Co₃Fe₇-CoFe₂O₄ catalytic system. The above-mentioned results indicated that the synergistic effects between Co₃Fe₇ alloy and CoFe₂O₄ spinel not only significantly improved the activity and long-term durability of the catalyst, but also accelerated the Co³⁺/Co²⁺ and Fe³⁺/Fe²⁺ redox cycles. Overall, the Co₃Fe₇-CoFe₂O₄/PMS system provides a novel advanced oxidation approach to further develop multifunctional transition metal-based nanomaterials responsible for producing surface-bound radicals and enhancing the remediation of refractory pollutants in the environmental application.

Radical-induced oxidation removal of multi-air-pollutant: A critical review

Sulfur dioxide (SO₂), nitric oxide (NO) and elemental mercury (Hg⁰) are three common air pollutants in flue gas. SO₂ and NO are the main precursors for chemical smog and Hg⁰ is a bio-toxicant for human. Cooperative removal of multi-air-pollutant in flue gas using radical-induced oxidation reaction is considered as one of the most promising methods due to the high removal efficiency, low cost and less secondary environmental impact. The common radicals used in air pollution control can be classified into four types: (1) hydroxyl radical (OH), (2) sulfate radical (SO₄^-), (3) chlorine-containing radicals (Cl, ClO₂, ClO, HOCl^-, etc.) and (4) ozone. This review summarizes the generation methods and mechanism of the four kinds of radicals, as well as their applications in the removal of multi-air-pollutant in flue gas. The reactivity, selectivity and reaction mechanism of the four kinds of radicals in multi-air-pollutant removal were comprehensively described. Finally, some future research suggestions on the development of new technique for cooperative removal of multi-air-pollutant in flue gas were provided.

Highly pure MgO2 nanoparticles as robust solid oxidant for enhanced Fenton-like degradation of organic contaminants

In typical Fenton/Fenton-like reactions, H₂O₂ was usually used as an oxidant to degrade organic contaminants. However, liquid H₂O₂ is unstable, easy to decompose and has high biological toxicity especially at high concentration. Herein, highly pure magnesium peroxide (MgO₂) nanoparticles were first synthesized and used instead of H₂O₂ to degrade organic dyes. The structure and morphology of as-prepared products were confirmed by XRD, SEM, TEM and FTIR techniques. The active oxygen content of MgO₂ nanoparticles reached up to 26.93 wt%, suggesting a high purity of the as-prepared sample. The degradation performance of MgO₂ nanoparticles towards organic contaminants was systematically investigated in the terms of the molar ratio of Fe³⁺ to MgO₂, the dosage of MgO₂, initial solution pH and different organic dyes. The results indicated the as-prepared MgO₂ exhibited excellent degradation ability to various types of organic dyes. 10 mg of MgO₂ nanoparticles could almost completely degrade 200 mL of 20 mg/L methylene blue (MB) in 30 min with a TOC removal rate of 70.2%. The efficient degradation performance was ascribed to the generation of hydroxyl radicals in the MgO₂/Fe³⁺ system. The pathways of MB degradation were also proposed based on the determination of the reaction intermediates.