Peroxymonosulfate catalyzed by rGO assisted CoFe2O4 catalyst for removing Hg0 from flue gas in heterogeneous system

Needle trap device technique: From fabrication to sampling

Needle Trap Device (NTD) as a novel, versatile, and eco-friendly technique has played an important role in analytical and environmental chemistry. The distinctive role of this interdisciplinary technique can be defended through the sampling and analysis of biological samples and industrial pollutants in gaseous and liquid environments. In recent years, significant efforts have been made to enhance the performance of the needle trap device resulting in the development of novel extraction routes by various packing materials with improved selectivity and enhanced adsorption characteristics. These achievements can lead to the facilitated pre-concentration of desired analytes. This review tries to have a comparative and comprehensive survey of the three important areas of NTD technique: I) Fabrication and preparation procedures of NTDs; II) Sampling techniques of pollutants using NTDs; and III) Employed materials as adsorbents in NTDs. In the packing-material section, the commercial and synthetic adsorbents such as carbon materials, metal-organic frameworks, aerogel, and polymers are considered. Furthermore, the limitations and potential areas for future development of the NTD technique are presented.

Spinel cobalt ferrite-based porous activated carbon in conjunction with UV light irradiation for boosting peroxymonosulfate oxidation of bisphenol A

Developing heterogeneous catalysts with high performance for peroxymonosulfate (PMS) activation to decontaminate organic pollutants from wastewater is of prominent importance. In this study, spinel cobalt ferrite (CoFe₂O₄) materials were coated on the surface of powdered activated carbon (CoFe₂O₄@PAC) via the facile co-precipitation method. The high specific surface area of PAC was beneficial for the adsorption of both bisphenol A (BP-A) and PMS molecules. The CoFe₂O₄@PAC-mediated PMS activation process under UV light could effectively eliminate 99.4% of the BP-A within 60 min of reaction. A significant synergy effect was attained between CoFe₂O₄ and PAC towards PMS activation and subsequent elimination of BP-A. Comparative tests demonstrated that the heterogeneous CoFe₂O₄@PAC catalyst had a better degradation performance in comparison with its components and homogeneous catalysts (Fe, Co, and, Fe + Co ions). The formed by-products and intermediates during BP-A decontamination were evaluated using LC/MS analysis, and then a possible degradation pathway was proposed. Moreover, the prepared catalyst exhibited excellent performance in recyclability with slight leaching amounts of Co and Fe ions. A TOC conversion of 38% was obtained after five consecutive reaction cycles. It can be concluded that the PMS photo-activation process via the CoFe₂O₄@PAC catalyst can be utilized as an effective and promising method for the degradation of organic contaminants from polluted-water resources.

Bisphenol A degradation by peroxymonosulfate photo-activation coupled with carbon-based cobalt ferrite nanocomposite: Performance, upgrading synergy and mechanistic pathway

Cobalt ferrite (CoFe₂O₄, CF) nanoparticles were anchored on the multiwalled carbon nanotube (MWCNT) for synthesis of CF@MWCNT nanocomposite and enhancing the catalytic activity of CF. After well characterization, it was applied as a catalyst towards photo-activation peroxymonosulfate (PMS) for degradation of bisphenol A (BPA). Based on the identified intermediates, a possible degradation pathway was proposed for BPA. CF@MWCNT coupled with PMS and UV (i.e., CF@MWCNT/PMS/UV) exhibited a better performance than homogeneous UV-assisted PMS processes under Fe and Co ions. A significant synergy on the degradation of BPA was observed in the simultaneous application of catalyst, UV light and PMS. Under optimum conditions, the removal efficiencies of 100 and 72.6% were attained respectively for BPA and TOC by CF@MWCNT/PMS/UV within 60 min reaction. These efficiencies were decreased to 88 and 61% after five times use of catalyst, respectively. The leaching of metal ions dissolved from the catalyst was slight during cyclic utilization of catalyst, confirming high stability of CF@MWCNT. In this process, the participation of radical mechanisms was approximately 60%, which SO₄^•- and HO^• species contributed as predominant oxidizing reactive species. It also showed the excellent catalytic performance towards decomposition of persulfate and hydrogen peroxide. Overall, UV-assisted PMS catalyzed by CF@MWCNT exhibited a good catalytic performance and so it can be potentially introduced as a promising method for efficient treatment of water contaminated by BPA.

A Critical Review on Removal of Gaseous Pollutants Using Sulfate Radical-based Advanced Oxidation Technologies

Excessive emissions of gaseous pollutants such as SO₂, NO_x, heavy metals (Hg, As, etc.), H₂S, VOCs, etc. have triggered a series of environmental pollution incidents. Sulfate radical (SO₄•^-)-based advanced oxidation technologies (AOTs) are one of the most promising gaseous pollutants removal technologies because they can not only produce active free radicals with strong oxidation ability to simultaneously degrade most of gaseous pollutants, but also their reaction processes are environmentally friendly. However, so far, the special review focusing on gaseous pollutants removal using SO₄•^--based AOTs is not reported. This review reports the latest advances in removal of gaseous pollutants (e.g., SO₂, NO_x, Hg, As, H₂S, and VOCs) using SO₄•^--based AOTs. The performance, mechanism, active species identification and advantages/disadvantages of these removal technologies using SO₄•^--based AOTs are reviewed. The existing challenges and further research suggestions are also commented. Results show that SO₄•^--based AOTs possess good development potential in gaseous pollutant control field due to simple reagent transportation and storage, low product post-treatment requirements and strong degradation ability of refractory pollutants. Each SO₄•^--based AOT possesses its own advantages and disadvantages in terms of removal performance, cost, reliability, and product post-treatment. Low free radical yield, poor removal capacity, unclear removal mechanism/contribution of active species, unreliable technology and high cost are still the main problems in this field. The combined use of multiactivation technologies is one of the promising strategies to overcome these defects since it may make up for the shortcomings of independent technology. In order to improve free radical yield and pollutant removal capacity, enhancement of mass transfer and optimization design of reactor are critical issues. Comprehensive consideration of catalytic materials, removal chemistry, mass transfer and reactor is the promising route to solve these problems. In order to clarify removal mechanism, it is essential to select suitable free radical sacrificial agents, probes and spin trapping agents, which possess high selectivity for target specie, high solubility in water, and little effect on activity of catalyst itself and mass transfer/diffusion parameters. In order to further reduce investment and operating costs, it is necessary to carry out the related studies on simultaneous removal of more gaseous pollutants.

Clinoptilolite mediated activation of peroxymonosulfate through spherical dispersion and oriented array of NiFe2O4: Upgrading synergy and performance

Inspired by the features of both transition metal oxide and natural clinoptilolite (flaky structure with suitable pore diameter and open skeleton structure), we adopted a robust strategy by immobilization of nickel ferrite nanoparticles (NiFe₂O₄) on the clinoptilolite surface via typical citric acid combustion method. The hybrid catalyst exhibited enhanced peroxymonosulfate (PMS) activation efficiency and bisphenol A (BPA) degradation performance. Calculated by effective equivalent of NiFe₂O₄, it is found that the reaction rate constant (k) of NiFe₂O₄/clinoptilolite/PMS system (0.1859 min^-1) was 11.9 times higher than that of bare NiFe₂O₄/PMS system (0.0156 min^-1), which demonstrated that catalyst would be conjugated to PMS or contaminant efficiently and renders the rapid degradation and mineralization in the presence of clinoptilolite. After comprehensive characterization analysis and DFT simulations, natural mineral carrier effect (i.e. decreased crystalline size, increased oxygen vacancy content, etc.), abundant surface-bonded and structural hydroxyl groups as well as effective bonding with iron or nickel ions charged for the potential activation mechanism of PMS by NiFe₂O₄/clinoptilolite composite. And it is indicated that not only ^•OH and SO₄^•-, but also ¹O₂ was involved into series reactions. Overall, this study put forward a green and promising technology for high-toxic wastewater treatment.

Synthesis of oxygen vacancy-enriched N/P co-doped CoFe2O4 for high-efficient degradation of organic pollutant: Mechanistic insight into radical and nonradical evolution

Oxygen vacancy-enriched N/P co-doped cobalt ferrite (NPCFO) was synthesized using ionic liquid as N and P sources, and then the catalytic performance and mechanism of NPCFO upon peroxymonosulfate (PMS) activation for the degradation of organic pollutants were investigated. The as-synthesized NPCFO-700 exhibited excellent catalytic performance in activating PMS, and the degradation rate constant of 4-chlorophenol (4-CP) increased with the increase of OV concentration in NPCFO-x. EPR analysis confirmed the existence of ·OH, SO₄^·-, and ¹O₂ in the NPCFO-700/PMS system, in which OV could induce the generation of ¹O₂ by PMS adsorption and successive capture, and also served as electronic transfer medium to accelerate the redox cycle of M²⁺/M³⁺ (M denotes Co or Fe) for the generation of radical to synergistically degrade organic pollutants. In addition, the contribution of free radical and nonradical to 4-CP degradation was observed to be strongly dependent on solution pH, and SO₄^·- was the major ROS in 4-CP degradation under acid and alkaline condition, while ¹O₂ was involved in the degradation of 4-CP under neutral condition due its selective oxidation capacity, as evidenced by the fact that such organic pollutants with ionization potential (IP) below 9.0 eV were more easily attacked by ¹O₂. The present study provided a novel insight into the development of transition metal-based heterogeneous catalyst containing massive OV for high-efficient PMS activation and degradation of organic pollutants.

Synergistic activation of peroxymonosulfate via in situ growth FeCo2O4 nanoparticles on natural rectorite: Role of transition metal ions and hydroxyl groups

Developing low-cost, high-efficiency catalysts for advanced oxidation processes remain a key issue for the degradation of organic pollutants. In this study, a novel FeCo₂O₄/rectorite composite was synthesized via a facile combustion process and employed to activate peroxymonosulfate (PMS) for dealing with atrazine (ATZ). The addition of rectorite could result in higher specific surface area, smaller pore size and more hydroxyl groups, which were beneficial to enrich pollutants to the adsorption sites and provide sufficient reactive sites. After meticulous evaluation, the degradation efficiency of FeCo₂O₄/rectorite composite towards ATZ exhibited improved PMS activation efficiency which was about 2.6 times than that of pure FeCo₂O₄. Based on the characterization results, the sulfate radicals and hydroxyl radicals were considered to be the main free radicals which were involved into the circulation of Co(II)-Co(III)-Co(II) as well as the oxidation of ≡Fe(II), which was responsible for the remarkable catalytic efficiency. In addition, the chemical stability and superior catalytic performance of FeCo₂O₄/rectorite should also be attributed to the chemical combination between metal ions and the surface hydroxyl groups of rectorite. Overall, these findings are beneficial for understanding the mechanism of PMS activation by natural mineral-based catalysts and contributing to the practical application of sulfate-based technology for organic wastewater treatment.

Catalytic degradation of mefenamic acid by peroxymonosulfate activated with MWCNTs-CoFe2O4: influencing factors, degradation pathway, and comparison of activation processes

The cobalt ferrite loaded on multi-walled carbon nanotubes (MWCNTs-CoFe₂O₄) was synthesized and used as a novel catalyst for the degradation of mefenamic acid (MFA) in the presence of peroxymonosulfate (PMS). The results showed that MWCNTs-CoFe₂O₄ has higher catalytic performance in the activation of PMS and degradation of MFA compared with MWCNTs, Co²⁺, Fe²⁺, and CoFe₂O₄. The highest kinetic constant rate (0.0198 min^-1) and MFA degradation (97.63%) were obtained at pH = 7, PMS = 4 mM, catalyst = 500 mg/L, MFA = 10 mg/L, and time = 150 min. MFA degradation accelerated with increasing PMS and catalyst dosage but decreased by initial pH. The influence of different anions and water matrix on the catalytic system was investigated, and the results explained a decrease in the MFA rate in the presence of the interfering substances. Scavenging experiments showed that both sulfate radical anion (SO₄^•-) and hydroxyl radical (^•OH) were effective on MFA degradation, but SO₄^•- had a greater effect on the degradation of MFA. In addition, the stability and recyclability of MWCNTs-CoFe₂O₄ were evaluated in the consecutive reaction cycle; the MFA degradation rate reached 89.75% after 4 cycles of reaction. The MFA degradation products were identified by gas chromatography-mass spectrometry (GC-MS) and their degradation pathway was suggested. Finally, a comparison was conducted among the methods used for PMS activation, and the results showed that the cobalt ferrite-based catalyst has high degradation efficiency. However, ultrasound, heat, and ultraviolet (UV) processes can be used to improve the degradation rate of the MWCNTs-CoFe₂O₄/PMS system at different reaction times.

Heterogeneous activation of peroxymonosulfate by hierarchically porous cobalt/iron bimetallic oxide nanosheets for degradation of phenol solutions

Bimetallic oxide nanomaterials have received much attention owing to their competing performances in heterogeneous catalysis. Herein, hierarchically porous cobalt-iron oxide nanosheets were successfully prepared using NaBH₄ as a reductant and high concentration cetyl trimethylammonium bromide (CTAB) as a surfactant. Characterization results showed that the CTAB would induce the form of a bilayer structure while NaBH₄ would promote the generation of enriched oxygen vacancies. As a result, the as-prepared Co₁Fe₁-300 exhibited high activity for activating peroxymonosulfate and achieved 100% phenol degradation within 30 min. This excellent catalytic activity can be attributed to its hierarchically porous structure, more active sites and oxygen vacancies. Co leaching test indicated that the Co₁Fe₁-300 exhibited excellent catalytic stability. Mechanistic studies suggested that two main degradation pathways were involved during phenol oxidation process, in which SO₄^•- played a significant role. This work may offer a novel strategy for the synthesis of high activity catalysts and a promising system for the remediation of environmental pollutant.

Magnetically retrievable ferrite nanoparticles in the catalysis application

In the present review, we summarized the applications of magnetic spinel ferrite nanoparticles as catalysts in organic reactions and transformations. Catalytic applications are comprised of using mostly cobalt, nickel, copper, and zinc ferrites, along with their mixed-metal combinations based on nano ferrites. The spinel ferrites (SFs) are gained principally by wet-chemical, sol-gel or co-precipitation methods, more infrequently by the mechanical high-energy ball milling, spark plasma sintering, sonochemical technique, microwave heating or hydrothermal route. Catalytic processes with the application of ferrite nanoparticles are included decomposition (in particular photocatalytic), reactions of dehydrogenation, oxidation, alkylation, CC coupling, removing organic/inorganic contaminants from aqueous solutions. As significant and remarkable advantages, ferrite nanocatalysts not only are environmentally benign and compatible with green chemistry aspects but also can be simply recovered from reaction systems and recycled up to several times almost without significant loss of their catalytic activity.