Catalytic activation of peroxymonosulfate with manganese cobaltite nanoparticles for the degradation of organic dyes

Activation of peroxymonosulfate for rhodamine-B removal from water: enhanced efficiency with cobalt-enriched, magnetically recoverable CNTs

Dyes are known to pose environmental threats due to their mutagenic and persistent effects. To address this concern, researchers have explored various unconventional dye degradation materials, such as metal oxides with carbon materials. However, challenges related to degradation efficiency and regeneration have been significant obstacles. Consequently, there has been a surge in interest in recent years toward using nanomaterials with carbon materials activated by peroxymonosulfate for organic pollutant degradation. In this study, we present a novel approach to prepare a hybrid nanocomposite catalyst, CoS/CoFe2O4-CNTs (CS/CF-CNTs), using a carbon nanotube decorated with cobalt ferrite and further enhanced by embedding with cobalt sulfide nanoflowers. This catalyst aims at enhancing Rhodamine-B degradation through advanced oxidation processes. The carbon nanotubes provide a stable substrate for the cobalt materials, with cobalt ferrite (CF) serving as a magnetic component, facilitating catalyst removal and regeneration for multiple uses. Due to the oxidation involved in the degradation process, high electronic conductivity of the carbon nanotubes and the active cobalt sites of the composite play a crucial role in activating peroxymonosulfate to generate reactive oxygen radicals. Notably, the CS/CF-CNTs catalyst showed a remarkable Rhodamine-B degradation rate of 98% in less than 10 min. The catalyst also exhibited excellent stability even after four cycles of regeneration. The operating reaction conditions were optimized by investigating the effects of pH, dye concentration, salinity with different salts, catalyst dose, and peroxymonosulfate dose, and the results demonstrated the superior effectiveness of CS/CF-CNTs compared to CS and to CF-CNTs, emphasizing the synergistic interaction between the carbon nanotubes and the two cobalt materials. Quenching experiments revealed the involvement of sulfate and hydroxyl radicals in the degradation reaction mechanism.

Zeolitic imidazolate framework-67 in chitosan-grafted hydrogel as an effective catalyst for peroxymonosulfate activation to degrade antibiotics and dyes

Zeolitic imidazolate framework-67 (ZIF-67) was synthesized in situ in the hydrogel of chitosan-grafted poly(acrylic acid) (chitosan-g-PAA) to activate peroxymonosulfate (PMS) and degrade tetracycline (TC). The catalytic performance of the composite hydrogel for TC degradation was evaluated under different conditions. The results showed rapid degradation, with enhanced degradation efficiency as the catalyst dosage, PMS dosage, and temperature increased. TC was degraded entirely within 30 min for catalyst and PMS dosages of 1 and 1 g per L, respectively. The composite hydrogel was effective across a broad pH range. A scavenging study and electron paramagnetic resonance experiments indicated that SO4˙-, HO˙, O2˙- and 1O2 were involved in the degradation process. The antibacterial test against E. coli showed that the products of the TC degradation were nontoxic. Additionally, the composite hydrogel was evaluated in the presence of anions and in real water samples. The reusability study showed that the composite hydrogel could be recovered through filtration and effectively used for five consecutive cycles. Moreover, the composite hydrogel could degrade 82% ciprofloxacin and 86% norfloxacin, while it could completely degrade rhodamine B, reactive red 141, and methylene blue dyes within 30 min.

Co2+-adsorbed chitosan-grafted-poly(acrylic acid) hydrogel as peroxymonosulfate activator for effective dye degradation

In this work, chitosan-grafted-poly(acrylic acid) (CS-g-PAA) was synthesized for use as a Co2+ adsorbent and circularly utilized as a peroxymonosulfate (PMS) activator in the degradation of rhodamine B (RhB) dye. CS-g-PAA demonstrated 3.7 times higher adsorption capacity toward Co2+ than pristine chitosan. The impact of the adsorption conditions was evaluated. The pseudo-second-order kinetic model and the Langmuir isotherm model best described the adsorption process. Under optimum conditions, the adsorption capacity of CS-g-PAA for Co2+ was 212 mg/g. The Co2+-adsorbed CS-g-PAA hydrogel was further utilized in the RhB degradation process. The effects of catalyst dosage, initial RhB concentration, pH, and the coexistence of anions on the degradation of RhB were studied. The hydrogel catalyst could remove 98 % of RhB within 5 min, at a degradation rate of 0.624 per min. Electron paramagnetic resonance (EPR) analysis and the radical scavenger experiment suggested that SO4•-, HO•, 1O2, and O2•- were involved in the degradation. Furthermore, when tested in various water systems, high degradation efficiencies of 98 % were attained after 20 min. The hydrogel catalyst performed excellent degradation over ten cycles without any chemical recovery processes. Moreover, high degradation efficiencies were observed between 95 % and 98 % when tested with other dyes.

Modification of the electronic structure of g-C3N4 using urea to enhance the visible light-assisted degradation of organic pollutants

Graphitic carbon nitride has been proven to be a good candidate for using solar energy for photo-induced pollutant degradation. However, the high photo-induced holes-electron recombination rate, unfavorable morphology, and textural properties limited their application. In this study, we present a novel g-C3N4 with a novel electronic structure and physiochemical properties by introducing a single nitrogen in the graphitic network of the g-C3N4 through a novel method involving step-by-step co-polycondensation of melamine and urea. Through extensive characterization using techniques such as XPS, UPS-XPS, Raman, XRD, FE-SEM, TEM, and N2 adsorption-desorption, we analyze the electronic and crystallographic properties, as well as the morphology and textural features of the newly prepared g-C3N4 (N-g-C3N4). This material exhibits a lower C/N ratio of 0.62 compared to conventional g-C3N4 and a reduced band gap of 2.63 eV. The newly prepared g-C3N4 demonstrates a distinct valance band maxima that enhances its photo-induced oxidation potential, improving photocatalytic activity in degrading various organic pollutants. We thoroughly investigate the photocatalytic degradation performance of N-g-C3N4 for Congo red (CR) and sulfamethoxazole (SMX), and removal of up to 90 and 86% was attained after 2 h at solution pH of 5.5 for CR and SMX. The influence of different parameters was examined to understand the degradation mechanism and the influence of reactive oxygenated species. The catalytic performance is also evaluated in the degradation of various organic pollutants, and it showed a good performance.

Synergistic Photoelectrochemical and Photocatalytic Properties of the Cobalt Nanoparticles-Embedded TiVO4 Thin Film

To optimize the semiconductor properties of TiVO4 thin films and enhance their performance, we incorporated cobalt nanoparticles as an effective co-catalyst consisting of a non-noble metal. Through an investigation into the impact of cobalt loading on spray pyrolyzed TiVO4 thin films, we observed a significant enhancement in the photoelectrochemical (PEC) performance. This was accomplished by carefully optimizing the concentrations of Co2+ (3 mM) to fabricate a composite electrode, resulting in a higher photocurrent density for the TiVO4:Co photoanode. When an applied potential of 1.23 V (vs RHE) was used, the photocurrent density reached 450 μA/cm2, approximately 5 times higher than that of bare TiVO4. We conducted a thorough characterization of the composite structure and optical properties. Additionally, electrochemical impedance spectroscopy analysis indicated that the TiVO4/Co thin film exhibited a smaller semicircle, indicating a significant improvement in charge transfer at the interface. In comparison to bare TiVO4, the TiVO4/Co composite exhibited a notable improvement in photocatalytic activity when degrading methylene blue (MB) dye, a widely employed model dye. Under light illumination, a TiVO4/Co thin film exhibited a notable dye degradation rate of 97% within a 45 min duration. The scalability of our fabrication method makes it suitable for large-area devices intended for sunlight-driven PEC seawater splitting studies.

Alginate@ZnCO2O4 for efficient peroxymonosulfate activation towards effective rhodamine B degradation: optimization using response surface methodology

A facile chemical procedure was utilized to produce an effective peroxy-monosulfate (PMS) activator, namely ZnCo₂O₄/alginate. To enhance the degradation efficiency of Rhodamine B (RhB), a novel response surface methodology (RSM) based on the Box-Behnken Design (BBD) method was employed. Physical and chemical properties of each catalyst (ZnCo₂O₄ and ZnCo₂O₄/alginate) were characterized using several techniques, such as FTIR, TGA, XRD, SEM, and TEM. By employing BBD-RSM with a quadratic statistical model and ANOVA analysis, the optimal conditions for RhB decomposition were mathematically determined, based on four parameters including catalyst dose, PMS dose, RhB concentration, and reaction time. The optimal conditions were achieved at a PMS dose of 1 g l^-1, a catalyst dose of 1 g l^-1, a dye concentration of 25 mg l^-1, and a time of 40 min, with a RhB decomposition efficacy of 98%. The ZnCo₂O₄/alginate catalyst displayed remarkable stability and reusability, as demonstrated by recycling tests. Additionally, quenching tests confirmed that SO₄˙^-/OH˙ radicals played a crucial role in the RhB decomposition process.

Orange G degradation by heterogeneous peroxymonosulfate activation based on magnetic MnFe2O4/α-MnO2 hybrid

Wastewater containing an azo dye Orange G (OG) causes massive environmental pollution, thus it is critical to develop a highly effective, environmental-friendly, and reusable catalyst in peroxymonosulfate (PMS) activation for OG degradation. In this work, we successfully applied a magnetic MnFe₂O₄/α-MnO₂ hybrid fabricated by a simple hydrothermal method for OG removal in water. The characteristics of the hybrid were investigated by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller method, vibrating sample magnetometry, electron paramagnetic resonance, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The effects of operational parameters (i.e., catalytic system, catalytic dose, solution pH, and temperature) were investigated. The results exhibited that 96.8% of OG degradation was obtained with MnFe₂O₄/α-MnO₂(1:9)/PMS system in 30 min regardless of solution pH changes. Furthermore, the possible reaction mechanism of the coupling system was proposed, and the degradation intermediates of OG were identified by mass spectroscopy. The radical quenching experiments and EPR tests demonstrated that SO₄^•̶, O₂^•̶, and ¹O₂ were the primary reactive oxygen species responsible for the OG degradation. The hybrid also displayed unusual stability with less than 30% loss in the OG removal after four sequential cycles. Overall, magnetic MnFe₂O₄/α-MnO₂ hybrid could be used as a high potential activator of PMS to remove orange G and maybe other dyes from wastewater.

Mechanistic insights into efficient peroxymonosulfate activation by NiCo layered double hydroxides

The efficient removal of organic refractory pollutants such as dyes and antibiotics in wastewater is crucial for protecting the environment and human health. In this work, a NiCo-layered double hydroxide (NiCo-LDH) with a uniform microspherical, hierarchical structure and a high surface area was successfully synthesized as an effective peroxymonosulfate (PMS) activator for the degradation of various organic dyes and antibiotics. The influence of various parameters on the catalytic activity of the NiCo-LDH was determined. Radical scavenger studies unveiled the major reactive oxygen species (ROSs) generated in the NiCo-LDH/PSM system to be ¹O₂, SO₄^•-, and O₂^•-. Ex-situ X-ray photoelectron spectroscopy (XPS) analysis uncovered the role of Co sites and oxygen vacancy as active sites and revealed the reversible redox properties of NiCo-LDH based on Co²⁺/Co³⁺ cycles. The activation mechanism and Rhodamine B (RhB) degradation pathways were experimentally studied and proposed. The NiCo-LDH is highly versatile, reusable and stable as shown by post-catalysis characterizations. This work shows the excellent catalysis performances and provides insights into the activation mechanism of PMS by NiCo-LDH for organic pollutant remediation.

Electronic structure modulation of multi-walled carbon nanotubes using azo dye for inducing non-radical reaction: Effect of graphitic nitrogen and structural defect

Multiwalled carbon nanotube (MWCNT) have a great potential for advanced oxidation process as a metal free catalyst. However, there catalytic activity is very low and needs to be appropriately tuned. Herein, we demonstrate a novel synthesis method for tuning the defect and surface functionality of MWCNT using azo dyes and the catalytic performance was tested for the degradation of different organic contaminates using PMS as an oxidant. The content, type of heteroatom functional groups, and the defect parameters were optimized by varying the pH and concentration of the organic dye. The quenching effect showed that singlet oxygen (¹O₂) is the primary reactive species generated by graphitic nitrogen, which can be boosted by the degree of graphitic structure disruption in MWCNT. The Linear sweep voltammetry (LSV) also confirmed that extrinsic doping enhanced the non-radical degradation by increasing the direct charge transfer rate from MB to PMS. Moreover, the designed catalyst showed a fast degradation performance with 35.1 kJ/mol activation energy and achieved the highest dye degradation rate and even surpassed some state-of-the-art metal-based and metal-free catalysts. The effect of inorganic anions study has also confirmed its industrial applicability.

Ag@AgCl nanoparticles grafted on carbon nanofiber: an efficient visible light plasmonic photocatalyst via bandgap reduction

A novel silver@silver chloride/carbon nanofiber (Ag@AgCl/CNF) hybrid was synthesized by electrospinning, heat treament, and subsequentin situchemical oxidation strategy. The synthesized materials were characterized using x-ray diffraction, Fourier-transform infrared, UV-Vis diffuse reflectance spectroscopy, scanning electron microscopy, and energy dispersive x-ray. The experimental results reveal that the electrospun AgNO₃/PAN was carbonized and reduced to Ag/CNF, the Ag/CNF was then partly oxidized to form Ag@AgCl/CNF in which Ag@AgCl nanoparticles (ca. 10-20 nm in diameter) were uniformly bounded to CNFs (ca. 165 nm in diameter). The obtained Ag@AgCl/CNF was employed for Na₂S₂O₈activation under visible light irradiation to treat Rhodamine B (RhB). A remarkable RhB removal of ca. 94.68% was achieved under optimal conditions, and the influence of various parameters on removal efficiency was studied. Quenching experiments revealed that HO•, SO₄^•-,¹O₂, and O₂^•-were major reactive oxygen species, in which O₂^•-played a pivotal role in RhB degradation. A possible mechanistic route for RhB degradation was proposed.

Cobalt-ferrite/Ag-fMWCNT hybrid nanocomposite catalyst for efficient degradation of synthetic organic dyes via peroxymonosulfate activation

The activation of peroxymonosulfate (PMS) by nanocatalysts has shown promise as an effective wastewater treatment protocol. Magnetic CoFe₂O₄/Ag-nanoparticles (NPs) anchored on functionalized multiwalled carbon nanotubes (fMWCNTs), a support material, were synthesized using a one-pot solvothermal method. The surface morphologies and physicochemical properties of the CoFe₂O₄/Ag-fMWCNT hybrid nanocomposite catalyst were investigated by powder X-ray diffraction analysis, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and nitrogen adsorption-desorption isotherms. The activity of the nanocomposite combined with PMS (serving as an activator) toward the degradation of rhodamine B, methylene blue, methyl orange, and methyl red was investigated. The obtained optimal 0.02 g CoFe₂O₄/Ag-fMWCNTs exhibited the highest PMS activation performance, with a removal percentage of 100% for 20 ppm dye concentration at pH 6.5 within 14 min. In addition, the rhodamine B degradation product was investigated by analyzing the intermediate products by liquid chromatography/mass spectrometry (LC-MS). The homogeneous distribution of CoFe₂O₄/Ag NPs on fMWCNTs accelerated PMS activation and enhanced the catalytic degradation of dyes. The effects of the reaction parameters on the dye degradation efficiency were investigated by using different nanocatalysts (fMWCNTs, CoFe₂O₄/fMWCNTs, and CoFe₂O₄/Ag-fMWCNTs) as well as by varying the pH (3-11), dye concentration (10-50 mg/l), catalyst dose (0.002-0.3 g), and PMS dose (0.02-0.1 g). Quenching experiments revealed that sulfate radicals are primarily responsible for rhodamine B degradation. A plausible mechanism for catalytic PMS activation was also proposed. Complete decolorization occurred within the first few minutes of the reaction. Furthermore, the catalytic activity of the CoFe₂O₄/Ag-fMWCNT/PMS hybrid nanocomposite remained stable after five successive cycles. This study verifies the applicability of CoFe₂O₄/Ag-fMWCNTs as an ultrafast catalyst for the complete removal of persistent organic pollutants via PMS activation, revealing their promising application in wastewater treatment.

Monodisperse-porous Mn5O8 microspheres as an efficient catalyst for fast degradation of organic pollutants via peroxymonosulfate activation

Monodisperse-porous Mn5O8 microspheres with multiple oxidation states were used as a highly stable, efficient heterogeneous catalyst for the fast degradation of organic pollutants via peroxymonosulfate activation.

A comprehensive study on the heterogeneous electro-Fenton degradation of tartrazine in water using CoFe2O4/carbon felt cathode

In this study, cobalt ferrite coated carbon felt (CoFe₂O₄/CF) was synthesized by solvothermal method and applied as cathode for electro-Fenton (EF) treatment of tartrazine (TTZ) in water. The materials were characterized by SEM, XRD, FTIR, CV, and EIS to explore their physical, chemical, and electrical properties. The effects of solvothermal temperature and metal content on the TTZ removal were examined, showing that 220 °C with 2 mM of Co and 4 mM of Fe precursors were the best synthesis condition. Various influencing factors such as applied current density, pH, TTZ concentration, and electrolytes were investigated, and the optimal condition was found at 8.33 mA cm^-2, pH 3, 50 mgTTZ L^-1, and 50 mM of Na₂SO₄, respectively. By radical quenching test, , ¹O₂, and HO were recognized as the key reactive oxygen species and the reaction mechanism was proposed for the EF decolorization of TTZ using CoFe₂O₄/CF cathode. The reusability and stability test showed that the highly efficient CoFe₂O₄/CF cathode is very promising for practical application in wastewater treatment, especially for dyes and other recalcitrant organic compounds to improve its biodegradability.

Oxidative Degradation of Tetracycline by Magnetite and Persulfate: Performance, Water Matrix Effect, and Reaction Mechanism

This study presents a strategy to remove tetracycline by using magnetite-activated persulfate. Magnetite (Fe3O4) was synthesized at high purity levels-as established via X-ray diffractometry, transmission electron microscopy, and N2 sorption analyses-and tetracycline was degraded within 60 min in the presence of both magnetite and persulfate (K2S2O8), while the use of either substance yielded limited degradation efficiency. The effects of magnetite and persulfate dosage, the initial concentration of tetracycline, and the initial pH on the oxidative degradation of tetracycline were interrogated. The results demonstrate that the efficiency of tetracycline removal increased in line with magnetite and persulfate dosage. However, the reaction rate increased only when increasing the magnetite dosage, not the persulfate dosage. This finding indicates that magnetite serves as a catalyst in converting persulfate species into sulfate radicals. Acidic conditions were favorable for tetracycline degradation. Moreover, the effects of using a water matrix were investigated by using wastewater treatment plant effluent. Comparably lower removal efficiencies were obtained in the effluent than in ultrapure water, most likely due to competitive reactions among the organic and inorganic species in the effluent. Increased concentrations of persulfate also enhanced removal efficiency in the effluent. The tetracycline degradation pathway through the magnetite/persulfate system was identified by using a liquid chromatograph-tandem mass spectrometer. Overall, this study demonstrates that heterogeneous Fenton reactions when using a mixture of magnetite and persulfate have a high potential to control micropollutants in wastewater.

Porous manganese-cobalt oxide microspheres with tunable oxidase mimicking activity for sulfide ion colorimetric detection

Here, we report the controllable synthesis of porous MnxCo1-xO microspheres and tunable catalytic activity in the oxidase mimicking reaction. Mn0.6Co0.4O possesses the best oxidase mimicking activity and can be used successfully in sulfide ion colorimetric detection with a low detection limit of 0.1 μM.

Perovskite and Spinel Catalysts for Sulfate Radical-Based Advanced Oxidation of Organic Pollutants in Water and Wastewater Systems

Since environmental pollution by emerging organic contaminants is one of the most important problems, gaining ground year after year, the development of decontamination technologies of water systems is now imperative. Advanced oxidation processes (AOPs) with the formation of highly reactive radicals can provide attractive technologies for the degradation of organic pollutants in water systems. Among several AOPs that can be applied for the formation of active radicals, this review study focus on sulfate radical based-AOPs (SR-AOPs) through the heterogeneous catalytic activation of persulfate (PS) or peroxymonosulfate (PMS) using perovskite and spinel oxides as catalysts. Perovskites and spinels are currently receiving high attention and being used in substantial applications in the above research area. The widespread use of these materials is based mainly in the possibilities offered by their structure as it is possible to introduce into their structures different metal cations or to partially substitute them, without however destroying their structure. In this way a battery of catalysts with variable catalytic activities can be obtained. Due to the fact that Co ions have been reported to be one of the best activators of PMS, special emphasis has been placed on perovskite/spinel catalysts containing cobalt in their structure for the degradation of organic pollutants through heterogeneous catalysis. Among spinel materials, spinel ferrites (MFe2O4) are the most used catalysts for heterogeneous activation of PMS. Specifically, catalysts with cobalt ion in the A position were reported to be more efficient as PMS activators for the degradation of most organic pollutants compared with other transition metal catalysts. Substituted or immobilized catalysts show high rates of degradation, stability over a wider pH area and also address better the phenomena of secondary contamination by metal leaching, thus an effective method to upgrade catalytic performance.

Facile synthesis of Mn-doped NiCo2O4 nanoparticles with enhanced electrochemical performance for a battery-type supercapacitor electrode

We report the synthesis of manganese-doped nickel cobalt oxide (Mn-doped NiCo2O4) nanoparticles (NPs) by an efficient hydrothermal and subsequent calcination route. The material exhibits a homogeneous distribution of the Mn dopant and a battery-type behavior when tested as a supercapacitor electrode material. Mn-doped NiCo2O4 NPs show an excellent specific capacity of 417 C g-1 at a scan rate of 10 mV s-1 and 204.3 C g-1 at a current density of 1 A g-1 in a standard three-electrode configuration, ca. 152-466% higher than that of pristine NiCo2O4 or MnCo2O4. In addition, Mn-doped NiCo2O4 NPs showed an excellent capacitance retention of 99% after 1000 charge-discharge cycles at a current density of 2 A g-1. The symmetric solid-state supercapacitor device assembled using this material delivered an energy density of 0.87 μW h cm-2 at a power density of 25 μW h cm-2 and 0.39 μW h cm-2 at a high power density of 500 μW h cm-2. The cost-effective synthesis and high electrochemical performance suggest that Mn-doped NiCo2O4 is a promising material for supercapacitors.