Urchin-like Co3O4 anchored on reduced graphene oxide with enhanced performance for peroxymonosulfate activation in ibuprofen degradation

Urchin-like Co₃O₄ anchored on reduced graphene oxide was easily prepared with hydrothermal reaction by using a cheap and green agent. First, the surface morphology and physicochemical properties of Co₃O₄-rGO were characterized. Compared with Co₃O₄, Co₃O₄-rGO possessed excellent activity in peroxymonosulfate (PMS) activation for ibuprofen (IBU) degradation. Then, the influences of Co₃O₄-rGO dosage, IBU concentration, PMS concentration and pH on IBU and TOC removal were investigated, respectively. Furthermore, both ·OH and SO₄^•- were identified to be the main active species, and SO₄^•- made the predominant contribution. In addition, residual PMS and SO₄^•- quantification demonstrated that Co₃O₄-rGO could activate PMS more effectively, and produce more SO₄^•-. The mechanistic study revealed that the valence state conversion of Co²⁺/Co³⁺ was the critical PMS activation mechanism. Moreover, the enhanced activity of Co₃O₄-rGO is accounted for the combination of multiple unique characteristics, including excellent electronic transmission (Co²⁺ to Co³⁺, Co²⁺ to PMS), more active sites, and chemical bonds between Co₃O₄ and rGO. 13 degradation products were determined and possible degradation routes were proposed based on the results of LC-MS/MS. Finally, the Co₃O₄-rGO/PMS system also exhibited satisfactory removal of IBU in real water matrices.

Amorphous CoV phosphate nanosheets as efficient oxygen evolution electrocatalyst

Oxygen evolution reaction (OER) is crucial for hydrogen production. However, OER with four-electron transfer requires electrocatalysts to speed up its sluggish kinetics in alkaline solutions. Herein, amorphous CoV phosphate (denoted as CoV-Pi) nanosheets synthesized by a straightforward one-step hydrothermal approach is reported, which provide a low overpotential of 320 mV at 10 mA cm-2 , a small Tafel slope down to 48.8 mV dec-1 and long-term durability over 80 h. The efficient activity is ascribed to the amorphous nanosheets structure, high electrochemically active surface area, enhanced surface wettability and the synergistic effect of the active metal atoms. This study significantly indicates that CoV-Pi is a promising alternative to replace expensive noble metal-based catalysts for electrochemical water splitting.

Ultrafine cobalt nanoparticle-embedded leaf-like hollow N-doped carbon as an enhanced catalyst for activating monopersulfate to degrade phenol

While cobalt (Co) stands out as the most effective non-precious metal for activating monopersulfate (MPS) to degrade organic pollutants, Co nanoparticles (NPs) are easily aggregated, losing their activities. As many efforts have attempted to immobilize Co NPs on supports/substrates to minimize the aggregation issue, recently hollow-structured carbon-based materials (HSCMs) have been regarded as promising supports owing to their distinct physical and chemical properties. Herein, in this study, a special HSCM is developed by using a special type of ZIF (i.e., ZIF-L) as a precursor. Through one-step chemical etching with tannic acid (TA), the resultant product still remains leaf-like morphology of pristine ZIF-L but the inner part of this product becomes hollow, which is subsequently transformed to ultrafine Co-NP embedded hollow-structured N-doped carbon (CoHNC) via pyrolysis. Interestingly, CoHNC exhibits superior catalytic activities than CoNC (without hollow structure) and the commercial Co₃O₄ NPs for activating MPS to degrade phenol. The E_a value of phenol degradation by CoHNC + MPS was determined as 44.3 kJ/mol. Besides, CoHNC is also capable of effectively activating MPS to degrade phenol over multiple-cycles without any significant changes of catalytic activities, indicating that CoHNC is a promising heterogeneous catalyst for activating MPS to degrade organic pollutants in water.

In-situ synthesis of manganese oxide‑carbon nanocomposite and its application in activating persulfate for bisphenol F degradation

In this work, manganese oxide‑carbon nanocomposite catalytic materials (MnO@CNs) with a "core-shell" structure were synthesized in the one-step synthesis using sodium alginate as a template. XRD and Raman spectroscopy proved that high calcination temperatures were beneficial to the graphitization of carbon and the formation of Mn₇C₃. Both SEM and TEM images of MnO@CNs identified that MnO nanoparticles were encapsulated in a three-dimensional carbon matrix and simultaneously protected by a "carbon-shell" with an adherent graphite structure, which could facilitate electron transfer. The MnO@CNs could activate PS to degrade BPF completely within 30 min in solutions with a wide pH range or coexisting anions and organics. The valence change of Mn could promote the generation and conversion of various free radicals and non-radicals, of which O₂·^- played a leading role in the decomposition of BPF. In addition, the potential degradation pathways and degradation mechanisms of BPF in the MnO@CNs/PS system were also explored according to DFT calculations and product detection results.

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.

Synthetic NiO catalyst-assisted peroxymonosulfate for degradation of benzoic acid from aqueous solution

A heterogeneous NiO catalyst was prepared by a precipitation process using nickel nitrate with oxalic acid and tested for heterogeneous oxidation of benzoic acid (BA) in the presence of peroxymonosulfate (PMS). It was found that the synthetic NiO is highly effective in heterogeneous activation of PMS to produce sulfate radicals ( SO 4 · - ) and hydroxyl radicals (^· OH), and also presents stable performance in the heterogeneous activation of PMS for BA degradation. Physicochemical properties of the NiO catalyst were characterized by several techniques, such as thermogravimetric analysis, Brunauer-Emmett-Teller, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. It was found that NiO and NiOOH were formed on the synthetic NiO catalyst and were stably distributed on the catalyst surface. Nearly 95% decomposition could be achieved in 30 min at the conditions of 500 ml 20 μM BA solution, 0.25 g catalyst, and [PMS]:[BA] = 30:1. The heterogeneous reactions, the effects of PMS concentration, and catalyst dosage on the BA degradation were investigated. The heterogeneous BA degradation reactions followed first-order kinetics. Additionally, quenching experiments proved that the dominant radical in the solution was ^· OH. The experiments results also showed that this approach is effective for the degradation of many other pollutants (such as tetracycline hydrochloride, 2, 4-dichlorophenol, Acid orange 7, rhodamine B, and methyl red). PRACTITIONER POINTS: A novel NiO material was fabricated for degradation of benzoic acid. The synthetic NiO catalyst comprised active NiO and NiOOH. The main radical for benzoic acid removal rate was ^· OH. A plausible mechanism for catalyzed degradation of the benzoic acid was proposed.

CuCo2O4 supported on activated carbon as a novel heterogeneous catalyst with enhanced peroxymonosulfate activity for efficient removal of organic pollutants

CuCo₂O₄ was synthesized via a relatively simple method, and innovatively supported onto the activated carbon (AC) by calcination to obtain a novel heterogeneous catalyst (AC-CuCo₂O₄). Brilliant red 3BF (3BF) was selected as the probe compound to investigate the catalytic activity of AC-CuCo₂O₄ in the presence of peroxymonosulfate (PMS). The results showed that 98% removal rate could be achieved and the reaction rate constant (0.476 min^-1) was 5.2 times greater than that of CuCo₂O₄ alone (0.091min^-1), suggesting that the introduction of AC could greatly enhance the catalytic activity of pure CuCo₂O₄. Typically, the 3BF removal was as high as 96% after five cycles, showing the good stability of catalyst reuse. Additionally, the effects of the initial pH, catalyst dosage, PMS concentration and reaction temperature on the 3BF removal were investigated, demonstrating that AC-CuCo₂O₄ effectively remove 3BF over a wide pH range (5.0-10.0) and possessed temperature-tolerant performance. To further explore the 3BF removal mechanism, electron paramagnetic resonance technology combining with trapping agents was employed to confirm the involvement of reactive oxygen species including SO₄^•-, ^•OH, O₂^•- and ¹O₂, which distinctly differed from the reported CuCo₂O₄ for PMS activation. These findings provided an addition promising strategy in environmental remediation.

Co2+ anchored on surface-functionalized PET non-woven fabric and used as high efficiency monoatom-like catalyst for activating Oxone in water

Fenton-like processes have emerged as most promising techniques for generating reactive oxygen-containing radicals to deal with increasing levels of environmental pollution. Developing novel catalysts with simple manufacturing requirements, excellent activity levels, and stability remains a long-term goal in terms of practical application. So herein, a new polyethylene terephthalate (PET) non-woven fabric based composite catalyst has been fabricated, using radiation-induced graft polymerization of a functionalized group to chelate Co²⁺ ions as heterogeneous catalysts in peroxymonosulfate (Oxone) activation. Several impact factors, including catalyst dosage, Oxone concentration, reaction temperature, pH value, Co²⁺ precipitation ratio (of Co@PET at different pH values), and highly concentrated NaCl have been investigated here. Notably, Co@PET has shown the lowest activation energy of any reported catalyst, for degrading RhB by activating Oxone. Interestingly, as experimental RhB and Oxone solutions were passed through single Co@PET sheets, the RhB was decomposed into a colorless solution in the penetration process. Based on radical trapping and quenching experiments, a channel was determined to dominate RhB degradation, and furthermore, Co@PET could be re-used for RhB degradation by activating Oxone. These results showed that Co@PET effectively provided improved Fenton-like catalytic performance and stability, and was suitable for practical applications.

Oxidation of flumequine in aqueous solution by UV-activated peroxymonosulfate: Kinetics, water matrix effects, degradation products and reaction pathways

The degradation of flumequine (FLU) in aqueous solution by ultraviolet (UV)-activated peroxymonosulfate (PMS) was investigated in this work. Under the conditions of [PMS]₀:[FLU]₀ = 1:1, T = 25 ± 2 °C, pH = 7.0 ± 0.1, nearly complete removal of FLU was achieved after 60 min. The effects of various operating parameters, including oxidant doses, pH, the presence of typical ions (NH₄⁺、Mg²⁺、Fe³⁺、Cl^-、NO₃^-、HCO₃^-) and humic acid were evaluated. It was found that the pseudo-first-order rate constants of FLU degradation increased with increasing PMS dosage and decreasing solution pH. The presence of Mg²⁺ could accelerate FLU removal, while Fe³⁺, HCO₃^-, NO₃^- and HA inhibited the reaction. Moreover, the degradation of FLU in different water matrices were also explored, and the removal followed the order of Tap water > Ultrapure water > River water > Secondary clarifier effluent. According to the control and radical quenching experiment results, direct photolysis and reactive radicals (SO₄^- and HO) contributed mainly to FLU degradation in the UV/PMS system. Initial FLU molecule underwent reactions such as hydroxylation, hydroxyl substitution, demethylation, decarboxylation/decarbonylation and ring opening, leading to the formation of nineteen oxidation products. The effective degradation by UV/PMS suggests a feasible technology for treating FLU in waters and wastewaters.

Degradation of methylene blue with magnetic Co-doped Fe3O4@FeOOH nanocomposites as heterogeneous catalysts of peroxymonosulfate

Magnetic Co-doped Fe₃O₄@FeOOH nanocomposites were prepared in one step using the hydrothermal synthesis process for catalyzing peroxymonosulfate (PMS) to degrade refractory methylene blue (MB) at a wide pH range (3.0–10.0). The catalysts' physiochemical properties were characterized by different equipment; Fe³⁺/Fe²⁺ and Co³⁺/Co²⁺ were confirmed to coexist in the nanocomposite by X-ray photoelectron spectroscopy. The nanocomposite effectively catalyzed PMS's decoloration (99.2%) and mineralization (64.7%) of MB. The formation of Co/Fe–OH complexes at the surface of nanoparticles was proposed to facilitate heterogeneous PMS activation. Compared with the observation for Fe₃O₄@FeOOH, the pseudo-first-order reaction constant was enhanced by 36 times due to Co substitution (0.1620 min⁻¹vs. 0.0045 min⁻¹), which was assigned to the redox recycle of Fe³⁺/Fe²⁺ and Co³⁺/Co²⁺ in Co-doped Fe₃O₄@FeOOH. Besides, the catalyst could be easily reused by magnetic separation and exhibited relatively long-term stability.

Magnetic Co-doped Fe₃O₄@FeOOH nanocomposites were prepared in one step using the hydrothermal synthesis process for catalyzing peroxymonosulfate (PMS) to degrade refractory methylene blue (MB) at a wide pH range (3.0–10.0).

Catalytic degradation of diclofenac from aqueous solutions using peroxymonosulfate activated by magnetic MWCNTs-CoFe3O4 nanoparticles

CoFe₃O₄ nanoparticles supported on multi-walled carbon nanotubes (MWCNTs-CoFe₃O₄) were synthesized by the co-precipitation method as a novel catalyst for degradation of diclofenac (DCF). The comparative experiments indicated that MWCNTs-CoFe₃O₄ has a better catalytic activity in degradation of DCF and activation of peroxymonosulfate (PMS) compared to other catalytic systems. This can be attributed to the interaction of MWCNTs with CoFe₃O₄ in accelerating the absorption process and activating the PMS (E_a = 22.93 kJ mol⁻¹). The removal efficiencies of DCF and total organic carbon (TOC) were 99.04% and 50.11%, under optimum conditions, e.g., pH of 7, PMS dosage of 4 mM, DCF concentration of 30 mg L⁻¹, catalyst dosage of 500 mg L⁻¹, and reaction time of 120 min. The oxidation of DCF was fitted by the pseudo-first-order kinetic model and the constant rate was increased by increasing the pH, temperature, dosage of PMS and catalyst. The production of reactive species was studied using scavengers such as TBA and ethanol and the results showed that sulfate radical is the reactive species responsible for the degradation of DCF. The MWCNTs-CoFe₃O₄ catalyst showed high stability and reusability based on five successful repeated reactions, X-ray diffraction and energy dispersive X-ray spectroscopy analysis. Based on the intermediates detected by gas chromatography-mass spectrometry (GC-MS), the possible pathways for DCF catalytic oxidation were proposed. The results explained that the PMS/MWCNTs-CoFe₃O₄ system is a promising method for treating DCF solution due to high efficiency, good reusability of catalyst and greater PMS activation.

The MWCNTs-CoFe₃O₄ as a novel catalyst showed high catalytic activity in activation of proxymonosulfate for degradation of diclofenac.

Degradation of Acid Orange 7 by peroxymonosulfate activated with the recyclable nanocomposites of g-C3N4 modified magnetic carbon

Carbon-based catalysts have attracted high attention since they are greener and cheaper, while magnetic nanomaterials are very useful in environmental application because of the easy recovery and operation given by the magnetic separability. Therefore, graphitic carbon nitride modified magnetic carbon nanocomposites Fe₃O₄@C/g-C₃N₄ was prepared herein for the first time as a new carbon-based catalyst for the activation of peroxymonosulfate (PMS). The catalytic properties of Fe₃O₄@C/g-C₃N₄ in activating PMS for the degradation of Acid Orange 7 (AO 7), a model organic pollutant, were investigated. AO 7 degradation efficiency was significantly enhanced after modification of Fe₃O₄@C with g-C₃N₄, and the composite Fe₃O₄@C/g-C₃N₄ from loading of 5 wt% g-C₃N₄ and calcined at 300 °C for 30 min exhibited the best performance. AO 7 could be efficiently decolorized using the "Fe₃O₄@C/C₃N₄ (5%) + PSM" system within the pH range of 2-6, and 97% of AO 7 could be removed in 20 min without pH adjustment (pH = 4). Radical quenching and EPR studies confirmed that both sulfate and hydroxyl radicals produced from PMS activation were the active species responsible for the oxidation of AO 7. The degradation mechanism was suggested based on the experimental results and XPS analyses. It was proposed that the CO groups on the carbon surface of Fe₃O₄@C rather than the CO in g-C₃N₄ played a key role as the active sites for PMS activation. The catalyst was magnetically separable and displayed good stability and reusability, thus providing a potentially green catalyst for sustainable remediation of organic pollutants.

Heterogeneous activation of peroxymonosulfate by LaCo1-xCuxO3 perovskites for degradation of organic pollutants

Recently cobalt-based heterogeneous catalysts have been widely investigated for peroxymonosulfate (PMS) activation in sulfate radical-based advanced oxidation processes. However, the improvement of the catalytic performance for PMS activation remains to be a challenge. As the limiting step, the rapid transformation of Co^II/Co^III redox pairs is crucial for PMS activation. Perovskites attract increasing attention due to their controllable oxidation state of B-site metal and formation of oxygen vacancies, which accelerates the cycle of redox pairs. LaCo_1-xM_xO₃ (M = Cu, Fe and Mn) perovskites as heterogeneous catalysts of PMS were synthesized for the degradation of phenol. The results showed that LaCo_0.4Cu_0.6O₃ exhibited the highest catalytic activity. The pseudo first-order kinetic constant of phenol degradation on LaCo_0.4Cu_0.6O₃ is 0.302 min^-1, being about 5 times as high as Co²⁺ with same molar concentration of cobalt in LaCo_0.4Cu_0.6O₃. XPS analysis confirmed that substitution of copper could promote the cycle of Co^II/Co^III, thus enhance the catalytic efficiency for PMS activation. The facilitated cycle of Co^II/Co^III played a crucial role in the generation of sulfate radicals, hydroxyl radicals and singlet oxygen. And sulfate radical was the primary radical responsible for pollutants degradation. The results provide insights into constructing novel perovskite catalysts for the removal of organic pollutants in water.

TiO2 nanodots anchored on nitrogen-doped carbon nanotubes encapsulated cobalt nanoparticles as photocatalysts with photo-enhanced catalytic activity towards the pollutant removal

Constructing hierarchical structure is an effective approach to improve the activities of catalysts. Herein, a novel hierarchical structure of TiO₂ nanodots anchored on N-doped carbon nanotubes encapsulated Co nanoparticles (TiO₂/Co@NCT) was synthesized by a simple pyrolysis method. Their catalytic performances were examined in the oxidative and light-assisted degradation of recalcitrant pollutants in the presence of the peroxymonosulfate (PMS). The Orange II removal efficiency within 15 min reached about 98.48% in TiO₂/Co@NCT/PMS system. In this system, Co⁰ is used to react with PMS to generate free radicals for the degradation of dyes. The carbon shell benefits the adsorption of dyes and prevents the catalysts from dissolving in the solution. Besides, under light irradiation, TiO₂ nanodots can be excited to generate photo-induced electrons, which can reduce inner Co²⁺ to Co⁰ in the degradation process, thus TiO₂/Co@NCT exhabited high activity and outstanding stability in degradation process. The as-prepared TiO₂/Co@NCT catalyst showed efficient degradation and superior stability, which would make it a great promise in practical applications for sewage treatment.

Cobalt-embedded carbon nanofiber derived from a coordination polymer as a highly efficient heterogeneous catalyst for activating oxone in water

Carbon fiber (CF) supported cobalt nanoparticles (NPs) are promising catalysts for activating Oxone because carbon is non-metal and earth-abundant, and CF-based catalysts exhibit a high aspect ratio, which affords more accessible and dense catalytic sites. Nevertheless, most of CF-supported catalysts are fabricated by post-synthetic methods, which involve complicated preparations. More importantly, metallic NPs are attached to the outer surface of CF rather than embedded within CF. However, there is still a great demand for developing Co-bearing carbon fibers for Oxone activation via simple and effective methods. Thus, this study proposes to develop a cobalt NP-embedded carbon nanofiber (CCNF) by a simple hydrothermal reaction of Co and nitrilotriacetic acid (NA), followed by one-step carbonization. Owing to the coordinative structure of CoNA, the derivative CCNF exhibits a fibrous carbon matrix embedded with evenly distributed and densely packed Co₃O₄ and magnetic Co⁰ nanoparticles. The fibrous structure, magnetism and embedded Co NPs enable CCNF to be a promising catalyst for Oxone activation. As degradation of Rhodamine B (RhB) is selected as a model reaction, CCNF not only rapidly activates Oxone to fully degrade RhB but also shows a much higher catalytic activity than the most common Oxone activator, Co₃O₄. CCNF also exhibits the lowest activation energy than any reported catalysts for Oxone activation to degrade RhB. In addition, CCNF could be re-used to activate Oxone for RhB degradation. These results indicate that CCNF is a conveniently prepared and highly effective fibrous Co/C hybrid material for activating Oxone to oxidize contaminants in water.

Synthesis of Co3O4-Bi2O3 using microwave-assisted method as the peroxymonosulfate activator for elimination of bisphenol A

In this work, Co₃O₄-Bi₂O₃ was successfully synthesized using a microwave-assisted method [Co₃O₄-Bi₂O₃(MW)] and employed as a peroxymonosulfate (PMS) activator for bisphenol A removal. A reference catalyst was prepared using the same preparation conditions but different heating mode and labeled as Co₃O₄-Bi₂O₃(CH). The series of Co₃O₄-Bi₂O₃ was characterized using XRD, SEM, and N₂ adsorption to detect their crystallinity, morphology, and surface area, among others. Results indicated that both microwave and calcination significantly affected the characteristic and catalytic activity of the catalyst. Moreover, the microwave-irradiated catalyst calcined at 300 °C showed higher catalytic activity and mineralization percentage for BPA degradation than the conventionally heated catalyst calcined at the same temperature. Microwave temperature and microwave time of the proposed microwave-assisted method were also investigated. Compared with other catalysts, the present catalyst showed considerably superior preparation time and degradation efficiency. This study broadens a new horizon for advanced oxidation process using a PMS activator.

One-step prepared cobalt-based nanosheet as an efficient heterogeneous catalyst for activating peroxymonosulfate to degrade caffeine in water

Two-dimensional (2D) planar cobalt-containing materials are promising catalysts for activating peroxymonosulfate (PMS) to degrade contaminants because 2D sheet-like morphology provides large reactive surfaces. However, preparation of these sheet-supported cobaltic materials typically involves multiple steps and complex reagents, making them less practical for PMS activation. In this study, a cobalt-based nanosheet (CoNS) is particularly developed using a one-step hydrothermal process with a single reagent in water. The resulting CoNS can exhibit a thickness as thin as a few nanometers and 2-D morphology. CoNS is also primarily comprised of cobalt species in a coordinated form of Prussian Blue analogue, which consists of both Co³⁺ and Co²⁺. These features make CoNS promising for activating PMS in aqueous systems. As degradation of an emerging contaminant, caffeine, is selected as a representative reaction, CoNS not only successfully activates PMS to fully degrade caffeine in 20 min but also exhibits a much higher catalytic activity than the most common PMS activator, Co₃O₄. Via studying inhibitive effects of radical scavengers, caffeine degradation by CoNS-activated PMS is primarily attributed to sulfate radicals and hydroxyl radicals to a lesser extent. The degradation products of caffeine by CoNS-activated PMS are also identified and a potential degradation pathway is proposed. Moreover, CoNS could be also re-used to activate PMS for caffeine degradation without activity loss. These results indicate that CoNS is a conveniently prepared and highly effective and stable 2-D catalyst for aqueous chemical oxidation reactions.

Ultrasound enhanced heterogeneous activation of peroxymonosulfate by a Co-NiOx catalyst

Sulfate radical-based advanced oxidation processes have had considerable attention due to the highly oxidizing function of sulfate radicals (SO₄^-·) resulting in acceleration of organic pollutants degradation in aqueous environments. A Co-Ni mixed oxide nanocatalyst, which was prepared by the sol-gel method, was employed to activate peroxymonosulfate (PMS, HSO₅^-) to produce SO₄^-· with Acid Orange 7 (AO7) selected as a radical probe. The catalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). The characterization results indicated that the ingredient of the catalyst had been changed and the amount of surface hydroxyl increased significantly with the addition of Ni. Therefore, it proved that Co-NiOx catalyst was more effective than CoOx to activate PMS. Moreover, ultrasound (US) can increase the degradation rate of AO7 and US/Co-NiOx/PMS system. This study also focused on some synthesis parameters and the system reached the maximum efficiency under the condition when [PMS] = 0.4 mM, [catalyst] = 0.28 g/L, Pus = 200 W. The AO7 removal in these systems follows first order kinetics. Last but not least, quenching studies was conducted which indicated that the amount of hydroxyl radicals (·OH) increases with the increase of initial pH and SO₄^-· was the primary reactive oxidant for AO7 degradation.

Synthesis of Magnetic Microspheres with Sodium Alginate and Activated Carbon for Removal of Methylene Blue

Based on the adsorption performance of composite microspheres with activated carbon (AC) and sodium alginate (SA), as well as the magnetic property of Fe₃O₄, we designed and explored an efficient strategy to prepare a unique, multifunctional Fe₃O₄/AC/SA composite absorbent (MSA-AC) that extracted dye from aqueous solution. The composite exhibited the following advantages: rapid and simple to prepare, environmentally friendly process, low-cost, recyclability, and multi-functionality. The physicochemical properties of the prepared magnetic microspheres were measured, and methylene blue (MB) was selected to investigate the performance of the magnetic absorbent. The results showed a maximum adsorption capacity of 222.3 mg/g for MB. Adsorption studies revealed that the data of adsorption isotherms and kinetics fit the pseudo-second-order kinetic model and Langmuir isotherm model.

CoMoO4 as a novel heterogeneous catalyst of peroxymonosulfate activation for the degradation of organic dyes

The catalytic performance of CoMoO₄ for peroxymonosulfate activation in an advanced oxidation process was investigated for the first time.

Prussian blue analogue derived magnetic carbon/cobalt/iron nanocomposite as an efficient and recyclable catalyst for activation of peroxymonosulfate

A Prussian blue analogue, cobalt hexacyanoferrate Co₃[Fe(CN)₆]₂, was used for the first time to prepare a magnetic carbon/cobalt/iron (MCCI) nanocomposite via one-step carbonization of Co₃[Fe(CN)₆]₂. The resulting MCCI consisted of evenly-distributed cobalt and cobalt ferrite in a porous carbonaceous matrix, making it an attractive magnetic heterogeneous catalyst for activating peroxymonosulfate (PMS). As Rhodamine B (RhB) degradation was adopted as a model test for evaluating activation capability of MCCI, factors influencing RhB degradation were thoroughly examined, including MCCI and PMS dosages, temperature, pH, salt and radical scavengers. A higher MCCI dosage noticeably facilitated the degradation kinetics, whereas insufficient PMS dosage led to ineffective degradation. RhB degradation by MCCI-activated PMS was much more favorable at high temperatures and under neutral conditions. The presence of high concentration of salt slightly interfered with RhB degradation by MCCI-activated PMS. Through examining effects of radical scavengers, RhB degradation by MCCI-activated PMS can be primarily attributed to sulfate radicals instead of a combination of sulfate and hydroxyl radicals. Compared to Co₃O₄, a typical catalyst for PMS activation, MCCI also exhibited a higher catalytic activity for activating PMS. In addition, MCCI was proven as a durable and recyclable catalyst for activating PMS over multiple cycles without efficiency loss and significant changes of chemical characteristics. These features demonstrate that MCCI, simply prepared from a one-step carbonization of Co₃[Fe(CN)₆]₂ is a promising heterogeneous catalyst for activating PMS to degrade organic pollutants.

Topotactic Transformation of Metal-Organic Frameworks to Graphene-Encapsulated Transition-Metal Nitrides as Efficient Fenton-like Catalysts

Innovation in transition-metal nitride (TMN) preparation is highly desired for realization of various functionalities. Herein, series of graphene-encapsulated TMNs (Fe_xMn_6-xCo₄-N@C) with well-controlled morphology have been synthesized through topotactic transformation of metal-organic frameworks in an N₂ atmosphere. The as-synthesized Fe_xMn_6-xCo₄-N@C nanodices were systematically characterized and functionalized as Fenton-like catalysts for catalytic bisphenol A (BPA) oxidation by activation of peroxymonosulfate (PMS). The catalytic performance of Fe_xMn_6-xCo₄-N@C was found to be largely enhanced with increasing Mn content. Theoretical calculations illustrated that the dramatically reduced adsorption energy and facilitated electron transfer for PMS activation catalyzed by Mn₄N are the main factors for the excellent activity. Both sulfate and hydroxyl radicals were identified during the PMS activation, and the BPA degradation pathway mainly through hydroxylation, oxidation, and decarboxylation was investigated. Based on the systematic characterization of the catalyst before and after the reaction, the overall PMS activation mechanism over Fe_xMn_6-xCo₄-N@C was proposed. This study details the insights into versatile TMNs for sustainable remediation by activation of PMS.

Graphene encapsulated FexCoy nanocages derived from metal–organic frameworks as efficient activators for peroxymonosulfate

Graphene encapsulated Fe_xCo_y nanocages derived from metal–organic frameworks were newly developed as excellent Fenton-like catalysts for PMS activation.