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

Degradation of fenamates

Fenamates are the most crucial non-steroidal anti-inflammatory drugs (NSAIDs) used to treat pain-related diseases. The clinically prescribed drugs of the fenamate group include mefenamic acid, tolfenamic acid, meclofenamic acid, flufenamic acid, and niflumic acid. Due to their widespread use, all these drugs are considered as the most common water and sewerage pollutants. Studies have been performed to remove these contaminants from water sources by various forced degradation procedures, but the number of studies in this area is limited. In this chapter, an effort has been made to review the degradation of multiple fenamates in different systems and the factors affecting the degradation rates with the proposed degradation pathways.

Carbon nanotube supported cobalt nickel sulphide nano-catalyst for degradation of chloroquine phosphate with peroxymonosulphate

Carbon nanotubes supported cobalt nickel sulphide nanoparticles (nano-NiCo2S4@CNTs) were successfully prepared by a hydrothermal method as heterogeneous catalyst which can be used as an activator of peroxymonosulphate (PMS) for the degradation of chloroquine phosphate (CQP). Based on characterisation techniques, the prepared catalyst has excellent surface properties and structural stability. When different concentrations of CQP were treated with 0.2 g/L nano-NiCo2S4@CNTs and 1.0 mM PMS, the highest degradation rate could reach 99.86% after 30 min. Under the interference of pH, common anions and humic acid in the water environment, the reaction system can still achieve high degradation efficiency, showing excellent anti-interference ability and practical applicability. Furthermore, in the nano-NiCo2S4@CNTs/PMS system, according to the identification results of reactive oxygen species, the free radical and non-free radical pathway are responsible for the degradation of CQP, and the PMS mechanism activation was comprehensively proposed. Twelve intermediate products were detected in the degradation process, and the possible degradation pathways of CQP were proposed. This toxicity analysis demonstrates that the intermediate products formed during CQP degradation pose lower environmental risks compared to the original pollutant. In addition, after using the catalyst four cycles, the removal efficiency of CQP remains above 80%, indicating the excellent reusability and low metal ion leaching characteristics. Therefore, the nano-NiCo2S4@CNTs synthesised in this research has broad application prospects in activating PMS for wastewater treatment.

Non-radical-dominated catalytic degradation of methylene blue by magnetic CoMoO4/CoFe2O4 composite peroxymonosulfate activators

In this study, magnetic CoMoO₄/CoFe₂O₄ (CMO/CFO) nanospheres with a core-shell structure were synthesized via two-step hydrothermal methods. The obtained particles were employed as catalysts to activate peroxymonosulfate (PMS) and degrade methylene blue (MB). The physico-chemical characterizations of the synthesized CMO/CFO showed that the CMO shell contributed to the enhancement of redox conversion and the increase in the concentration of oxygen vacancies (OVs). By examining reactive oxygen species (ROS) in the CMO/CFO/PMS system, the MB degradation was dominated by a non-radical pathway, and ¹O₂ was identified as the most abundant ROS. Besides, the CMO/CFO exhibited faster reaction kinetics than the pristine CFO. Moreover, the magnetic properties guaranteed the recycling and reuse of CMO/CFO, and the removal rate of MB was maintained at ∼94% after continuous use five times. Both the tolerance to SO₄^2-and the wide pH range where the material is applicable make it a promising catalyst for dyeing wastewater treatment.

Photocatalysis coupled with adsorption of AC@Ni0.5Cu0.5Fe2O4 in peroxydisulfate assisted system efficiently enhance ciprofloxacin removal

Nickle-copper ferrite (Ni_0.5Cu_0.5Fe₂O₄) supported on activated carbon (AC) (AC@Ni_0.5Cu_0.5Fe₂O₄) was synthesized and used as adsorbent, photocatalyst, and activator of peroxydisulfate (PDS) to realize the removal of ciprofloxacin (CIP). AC@Ni_0.5Cu_0.5Fe₂O₄ properties were characterized by scanning electron microscope equipped with energy-dispersive X-ray (SEM-EDX), X-ray diffraction (XRD), N₂ adsorption-desorption isotherm plot of Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH), vibrating sample magnetometer (VSM). A rapid removal rate (94.30%) of CIP was achieved on AC@Ni_0.5Cu_0.5Fe₂O₄/PDS/UV system with the condition of catalyst dosage 0.30 g/L, initial pH 7.3, PDS addition 0.20 mM, CIP concentration 10 mg/L (200 mL), UV 28 W, in 30 min. Free radical quenching experiments indicate that reactive species of superoxide (·O₂^-), holes (h⁺), sulfate radicals (SO₄^-·) and hydroxyl radicals (·OH) were produced and all worked. The reusability test demonstrated that AC@Ni_0.5Cu_0.5Fe₂O₄ could be recycled five times with minimal performance reduction for the removal of CIP. The XRD and SEM of the after used AC@Ni_0.5Cu_0.5Fe₂O₄ did not change significantly, which further showed its stability and recyclability. This work might provide new insight into the application of AC@Ni_0.5Cu_0.5Fe₂O₄ in photocatalysis coupled with adsorption in peroxydisulfate assisted system and has high potential in CIP removal.

Treatment of fluorine-containing pharmaceutical wastewater by VUV/UV process

As an advanced oxidation process, vacuum ultraviolet/ultraviolet (VUV/UV) has been intensively studied for drinking water treatment, but assessment of its feasibility for wastewater treatment has rarely been conducted. This study investigated the treatment of fluorine-containing pharmaceutical wastewater by VUV/UV process and examined the defluorination and therefore the improvement of biodegradability of the wastewater after the process. The results indicated that the degradation of a model fluorine-containing organic compound (namely, 4-fluorophenol) was mainly achieved via the attack of the fluorine atom linking directly to the aromatic ring by the HO^• generated from VUV photolysis of water. As the solution pH increased from 4.0 to 10.0, the COD removal efficiency of the real pharmaceutical wastewater decreased slightly from 18.1 to 15.9%, while the release ratio of F^- increased from 50.8 to 75.5%. As the dissolved oxygen increased from 0.15 to 12 mg L^-1, the removal efficiency of COD and the release ratio of F^- increased from 9.2 to 17.1% and from 48.2 to 75.5%, respectively. The biodegradability index (BOD/COD) increased significantly from 0.24 to 0.47 after the VUV/UV irradiation, which confirmed the feasibility of applying the VUV/UV process for improving biodegradability of the pharmaceutical wastewater.

Insight into the performance and mechanism of magnetic Ni0.5Cu0.5Fe2O4 in activating peroxydisulfate for ciprofloxacin degradation

Magnetic nickel-copper ferrite (Ni_xCu_yFe₂O₄) nano-catalyst was synthesized by co-precipitation method, and it exhibited excellent ability for activating peroxydisulfate (PDS) in the degradation of ciprofloxacin (CIP). As-prepared Ni_0.5Cu_0.5Fe₂O₄ properties were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope equipped with an energy-dispersive X-ray (SEM-EDX), transmissions electron microscopy (TEM), N₂ adsorption-desorption isotherm plot of Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH), vibrating sample magnetometer (VSM). The maximum degradation efficiency is 80.2% by using 0.500 g/L of Ni_0.5Cu_0.5Fe₂O₄ for activating 5.00 mmol/L of PDS to degrade CIP (20.0 mg/L) at 25 ± 2 °C for 50 min (pH = 6.00). The presence of interfering ions Cl^-, NO₃^-, and HCO₃^- inhibited the reaction by producing reactive species with low oxidation potential, inducing the degradation efficiency down to 60.0%, 58.1% and 21.5% respectively. Ni_0.5Cu_0.5Fe₂O₄ displayed great magnetic separation characteristic for the satisfactory magnetization; saturation value is ∼8.6 emu/g. The degradation efficiency of recycled samples has no significant difference after using three times, which is about 60%, indicating that Ni_0.5Cu_0.5Fe₂O₄ is a reusability catalyst in activating PDS for CIP degradation. This work might provide an efficient and promising approach to construct recyclable magnetic materials that can be used for wastewater treatment.

Preparation of magnetic copper ferrite nanoparticle as peroxymonosulfate activating catalyst for effective degradation of levofloxacin

Magnetic CuFe₂O₄ nanoparticles were successfully synthesized with a coprecipitation method at 500 °C calcination temperature, and were utilized to degrade levofloxacin (LEV) as a peroxymonosulfate (PMS) activator. The structure and composition of the nanocatalyst were characterized by a series of methods, including scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometer and thermogravimetric analysis. The effects of the PMS concentration, the catalyst dosage, the LEV initial concentration, the pH value and the inorganic anions on the LEV degradation were also explored. The results revealed that the designed CuFe₂O₄/PMS system had high activity and excellent stability in the complex conditions. The degradation efficiency of LEV still reached above 80% after four recycles of CuFe₂O₄ catalyst. The reactive species quenching experiments and electron paramagnetic resonance analysis suggested the existence of superoxide radicals, single oxygen, hydroxy radicals and sulfate radicals, and the first two were dominant radical oxygen species. Based on the mechanism analyses, the efficient degradation of LEV was probably due to the continuous generation of reactive species under the condition of Fe(III)/Fe(II) and Cu(II)/Cu(I) redox cycles. The research provided a reasonable reference for the PMS activation mechanism-based spinel-type ferrite catalysis.

Magnetic CuNiFe2O4 nanoparticles loaded on multi-walled carbon nanotubes as a novel catalyst for peroxymonosulfate activation and degradation of reactive black 5

Novel copper-nickel ferrite nanocatalyst loaded on multi-walled carbon nanotube (MWCNTs-CuNiFe₂O₄) was synthesized and applied to activate peroxymonosulfate (PMS) in the degradation of the reactive black 5 (RB5). The structure of the catalyst was well characterized by scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). The MWCNTs-CuNiFe₂O₄/PMS system showed a high performance in the degradation of RB5 with a kinetic rate of 1.5-2.5 times higher than homogeneous and heterogeneous systems. Maximum degradation efficiency (99.60%) was obtained at an initial pH of 7, catalyst dosage of 250 mg/L, PMS dosage of 4 mM, the temperature of 25 °C, and reaction time of 15 min. Anion experiments emphasized that the presence of nitrate, carbonate, and phosphate in the solution reduced the degradation efficiency by producing reactive species with low oxidation potential. The RB5 degradation rate evolved with temperature, and the activation energy was obtained to be 44.48 kJ/mol. The mechanism of PMS activation and production of free radicals was proposed based on tert-butyl alcohol (TBA), ethanol (EtOH), and potassium iodide (KI) scavengers. Trapping experiments showed that both sulfate (SO₄^•-) and hydroxyl (^•OH) radicals are involved in the catalytic degradation of RB5. The effective treatment of real wastewater and tap water by the MWCNTs-CuNiFe₂O₄/PMS system requires a long reaction time. Gas chromatography-mass spectrometry (GC-MS) analysis indicated that RB5 can be degraded via methylation, decarboxylation, hydroxylation, and ring/chain cleavage pathways. The stable catalytic activity after three consecutive cycles suggested that MWCNTs-CuFe₂O₄ is a novel reusability catalyst in PMS activation.