Cobalt tetracarboxyl phthalocyanine-manganese octahedral molecular sieve (OMS-2) as a heterogeneous catalyst of peroxymonosulfate for degradation of diclofenac

Enhanced removal of bisphenol S in ozone/peroxymonosulfate system: Kinetics, intermediates and reaction mechanism

The degradation process of bisphenol S (BPS) in ozone/peroxymonosulfate (O3/PMS) system was systematically explored. The results showed that the removal efficiency of BPS by O3 could be significantly improved with addition of PMS. Compared with ozonation alone, the pseudo-first-order constant (kobs) was increased by 2-5 times after adding 400 μM PMS. In O3/PMS system, accelerated removal of BPS was observed under neutral and alkaline conditions. The removal efficiency of BPS reached 100% after 40 s of reaction at pH 7.0, with the kobs of 0.098 s-1. Moreover, Cu2+ had a catalytic effect on the O3/PMS system, because it could catalyze the decomposition of ozone and PMS to produce •OH and SO4•-, respectively. Electron paramagnetic resonance illustrated that •OH and SO4•- were the reactive species in O3/PMS system. Twelve intermediates were identified by mass spectrometry, and the degradation reactions in O3/PMS system mainly included hydroxylation, sulfate addition, polymerization and β-scission. Finally, the toxicity of the products was evaluated by the EOCSAR program. Our results introduce an efficient method for BPS removal and would provide some guidance for the development of O3-based advanced oxidation technology.

Peroxymonosulfate Activation by Cu-OMS-2 Nanofibers for Efficient Degradation of N-Containing Heterocycles in Aquatic Solution

In this research, the degradation of different types of N-containing heterocycle (NHC) contaminants by Cu-OMS-2 via peroxymonosulfate (PMS) activation in an aqueous environment was investigated. First, the effects of different reaction parameters were optimized using benzotriazole (BTR) as the model contaminant, and the optimal reaction conditions were 8 mM PMS, 0.35 g/L Cu-OMS-2, and 30 °C. Nine different types of NHC contaminants were effectively degraded under these reaction conditions, and the degradation efficiencies and the mineralization rates of those NHCs were more than 68 and 46%, respectively. Moreover, the Cu-OMS-2/PMS process presented excellent performance at a wide pH ranging from 3.0 to 11.0 and in the presence of some representative anions (NO3- and SO42-) and dissolved organic matter (fumaric acid). The inhibition sequence of anions on BTR removal during the Cu-OMS-2/PMS process was H2PO4- > HCO3- > Cl- > CO32- > NO3- > SO42-. It was also found that 74.5 and 71.3% BTR degradation rates were achieved in actual water bodies, such as tap water and Yellow River water, respectively. Besides, the Cu-OMS-2 heterogeneous catalyst had excellent stability and reusability, and the degradation rate of BTR was still at 77.0% after 5 cycles. Finally, electron paramagnetic resonance analysis and scavenging tests showed that 1O2 and SO4- • were the primary reactive oxygen species. Accordingly, Cu-OMS-2 nanomaterial was an efficient and sustainable heterogeneous catalyst to activate PMS for the decontamination of BTR in water remediation.

Comparison of the degradation mechanisms of diclofenac in the presence of iron octacarboxyphthalocyanine and myeloperoxidase

The degradation process of diclofenac (DCF) by hematoprotein myeloperoxidase (MPO) and iron octacarboxyphthalocyanine (FePcOC) in the presence of hydrogen peroxide was compared. During the oxidation of diclofenac, in the presence of iron octacarboxyphthalocyanine (FePcOC) and hydroxyl radicals (HO^•) (from H₂O₂), an intermediate product (dimer with an m/z value of 587) with the characteristic yellow colouration and an intense band at λ_max = 451 nm is formed. Iron octacarboxyphthalocyanine oxidises in the presence of hydrogen peroxide, following the first-order reaction kinetics for FePcOC and H₂O₂. The concentration of diclofenac does not affect the initial reaction rate. For comparison, the oxidation of DCF in the presence of myeloperoxidase and hydrogen peroxide also provided yellow-coloured solutions with an absorption maximum at λ_max = 451 nm. However, LC-MS/MS analysis indicates the presence of at least seven main products of the diclofenac oxidation process in the final reaction mixture, including two dimers with the ion mass [M-H]^¯ = 587.01. The mechanism of the diclofenac degradation with hematoprotein myeloperoxidase is more complex than with iron octacarboxyphthalocyanine. Furthermore, the biological activity of diclofenac and DCF dimer (iron octacarboxyphthalocyanine and hydroxyl radicals degradation product) was tested. In this case, the long-term assayed in vitro against E. coli, colorectal HCT116 and melanoma Me45 cancer cells were performed.

Ascorbic acid enhanced MnFe2O4/peroxymonosulfate oxidation of organic pollutant: Key role of singlet oxygen generation and Fe/Mn cycling

The activated peroxymonosulfate (PMS) process has been widely applied for degrading organic pollutants. However, its application is limited by low metal cycling, and the contribution of oxygen species remains unclear. Here, the crystal structure, surface morphology, and elemental valence of the synthesized manganese ferrite (MnFe₂O₄) catalyst were investigated by SEM, HRTEM, XRD, and XPS. A novel MnFe₂O₄/PMS/ascorbic acid (AA) system was constructed to enhance the Fe/Mn cycling on the surfaces of the MnFe₂O₄ catalyst. The addition of AA can significantly increase the decomposition of organic pollutants, and the apparent rate constant of the MnFe₂O₄/PMS/AA system is 8.2 times higher than that of MnFe₂O₄/PMS. AA facilitates the reduction of Fe/Mn(III) and the dissolution of Fe/Mn(II), creating a Fe/Mn cycle between the heterogeneous and homogeneous interfaces of the catalyst. Furthermore, AA greatly increases the activity of adsorbed oxygen on the catalyst surfaces, generating a large amount of singlet oxygen (¹O₂), which contributes significantly to the destruction of organic pollutants. The efficient, fast, and environmentally friendly PMS activation method in this study can provide reliable technical support for treating refractory organic pollutants in water.

Brønsted-acid sites promoted degradation of phthalate esters over MnO2: Mineralization enhancement and aquatic toxicity assessment

Advanced oxidation processes (AOPs) are important technologies for aqueous organics removal. Despite organic pollutants can be degraded via AOPs generally, high mineralization of them is hard to achieve. Herein, we synthesized a manganese oxide nanomaterial (H2-OMS-2) with abundant Brønsted-acid sites via ion-exchange of cryptomelane-type MnO₂ (OMS-2), and tested its catalytic performance for the degradation of phthalate esters via peroxymonosulfate (PMS) activation. About 99% of dimethyl phthalate (DMP) at a concentration of 20 mg/L could be degraded within 90 min and 82% of it could be mineralized within 180 min over 0.6 g/L of catalyst and 1.8 g/L of PMS. The catalyst could activate PMS to generate SO₄^-˙ and ·OH as the dominant reactive oxygen species to reach complete degradation of DMP. Especially, the higher TOC removal rate was obtained due to the rich Brønsted-acid sites and surface oxygen vacancies on the catalyst. Kinetics and mechanism study showed that Mn^II/Mn^III might work as the active sites during the catalytic process with a lower reaction energy barrier of 55.61 kJ/mol. Furthermore, the catalyst could be reused for many times through the regeneration of the catalytic ability. The degradation and TOC removal efficiencies were still above 98% and 65% after seven consecutive cycles, respectively. Finally, H2-OMS-2-catalyzed AOPs significantly reduced the organismal developmental toxicity of the DMP wastewater through the investigation of zebrafish model system. The present work, for the first time, provides an idea for promoting the oxidative degradation and mineralization efficiencies of aqueous organic pollutants by surface acid-modification on the catalysts.

Oxidative Degradation of Pharmaceuticals: The Role of Tetrapyrrole-Based Catalysts

Nowadays, society’s widespread consumption of pharmaceutical drugs and the consequent accumulation of such compounds or their metabolites in effluents requires the development of efficient strategies and systems that lead to their effective degradation. This can be done through oxidative processes, in which tetrapyrrolic macrocycles (porphyrins, phthalocyanines) deserve special attention since they are among the most promising degradation catalysts. This paper presents a review of the literature over the past ten years on the major advances made in the development of oxidation processes of pharmaceuticals in aqueous solutions using tetrapyrrole-based catalysts. The review presents a brief discussion of the mechanisms involved in these oxidative processes and is organized by the degradation of families of pharmaceutical compounds, namely antibiotics, analgesics and neurological drugs, among others. For each family, a critical analysis and discussion of the fundamental roles of tetrapyrrolic macrocycles are presented, regarding both photochemical degradative processes and direct oxidative chemical degradation.

Efficient activation of peroxymonosulfate by Co-doped mesoporous CeO2 nanorods as a heterogeneous catalyst for phenol oxidation

Sulfate radical-based advanced oxidation processes have received considerable attentions in the remediation of organic pollutants due to their high oxidation ability. In this study, a novel Co3O4/CeO2 catalyst was fabricated and employed as a peroxymonosulfate (PMS) activator to generate SO4•- for phenol degradation. The Co3O4/CeO2 catalyst exhibited a good catalytic performance at a wide pH range of 3.4 to 10.8, and 100% phenol (20 mg/L) was removed within 50-min reaction under optimal conditions with 0.2 g/L catalyst and 2.0 g/L PMS at room temperature. The transformation products and total organic carbon during the degradation process were also determined. The quenching experiments and electron paramagnetic resonance spectra revealed that sulfate radical (SO4•-) rather than other species such as singlet oxygen (1O2) and hydroxyl radical (•OH) was primarily responsible for phenol degradation in the Co3O4/CeO2/PMS system, and a rational mechanism was proposed. Moreover, the recycling experiments as well as low cobalt leaching concentration manifested satisfactory reusability and stability. The effects of various inorganic anions and natural organic matter in real water matrix on phenol oxidation were further evaluated. We believe that the Co3O4/CeO2 composites have promising applications of PMS activation for the degradation of organic pollutants in wastewater treatment.

Transition element doped octahedral manganese molecular sieves (Me-OMS-2) as diclofenac adsorbents

Diclofenac (DCF) control measures have become an area of increased interest for environmental researchers due to the high environmental concentration and risk of DCF. Adsorption seems to be promising for DCF removal from the aqueous phase because of its specific superiority in comparison with biodegradation, membrane separation, and advanced oxidation or reduction. In this study, OMS-2 and metal-doped OMS-2 ((Me-OMS-2, with Me = Co, Cu or Ce) were prepared and tested as adsorbents for the removal of DCF. It was evident that the maximum adsorption capacity and rate of Ce-OMS-2 were much higher than those of the other adsorbents, which could be attributed to its large specific surface area and stereoscopic aperture structure. The experimental data are fitted the pseudo-second-order model, the Elovich equation and the Langmuir model well; moreover, the process is an endothermic and spontaneous thermodynamic process, during which the entropy increased, based on the experimental results, indicating that chemisorption was dominant during the DCF adsorption process onto Ce-OMS-2. By the integral of the peak deconvoluted from the XPS spectrum, the ratio of Mn³⁺/Mn⁴⁺ increased from 0.393 to 0.407, revealing that Mn(IV) is rarely reduced into Mn(III) during the DCF adsorption process.

Ultrasound-assisted heterogeneous peroxymonosulfate activation with Co/SBA-15 for the efficient degradation of organic contaminant in water

A potential advanced oxidation process is provided by SBA-15 supported cobalt (Co/SBA-15) activated peroxymonosulfate (PMS, HSO₅^-) in the ultrasound (US) enhanced system, named Co/SBA-15/PMS/US process, for the elimination of refractory organic contaminants (ROCs) in water. This process exhibited favorable behavior with 95.5 % C.I. Acid Orange 7 (AO7) degradation using 5 mM PMS, 0.5 g/L Co/SBA-15 catalyst, 190 W US power at initial pH of 6.0 after 90 min reaction. Co/SBA-15 particles remained satisfied catalytic activity and stability with very low level of cobalt release in 10 successive cycles. The scavenge tests and electron paramagnetic resonance (EPR) result as well as the cobalt leaching concentration revealed that the reactive radicals (SO₄^- and OH) on catalyst surface were primarily responsible for AO7 oxidation, and a rational mechanism was elucidated accordingly. The presence of chloride ions and bicarbonate could improve AO7 removal. The probable pathway of AO7 degradation was proposed based on the intermediates identified. This Co/SBA-15/PMS/US process could be well applied for the destruction of other typical ROCs (bisphenol A, clofibric acid, and rhodamine B) and the treatment of lake and river water spiked with AO7, and this study may provide an efficient PMS technique for the remediation of ROCs in water.

In situ coupling of TiO2(B) and ZIF-8 with enhanced photocatalytic activity via effective defect

A composite photocatalyst was obtained by coupling ZIF-8 and TiO₂(B) via a simple method, which showed the enhanced photocatalytic due to the oxygen vacancies/Ti³⁺.

Binuclear cobalt phthalocyanine supported on manganese octahedral molecular sieve: High-efficiency catalyzer of peroxymonosulfate decomposition for degrading propranolol

Propranolol (PRO) is widely detected in the aquatic environment and proved to be detrimental to multifarious aquatic organisms. In view of some virtues of sulfate radicals than hydroxyl radicals, advanced oxidation technologies that involve the activation of peroxymonosulfate (PMS) have stimulated wide-ranging research on the PRO removal. In this paper, a composite (C₂NOMS-2) of amino-functionalized manganese octahedral molecular sieve (NOMS-2) and binuclear cobalt phthalocyanine (Co₂CPc) was synthesized easily, and utilized as a catalyzer for PMS to degrade PRO in water. The apparent rate constants of PRO degradation by PMS with C₂NOMS-2 as a catalyst was found to be higher than with NOMS-2, Co₂CPc and the composite of uninuclear cobalt phthalocyanine (CoCPc) and NOMS-2. The catalytic ability of C₂NOMS-2 was investigated under various reaction conditions: catalyst dosages (0.5-2.0 g/L), PMS doses (50-500 mg/L), initial pH (5-11), reaction temperature (20-35 °C), and natural water constituents (Cl^-, HCO₃^-, and sodium huminate). Radical scavenging tests and electron paramagnetic resonance spectroscopy showed that ¹O₂ was the most critical reactive oxygen species, and conceivable mechanisms of PMS activation with C₂NOMS-2 were proposed established on the curve estimation of high-resolution XPS spectra, revealing that the generation of reactive oxygen species was mainly resulted from the cycles of Mn³⁺/Mn⁴⁺, Co³⁺/Co²⁺ and surface lattice oxygen/surface adsorbed oxygen. The intermediate products of propranolol degradation were identified by LC-MS/MS. Cycling experiments and ion dissolution detection suggested that C₂NOMS-2 could maintain satisfactory stability in an aqueous system.