Degradation of Malachite green by Potassium persulphate, its enhancement by 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane nickel(II) perchlorate complex, and removal of antibacterial activity

Degradation of p-Nitrophenol by activated persulfate with carbon-based materials

The removal of p-nitrophenol (PNP) from wastewater was evaluated by the activated persulfate process using different materials - carbon xerogels (XG), carbon nanotubes (CNT), and activated carbon (AC) -, and also using such materials doped with nitrogen (XGM, CNTM and ACM). These carbon materials were impregnated with 2 wt.% of iron and tested in the oxidative process to assess the influence of their textural and surface chemical properties. The carbon-based materials' properties influence the efficiencies of the adsorption and oxidative processes; in adsorption, the materials with higher specific surface areas (S_BET), i.e. AC (824 m²/g) and Fe/AC (807 m²/g), have shown to be the most promising (having achieved a PNP removal of about 20%); on the other hand, in the activated persulfate process the carbon or iron-containing carbon materials with the highest mesoporous areas (S_meso) were the preferential ones - XG and Fe/XG, respectively - reaching removals of 47.3% and 75.7% for PNP and 44.9 and 63.3% for TOC, respectively. Moreover, the presence of nitrogen groups on the samples' surface benefits both processes, being found that PNP degradation and mineralization increase with the nitrogen content. The stability of the best materials (XGM and Fe/XGM) was evaluated during four cycles, being noticed that while XGM lost catalytic activity, the Fe/XGM sample remained stable without leaching of iron. The quantification of intermediate compounds formed during persulfate oxidation was performed, and only oxalic acid was detected, in addition to PNP, being that their contribution to the TOC measured was higher than 99%. Experiments carried out in the presence of radical scavengers proved that only the sulfate radical is present under the acidic conditions used. Complete PNP oxidation and TOC removal of ∼96% were reached for the activated persulfate process, proving to be more attractive than the Fenton one.

Sonochemical degradation of 3-methylpyridine (3MP) intensified using combination with various oxidants

3-Methyl pyridine (3MP) is a toxic and hazardous organic compound having considerable negative impact on environment and living organisms. The objective of this work to report a novel treatment strategy based on sonochemical degradation of 3MP, in combination with oxidants such as hydrogen peroxide, Fenton's reagent, peroxymonosulphate (PMS), and potassium persulphate (KPS) as well as solar irradiations. A bath sonicator operating at 25 kHz frequency and rated power dissipation of 100 W was applied in the work to study different approaches with an objective to enhance the removal of 3MP in lesser time. Effect of operating parameters such as pH (over the range of 2-10), treatment time, temperature (25-55 °C) and ultrasonic power (25 W to 150 W) on the degradation has been studied and the best conditions were used in subsequent combination approaches. It was demonstrated that ultrasound in combination with PMS, ferrous sulphate (FeSO₄) and solar irradiations (approach of US/PMS/FeSO₄/solar irradiation) is the best treatment strategy yielding maximum degradation as 97.4% with highest cavitational yield as 1.920 × 10^-4 mg/J and highest synergetic Index as 2.70. Kinetic analysis revealed that first order mechanism fitted well to all the approaches involving different combinations of ultrasound, oxidising agents and solar irradiation. Degradation products were also analysed that established the degradation mechanism as C₂ and C₃ ring cleavages forming 1, 4-dihydro3-methylpyridine followed by Levulinic acid as non -toxic main by-product. Overall the work clearly demonstrated an effective treatment approach involving combined sonication with oxidants for remediation of 3MP also providing insights on kinetics and mechanism of degradation.

Fe3O4/graphene aerogels: A stable and efficient persulfate activator for the rapid degradation of malachite green

Encapsulation metal oxides into carbon frameworks is a good strategy to synthesis high activity and stable catalyst. Here, Fe₃O₄ nanoparticles (∼20 nm) were firmly encapsulated in the graphene aerogels by a simple and environmentally friendly method (Fe₃O₄/GAs), for activating persulfate (PS) to degrade malachite green (MG) under simulated sunlight. A strong electron conduction was generated between the Fe₃O₄ nanoparticles and graphene sheets to improve the cycle of Fe(II)/Fe(III), and the MG degradation over a wide pH rage (3-9) was enhanced greatly. The MG molecule was decomposed into 12 intermediates and two possible pathways was proposed. More importantly, toxicity test and Toxicity Estimation Software (T.E.S.T.) proved that the toxicity of MG can be effectively controlled by Fe₃O₄/GAs + PS + light system. In addition to the high catalytic activity, Fe₃O₄/GAs exhibited a good stability and reusability due to the strong interaction between Fe₃O₄ and graphene layers. The degradation efficiency remained above 87% after six cycles, and the leaching amount of iron in each cycle was less than 0.125 wt%. SO₄•^- was the dominate radical for MG degradation and the heterogeneous Fenton-like reaction was mainly performed on the surface of catalyst. This work lay a foundation for applying Fe₃O₄/GAs as a highly efficient, stable and reusable heterogeneous Fenton-like catalyst for future applications.

Enhanced degradation of antibiotics by photo-fenton reactive membrane filtration

Micropollution such as pharmaceutical residuals potentially compromises water quality and jeopardizes human health. This study evaluated the photo-Fenton ceramic membrane filtration toward the removal of sulfadiazine (SDZ) as a common antibiotic chemical. The batch experiments verified that the photo-Fenton reactions with as Goethite (α-FeOOH) as the photo-Fenton catalyst achieved the degradation rates of 100% within 60 min with an initial SDZ concentration of 12 mg·L^-1. Meanwhile, a mineralization rate of over 80% was obtained. In continuous filtration, a negligible removal rate (e.g., 4%) of SDZ was obtained when only filtering the feed solution with uncoated or catalyst-coated membranes. However, under Ultraviolet (UV) irradiation, both the removal rates of SDZ were significantly increased to 70% (no H₂O₂) and 99% (with H₂O₂), respectively, confirming the active degradation by the photo-Fenton reactions. The highest apparent quantum yield (AQY) reached up to approximately 25% when the UV₂₅₄ intensity was 100 μW·cm^-2 and H₂O₂ was 10 mmol·L^-1. Moreover, the photo-Fenton reaction was shown to effectively mitigate fouling and prevent flux decline. This study demonstrated synchronization of photo-Fenton reactions and membrane filtration to enhance micropollutant degradation. The findings are also important for rationale design and operation of photo-Fenton or photocatalytic membrane filtration systems.

Combined hydrodynamic cavitation based processes as an efficient treatment option for real industrial effluent

In the present work, hydrodynamic cavitation (HC) operated alone and in combination with chemical oxidants has been applied for the treatment of real industrial effluent obtained from a local industry. Initially, the analysis of literature related to the hybrid methods involving hydrodynamic cavitation has been presented along with recommendations for the selection of important operating conditions for the HC operated individually and in combination with oxidation processes based on hydrogen peroxide (H₂O₂), ozone (O₃) and persulphate (KPS). Subsequently, the treatment of real industrial effluent has also been investigated in details using HC alone and in combined mode with other oxidation processes focusing on the main objective of COD reduction. The reduction in the COD achieved using individual treatment of HC under the optimized conditions of inlet pressure as 4 bar and pH as 4 was only 7.9%. The application of different hybrid approaches based on HC such as HC + H₂O₂, HC + O₃, HC + KPS and HC + H₂O₂ + O₃ established higher COD reduction as compared to only HC. The maximum extent of COD reduction as 60.8% was achieved using HC + H₂O₂ + O₃ combination whereas, relatively lower extent of COD was achieved for operations of HC + H₂O₂, HC + O₃ and HC + KPS with the actual COD reduction being 40.3%, 38.7% and 8.5% respectively. It was also observed that 30.4%, 28.2%, 15.6%, and 4.7% of TOC reduction was obtained for the combined process of HC + H₂O₂ + O₃, HC + H₂O₂, HC + O₃, and HC + KPS respectively. Based on the kinetic study, it was established that the degradation fitted the first order kinetics for all the approaches. The combined processes of HC with oxidants were also compared with ultrasound reactors (both individual and combined operation) in terms of COD reduction, cavitational yield calculations, and treatment cost. HC reactors were established to be more energy efficient and also yielded treatment costs significantly lower than ultrasonic reactors.

Subcritical water oxidation of 6-aminopenicillanic acid and cloxacillin using H2O2, K2S2O8, and O2

This study was undertaken to investigate the degradation of 6-aminopenicillanic acid (6-APA) and cloxacillin in aqueous solution by the combined effect of subcritical water and the oxidising agents O₂, H₂O₂, and K₂S₂O₈. Nano ZnO was used as a solid catalyst. Response surface methodology was used to determine the optimum experimental parameters (temperature, treatment time, and concentration of oxidising agent). For 6-APA, the maximum organic carbon (TOC) removal rates of 83.54%, 81.11% and 42.42% were obtained using H₂O₂, K₂S₂O₈, and O₂, respectively. For cloxacillin, the maximum TOC removal rates of 67.69%, 76.02% and 14.45% were obtained using H₂O₂, K₂S₂O₈, and O₂, respectively. Additionally, the impact of nano and commercial ZnO on TOC removal rates was determined. Secondary ions produced during the degradation process-such as nitrite, nitrate, sulphate and chloride-were determined using ion chromatography.

Encapsulation of a hexaaza macrocyclic nickel(ii) complex in zeolite Y: an experimental and theoretical investigation

In this study, a 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane nickel(ii) complex was encapsulated in the supercages of zeolite Y for the photocatalytic removal of methylene blue under visible light.

Degradation and detoxification of the triphenylmethane dye malachite green catalyzed by crude manganese peroxidase from Irpex lacteus F17

Malachite green (MG), a recalcitrant, carcinogenic, and mutagenic triphenylmethane dye, was decolorized and detoxified using crude manganese peroxidase (MnP) prepared from the white rot fungus Irpex lacteus F17. In this study, the key factors (pH, temperature, MG, Mn(2+), H2O2, MnP) in these processes were investigated. Under optimal conditions, 96 % of 200 mg L(-1) of MG was decolorized when 66.32 U L(-1) of MnP was added for 1 h. The K m, V max, and k cat values were 109.9 μmol L(-1), 152.8 μmol L(-1) min(-1), and 44.5 s(-1), respectively. The decolorization of MG by MnP followed first-order reaction kinetics with a kinetic rate constant of 0.0129 h(-1). UV-vis and UPLC analysis revealed degradation of MG. Furthermore, seven different intermediates formed during the MnP treatment of 0.5 h were identified by LC-TOF-MS. These degradation products were generated via two different routes by either N-demethylation of MG or the oxidative cleavage of the C-C double bond in MG. Based on ecotoxicity analyses performed on bacteria and algae, it was confirmed that MG metabolites produced by the MnP-catalyzed system were appreciably less toxic than the parent compound. These studies indicate the potential use of this enzyme system in the clean-up of aquatic and terrestrial environments.

Combined experimental and theoretical investigations on the encapsulation of nickel(ii)tet-a complex in zeolite Y and its photocatalytic activity

Photocatalytic mechanism of the 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane [tet-a] nickel(ii) encapsulated in zeolite Y.

Nickel azamacrocyclic complex activated persulphate based oxidative degradation of methyl orange: recovery and reuse of complex using adsorbents

The use of adsorbents for the recovery and reuse of metal complex based persulphate activator is demonstrated.

Synthesis and bactericidal evaluation of imide N-halamine-loaded PMMA nanoparticles

Antibacterial imide N-halamine-loaded PMMA nanoparticles were fabricated, and their bactericidal activities were systematically evaluated.

Role of inorganic ions and dissolved natural organic matters on persulfate oxidation of acid orange 7 with zero-valent iron

The impacts of common anions and organic matter, initial pH and PS dosage on the oxidation of acid orange 7 (AO7) by persulfate (PS) activated with zero-valent iron (ZVI) were investigated.