Heterogeneous oxidation of the dye Brilliant Green with H 2 O 2 catalyzed by supported manganese porphyrins

Cu2(OH)3NO3/γ-Al2O3 catalyzes Fenton-like oxidation for the advanced treatment of effluent organic matter (EfOM) in fermentation pharmaceutical wastewater: The synergy of Cu2(OH)3NO3 and γ-Al2O3

The secondary effluent of fermentation pharmaceutical wastewater exhibits high chromaticity, elevated salinity, and abundant refractory effluent organic matter (EfOM), presenting significant treatment challenges and environmental threats. Herein, Cu2(OH)3NO3/γ-Al2O3 was fabricated through ultrasound-assisted impregnation and calcination to catalyze the Fenton-like oxidation for degrading organic pollutants in this secondary effluent. Under neutral conditions, with 400.00 mg/L H2O2, 8 g/L catalyst, and at 30 ℃, the EfOM and CODCr removal efficiencies can reach 96.90 % and 51.56 %, respectively. The Cu2(OH)3NO3/γ-Al2O3 catalyst possesses ideal reusability, maintaining CODCr, chromaticity, and EfOM removal efficiencies at 44.44 %-64.59 %, 85.45 %-93.45 %, and 61.00 %-95.00 % over 220 h in a continuous-flow catalytic oxidation system operated at room temperatures (15-25 ℃). Electron paramagnetic resonance results and density functional theory calculations indicate that •OOH may be the predominant reactive oxygen species, facilitated by the easier elongation of the OH bond in H2O2 compared to the OO bond. The adjusted electronic structure endows Cu2(OH)3NO3/γ-Al2O3 composite sites with superior catalytic selectivity for H2O2 activation compared to Cu2(OH)3NO3 single crystal sites, with γ-Al2O3 additionally facilitating H2O2 activation through electron donation. This research highlights the efficacy of Cu2(OH)3NO3/γ-Al2O3 in the advanced treatment of complex industrial wastewater, elucidating its catalytic mechanisms and potential applications.

Synthesis and characterization of Co(II) porphyrin complex supported on chitosan/graphene oxide nanocomposite for efficient green oxidation and removal of Acid Orange 7 dye

Catalytic degradation of Acid Orange 7 (AO7) by hydrogen peroxide in an aqueous solution has been investigated using cobalt(II) complex of 5, 10, 15, 20 Tetrakis [4-(hydroxy)phenyl] porphyrin [Co(II) TPHPP] covalently supported chitosan/Graphene Oxide nanocomposite [Co(II) TPHPP]-Cs/GO, as highly efficient and recoverable heterogeneous catalyst. The structures and properties of [Co(II) TPHPP]-Cs/GO nanocomposite were characterized by techniques such as UV-Vis, FT-IR, SEM, EDX, TEM, and XRD. The oxidation reaction was followed by recording the UV-Vis spectra of the reaction mixture with time at λmax = 485 nm. [Co(II) TPHPP]-Cs/GO nanocomposite demonstrated high catalytic activity and could decompose 94% of AO7 within 60 min. The factors that may influence the oxidation of Acid Orange 7, such as the effect of reaction temperature, pH, concentration of catalyst, Acid Orange 7, and hydrogen peroxide, have been studied. The results of total organic carbon analysis (TOC) showed 50% of dye mineralization under mild reaction conditions of AO7 (1.42 × 10-4M) with H2O2 (8 × 10-2M) in the presence of [Co(II) TPHPP]-Cs/GO nanocomposite (15 × 10-3 g/ml) and pH = 9 at 40 °C. The reuse and stability of the nanocomposite were examined and remarkably, even after six cycles of reuse, there was no significant degradation or deactivation of the recycled catalyst. Residual organic compounds in the reaction mixture were identified by using GC-MS analyses. The radical scavenging measurements and photoluminescence probing technology of disodium salt of terephthalic acid indicated the formation of the hydroxyl radical as the reactive oxygen species in the [Co(II) TPHPP]-Cs/GO nanocomposite/H2O2 system. A mechanism for the oxidation reaction has been discussed.

Degradation of Dyes Catalyzed by Aminophenyl-Substituted Mn-Porphyrin Immobilized on Chloropropyl Silica Gel and Evaluation of Phytotoxicity

A heterogenized Mn(III) porphyrin-based catalyst was prepared for dye degradation. The new Mn(III) complex of 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin was immobilized, via covalent bond, in chloropropyl silica gel, generating the material (Sil-Cl@MnP) with a loading of 23 μmol manganese porphyrin (MnP) per gram of Sil-Cl. This material was used as a catalyst in degradation reactions of model dyes, a cationic dye [methylene blue (MB)] and an anionic dye (reactive red 120, RR120), using PhI(OAc)2 and H2O2 as oxidants. The oxidation reactions were carried out after the dye reached adsorption/desorption equilibrium with the catalytic material, with a much higher percentage of adsorption being observed for the cationic MB dye (20%) than for the anionic RR120 dye (3%), which may be associated with electrostatic attraction or repulsion effects, respectively, with the negatively charged surface of the silica (zeta potential measurement for Sil-Cl@MnP, ζ = -19.2 mV). In general, there was a higher degradation percentage for MB than for RR120, probably because the size and charge of RR120 would hinder its approach to the MnP active species on the silica surface. With respect to the oxidant, the PhI(OAc)2-based systems showed a higher degradation percentage than those of H2O2. It was observed that the increase in the oxidant concentration promoted a significant increase in the degradation of MB, with a degradation of approximately 65%. The efficiency of the catalyst was also evaluated after successive additions of the oxidant every 2 h, and it can be seen that the catalyst had no loss of efficiency, with a degradation percentage greater than 80% being observed after 8 h of reaction. The phytotoxicity of the products formed in the system was evaluated in a 1:23.5:188 molar ratio Sil-Cl@MnP: MB:PhI(OAc)2 was used. In these studies, phytotoxicity was found for the germination of lettuce seeds when the original solution was used without dilution; however, when diluted (10% V/V), the results were close to the positive and negative controls. Thus, the material obtained proved to be a potential candidate for application in the degradation reactions of environmental pollutants.

Robust Mn(III) N-pyridylporphyrin-based biomimetic catalysts for hydrocarbon oxidations: heterogenization on non-functionalized silica gel versus chloropropyl-functionalized silica gel

Two classes of heterogenized biomimetic catalysts were prepared and characterized for hydrocarbon oxidations: (1) by covalent anchorage of the three Mn(iii) meso-tetrakis(2-, 3-, or 4-pyridyl)porphyrin isomers by in situ alkylation with chloropropyl-functionalized silica gel (Sil-Cl) to yield Sil-Cl/MnPY (Y = 1, 2, 3) materials, and (2) by electrostatic immobilization of the three Mn(iii) meso-tetrakis(N-methylpyridinium-2, 3, or 4-yl)porphyrin isomers (MnPY, Y = 4, 5, 6) on non-modified silica gel (SiO2) to yield SiO2/MnPY (Y = 4, 5, 6) materials. Silica gel used was of column chromatography grade and Mn porphyrin loadings were deliberately kept at a low level (0.3% w/w). These resulting materials were explored as catalysts for iodosylbenzene (PhIO) oxidation of cyclohexane, n-heptane, and adamantane to yield the corresponding alcohols and ketones; the oxidation of cyclohexanol to cyclohexanone was also investigated. The heterogenized catalysts exhibited higher efficiency and selectivity than the corresponding Mn porphyrins under homogeneous conditions. Recycling studies were consistent with low leaching/destruction of the supported Mn porphyrins. The Sil-Cl/MnPY catalysts were more efficient and more selective than SiO2/MnPY ones; alcohol selectivity may be associated with hydrophobic silica surface modification reminiscent of biological cytochrome P450 oxidations. The use of widespread, column chromatography, amorphous silica yielded Sil-Cl/MnPY or SiO2/MnPY catalysts considerably more efficient than the corresponding, previously reported materials with mesoporous Santa Barbara Amorphous No 15 (SBA-15) silica. Among the materials studied, in situ derivatization of Mn(iii) 2-N-pyridylporphyrin by covalent immobilization on Sil-Cl to yield Sil-Cl/MnP1 showed the best catalytic performance with high stability against oxidative destruction and reusability/recyclability.

Synthetic Mn(III) porphyrins as biomimetic catalysts of CYP450: Degradation of antibiotic norfloxacin in aqueous medium

Norfloxacin (NOR) is a synthetic broad-spectrum fluoroquinolone antibiotic classified as an emerging contaminant. Here, we investigate Mn(III) porphyrin-catalyzed NOR degradation using peroxides or peracids (H₂O₂, t-BuOOH, or Oxone®) as oxidants. We evaluate three Mn(III) porphyrins: the 1^st-generation tetraphenylporphyrin and 2^nd -generation porphyrins bearing halogen atoms at the ortho-positions of the porphyrin macrocycle meso-aryl groups. Experiments were carried out in aqueous medium under mild conditions. NOR degradation was 67%. Products were proposed by mass spectrometry (MS) analysis. Oxone® was the best oxidant for NOR degradation despite its possible decomposition in the reaction medium. The second-generation Mn(III) porphyrins were more resistant than the first-generation Mn(III) porphyrin, indicating that the bulky groups introduced into the porphyrin macrocycle meso-aryl groups led to more robust catalysts. The degradation products did not present cytotoxic behavior under the employed conditions. In conclusion, Mn(III) porphyrin-catalyzed NOR degradation is a promising strategy to degrade fluoroquinolones and other pollutants.

Investigations on Cationic Dye Degradation Using Iron-Doped Carbon Xerogel

Iron-doped carbon xerogels were prepared using sol-gel synthesis, with potassium-2,4-dihydroxybenzoate and formaldehyde as starting materials, followed by an ion exchange step. The obtained samples were characterized (XRD, FTIR, SED-EDX, TEM) and investigated as catalysts in heterogeneous Fenton and catalytic wet air oxidation (CWAO) processes. Experiments were conducted in the same conditions (0.1 g catalysts, 25 mL of 100 mg/L dye solution, 25 °C, initial solution pH, 3 h) in thermostated batch reaction tubes (shaking water bath, 50 rpm) at atmospheric pressure. A series of three cationic dyes were considered: Brilliant green (BG), crystal violet (CV), and methyl green (MG). Dyes and TOC removal efficiencies up to 99% and 92%, respectively, were obtained, in strong correlation with the iron content of the catalyst. Iron content measured in solution at the end of the reaction, indicated that its amount was less than 2 ppm for all tested catalysts.

Comparison between catalytic activities of two zinc layered hydroxide salts in brilliant green organic dye bleaching

This paper reports the use of two layered hydroxide salts (LHS) (zinc hydroxide nitrate - ZHN - Zn₅(OH)₈(NO₃)₂·2H₂O, and zinc hydroxide chloride - ZHC - Zn₅(OH)₈Cl₂·H₂O) as catalysts for brilliant green (BG) organic dye bleaching, using hydrogen peroxide as oxidant. The LHS were prepared by precipitation reaction between an aqueous solution of zinc salts and an aqueous ammonia solution. The solids were characterized by powder X-ray diffraction (XRD), electron paramagnetic resonance (EPR), ultraviolet-visible electronic spectroscopy (UV-Vis) and Fourier-transform infrared spectroscopy (FTIR). The catalytic activity of the solids was investigated at temperatures of 25, 35 and 45 °C, using different molar ratios of oxidant:dye:Zn²⁺ ions (present in the catalyst), in the absence and presence of ambient light. The kinetic aspect of the reaction was investigated considering that the reaction showed pseudo-first order behavior in relation to BG dye concentration. We propose a mechanism where superoxide radicals account for most of the bleaching taking place. The catalytic results obtained, along with the low cost and low toxicity of zinc compounds, establish ZHN and ZHC as novel catalysts for dye wastewater treatment, an area with constant demand for new methods and materials given its relationship with environmental equilibrium and human health.

Double role of metalloporphyrins in catalytic bioinspired supramolecular metal-organic frameworks (SMOFs)

Heterogeneous catalysts are of great interest in many industrial processes for environmental reasons and, during recent years, a great effort has been devoted to obtain metal-organic frameworks (MOFs) with improved catalytic behaviour. Few supramolecular metal-organic frameworks (SMOFs) are stable under ambient conditions and those with anchored catalysts exhibit favourable properties. However, this paper presents an innovative approach that consists of using metal nodes as both structural synthons and catalysts. Regarding the latter, metalloporphyrins are suitable candidates to play both roles simultaneously. In fact, there are a number of papers that report coordination compounds based on metalloporphyrins exhibiting these features. Thus, the aim of this bioinspired work was to obtain stable SMOFs (at room temperature) based on metallo-porphyrins and explore their catalytic activity. This work reports the environmentally friendly microwave-assisted synthesis and characterization of the compound [H(bipy)]2[(MnTPPS)(H2O)2]·2bipy·14H2O (TPPS = meso-tetra-phenyl-porphine-4,4',4'',4'''-tetra-sulfonic acid and bipy = 4,4'-bi-pyridine). This compound is the first example of an MnTPPS-based SMOF, as far as we are aware, and has been structurally and thermally characterized through single-crystal X-ray diffraction, IR spectroscopy, thermogravimetry and transmission electron microscopy. Additionally, this work explores not only the catalytic activity of this compound but also of the compounds μ-O-[FeTCPP]2·16DMF and [CoTPPS0.5(bipy)(H2O)2]·6H2O. The structural features of these supra-molecular materials, with accessible networks and high thermal stability, are responsible for their excellent behaviour as heterogeneous catalysts for different oxidation, condensation (aldol and Knoevenagel) and one-pot cascade reactions.

Immobilized Lignin Peroxidase-Like Metalloporphyrins as Reusable Catalysts in Oxidative Bleaching of Industrial Dyes

Synthetic and bioinspired metalloporphyrins are a class of redox-active catalysts able to emulate several enzymes such as cytochromes P450, ligninolytic peroxidases, and peroxygenases. Their ability to perform oxidation and degradation of recalcitrant compounds, including aliphatic hydrocarbons, phenolic and non-phenolic aromatic compounds, sulfides, and nitroso-compounds, has been deeply investigated. Such a broad substrate specificity has suggested their use also in the bleaching of textile plant wastewaters. In fact, industrial dyes belong to very different chemical classes, being their effective and inexpensive oxidation an important challenge from both economic and environmental perspective. Accordingly, we review here the most widespread synthetic metalloporphyrins, and the most promising formulations for large-scale applications. In particular, we focus on the most convenient approaches for immobilization to conceive economical affordable processes. Then, the molecular routes of catalysis and the reported substrate specificity on the treatment of the most diffused textile dyes are encompassed, including the use of redox mediators and the comparison with the most common biological and enzymatic alternative, in order to depict an updated picture of a very promising field for large-scale applications.