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

Abstract

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.

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“…Behind both mechanisms, enzymes are well involved to degrade recalcitrant compounds in the microbial system. 120 Several reports demonstrate the degradation of complex organic substances by different enzymes including laccase, 121,122 azoreductase, 123,124 lignin peroxidase, 6 NADH-DCIP reductase 99 and hexane oxidase. 25 Among these families of enzymes, laccases and azoreductases have shown a great potential to decolorize a large range of known industrial dyes.…”

“…5 Textile industries consume huge volumes of freshwater for its various wet processes and release equal amounts of wastewaters. 6 During the dyeing process, not all the dyes are fixed to the fabrics. There is always a portion of unfixed dye which is discharged into the wastewater that forms the major pollutant in this effluent.…”

Second-Generation Manganese(III) Porphyrins Bearing 3,5-Dichloropyridyl Units: Innovative Homogeneous and Heterogeneous Catalysts for the Epoxidation of Alkenes

“…Metalloporphyrins are effective and well-known biomimetic catalysts of the cytochrome P450 (CYP450) enzymes in the oxidation of several organic compounds [1][2][3][4][5][6][7][8][9][10][11]. The first porphyrinic model system for alkenes' epoxidation and alkanes' hydroxylation was reported by Groves by using the iron(III) complex of 5,10,15,20-tetraphenylporphyrin (CAT-1) as the catalyst and iodosylbenzene (PhIO) as the oxygen atom donor [12].…”

“…Furthermore, the second-generation metalloporphyrins are, in general, more easily prepared and an increase in selectivity to the desired products can be obtained by varying other parameters, such as solvent, oxidant and axial ligands [18]. In recent years the use of heterogeneous catalysts based on metalloporphyrins has been explored, especially due to the possibility of recovery and reuse [3,10,[21][22][23][24][25][26]. Most of those studies are based on 5,10,15,20-tetraarylporphyrins of the first-and second-generations, having suitable groups to covalently graft them to a support [27].…”

“…Considering that 3,5-dichloro-4-pyridinecarboxaldehyde is commercially available and the pyridine unit is complemented with electron-withdrawing and bulky substituents at adequate positions to protect the porphyrin ligand from oxidative degradation or inactivation, we envisaged that porphyrins built from that aldehyde would afford stable catalysts with excellent features for further immobilization through the pyridine unit(s). Thus, in the present work, two In recent years the use of heterogeneous catalysts based on metalloporphyrins has been explored, especially due to the possibility of recovery and reuse [3,10,[21][22][23][24][25][26]. Most of those studies are based on 5,10,15,20-tetraarylporphyrins of the first-and second-generations, having suitable groups to covalently graft them to a support [27].…”