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Manganese-sulfonato porphyrin adsorbed on amino kaolinite as heterogeneous catalyst for oxidation and polymerization reactions
Abstract Due to its medical applications, poly-caprolactone (PCL) is one of the most studied polymers. Herein, adsorption was used as a route to synthesize a new kaolinite/metalloporphyrin-based material for application in caprolactone (ε-CL) polymerization. Kaolinite (Kaol) was modified with tris(hydroxymethyl)aminomethane (TRIS), and the resulting Kaol-TRIS was used as adsorbent for 5,10,15,20-tetrakis(4-sulfonatophenyl)manganese(III) porphyrinate (MnTSPP). Kaol-MnTSPP was also prepared for comparison purposes. Kaolinite grafting with TRIS molecules increased the Kaol basal value from 7.2 to 12.7 Å. MnTSPP immobilization on Kaol-TRIS decreased the intensity and broadened the Kaol-TRIS reflection peaks, evidencing Kaol-TRIS exfoliation. Mathematical equation models of Sips and Langmuir were used to fit the adsorption data, indicating a monolayer adsorption model (maximal adsorption = 8.78 mg·g−1). Kaol-TRIS-MnTSPP stability and efficiency as a catalyst of cis-cyclooctene (C8) and cyclohexane oxidations were tested. Kaol-TRIS-MnTSPP obtained from 600 mg·L−1 MnTSPP aqueous solution provided the highest C8 conversion to cyclooctenoxide (81%). MnTSPP did not leach from Kaol-TRIS-MnTSPP, evidencing that TRIS acted as a binder for MnTSPP and enhanced its attachment to the matrix. In contrast, purified Kaol interacted with MnTSPP weakly: MnTSPP completely leached from Kaol-MnTSPP after the first catalytic cycle. Finally, Kaol-TRIS-MnTSPP was used to initiate ε-CL polymerization. Monitoring of the reaction by infrared absorption spectroscopy showed that the bands around 3438 cm−1, attributed to free hydroxyls in the ε-CL monomer aliphatic structure, became less intense. This indicated that the ε-CL cyclic monomer structure was lost, with subsequent polymerization. This work has proven that the chemical modification of Kaol with subsequent adsorption of a metalloporphyrin is an important route for synthesizing initiator catalysts of polymerization reactions in the synthesis of new materials.
Graphical Abstract Display Omitted
Highlights Manganese (III) sulfonato porphyrin was immobilized on Kaol and Kaol-TRIS solids. Adsorption promotes the dispersion of MnTSPP on Kaol-TRIS hybrid matrix. SAXS data reveal the intercalation of MnTSPP at Kaol-TRIS interlayer space. Selectivity of cyclohexane oxidation is dependent of MnTSPP content on Kaol-TRIS. Ring opening and polymerization of ε-caprolactone were done under mild conditions.
Manganese-sulfonato porphyrin adsorbed on amino kaolinite as heterogeneous catalyst for oxidation and polymerization reactions
Abstract Due to its medical applications, poly-caprolactone (PCL) is one of the most studied polymers. Herein, adsorption was used as a route to synthesize a new kaolinite/metalloporphyrin-based material for application in caprolactone (ε-CL) polymerization. Kaolinite (Kaol) was modified with tris(hydroxymethyl)aminomethane (TRIS), and the resulting Kaol-TRIS was used as adsorbent for 5,10,15,20-tetrakis(4-sulfonatophenyl)manganese(III) porphyrinate (MnTSPP). Kaol-MnTSPP was also prepared for comparison purposes. Kaolinite grafting with TRIS molecules increased the Kaol basal value from 7.2 to 12.7 Å. MnTSPP immobilization on Kaol-TRIS decreased the intensity and broadened the Kaol-TRIS reflection peaks, evidencing Kaol-TRIS exfoliation. Mathematical equation models of Sips and Langmuir were used to fit the adsorption data, indicating a monolayer adsorption model (maximal adsorption = 8.78 mg·g−1). Kaol-TRIS-MnTSPP stability and efficiency as a catalyst of cis-cyclooctene (C8) and cyclohexane oxidations were tested. Kaol-TRIS-MnTSPP obtained from 600 mg·L−1 MnTSPP aqueous solution provided the highest C8 conversion to cyclooctenoxide (81%). MnTSPP did not leach from Kaol-TRIS-MnTSPP, evidencing that TRIS acted as a binder for MnTSPP and enhanced its attachment to the matrix. In contrast, purified Kaol interacted with MnTSPP weakly: MnTSPP completely leached from Kaol-MnTSPP after the first catalytic cycle. Finally, Kaol-TRIS-MnTSPP was used to initiate ε-CL polymerization. Monitoring of the reaction by infrared absorption spectroscopy showed that the bands around 3438 cm−1, attributed to free hydroxyls in the ε-CL monomer aliphatic structure, became less intense. This indicated that the ε-CL cyclic monomer structure was lost, with subsequent polymerization. This work has proven that the chemical modification of Kaol with subsequent adsorption of a metalloporphyrin is an important route for synthesizing initiator catalysts of polymerization reactions in the synthesis of new materials.
Graphical Abstract Display Omitted
Highlights Manganese (III) sulfonato porphyrin was immobilized on Kaol and Kaol-TRIS solids. Adsorption promotes the dispersion of MnTSPP on Kaol-TRIS hybrid matrix. SAXS data reveal the intercalation of MnTSPP at Kaol-TRIS interlayer space. Selectivity of cyclohexane oxidation is dependent of MnTSPP content on Kaol-TRIS. Ring opening and polymerization of ε-caprolactone were done under mild conditions.
Manganese-sulfonato porphyrin adsorbed on amino kaolinite as heterogeneous catalyst for oxidation and polymerization reactions
Ferreira, Breno F. (author) / do Prado, Marcus V. (author) / Marçal, Liziane (author) / Ciuffi, Katia J. (author) / Vicente, Miguel A. (author) / Gil, Antonio (author) / de Faria, Emerson H. (author)
Applied Clay Science ; 235
2023-02-16
Article (Journal)
Electronic Resource
English
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