Immobilization of metalloporphyrins into nanotubes of natural halloysite toward selective catalysts for oxidation reactions

Abstract

This paper describes the immobilization of anionic and cationic metalloporphyrins into the nanotubes/nanoscrolls of natural halloysite and investigates the catalytic activity of these novel materials in the oxidation of organic substrates. Two methods for metalloporphyrin immobilization were tested: immobilization under pressure and immobilization under stirring/reflux conditions. The best immobilization rate (100%) was obtained with the anionic iron(III) porphyrin immobilized via the pressurized system. A cationic iron(III) porphyrin was also immobilized into the support with relatively good yields, but no encouraging results were obtained for the immobilization of a neutral iron(III) porphyrin. The obtained materials were characterized by UV–vis and infrared spectroscopies, X-ray diffraction, and transmission electron microscopy. The catalytic activity of a fully immobilized iron(III) porphyrin was evaluated in the oxidation of cyclo-octene, cyclohexane and n-heptane, using iodosylbenzene as the oxygen donor. It has been shown that these novel immobilized catalysts are a promising system for selective oxidation reactions.