Design, fabrication and the relative catalytic properties of metal–organic framework complexes based on tetra(4-carboxyphenyl)porphyrin and cerium ions

Abstract

Two metal–organic framework compounds composed of cerium ions coordinated with tetra(4-carboxyphenyl) porphyrin H₂TCPP (3) and its cobalt congener CoTCPP (4), namely H₂TCPP/Ce (1) and CoTCPP/Ce (2) were synthesized. Their self-assembly behaviors were systematically investigated using electronic absorption spectra, scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, and energy dispersive X-ray spectroscopy (EDX). The formation of H₂TCPP/Ce (1) nanoparticles with an average diameter of 500 nm depended mainly on the Ce–O coordination bond between the additive cerium ion and the oxygen atom of the carboxy group of the porphyrin 3 molecule. However, additionally formed Co–C coordination bonds between the central cobalt ion of 4 to the carbon atom of the adjacent porphyrinato 4 ring, in combination with Ce–O coordination bond between the additive cerium ion and the oxygen atom of the carboxy group of porphyrinato 4 molecules, induced the formation of CoTCPP/Ce (2) nanoparticles with apparently smaller average diameters (380 nm). After calcining the corresponding H₂TCPP/Ce (1) and CoTCPP/Ce (2) metal–organic frameworks, two types of morphology-preserved CeO₂ were obtained, both of which showed excellent catalytic properties towards the oxidation of CO to CO₂.