Interfacial self-assembly of porphyrin-based SURMOF/graphene oxide hybrids with tunable pore size: An approach toward size-selective ambivalent heterogeneous photocatalysts

Abstract

New photocatalysts were synthesized from graphene oxide (GO) and zinc porphyrins via non-covalent self-assembly in Pickering emulsions. The formation of surface-attached metal organic frameworks (SURMOFs) with different size of mesopores (1.1. and 1.6 nm) was confirmed by X-ray powder diffraction and BET nitrogen absorption methods. The activity of the SURMOF/GO materials in photodegradation of rhodamine 6G (Rh6G) and 1,5-dihydroxynaphtalene (DHN) were studied spectroscopically. The photocatalysts initiate aerobic oxidative photodestruction with k up to 2.3 × 10−1 min−1 through generation of singlet oxygen on porphyrin centers. Under anaerobic conditions, these materials assist photoreduction of the same dyes in the SURMOF micropores. The mechanisms of photodegradation assisted by SURMOF/GO hybrids were confirmed by a combination of MALDI-TOF spectroscopy, Sensor Green and terephthalic acid probing. The size of the SURMOF pores controls the reduction, which occur due to the effective charge separation between porphyrin SURMOFs and GO. The photocatalyst with larger pores can transform both Rh6G and DHN, whereas that one with smaller pores is active only with respect to small DHN molecules. The ability of as-formed SURMOF/GOs to exploit two mechanisms yielding different products of photodestruction provides a basis for creating novel ambivalent photocatalysts for selective transformations of targeted compounds in molecular mixtures.