Surface-nucleated heterogeneous growth of zeolitic imidazolate framework – A unique precursor towards catalytic ceramic membranes: Synthesis, characterization and organics degradation

Abstract

A novel Co3O4 nanocatalyst functionalized Al2O3 ceramic membrane (CoFCM) with a honeycomb structure was prepared via an optimized surface-nucleated zeolitic imidazolate framework (ZIF-67) growth method. The Co3O4 hollow structure which was confirmed via chemical characterizations (XRD, FTIR, Raman and XPS), was formed on the membrane surface by one-step calcination of ZIF-67 membrane. The CoFCM was characterized by various techniques including the field emission scanning electron microscopy and atomic force microscopy. The results revealed the formation of well-defined Co3O4 layer on the porous Al2O3 ceramic membrane with the thickness of 1.5–2 µm. The growth mechanism of CoFCM was further proposed via XPS and the catalytic activity of CoFCM was investigated for the removal of sulfamethoxazole (SMX) with the addition of Oxone. The membrane performance was examined under a home-made dead-end mode. Results indicated that CoFCM has a rougher surface with an initial membrane resistance of 1.19 × 1011 m−1 and performs outstanding catalytic activity. The pure water permeability of CoFCM is 3024 L m−2 h−1 bar−1, which is comparable to that of the pristine ceramic membrane (<10% difference). The SMX removal efficiency achieved to >90% in 90 min with an Oxone addition of 0.1 g L−1. Meanwhile, the membrane showed excellent durability by retaining >95% of initial flux for at least 3 operational cycles with a low cobalt ion leaching via Oxone-assisted cleaning. Furthermore, the reaction mechanism of Oxone activation by CoFCM was proposed from the results of the electron paramagnetic resonance (EPR) and radical scavenger experiments.