Multi-walled carbon nanotubes immobilized on zero-valent iron plates (Fe0-CNTs) for catalytic ozonation of methylene blue as model compound in a bubbling reactor

Regarding that solution pH is often a limiting factor for ozone technology, composite heterogeneous catalyst was developed accordingly in this work by virtue of carbon nanotube and zero-valent iron. This hybrid material labeled as Fe0-CNTs was deliberately prepared by immobilizing oxidized multi-walled carbon nanotubes (CNTs) onto the surface of zero-valent iron plates through electrophoresis deposition (EPD) and high-temperature calcinations. The catalytic effect of Fe0-CNTs during ozonation was examined by comparative study on degradation of methylene blue (MB) as model compound. Fe0-CNTs material, as expected, exhibited appreciable pH adaptability with high performance either in acidic (pH 3) or basic (pH 9) conditions, while follow dissimilar catalytic pathway as analyzed referring to material characterization by X-ray photoelectron spectroscopy (XPS). The surface localized layer of CNTs was considered for pH 3 to act mainly as active mediator sensitizing zero-valent iron and promote catalytic process, whereas for pH 9 it would play a role as effective ozone catalyst. The superiority for use of CNTs as carbon-material was also reflected by comparison with granular activated carbon (GAC) on decolorization kinetics. Time of EPD was experimentally optimized to be 3 min for a better capability of Fe0-CNTs in catalytic ozonation.