Catalyst-free CNTs growth on red mud-based alkali activated adsorbents: Innovative route to boost heavy metals adsorption from wastewaters

Abstract

The synthesis and growth of carbon nanotubes (CNTs) on red mud containing alkali activated materials (AAMs) envisioned for wastewater treatment applications is reported for the first time. This novel avenue takes advantage of the iron present in the red mud (RM), a massively produced industrial waste, promoting the growth of CNTs and avoiding the need for commercial catalysts. X-ray diffraction shows that upon heat treatment hematite is transformed into magnetite and metallic iron after 1 min, while longer exposure times increase the crystallinity of the specimens and lead to the transformation of magnetite into metallic iron. XRD also shows the presence of iron carbide phases and graphite, suggesting the formation of carbon-based structures. The modified AAMs showed a remarkable lead removal capacity reaching 117.8 mg/g, this being 7 times higher than the value seen with the non-modified specimen.