Production of nanostructured magnetic composites based on Fe0 nuclei coated with carbon nanofibers and nanotubes from red mud waste and ethanol

In this work, a catalytic CVD process using ethanol as carbon source was used to convert an iron rich waste, i.e. red mud (RM), in a magnetic composite. TPCVD (temperature programmed CVD), XRD, Mössbauer, EDS, magnetic measurements, TG/DTA, CHN, BET, Raman, SEM and TEM showed that ethanol gradually reduces the iron phases in the RM to Fe3O4 at 500 °C and to Fe1−xO at 600 °C. At higher temperatures Fe0 and Fe carbide are the main phases produced with the formation of large amounts of carbon (30–50 wt%) especially as nanotubes and nanofibers. These magnetic materials can be separated into two fractions by simple dispersion in water, i.e. a settled material composed of large magnetic particles and the suspended material composed of nanoparticles with average size of 10–100 nm. The carbon in the composites can be activated with CO2 increasing the surface area from 79 to 185 m2 g−1. The magnetic composites were used as adsorbent of model dyes methylene blue and indigo carmine showing excellent results. The composites were also used as support to produce a recyclable Pd catalyst. Tests for the 1,5-cyclooctadiene hydrogenation showed that the catalyst can be easily magnetically separated from the reaction medium and reused for five consecutive times with no deactivation or change in selectivity.

.Figure optionsDownload as PowerPoint slideHighlights
► Conversion of the waste red mud in a magnetic composite by CVD with ethanol.
► Formation of large amounts of carbon (30–50 wt%) especially as nanotubes/nanofibers.
► The product can be separated into two fractions, one with average size of 10–100 nm.
► The carbon in the composites can be activated with CO2 to double its surface area.
► The composite can be used as adsorbent and support to produce recyclable catalysts.