Ultrasonic spray pyrolysis synthesis of nitrogen-doped porous Fe/C composites from glycerol for hexavalent chromium removal

Nitrogen-doped porous carbon spheres impregnated with iron nanoparticles (Fe/C-N) are prepared from glycerol, a by-product of the biodiesel industry, and ferric ammonium citrate (FAC) via ultrasonic spray pyrolysis (USP). Carbon microspheres are generated during rapid (<10 s) pyrolysis of an aerosolized liquid precursor, resulting from acid induced dehydration, polymerization, and carbonization of glycerol. Fe/C-N composites are predominantly meso and macroporous, caused by iron-mediated carbon gasification during heating and salt templating. Iron impregnation (up to 6.6 wt%) and nitrogen doping (up to 3.3 wt%) are achieved simultaneously because FAC acts as both iron precursor and reducing agent. Reducing gases released from thermally decomposed FAC react with carbon surfaces to deposit nitrogen while facilitating in situ generation of Fe0 and Fe3O4. Cr(VI) removal capacity up to 33 mg/g is reported, attributed to combined adsorption and reduction when applying Fe/C-N composites. The described synthesis, therefore, converts an industrial by-product into value-added materials with potential for use in environmental remediation.