Temperature-Dependent Carbothermally Reduced Iron and Nitrogen Doped Biochar Composites for Removal of Hexavalent Chromium and Nitrobenzene

Synthesizing new composites with better efficiency and stability from abundant sources offers an appealing prospect for heavy metals and organic pollutants removal. In this study, iron (Fe) and nitrogen (N) doped biochar (BC) composites were investigated for heavy metals (hexavalent chromium, Cr(VI)) and organic pollutants (nitrobenzene, NB) removal to address water pollution concerns. Specifically, temperature-dependent Fe-N-BC composites were synthesized with different mass ratios of FeCl 3 as Fe, melamine as N, and pinewood sawdust (PWS) as BC precursors via carbothermal reduction at different temperatures (300 – 900 ℃) . Detailed characterizations of synthesized composites indicated that low-temperature composites possessed superior N and high-temperature composites contained superior Fe species. The Cr(VI) and NB removal were carried out with synthesized composites and experimental results were attested with standard isotherm and kinetic models. The N and Fe were transformed during carbothermal reduction and played role in Cr(VI) and NB removal, respectively. Low-temperature composite (Fe 1 -N 1 -BC 1 -300) presented effective Cr(VI) removal and high-temperature composite (Fe 1 -N 1 -BC 1 -700) removed NB completely from solution. In comparison to Fe-BC, N-BC, Fe-N, Fe-N-BC was efficient for pollutants removal, describing the synergistic effect of Fe, N, and BC for better pollutant interaction and removal. Effect of different factors on Cr(VI) and NB removal was studied to reveal removal mechanism insights of Fe-N-BC. Fe-N-BC composites had restored removal capacity for four months and more. This study offers a benign approach for synthesis and application of Fe-N-BC for pollutants removal and exploring the reaction mechanisms