Synthesis of 3D lotus biochar/reduced graphene oxide aerogel as a green adsorbent for Cr(VI)

A novel binary composite aerogel of lotus biochar and reduced graphene oxide (BrGA) was fabricated by hydrothermal reaction. The BrGA was used as a adsorbent for the Cr(VI) removal from aqueous solution. The BrGA has a low density with 7.556 mg/cm(3) and the adsorption capacity of BrGA is up to 232.56 mg/g for Cr(VI), displaying a high efficiency for removal of Cr(VI), which is much higher than pure reduced graphene oxide aerogel (rGO). In order to reveal the adsorption mechanism, the adsorption process of Cr(VI) removal was described well by pseudo-second-order adsorption kinetic, and the Langmuir adsorption isotherm(R-2 = 0.994) matches the experimental data better than the Freundlich adsorption isotherm(R-2 = 0.878). Additionally, the Cr (VI) adsorption mechanisms including direct adsorption process, redox reaction process and re-adsorption process have been offered by discussing X-ray photoelectron spectroscopy(XPS) before and after adsorption. Compared with high adsorption capacity with other adsorbents, the BrGA has been proved to have a promisingly widespread application in practical water purification.