Microalgae-enhanced bioremediation of Cr(VI) ions using spent coffee ground-derived magnetic biochar MoS-Ag composites.

Composites of magnetic biochar derived from spent coffee grounds were prepared using MoS decorated by plasmonic silver nanoparticles (MoS-Ag), which were used for the bioremediation Cr ions. The composites were characterized by electron microscopy, X-ray diffraction, Raman, and UV-VIS spectroscopy. The bioremediation of Cr ions was enhanced almost two times compared to microalgae, Spirulina maxima. Such an increased activity is attributed to heterojunction formation of Biochar@MoS-Ag composite due to the synergetic effects of surface plasmon resonance of AgNPs inducing amplified local electric field, thus simultaneously increasing the absorption of MoS under visible or near-infrared light. The combination of Biochar@MoS-Ag and Spirulina maxima powder was effective for the separation (microalga-based absorption and accumulation of Cr ions) of photo-induced carriers (composite-assisted to breakdown Cr ions). This study offers efficient eco-friendly treatment of Cr ions by reporting the first enhanced bioremediation of Cr(VI) ions by microalgae using MoS-Ag-modified biochar obtained from consumed coffee grounds.