Microalgae-enhanced bioremediation of Cr(VI) ions using spent coffee ground-derived magnetic biochar MoS₂-Ag...

Composites of magnetic biochar derived from spent coffee grounds were prepared using MoS₂ decorated by plasmonic silver nanoparticles (MoS₂-Ag), which were used for the bioremediation Cr⁶⁺ ions. The composites were characterized by electron microscopy, X-ray diffraction, Raman, and UV-VIS spectroscopy. The bioremediation of Cr⁶⁺ ions was enhanced almost two times compared to microalgae, Spirulina maxima. Such an increased activity is attributed to heterojunction formation of Biochar@MoS₂-Ag composite due to the synergetic effects of surface plasmon resonance of AgNPs inducing amplified local electric field, thus simultaneously increasing the absorption of MoS₂ under visible or near-infrared light. The combination of Biochar@MoS₂-Ag and Spirulina maxima powder was effective for the separation (microalga-based absorption and accumulation of Cr⁶⁺ ions) of photo-induced carriers (composite-assisted to breakdown Cr⁶⁺ ions). This study offers efficient eco-friendly treatment of Cr⁶⁺ ions by reporting the first enhanced bioremediation of Cr(VI) ions by microalgae using MoS₂-Ag-modified biochar obtained from consumed coffee grounds.