Speedy synthesis of magnetite/carbon dots for efficient chromium removal and reduction: a combined experimental and DFT approach

Abstract Magnetic carbon dots (Fe 3 O 4 /N–CQDs) was prepared by and eco-friendly and one-step microwave method using sugarcane bagasse (SB) as a starting material, and applied to remove ad reduce Cr(VI) in wastewater. The magnetization process was performed by a novel microwave method instead of the long time conventional co-precipitation method. The prepared Fe 3 O 4 /N–CQDs showed high saturated magnetization (Ms ~ 38.047 emu/g). When neat N–CQDs and Fe 3 O 4 /N–CQDs were applied to adsorb Cr(VI), the R% was slightly higher in the case of Fe 3 O 4 /N–CQDs (93.86%) compared to N–CQDs (91.73%). Moreover, the reduction rate of Cr(VI) by Fe 3 O 4 /N–CQDs was higher than the N–CQDs. The study confirmed the presence of magnetic iron oxide (Fe-O) in the N–CQDs at 655 cm −1 using FTIR spectroscopy. Interestingly, XRD analysis revealed peaks indicative of elemental iron (Fe(0)) alongside the iron oxide. Furthermore, TGA/DTG analysis showed a significantly higher weight residue (∑RW) for Fe 3 O 4 /N–CQDs compared to N–CQDs alone, suggesting enhanced thermal stability due to the Fe 3 O 4 component. This stability is further supported by higher activation energy (∑A) and pre-exponential factor (∑s) obtained for Fe 3 O 4 /N–CQDs compared to N–CQDs. The prepared Fe 3 O 4 /N–CQDs showed higher fluorescence compared to the N–CQDs, which make them suitable as a chemosensor for the future work. In addition, DFT calculations confirmed the high stability of the Fe 3 O 4 /N–CQDs compared to N–CQDs. Graphical Abstract