Nitrogen and bismuth-doped rice husk-derived carbon quantum dots for dye degradation and heavy metal removal

Abstract In this study, heteroatoms doped carbon quantum dots were synthesized using rice husk as a biowaste precursor. The effects of nitrogen and bismuth doping are investigated by adjusting the amount of ethylenediamine (EDA) as the nitrogen source, and bismuth nitrate pentahydrate as the bismuth source. HRTEM analysis depicted the formation of spherical carbon quantum dots, with a size of less than 10 nm. FTIR and XPS analysis confirmed the presence of essential functional groups and chemical composition in both of the doped carbon quantum dots. UV–Vis spectra showed peaks which are associated to the electronic transition of the C = C bonding. The addition of EDA and bismuth nitrate pentahydrate tuned the fluorescence intensity and shifted the emission wavelength from the blue region to green one. The performance of the doped rice husk derived carbon quantum dots (RHCQDs) was evaluated via photodegradation of the methylene blue (MB), under a 300 W Xenon lamp. as well as via copper (II) removal. N-RHCQDs (10 vol%) and Bi-RHCQDs (5 wt%) demonstrated the highest MB degradation performance, at 72.16% and 68.91%, respectively. The degradation of MB of the two doped RHCQDs fitted with the pseudo-second kinetic model. The doped RHCQDs were then tested for copper (II) removal, obtaining removal performance of 56.23% and 33.13%, respectively. The results suggest that the Cu (II) adsorption onto the N-RHCQDs and Bi-RHCQDs agrees with the pseudo-second kinetic model and the Langmuir isotherm, with maximum adsorption capacity of 5.73 and 4.08 mg/g, respectively.