Efficient Adsorptive Removal of Methylene Blue Dye from Aqueous Solution Using Eragrostis Teff Biomass-Derived Nitrogen and Phosphorus-Codoped Carbon Quantum Dots

Carbon quantum dots have a great application potential in environmental protection via adsorption technology due to their large specific surface area and negative zeta potential. In this work, nitrogen and phosphorus-codoped carbon quantum dots (NP-CQDs) with a large specific surface area and negative zeta potential were successfully synthesized by a single-step hydrothermal synthesis. Batch adsorption studies were utilized to assess the adsorbent's capacity to remove common methylene blue (MB) dye contaminants from an aqueous solution. The experiment showed that MB dye could be removed in 30 min under optimum experimental conditions, with a removal efficiency of 93.73%. The adsorbent's large surface area of 526.063 m2/g and negative zeta potential of −12.3 mV contribute to the high removal efficiency. The Freundlich isotherm model fits the adsorption process well at 298 K, with R2 and n values of 0.99678 and 4.564, respectively, indicating its applicability. A kinetic study demonstrated that the pseudo-second-order model, rather than the pseudo-first-order model, is more suited to represent the process of MB dye adsorption onto NP-CQDs. This research established a simple and cost-effective method for developing a highly efficient NP-CQD adsorbent for organic dye degradation by adsorption.