Abstract
The primary goal of this study is to examine PO(4) (3-) adsorption from aqueous solutions using zinc-doped carbon dots (Zn-N-CDs) as a new adsorbent and cost-effective technique. Zn-N-CDs were produced through a hydrothermal process and subsequently identified using various techniques. The effect of reaction time, temperature, pH, ionic strength, adsorbent dosage, initial PO(4) (3-) concentration, and anion competition (NO(3) (-), Cl(-), HCO(3) (-), and SO(4) (2-)) on PO(4) (3-) adsorption using Zn-N-CDs were investigated. The characterization results depicted that Zn-N-CDs have a spherical structure without obvious aggregation and revealed the amorphous nature of carbon dots with many pores. Zn-N-CDs had a high affinity for adsorbing PO(4) (3-), reaching equilibrium within 5 minutes. While PO(4) (3-) adsorption reduced with an increase in temperature, it increased with pH and ionic strength. The optimal conditions for PO(4) (3-) adsorption were determined to be pH 8, 100 mM KCl as an ionic strength, and 5 g L(-1) of Zn-N-CDs. The presence of SO(4) (2-) and HCO(3) (-) as competing anions slightly decreased PO(4) (3-) adsorption. Thermodynamic studies revealed that PO(4) (3-) adsorption onto Zn-N-CDs was endothermic, spontaneous, and disordered, as evidenced by ΔG° < 0, ΔH° > 0, and ΔS° > 0. The experimental data fit well with a pseudo-second-order kinetic model (R (2) = 0.999) and the Freundlich isotherm model (R (2) = 0.9754), signifying that PO(4) (3-) adsorption onto Zn-N-CDs occurs through multi-layer and chemi-sorption mechanisms. Overall, Zn-N-CDs indicated a great capability to adsorb high concentrations of PO(4) (3-) across a wide range of pH values, indicating their potential for environmental remediation.