Efficiency of magnetite decorated with carbon quantum dot nanocomposites for the adsorptive removal of methylene blue from wastewater: Kinetic and modeling studies

• An eco-friendly adsorbent for MB removal was developed from watermelon peel waste. • Fe 3 O 4 @CQDs nanocomposites demonstrated excellent adsorption capabilities. • The maximum equilibrium adsorption capacity was 83.51 mg/g, achieved within 45 min. • The Fe 3 O 4 @CQDs adsorbent can be reused multiple times for methylene blue removal. • The adsorption mechanism was explored using theoretical calculations, adsorption studies, and experimental analysis. In this study, a green and straightforward hydrothermal approach was employed to synthesize magnetite decorated with carbon quantum dots (Fe 3 O 4 @CQDs) nanocomposites for the effective removal of excess methylene blue (MB) from contaminated water. The textural and chemical proprieties of the Fe 3 O 4 @CQDs nanocomposites were comprehensively characterized using various techniques, including FTIR, XRD, SEM, UV–visible, and nitrogen adsorption–desorption analysis. Batch experiments were conducted to optimize process parameters, such as contact time, initial concentration, adsorbent dosage, initial pH, and temperature. The maximum monolayer adsorption capacity was found to be 83.51 mg/g within 45 min. Isotherm and kinetic studies indicated that the adsorption process followed Langmuir and pseudo-second-order models. Detailed analysis revealed that the adsorption mechanism of MB onto Fe 3 O 4 @CQDs nanocomposites involves hydrogen bonding, electrostatic interactions, and chemical binding between the adsorbent and adsorbate. The reusability of Fe 3 O 4 @CQDs was assessed, showing no significant decline in adsorption capacity over four regeneration cycles. These findings highlight the remarkable potential of Fe 3 O 4 @CQDs nanocomposites as efficient adsorbents for dyes removal and provide valuable insights for developing advanced strategies to eliminate cationic dye pollutants from wastewater.