Optimization of BTEX removal from produced water using functionalized carbon nanodots synthesized from unripe plantain (Musa paradisiaca) peels

Produced water generated during petroleum exploration and production contains hazardous benzene, toluene, ethylbenzene, and xylene (BTEX), which pose significant environmental and public health risks because of their toxicity and persistence. This study investigated the synthesis, characterization, and application of functionalized carbon nanodots derived from unripe plantain ( Musa paradisiaca) peels for the adsorption of BTEX from produced water. The carbon nanodots were synthesized using a modified thermal carbonization approach and functionalized with 0.5 M sodium hydroxide to enhance surface reactivity. The synthesized adsorbent was characterized using X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), photoluminescence (PL), and Brunauer–Emmett–Teller (BET) surface area analysis. Characterization confirmed the successful synthesis of functionalized carbon nanodots possessing a semi-crystalline graphitic structure, abundant oxygen-containing functional groups, green photoluminescence, an average particle size of 6.5 nm, a high specific surface area of 990.50 m²/g, a pore volume of 0.700 cm³ /g, and an average pore diameter of 2.824 nm. Batch adsorption experiments demonstrated a substantial reduction in BTEX concentration from 173.32 mg/L to 0.015 mg/L after 150 min and to 0.008 mg/L at an adsorbent dosage of 2.5 g, corresponding to removal efficiencies greater than 99.9%. Adsorption equilibrium was best described by the Langmuir isotherm (R² = 0.9664), while kinetic data followed the pseudo-second-order model, indicating that chemisorption predominantly governed the adsorption process. The Weber–Morris intraparticle diffusion model showed that pore diffusion contributed to adsorption but was not the sole rate-controlling mechanism. Response Surface Methodology identified the optimum operating conditions as 150 min contact time, 2.5 g adsorbent dosage, and 50°C, producing an optimum BTEX removal efficiency of 96%. The study demonstrates that functionalized carbon nanodots synthesized from unripe plantain peels are efficient, sustainable, and low-cost adsorbents with significant potential for produced water remediation.