GREEN-SYNTHESIZED CARBON DOTS FROM PAWPAW (Carica papaya) PEELS FOR REMOVAL OF TOTAL SUSPENDED SOLIDS AND TOTAL DISSOLVED SOLIDS FROM PRODUCED WATER: RESPONSE SURFACE APPROACH

This study presents the preparation and use of nanostructured carbon dots derived from pawpaw (Carica papaya) peels to remove Total Suspended Solids (TSS) and Total Dissolved Solids (TDS) from petroleum-produced water during oil and gas extraction. Carbon dots were prepared via hydrothermal carbonization at 180°C for 6 hours, and subsequently functionalized with H₂O₂/NaOH to introduce oxygen-containing groups on the surface. Thorough characterization of carbon dots by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD). Process optimization was performed using Response Surface Methodology with Central Composite Design, implemented in Design-Expert Version 13, to evaluate the effects of contact time (30-150 minutes) and adsorbent dosage (0.5-2.5g/100mL) on removal efficiency. Fourier Transform Infrared Spectroscopy (FTIR), UV-Vis Spectroscopy, and Thermogravimetric Analysis (TGA) confirmed the successful synthesis of carbon dots with 67.20 wt% composition of carbon, having a graphitic structure with characteristic peaks at 2θ ≈ 28°, and thermal stability up to 285°C. TSS (100.2mg/l) and TDS (403.8mg/l) were maximally removed using the gravimetric method. Maximum removal efficiencies of 72.5% (TSS) and 67.3% (TDS) were achieved at a contact time of 150 minutes and a dosage of 2.5 g/100mL, with adsorption capacities of 2.88mg/g and 10.94mg/g, respectively. The statistical results showed that a significant linear model (F-values >640, p<0.0001, R²>0.99) identified adsorbent dosage as the primary controlling variable. This study demonstrates that carbon dots produced from pawpaw peels offer an efficient, sustainable, and cost-effective approach to treating produced water while addressing agricultural waste valorization.