The utilization of activated carbon derived from polyethylene terephthalate bottle waste, as a sustainable source for removal and recovery of methylene blue and picric acid from aqueous solutions

In this study, waste polyethylene terephthalate (PET) from discarded bottles was recycled via KOH treatment to produce activated carbon (AC) to remove methylene blue (MB) and picric acid (PA) from contaminated water. The AC produced was characterized by using physicochemical methods to assess its surface porosity, morphology and function groups. Batch adsorption experiments were performed the impact of pH, sorbent amount, time, sample volume, and initial concentration of the target dye on the adsorption efficiency. Adsorption followed the Langmuir isotherm model indicating monolayer adsorption behavior, while kinetics fitted with the pseudo-second-order model. The prepared AC exhibited high maximum adsorption capacities reached 334.4 mg g⁻¹ for MB and 271.7 mg g⁻¹ for PA. Quantitative dye desorption (> 97% recovery) was achieved using H₂SO₄ for MB and NaOH for PA. The method was also applied to spectrophotometric quantification of both analytes, yielding linear calibration curves for MB (0.15-5.76 mg L⁻¹, R² = 0.9997) and PA (0.01-1.68 mg L⁻¹, R² = 0.9980). Detection limits were 0.04 mg L⁻¹ (MB) and 0.003 mg L⁻¹ (PA), with quantification limits of 0.15 mg L⁻¹ (MB) and 0.013 mg L⁻¹ (PA). Successful application to diverse water samples confirmed the method's efficacy for dye removal and quantification.