Adsorption study of Bisphenol A (BPA) by Base Activated coconut shaft as a Low-Cost Adsorbent (Isotherm, Kinetics and thermodynamic studies)

Abstract

This study investigated the effect of base-modified coconut shaft (BAC) on the elimination of Bisphenol A (BPA) from aqueous solution. An alkali (NaOH) was employed to activate the coconut shaft. The characterization of the activated adsorbent before and after adsorption was done using Fourier Transform Infrared (FTIR) spectroscopy. Various operational parameters, such as pH, adsorbent dosage, temperature, contact time, and initial BPA concentration, were examined in batch experiments. The functional groups such as hydroxyl, carboxyl, and aromatic groups which are responsible for the adsorption of the contaminant were revealed by FTIR characterization. It was determined that the optimal factors for BPA removal were pH 2, adsorbent dosages of 0–5 g/L, contact time 80 min, 100ppm initial concentration and 45°C. Kinetic studies indicated that the adsorption process followed pseudo-second-order kinetics, suggesting that chemisorption was the rate-limiting step. The Langmuir model provided a maximum monolayer adsorption capacity of 35 mg/g, while the Freundlich model more accurately described the adsorption isotherms, indicating a heterogeneous adsorption process. Thermodynamic analysis showed that adsorption was impulsive and endothermic, with positive values for enthalpy (ΔH° = 5. 76 kJ/mol) and entropy (ΔS° = 8. 27 kJ/mol·K), and negative Gibbs free energy (ΔG°) values ranging from -1. 08 to -2. 13 kJ/mol across the temperature range of 25–65°C. The study demonstrates that base-modified coconut shaft (BMC) is a promising, eco-friendly, and cost-effective biosorbent for BPA removal from solutions. Its performance, characterized by favorable thermodynamics, kinetics along with excellent adsorption capacity qualify it as a viable alternative adsorbent to be considered for adsorption purpose.