Removal of Bisphenol-A from Aqueous Solution Using Rice Husk Nanosilica: Adsorption Kinetics, Equilibrium and Thermodynamic Studies

This study evaluates the adsorption of bisphenol-A (BPA) from aqueous solutions using nanosilica obtained from rice husk. Nanosilica (79 nm) was extracted from acid and thermal treated rice husk waste. The rice husk nanosilica (RHS) was fully characterized through X-Ray Diffraction Spectroscopy (XRD), Scanning Electron Microscopy (SEM), X-Ray Fluorescence Spectroscopy (XRF) and Fourier Transmittance Infrared Spectroscopy (FTIR). The spectroscopic analyses results revealed that the rice husk ash contains large fraction of amorphous silica. Batch adsorption experiments were carried out on BPA as a function of initial concentration, contact time, pH, adsorbent dosage and temperature. The maximum amount of BPA adsorbed was 4.267 mg/g with an optimum contact time of 45 min for 50 mg/L BPA solution at pH 8. The adsorption data were analyzed with adsorption isotherms and fitted best into the Langmuir model with R2 value of 0.994. The adsorption process followed the pseudo second order kinetics and was exothermic while the negative value of Gibbs free energy obtained revealed that the process is feasible at lower temperature.