Response Surface Optimization of Crystal violet Removal onto Sodium Hydroxide-modified Watermelon Rind

The increasing global demand for water and the widespread contamination of water bodies by harmful dyes necessitate sustainable solutions.This study investigates the potential of sodium hydroxide modifiedwatermelon rind as an adsorbent for Crystal violet (CV) sequestration from aqueous media.Batch adsorption tests were conducted to examine the effects of pH, adsorbent dosage, initial dye concentration, temperature, and contact time on adsorption efficiency.Adsorbent properties analysis was done using pH-point-of-zero charge, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy.Analysis of factors' effects and interactions on the adsorption process was conducted using Historical Data Design in Response Surface Methodology.Experimental data were fitted into four isotherm model (Freundlich, Temkin, Dubinin-Raduskevich and Redlich-Peterson).The order of their fitness based on their coefficient of determination, chisquare and RMSE values was Freundlich > Dubinin-Raduskevich > Redlich-Peterson > Temkin.The maximum adsorption capacity of the adsorbent was found to be 76.05 mg/g.The Pseudo-second order kinetic model represented the best fit for the adsorbent.Response Surface Methodology (RSM) results showed that among the four factors (pH, concentration, contact and dosage) examined, only concentration and dosage were significant terms for the adsorption process both having p values <0.05.