Non linear regression analysis and response surface modeling for Cr (VI) removal from aqueous solution using poly-aniline coated sugarcane bagasse (PANI@SB) composites as an adsorbent

Abstract

Hexavalent chromium has been found most hazardous pollutants being discharge from many industrial sectors like chromite mines, electroplating industries, leather and tanning industries etc. and need to be controlled before discharge to save natural water resources. Adsorption is one of the best and economic process for hexavalent chromium removal. In present investigation, agricultural waste sugarcane bagasse has been coated with polyaniline and PANI@SB composites were synthesized as an adsorbent for the removal of Cr (VI) from its aqueous solution by adsorption process. Batch adsorption was conducted to optimize the dose of adsorbent, pH, time and concentration. The optimum condition has been found are pH 2.0, 0.3 g adsorbent dose, 10 mgL−1 initial concentration at 303 K. Multilayer adsorption of Cr (VI) was found to occur on the heterogeneous surface of PANI@SB with maximum adsorption capacity of 35.2 mgg−1 at 303 K. It was observed that adsorption data fitted well to the Freundlich isotherm model and pseudo- second-order model with high R2, low chi square (χ2), low root mean square error (RMSE) and low standard deviation (SD) values by applying non linear regression method. Positive values of enthalpy and Gibbs free energy of adsorption suggest endothermic and spontaneous nature of adsorption occurs. FESEM, EDX, XRF, HR-TEM, FTIR, XRD, AFM, BET surface area and XPS analysis were conducted to understand the surface characteristics of PANI@SB before and after adsorption of Cr (VI). Response surface modeling (RSM), a statistical tool, was applied to experimental data to optimize the process parameters. A quadratic model equation was generated between the process parameters and response for Cr (VI) removal. The optimization study from RSM showed that pH and adsorbent dose has significant effect on removal of Cr (VI) due to higher lack of fit (F) value. The optimum conditions for maximum removal of 97% Cr (VI) are found at pH 2.0 with 0.3 g of adsorbent dose, time of 90 min at 303 K obtained by RSM. PANI@SB is regenerated with 0.2 N NaOH and can be reused up to two desorption-adsorption cycles (removal 92%) with slight decreases in its original sorption capacity. On the basis of this study it is found that PANI@SB is very efficient, stable, reusable and effective adsorbent for removal of Cr (VI) from aqueous medium and it can be used in industrial scale.