Cd2+ removal efficiency of activated carbon from Prosopis juliflora: Optimization of preparation parameters by the Box-Behnken Design of Response Surface Methodology

Abstract

The study focuses on the preparation of activated carbon from Prosopis juliflora (PJAC) wood by pyrolysis and chemical activation. The objective is to assess its effectiveness as an adsorbent for synthesizing a composite adsorbent coating (CAC) for Cadmium (Cd2+) removal from aqueous solution. The effect of preparation factors related to Cd2+ removal efficiency was assessed. The Design of Experiments (DoE) for the adsorption of Cd2+ on the PJAC were done using the Box-Behnken Design (BBD) of the Response Surface Methodology (RSM) (Design Expert software version 11). The influence of impregnation ratio (IR), carbonization time (t), and carbonization temperature (T) on the Cd (II) percent (%) removal was evaluated. The response surface graphs in 3D were also generated for the response variable, and the higher R2 coefficient values were fitted into the polynomial quadric model. The results indicated that all the variable preparation factors were significant in the Cd2+ removal by PJAC with carbonization temperature being the most significant. At the optimum conditions i.e. impregnation ratio (1.8), carbonization temperature (595 °C) and carbonization time (174 min), the model predicted a 99.9 % Cd2+ removal efficiency while the adsorption experiment obtained a 96.7 % removal efficiency, respectively. Later, the morphological and chemical properties of the PJAC prepared with optimal parameters were analyzed using different characterization techniques including SBET, SEM-EDX, pHPZC, FTIR and XRD. The SEM images revealed a rough and porous morphological surface with an SBET of 600.4 m2/g and a near neutral pHPZC of 6.92. The XRD pattern indicated the crystalline nature of the prepared adsorbent. The pre and post adsorption FTIR spectrum of the PJAC demonstrated a distinct difference with the latter showing a reduction in peak intensity and height. These results underpin the potential of utilizing invasive plants like Prosopis Juliflora as adsorbents for heavy metal removal.