Pomegranate peels as versatile adsorbents for water purification: Application of box–behnken design as a methodological optimization approach

Pomegranate peels (PGP) were tested as a green adsorbent for the removal of Ni(II) from contaminated water samples. Both raw (RPG), and char/burnt peels (BPG) were tested. A multivariate analysis approach, Box–Behnken (BB) design was executed to augment the efficiency of BPG as adsorbent. Three factors were considered thereof; contact time (CT), adsorbent dose (AD), and heavy metal concentration (HMC). The percentage of heavy metal removal was the designated response (Y). Main effects plot together with analysis of variance (ANOVA) were used to decide on the substantial factors. Obtained results showed that AD was the most significant linear factor, while the interaction between AD*HMC was the most influential two-way interaction. Contour and response surface plots were used to study the factorial interactions and optimize the response. Desirability function was used to find the best factorial combination for maximum removal of Ni(II). Efficacies of both adsorbents were compared and BPG was more effectual achieving 99.99% removal of Ni(II). Surface morphology was characterized using FTIR, BET, SEM, and EDX analyses. Results indicated that functional groups such as hydroxyl, amino, carboxylic acid are available on surface of PGP and might be responsible for the adsorption process.