How Can a Pomegranate Peel Turn Into a Sponge to Clean Water?

Modern farming uses many chemicals to boost yields. Some contain heavy metals like copper and nickel, which can seep into groundwater. Removing these pollutants is crucial for health and the environment. One promising solution is adsorption with biosorbents, natural materials that "capture" unwanted substances. In this study, researchers made hydrogels from sodium alginate, a seaweed-derived polymer, and pomegranate peel powder, an agricultural waste. After synthesis, the hydrogels were examined with FTIR spectroscopy, scanning electron microscopy (SEM), and water uptake tests. Results showed that pomegranate peel makes the gel rougher and more porous, increasing water retention by 1.58 times compared to alginate alone. When placed in contaminated water, these hydrogels adsorbed copper and nickel efficiently. For copper, optimal contact was 60 minutes at pH around 5, using 0.01 g of gel. For nickel, only 5 minutes of contact were needed. These findings suggest that pomegranate‑based hydrogels could become a green technology for water purification, turning food waste into an environmental asset.

The hydrogel was synthesized via ionic cross‑linking between sodium alginate chains and calcium ions, in the presence of pomegranate peel powder (PPP). PPP, rich in polysaccharides, pectin, and phenolic compounds, provides functional groups –COOH and –OH that enhance metal ion binding. FTIR analysis revealed characteristic bands at 1600 cm⁻¹ (C=O) and 3400 cm⁻¹ (O–H), confirming interaction between alginate and PPP. SEM images displayed a more irregular and porous surface in PPP‑containing samples, with micrometric pores that facilitate water and contaminant diffusion. Water uptake tests showed a 58 % increase in retention capacity, attributable to the larger surface area and the hydration ability of phenolic groups. For metal removal, the effects of pH, contact time, and adsorbent dose were evaluated. The optimal pH of 5 for copper corresponds to partial protonation of –COO⁻ groups, maximizing electrostatic interaction with Cu²⁺. The adsorption isotherm follows the Langmuir model, indicating a monolayer of ions on active sites. The maximum adsorption capacity (qₘ) for Cu²⁺ was estimated at 45 mg g⁻¹, while for Ni²⁺ it was 38 mg g⁻¹, values competitive with traditional biosorbents. The rapid nickel adsorption kinetics (5 min) suggest an ion‑exchange mechanism dominated by –OH groups of PPP. From a sustainability perspective, using pomegranate waste reduces agro‑industrial residues and lowers hydrogel production costs, making it an eco‑friendly solution for treating contaminated water.