Acid-activated clay-polyphenols hybrids from pomegranate peel waste: Towards multifunctional optical and antioxidant materials

A novel multifunctional hybrid material was developed here, in the context of circular economy, by immobilizing polyphenols recovered from pomegranate peels waste onto acid-activated clay. Smectite clay was activated with sulfuric acid (3N) for 1 h and 4 h. Characterization techniques including, Fourier Transform Infrared (FTIR), X-Ray diffraction (XRD), X-Ray fluorescence (XRF), Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) and Scanning Electron Microscopy (SEM)) confirmed the changes induced by acid activation. The main parameters, affecting the adsorption process of polyphenols on acid-activated clays were examined. Maximum adsorption (56.81 mg/g) was noted for the clay activated for 1h, at pH 4-6 and 4h contact time. The process followed a pseudo-second-order kinetic model and fitted the Langmuir isotherm, with thermodynamic data indicating an exothermic and spontaneous mechanism. Retention was mainly chemical, involving π-interactions, hydrogen bonding, and coordination bonds depending on surface acidity. Optical study demonstrated stable white light emission, while biological assay revealed significant antioxidant activity, highlighting the potential of these hybrids as sustainable multifunctional materials.