Biovalorization of mandarin waste peels into silver nanoparticles and activated carbon

Abstract

This work aims to upcycle mandarin (Citrus reticulum) waste peels into valuable compounds with diferent applications. The one-factor-at-a-time method was applied to optimize the biosynthesis of silver nanoparticles using the hot water extract of mandarin peels’ waste. The maximum production reached 2.5 g L−1 in a 4-h, pH9, 100 rpm continuous stirring batch process, operating at 30 °C, under fuorescent illumination of 36 W/6400 K, using 3000 mg L−1 extract solution and 2 mmol AgNO3. Dynamic light scattering, zeta potential, X-ray difraction, energy-dispersive X-ray, Fourier transform infrared spectroscopy, feld emission scanning electron microscope and high-resolution transmission electron microscope were employed to char- acterize the prepared silver nanoparticles, which revealed highly stable, uniformly distributed, nonagglomerated crystalline silver nanoparticles, with spherical/oval shapes and a size range of 10–19 nm. The preliminary cost analysis proved the cost- efectiveness of the valorization of mandarine peels into silver nanoparticles, which costs approximately 7.6 US$/g green synthesized silver nanoparticles with good savings relative to the global prices of the chemically synthesized ones. Moreover, to reach the point of zero waste and maximize the proftability of the valorization, the mandarin spent waste disposed from the batch process were upcycled to activated carbon which has diferent applications.