Eco-sustainable synthesis of chromium oxide (Cr <sub>2</sub> O <sub>3</sub> ) nanoparticles via pomegranate husk extract: calcination-driven control of structure and properties
Shi-Yan Cheah, You-Kang Phang, Ming-Xiu Koh, Sharon Chia-Yen Lim, Sinouvassane Djearamane, Hemaroopini Subramaniam, Boon-Hoe Lim, Fang Li, Mohammod Aminuzzaman, Ling-Shing Wong, Lai‐Hock Tey
Abstract
Abstract This study presents an eco-friendly synthesis of chromium oxide nanoparticles (Cr 2 O 3 NPs) using pomegranate ( Punica granatum ) husk extract as a natural reducing, capping, and stabilizing agent. The process converts agricultural waste into a valuable precursor, avoiding toxic chemicals and minimizing environmental pollution. The synthesized material was calcined at temperatures from 60 to 700 °C to assess thermal effects on its properties. Quantitative analysis revealed an average crystallite size of 21.4 nm (Scherrer equation) for the optimally calcined sample at 500 °C. Characterizations by UV–Vis, PL, FTIR, XRD, SEM, TEM, EDX, Raman, and XPS showed that calcination strongly affects particle morphology, crystallinity, and surface composition. Low temperatures produced amorphous, irregular aggregates with residual organics, while intermediate temperatures yielded highly crystalline, quasi-spherical particles with enhanced optical emission and minimal defects. High-temperature treatment achieved maximum purity and ordering but led to grain coarsening. This work provides a systematic correlation between structural (XRD, FTIR) and optical (UV–Vis, PL) characteristics of Cr 2 O 3 NPs synthesized through a green route – an aspect not comprehensively reported in earlier fruit-extract-based Cr 2 O 3 studies. The results highlight the potential of plant-mediated synthesis combined with controlled thermal processing to produce high-purity, tunable Cr 2 O 3 NPs for catalytic, optical, and coating applications.