Synthesis of Copper(I) Oxide Nanoparticles using Dillenia retusa Fruit Extract as a Sustainable Capping Agent

Objectives: Natural and biocompatible capping agents are increasingly sought as sustainable alternatives to synthetic surfactants in nanoparticle synthesis. This study evaluated whether Dillenia retusa (Godapara), an endemic Sri Lankan plant, fruit extract which was not previously investigated for copper-based nanoparticle synthesis can act as an effective natural capping agent for the green synthesis of copper(I) oxide (Cu2O) nanoparticles. Method: Cu2O nanoparticles were synthesized via chemical reduction of CuSO4·5H2O with ascorbic acid under alkaline conditions, both with and without D. retusa fruit extract as a capping agent. Synthesis of each condition was independently repeated in triplicate to confirm reproducibility. The uncapped nanoparticles served as the benchmark for comparison. Products were characterized by FTIR, SEM, EDXS, and XRD, and crystallite size/lattice strain were quantified using the Williamson–Hall method. Findings: FTIR confirmed Cu–O bonding in both samples and revealed extract-derived phenolic and aliphatic bands unique to the capped sample. SEM showed that capping reduced the average particle size from 64 nm (38–86 nm range, uncapped) to 47 nm (28–68 nm range, capped), with the capped particles well-dispersed and free of agglomeration. XRD confirmed phase-pure cuprite, Cu2O, in both samples, and Williamson–Hall analysis showed the crystallite size decreased from 51.1 nm (uncapped) to 29.2 nm (capped), a ~43% reduction, accompanied by a small increase in microstrain (0.405% to 0.447%), consistent with phytochemical adsorption restricting crystal growth. Novelty: Although D. retusa extracts have recently been employed in the green synthesis of silver nanoparticles, their use in the synthesis of copper-based nanoparticles has not been reported to date. To the best of our knowledge, this study represents the first report of D. retusa fruit extract mediated synthesis of Cu₂O nanoparticles and the first demonstration of its role as a capping agent in the preparation of a copper oxide nanomaterial. This work therefore expands the reported applications of D. retusa for the synthesis of nanoparticles further with the quantitative data on particle and crystallite sizes.