Circular valorization of Hypericum perforatum biomass into CuO-lignin and CuO-cellulose bionanocomposites for mitigating copper nanotoxicity in plants.

We present a circular biomass valorisation strategy for the synthesis of CuO-based nanocomposites (NCs) using Hypericum perforatum L. In this approach, H. perforatum serves a dual purpose: its phytochemicals are used to synthesize CuO nanoparticles (NPs), while the remaining biomass is used to extract lignin and cellulose. The extracted lignin and cellulose were then processed into lignin nanoparticles (LNPs) and cellulose nanofibers (CNFs). These were subsequently functionalized with CuO NPs to fabricate CuO-LNPs NC and CuO-CNFs NC. Characterization using UV-Vis, FTIR, DLS, pXRD, and UPLC-PDA confirmed the successful formation of all nanocomposites. Microscopy analysis showed CuO NPs encapsulated within spherical LNPs and embedded in a net-like structure formed by CNFs. The release of Cu ions measured by TXRF over 15 days showed that CuO-LNPs release Cu ions significantly slower than CuO NPs due to the strong interactions between CuO and LNPs. In contrast, CuO-CNFs NC exhibited similar release rates to CuO NPs, attributed to weaker binding. In vitro testing on tobacco BY-2 cells corroborated with slow release profile. CuO NPs and CuO-CNFs NC, which reduced cell viability after 7 days, CuO-LNPs NC maintained plant cell viability and showed no cytotoxicity. Overall, this integrated approach increases the value of biomass for the production of high-value nanomaterials that promotes environmental and economic sustainability, while envisaging CuO-LNPs NC as a potential slow-release nanomaterial for sustainable agriculture.