Nanomodification of viscose fibers using copper nanoparticles (Cu NPs) and copper oxides (CuO and Cu2O): Toward multifunctional and multipurpose viscose fibers.

Herein, a novel, facile, and scalable approach for multifunctional viscose fibers decorated with Cu, CuO, and Cu₂O was designed by a one-pot synthesis route using a single copper sulfate pentahydrate as a source of Cu2+ ions, along with sodium hydroxide and ascorbic acid as reducing agent under adjustable reaction conditions. The results show that VF@Cu, VF@CuO, and VF@Cu2O exhibited enhanced coloration, antimicrobial properties, UV protection, ammonia sensing, and catalytic activity. The modified viscose fibers demonstrated excellent color uniformity and durability, with color ranging from pale yellow, dark brown, and golden-brown for Cu NPs, CuO, and Cu2O, respectively. The modified viscose fibers demonstrated excellent antimicrobial activities against different microorganisms with inhibition zones up to 23 mm and microbial reduction rates exceeding 98 %. UV protection was significantly improved, with ultraviolet protection factor (UPF) values exceeding 45. The modified viscose fibers exhibited notable sensitivity as naked-eye colorimetric sensors for the detection of ammonia through rapid (<60 s) visible color change of fibers from brown/yellow to green. Furthermore, modified viscose fibers exhibited remarkable catalytic capabilities for one-pot imine synthesis. Catalytic performance in imine synthesis via benzylamine self-coupling achieved 97 % yield using VF@Cu2O (60 mg catalyst, 2 h reaction time, ethanol solvent).