Synthesis of Plant-Mediated Silver-Doped Metal Oxides Using Catharanthus roseus and Evaluation of Their Catalytic and Biological Activities

This study explores the green synthesis of silver-doped lanthanum oxide (La/Ag), silver-doped yttrium oxide (Y/Ag), and silver-doped lanthanum–yttrium oxide (La/Y/Ag) nanocomposites using Catharanthus roseus extract as a natural reducing and stabilizing agent. The nanocomposites were characterized using various spectroscopic techniques to confirm their morphology, composition, crystallinity, and functional groups. La/Ag, Y/Ag, and La/Y/Ag exhibited significant catalytic activity in the reduction and degradation of methylene blue (MB), methyl orange (MO), acridine orange (AO), and 4-nitrophenol (4-NP). Optimization studies showed that La/Ag achieved complete MB reduction within 3 min, while La/Y/Ag reduced MO in 90 s. Both catalysts maintained high activity over multiple cycles, with only slight efficiency loss. In real water media, La/Ag and La/Y/Ag achieved reduction efficiencies of 98% and 97%, respectively. La/Ag also demonstrated excellent photocatalytic degradation of AO under UV light, achieving complete degradation in 80 min, and 98% degradation in tap and seawater samples. Additionally, the nanocomposites demonstrated broad-spectrum antimicrobial activity against bacterial and fungal pathogens, with varying inhibition levels across species.