Synthesis of Stabilized Bismuth Nanoparticles with Biocompatible Capping Agents for Catalysis

Bismuth nanoparticles (BiNPs) are gaining considerable attention due to their low toxicity, biocompatibility, and promising catalytic properties. However, achieving stable BiNPs remains a major challenge, as they readily undergo oxidation and aggregation during synthesis. This instability significantly reduces their catalytic efficiency and limits their broader application. Although various synthesis methods have been explored, many require harsh chemicals or fail to provide long-term colloidal stability. Thus, there is a clear research gap in developing a simple and reproducible synthesis route that ensures colloidal stability through the use of effective capping agents. The objective of this study is to synthesize stable colloid of BiNPs using a controlled wet-chemical reduction method supported by suitable capping agents, and to evaluate their catalytic activity. BiNPs were synthesized using sodium borohydride as a reducing agent to facilitate particle formation, while the starch, β-cyclodextrin, and tannic acid acts as capping agent for preventing oxidation and aggregation and to form colloidal stable BiNPs. UV–visible (UV-Vis) and Fourier Transform Infrared Spectroscopy (FTIR) analyses confirmed the formation of BiNPs and demonstrated effective stabilization by the applied capping agents. FTIR spectra revealed distinct surface interactions, with the combined starch/β-cyclodextrin/tannic acid system exhibiting the strongest binding. The catalytic performance of the nanoparticles was assessed via the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using sodium borohydride, indicated by the decrease of the 401 nm peak alongside the growth of the 4-AP absorption band. Among the three samples, the ternary-capped BiNPs displayed the highest catalytic efficiency and superior stability, highlighting the essential role of surface capping in optimizing nanoparticle functionality. Overall, the study can provide a pathway for the future development of stable BiNPs and their applications.

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