Green Synthesis of Vanadium Dioxide Nanoparticles by sp. Strain HN-41.

Vanadium dioxide (VO) nanoparticles have various application potentials such as smart windows and electronic devices due to their unique phase transition properties. However, conventional VO synthesis methods require harsh conditions and toxic reducing agents, leading to environmental problems. In this study, we developed an eco-friendly method to biosynthesize VO nanoparticles using sp. strain HN-41 under anaerobic conditions at 30°C and neutral pH. Morphological observations revealed that biogenic VO nanoparticles with an average size of 4.3 nm were in the form of granules presented inside and outside the cells. These nanoparticles were identified as VO by differential scanning calorimetry (DSC) analysis, which showed a phase transition temperature of 61.9°C, consistent with that of VO. Furthermore, we observed an active formation of vesicles containing VO nanoparticles by the cross-sectioned transmission electron microscopy (TEM) analysis. Thus, in addition to the direct extracellular formation of VO nanoparticles through anaerobic respiration, bacterial membrane vesicles likely play a role in expelling nanoparticles from the cell, potentially mitigating their toxicity. These findings highlight metal reducing bacteria could be a biological green agent for the production of valuable VO nanoparticles under anaerobic environmental conditions.