Optimization of process parameters for the microbial synthesis of silver nanoparticles using 3-level Box-Behnken Design

Extracellular biosynthesis of silver nanoparticles (AgNPs) has been investigated by screening the cell free supernatant of five marine bacterial isolates. Among the screened isolates, cell free supernatant of Microbacterium sp. NV4 mediated effective synthesis of AgNPs. The synthesized nanoparticles were characterized using UV-vis spectroscopy (UV), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Transmission Electron Microscopy (TEM). The UV spectral analysis exhibited a peak at 420 nm confirming the synthesis of AgNPs. The face centered cubic structure and the average particle size (17-26 nm) of the biosynthesized AgNPs were confirmed by XRD and TEM analysis, respectively. FTIR spectrum showed the involvement of biomolecules in the formation of AgNPs. Further, biosynthesis of AgNPs was optimized using Response Surface Methodology (RSM) based on three-level Box-Behnken Design (BBD) in order to enhance the synthesis of AgNPs. The optimum synthesis was observed at pH 7, temperature 45 °C, and incubation time of 72 h. The biosynthesized AgNPs were applied for the photocatalytic degradation of the dye methylene blue under visible light irradiation. The electrons excited on exposure to light are accepted by the dissolved oxygen present in the reaction medium and converted to oxygen anion radicals. These radicals might cause the degradation of the dye into simpler molecules. The result obtained reveals that the synthesized AgNPs could effectively degrade the dye (92.2%) after 8 h of incubation.