Tamed synthesis of AgNPs for photodegradation and anti-bacterial activity: Effect of size and morphology

Organic dyes present in the effluents of paints, and textile industries are posing major environmental threats. Rapid decomposition of these dyes using non-toxic, renewable and cost-effective silver nanoparticles (AgNPs) is a pragmatic strategy. Therefore, in current research work, AgNPs with different size ranges have been prepared following the polyol reduction method by controlled exploitation of substrate/reducing agent molar ratio and pH of reaction media. AgNPs have been characterized by UV-Visible spectroscopy, Scanning Electron Microscope (SEM), Powder X-Ray Diffraction (XRD) and Energy Dispersive X-ray spectroscopy (EDS). Absorption peaks ranging from 420 to 465 nm confirmed the synthesis of AgNPs using surface plasmon resonance (SPR) bands. The increase in molar ratio and pH led to the blue shift in absorption bands which revealed the size reduction of AgNPs. XRD analysis confirmed the crystallite size (16-21 nm) and Face centered cubic (FCC) crystalline structure of AgNPs. EDS was utilized to check the purity of AgNPs. SEM confirmed the spherical morphology of AgNPs with a size range between 70 and 110 nm. The energy band gap was determined using the Tauc plot equation to correlate the catalytic properties of NPs with size. Different-sized AgNPs were utilized as photocatalysts for the degradation of Methylene blue (MB) dye under sunlight irradiation. AgNPs having an average size of 70 nm showed improved photocatalytic potential by 94% degradation of MB in 80 min. The AgNPs were also evaluated for their antibacterial activities against gram-positive and gram-negative strains of bacteria. Small-size AgNPs were found more active against gram-negative strains of bacteria.