Biosynthesized gold nanoparticles as photocatalysts for selective degradation of cationic dye and their antimicrobial activity

Herein, polyphenol stabilized gold nanoparticles (AuNPs) have been synthesized for selective removal of cationic dyes from aqueous solution. Gold nanoparticles have been synthesized using Cassytha filiformis plant extract and characterized by UV-vis spectroscopy (UV-vis), High-Resolution Transmission Electron Microscopy (HR-TEM) and X-ray diffraction (XRD). The size of AuNPs was found to be in the range of 8-20 nm with an average size of 12 nm. The newly generated AuNPs demonstrate excellent potential in removing cationic dye such as methylene blue (MB) via photocatalytic degradation under sunlight. The adsorption/degradation behaviour of cationic MB on AuNPs adsorbent from the aqueous solution was studied by varying parameters such as pH and different light sources. Alkaline pH and sunlight were found to be crucial in dye degradation. The adoption of the ultrasonic waves (UW) leads to reduce sorption time significantly with an increase in the sorption ability and at the optimum condition. The AuNPs appear to be promising with a maximum dye loading capacity of 595.23 mg/g and dye degradation efficiency was found to be 87 % after 20 min. Additionally, the antimicrobial studies confirm the significant inhibition (zone of inhibition: 20 mm) of growth of Mycobacterium smegmatis, a model organism for Mycobacterium tuberculosis, suggesting the advancement of a novel new generation eco-friendly and cost-effective 'green' AuNPs.