Enhanced catalytic reduction of 4-nitrophenol and congo red dye By silver nanoparticles prepared from Azadirachta indica leaf extract under direct sunlight exposure

ABSTRACT

The manuscript reports an efficient approach for the synthesis of biogenic silver (Ag) nanoparticles from Azadirachta indica leaf extract-mediated reduction of silver nitrate under solar radiation at mild temperature conditions for nanoparticles (NPs) preparation. Spectroscopic and electron microscopic characterization studies revealed the formation of stable and monodisperse Ag NPs with sharp absorption band at 438 nm and average diameter of 10–15 nm. Catalytic potential of the NPs was descriptively investigated for the reduction of 4-nitrophenol to 4-aminophenol in alkaline medium. Apparent rate constant ($$K_{\mathrm{a}\mathrm{p}\mathrm{p}}^{\mathrm{\prime }}$$) values were determined to be 0.014, 0.0238, 0.0338, 0.063, and 0.0794 at 5, 10, 15, 20, 40, and 50 µL Ag NPs volume, respectively, thereby depicting linear relationship between the variables under study. Catalytic reduction of Congo red dye was achieved within 2 h, thus validating the efficacy of Ag NPs as a photocatalyst. The NPs also exhibited linear increment in antibacterial activity on cultured Escherichia coli plates with increasing volumes. These catalytic capabilities firmly advocate the applications of Ag NPs in purification of polluted water by the removal of toxic and contaminant materials and harmful/pathogenic bacteria.

KEYWORDS:

• Azadirachta indica
• catalytic reduction
• green synthesis
• silver nanoparticles
• sunlight exposure
• transmission electron microscopy
• UV–visible spectroscopy

Additional information

Funding

This work was supported by financial assistance received from Shromani Gurdwara Prabhandak Committee (SGPC), Amritsar. Author Dr. Deepak Kukkar, acknowledges DST-SERB, Government of India for financial support under Young Scientist Scheme (No. YSS/2015/000212). Authors are also thankful to Vice-Chancellor, SGGSW University for providing necessary laboratory facilities.