Chlorophyll Coated Silver Nanoparticles Synthesized by Microwave Assisted Method for the Colorimetric Detection of Cr (VI) Ions in Aqueous Medium

Abstract

The study aims at synthesizing a simple, cost-effective, selective, and sensitive colorimetric sensor based on chlorophyll-coated silver nanoparticles (Chl-AgNPs) using microwave-assisted method for the determination of Cr(VI) ions in an aqueous medium. The characterization reveals that synthesized nanoparticles are 20–30 nm in size and spherical in shape. The presence of methyl, carboxyl, aldehyde, and ketone groups on the surface of Chl-AgNPs results in the formation of size controlled, well dispersed, and stable silver nanoparticles. The prepared nano-colloidal solution has been used for selective and sensitive determination of Cr(VI) in water samples. The addition of single drop of Chl-AgNPs solution immediately changes the color of water samples containing Cr(VI) to red displaying good sensitivity from 10 to 100 µM and high selectivity even in the presence of other metal ions. The ultraviolet–visible spectra show that in the presence of Cr(VI), the localized surface plasmon resonance (LSPR) band of Chl-AgNPs at 410 nm shifts to 470 nm with a new peak at 357 nm. Furthermore, the absorbance of the LSPR band decreases and the absorbance at 357 nm increases linearly with the concentration of Cr(VI). The functional groups on the surface of nanoparticles bind Cr(VI) on the surface leading to agglomeration and alterations in interparticle distance that are observed as changes in the color and LSPR profile. The limits of detection and quantification for Cr(VI) ions were determined to be 0.62 µM and 1.88 µM, respectively.

Keywords:

• chlorophyll coated silver nanoparticles
• chromium(VI) ion
• colorimetry
• microwave assisted synthesis
• spectrophotometry
• ultraviolet–visible spectroscopy

Acknowledgments

Miss Aparna Tiwari is thankful to UGC, New Delhi, for the financial assistance in the form of fellowship. Mr. S. K. Sharma is thankful to Prof. S. K. Trivedi, Director, Faculty of Engineering and Technology, KMCLU, Lucknow for kind cooperation during the present work. The authors are also grateful to UGC, New Delhi, for providing financial assistance by the DST-FIST program to create the confocal Raman microspectroscopy facility in the Department of Physics, University of Allahabad, Prayagraj.