Ag decorated CoO NPs supported on chitosan matrix for colorimetric detection of L-cysteine, antibacterial application and photocatalytic reduction of hexavalent chromium ions

Abstract

This work describes the synthesis of Ag decorated CoO nanocomposites (NCs) supported on chitosan (CS-Ag/CoO NCs) for simple, low cost and rapid colorimetric detection of L-cysteine, and for the photocatalytic reduction of hexavalent chromium (Cr(VI)) ion. The NCs was characterized thoroughly by using UV–vis spectrophotometer, fourier transform-infrared spectroscopy (FT-IR), high resolution transmission electron microscopy (HR-TEM), thermogravimetric analysis (TGA), X-ray diffraction spectroscopy (XRD), energy dispersive x-ray spectroscopy (EDAX), and X-ray photoelectron spectroscopy (XPS). The NCs displayed high specificity, sensitivity and selectivity towards the L-cysteine detection and quantification from aqueous samples. The limit of detection of the prepared probe was 4.67 nM. The particle size of CS-Ag/CoO NCs was found to be 8.52 ± 0.13 nm. The CS-Ag/CoO NCs interaction with L-cysteine, interestingly causes the aggregation of NCs with increase in particle size to 956 ± 0.23 nm. The color change was observed from yellow to color less. An excellent linear correlation exists between the absorbance vs logarithmic concentration of L-cysteine (10 nM- 1 mM). Here, 250 mg/L of NCs reduced 100 mg/L of Cr(VI) to Cr(III) within 180 min. The kinetic data suggested that the NCs exhibited greater photocatalytic reduction efficiency than CoO and Ag/CoO. The paper-based test strips were developed and applied for the rapid colorimetric assay for the onsite monitoring of L-cysteine from real samples. The study demonstrated a specific detection of L-cysteine irrespective of the source of samples using CS-Ag/CoO NCs. Hence, the prepared NCs can be used as a colorimetric probe and provides a practical application for photocatalytic reduction of Cr(VI). The NCs also exhibitted excellent antimicrobial activity.