Optical and surface plasmon resonance sensing properties for chitosan/carboxyl-functionalized graphene quantum dots thin film

In this study, chitosan/carboxyl-functionalized graphene quantum dots thin film was developed. Its optical and surface plasmon resonance sensing properties were explored. Fourier transform infrared spectroscopy proved the presence of O-H bond, C-H bond, C=O bond, and C-O bond in chitosan/carboxyl-functionalized graphene quantum dots thin film. The optical properties of the composite thin film were studied using UV-vis and photoluminescence spectroscopy. The chitosan/carboxyl-functionalized graphene quantum dots thin film showed the high absorbance value with an optical band gap of 4.012 eV. From photoluminescence spectroscopy, red light emission spectra are emitted due to the absorption peak of about 725 nm to 775 nm that corresponds to pi-pi transitions of C=O bond. The surface morphology of thin film was observed using atomic force microscopy indicates a granular structure with an average height of 18.4 nm of the composite thin film. The experimental surface plasmon resonance curves were obtained for different concentration in a range from 0 to 100 ppm of Hg2+ solution. A linear relationship between the shifts of resonance angle for chitosan/carboxyl-functionalized graphene quantum dots thin film in contact with Hg2+ solution with a sensitivity of 0.00062 degrees ppm(-1) has been observed. These results confirmed that the chitosan/carboxyl-functionalized graphene quantum dots thin film shows potential for the detection of Hg2+ using surface plasmon resonance technique.