Carbon Dot grafted pH sensitive smart paper for highly efficient separation of anionic/cationic dyes from a mixture

Abstract

In the presented work, for the first time, a cheap green pH sensitive smart paper has been developed that contains in-situ generated carbon dots deposited uniformly over the fibrous surface of the paper via a one-step method from chitosan gel. The polymer carbon dot paper (PCD) has been characterized using Field Emission Scanning Electron Microscope (FE-SEM), Energy Dispersive X-Ray (EDX), Fourier Transformed Infrared spectroscopy (FT-IR), Raman Microscopy, UV-Vis spectroscopy, Fluorescence spectroscopy, Thermogravimetric analyzer (TGA), Dynamic Light Scattering (DLS), Zeta Potential Measurements, Atomic Force Microscopy (AFM), Laser Confocal Microscopy (LCSM), X-ray Diffraction (XRD), and X-ray photoelectron Spectroscopy (XPS). The paper has been demonstrated to have very high selectivity for the absorptive removal of anionic dye from a mixture of cationic and anionic dyes in both acidic and neutral pH conditions. However, under basic conditions, the paper is found to be selective for the adsorption of Methylene Blue from a mixture of dyes. The dye separation experiment was carried out in an aqueous phase that was analyzed using UV–Visible spectrophotometer at a definite time interval and above 98% of the separation has been achieved working with a pair of various dye mixtures. The adsorbed dye from the paper can also be recovered very easily simply by agitating and tuning the pH conditions to basic up to the extent of 76%. The probable mechanism of the system in the separation of cationic and anionic dye is also discussed in the manuscript.