Investigation on the pH‐independent photoluminescence emission from carbon dots impregnated on polymer matrix

Abstract

Highly luminescent, polymer nanocomposite films based on poly(vinyl alcohol) (PVA), and monodispersed carbon dots (C-dots) derived from multiwalled carbon nanotubes (MWCNTs), as coatings on substrates as well as free standing ones are obtained via solution-based techniques.The synthesized films exhibit pH-independent photoluminescence (PL) emission, which is an advantageous property compared with the pH-dependent photoluminescence intensity variations, generally observed for the C-dots dispersed in aqueous solution. The synthesized Cdots and the nanocomposite films are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR), ultraviolet (UV) − visible spectroscopy and photoluminescence spectroscopy (PL) techniques. The TEM image provides clear evidence for the formation of C-dots of almost uniform shape and average size of about 8 nm, homogeneously dispersed in aqueous medium.The strong anchoring of C-dots within the polymer matrix can be confirmed from the XRD results. The FTIR spectral studies conclusively establish the presence of oxygen functional groups on the surfaces of the C-dots. The photoluminescence (PL) emission spectra of the nanocomposite films are broad, covering most part of the visible region. The PL spectra do not show any luminescence intensity variations, when the pH of the medium is changed from 1 to 11. The pH-independent luminescence, shown by these films offers ample scope for using them as coatings for designing diagnostic and imaging tools in bio medical applications. The non-toxic nature of these nanocomposite films has been established on the basis of cytotoxicity studies.

Green Synthesis of Tunable Fluorescent Carbon Quantum Dots from Lignin and Their Application in Anti-Counterfeit Printing

“…The optimal PL excitation and emission wavelengths are centered at 450 and 520 nm, respectively, with negligible change, indicating the high stability of Y-CQDs in such a broad pH range. According to previous reports, the pH-sensitive behavior is commonly influenced by the protonation and deprotonation of (many) carboxyl and amine-type nitrogen functional groups attached to the CQDs in acidic and alkaline environments, which could change the distribution of the electron cloud between the functional groups and the carbon backbone. ,− Therefore, the pH-independent performance of Y-CQDs might be related to the exceedingly resistant surface structural morphology (fewer amino and carboxyl groups). , …”

Applications of Carbon Dots for the Photocatalytic and Electrocatalytic Reduction of CO2

“…Moreover, acidic oxidation is the treatment of graphene oxide, soot, coal, carbon black, or activated carbon with an oxidizing agent at temperatures of 60–100 °C, which exposes the edge sites from which the carbon material is exfoliated. For example, GQDs have been obtained from Multi-Walled CNTs oxidized with a mixture of HNO 3 /H 2 SO 4 [ 40 , 41 , 42 ], from carbonized coal treated with HNO 3 [ 43 ], from anthracite coal treated with H 2 SO 4 and HNO 3 [ 44 ] and from graphene oxide treated with periodic acid, H 2 SO 4 or HCl [ 17 , 45 , 46 , 47 ]. Furthermore, the electrochemical exfoliation of carbon-based materials revealed to be an effective synthetic method to obtain GDQs.…”

“…For both types of synthesis, depending on the temperature or power, reaction time and precursor, the physicochemical properties of the CDs, such as size, crystallinity, solubility, can be controlled. Precursors can be obtained from renewable sources, such as orange juice [ 61 ], shrimp egg [ 62 ], ginkgo leaves [ 63 ], extract of waste tea [ 64 ], pine pollen [ 65 ], Camellia japonica flowers [ 66 ], or waste cotton linter [ 42 ]. Other renewable sources are reviewed elsewhere [ 67 ].…”

Recent Advances in Synthesis, Modification, Characterization, and Applications of Carbon Dots

“…The crystallinity, size, and solubility of the CDs can be tuned by changing the power, reaction temperature, reaction time, and types of precursors. Precursors can be citric acid, saccharides, ethylene glycol, and even the abundantly available biomass, such as waste cotton linter [ 18 ], olive solid wastes [ 19 ], orange juice [ 20 ], bitter apple peel [ 21 ], shrimp egg [ 22 ], muskmelon peel [ 23 ], ginkgo leaves [ 24 ], eggshell membranes [ 25 ], extract of waste tea [ 26 ], egg yolk [ 27 ], pine pollen [ 28 ], Colocasia esculenta leaves [ 29 ], Camellia japonica flowers [ 30 ], and other organic wastes [ 31 , 32 ].…”