Uniform blue emitting carbon nanodots synthesized from fig fruit using reverse diffusion purification

Abstract

In this investigation, blue-emitting carbon nanodots (B.CNDs) with exceptional color purity were successfully synthesized from fresh fig fruit using a one-step pyrolysis method. These B.CNDs are small and spherical (3.7 nm) with an amorphous carbon core encapsulated inside a passivated layer primarily composed of oxygen-related functional groups. They demonstrated an emission property that is independent of excitation, showing the highest emission intensity in the deep blue region at 450 nm with a narrow full-width at half maximum (FWHM) at 44 nm and a quantum yield of 15.5%. This exceptional value of FWHM is attributed to the remarkable uniformity in both morphological and chemical composition that was achieved through the utilization of the reverse diffusion technique combined with the dialysis method for purification and separation of B.CNDs. This work not only contributes to the expanding field of carbon nanomaterials but also introduces a novel and sustainable approach to fabricate CDs with unparalleled color purity and optical performance.

Keywords: Blue emission; Green carbon sources; Narrow bandwidth; Pyrolysis synthesis; Reverse diffusion technique.

Fig. 1

The schematic diagram of the experimental procedure to synthesize B.CNDs, as confirmed by the excitation-emission map of the diluted B.CNDs in water (Fig. 2.h).

Fig. 2

The schematic illustration of the purification and separation process of the B.CND solution. (a) CD solution after being filtered by 0.22 μm and centrifuged at 10 k rpm for 30 min. (b) CDs purified with a 0.5 k Da dialysis bag. (c) B.CNDs extracted using a 1.0 k Da dialysis bag.

Fig. 3

(a-c) SEM images show well-distributed spherical carbon nanoparticles. (d) the EDS spectrum shows only carbon and oxygen element on silicon substrate.

Fig. 4

Structural and chemical composition properties of B.CNDs. (a) TEM image of the B.CNDs shows a wide range of particle distribution (top inset image). (b) a low contrast TEM image between B.CNDs and a thin carbon-coated copper of TEM grid shows a poor contrast between B.CNDs and TEM grid (upper inset image) and FFT pattern demonstrating their amorphous structure (lower inset image). (c) XRD of B.CNDs shows its amorphous. (d) FT-IR of B.CNDs shows their surface are rich with oxygen and some nitrogen related function groups.

Fig. 5

(a) Dynamic light scattering (DLS) size distribution curve of B.CNDs dissolved in water. (b) the zeta potential curve of B.CNDs in water shows a negative charge surface.

Fig. 6

(a) XPS spectra of as-synthesized B.CNDs shows it consists mainly of carbon, nitrogen and oxygen. (b) High-resolution XPS of C 1s. (c) High-resolution XPS of N 1s. (d) High-resolution XPS of O 1s.

Fig. 7

Photograph images of the B.CNDs depressed in water (a) normal daylight and (b) normal daylight under UV light at 365 nm.

Fig. 8

Optical properties of the B.CNDs in in high purity water (a) Excitation-emission color map (b) Optical absorption spectrum, (2) normalized spectrum of PL excitation (400 nm), and PL emission (450 nm).

Fig. 9

(a) Photoluminescence spectrum of the B.CNDs with increasing of excitation wavelengths from 300 to 420 nm (b) normalized PL spectra of the B.CNDs. (c) Photostability of the B.CNDs after continued irradiation with a 55 W xenon lamp for 60 min at wavelength of 365 nm. (d) Excitation-emission relation for both UV and blue region of B.CNDs.