Novel furfural-complexed approach to synthesizing carbon-Doped ZnO with breakthrough photocatalytic efficacy

Abstract

Introduction: The efficiency of zinc oxide (ZnO) nanoparticles for environmental decontamination is limited by their reliance on ultraviolet (UV) light and rapid charge carrier recombination. Carbon doping has been proposed to address these challenges by potentially enhancing visible light absorption and charge separation.

Objectives: This study aims to introduce a novel, single-step synthesis method for carbon-doped ZnO (C-Z) nanoparticles, leveraging the decomposition of zinc nitrate hexahydrate and furfural under a nitrogen atmosphere to improve photocatalytic activity under visible light.

Methods: A series of C-Z variants (C-Z-1 to C-Z-5) and an undoped sample (ZnO-0) were synthesized. The influence of furfural on the synthesis process and doping mechanism was analyzed by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV-visible diffuse reflectance spectroscopy (DRS).

Results: XPS confirmed the integration of carbon within the ZnO matrix, and XRD indicated increased lattice dimensions owing to doping. DRS revealed bandgap narrowing, suggesting enhanced charge separation. Among the variants, C-Z-3 significantly outperformed the others, showing a 12-fold increase in the photocatalytic degradation rate of Rhodamine B compared to undoped ZnO.

Conclusion: The developed single-step synthesis method for C-Z nanoparticles represents a major advancement in materials engineering for ecological applications. The enhanced photocatalytic activity under visible light, as demonstrated by C-Z-3, underscores the potential of these nanoparticles for environmental decontamination.

Keywords: C-ZnO; Dye degradation; Furfural, Visible light; Photocatalysis.

Graphical abstract

Fig. 1

Proposed mechanism and possible pathways involved for the synthesis of the carbon doped ZnO nanoparticles (C-Z-1, C-Z-2, C-Z-3, C-Z-4, and C-Z-5).

Fig. 2

(a) XRD pattern of the ZnO-0, C-Z-1, C-Z-2, C-Z-3, C-Z-4, and C-Z-5, (b & c) enlarged XRD pattern of the ZnO-0, C-Z-1, C-Z-2, C-Z-3, C-Z-4, and C-Z-5.

Fig. 3

(a-d) SEM images of the C-Z-4 at different magnification, (e-g) surface mapping of the C-Z-4 nanoparticles.

Fig. 4

(a-e) TEM and HRTEM of the C-Z-4 at different magnification, (f-h) elemental mapping of the C-Z-4 nanoparticles, and (i) EDS spectra of the C-Z-4 nanoparticles.

Fig. 5

(a) Zn 2p XPS high resolution spectra of ZnO-0, C-Z-2, C-Z-3, C-Z-4, and C-Z-5, (b) O 1 s XPS high resolution spectra of ZnO-0, C-Z-2, C-Z-3, C-Z-4, and C-Z-5, (c) O 1 s fitted XPS spectra of ZnO-0, (d) O 1 s fitted XPS spectra of C-Z-2, (e) O 1 s fitted XPS spectra of C-Z-3, (f) O 1 s fitted XPS spectra of C-Z-4, (g) O 1 s fitted XPS spectra of C-Z-5, (h) C 1 s XPS high resolution spectra of C-Z-2, C-Z-3, C-Z-4, and C-Z-5, (i) C 1 s fitted XPS spectra of C-Z-2, (j) C 1 s fitted XPS spectra of C-Z-3, (k) C 1 s fitted XPS spectra of C-Z-4, and (l) C 1 s fitted XPS spectra of C-Z-5.

Fig. 6

(a) Raman spectra of the ZnO-0, C-Z-2, C-Z-3, C-Z-4, and C-Z-5, (b & c) enlarged Raman spectra of the ZnO-0, C-Z-1, C-Z-2, C-Z-3, C-Z-4, and C-Z-5.

Fig. 7

(a) Illustration of Photocatalytic Processes: A visual representation highlighting the mechanisms and effectiveness of photocatalysis, (b) Kinetic Graph of RhB Degradation: A plot depicting the rate of Rhodamine B (RhB) degradation under visible light, comparing the performance of various catalysts including ZnO-0 and C-Z series (C-Z-1 to C-Z-5), (c) Schematic Diagram of Photoexcited Charge Carriers: A detailed model showing the excitation, separation, and formation of reactive radicals in ZnO-0 and the C-Z series catalysts under visible light exposure, (d) Cyclic Degradation Efficiency Graph: A chart demonstrating the efficiency of C-Z-4 catalyst over multiple cycles of photocatalytic degradation.

Fig. 8

(a) Diffuse absorption spectra of ZnO-0 and C-Z series (C-Z-1 to C-Z-5) and (b) mobility band gap of ZnO-0 and C-Z series (C-Z-1 to C-Z-5).

Fig. 9

Displays the XPS valence band spectra for various samples. Part (a) showcases the spectra for ZnO-0, and part (b) presents the spectra for C-Z-2, C-Z-3, C-Z-4, and C-Z-5. Additionally, part (c) includes a schematic representation of the Density of States (DOS) for both ZnO-0 and the C-Z series samples.

Fig. 10

(a) Room temperature PL spectra of ZnO-0, C-Z-1, C-Z-2, C-Z-3, C-Z-4, and C-Z-5 and (b) I_DL/I_NBE ratio bar graph of the photocatalysts.