Synergistic effect of ZnO/Ag2O@g-C3N4 based nanocomposites embedded in carrageenan matrix for dye degradation in water

Abstract

This research achieved success by synthesizing innovative nanocomposite composed of zinc oxide (ZnO), graphitic carbon nitride (g-C₃N₄) and silver oxide (Ag₂O) nanomaterials incorporated into a carrageenan matrix, thus creating an environmentally friendly and stable support structure. The synthesis process involved hydrothermal and chemical precipitation methods to create photocatalytic g-C₃N₄, ZnO, and Ag₂O nanocomposites. The success is evident through the characterization results, which unveiled distinctive peaks corresponding to Zn-O (590-404 cm^-1) and Ag-O (2072 cm^-1) stretching in the Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analyses, conclusively confirming the successful synthesis of g-C₃N₄, ZnO, Ag₂O, and their respective nanocomposites. Further validation through a scanning electron microscope coupled with an energy dispersive spectrometer (SEM-EDX) and elemental mapping affirmed the presence of Zn, O, Ag, C, and N. Additionally, transmission electron microscope (TEM) imaging unveiled the nanosheet morphology of g-C₃N₄, the nanorod structure of ZnO, and the spherical form of Ag₂O nanomaterials. ZnO and Ag₂O nanomaterials demonstrated a consistent 10-20 nm size range. To underscore their ability to harness visible light, the nanomaterials were excited at 380 nm, emitting visible light emission within the 400-450 nm range. The synthesized nanocomposites showcased outstanding adsorption and photocatalytic properties, achieving efficiency ranging from 80 % to 98 %, attributed to the synergistic interactions between the various components. These findings culminate in a confirmation of the research's success, validating the exceptional potential of these nanocomposites for various applications.

Keywords: Carrageenan; Graphitic carbon nitride; Nanocomposite; Nanomaterial; Photocatalysis; Visible light.

Graphical abstract

Fig. 1

(a) FTIR spectrum of synthesized g-C₃N₄ nanosheets, ZnO, Ag₂O and nanocomposites (b) carrageenan and their nanocomposites.

Fig. 2

(a) XRD patterns of Ag₂O, ZnO, g-C₃N₄ and composites, and (b) carrageenan nanocomposites.

Fig. 3

SEM and TEM micrographs and SEM-EDX/mapping for a) g-C₃N₄, ZnO, GZ, GZA and b) carrageenan nanocomposites.

Fig. 4

The energy band gap of different nanomaterials and nanocomposites estimated by the extrapolation of the linear part of (αhν)² versus hν plots.

Fig. 5

PL spectra for a) g-C₃N₄, ZnO (inset), GZ, Ag₂O, GA and GZA (inset) and b) g-C₃N_4-Carr, ZnO_Carr (inset), GZ_ Carr, Ag₂O_Carr, GA_ Carr and GZA_Carr (inset) at 380 nm excitation.

Fig. 6

Zeta potential of g-C₃N₄, ZnO and GZA and carrageenan nanocomposites.

Fig. 7

Photocatalytic degradation of a) CR, b) MV, c) MB, d) MG under visible light by g-C₃N₄, ZnO, Ag₂O, GA, GZ, GZA and carrageenan nanocomposites photocatalysts.

Fig. 8

Pseudo-1st-order rate kinetics for photocatalytic degradation of a) Congo red, b) methylene violet, c) methylene blue, and d) methylene green using the synthesized nanomaterials and nanocomposites.

Fig. 9

Pseudo-2nd-order rate kinetics for photocatalytic degradation of a) Congo red, b) methylene violet, c) methylene blue, and d) methylene green using the synthesized nanomaterials and nanocomposites.

Fig. 10

Reusability test of a) g-C₃N₄/ZnO/Ag₂O and b) g-C₃N₄/ZnO/Ag₂O_Carr on methylene blue, Congo red, methylene green and methyl violet for five successive recycling runs.

Fig. 11

Schematic representation of the photocatalytic mechanism of the g-C₃N₄/ZnO/Ag₂O (GZA) nanocomposite under visible light irradiation.