ZnO-Modified g-C3N4: A Potential Photocatalyst for Environmental Application

Abstract

Solar energy-driven practices using semiconducting materials is an ideal approach toward wastewater remediation. In order to attain a superior photocatalyst, a composite of g-C₃N₄ and ZnO (GCN-ZnO) has been prepared by one-step thermal polymerization of urea and zinc carbonate basic dihydrate [ZnNO₃]₂·[Zn(OH)₂]₃. The GCN-ZnO0.4 sample showed an evolved morphology, increased surface area (116 m² g^-1), better visible light absorption ability, and reduced band gap in comparison to GCN-pure. The GCN-ZnO0.4 sample also showed enhanced adsorption and photocatalytic activity performance, resulting in an increased reaction rate value up to 3 times that of GCN-pure, which was attributed to the phenomenon of better separation of photogenerated charge carriers resulting because of heterojunction development among interfaces of GCN-pure and ZnO. In addition, the GCN-ZnO0.4 sample showed a decent stability for four cyclic runs and established its potential use for abatement of organic wastewater pollutants in comparison to GCN-pure.

Figure 1

XRD patterns of GCN–pure, ZnO, and synthesised GCN–ZnOx samples.

Figure 2

FTIR spectra of (a) ZnO, (b) GCN pure, (c) GCN–ZnO0.2, (d) GCN–ZnO0.4, and (e) GCN–ZnO0.6.

Figure 3

(a,b) SEM images and (c,d) HR-TEM images of GCN–pure and GCN–ZnO0.4.

Figure 4

(a,d) SEM image, (b,e) elemental mapping, and (c,f) EDX spectra of GCN–pure and GCN–ZnO0.4.

Figure 5

XPS spectrum of (a) GCNZn0.04 with the elemental composition shown in the inset and short scan for (b) C 1s, (c) N 1s, (d) O 1s, and (e) Zn 2p.

Figure 6

TGA curves of (a) GCN–ZnO0.2, (b) GCN–ZnO0.4, (c) GCN–ZnO0.6, (d) GCN–pure, and (e) ZnO.

Figure 7

Nitrogen adsorption–desorption isotherm of (a) GCN–ZnO0.4 and (b) GCN–pure. (c) BET adsorption isotherm of GCN–ZnO0.4 and GCN–pure.

Figure 8

(a) UV–vis diffused absorbance spectra and (b) band gaps of ZnO, GCN–pure, and GCN–ZnOx samples.

Figure 9

(a) Comparison of photocatalytic activity. (b) ln(C₀/C(t)) for MB degradation as a function of visible light irradiation time for GCN–ZnOx samples, GCN–pure, and ZnO.

Figure 10

UV–vis absorbance spectra of MB dye using (a) GCN–ZnO0.2, (b) GCN–ZnO0.4, (c) GCN–ZnO0.6, (d) GCN–pure, and (e) ZnO.

Figure 11

(a) Comparison of the degradation efficiency. (b) ln(C₀/C(t)) as a function of visible light irradiation time for MB degradation under different pH conditions using GCN–ZnO0.4. (c) Relation between the surface zeta potential value of GCN–ZnO0.4 and the degradation percentage of the MB dye at different pH values. (d) Zeta potential of GCN–ZnO0.4 at different pH values.

Figure 12

Recyclability experiment of photocatalytic degradation of MB dye using the GCN–ZnO0.4 sample.

Figure 13

Influence of hole, electron, ^•OH, and O₂^•– scavengers on the degradation of MB dye after 120 min of visible light irradiation.

Figure 14

Proposed photocatalytic mechanism showing the separation and transfer of photogenerated electron–hole pairs over the GCN–ZnO photocatalyst under visible light irradiation.

Figure 15

Schematic illustration of the synthesis of GCN–ZnOx samples.