Combination Mechanism and Enhanced Visible-Light Photocatalytic Activity and Stability of CdS/g-C3N4 Heterojunctions

doi:10.1016/j.jmst.2016.04.008

Abstract

Abstract:

In this study, CdS/g-C₃N₄ (CSCN) heterojunctions were in situ fabricated with a large amount of CdS nanoparticles anchored on g-C₃N₄ nanosheets. A wet chemical method was developed for the first time to determine the actual content of CdS in CSCN composites. X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), high-resolution transmission electron microscopy (HRTEM) and UV-vis diffuse reflectance spectra (DRS) were employed to characterize the composition, structure and optical property of CSCN composites. Based on the isoelectric point (IEP) analysis of g-C₃N₄, a conclusion was obtained on the combination mechanism between CdS nanoparticles and g-C₃N₄ nanosheets. The photocatalytic activity of CSCN composites was much better than those of individual CdS and g-C₃N₄ for the degradation of azo dye Methyl Orange (MO) by 40min adsorption in the dark followed by 15min photocatalysis under visible light irradiation. After 5 cycles, CSCN composites still maintained high reactive activity with the MO degradation efficiency of 93.8%, exhibiting good photocatalytic stability. The Cd²⁺ concentration dissolved in the supernatant detected by atomic absorption spectroscopy (AAS) of CSCN composites was lower than that of pure CdS, implying that the photocorrosion of CdS could be suppressed via the combination with g-C₃N₄. Photoluminescence emission spectra (PL) results clearly revealed that the recombination of photogenerated electron-hole pairs in CSCN composites was effectively inhibited due to the formation of heterojunctions. Based on the band alignments of g-C₃N₄ and CdS, the possible photocatalytic mechnism was discussed.

Key words: CdS/g-C3N4, Heterojunctions, Photocatalytic stability, Photocatalytic mechanism

Xu Huanyan,Wu Licheng,Jin Liguo,Wu Kejia. Combination Mechanism and Enhanced Visible-Light Photocatalytic Activity and Stability of CdS/g-C₃N₄ Heterojunctions[J]. J. Mater. Sci. Technol., 2017, 33(1): 30-38.

Figures/Tables 13

Table 1 Estimated and actual CdS content, BET surface area and band gap of CSCN composites

Sample	Estimated CdS content (wt%)	Actual CdS content (wt%)	BET surface area (m²/g)	Band gap (eV)
g-C₃N₄	0	0	23.2	2.69
CSCN303	30	30.3	38.3	2.20
CSCN545	40	54.5	32.5	2.25
CSCN608	50	60.8	39.4	2.23
CSCN717	60	71.7	54.2	2.22
CSCN733	70	73.3	50.7	2.19
CSCN806	80	80.6	57.4	2.21
CSCN912	90	91.2	74.9	2.23
CdS	100	100	59.2	2.16

Fig.1 XRD patterns of g-C3N4, CdS and CSCN composites

Fig.2 FTIR spectra of g-C3N4, CdS, CSCN303 and CSCN733

Fig.3 TEM and HRTEM images of (a and b) g-C3N4, (c and d) CSCN303 and (e and f) CSCN733

Fig.4 Zeta potentials of g-C3N4 with different pHs

Fig.5 Schematic diagram of the combination process between g-C3N4 sheets and CdS NPs

Fig.6 (a) UV-vis DRS spectra of g-C3N4, CdS and CSCN composites, and (b) relationships between [F(R)?hυ]0.5 and photon energy (hυ)

Fig.7 Adsorption and photocatalytic degradation of MO over g-C3N4, CdS and CSCN composites

Fig.8 Adsorption and photocatalytic degradation of MO over g-C3N4, CdS and CSCN composites

Fig.9 Cycling tests on MO degradation using CSCN 733 as photocatalyst

Fig.10 PL spectra of g-C3N4, CdS and CSCN composites (CSCN303 and CSCN 733)

Fig.11 UV-Vis absorption spectra and color change (inset) of MO solution after different periods of the photocatalytic reaction over CSCN 733

Fig.12 Schematic diagram of the photocatalytic mechanism of CSCN heterojunctions

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Combination Mechanism and Enhanced Visible-Light Photocatalytic Activity and Stability of CdS/g-C₃N₄ Heterojunctions

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