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. 2024 Jun 13;14(27):19014-19028.
doi: 10.1039/d4ra02658f. eCollection 2024 Jun 12.

Graphitic carbon nitride supported silver nanoparticles (AgNPs/g-C3N4): synthesis and photocatalytic behavior in the degradation of 2,4-dichlorophenoxyacetic acid

Phung Thi Lan  1 , Nguyen Hoang Hao  2 , Nguyen Trung Hieu  1 , Nguyen Thi Thu Ha  1 , C Trevor Brown  3 , Le Minh Cam  1   4
Affiliations

Graphitic carbon nitride supported silver nanoparticles (AgNPs/g-C3N4): synthesis and photocatalytic behavior in the degradation of 2,4-dichlorophenoxyacetic acid

Phung Thi Lan et al. RSC Adv. .

Abstract

Graphitic carbon nitride supported silver nanoparticles (AgNPs/g-C3N4) with 1%, 3%, and 5% AgNPs were successfully synthesized by an "ex situ" method with ultrasound of a mixture of AgNP solution and g-C3N4. The AgNP solution was prepared by chemical reduction with trisodium citrate, and g-C3N4 was synthesized from the urea precursor. The supported nanoparticles were characterized by X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption (BET), Fourier transformation infrared (FTIR) and Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), photoluminescence spectroscopy (PL), electron paramagnetic resonance (EPR) and electrochemical impedance spectroscopy (EIS) Nyquist plots. The visible light-driven photocurrent measurement was performed by three on-off cycles of intermittent irradiation. The analyses show that AgNPs were evenly dispersed on g-C3N4, and have sizes ranging from 40 to 50 nm. The optical properties of the AgNPs/g-C3N4 material were significantly enhanced due to the plasmonic effect of AgNPs. The photocatalytic activity of catalysts was evaluated by 2,4-D degradation under visible light irradiation (λ > 420 nm). In the reaction conditions: pH 2.2; C o (2,4-D) 40 ppm; a m/v ratio of 0.5 g L-1, AgNPs/g-C3N4 materials exhibit superior photocatalytic activity compared to the pristine g-C3N4. The studies on the influence of free radicals and photogenerated holes, h+, show that ˙OH, O2˙-, and h+ play decisive roles in the photocatalytic activity of AgNPs/g-C3N4. The TOC result indicates the minimal toxicity of the by-products formed during the 2,4-D degradation. In addition, the AgNPs/g-C3N4 catalytic activity under direct sunlight irradiation was similar to that under artificial UV irradiation. Based on these results, a possible mechanism is proposed to explain the enhanced photocatalytic activity and stability of AgNPs/g-C3N4. Theoretical calculations on the interaction between 2,4-D and g-C3N4, Ag/g-C3N4 was also performed. The calculated results show that the adsorption of 2,4-D on Ag-modified g-C3N4 is significantly more effective compared to pristine g-C3N4.

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Conflict of interest statement

The authors declare that they have no conflicts of interest.

Figures

Fig. 1
Fig. 1. XRD patterns of g-C3N4, 3 wt% AgNPs/g-C3N4 and 5 wt% AgNPs/g-C3N4.
Fig. 2
Fig. 2. FT-IR spectra of pristine g-C3N4 and AgNPs/g-C3N4 samples.
Fig. 3
Fig. 3. Raman spectra of pure g-C3N4, and AgNPs/g-C3N4 composites.
Fig. 4
Fig. 4. Adsorption and desorption isotherms of N2 at 77 K of g-C3N4, 3 wt% AgNPs/g-C3N4 and 5 wt% AgNPs/g-C3N4.
Fig. 5
Fig. 5. UV-Vis DRS spectra of g-C3N4, 3 wt% AgNPs/g-C3N4 and 5 wt% AgNPs/g-C3N4 (a); plots of (αhv)1/2 against hv for g-C3N4, 3 wt% AgNPs/g-C3N4 and 5 wt% AgNPs/g-C3N4 (b).
Fig. 6
Fig. 6. PL spectra of the pristine g-C3N4 and AgNPs/g-C3N4 composites.
Fig. 7
Fig. 7. Electron paramagnetic resonance (EPR) of pristine g-C3N4 and AgNPs/g-C3N4 composites.
Fig. 8
Fig. 8. SEM images and Energy dispersive X-ray (EDX) mapping analysis of carbon, nitrogen, silver and mixed for (A) g-C3N4, (B) 3% AgNPs/g-C3N4 and (b) 5% AgNPs/g-C3N4.
Fig. 9
Fig. 9. TEM images of (a) g-C3N4 (b) 3% AgNPs/g-C3N4 and (c) 5% AgNPs/g-C3N4.
Fig. 10
Fig. 10. Relative concentrations of 2,4-D as a function of illumination time in g-C3N4 and in 3% and 5% AgNPs/g-C3N4. Illumination commenced at 30 minutes.
Fig. 11
Fig. 11. The dependence of ln(Co/C) vs. time (t) for photocatalytic degradation of 2,4-D over synthesized materials.
Fig. 12
Fig. 12. Stability study for the photocatalytic 2,4-D degradation by 3%AgNP/g-C3N4 under visible light illumination.
Fig. 13
Fig. 13. XRD of 3% AgNPs/g-C3N4 before and after cycles of 2,4-D photodegradation.
Fig. 14
Fig. 14. (A) The efficiency, H% of 2,4-D treatment as a function of initial concentration, Co (pH = 2.2; 210 minutes illumination). (B) The efficiency of 2,4-D treatment with 3% AgNPs/g-C3N4 at different pH (Co = 40 ppm; 210 min illumination). (C) The influence of m/v ratio on the 2,4-D treatment (Co = 40 ppm, pH = 2.2 and 3% AgNPs/g-C3N4).
Fig. 15
Fig. 15. TOC measurement during 2,4-D degradation process on 3%AgNPs/g-C3N4.
Fig. 16
Fig. 16. (a) Transient photocurrents, (b) EIS Nyquist plots under visible light irradiation.
Fig. 17
Fig. 17. The influence of O2˙−, ˙OH radicals and photogenerated holes h+ on the 2,4-D treatment (Co = 40 ppm, pH = 2.2, 3% AgNPs/g-C3N4, 16 mL of 0.1 M Na-EDTA, 16 mL of isopropyl alcohol (IPA) and 1 mL of AA).
Fig. 18
Fig. 18. 2,4-D photodegradation over 3% AgNPs/g-C3N4 and g-C3N4 under UV irradiation and direct sunlight irradiation.
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