Ag-modified g-C₃N₄ with enhanced activity for the photocatalytic reduction of hexavalent chromium in the presence of EDTA under ultraviolet irradiation

ABSTRACT

The photocatalytic reduction of Cr⁶⁺ to Cr³⁺ in an aqueous solution, using 3 wt% Ag/g-C₃N₄ in the presence of ethylenediaminetetraacetic acid (EDTA), has been investigated here. The photocatalytic reduction of Cr⁶⁺ with pure g-C₃N₄ was very low. The addition of Ag and EDTA can significantly improve the photocatalytic reduction of Cr⁶⁺ using g-C₃N₄. In the presence of EDTA, the efficiency with Ag/g-C₃N₄ was better than those with Au/g-C₃N₄ and Cu/g-C₃N₄. With EDTA, the reduction rate constant increased from 0.0005 for pure g-C₃N₄ to 0.12 min⁻¹ for 3 wt% Ag/g-C₃N₄. By increasing the concentration of EDTA from 0 to 500 mg L⁻¹, the reduction efficiency of Cr⁶⁺ increased extremely, and the rate constant raised from 0.008 to 0.12 min⁻¹. The optimal EDTA concentration was 500 mg L⁻¹ for the photocatalyst Ag/g-C₃N₄. The Ag-EDTA complex may be reduced to metallic silver by the conduction band electrons of g-C₃N₄. The electron–hole recombination was significantly suppressed by the electron trapping of Ag. EDTA may act in by the formation of Cr³⁺-complex and the separation of Cr³⁺ from the g-C₃N₄ surface and by the valence band hole scavenger of g-C₃N₄. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), UV–Vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectra (PL) were used to characterize g-C₃N₄ and Ag/g-C₃N₄ nanoparticles. A possible mechanism for photocatalytic Cr⁶⁺ reduction has also been demonstrated.

GRAPHICAL ABSTRACT

KEYWORDS:

• Cr⁶⁺
• photocatalytic reduction
• Ag/g-C₃N₄
• EDTA
• UV irradiation

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article and its supplementary material. Raw data that supports the findings of this study are available from the corresponding author, upon reasonable request.

Additional information

Funding

The present research was partly supported by Grant-in-Aid for Scientific Research (C) 18K11909 from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.