Photocatalytic Reduction of Re (VII) on Amorphous TiO2/g-C3N4 Derived from Different N Sources

doi:10.15541/jim20200133

Abstract

Abstract:

To clarify the effect of N sources on the photocatalytic reduction of Re (VII) in amorphous TiO₂/g-C₃N₄ (TCN) composites, g-C₃N₄ were prepared via a thermal decomposition of three precursors (Urea, Thiourea and Melamine). Three kinds of TCN composite photocatalysts were then prepared by recombining with amorphous TiO₂ separately. All three photocatalysts were characterized by differnent methods, and their differences in photocatalytic reduction of Re(VII) were compared in detail. The experimental results show that U-TCN using urea as the N source has more uniform appearance, the largest specific surface area (474 m²/g), and the most excellent light absorption performance, leading to its photocatalytic reduction efficiency (90%) for Re (VII) being significantly higher than T-TCN (20%) and M-TCN (15%). Transient photocurrent and electrochemical impedance (EIS) analyses prove that U-TCN exhibits the highest efficiency of photo-generated electron/holes separation. Electron paramagnetic resonance spectroscopy (EPR) analysis shows that U-TCN generates more hydroxyl radicals (?OH), so that there are stronger reducing ?CO₂ radicals produced by the reaction with formic acid, which is more conducive to the reduction of Re (VII). X-ray absorption spectra are employed to analyze the valence state and coordination environment of Ti element, which demonstrates an excellent photochemical stability of U-TCN. The study not only illustrates the effects of N sources on the photocatalytic performance of TCN composites, but also provides a promising photocatalyst for reduction and removal of Tc(VII) from waste water.

Key words: N sources, amorphous TiO₂/g-C₃N₄ composites, photocatalytic reduction, Re(VII)/Tc(VII)

CLC Number:

TQ174

WANG Xucong, DENG Hao, JIANG Zhongyi, YUAN Liyong. Photocatalytic Reduction of Re (VII) on Amorphous TiO₂/g-C₃N₄ Derived from Different N Sources[J]. Journal of Inorganic Materials, 2020, 35(12): 1340-1348.

Figures/Tables 12

Fig. 1 XRD patterns of M-CN, T-CN, U-CN, M-TCN, T-TCN and U-TCN samples

Fig. 2 FT-IR spectra of (a) M-CN, T-CN and U-CN samples, and (b) M-TCN, T-TCN and U-TCN samples

Fig. 3 SEM images of (a) U-CN, (b) U-TCN, (c) T-CN, (d) T-TCN, (e) M-CN and (f) M-TCN

Fig. 4 (a) N2 adsorption-desorption isotherms and (b) corresponding pore size distribution curves of M-TCN, T-TCN and U-TCN samples

Fig. 5 UV-Vis spectra of (a) M-CN, T-CN and U-CN samples and (b) M-TCN, T-TCN and U-TCN samples

Fig. 6 PL spectra of M-TCN, T-TCN, U-TCN and Am-TiO2

Fig. 7 Photocatalytic reduction and removal of Re(VII) using (a) U-CN, T-CN, M-CN, Am-TiO2 and (b) U-TCN, T-TCN and M-TCN composites under UV-Vis irradiation; (c) Linear fitting of Langmuir-Hinshelwood equation; The photodegradation of RhB using 0.4 g?L-1 (d) U-TCN, (e) T-TCN and (f) M-TCN under UV-Vis irradiation

Table 1 Kinetic parameters of photocatalytic reduction and removal of Re(VII) using TCN composites

Sample	Re(VII) removed	k/min^-1	R²
U-TCN	90%	0.0788	0.9524
T-TCN	20%	0.0063	0.9861
M-TCN	15%	0.0021	0.7954

Fig. 8 (a) Transient photocurrent responses and (b) EIS curves of U-TCN, T-TCN and M-TCN composites under UV-Vis irradiation

Fig. 9 EPR spectra of U-TCN, T-TCN and M-TCN composites (a) in the dark and (b) under UV-visible light irradiation

Fig. 10 (a) Ti K-edge XANES analysis and (b) EXAFS analysis for the Am-TiO2, U-TCN and U-TCN/Re

Table 2 Fitting parameters from the analysis of EXAFS data

Sample	Bond	N^a	R/nm^b	σ²/nm^{2 c}	R-factor^d
Am-TiO₂	Ti-O	1.2	0.198(3)	3×10^-6
	Ti-O	1.2	0.183(2)	0	0.001
	Ti-Ti	1.0	0.306(2)	6.5×10^-5
U-TCN	Ti-O	1.5	0.192(2)	2×10^-5
	Ti-O	1.0	0.184(3)	0	0.017
	Ti-Ti	1.7	0.312(2)	8.9×10^-5
U-TCN/Re	Ti-O	1.2	0.203(3)	1.0×10^-5
	Ti-O	1.2	0.188(2)	3×10^-6	0.017
	Ti-Ti	1.6	0.314(2)	9.8×10^-5

References 36

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Photocatalytic Reduction of Re (VII) on Amorphous TiO₂/g-C₃N₄ Derived from Different N Sources

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