Molten Salt-assisted Microwave Synthesis and Nitrogen Photofixation Ability of Nickel Doped Graphitic Carbon Nitride†

doi:10.7503/cjcu20170223

Abstract

Abstract:

In this work, nickel doped g-C₃N₄ was synthesized via a novel molten salt-assisted microwave process. X-ray diffraction(XRD), N₂ adsorption, UV-Vis spectroscopy, scanning electron microscopy(SEM), temperature-programmed desorption(TPD), X-ray electron spectroscopy(XPS), photoluminescence spectroscopy(PL) and electrochemical impedance spectroscopy(EIS) were used to characterize the prepared catalysts. The results show that the molten salt-assisted microwave process changes the morphology of prepared catalyst from layered structure to nanoparticles. These nanoparticles are closely packed with each other to form many secondary pores, which increases the catalyst surface area. Besides, due to that the raw materials are wrapped by the liquid-phase molten salt during the microwave process and can not be in contact with oxygen, Ni is not only present as inactive oxide but inserts at the interstitial position to form active Ni(Ⅰ)—N bonds. This Ni(Ⅰ)—N active sites can activate N₂ molecules, promote separation rate of electrons and holes, and accelerate interfacial charge transfer from catalysts to N₂ molecules, thus significantly improving the nitrogen photofixation ability.

Key words: Molten salt assisted microwave synthesis, g-C₃N₄, Ni(Ⅰ)—N active site, N₂ photofixation

TrendMD:

QU Xiaoyu, HU Shaozheng, LI Ping, WANG Fei, ZHAO Yanfeng, WANG Qiong. Molten Salt-assisted Microwave Synthesis and Nitrogen Photofixation Ability of Nickel Doped Graphitic Carbon Nitride^†[J]. Chem. J. Chinese Universities, 2017, 38(12): 2280.

Figures/Tables 12

Fig.1 Control experiment result of N2 photofixation reaction

Fig.2 NH4+ production ability over as-prepared catalysts

Fig.3 Influence of pH value of reaction system on the N2 photofixation ability of CN(MS)

Fig.4 NH4+ production ability of NiCN(MS) using AgNO3 as the electron scavenger(A) or in aprotic solvents DMF and DMSO(B)

Fig.5 pH value change of NiCN(MS) suspension during the nitrogen photofixation process

Fig.6 Comparison of NH4+ production ability(A) and stability(B) of NiCN(MS) and nitrogen vacancies doped g-C3N4

Fig.7 SEM images of CN(MV)(A), NiCN(MV)(B), CN(MS)(C) and NiCN(MS)(D)

Fig.8 XRD patterns(A), UV-Vis spectra(B), plots of the transformed Kubelka-Munk function versus the energy of light(C) and N2 adsorption-desorption isotherms(D) of as-prepared catalystsa. CN(MV); b. CN(MS); c. NiCN(MV); d. NiCN(MS).

Fig.9 XPS of as prepared catalysts in the region of C1s(A), N1s(B), Ni2p(C) and VB XPS(D)(A), (B), (D) a. CN(MV); b. NiCN(MS). (C) a. NiCN(MV); b. NiCN(MS); c. NiCN(MS)-1;d. NiCN(MS)-2; e. NiCN(MS)-3.

Fig.10 N2-TPD of as-prepared catalysts(A) and NH4+ production ability of fresh and annealed NiCN(MS)as a function of the ratio of peak area of Ni+ to total Ni in the XPS result(B)

Fig.11 EIS(A) and PL(B) spectra of as-prepared catalysts, the comparison of PL intensity of fresh and annealed NiCN(MS) under N2 atmosphere(C) and the comparison of PL intensity of CN(MV) and NiCN(MS) under Ar and N2 atmospheres(D)(A), (B) a. NiCN(MS); b. NiCN(MV); c. CN(MS); d. CN(MV). (C) a. NiCN(MS); b. NiCN(MS)-1; c. NiCN(MS)-2; d. NiCN(MS)-3; (D) a. CN(MV); b. NiCN(MS).

Scheme 1 Possible nitrogen photofixation process over g-C3N4 with Ni(Ⅰ)—N active cites

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