镍掺杂石墨相氮化碳的熔盐辅助微波法制备及光催化固氮性能

doi:10.7503/cjcu20170223

摘要/Abstract

摘要：

采用熔盐辅助微波法制备了可见光下具有优越光催化固氮性能的镍掺杂石墨相氮化碳. 采用X射线衍射(XRD)、扫描电镜(SEM)、氮气吸附-脱附、紫外-可见光谱(UV-Vis)、 X射线光电子能谱(XPS)、荧光光谱(PL)、程序升温脱附(TPD)和电化学阻抗谱(EIS)等手段对催化剂进行了表征. 结果表明, 熔盐辅助微波法使氮化碳催化剂从层状结构变为纳米颗粒状, 并相互紧密堆积形成很多二次孔, 增大了催化剂的比表面积. 同时, 在催化剂制备过程中, 熔盐包裹住了催化剂原料, 避免了镍离子与氧气的接触, 使镍离子呈现出活性的Ni(Ⅰ)—N态和非活性的氧化镍态2种存在形式. Ni(Ⅰ)—N作为反应活性中心, 能有效捕获光电子, 提高电子-空穴分离效率, 促进电子从掺杂镍离子向N₂分子的迅速转移, 实现氮气分子的活化, 进而提高固氮性能.

关键词: 熔盐辅助微波合成, 石墨相氮化碳, Ni—N活性位, 光催化固氮

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:

曲晓钰, 胡绍争, 李萍, 王菲, 赵艳锋, 王琼. 镍掺杂石墨相氮化碳的熔盐辅助微波法制备及光催化固氮性能. 高等学校化学学报, 2017, 38(12): 2280.

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^†. Chem. J. Chinese Universities, 2017, 38(12): 2280.

图/表 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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