物理化学学报 >> 2020, Vol. 36 >> Issue (7): 1905056.doi: 10.3866/PKU.WHXB201905056

所属专题: 纳米复合材料

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氨氛围热处理g-C3N4控制N空位浓度提高光催化制氢性能

黄娟娟,杜建梅,杜海威*(),徐更生,袁玉鹏*()   

  • 收稿日期:2019-05-15 录用日期:2019-06-28 发布日期:2020-03-21
  • 通讯作者: 杜海威,袁玉鹏 E-mail:haiwei.du@ahu.edu.cn;yupengyuan@ahu.edu.cn
  • 基金资助:
    国家自然科学基金(551872003);国家自然科学基金(51572003);安徽省自然科学基金(1908085J21);安徽省自然科学基金(1908085QB83)

Control of Nitrogen Vacancy in g-C3N4 by Heat Treatment in an Ammonia Atmosphere for Enhanced Photocatalytic Hydrogen Generation

Juanjuan Huang,Jianmei Du,Haiwei Du*(),Gengsheng Xu,Yupeng Yuan*()   

  • Received:2019-05-15 Accepted:2019-06-28 Published:2020-03-21
  • Contact: Haiwei Du,Yupeng Yuan E-mail:haiwei.du@ahu.edu.cn;yupengyuan@ahu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(551872003);the National Natural Science Foundation of China(51572003);the Anhui Provincial Natural Science Foundation, China(1908085J21);the Anhui Provincial Natural Science Foundation, China(1908085QB83)

摘要:

热处理氧化石墨相氮化碳(g-C3N4)材料产生氮缺陷、提升其光催化制氢性能的研究备受关注,但其N空位浓度高且不可控、一定程度破坏g-C3N4晶体结构,降低g-C3N4的结晶度,导致光生电子-空穴对复合率高,致使其光催化制氢效率较低。基于上述问题,本研究以二氰二胺为前驱体制备了g-C3N4,与不同含量的尿素混合,在空气中加热快速热处理,通过X-射线衍射仪(XRD)、扫描电子显微镜(SEM)等测试手段,对其物相组成、微观形貌、光学吸收等进行了表征,在可见光条件下对样品进行了光催化制氢性能测试,研究了尿素的加入对热处理后g-C3N4材料的N空位浓度、结晶度及光催化制氢性能的影响。研究表明,尿素的加入降低了N空位的浓度,且提升了其结晶度。在优化的尿素添加量下,g-C3N4的可见光光催化制氢速率为6.5 μmol·h-1,是没有添加尿素处理的样品的3倍。该研究结果表明,利用尿素原位分解产生的NH3,可以抑制g-C3N4热处理过程中氮原子的氧化程度、实现调控N空位浓度,同时提高了结晶度,最终提升了其光催化制氢性能。

关键词: 半导体, 氮化碳, 水分解, 氨气, N空位

Abstract:

Graphite phase carbon nitride (g-C3N4) has shown excellent potential when applied to photocatalytic hydrogen (H2) generation upon exposure to visible light. However, the photocatalytic activity during hydrogen generation remains very low because of the high recombination rate of photogenerated electron-hole pairs and poor conductivity. Of the various strategies to improve H2 generation efficiency, N vacancies have proven to be effective at increasing the photocatalytic performance of g-C3N4. However, creating a N vacancy is primarily dependent on the post-heating of g-C3N4 in air at an elevated temperature, which generates a high concentration of N vacancies and consequent decreased crystallinity of g-C3N4. Thus, as-produced g-C3N4 offers low photocatalytic efficiency owing to the high recombination rate of photogenerated electron-hole pairs. Currently, controlling the concentration of N vacancy in g-C3N4 is an immense challenge. Herein, we report an effective means of achieving controllable N vacancies in g-C3N4 via urea in-situ generated NH3 at an elevated temperature. Specifically, g-C3N4 was first prepared with dicyandiamide as a precursor and subjected to rapid post-thermal treatment at 650 ℃ in a tubular furnace for 10 min, in which a desired amount of urea was mixed with g-C3N4 as the source material for NH3. X-ray diffraction analysis showed increased crystallinity and an unchanged crystal structure as compared to pristine g-C3N4. X-ray photoelectron spectroscopy and elemental analysis verified the reduced levels of N-vacancy concentration with urea added as the NH3 source when compared to the g-C3N4 post-heated in air without the addition of urea. In addition, UV-Vis spectra displayed an increased visible light absorption due to the generated N vacancies. Moreover, the specific surface area of g-C3N4 was progressively enlarged with an increase in the amount of urea added. The high crystallinity, low N-vacancy concentration, increased light absorption, and enlarged surface area translated into markedly increased photocatalytic H2 generation. The highest H2 generation rate from the optimized added amount of urea was 6.5 μmol·h-1, which was three times higher than that when using a g-C3N4 sample thermally treated without urea addition. The H2 generation enhancement was also the result of the increased separation efficiency of photogenerated electron-hole pairs as exemplified by the significantly decreased photoluminescence spectra and large transient photocurrent. The results of this study demonstrate the simultaneous production of highly crystalline g-C3N4 and controllable creation of N vacancy by in-situ generated NH3 through thermal decomposition of urea. This study reveals the immense potential of NH3 at controlling the N-vacancy concentration of g-C3N4 for increased photocatalytic H2 generation.

Key words: Semiconductor,

可视化

0

摘要:

热处理氧化石墨相氮化碳(g-C3N4)材料产生氮缺陷、提升其光催化制氢性能的研究备受关注,但其N空位浓度高且不可控、一定程度破坏g-C3N4晶体结构,降低g-C3N4的结晶度,导致光生电子-空穴对复合率高,致使其光催化制氢效率较低。基于上述问题,本研究以二氰二胺为前驱体制备了g-C3N4,与不同含量的尿素混合,在空气中加热快速热处理,通过X-射线衍射仪(XRD)、扫描电子显微镜(SEM)等测试手段,对其物相组成、微观形貌、光学吸收等进行了表征,在可见光条件下对样品进行了光催化制氢性能测试,研究了尿素的加入对热处理后g-C3N4材料的N空位浓度、结晶度及光催化制氢性能的影响。研究表明,尿素的加入降低了N空位的浓度,且提升了其结晶度。在优化的尿素添加量下,g-C3N4的可见光光催化制氢速率为6.5 μmol·h-1,是没有添加尿素处理的样品的3倍。该研究结果表明,利用尿素原位分解产生的NH3,可以抑制g-C3N4热处理过程中氮原子的氧化程度、实现调控N空位浓度,同时提高了结晶度,最终提升了其光催化制氢性能。

关键词: 半导体, 氮化碳, 水分解, 氨气, N空位

Abstract:

Graphite phase carbon nitride (g-C3N4) has shown excellent potential when applied to photocatalytic hydrogen (H2) generation upon exposure to visible light. However, ontrolling the concentration of N vacancy in g-C3N4 is an immense challenge. Herein, we report an effective means of achieving controllable N vacancies in g-C3N4 via urea in-situ generated NH3 at an elevated temperature. Specifically, g-C3N4 was first prepared with dicyandiamide as a precursor and subjected to rapid post-thermal treatment at 650 ℃ in a tubular furnace for 10 min, in which a desired amount of urea was mixed with g-C3N4 as the source material for NH3. X-ray diffraction analysis showed increased crystallinity and an unchanged crystal structure as compared to pristine g-C3N4. X-ray photoelectron spectroscopy and elemental analysis verified the reduced levels of N-vacancy concentration with urea added as the NH3 source when compared to the g-C3N4 post-heated in air without the addition of urea. In addition, UV-Vis spectra displayed an increased visible light absorption due to the generated N vacancies. Moreover, the specific surface area of g-C3N4 was progressively enlarged with an increase in the amount of urea added. The high crystallinity, low N-vacancy concentration, increased light absorption, and enlarged surface area translated into markedly increased photocatalytic H2 generation. The highest H2 generation rate from the optimized added amount of urea was 6.5 μmol·h-1, which was three times higher than that when using a g-C3N4 sample thermally treated without urea addition. The H2 generation enhancement was also the result of the increased separation efficiency of photogenerated electron-hole pairs as exemplified by the significantly decreased photoluminescence spectra and large transient photocurrent. The results of this study demonstrate the simultaneous production of highly crystalline g-C3N4 and controllable creation of N vacancy by in-situ generated NH3 through thermal decomposition of urea. This study reveals the immense potential of NH3 at controlling the N-vacancy concentration of g-C3N4 for increased photocatalytic H2 generation.

Key words: Semiconductor, 2000 ontrolling the concentration of N vacancy in g-C3N4 is an immense challenge. Herein, we report an effective means of achieving controllable N vacancies in g-C3N4 via urea in-situ generated NH3 at an elevated temperature. Specifically, g-C3N4 was first prepared with dicyandiamide as a precursor and subjected to rapid post-thermal treatment at 650 ℃ in a tubular furnace for 10 min, in which a desired amount of urea was mixed with g-C3N4 as the source material for NH3. X-ray diffraction analysis showed increased crystallinity and an unchanged crystal structure as compared to pristine g-C3N4. X-ray photoelectron spectroscopy and elemental analysis verified the reduced levels of N-vacancy concentration with urea added as the NH3 source when compared to the g-C3N4 post-heated in air without the addition of urea. In addition, UV-Vis spectra displayed an increased visible light absorption due to the generated N vacancies. Moreover, the specific surface area of g-C3N4 was progressively enlarged with an increase in the amount of urea added. The high crystallinity, low N-vacancy concentration, increased light absorption, and enlarged surface area translated into markedly increased photocatalytic H2 generation. The highest H2 generation rate from the optimized added amount of urea was 6.5 μmol·h-1, which was three times higher than that when using a g-C3N4 sample thermally treated without urea addition. The H2 generation enhancement was also the result of the increased separation efficiency of photogenerated electron-hole pairs as exemplified by the significantly decreased photoluminescence spectra and large transient photocurrent. The results of this study demonstrate the simultaneous production of highly crystalline g-C3N4 and controllable creation of N vacancy by in-situ generated NH3 through thermal decomposition of urea. This study reveals the immense potential of NH3 at controlling the N-vacancy concentration of g-C3N4 for increased photocatalytic H2 generation.

Key words: Semiconductor, Carbon nitride, Photocatalytic water splitting, NH3, Nitrogen vacancy

MSC2000: 

  • O649