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Acta Physico-Chimica Sinca  2016, Vol. 32 Issue (10): 2488-2494    DOI: 10.3866/PKU.WHXB201606222
ARTICLE     
Band Structure Modulation and Carrier Transport Process of g-C3N4 Doped with Alkali Metals
Lin ZHU1,2,Xin-Guo MA1,2,*(),Na LIU1,Guo-Wang XU1,2,Chu-Yun HUANG1,2,*()
1 School of Science, Hubei University of Technology, Wuhan 430068, P. R. China
2 Hubei Collaborative Innovation Center for High-efficiency Utilization of Solar Energy, Hubei University of Technology, Wuhan 430068, P. R. China
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Abstract  

The effects of Li, Na, and K alkali metal ions on the band structures and carrier transfer of graphitic carbon nitride (g-C3N4) are investigated using the plane-wave ultrasoft pseudopotential method. The generalized gradient approximation and local density approximation are used to calculate total energies of six adsorption configurations. The three alkali ions all tend to adsorb on the large central cavity (F position) in g-C3N4 layers. The calculated band structures and work function values indicate that the interface charge balance of the n-type Schottky junctions formed between the alkali metal ions and g-C3N4 induces the total band edge potential of g-C3N4 to shift down by 1.52 V (Li), 1.07 V (Na), and 0.86 V (K). The incorporation of K ion adjusts the valence and conduction bands to more appropriate redox potentials than those of pure g-C3N4, and increases the distribution of the HOMO and LOMO of g-C3N4, which helps to improve the mobility of carriers. Meanwhile, the non-coplanar HOMO and LOMO favor the separation of electrons and holes.



Key wordsPhotocatalysis      g-C3N4      Band structure      Carrier transport     
Received: 18 March 2016      Published: 22 June 2016
MSC2000:  O649  
Fund:  The project was supported by the National Natural Science Foundation of China(51102150,51472081);Foundation of Hubei University of Technology for High-level Talents, China(GCRC13014);Development Founds of Hubei Collaborative Innovation Center, China(HBSKFZD2014003,HBSKFZD2014011,HBSKFZD2015004);and Students Research Fund of Hubei Collaborative Innovation Center, China(HBSDY201511)
Corresponding Authors: Xin-Guo MA,Chu-Yun HUANG     E-mail: maxg2013@sohu.com;chuyunh@163.com
Cite this article:

Lin ZHU,Xin-Guo MA,Na LIU,Guo-Wang XU,Chu-Yun HUANG. Band Structure Modulation and Carrier Transport Process of g-C3N4 Doped with Alkali Metals. Acta Physico-Chimica Sinca, 2016, 32(10): 2488-2494.

URL:

http://www.whxb.pku.edu.cn/10.3866/PKU.WHXB201606222     OR     http://www.whxb.pku.edu.cn/Y2016/V32/I10/2488

Fig 1 Top views of the six doped configurations of alkali metal adsorbed on g-C3N4 The letters A-F represent the absorption positions of alkali metal atom,respectively.
Doping model Formation energy/eV
doped Li doped Na doped K
A -2.652 -0.376 2.130
B -1.919 -0.022 2.205
C -1.585 1.036 4.475
D -2.464 -0.517 2.163
E -2.386 -0.478 1.768
F -4.477 -4.144 -3.603
Table 1 Adsorption energies of six different adsorption configurations (A-F) for doped g-C3N4 with three alkali metals
Doped elementDistance/nmMulliken population/e
M―N1M―N2M―N3M―N4M―N5M―N6N1N2N3N4N5N6bridge NM
g-C3N4-------0.37-0.37-0.36-0.38-0.38-0.26-0.28-
Li0.2340.2340.2400.2410.2410.240-0.47-0.47-0.45-0.48-0.48-0.45-0.271.09
Na0.2370.2370.2410.2420.2420.241-0.45-0.45-0.44-0.46-0.46-0.44-0.281.75
K0.2420.2420.2420.2430.2430.242-0.47-0.47-0.47-0.49-0.49-0.47-0.282.26
Table 2 Distances between the alkali metal ion M and its neighboring six N atoms and the Milliken population of alkali metal ion M and its neighboring six N atoms for adsorption configuration F
Method Band gap/eV
g-C3N4 doped Li doped Na doped K
GGA-PW91 1.27 0.74 0.78 0.82
LDA-CAPZ 1.11 0.59 0.61 0.65
experimental 2.70 10 - - 2.52-2.65 30
calculated31 1.1 - 0.84 0.98
calculated32 1.0 - - -
Table 3 Band gap of g-C3N4before and after doping
Fig 2 Work functions in the vertical direction of g-C3N4(001) plane (a) pure g-C3N4; (b) Li doped g-C3N4; (c) Na doped g-C3N4; (d) K doped g-C3N4
Fig 3 Valence band and conduction band potentials for pure 2-C3N4 and alkali metal doped 2-C3N4
Fig 4 Partial density of states (PDOS) for pure g-C3N4 and alkali metal doped 2-C3N4
Fig 5 Distribution of LUMO and HOMO (a) the LUMO of pure g-C3N4; (b) the HOMO of pure g-C3N4;(c) the LUMO of K doped g-C3N4; (d) the HOMO of K doped g-C3N4. The upper green part represents LUMO and the lower red part represents HOMO. color online
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