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采用基于色散修正的平面波超软赝势方法研究了二硫化钼/石墨烯异质结的界面结合作用及其对电荷分布和带边电位的影响. 研究表明二硫化钼与石墨烯之间可以形成范德瓦耳斯力结合的稳定堆叠结构. 通过能带结构计算，发现二硫化钼与石墨烯的耦合导致二硫化钼成为n型半导体，石墨烯转变成小带隙的p型体系. 并通过电子密度差分图证实了界面内二硫化钼附近聚集负电荷，石墨烯附近聚集正电荷，界面内形成的内建电场可以抑制光生电子-空穴对的复合. 石墨烯的引入可以调制二硫化钼的能带，使其导带底上移至-0.31 eV，提高了光生电子还原能力，有利于光催化还原反应.To improve the efficiency of water-splitting, a key way is to select suitable semiconductor or design semiconductor based heterostructure to enhance charge separation of photogenerated h+-e- pairs. It is possible for a two-dimensional (2D) heterostructure to show more efficient charge separation and transfer in a short transport time and distance. Among numerous heteromaterials, the 2D layered MoS2 has become a very valuable material in photocatalysis-driven field due to the appropriate electronic structure, peculiar thermal and chemical stability, and low-cost preparation. To couple with MoS2, layered graphene will be an ideal candidate due to extremely high carrier mobility, large surface area, and good lattice match with MoS2. At present, a lot of researches focus on the synthesis and modification of MoS2/graphene heterostructure. However, it is hard to detect directly the weak interaction between MoS2 and graphene through the experiment. Here, an effective structural coupling approach is described to modify the photoelectrochemical properties of MoS2 sheet by using the stacking interaction with graphene, and the corresponding effects of interface cohesive interaction on the charge redistribution and the band edge of MoS2/graphene heterostructure are investigated by using the planewave ultrasoft pseudopotentials in detail. Three dispersion corrections take into account the weak interactions between MoS2 and graphene, resulting in an equilibrium layer distance d of about 0.34 nm for the MoS2/graphene heterostructure. The results indicate that the lattice mismatch between monolayer MoS2 and graphene is low in contact and a van der Waals interaction forms in interface. Further, it is identified by analyzing the energy band structures and the threedimensional charge density difference that in the MoS2 layer in interface there appears an obvious electron accumulation, which presents a new n-type semiconductor for MoS2 and a p-type graphene with a small band gap ( 0.1 eV). In addition, Mo 4d electrons in the upper valence band can be excited to the conduction band under irradiation. And the orbital hybridization between Mo 4d and S 3p will cause photogenerated electrons to transfer easily from the internal Mo atoms to the external S atoms. The build-in internal electric field from graphene to MoS2 will facilitate the transfer and separation of photogenerated charge carriers after equilibrium of the MoS2/graphene interface. It is identified that the hybridization between the two components induces a decrease of band gap and then an increase of optical absorption of MoS2 in visible-light region. It is noted that their energy levels are adjusted with the shift of their Fermi levels based on our calculated work function. The results show that the Fermi level of monolayer MoS2 is located under the conduction band and more positive than that of graphene. After the equilibrium of the MoS2/graphene interface, the Fermi level shifts toward the negative direction for MoS2 and the positive direction for graphene, respectively, until they are equal. At this time, the conduction band and valence band of MoS2 are pulled to the negative direction a little, and then form a slightly upward band bending close to the interface between MoS2 and graphene. Combining the decrease of the band gap of MoS2 in heterostructure, the potential of the conduction band minimum of MoS2 in heterostructure will increase to -0.31 eV, which enhances its reduction capacity. A detailed understanding of the microcosmic mechanisms of interface interaction and charge transfer in this system can be helpful in fabricating 2D heterostructure photocatalysts.
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Keywords:
- heterostructure photocatalysis /
- MoS2 /
- band modulation /
- first-principles
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[1] Li Y, Wang H, Xie L, Liang Y, Hong G, Dai H 2011 J. Am. Chem. Soc. 133 7296
[2] Bernardi M, Palummo M, Grossman J C 2013 Nano Lett. 13 3664
[3] Britnell L, Ribeiro R M, Eckmann A, Jalil R, Belle B D, Mishchenko A, Kim Y J, Gorbachev R V, Georgiou T, Morozov S V, Grigorenko A N, Geim A K, Casiraghi C, Neto A H C, Novoselov K S 2013 Science 340 1311
[4] Patil S, Harle A, Sathaye S, Patil K 2014 Cryst. Eng. Comm. 16 10845
[5] Nrskov J K, Bligaard T, Logadottir A, Kitchin J R, Chen J G, Pandelov S, Stimming U 2005 J. Electrochem. Soc. 152 J23
[6] Karunadasa H I, Montalvo E, Sun Y J, Majda M, Long J R, Chang C J 2012 Science 335 698
[7] Garrett B R, Polen S M, Click K A, He M F, Huang Z J, Hadad C M, Wu Y Y 2016 Inorg. Chem. 55 3960
[8] Cheah A J, Chiu W S, Khiew P S, Nakajima H, Saisopa T, Songsiriritthigul P, Radiman S, Hamid M A A 2015 Catal. Sci. Technol. 5 4133
[9] Weng B, Zhang X, Zhang N, Tang Z R, Xu Y J 2015 Langmuir 31 4314
[10] Chen Y J, Tian G H, Shi Y H, Xiao Y T, Fu H G 2015 Appl. Catal. B: Environ. 164 40
[11] Meng F, Li J, Cushing S K, Zhi M, Wu N 2013 J. Am. Chem. Soc. 135 10286
[12] Zhao M, Chang M J, Wang Q, Zhu Z T, Zhai X P, Zirak M, Moshfegh A Z, Song Y L, Zhang H L 2015 Chem. Commun. 51 12262
[13] Liu Z F, Liu Q, Huang Y, Ma Y F, Yin S G, Zhang X Y, Sun W, Chen Y S 2008 Adv. Mater. 20 3924
[14] Fu Y S, Wang X 2011 Ind. Eng. Chem. Res. 50 7210
[15] Yun H N, Iwase A, Kudo A, Amal R 2010 J. Phys. Chem. Lett. 1 2607
[16] Xu T G, Zhang L W, Cheng H Y, Zhu Y F 2011 Appl. Catal. B: Environ. 101 382
[17] Li H L, Yu K, Li C, Tang Z, Guo B J, Lei X, Fu H, Zhu Z Q 2015 Sci. Rep. 5 18730
[18] Chang K, Mei Z W, Wang T, Kang Q, Ouyang S X, Ye J H 2014 ACS Nano 8 7078
[19] Kumar N A, Dar M A, Gul R, Baek J B 2015 Mater. Today 18 286
[20] Min S X, Lu G X 2012 J. Phys. Chem. C 116 25415
[21] Carraro F, Calvillo L, Cattelan M, Favaro M, Righetto M, Nappini S, P I, Celorrio V, Fermn D J, Martucci A, Agnoli S, Granozzi G 2015 ACS Appl. Mater. Interfaces 7 25685
[22] Deng Z H, Li L, Ding W, Xiong K, Wei Z D 2015 Chem. Commun. 51 1893
[23] Jaramillo T F, Jrgensen K P, Bonde J, Nielsen J H, Horch S, Chorkendorff I B 2007 Science 317 100
[24] Jin C J, Rasmussen F A, Thygesen K S 2016 J. Phys. Chem. C 120 1352
[25] Aziza Z B, Henck H, Felice D D, Pierucci D, Chaste J, Naylor C H, Balan A, Dappe Y J, Johnson A T C, Ouerghi A 2016 Carbon 110 396
[26] Ebnonnasir A, Narayanan B, Kodambaka S, Ciobanu C V 2014 Appl. Phys. Lett. 105 031603
[27] Vanderbilt D 1990 Phys. Rev. B 41 7892
[28] Tkatchenko A, Scheffler M 2009 Phys. Rev. Lett. 102 073005
[29] Grimme S 2006 J. Comput. Chem. 27 1787
[30] Ortmann F, Bechstedt F, Schmidt W G 2006 Phys. Rev. B 73 205101
[31] Monkhorst H J, Pack J D 1976 Phys. Rev. B 13 5188
[32] Segall M D, Lindan P J D, Probert M J, Pickard C J, Hasnip P J, Clark S J, Payne M C 2002 J. Phys: Condens. Matter 14 2717
[33] Wu M S, Xu B, Liu G, Ouyang C Y 2012 Acta Phys. Sin. 61 227102 (in Chinese) [吴木生, 徐波, 刘刚, 欧阳楚英 2012 61 227102]
[34] Jiang J W 2015 Front. Phys. 10 287
[35] Pierucci D, Henck H, Avila J, Balan A, Naylor C H, Patriarche G, Dappe Y J, Silly M G, Sirotti F, Johnson A T, Asensio M C, Ouerqhi A 2016 Nano Lett. 16 4054
[36] Zhu J D, Zhang J C, Hao Y 2016 Jpn. J. Appl. Phys. 55 080306
[37] Ma Y D, Dai Y, Guo M, Niu C W, Huang B B 2011 Nanoscale 3 3883
[38] Liu J J 2015 J. Phys. Chem. C 119 28417
[39] Low J X, Cao S W, Yu J G, Wageh S 2014 Chem. Commun. 50 10768
[40] Mak K F, Lee C, Hone J, Shan J, Heinz T F 2010 Phys. Rev. Lett. 105 136805
[41] Huang Z Y, He C Y, Qi X, Yang H, Liu W L, Wei X L, Peng X Y, Zhong J X 2014 J. Phys. D: Appl. Phys. 47 75301
[42] Roy K, Padmanabhan M, Goswami S, Sai T P, Ramalingam G, Gaghavan S, Ghosh A 2013 Nat. Nanotechnol. 8 826
[43] Liu B, Wu L J, Zhao Y Q, Wang L Z, Cai M Q 2016 RSC Adv. 6 60271
[44] Kim J H, Hwang J H, Suh J, Tongay S, Kwon S, Hwang C C, Wu J Q, Park J Y 2013 Appl. Phys. Lett. 103 171604
[45] Xu Y, Schoonen M A A 2000 Am. Mineral. 85 543
[46] Ma X G, Lu B, Li D, Shi R, Pan C S, Zhu Y F 2011 J. Phys. Chem. C 115 16963
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