石墨烯及其复合材料-(完整版)实用资料

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1、石墨烯及其复合材料 （完整版）实用资料(可以直接使用，可编辑 完整版实用资料，欢迎下载）Graphene is the first example of a truly 2D atomic crystal 1. It has unique electronic, optical and mechanical properties, and has also been widely investigated for catalysis, includ-ing electrocatalysis 2,3, photocatalysis 4 and conventional heteroge-neou

2、s catalysis 5 (Table 1. It has, in particular, been shown that perturbations to the perfect hexagonal graphene structure, such as dislocations, vacancies, edges (Fig. 1a, impurities (Fig. 1b and functional groups (Fig. 1c, readily modify the density of states in graphene and promote its catalytic pr

3、operties 69.Recently, other 2D atomic crystals, and their possible applications in catalysis, have attracted considerable interest 10. Many of these layered materials (for example MoS 2 and WS 2 have long been used as catalysts in their 3D forms. But the considerable changes in the electronic struct

4、ure of 2D mate-rials in comparison with their 3D bulk structures, as well as the possibility of chemical and structural modifications, offer new opportunities to use the 2D materials in many different chemical reactions.Recent advances in creating heterostructures based on 2D atomic crystals 11,12 a

5、lso provide new possibilities in catalysis. The ability to control the electronic state at the surface of the crystals through differences in work function 1316 (Fig. 1d, the creation of nanoreactors in the space between different 2D crystals 17,18 (Fig. 1e and the formation of sandwich structures b

6、ased on dif-ferent 2D crystals (Fig. 1f deliver unprecedented flexibility in controlling the chemical reactivity of such 3D stacks.I n this Review, we briefly overview recent advances in graphene catalysis before concentrating on the catalytic properties of other 2D materials and the catalytic prope

7、rties of heterogeneous systems, such as van der Waals heterostructures and combinations of 2D materials (Table 1. We analyse the new opportunities in catalysis provided by 2D crystals, and the various routes (Fig. 1 to tune their electronic states and corresponding active sites. We also go beyond th

8、e fundamental properties of these structures and discuss the potential of using such materials for future applications in catalysis.Catalysis with two-dimensional materials and their heterostructuresDehui Deng 1, K. S. Novoselov 2*, Qiang Fu 1, Nanfeng Zheng 3, Zhongqun Tian 3* and Xinhe Bao 1*Graph

9、ene and other 2D atomic crystals are of considerable interest in catalysis because of their unique structural and electronic properties. Over the past decade, the materials have been used in a variety of reactions, including the oxygen reduction reac-tion, water splitting and CO 2 activation, and ha

10、ve been shown to exhibit a range of catalytic mechanisms. Here, we review recent advances in the use of graphene and other 2D materials in catalytic applications, focusing in particular on the catalytic activity of heterogeneous systems such as van der Waals heterostructures (stacks of several 2D cr

11、ystals. We discuss the advantages of these materials for catalysis and the different routes available to tune their electronic states and active sites. We also explore the future opportunities of these catalytic materials and the challenges they face in terms of both fundamental understanding and th

12、e development of industrial applications.Graphene and its derivativesThe fascination with graphene-based catalysts originates from their unique structural and electronic properties. Graphene is a 2D atomic crystal consisting of a single layer of sp 2-hybridized carbon 1. It can be considered as a ba

13、sic structural element of various carbon allotropes, including 3D bulk graphite, 1D carbon nanotubes and 0D fullerenes 19. Such unique structural features endow graphene-based catalysts with the following advantages. First, they have a very high specific surface area (2,600 m 2 g 120, allowing a hig

14、h density of surface active sites. Second, they have excellent mechanical prop-erties 21, and therefore high stability and durability can be expected when graphene materials are used as either the catalyst or catalyst support. Third, they have high thermal and electric conductivity 22: the high ther

15、mal conductivity of graphene is beneficial to the con-duction and diffusion of the heat generated during catalytic reac-tions, especially for strongly exothermic reactions; the high electric conductivity of graphene makes the material a good candidate for electrocatalysts or electrocatalyst supports

16、. Fourth, they offer a set-up in which to combine theoretical research, model research and realistic applications in catalysis: it is possible to characterize the active sites on graphene by high-resolution imaging tools such as transmission electron microscopy (TEM and scanning tunnelling microscop

17、y even during the reaction process, which is challenging for traditional complex carbon materials such as activated carbon. The electronic structure of graphene, however, presents both challenges and opportunities for catalytic applications. The chal-lenges originate from the fact that graphene is a

18、 zero-overlap semi-metal with quasiparticles obeying a linear dispersion relation 19,23, resulting in the very low density of states at the Fermi level for typical doping levels (zero at the Dirac point. Therefore, pristine graphene is inert in catalysis. But the very same fact provides new opportun

19、ities, as the electronic properties of graphene can be easily tuned by introducing perturbations, offering possibilities to induce catalytic activity in the material.There are various routes to tune the electronic states of gra-phene. (1 The size effect: a bandgap is opened in the electronic1State K

20、ey Laboratory of Catalysis, iChEM, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road 457, Dalian 116023, China. 2School of Physics and Astronomy, University of Manchester, Oxford Road, M13 9PL Manchester, UK. 3State Key Laboratory of Physical Chemistry of Solid Surfac

21、es, iChEM, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.*e-mail: Konstantin.Novoselovmanchester.ac.uk ; zqtianxmu.edu ; xhbaodicp.ac spectrum of graphene nanoribbons owing to the quantum confine-ment effect, and the size of the gap w

22、ill increase when decreasing the size of the nanoribbon 24,25. (2 The layer effect: the electronic structure of graphene strongly depends on the number of layers 26. (3 The edge and defect effects: the electronic density of states can be strongly enhanced at the edges compared with the plane of gra-

23、phene, with armchair and zigzag edges also having different elec-tronic structure 24,27. I n addition, defects, such as vacancies and dislocations, can induce additional electronic states and also affect the electron transfer rate in graphene 2830. (4 The curvature effect: graphene, being only one a

24、tom thick, is extremely flexible and can be easily bent (intentionally or unintentionally. The bent or folded graphene will display distinct electronic states from those of the flat network of graphene 31,32. (5 The dopant and functional group effect: the introduction of dopants such as nitrogen 8,3

25、3,34, boron 35,36, phosphorus 37,38, sulfur 39,40 and even metal atoms 4143 into the gra-phene matrix can efficiently tune the electronic states of the 2D structure. In addition, the modification of graphene with different functional groups, such as those containing oxygen 4446, hydro-gen 47 and hal

26、ogens 48,49 (F, Cl, Br, I, also affects its electronic states. An increase in the density of states (especially around the Fermi energy usually enhances the catalytic activity of the material.Graphene that has a large number of edges or defects (Fig. 1a can be directly used as a catalyst 6,50. Densi

27、ty functional theory (DFT calculations from Dai and co-workers indicated that the zigzag edges are chemically active, tending to form CH bonds 51. Using DFT calculations, Deng et al . found that the oxygen reduction reaction (ORR can proceed at the zigzag edges of gra-phene whereas the armchair edge

28、s and in-plane network of gra-phene are inactive 6. Experimentally, the ball milling method was applied to cut graphene into small nanosheets and increase the zigzag edge density. The ORR activity can be significantly increased by decreasing the size of the graphene nanosheets (Fig. 2a,b, as this wi

29、ll increase the ratio of edge atoms to bulk atoms in the gra-phene network.Besides the edges of graphene, heteroatoms can substitute for C atoms of the graphene matrix (Fig. 1b, and the dopants can act as an electron donor or acceptor depending on their electronegativ-ity compared with C. For exampl

30、e, the N atom possesses higher electronegativity than the C atom, leading to electron transfer from C to N in N-doped graphene, whereas in B-doped graphene a B atom has lower electronegativity than a C atom, resulting in elec-tron transfer from B to C. This difference can generate two different acti

31、ve sites. In a substitutive doping case, the active sites were gen-erally considered to be the C atoms adjacent to the N-dopants in the N-doped graphene 9,34, whereas the B atoms were considered as the active sites in B-doped graphene 38,52. Among all heteroatom-doped graphene structures, N-doped gr

32、aphene is the most intensively investigated system in catalysis 8,9,34,53,54. For example, many groups have shown that N-doped graphene can be used as a metal-free catalyst for the ORR in H 2O 2 fuel cells 8,34 and Liair batteries 55,56. DFT calculations by Yu et al . present two reasons for changes

33、 in the electronic structure in N-doped graphene 9,57. One is the higher electronegativity of N than C, which induces positive charges on C, and the other is the back-donation of the lone-pair electrons from N to C. Both effects synergistically increase the density of states at the Fermi level of th

34、e adjacent C atoms, as shown in Fig. 2d, which increases their ORR activity. The reaction energy barrier of the ORR occurring at the adjacent C atoms of N atoms is rather mild, and therefore the reaction can proceed well with an associa-tive mechanism by a four-electron transfer pathway 9. It should

35、 be noted that different N species and carbon structures can change the selectivity of oxygen activation. For instance, several groups have shown that N-doped graphene or mesoporous carbon can be used for H 2O 2 production via a two-electron transfer pathway 58,59. Besides this, N-doped graphene can

36、 also be used as an efficient cat-alyst for selective oxidation. For example, Gao et al . and Long et al . reported independently that N-doping can promote the selective oxidation of ethylbenzene and aromatic alcohol 53,60. Apart from N and B doping, other heteroatoms such as P , S and Se have also

37、received great interest in graphene-based catalysis 3740,61. For exam-ple, a recent study indicates that P-doped or S-doped graphene can serve as an efficient ORR catalyst in alkaline electrolytes 37,39.Besides non-metal atoms, metal atoms such as W , Pt, Co, In and Fe can also be introduced into th

38、e graphene matrix 4143. Single metal atom sites embedded in graphene can affect the electronic structure of the adjacent C atoms, and more importantly they can be directly used as active sites. DFT calculations from Lu et al .62 indicated thatabde fce e e Figure 1 | Schematics of catalysis or active

39、 sites for various graphene structures and their heterostructures. a , Active sites from defects and edges. b , Active sites from doped heteroatoms. c , Active sites from functional groups and metal clusters. d , Catalytic activity due to electron (e transfer from metal to graphene layer. e , Cataly

40、sis in the space between a metal surface and 2D crystal. f , Catalytic activity from sandwich structure based on 2D materials, for example graphene or MoS 2.REVIEW ARTICLENATURE NANOTECHNOLOGY DOI: 10.1038/NNANO.2021.340in Au-doped graphene the single Au sites can efficiently catalyse CO oxidation,

41、and the highest barrier is only 0.31 eV. The problem for the metal-doped graphene, however, is the low stability of the metal sites owing to the weak bonding between metal and carbon atoms. For example, the single W atom is mobile under electron beam irra-diation, implying instability in realistic c

42、atalytic conditions41. One possible route to stabilize the metal atoms in graphene is to use het-eroatoms as the anchor. Recently, Deng et al. reported that single-atom Fe can be confined in a graphene matrix by bonding with N atoms to form a stable single FeN4 centre, which can catalyse ben-zene ox

43、idation to phenol at room temperature with good stability63. Graphene structures functionalized with oxygen-containing groups including graphene oxide (GO and reduced gra-phene oxide (RGO (Fig. 1c can be produced on a large scale and have been used as a catalyst. Boehm et al. 64 first used RGO as a

44、cata-lyst to synthesize HBr in 1962. In 2021, Bielawski and co-workers reported that GO can catalyse the oxidation of various alco-hols and alkenes, and the hydration of various alkynes into their REVIEW ARTICLE NATURE NANOTECHNOLOGY DOI: 10.1038/NNANO.2021.340corresponding aldehydes and ketones wit

45、h good yields 65,66 (Fig. 2e,f. Recently, Gao et al . reported that RGO can be used as an effective catalyst for the hydrogenation of nitrobenzene even at room tem-perature 67. Other oxygen-containing groups (for example SO x , NO x , PO x on graphene have recently also received wide atten-tion in c

46、atalysis 45,68. For example, Xiao and co-workers reported that sulfated graphene can be used as an efficient solid catalyst for acid-catalysed liquid reactions 45. The oxygen-containing groups or adjacent defects with ability to modify the electronic structure of graphene are usually considered as t

47、he possible active sites, depend-ing on the different reaction systems.Other 2D materials One important outcome of graphene research is that it has led to many other 2D materials (for example MoS 2, C 3N 4 being researched and used 10. Currently, more than two dozen 2D materials have been investigat

48、ed 11,12,69,70. Surprisingly, many of these are stable in ambi-ent conditions, and more often than not the electronic properties of 2D crystals are different from those of their 3D counterparts. These differences in electronic properties may create different reactivity on 2D crystals compared with t

49、heir 3D relatives. As well as showing effects similar to the five routes to tune electronic states listed above for graphene, the enlarged family of 2D materials can significantly increase the range of catalytic applications in comparison with gra-phene (Table 1. For example, the surface acidity or

50、basicity of some 2D materials (such as C 3N 4 can significantly affect catalytic activity and selectivity 71. In addition, the surfaces of some pure 2D metal crystals can be active in catalysis, which will significantly increase the active sites compared with their 3D counterparts.Two-dimensional gr

51、aphitic C 3N 4 (g-C 3N 4 is a widely investi-gated catalyst 7275. It consists of cyamelluric tri-s -triazine building blocks as shown in Fig. 3a (ref. 72 and has a 2D structure similar to that of graphene. Unlike graphene, g-C 3N 4 has a bandgap, with significant electronic density of states at the

52、band edge. Interest in the use of 2D g-C 3N 4 in catalysis originates not only from its unique electronic structure, but also from the rich Lewis basic functions, Brnsted basic functions, H-bonding motif and high specific sur-face area 71. Therefore, g-C 3N 4 shows promise for many applications in c

53、onventional heterogeneous catalysis, photo- and electrocataly-sis. For instance, Goettmann et al . found that g-C 3N 4 can promote the conversion of CO 2 and benzene to phenol or benzoic acid 73. Furthermore, g-C 3N 4 can catalyse many FriedelCrafts reactions 76. By measuring optical absorption spec

54、tra, Wang et al . 72 found that the bandgap of g-C 3N 4 is 2.7 eV , showing an intrinsic semiconduc-tor-like absorption in the blue region of the visible spectrum. This bandgap is large enough to overcome the endothermic character of the water-splitting reaction. Therefore, by using g-C 3N 4, it is

55、possi-ble to achieve steady H 2 production from water containing triethan-olamine as a sacrificial electron donor on light illumination, even in the absence of noble metal catalysts such as Pt (Fig. 3b72.aGraphene size (nmC u r r e n t (m A c m 2b0.30 nmc0.00.51.0Energy (eVP r o j e c t e d d e n s

56、i t y o f s t a t e s (a .u .321+0.66+0.60+0.622.672.67+0.84+0.60+0.66+0.17+0.17Fermi levelN1C2C3d2 nmRRO HHRROHRRO fFigure 2 | Graphene as a catalyst, through perturbations to the hexagonal structure. a ,b , Small-size graphene nanosheets as a catalyst for the ORR.a , Zigzag configuration at the ed

57、ge of a hole in graphene. The inset diagram illustrates part of a continuous zigzag segment, 12 hexagons long 27.b , The effect of graphene sheet size on the electroactivation of O 2, as indicated by the oxygen reduction current at potentials of 0.1, 0.15 and 0.2 V (versus Hg/HgO6.c ,d , Nitrogen-do

58、ped graphene as a catalyst. c , Scanning tunnelling microscopy image of bilayer N-doped graphene. The grey and blue balls of the inserted network represent C and N atoms, respectively 34. d , Projected density of states on p z orbital of the N and C atoms denoted in the inset. The inset shows the ne

59、t charges on N and its adjacent C atoms 57. a.u., arbitrary units. e ,f , Graphene oxide as a catalyst for catalytic oxidation. e , High-resolution transmission electron microscopy image of graphene oxide 149. f , Graphene oxide as a catalyst for oxidation of alcohols and alkenes, as well as the hyd

60、ration of alkynes 65. Figure adapted with permission from: a , ref. 27, AAAS; b , ref. 6, RSC; c , ref. 34, American Chemical Society; e , ref. 149, Wiley; f , ref. 65, Wiley.REVIEW ARTICLENATURE NANOTECHNOLOGY DOI: 10.1038/NNANO.2021.340I n addition, the Muellen group and Qiao group found that g-C

61、3N 4 can be used as a high-efficiency metal-free electrocatalyst for the ORR 74,77, hydrogen evolution reaction (HER75,78 and oxy-gen evolution reaction (OER37,79. Combining g-C 3N 4 with other 2D materials, such as graphene or its derivatives, can further improve the catalytic performance of g-C 3N

62、 4 because of the increase of the active sites or the synergistic effect of different active sites. Qiao et al .75 found that g-C 3N 4 coupled with N-doped graphene can be used as a hybrid catalyst, which shows an unexpected HER activity with comparable overpotential and Tafel slope to some well-est

63、ablished metallic catalysts. Its unusual electrocatalytic properties are considered to originate from an intrinsic chemical and elec-tronic coupling that synergistically promotes the proton adsorption and reduction kinetics.Another carbon-based 2D material, graphyne (consisting of 2D sp 2 and sp car

64、bon networks that produce in effect a lattice of benzene rings connected by acetylene bonds, has recently been successfully synthesized 80, as has graphdiyne (graphyne with diacet-ylene bonds80. The high degrees of -conjunction, uniformly dis-tributed pores, and tunable electronic properties make th

65、e new 2D carbon materials promising for catalysis applications. For example, N-doped graphdiyne has been used as a metal-free electrode that shows a comparable electrocatalytic activity to commercial Pt/C catalysts for the ORR in alkaline fuel cells 81. Moreover, their poten-tial applications in CO oxidation 82 and dehydrogenation reactions 83 have been theoretically predicted.Recently, 2D transition metal dichalcogenides (TMDCs such as MoS 2 and WS 2 nanosheets have attracted great research interest.N N NNN N N NNNPerfect graphitic nitride sheetTri-s -triazine