Construction of Layered B3N3-Doped Graphene Sheets from an

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Functional Nanostructured Materials (including low-D carbon) 3

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Construction of Layered BN-doped Graphene Sheets from Acetylenic Compound-containing BN by a Semisynthetic Strategy 3

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Chen Chen, Kangkang Guo, Yaping Zhu, Fan Wang, Weian Zhang, and Huimin Qi ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b10582 • Publication Date (Web): 20 Aug 2019 Downloaded from pubs.acs.org on August 20, 2019

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ACS Applied Materials & Interfaces

Construction of Layered B3N3-doped Graphene Sheets from Acetylenic Compound-containing B3N3 by a Semisynthetic Strategy Chen Chen,† Kangkang Guo,†,‡ Yaping Zhu,† Fan Wang,† Weian Zhang,*,† and Huimin Qi *,† †Key

Laboratory of Specially Functional Polymeric Materials and Related Technology of

Ministry of Education, Shanghai Key Laboratory of Functional Materials Chemistry, School of Materials Science and Engineering, East China University of Science & Technology, Shanghai 200237, China ‡Shanghai

electric tools Research Institute, Shanghai 200233, China

KEYWORDS: nitrogen, boron, co-doped, graphene, borazine, structure controllability, catalysts and semiconductor

ACS Paragon Plus Environment

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ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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ABSTRACT

The structural modification of graphene at the atomic level is crucial for electrochemical applications. Doping heteroatoms to modify the structure of graphene has widely been adopted. However, the construction and controllable doping of heteroatom-doped graphene remains a challenge. Herein, a novel semisynthetic method is developed to synthesize a borazine (B3N3)containing acetylenic compound as a precursor, and a series of B3N3-doped few-layer graphene nanosheets are prepared after annealing at different temperatures. To form graphene sheets, the in situ forming MgBrCl salt is used as an intercalation agent to enlarge the mutual distance between molecules, which can inhibit the unwanted crosslinking reaction. Nanosheets with different thicknesses of 2.5 nm, 3.5 nm and 4.1 nm can be obtained at annealing temperatures of 1500 ℃, 1200 ℃ and 1000 ℃, respectively. The results demonstrate that the B and N atoms are co-doped in the graphene by the structure of B3N3, and the doping site can be changed with different annealing temperatures. The optical gap of graphene can be successfully opened by doping with B3N3, and the resultant material can be potentially utilized as a catalyst and semiconductor material. Furthermore, this new semisynthetic strategy will offer the opportunity to fabricate more carbon materials via controllable heteroatom doping.


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1. Introduction The graphene, a two-dimensional monolayer structure of sp2-hybridized carbon, has already attracted great attention from wide range of fields because of its extraordinary high optical transparency, superior mechanical strength, and excellent charge carrier mobility, which make it suitable for device applications, such as electronics, optoelectronics, photonics, and spintronics.14

However, the absence of a band gap and low surface functionality greatly limit graphene’s

application in electronics.5 Consequently, tailoring the electronic structure of graphene to open the band gap and improve the surface activity is currently one of the most important and urgent research areas, which can enhance the material’s electronic, magnetic, optical and electrochemical properties.6,

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Doping with heteroatoms such as nitrogen, boron, sulphur and

phosphorus has been demonstrated in many theoretical and experimental studies, and it can be a promising method to modify the chemical activities and electrical properties of graphene and other carbonaceous materials.8-12 Furthermore, doping carbon with two elements has been found to effectively enhance its properties over those of the singularly doped counterparts, which is a result of the synergistic coupling effects between heteroatoms.13 In particular, boron and nitrogen have attracted great interest because B-N is isoelectronic and isosteric with C-C, having similar structural features to graphene, such as the bond-length equalization. Thus, the substitution of the C-C units with B-N does not alter the structural features, but the strong polarity of B-N can create a unique electronic structure, which changes the electronic properties and widens the band gap of raw materials.14,

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Borazine (B3N3), as a novel B-N compound, has presented great

potential in tailoring the band gap of graphene due to its electronegativity (5.04) as a doping unit being higher than that of boron (2.04) and nitrogen (3.04).16, 17


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The current approaches for the synthesis of dual-doped graphene are always in situ doping like chemical vapor deposition (CVD), solvothermal progress18, 19 and ex situ doping including the post-treatment of graphene and oxide graphene (GO) with doping sources.7 For example, Wang et al. have found that boron-nitrogen can in situ co-dope during the CVD growth of graphene on Cu (111) surface.20 Liu et al. have carried out a CVD synthesis of B- and N- doped graphene.21 However, most current methods are based on harsh conditions and high temperatures, such as carbonization, pyrolysis, and CVD. These “top-down” processes evidently limit the ability to control functionalization and structure.22,

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These approaches complicate the fabrication of

controllable boron and nitrogen co-doped graphene sheets because of the limited controllability over the doping configuration and distribution of the heteroatoms in graphene.24 Rather than a top-down approach, a stepwise, “bottom-up” strategy to carbon-based nanomaterials can afford defined structures.25 However, a rational synthesis requires multiple synthetic and purification steps, both of which are time-consuming and tedious.26 Moreover, most of physical and chemical strategies often lead to undesired by-products, such as hexagonal boron nitride (h-BN).27 Recently, some studies have reported that the direct synthesis of doped graphene sheets by in situ organic reactions can provide supreme controllability of graphene at the molecular structure level.28 Therefore, a method residing somewhere in the middle, between the top-down and bottom-up approaches, based on a “semisynthetic” tactic seems to be an effective and controllable strategy to prepare the boron and nitrogen co-doped graphene sheets. In this case, well-defined molecular precursors could be directed into a defined arrangement and then converted to the desired B, N-co-doped graphene through an external stimulus such as heating. This method would seem to offer the best of both worlds, by relying on the scalable synthesis of precursors, and offering functional carbon-rich products with well-defined structures.29-33


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However, the conventional organic synthesis for doping graphene often faces difficulty in further expanding the sheets due to their limited solubility and the occurrence of side reactions.28 Therefore, it is of great significance to design a chemical reaction that exhibits excellent reactivity, few side reactions and forms specific doping structures with heteroatoms. Recently, the chemical reactions based on the carbon-carbon triple bond, such as the coupling reaction, cyclotrimerization and Diels-Alder reaction have attracted great attention, since they can offer a rather unique starting point to form carbon-rich materials and new carbon allotropes with high controllability by the bottom-up approach.34-39 For example, graphene-related structures have been fabricated through the cycloaddition of acetenyl compounds.40, 41 To our best knowledge, there have been few reports on the fabrication of B, N-graphene with a high-phase purity through chemical reactions based on the carbon-carbon triple bond, especially for B3N3, where B and N atoms replace C atoms in the graphene framework at well-defined doping sites. In this study, we propose a novel semisynthetic method based on a carbon-carbon triple bond reaction to construct a series of B3N3-doped few-layer graphene by using a B3N3-containing arylacetylene compound. The hybridization of atoms in the arylacetylene resin, sp2 for boron in B3N3, sp2 for carbon in the benzene ring and sp for carbon in the acetenyl group, ensures the coplanarity of B3N3, the acetenyl group and the carbon atoms of the benzene ring, which is convenient to provide a basic plane for producing graphene. According to our previous work,42 a B3N3-containing arylacetylene resin precursor was prepared through the condensation reaction between B, B′, B″-trichloroborazine and an arylacetylene Grignard reagent. The MgBrCl produced in situ from the the above reaction was used as an intercalation agent to enlarge the mutual distance between molecules, which can inhibit the unwanted crosslinking. The precursor was further used to prepare B3N3-doped few-layer graphene, moreover, the doping site of B3N3


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was well controlled by varying the annealing temperature. The structures and properties of the doped few-layer graphene were characterized by pyrolysis gas chromatography-mass spectrometry (Py-GC-MS), Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Raman spectrum, UV-vis spectra, X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) specific surface areas. In addition, the oxygen reduction reaction (ORR)

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and Hall effect were used to further suggest the

successful opening of an optical energy gap and the potential application in electrochemical fields.

X

X

N B

HN B NH B N B H

X

MgBrCl

N

Ⅰ

X

MgBrCl

B

N B

MgBrCl

N B

X

X

B N

N B

PAH-BN

B N

H N B

B N

B N

N B

N B

Ⅱ MgBrCl X

HN B NH B N B H

X: H, B

N B

X

Pre-heat treatment X

X

B N

Higher heat treatment

B

H N

B N

B

N B

N

Ⅲ MgBrCl

MgBrCl

B N N B

B N

N B

BNGs

H N B

Acid washing B N

B N N B

B N

H N B

B N

N B

BNGs

Scheme 1. Schematic representation of the synthesis of PAH-BN and BNGs.

2. Experimental Section 2.1 Materials


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Boron trichloride was purchased from Beijing Multi Technology Co. Ltd. Diethynylbenzene was supplied by Fine Chemical Institute of East China University of Science and Technology and distilled on a vacuum line before using. Toluene, tetrahydrofuran (THF), ethyl bromide, and magnesium powder were purchased from Shanghai Titan Scientific Co. Ltd. Tetrahydrofuran and toluene were refluxed over sodium and freshly distilled in nitrogen before use. 2.2 Preparation of B3N3-containing arylacetylene precursor All synthetic reactions described below were carried out in a nitrogen atmosphere using Schlenk techniques. B, B′, B″-trichloroborazine (TCB) was prepared by allowing BCl3 to react with NH4Cl in toluene at 110 ℃ and was purified by sublimation. The B3N3-containing arylacetylene was prepared as follows: In a 250 mL four-necked flask equipped with a condenser, thermometer, mechanical stirrer, and funnel, ethynylphenylethymylmagnesium bromide (9.95 g, 0.03 mol) in 100 mL THF was added under a nitrogen atmosphere, and then TCB (1.84 g, 0.01 mol) in 70 mL toluene was dropwise added with an ice bath. After that, the mixture was allowed to heat up to 50 ℃ and stirred for an additional 4 h. Then the solution was cooled to room temperature and dioxane was added to the solution until no more precipitation occurred. Subsequently, the suspension was reserved for later use. 2.3 Preparation of B3N3-doped few-layer graphene (BNG) sheets The synthesis process of B3N3-doped few-layer graphene (BNG) sheets is illustrated schematically in Scheme 1. The suspension was transferred to a dish and the THF solvent was removed at 70 ℃ in a vacuum oven over 2 h. Then, the B3N3-containing arylacetylene resin could be polymerized to form B3N3-based polyaromatic hydrocarbons (PAH-BN) by pre-heating under vacuum conditions according to the procedure: 120 ℃ for 2 h, 140 ℃ for 2 h, 150 ℃ for 4


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h, and 180 ℃ for 2 h. The in situ formation of MgBrCl from the reaction in 2.2 was used as an intercalation agent to enlarge the mutual distance of molecules and inhibit the unwanted crosslinking. The PAH-BN containing the intercalation agent MgBrCl was heated to different temperatures (700 ℃, 1000 ℃, 1200 ℃ and 1500 ℃) at a heating rate of 5 ℃/min, and then annealed at that temperature for another 4 h. After annealing, the furnace was cooled down to room temperature under the same atmosphere. Finally, the corresponding BNGs (BNG-700, BNG-1000, BNG-1200 and BNG-1500) were obtained by washing in a 2 M acid solution and drying in an oven under vacuum. 2.4 Characterization The structure of PAH-BN and various BNG samples were analysed using Fourier transform infrared spectroscopy (Nicolet-6700, Thermo Fisher Scientific Company, USA) and pyrolysis gas chromatography-mass spectrometry (7890A GC/5975C MSD, Agilent Company, USA). The X-ray diffraction patterns were determined by a Bruker D8 Advance X-ray powder diffraction instrument with 2θ between 5° to 80°. The surface morphology of all samples was observed by a field-emission scanning electron microscopy (S-4800, Hitachi Company, Japan) and highresolution transmission electron microscopy (JEM-2100, JEOL Company, USA). Raman spectra were acquired by using a micro-Raman spectroscopy system (Iuvia reflex, Ren-ishaw Company, US), with an excitation energy of 2.41 eV, 514 nm. The XPS spectra were acquired on an X-ray photoelectron spectrometer (EscaLab 250Xi, Thermo Fisher Scientific Company, USA). The thickness of the dispersed BNG-1000, BNG-1200 and BNG-1500 nanosheets on silicon substrates were obtained by using an atomic force microscope (Veeco, DI Dimension3100) with a sharp silicon probe (radius of curvature of the tip was

Construction of Layered B3N3-Doped Graphene Sheets from an

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