通过简单方法合成先驱体并利用电纺法制备BCN微米空心球

李 霞温广武＊,,张 涛夏 龙钟 博

(1材料科学与工程学院，哈尔滨工业大学，哈尔滨 150001)

(2材料科学与工程学院，哈尔滨工业大学(威海)，威海 264209)

通过简单方法合成先驱体并利用电纺法制备BCN微米空心球

李 霞1温广武＊,1,2张 涛1夏 龙2钟 博2

(1材料科学与工程学院，哈尔滨工业大学，哈尔滨 150001)

(2材料科学与工程学院，哈尔滨工业大学(威海)，威海 264209)

以三氯硼吖嗪(B3N3H3Cl3)和苯胺在N-甲基吡咯烷酮(NMP)溶剂中合成的聚合物为电纺液，由改进的电纺设备制备具有六方结构的BCN微米球。通过控制纺丝电压来控制BCN球体的直径。对其进行元素分析，并通过扫描电子显微镜，能量色散谱，X射线衍射和X射线光电子能谱进行表征。结果表明BCN微米空心球表面微凹，直径在10～30μm之间。硼碳氮间的比例约为1∶1.12∶0.94。

聚合；BCN微米球；电纺

0 Introduction

Recently,a great variety of ternary compounds with differentphysicochemicalpropertieshaveattracted considerable attention because of their unique structural characters.Among them,BCN architectures have recently been attracted great deal attention because BCN compounds have higher thermal and chemical stabilities,and ideal mechanical properties than those of carbon architectures[1-3].Analogues to graphite,BCN materials have a two-dimensional network of sp2-hybridesed structure[4-5].These BCN structures have the potential for application as photoluminescent materials,emitters for flat paneldisplays,high temperature transistors,and high temperature lubricants[6-7].There are some reports about BxCyNzspheres and nanotubes of different chemical compositions[8-17].Commonly,BCN nanotubes are prepared by nitridation ofboric oxide in the presence of carbon nanotubes,CuO4and Au2O3[18].The products demonstrate different morphologies,and also usually contain oxide or catalysts impurities,thus it is difficult to obtain high-purity BCN structures with good crystallinity.Several groups have achieved BCN architectures through different routes,such as thermolysis of inorganic and polymeric precursors[19-20]. Ball-milling[21],Laser ablation[22]and arc-assisted[23]methodshavebeen used forsynthesisof BCN structures with solid state B,C and N sources.

However,to the best of our knowledge there have been only a few reportson the preparation ofhigh purity BCN microspheres in bulk quantities.Therefore,the selection of a suitable fabrication method and starting materials for the synthesis of high-purity BCN microspheres is important.In this respect,an easily prepared precursor from polymerization of trichloroborazine(B3N3H3Cl3)and anilinewas selected as the starting material and N-methyl pyrrolidone was used as the solvent to fabricate BCN green microspheres via an improved electrospray approach. This approach can control the diameter of the asprepared spheres by manipulating the voltage of the electrospray apparatus.

1 Experimental

A 250 mL single-necked flask equipped with a magnetic stirrer was loaded with 10 g(542 mmol)of trichloroborazine(B3N3H3Cl3)[17]dissolved in 30wt%of toluene.Then,6.25 mL(68.5 mmol)of dried aniline was loaded into themixture at room temperature under vigorous stirring for 2 h.After that,the solution was heated to 65℃with stirring to remove residual toluene, giving the original product.The polymerization was continued in a nitrogen atmosphere at 120℃for 20 h. Then,the as-polymerized precursor was dissolved in 40wt%of N-methyl pyrrolidone to form the starting materials forelectrospray.

Fig.1 Schematic diagram of improved electrospray approach to spin green BCN microspheres

Fig.1 illustrates the schematic setup for the electrospray of the BCN green microspheres.A high voltage of 9 kV is applied using a high voltage supply (DW-N503-4ACCD of Tianjin Dongwen High Voltage Research Inc).The distance between the source and the collectorwas8 cm.

The green microspheres were slowly heated to 1 550℃ata heating rate of1℃·min-1andmaintained at this temperature for 1 h in nitrogen atmosphere.In the end,the as-formed gray product was collected without any further purification.The surface chemical compositions of the product and precursor were examined using X-ray photoelectron spectrometer(XPS, Physical Electronics PHI 5700 with Mg exciting source).Themorphology and elemental constituents of the as-prepared products were observed using field emission scanning electron microscopy(SEM, MX2600FE)and energy dispersive spectroscopy(EDS). The structures of the productwere characterized by X-ray diffraction(XRD,Rigaku D/Max 2000 VPCwith Cu Kαradiation,λ=0.1541 8 nm).Scan speed(2θ):4°· min-1,step size:0.03°(2θ),30 kV,60mA).

2 Resultsand discussion

Fig.2 XPS spectra of (a) the precursor and (b) the as-prepared products

The XPS spectrum of full range scanning(Fig.2a) indicates the existence of boron,carbon,nitride, chlorine and oxygen(owing to the absorbed H2O)in the precursor.Fig.2b shows the XPSspectrum of full range scanning of the products annealed at1 550℃.It shows that only boron,carbon and nitride are examined after the green sample anneals at 1 550℃in a heating rate of1℃·min-1.No chlorine oroxygen peaksare detected in the XPS spectrum,indicating the absence of oxide compounds such as B2O3in the products.Fig.2b showsa sharp peak at189.4 eV,indicating the presence of B-C bonding(the binding energy is 188.6 eV)since the typical bonding energy of B-N(the binding energy is 190.2 eV)is higher than 190 eV.The chemical shift toward lower energy suggests a considerable contribution of B-C bonding,since the electronegativity ofCatoms is lower than thatofN atoms[24].The binding energy at 285.4 eV and 398.3 eV implies the C1s of graphitic structure(C-C bonding)and N 1s of hybrid structure(B-N and C-N bonding),respectively, suggesting the hybrid network in chemical compositions of the product.The B∶C∶N atomic ratio calculated from the XPSspectra isabout1∶1.12∶0.94.

Scanning electronmicroscopy(SEM)imagesof the as-prepared spheresare shown in Fig.3.Fig.3a displays a representative overview of the precursor microspheres,which shows that the as-prepared products are composed of large-scale spherical morphology.The high-magnification SEM image(inset of Fig.3a)shows that the sphericalstructureshave burrlike surface(inset of Fig.3a)and the size of the microspheres are of 10～30μm in diameter.The productsannealed at1 550℃are shown in Fig.3(b～h). Detailed SEM observations reveal that there exist two types of sphericalmorphologies:smooth microspheres (Fig.3c,d)and concave-like 3D microspheres(Fig.3e, f).Fig.3d shows themorphology of two smooth spheres with a diameter ofabout30μm.The highmagnification SEM image(Fig.3g)of the smooth sphere indicates that the surface of the sphere is composed of uniform nanodots(with a diameter of about 100 nm)and irregular cracked bubbles.Fig.3e shows an individual concave-like sphere with a diameter of about 20μm. The high-magnification SEM images(Fig.3 f,h)exhibit detailed information about the concave-like sphere, which is composed of massif-like tapers(with adiameter of about 800 nm and height about 500 nm) and irregular pits(with a diameterof3～5μm and depth about3μm)on the surface of the sphere.All the tapers and pits are randomly distributed on the spherical surface leading to the formation of a superstructure.In addition,a few non-spherical particleswith a diameter ofabout25μm can be occasionally observed in Fig.3c.

Fig.3 SEM images of (a) the as-produced green microspheres and (b～h) annealed products at different magnifications

The EDSanalysis(Fig.4)shows that the annealed productat1 550℃is composed of the elementsof B,C and N,indicating the purity of as-synthesized microspheres.The EDS result implies that the entire precursor hasbeen converted to BCN structure.

Fig.4 EDS of the annealed microspheres at 1 550 ℃ and the morphology of the microspheres (inset)

The XRD pattern of the product is shown in Fig.5. The strong and sharp diffraction peaks in Fig.5 indicate that the as-produced BCN structures are principally crystalline.All the peaks of the product can be indexed to a hexagonal structure,similar to the reported BCN structure.The sharp peak at the diffractive plane of (002)indicating,indicating the[100]graphitic sheets is well crystallized.No characteristic peaks of other impurities,such as B2O3or H3BO3,can be detected from the XRD pattern,indicating that the as-prepared producthashigh phase purity.

Fig.5 XRD patterns of the as-prepared product

Based on the above experimental observations,a mechanism of the formation of BCN precursor spheres can be proposed.As shown in Fig.6,the procedure of the electrospray of BCN precursor spheres can be divided into four steps.The first step:the precursor filled in the syringe receives surface charges and extrudes from the apex of the syringe at about 90℃in proper electric field strength.The precursor is stretched to a needle-like structure due to the presence of electric field force.The second step:the needle-like precursor further shrinks to a rod-like structure because of the coexistence of viscoelastic property and surface tension of the precursor at lower temperature.The third step:The precursor forms a spherical structure owing to the presence of surface charge and surface tension at the viscoelastic stage. At this stage burring surface of the precursor spheres is formed because of higher charge density at the external surface than internal(this result has been confirmed by the SEM image of inset in Fig.3a).The fourth step:the spheres shrink to concave-like morphology when the precursor cools to room temperature.

Fig.6 Formation mechanism of the precursor microspheres at the electrospray process

3 Conclusions

In summary,high pur ity hexagonal BCN microspheres with two kinds of morphology were synthesized using an improved electrospray method. The results show that the fabricated BCN microspheres have featureless and concave surface characterswith a diameter ranging from 10 to 30μm. Formationmechanism of the precursormicrospheres is proposed according to the observed morphology of the products.A simple,efficientway tosynthesizehexagonalBCNmicrosphersin largequantitywasdeveloped in this work.

Acknow ledgements:Thiswork was supported by the National Natural Science Foundation of China(51021002, 51172050,51102060,51102063),the Fundamental Research Funds for the Central Universities(HIT.ICRST.2010009),the Natural Scientific Research Innovation Foundation in Harbin Institute of Technology(HIT.NSRIF.2011109,HIT.NSRIF. 2010121),and the Scientific Research Foundation of Harbin Institute of Technology atWeihai(HIT(WH)X201108).

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Bulk Quantity BCN M icrospheres Fabricated by Electrospray from Easily Prepared Precursor

LIXia1WEN Guan-Wu＊,1,2ZHANG Tao1XIA Long2ZHONG Bo2
(1School ofMaterials Science and Engineering,Harbin Institute of Technology,Harbin 150001,China)
(2School of Materials Science and Engineering,Harbin Institute of Technology(Weihai),Weihai,Shandong 264209,China)

An easily prepared precursor from polymerization of trichloroborazine(B3N3H3Cl3)and aniline was selected as the startingmaterial and N-methyl pyrrolidone(NMP)was used as the solvent to synthesize hexagonal BCN microspheres in bulk quantity via an improved electrospraymethod.This approach can control the diameter of the as-prepared spheres by manipulating the voltage of the electrospray apparatus.The product was characterized by scanning electron microscopy,energy dispersive spectroscopy,X-ray diffraction and X-ray photoelectron spectrometry.The results show that the fabricated BCN microspheres have smooth and concave surface characterswith diameter ranging from 10 to 30μm.The B∶C∶N atomic ratio is about 1∶1.12∶0.94.

synthesis;BCNmicrosphere;electrospray

book=2507,ebook=22

O613.8+1；O613.71；O613.81；TQ128+.1

A

1001-4861(2012)11-2458-05

2011-12-06。收修改稿日期：2012-03-31。

国家自然科学基金(No.50672018)，863计划课题(2007AA03Z340)资助项目。

＊通讯联系人。E-mail：wgw@hitwh.edu.cn