Controlled Synthesis of Sea-urchin-like ZnO Nanomaterials with the Aid of Ethylene Glycol Using a So

29卷1期结构化学(JIEGOUHUAXUE)VoL. 29, No.12010.1Chinese J. Struct. Chem.126-133Controlled Synthesis of Sea-urchin-like ZnONanomaterials with the Aid of EthyleneGlycol Using a Solvothermal MethodDU Jji-Min”CHEN Zhi-Qiang GUO Wei .(College of Chemistry and Chemical Engineering,Anyang Normal Universiy, Anyang, Henan 455000, China)ABSTRACT Sea-urchin-like ZnO nanomaterials were sucessfully synthesized by decomposi-tion of zinc acetate precursor in the presence of sodium hydroxide and ethylene glycol (EG) in anethanol solution using a solvothermal method at 180 C for 12 h. The erystalline phase andmorphology of the resultant nanomaterials were characterized by X-ray diffraction (XRD), scanningelectron microscopy (SEM), transmission electron microscopy (TEM), selected- area electronicdiffraction (SAED) and high-resolution electron microscopy (HRTEM). Interestingly, the sizes andprod length of the samples can be easily tuned by changing the amount of directing agent EG andkeeping other reaction conditions unchangeable. On the basis of our experimental outcomes,EG-controlled-nucleation-growth formation mechanism was proposed to correspond for thesea-urchin-like ZnO growth processes. And the photoluninescence (PL) spectra of the as-selectedsamples were measured at room temperature, presenting two emission peaks centered at ~ 388 and480 nm.Keywords: nanostructures, electron microscopy, solvothermal method, optical properties1 INTRODUCTION .of nanomaterials have displayed size and shapedependent properties'~”. Therefore, systemic inves-Recently, materials in nanosized ranges have attrac-ttigation of the size and shape controlled nano-ted more attention because of some promising per-crystals is helpful to understand nanomaterial chara-formances such as delivery of drugs, enhanced mag-cteristics and gain deep insight into the crystalliza-netic image resonance, and favorable optical andtion mechanism. Up to date, remarkable achieve-catalytic properties in comparison with bulk mate-ments have been made in controlled synthesis orials owing to the high surface energy, small-sizenanomaterials using bottom-up and top-down me-effect and quantum effectl" 5. With the developmentthods!8~10]. Alivisatos et al. have monitored the sizeof nanoscience and nanotechnology, the elucidationand shape of CdSe nanocrystals in the presence ofand applications of these novel properties have ledstrong ligandst. 2. Lieber et al. developed a laser-to breakthrough in various fields of fundamentalassisted catalytic growth technique to synthesize aresearch and potential applications'!. Espcially, thebroad range of binary and ternary nanosemicon-electrical, catalytic, magnetic and optical propertiesducto中国煤化工mechanism'l ”Received 4 January 2009; aceped 13 Jaouary 2009TTHCNMHG0 This work Was spported by the Research Foundation of Key Young Teacher of Anyang Normal University②Corespoding autbor. Male, born in 1975, astat researcher, majoring in the synbesisand properties of functional nanomaterials. E mail: djm@iccas.ac.cn2010 Vol. 29结构化学(JIEGOUHUAXUE) Chinese J. Sruct. Chem.127Amongst the semiconductor family, ZnO is aby Beijing Chemicals Co. Ltd. All chemicals were ofwide-band gap semiconductor (3.37 eV) that dis-analytical grade and used without further purifica-plays interesting luminescent properties, whichtion. Deionized water was used in experiments. In ainclude the recent demonstration of ultraviolet lasingtypical synthesis of ZnO materials, Zn(AC)2 2H2Ofrom nanowiresl. 159. Moreover, it is piezoelectric(22.19 mg, 0.1 mmol) was dissolved in 10 mLdue to its noncentrosymmetric symmetry, which is aethanol with EG (0.5 mL) and NaOH (40 mg, 1key phenomenon in building electro mechanicalmmol) with stirring for about 30 min. The mixturesensors and transducersto. Up to now, many synthe-solution was loaded into a Teflon-lined autoclavesis methods, such as solid-state process, precipita-(20 mL), which was sealed and maintained at 180tion, hydrolysis, pyrolysis and bydrothermal meC for 12 b, and then cooled to room temperaturethods, have been introduced to prepare nano- ornaturally. The white precipitates depositing on themicro-scaled ZnO with various morphologies suchbottom of the Teflon-lined autoclave were collectedas nanobows, nanonails, nanobelts, nanotubes, nano-nd washed with ethanol and deionized water forneedles, dendritic nanowires, and nanoflakes'three times, respectively, and then dried in a vacuumFor instance, Zhou et al. reported that the sphereat 65 C for 4 b. The compared experiments wereorganization of cone-shaped ZnO nanorods, similarperformed under the same experimental reactionto sea-urchin-like nanostructures, was obtained'conditions except for using 1,2, 3, 4 mL and withoutTo the best of our knowledge, sea-urchin-like nano-EG instead of0.5 mL EGstructures mostly consist of low-dimensional nano-2.2 Characterizationrods with pointed ends, showing the improvedX-ray diffraction (XRD) patterns were recorded onoptical emission due to the field effect. For example,a Japan Rigaku D/max-A X-ray diffractometerDjurisicC and coworkers detailedly researched theequipped with a graphite-monochromatized high-photoluminescence and electron paramagnetic reso-intensity CuKa (h = 1.54 A) radiation. The fieldnance of ZnO tetrapod and found that green lumine-emission scanning electron microscopy (FE-SEM)scence probably originates from some non-para-images were recorded on JEOL JSM- 6700F SEM.magnetic defects25The transmission electron microscopy (TEM) ima-Amongst all these reported methods, the solutionges and selected-area electronic iffraction (SAED)synthesis, followed by thermal treatment of thepatterns were taken on a Hitachi model H-800starting reagent in different solvents, may beinstrument, using an accelerating voltage of 200 kV.simple and effective method to prepare suficientlyThe high-resolution transmission electron micro-crystallized nanomaterials. Besides, the benefits ofscopy (HRTEM) images were recorded on JEOL-utilizing solution-based method have also involved2010 TEM at acceleration voltage of 200 kV. Thethe considerable influence on the final sizes androom temperature photoluminescence (PL) spectramorphologies of the prepared samples. We success-were recorded on a Jobin Yvon-Labram spectrometerfully synthesized sea-urchin-like ZnO nanomaterialswith a He-Cd laser.with the directing agent EG in an ethanol solutionusing a solvothermal method. Interestingly, ZnO3 RESULTS AND DISCUSSIONnanoprod length of sea-urchin-like nanostructureswas facilely tuned by changing the quantity of EG3.1 XRD analysisand remained other reaction conditions the same.The XRD patterms of the as-obtained products with0.5 and 4 mL EG are shown in Fig. 1a and b. AIll2 EXPERIMENTALpeak:中国煤化工tzite phase ZnO(JCP3.249, c = 5.2062.1 Synthesis of the samplesEthylene glycol (EG), ethanol, NaOH and Zn-TYHCN.M H G (02) ifrction(CHzCOO):2H2O (Zn(AC) 2H20) were suppliedpeaks, the calculated lattice constants a and c of this128DU J M. et al: Nanomaterials with the Aid of Ethylene Glycol Using a Solvothermal MethodNo. 1hexagonal phase for both samples are 3.22 and 5.20patterm, indicating that pure wurtzite phase ZnO wasA, consistent with the standard values for bulkobtained under the present synthesis conditions.ZnO[26. No impurities can be detected from the|a_星 呈号建是b20304050607020 (degree)Fig. 1. XRD patterns (2) and (b) of the products synthesized with 0.5 and4 mL EGat 180 C for 12 h1 um(a)b)(110)(112)[0001]m(002)dooz-026m不中国煤化工(cIYHCNMHGFig.2. SEM and TEM images of ZnO samples formed in the presence of 0.5 mL EG:(a) Low-magnification, (b) high-magnification SEM images of the samples, (C) Low-resolution and (d) high-resolution TEM images of the samples. Inset (C) is an SAED pattern2010 Vol. 29结构化学(JIEGOUHUAXUE) Chinese J._ Struct. Chem.1293.2 Morphology of ZnO samplesthe prepared ZnO material is similar to a sea-Low-magnification SEM image (Fig. 2a) showsurchin-like motif The prods of sea-urchin-like ZnOthat the sea-urchin-like ZnO was produced in highproducts are single-crystalline, as evidenced byyield when 0.5 mL EG was added in the reaction SAED pattemns with (002), (110) and (112) reflectionsystem mentioned above. A close observation byspots (Inset in Fig. 2c). High-resolution TEM imagehigh-magnifcation SEM image (Fig. 2b) reveals that(Fig. 2d) shows that the interplanar spacing of ZnOthe prods of ZnO nanomaterials grow from the samesamples is 0.26 nm, corresponding to the distancecenter with ~6 um in length. Low-resolution TEMbetween (002) planes of wurtzite ZnO, suggestingimage (Fig.2c) also confirms that the morphology ofthe preferred growth along the [0001] direction.2um500 nma)(b)200 nm400 nmVD155hmum 15. OkVxEc)(d)Fig.3. (a), (C) Low-magnifcation and (b) (d) high-magnification SEM images of sea-urchin-likeZnO samples formed with 1 and 2 mL EG in an ethanol solution at 180 C for 12 hTo study the influence of the amount of EG on thealso synthesized with 1 mL EG as known from thesizes and morphologies of ZnO samples, the com-low-n中国煤化工Fig 3a High.pared experiments were carried out in the presencemagni|YHCNMHGtsthatthelengthof 1 and 2 mL EG by keeping other reaction con-of ZaO prods with hexagonal characteristics is aboutditions the same. Sea-urchin-like ZnO samples were2.5 μm. These bundles are not easily destroyed even130DUJ. M. et al: Nanomaterials with the Aid of Ethylene Glyeol Using a Solvothermal MethodNo. 1with ultrasonic treatment for a long time, testifyingconfirming that the sea-urchin-like ZnO samplesthe existence of strong interaction among the ZnOwere yielded with short ZnO prods compared withhomocentric bundles. This phenomenon was alsothose synthesized with 0.5, 1 and 2 mL EGfound by Zhang et al.!er. Further increasing theFurthermore, high magnification SEM image (Fig.amount of EG up to 2 mL, the low-magnification4b) obviously shows the length of ZnO prods to beSEM image (Fig. 3c) demonstrates that sea-urchin-about 150 nm with the hexagonal suface. Furtherlike ZnO nanomaterials were produced withaugmenting the amount of EG to 4 mL, the sea-relatively small sizes of ~1 μm compared to thoseurchin-like ZnO products were also obtained asobtained with 1 mL EG And the length of ZnO known from the low. magnification SEM image Fig.prods becomes short with sizes of ~500 nm as seen4c). Meanwhile, high-mgnification SEM image infrom the high-magnification SEM image in Fig. 3d.Fig. 4d clearly demonstrates that the length of ZnOFurther to increase the quantity ofEG to 3 mL, theprods is about 100 nm, shorter than that of samplescompared experiment was performed and otherprepared at low quantity of EG, which means thatreaction conditions were kept unchanged. Moreover, EG plays an important role in growing the sea-the morphologies of produced ZnO were charac-urchin-like ZnO nanomaterials.terized with low-magnification SEM, as given in Fig.4a,2.00mm100nm(a(b)200 nm中国煤化工YHCNMHGx1201Fig.4. (a), (C) Low-magnifcation and (b), (d) high- magnification SEM images of sea-urchin-like ZnOsamples formed in the presence of3 and 4 mL EG in an ethanol solution at 180C for12 h2010 Vol. 29结构化学(JIEGOUHUAXUE) Chinese_ J. Struct. Chem.1313.3 Formation mechanism of sea-urchin-likemagnification SEM image (Fig. 5b) is fairly com-ZnO nanomaterialsmon, suggesting that multiple nanorods often growTo investigate the growth mechanism of sea-single aggregate of ZnO nanoparticles. It should beurchin-like ZnO materials, the compared experi-pointed out that the initial deposition of nanocrystalsments were carried out without EG and other reac-is critical for the formation of the current shapes oftion conditions remained unchanged. The productsnanorods. Hence, the compared experimental resultsconsist of a large quantity of straight and smoothshow that EG plays an important role in synthesizingsolid with an aspect ratio in the range of~ 5 assea-urchin-like ZnO nanomaterials in our experi-known from low-magnification SEM image (Fig. 5a).ments.Further, the morphology shown in the high-2 um200 nmMD26 S5m 215 Qkv x40k u(a)(b)Fig.5. a) Low-magifcation and (b) high-magnification SEM images of ZnO nanomaterialssynthesized in the absence of EG in an ethanol solution at 180C for 12 hAs known from the results described above, therepulsive force formed among the ZnO polarquantity of EG plays a key role in synthesizingsurfaces28. 29]. During the heating process, nuclei aresea-urchin-like ZnO nanomaterials and changing thevery stable due to their connection via co-occupiedprod length. On the basis of our experimental results,crystal surfaces. The nuclei contain multiple (0001)we proposed the EG-controlled-nucleation-growthbasal facets which are the fast growth orientation.formation mechanism to be responsible for theConsequently, multiple fast growth orientations leadgrowth of sea-urchin-like ZnO nanomaterials. It ito sea-urchin-like ZnO formation along the [0001]known that material morphology is dependent ondirection5o. When the experiment was carried out inextrinsic and intrinsic properties. From its intrinsicthe presence of 4 mL EG the newly produced ZnOproperty, ZnO possesses polar surfaces, showingnuclei were covered with EG and the growth ratethree types of the fastest growth directions ofwas getting slow, leading to the short length of ZnO<0001>, <0110> and <2110>, which are advanta-prods. When low amount of EG (3 mL) was addedgeous to grow low-dimensional structures. When theinthe中国煤化工clei could growexperiments were performed in the presence of EGfaster tMH.CNMHhan those with 4the ZnO nuclei were coordinated with EG which canmLIcauiun suluUN. Hence, lowincrease the nuclei supersaturation and decrease thequantities of EG are favorable to the synthesis of132DU J. M. et al: Nanomaterials with the Aid of Ethylene Glycol Using a Solvothermnal MethodNo. 1sea-urchin-like ZnO nanomaterials with long prods.at 388 nm was observed in both ZnO samples,When decreasing the amount of EG to 2, 1 and 0.5resulting fom the recombination of excitonicmL and keeping other reaction conditions unchanged,centers in the obtained ZnO materias2. And athe longer prods of sea urchin-like ZnO materialsweak broad emission band appeared due to the .were produced in our experiments.recombination of a photo-generated hole with an3. 4 Photoluminescence of sea-urchin-like ZnOionized charge state of specific defcts/33. By closenanomaterialsobservation, the intensity of the emission peakIt is well known that ZnO can exhibit a direct-bandcentered at 388 nm of sample (a) is stronger that thatgap of 3.37 eV with a large exciton binding energyof (b). This is likely due to the (b) sample containingof 60 mV, suitable for effective UV emission[31more defects than (a), which facilitates transformingThe room temperature PL spectra of as-obtainedlight energy into electron and/or crystal latticeZnO samples were recorded, as shown in Fig.6. Thethermal-vibration energy.excited wavelength was 320 nm. The emission peaka食|星|/b400600W avelength (nm )Fig. 6. PL spectra of (2) and (b) products synthesized with 0.5 and 4 mLEG at 180°C for12 h4 CONCLUSIONtion-growth formation mechanism was proposed toaccount for the growth behavior of sea-urchin-likeSea-urchin-like ZnO materials with different sizesZnO. In addition, PL spectra were recorded tocan be controllably synthesized in the presence ofexamine the emission property of ZnO samples,various quantities of EG in an ethanol solution atshowing that both selected ZnO samples display an180 C for 12 h applying a solvothermal method.emission peak centered at ~388 nm owing to theThe more amount of EG in the reaction system, theexcitonic combination and a weak emission peak atshorter ZnO prods were produced. On the basis of ~ 480 nm due to the defects amongst our samples.our experimental results, the EG-controlled-nuclea-REFERENCES .(1) Yh, D; Yam, V.J. Am Chem Soc 2004, 126, 13200 -13201.(2) Ding.T. Y; Guo,G C; Wang. M. s; Chen, Q. Y; Zhou, W. w; Huang, J. s. ChineseJ Stmnc. Chem. 2009, 28, 19-24.Lli,R F; Shang z. E; Wang. G C;X, X. R. Chinese J Sruct. Chem. 209.28,中国煤化工(4) Zhang, Y; lia, H;Luo, x; Chen, X; Yu, D; Wang. R J. Phys. Chem. B 2003,1LHCNMH G(5) Wul,K 1; Wang, M. s; Zou,J. P; Xn, G; Ding, τ Y; Guo, G c; Huang,J. s. 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