水热法制备纳米ZnSWord下载.docx

1、以十六烷基三甲基溴化铵（CTAB）为表面活性剂，利用水热法通过二吡啶硫氰酸锌分解制备了ZnS纳米线，并用SEM、XRD.EDX和HR-TEM等方法对其纳米结构进行了表征。实验结果表明，反应时间和表面活性剂浓度是决定纳米ZnS最终形貌的关键凶素CTAB起到了纳米线生长的分子一诱导模板作用。Nanostructure has arose treruendous interest aruong the researchers working in all fields including physics to bioscience. From basic science to technologis

2、ts for their improved physical and chemical properties and applications superior to their bulk counterparts.Since the first discovery of carbon nanotubes.one-dimensional （ID） semiconductor materials such asnanorods.nanowires. nanotubes and nanobelts/nanoribbons have attracted extensive interest beca

3、use of their fundamental physical. chemical, optical, electrical andmagnetic properties, and their potential applications innano-scale devices. It is well known that ID nanostructure can play an important role both as interconnectand functional units in fabricating electronic, optoelectronic. electr

4、ocheruical and electroruechanical devices with nanoscale dimension. 1D nanostructure have been synthesized through a variety of synthes is technique such as template-directed synthesis c5l, Vaporsolid growth, vapor-liquid-solid （VLS） growthm. solu-tion-liquid-solid （SLS） growthcs etc. A variety of m

5、etalc9Lsemiconducting oxides uo in different ID nanoforms have been reported so far. Out of these materials. zinc sulfide. a II -VI semiconductor. is one of the most studied materials for itswide range of technologically important properties. ZincSulfide （ZnS） has a wide band gap of 3.72 eV for cubi

6、c phasec and 3.77 eV for theat rooru teruperature. It is alight-eruitting diodes, injection lasers. cathode raytubes, flat panel displays and IR windows. ZnS is alsoimportant for photoluminescence. electroluminescence.etc. Recently, optical wave confining and lasing hasbeen demonstrated in ZnS nanor

7、ibbons U3l In recentyears, nanocrystalline ZnS has attracted much attentionbecause properties in nanoforms differ significantlyfrom those of their bulk counterparts. Therefore. Much effort has been devoted to control the size. morphologyand crystallinity of the ZnS nanocrystals with a view to tune t

8、heir physical properties. In this study, we present a relatively simple and effective procedure for synthesis of l-D ZnS via hydrothermal reaction at 200 0C using a dipyridylzincthiocyanate colloidal solution, cetyl trimethyl ammonium bromide （CTAB） as a surfactant. The influence of surfactant and r

9、eaction time on the morphology hasbeen investigated.1 Experiment Hydrothermal reaction of ZnS nanowire with surfactant CTAB All reagents were analytical grade CTAB （0, 0.12,0.24 0r 1.44 mmoI-L1） and 3 mL of methoxy ethanol solution of dipyridylzinc thiocyanate （0.24 mmol L-）were put into Teflonlined

10、 autoclave of 50 mL capacity,and then was filled with double distilled water up to 80% of the total volume. After being sealed, the autoclave was heated t0 200OC and maintained for 2 h. and then cooled to room temperature. The resulting black solid fraction was washed with deionized water and then w

11、ith absolute ethanol. Finally the products were dried under vacuum at 40 0C.有表面活性剂的硫化锌纳米线的水热反应实验时把所有的试剂析，不同等级的CTAB和3毫升联吡啶硫氰酸甲氧基乙醇溶液放入盛有50毫升的聚四氟乙烯容器内，然后加入蒸馏水直至占总体积的百分之八十。之后加热到二XX保持两个小时，接着冷却至室温。把生成的黑色固体用等离子水冲洗接着再用纯酒精清洗一次，最后把产品放到四十度真空中干燥。1.2 Characterization High resolution transmission electron micros

12、copy（HRTEM） observations were done on Hitachi modesH700A-2 apparatus equipped with an EDAX EDS detector with an accelerated voltage of 200 kV. High resolution scanning electron microscopy （HR-SEM） images were obtained by OPTON CSM-950 with an accelerated voltage of 160 kV. UV-V spectra were recorded

13、 on a Unico UV-2201 UV-Vis spectrometer with rueasured wavelength range from 900 nm to 200 nm and slit of 1 mu and scan speed of 300 nm.min-l. X-ray diffraction（XRD） patterns were obtained on a Rigaku D/Max2550X with Cu Kce radiation （40 kV. 200 ruA. A =0.154 186 nm） and 20 range of 200-800 and scan

14、 speed of 0.020.s-. PL study was performed on Hitachi F-2500 with slit of 1nm and scan speed of 300 nm.min-l.在装有一个200千伏的加速电压的设备的高分辨率的日立H700A-2 上进行电子显微检测.,高分辨率扫描显微图像通过OPTON CSM-950用160伏特的加速电压来获得.通过Unico UV-2201 UV-V分光仪波长在九百纳米到二百纳米、缝宽为1微米、扫描速率为300纳米每分钟得到紫外光谱。X衍射图像铜电子辐射在D/Max2550X衍射机，扫描速率为0.020.s-.缝宽1n

15、m。扫描速率为每分钟300纳米在 Hitachi F-2500上进行试验2 Results and discussion2.1 Effect of the concentration of CTAB on themorphology of nano-ZnS Figs.la-d show SEM images of the ZnS nanostructure synthesized with varied amounts of CTAB surfactant. These iruages clearly reveal that the morphology ofZnS nanostructure

16、 varies significantly with the amountof CTAB. The shape of ZnS nanostructure varies froruspherical at the ratio of Zn:CTAB=I:O （Fig.la） to high-yield wires like at the ratio of Zn:CTAB =1 :6 （Fig.ld）with the reaction time of 2 h. The similar phenomena were observed from UV-Vis spectra of ZnS nanostr

17、ucture （Fig.2）. Curve a inFig.2 shows the absorption of ZnS nanostructure pre-pared without CTAB and there is a peak at about 337nru corresponding to a band gap of 3.68 eV. a bulk cubic ZnS reported in reference 14l With the increase of CTAB. the absorption peak shifts shorter （blue） to330 nm （Curve

18、 b）, 325 nm （Curve c） and 289 nm （Curved）, respectively, which corresponds to a band gap ofhexagonal ZnS. The band gap of bulk hexagonal ZnS is3.80 eV4. SO it suggests that the presence of CTAB2.2 Effect of reaction time on the morphology of nano-ZnS In addition to the effect of CTAB concentration.r

19、eaction time is another important factor that influences the shape and size of ZnS nanostructure. A comparison betwe.en the images of ZnS nanostuctures, prepared with the same CTAB concentration and with various （0.5 and 2 h） reaction times. shows the time-related shape evolution process of ZnS nano

20、structure. As mentioned above.the nanowires obtained with l.44 mmol .L-I of CTAB with a reaction tirue up t0 0.5 h consist only of a few in-dividual wire-like structures with a width of 40 nm and a length of 150 nru as we ll as the spherically shaped ZnS （60 nm in diameter） （Fig.3a）. After 2 h of sy

21、nthesis.the yield of wire-shaped ZnS increases: wire-like structures with a width of 60 nm and a le.ngth of 2 000 nm are seen （Fig.3b）. In all the cases de.scribed （reaction with surfactant）, at the shorter reaction time duration respectively（0.5 h） we see only the beginning of the evolution of ZnS

22、from cubic shaped wire-like morphological asserublies.while after 2 h of synthesis, the ZnS nanowires yield increases with increasing sizes of ZnS crystal. From the time-related shape-evolution process, it seems that incrasing the re.action duration t0 2 h, using variousCTAB concentrations leads to

23、a high yield of wire-like structures.2.3 Further characterization of ZnS nanostructure Fig.4a, b and c are the XRD patterns of the synthesized ZnS nanostucture prepared without CTAB andin presence of 0.24 mruol-L-. 1.44 rumol . L-1 0f CTAB with the reaction time of 2 h. respectively. All the of ZnS

24、nanostucture prepared without CTAB （a） and in presence of 0.24 mmol L-I （b）,（c） of CTAB with the reaction time of 2 h, respectivelv diffraction peaks in Fig 4a can be indexed to cubic ZnS （PDF Card No.5-566） and in Fig.4b,c can be indexed to hexagonal phase ZnS （PDF Card No.12-688）, which is in good

25、 agreement with the results obtained from UVVis spectra （Fig.2）. No impurities such as Zn. Nio or intermediary phase zinc sulfides are detected in the XRD patterns of Fig.4b and c. But the characteristic diffraction peaks in Fig.4b is less obvious than those in Fig.4c, which indicates that the conce

26、ntration of CTABdlfects the crystal integrality. Typical EDX pattem of as-obtained ZnS sample is shown in Fig.5. The results show that the ZnS nanowires are coruposed of Zn and S and the ratio of Zn to S is 1.08 : l, in agreement with the expected value. Energy l keV In Fig.6, HR-TEM image of ZnS sh

27、ows that they are composed of about 7 nm ZnS nanocrvstals asseru Fig.6 TEM image of ZnS nanowire and HR-TEM image of the ZnS nanowire（inset） prepared using 1.44 mmol L-l of 2 h blies because neck-like connections aruong the adjacent nanocrystals are clearly observed. The lattice planes of ZnS nanocr

28、ystals are clearly visible in the inset of Fig.6. Fig.7 illustrates the photoluminescence （PL） spectrum of ZnS nanowires with an excitation wavelength of 335 nm. The appearance of a narrow eruission peak at about 452 mu is weak. A broad band at about 520 nm is also observed. which can be divided int

29、o two peaks at 523 mu and 533 nm, repectively, deruonstrating that these nonawires ruay have potential applications in op-toelectronic devices. The nucleation and growth conditions of nano-ZnS were exaruined without and with various concentrations of cationic surfactant CTAB. This growth process cou

30、ld be related to the interaction of oriented surfactant chains and formatted ZnS nanowires. Uniform and ordered chain structure （16 carbon atoms） is easily adsorbed on the surface of ZnS colloidal particles.When the surface of the colloidal ZnS adsorbs CTAB.the activities of colloid greatly decrease

31、 and the growth rate of the colloid in some certain direction will be confined. The addition of more CTAB in the colloidal solution ruodifies the growth kinetics of the growing colloids. which finally leads to anisotropic growth of nanocrystals. Investigations have been done with different concentratio