水熱法制備納米ZnS

1、Hydrothermal Preparation of ZnS NanowiresAbstract:Nanowires of ZnS were synthesised by using a surfactant assisted hydrothermal approach. The synthesis isbased on decoruposition of dipyridylzinc thiocyanate with cetyl triruethyl aruruonium bromide (CTAB) as a surfactant.The nanostructure was charact

2、erized by SEM,XRD and EDX. HR-TEM. The experiruental results indicate that thereaction tirue and concentration of surfactant play key roles in deterruining the final ruorphologies of nano-ZnS. And CTAB acts as a molecule-directing teruplate for the growth of nanowires.摘要：以十六烷基三甲基漠化銨(CTAB)為表面活性劑，利用水熱

3、法 通過(guò)二毗啶硫氰酸鋅分解制備了 ZnS納米線(xiàn)，并用SEM、XRD.EDX和HR-TEM等方法對(duì)其納米結(jié)構(gòu)進(jìn)行了表征。實(shí)驗(yàn)結(jié)果表明，反應(yīng) 時(shí)間和表面活性劑濃度是決定納米ZnS最終形貌的關(guān)鍵兇素.CTAB 起到了納米線(xiàn)生長(zhǎng)的分子一誘導(dǎo)模板作用。Nanostructure has arose treruendous interest aruong the researchers working in all fields including physics to bioscience. From basic science to technologists for their improved p

4、hysical 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 because of their fundamenta

5、l 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. electrocheruical and electroru

6、echanical 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 metalc9Lsemiconducting ox

7、ides 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 cubic phasec and 3.77 eV for

8、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 nanoribbons U3l In recentyears

9、, 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 their physical properties.I

10、n 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 reaction time on the morphol

11、ogy hasbeen investigated.1 ExperimentHydrothermal reaction of ZnS nanowire with surfactant CTABAll 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 autoclave of 50 mL capacity,

12、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 with absolute ethanol. Finally

13、 the products were dried under vacuum at 40 0C.有表面活性劑的硫化鋅納米線(xiàn)的水熱反應(yīng)實(shí)驗(yàn)時(shí)把所有的試劑析，不同等級(jí)的CTAB和3毫升聯(lián)毗啶 硫氤酸甲氧基乙醇溶液放入盛有50毫升的聚四氟乙烯容器 內(nèi)，然后加入蒸餾水直至占總體積的百分之八十。之后加熱 到二百度保持兩個(gè)小時(shí)，接著冷卻至室溫。把生成的黑色固 體用等離子水沖洗接著再用純酒精清洗一次，最后把產(chǎn)品放 到四十度真空中干燥。CharacterizationHigh resolution transmission electron microscopy(HRTEM) observations were

14、 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 on a Unico UV-2201 UV-Vis sp

15、ectrometer 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 speed of 0.020.s-. PL study

16、 was performed on Hitachi F-2500 with slit of 1nm and scan speed of 300 nm.min-l.在裝有一個(gè)200千伏的加速電壓的設(shè)備的高分辨率的日立H700A-2上進(jìn)行電 子顯微檢測(cè).，高分辨率掃描顯微圖像通過(guò)OPTON CSM-950用160伏特的加 速電壓來(lái)獲得.通過(guò)Unico UV-2201 UV-V分光儀波長(zhǎng)在九百納米到二 百納米、縫寬為1微米、掃描速率為300納米每分鐘得到紫外光譜。 X衍射圖像銅電子輻射在D/Max2550X衍射機(jī)，掃描速率為0.020.s-. 縫寬1nm。掃描速率為每分鐘300納米在Hitachi

17、F-2500上進(jìn)行試驗(yàn)2 Results and discussionEffect of the concentration of CTAB on themorphology of nano-ZnSFigs.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 varies significantly with the

18、 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 nanostructure (Fig.2). Curve a inFig.

19、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 b), 325 nm (Curve c) and 289

20、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 CTABEffect of reaction time on the morphology of nano-ZnSIn addition to the effect of CTAB concentration.reaction time isanother important fa

21、ctor 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 nanostructure. As mentioned above.the na

22、nowires 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 synthesis.the yield of wire-shaped ZnS

23、 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 from cubic shaped wire-like morpholo

24、gical 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 a high yield of wire-like structures

25、.Further characterization of ZnS nanostructureFig.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 nanostucture prepared without CTAB (a) an

26、d in presence of 0.24 mmol L-I (b),(c) of CTAB with the reaction time of 2 h, respectively 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 agreement with the results obtained from

27、 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 concentration of CTABdlfects the crystal integ

28、rality.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 shows that they are composed of about 7 nm Zn

29、S 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 CTAB with the reaction time of 2 h blies because neck-like connections aruong the adjacent nanocrystals are clearly observed. The lattice planes of ZnS nanocrystals are c

30、learly 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 into two peaks a

31、t 523 mu and 533 nm, repectively, deruonstrating that these nonawires ruay have potential applications in optoelectronic devices.The nucleation and growth conditions of nano-ZnS were exaruined without and with various concentrations of cationic surfactant CTAB. This growth process could be related t

32、o 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 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 le