Solvothermal Synthesis of CdS Nanowires for Photocatalytic

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Solvothermal Synthesis of CdS Nanowires for Photocatalytic Hydrogen and Electricity Production Jum Suk Jang, Upendra A. Joshi, and Jae Sung Lee* Eco-friendly Catalysis and Energy Laboratory (NRL), Department of Chemical Engineering and School of EnVironmental Science and Engineering, Pohang UniVersity of Science and Technology, San 31 Hyoja-dong, Pohang 790-784, Korea ReceiVed: April 5, 2007; In Final Form: July 10, 2007

To investigate the formation of one-dimensional CdS nanowires, we synthesized them by a solvothermal method in ethylenediamine as a single solvent at different temperatures and times. The sample synthesized at 160 °C for 72 h had an average diameter of ca. 50 nm and a length of ca. 3-4 µm and hexagonal phase with high crystallinity. It was revealed that the formation of CdS nanowires followed three-step processes during the solvothermal synthesis; the seed formation process yielded nanosheets emanating from a mirosphere followed by the nanorod formation and growth of nanorods to nanowires. The CdS nanowires with higher crystallinity showed a higher rate of photocatalytic hydrogen production from water containing 0.1 M Na2S and 0.0 2M Na2SO3 as sacrificial reagents under visible light irradiation (λ g 420 nm). A high and stable photocurrent generation was also observed from the CdS nanowire film under visible light.

Introduction Fabrication of one-dimensional (1-D) semiconductor nanostructures has received considerable attention because of their various physical properties, depending on crystal structure, size, and shape.1-3 CdS is a II-VI semiconductor, which has a direct band gap of 2.4 eV. Recently, there have been many reports on the synthesis of 1-D CdS nanorods or nanowires with various approaches such as thermal evaporation, chemical vapor deposition, electrochemical deposition, and solvothermal route.4-7 Among these approaches, the sovothermal method is a simple synthetic method for the preparation of 1-D nanostructures, and the process could be easily controlled.8-13 CdS nanowires or nanorods were synthesized in ethylenediamine or other amines as a single solvent or a mixture of solvents through the solvothermal route.14-17 Understanding the formation mechanism of 1-D nanostructures is very important to control its morphology and size such as diameter and length. Liu18 synthesized a sea-urchinlike CdS nanorod-based material and divided its formation process into several steps. Yang and coworkers19 investigated the formation process of CdS nanorods and proposed an accordionlike folding process. Recently, Xu et al.17 reported that the formation of CdS nanowires in a mixed solvent of ethylenediamine and dodecanethiol could be divided into four distinctive stages, but the formation mechansim would be different, depending on the solvothermal conditions such as precursor, reaction temperature, reaction time, and solvent. Also, to the best of our knowledge, there is no report about the photocatalytic activity of hydrogen production as well as the photoelectrochemical property of CdS nanowires prepared by solvothermal synthesis. In this work, we investigate the formation of CdS nanowires via a solvothermal route in ethylenediamine as single solvent at different reaction temperatures and reaction times and evaluate their photoelectrochemical properties as well as photoactivities * Corresponding author. Telephone: 82-562-279-2266. Fax: 82-562279-5528. E-mail: [email protected].

for hydrogen production from aqueous solution containing sulfide and sulfite as hole scavengers under visible light irradiation (λg 420 nm). Experimental Section Materials Preparation. In a typical procedure, 16.2 mmol Cd(NO3)2‚4H2O and 48.6 mmol NH2CSNH2 were added into a Teflon-lined, stainless steel autoclave which had been filled with ethylenediamine to 60% of its capacity (130 mL). The autoclave was maintained at 80-160 °C for 12 - 72 h and allowed to cool down to room temperature. A yellow precipitate was filtered and washed several times with absolute ethanol and deionized water to remove completely the residue of organic solvent. Preparation of Film Electrodes. As-synthesized CdS nanowires were thoroughly mixed with polyethylene glycol (PEG, Junsei, Mw 20,000) as a binder material with 30 wt % of CdS content and then cast on In:SnO2 (ITO) conducting glass (1 × 1 cm2). The film was dried at room temperature and calcined under air at 400 °C for 1 h to remove the binder. The ITO substrate was connected to a copper wire by silver paste to make Ohmic contact. Then the portion of silver paste on ITO substrate is again covered with epoxy resin to isolate it from an aqueous electrolyte solution. Characterization. The crystalline phases of the products were determined by powder X-ray diffraction (XRD) on a diffractometer (Mac Science Co., M18XHF) with monochromatic Cu KR radiation at 40 kV and 200 mA. The optical property was analyzed by UV-visible diffuse reflectance spectrometer (Shimadzu, UV 2401). The morphology of photocatalysts was investigated by field emission scanning electron microscopy (SEM, Hitachi, S-4200) and transmission electron microscope (TEM, JEOL JEM 2010F) operated at 200 kV. The TEM was also equipped with capabilities of energy dispersive X-ray spectroscopy (EDAX) and selected area electron diffraction

10.1021/jp072683b CCC: $37.00 © 2007 American Chemical Society Published on Web 08/15/2007

Solvothermal Synthesis of CdS Nanowires

J. Phys. Chem. C, Vol. 111, No. 35, 2007 13281

Figure 1. SEM images of CdS synthesized by solvothermal reaction at (a) 80 °C, (b) 100 °C, (c) 120 °C, (d) 140 °C for 24 h. TEM images are shown as insets for samples (b) and (c).

(SAED). The BET surface area was evaluated by N2 adsorption in a constant volume adsorption apparatus (Micrometrics, ASAP 2012). Photocatalytic Reactions. The photocatalytic reactions were carried out at room temperature under atmospheric pressure in a closed reactor using a Hg-arc lamp (500 W) equipped with a UV cutoff filter (λ g 420 nm). Before the reaction, 1 wt % of Pt was deposited on photocatalysts by a photodeposition method under visible light (λ g 420 nm). The rate of H2 evolution was determined in an aqueous solution (100 mL) containing 0.1 g of catalyst and 0.1 M Na2S + 0.02 M Na2SO3. The evolved amounts of H2 were analyzed by gas chromatography (TCD, molecular sieve 5-Å column and Ar carrier). Photoelectrochemical Measurements. The electrochemical cell was made of three electrodes of a CdS nanowire film electrode (1 × 1 cm2), Ag/AgCl, and Pt gauze as photoanode, reference electrode, and cathode, respectively. The photoanode was illuminated with a Hg-arc lamp (500 W) equipped with a UV cutoff filter (λ g 420 nm). Light source with 1.5 in. diameter was illuminated on the film electrode (1 × 1 cm2), and the light intensity was measured to be 516 mW/cm2. The photocurrent vs potential (I-V) was measured in an aqueous electrolyte solution (70 mL) consisting of 0.1 M Na2S + 0.02 M Na2SO3 at 25 °C using a potentiostat/galvanostat (EG&G model 263A) under illumination conditions (λ g 420 nm). The chronoamperometry curves were also obtained at -0.3V vs Ag/AgCl for the photosensitivity of CdS nanowire thin film under dark and illumination conditions.

Results and Discussion Effect of Solvothermal Temperature. It is well-known that the solvothermal temperature plays an important role in formation of crystal structure, shape, and size.17 Figure 1 shows SEM images of the samples prepared at various temperatures for 24 h. The morphology of sample synthesized at 80 °C was observed to be folding lamellar structures formed on the surface of microspheres with a diameter of ca. 0.5-1 µm. As the solvothermal temperature increases, the samples seem to grow into 1-D nanostructures still on the surface of microspheres. This lamellar-to-rod transition has been observed in many other systems and is known to proceed via the rolling mechanism.20,21 The samples obtained in the temperature range of 100-140 °C had an irregular rodlike shape. In Figure 1 TEM images of the samples obtained from solvothermal reactions at 100 °C and 120 °C for 24 h are shown in the insets of (a) and (b), respectively. Although it was clear that the samples grew into 1-D nanostructures, their morphology did not appear to be fully developed into nanorods or nanowires. The samples still contained some nanosheets, the precursor morphology before rolling into nanorods (inset of Figure 1b). The product obtained at 140 °C had much better developed rodlike CdS nanostructure with a length of ca. 500 nm to 1 µm and a diameter of ca. 50 nm (Figure 1d). The cross section of these nanorods showed hexagonal shape as shown in inset. During this process of CdS synthesis at different temperatures of solvothermal reaction, the surface area of the sample decreased from 139 to 29 m2/g. Thus, it appears that the sample prepared at 80 °C with the lamellar structure formed on the microsphere has a high porosity. As

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Figure 3. Intensity (A) and fwhm (B) ratios of (002) to (100) and (002) to (101) peaks in XRD patterns of the samples synthesized by solvothermal reaction at (a) 80 °C, (b) 100 °C, (c) 120 °C, (d) 140 °C, (e) 160 °C for 24 h.

Figure 2. (A) X-ray diffraction patterns of CdS synthesized by solvothermal reaction at (a) 80 °C, (b) 100 °C, (c) 120 °C, (d) 140 °C, (e) 160 °C for 24 h. (B) UV-vis diffuse reflectance spectra of the corresponding samples.

well-defined nanorod structures are developed, the surface area naturally decreases. Figure 2A displays XRD patterns of the samples obtained at different temperatures of 80-160 °C for the fixed reaction time of 24 h. The reflections of all samples were indexed to the hexagonal phase CdS,22,23 of which cell constants are known as a ) 4.136 Å and c ) 6.713 Å. As shown in Figure 2A(a), the sample obtained at 80 °C had the hexagonal phase CdS, but poor crystallinity. As the solvothermal temperature increased, the crystallinity of the samples continuously improved as indicated by stronger and narrower XRD peaks. For samples prepared at low temperatures the relative intensity of the (002) peak was stronger than those of the other diffraction peaks of (100) and (101). This indicates that there is already a relatively high crystalline order along the c-axis, whereas the order in the x-y plane is very poor at these low temperatures, as verified from all other broad lines. However, as the solvothermal

temperature increased, the intensities of (100) and (101) peaks increased, while that of (200) peak decreased. The intensity (Figure 3A) and fwhm (Figure 3B) ratios of (002)/(100) and (002)/(101) peaks clearly reveal this trend. The intensity ratios decreased and fwhm ratios increased as the solvothermal temperature increased. This represents the development of crystallinity in the x-y plane and the preferential orientation along the c-axis of nanorods formed at high temperatures, which lie mostly with their c-axis parallel with the experimental plane during the XRD measurements.20 This intensity distribution also indicates a preferential growth of the nanorods along the c-axis of the hexagonal CdS structure.24 Diffuse reflectance spectra of the samples were analyzed using the Kubelka-Munk function: F(R) ) (1 - R)2/2R ) K/S, where K and S represent the absorption (K) and scattering (S) coefficient.25 Figure 2B shows UV diffuse reflection (UV-DR) spectra of the samples obtained from solvothermal reaction at different temperatures of 80-160 °C for 24 h. The position and shape of absorption edges were not much different. The absorption edges were determined to be ca. 520 nm, which is close to that of bulk CdS with a band gap energy of 2.42 eV. However, unlike other samples, the sample obtained at 80 °C did not show a sharp absorption spectrum, probably due to poor crystal quality. The sample obtained at 160 °C showed the lower intensity of the absorbance spectrum compared with other samples.



Figure 4. SEM images of CdS synthesized by solvothermal reaction at 160 °C for (a) 12 h, (b) 24 h, (c) 48 h, (d) 72 h.

Effect of Solvothermal Reaction Time. Figure 4 shows SEM images of the samples prepared at 160 °C for different solvothermal reaction times. The morphology of products prepared at 160 °C for 12 h was nanorods with a length of ca. 200-400 nm and a diameter of ca. 40-50 nm. These dimensions were not uniform among nanorods. As solvothermal time increased, the morphology of the samples changed from nanorods to nanowires with their aspect ratio increased, indicating the growth not in diameter but in length. The XRD patterns of the samples obtained at 160 °C for 12 and 24 h seemed to be similar, and the length of product was almost the same as shown in Figure 4a,b. The sample obtained at 160 °C for 48 h showed the morphology of nanowire with a length of ca. 2-3 µm and a diameter of ca. 50 nm. The dimensions became much more uniform among individual nanowires. The cross section of nanowire was hexagonal in shape as shown in the inset of Figure 4c. When the reaction time was extended to 72 h, the length of the CdS nanowire increased up to ca. 4-5 µm with its diameter preserved at ca. 50 nm as shown in Figure 4d. Compared with the temperature-variation experiments, the surface area of the samples varied to a smaller degree between 98 m2/g and 30 m2/g. Figure 5 shows the TEM image, high-resolution (HR) TEM image, EDAX spectrum and SAED pattern of CdS nanowires obtained at 160 °C for 48 h. The TEM image of the sample shown in Figure 5a demonstrates the morphology of welldeveloped CdS nanowires with lengths of ca. 2-3 µm and diameters of ca. 50 nm; the EDAX spectrum of CdS showed that the nanowires were composed of Cd and S (Figure 5b). HRTEM image given in Figure 5c demonstrates the structural perfection of a CdS nanowire. The crystal lattice fringes are

clearly observed and the measured interplanar distance is in agreement with the typical hexagonal CdS (002) fringe (0.67 nm), which indicates that the CdS nanowires grow along the direction of c-axis. As shown in Figure 5d, the SAED pattern was recorded with an electron beam perpendicular to the long axis of a single nanowire. Evidently, the CdS nanowire is a single crystal of hexagonal CdS, and the bright diffraction spots are indicative of its high crystallinity. Moreover, the SAED pattern can be indexed for the [001] zone axis of hexagonal CdS, also indicating that preferential growth may occur along its c-axis direction.26 This result is in agreement with that of the XRD pattern of CdS samples as discussed below along with Figure 6A. Figure 6A displays XRD patterns of the samples obtained at different reaction times of 12-72 h at 160 °C. The sample obtained at the solvothermal time of 12 h had the hexagonal structure of CdS. As the solvothermal time increased, the relative intensity of (100) and (110) peaks became relatively stronger, while that of (002) peak became weaker. As mentioned previously, this is due to a preferential orientation along the c-axis of the nanowires which lie mostly with their c-axes parallel with the experimental plane during XRD measurements.20 However, diffraction peaks in Figure 5A are more intense and narrower than those in Figure 2A, indicating their higher crystallinity. Figure 6B shows the UV-diffuse reflection (UV-DR) spectra of the samples obtained in solvothermal reaction at 160 °C for 12-72 h. The position and shape of absorption edges were almost the same. But, the samples obtained at 160 °C for 12 and 24 h showed the higher intensity of absorbance than those of the other samples.


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Figure 5. TEM image (a), EDAX spectra (b), HRTEM image (c), SAED pattern (d) of CdS nanowires. This sample was solvothermally treated at 160 °C for 48 h.

Mechanism of CdS Nanowire Formation. In the present work the solvothermal temperatures and times were controlled to understand the formation mechanism of CdS nanowires in ethylenediamine. The growth of 1-D CdS nanostructure could be identified with XRD data and TEM and SEM images. It appears that the formation of CdS nanowires followed three steps: (1) the formation of nanowhiskers on microspheres as seeds for 1-D nanostructure, (2) transformation of nanowhisker into the CdS nanorods on the surface of microspheres, and (3) growth of CdS nanowires from CdS nanorods preferentially along the c-axis. In this hydrothermal reaction, ethylenediamine acts as a solvent as well as a complexing agent. At first, cadmium ions could combine with an ethylenediamine molecule (which acts as a bidentate ligand) to form a Cd-ethylenediamine complex,7 which is stabilized in the solution. As the hydrothermal temperature increases, the Cd-ethylenediamine complex decomposes to form CdS nuclei. Thiourea would also decompose under the solvothermal condition and provide sulfur needed for the formation of CdS. These nuclei grow to form a microsphere composed of nanosheets emanating from their surface (Figure 1a). With increasing the temperature to around 100 °C, nanosheets become unstable and start rolling into nanorods to achieve stability. Interestingly, nanorods are formed with hexagonal cross sections (inset of Figure 1d). As we carry out the reaction at 160 °C for 48 and 72 h (Figure 7a,b), the nanorods grow into nanowires with uniform diameters of ca. 50 nm and lengths of ca. 3-4 µm having a hexagonal phase and high crystallinity on the surface of microspheres. All these events are schematically represented in Figure 8. At 80 °C for 24 h, nanosheets are formed on the surface of microspheres; at 120 °C for 24 h, nanosheets change to nanorods; and finally at 160 °C for 48 h, nanowires are obtained. Recently, Xu et al.17 reported that in the growth of CdS nanowires, clewlike particles rupture into polydispersed nanow-

ires at 180 °C for 48 h under the hydrothermal reaction using ethylenediamine and dodecanethiol mixture. In our observation from the SEM images of the sample prepared at 160 °C for 48 and 72 h (Figure 7a,b), it appeared that CdS nanowires grew from the irregular microspheres. Although a few microspheres are broken down to give isolated nanowires, there was no apparent rupture of the microspheres into nanowires. The microspheres still remain when the nanowires are completely grown or when sample was washed several times with deionized water and ethanol (inset TEM and SEM of Figure 7a). The reason to obtain this type of morphology is not yet clear, but the required thermal energy and the time needed to rupture microspheres are higher and longer than 160 °C and 72 h, respectively. Photocatalytic Performance of CdS Nanowires. Shown in Figure 9A are the evolution rates of H2 and the specific BET surface areas of the samples prepared by solvothermal reaction at different temperatures for 24 h. These rates are average values during the first 3 h of the reaction during which the reaction showed stable rates. There was no appreciable change in the morphology of the CdS nanowires after the reaction, indicating the stability of the catalyst during the reaction. The photocatalytic reaction was carried out in an aqueous electrolyte solution containing 0.1 M Na2S and 0.02 M Na2SO3 as sacrificial reagent under visible light irradiation (using a cutoff filter of λ g 420 nm) for Pt(1 wt %)-loaded CdS catalysts.27 The rates of hydrogen evolution over CdS samples prepared at the higher solvothermal temperatures were higher than those of photocatalysts prepared at lower temperatures. Meanwhile, the surface area of the samples dramatically decreased according to the solvothermal temperatures. It is interesting to note that there was no apparent difference in photocatalytic activity of the samples prepared at 120 °C and 140 °C. In contrast, CdS samples prepared at 160 °C showed activity higher than those of the two samples. This is consistent with the conspicuous



Figure 7. Detailed SEM images of CdS synthesized by solvothermal reaction at 160 °C for 48 h (a) and 72 h (b).

Figure 6. (A) X-ray diffraction patterns of CdS synthesized by solvothermal reaction at 160 °C for (a) 12 h, (b) 24 h, (c) 48 h, (d) 72 h. (B) UV-vis diffuse reflectance spectra of the corresponding samples.

improvement in the crystallinity for the sample prepared at 160 °C as shown in Figure 2A. There is no correlation between activity and surface area nor between the activity and absorbance of the samples shown in Figure 2B. Thus, crystallinity seems to be more important factor for high activity than surface area or absorbance. In general, an efficient photocatalyst requires a high surface area and a high crystallinity because many reaction steps of photocatalysis take place on the surface, and a defect in the material structure could provide a site for energy-wasteful electron-hole recombination that reduces the efficiency of photocatalysis by absorbed photons.28-30 In many cases, a synthesis condition favoring one deteriorates the other. The hydrothermal temperature in this work is a good example. As the temperature increases, the crystallinity improves, but surface area decreases. Under our preparation conditions, the favoring

effect of improved crystallinity seems dominant over the negative effect of decreased surface area. Figure 9B shows the performance of photocatalytic hydrogen production and specific BET surface areas of the samples prepared at 160 °C for various solvothermal reaction times. The rates of hydrogen evolution over the samples prepared in the reaction for longer times (48 and 72 h) were higher than those of photocatalysts prepared at shorter reaction times (12 and 24 h). The surface area showed opposite trend of change. Again, a clear correlation was demonstrated between photocatalytic activity and the crystallinity of the samples. Effects of the surface area and absorbance were negligible. It should also be noted that these activities of CdS nanofibers are generally slightly lower than that of CdS particles prepared by the hydrothermal method (13 µmol/h) under the similar reaction conditions.31 Photoelectrochemical Property of CdS Nanowires. Among our samples prepared by different conditions, we selected the sample having the best photocatalytic activity for hydrogen production to investigate its photoelectrochemical property. Without loading of Pt cocatalyst, we fabricated the CdS nanowire thin film electrode by the screen printing method and measured its photocurrent in 0.1 M Na2S and 0.02 M Na2SO3 aqueous solution under visible light irradiation (λ g 420 nm). The morphology of the surface and cross section of CdS nanowire film prepared by the screen printing method was observed by SEM as shown in Figure 10. A partial aggregation of CdS nanowires and a vacant space between them were observed on the film surface, but homogeneity of CdS nanowire


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Figure 8. Schematic representation of the mechanism. In the first step the nuclei undergoes the transformation to a microsphere with nanosheets covering the surface; in the second step, the nanorods are formed on the surface; and in the last stage nanorods grow to nanowires.

Figure 9. (A) Rates of H2 evolution and the specific BET surface areas of CdS samples synthesized by solvothermal reaction at (a) 80 °C, (b) 100 °C, (c) 120 °C, (d) 140 °C, (e) 160 °C for 24 h. (B) Rates of H2 evolution and the specific BET surface areas of CdS samples synthesized by solvothermal reaction at 160 °C for (a) 12 h, (b) 24 h, (c) 48 h, (d) 72 h. The conditions of photocatalytic reaction are as follows; Catalysis: 0.1 g CdS loaded with 1 wt % Pt, electrolyte solution: 0.1 M Na2S + 0.02 M Na2SO3, light source: 500-W Hg lamp with a cutoff filter (λ g 420 nm).

film was satisfactory. The film thickness of CdS nanowires was ca. 4.4 µm, and it seemed to be well attached on ITO glass (Figure 10B). It is also noted that most nanowires lie with their axis parallel with the surface of the ITO glass.

Figure 10. SEM Images of CdS nanowire film electrode: (a) surface and (b) cross section. CdS was synthesized by a solvothermal reaction at 160 °C for 72 h.

As shown in Figure 11, the film electrode of CdS nanowires prepared at 160 °C for 72 h generated photocurrent in the direction of anodic potential under visible light irradiation, while no current was generated under the dark condition. The photocurrent density at 0 V vs Ag/AgCl is ca. 3.0 mA/cm2, and the photocurrent (Ip) response is rapid and reaches saturation immediately under illumination. This is a characteristic of an n-type semiconductor. The value of the onset potential for n-type CdS nanowire film from the photoresponse in Figure 11 was -1.35 V versus Ag/AgCl at pH 12.9. This onset potential and


J. Phys. Chem. C, Vol. 111, No. 35, 2007 13287 increase, the morphology of CdS changed from nanosheet on microsphere to nanorods, and then to nanowires; these changes induce the high crystallinity and high aspect ratio of CdS nanostructure. This evolution of morphology could be understood in terms of the rolling mechanism followed by unidirectional growth. CdS nanowires with the higher crystallinity showed the higher rate of photocatalytic hydrogen production from water containing Na2S and Na2SO3 as sacrificial reagents under visible light irradiation. Furthermore the photocatalytic activity is correlated with the crystallinity of the samples. The CdS nanowires could be used to fabricate a thin film electrode that demonstrated the possibility as a photoelectrochemical electrode for hydrogen production and solar cell systems. Acknowledgment. This work was supported by the Hydrogen Energy R&D Center, one of the 21st Century Frontier R&D Programs, National Research Laboratory, General Motors R&D Center, National R&D Project for Nano Science and Technology.

Figure 11. Photocurrent density-potential curves of CdS nanowire thin film electrode in 0.1 M Na2S + 0.02 M Na2SO3 (pH 12.9) under illumination (a) and dark conditions (b). Light source: 500-W Hg lamp with a cutoff filter (λ g 420 nm). (Inset) CdS nanowire film electrode.

Figure 12. Photocurrent-time transient response of CdS nanowire thin film electrode under dark (a) and illumination (b) conditions. Light source: 500-W Hg lamp with a cutoff filter (λ g 420 nm). Electrolyte: 0.1 M Na2S + 0.02 M Na2SO3 (pH 12.9). The potential was applied at -0.3 V vs Ag/AgCl for the photosensitivity of CdS nanowire thin film.

the photocurrent value are consistent with those of the previous works of other groups.32-34 From photoelectrochemical study it was demonstrated that CdS nanowires could generate photoelectrons and holes under visible light irradiation and become good photocatalysts with a proper potential for hydrogen production. Figure 12 shows the current-time transient response of CdS thin film electrode under dark and illumination conditions. It was observed that the photoresponse of CdS showed a high photosensitivity, i.e. a high photocurrent under illumination relative to the dark current. Hence, CdS nanowire thin film can be considered as a good candidate for the photoelectrochemical energy conversion device. Conclusion CdS nanowires were synthesized successfully by a solvothermal route at 160 °C for 48 h, and the morphology of 1-D CdS nanostructure could be controlled by solvothermal reaction temperatures and times. As the temperature and reaction time

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Solvothermal Synthesis of CdS Nanowires for Photocatalytic

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