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Synthesis and photoluminescence properties of hydrophilic ZnS nanoparticles
Materials Letters 64 (2010) 1521–1523
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
Synthesis and photoluminescence properties of hydrophilic ZnS nanoparticles Yue Zhang ⁎, Xihui Liang, Langchen Li Institute of Material Science and engineering, Ocean University of China, Qingdao 266100, Shandong Province, PR China
a r t i c l e
i n f o
Article history: Received 18 January 2010 Accepted 6 April 2010 Available online 10 April 2010 Keywords: ZnS nanoparticles Nanomaterials Surfactant Luminescence Hydrophilic
a b s t r a c t ZnS nanoparticles with an average diameter of 10 nm were synthesized by a solvothermal method under easily controlled and mild conditions. A composite surfactant for the preparation of ZnS nanoparticles was reported in order to improve the hydrophilicity. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize ZnS nanoparticles. The selected area electron diffraction (SAED) pattern indicated that ZnS was of high crystalline. The photoluminescence (PL) properties and water solubility of ZnS were investigated too. The photoluminescence characteristics indicated that ZnS nanoparticles exhibited a strong luminescent at 450 nm. Results of the contact angle demonstrated that the hydrophilicity has been improved greatly. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Nanomaterials find many applications in nanobiotechnology because the mere change of their diameters significantly shifts their emission spectra [1]. As now well recognized, besides their narrow, tunable, and symmetric emission spectra, nanomaterials have much greater temporal stability and resistance to photobleaching than fluorescent dyes do. Semiconductor nanomaterials have attracted widespread attention because of their special optical and electronic properties arising from the quantum confinement of electrons and large surface area [2–4]. Consequently, semiconductor nanomaterials might be ideal probes for spectrally multiplexed, time-gated cellular detection with enhanced selectivity and sensitivity. However, the agglomeration phenomena of nanomaterials impact many applications in nanobiotechnology. In order to overcome this drawback, the capping/stabilizing agents have recently been extensively applied to synthesis and design of materials with new structures and properties [5–7]. But, water solubility of nanomaterials has not been improved. Usually, the nanomaterials require good water solubility in order to meet the needs in nanobiotechnology [8–10]. The use of the coating is known to yield excellent results with respect to stability of phosphor in applying environments. In all these studies the coating was precipitated onto particles dispersed in an aqueous solution. However, this method is too complicated. Now, a composite surfactant for the preparation of ZnS nanoparticles is reported in order to obtain nanoparticles with good dispersity and hydrophilicity. The photoluminescence (PL) properties and hydrophilicity of ZnS nanoparticles are investigated too. The hydrophilicity of ZnS nanoparticles is recorded by the contact angle experiment. There are few of literatures to report about
⁎ Corresponding author. E-mail address: [email protected] (Y. Zhang). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.04.009
this method. However, the contact angle experiment is effective and easy for studying surface properties. 2. Experimental section 2.1. Synthesis of ZnS nanoparticles The analytical grade regents of ZnAc2, Na2S were used as starting materials. Stearic acid and sodium dodecyl sulfate were used as the capping agent. In typical procedure, firstly, stearic acid was dissolved in alcohol under stirring at 40 °C. 15 ml 0.3 M ZnAc2 aqueous solution was added into 15 ml stearic acid alcoholic solution. Subsequently, 15 ml Na2S and 5 ml sodium dodecyl sulfate aqueous solution were added into
Fig. 1. XRD patterns of ZnS prepared in different surfactant systems (a) without surfactant; (b) in stearic acid; and (c) in stearic acid and sodium dodecyl sulfate.
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Y. Zhang et al. / Materials Letters 64 (2010) 1521–1523
the above mixture. Finally, the above resulting reactants were sealed in a 90 ml Teflon-lined autoclave and placed in an air oven at 200 °C for 6 h. After the reaction was completed, the autoclave was taken out of the oven and allowed to cool to room temperature. Then the resulting particles were separated by centrifugation, washed with distilled water and ethanol and then dried at 60 °C. 2.2. Property characterizations of ZnS nanoparticles The XRD patterns of nanoparticles were obtained on a Bruker D8 Advanced X-ray diffractometer with Cu–Kα radiation (λ = 1.5418 Å). The observation of the morphology and electron diffraction patterns was performed on a Hitachi Model 800 transmission electron
microscopy at an acceleration voltage 200 kV. The samples for TEM were prepared by making clear dispersion of the nanoparticles in ethanol and putting a drop of it on a carbon coated copper grid. The photoluminescence and photoluminescence excitation spectra were taken by a Jobin Yvon INC Flurolog-3-21spectrofluorometer at room temperature. The measurement of contact angle was performed on a JC2000C1 powder contact angle measuring instrument by pressed disc method. Firstly, the samples for contact angle were pushed into the tablet by 769yb-24b tablet machine at 5 MPa pressure for 5 min, then put a drop of water on a tablet. 3. Results and discussions Powder XRD patterns of the various ZnS nanoparticles prepared in different surfactant systems are shown in Fig. 1. The broadening of peaks in the XRD pattern compared to those of bulk ZnS indicates the nanocrystalline nature of the samples. These diffraction features appearing at 28.5°, 47.5°, and 56.3° correspond to the (111), (220), and (311) planes of the cubic zinc blende structure, which is very consistent with the values in the standard card (JCPDS No. 5-0566). The mean nanoparticle size is obtained from full-width at half-maximum of the (111) zinc blende reflection according to the Debye–Scherrer equation L=0.9λ/βcosθ. The nanoparticle size of ZnS prepared in different surfactant systems is not similar. The nanoparticle sizes of three samples estimated from the Debye–Scherrer formula are 20 nm, 15 nm and 10 nm. The size of ZnS nanoparticle prepared in composite surfactant system is the smallest. Fig. 2 shows the TEM images of ZnS nanoparticle prepared in different surfactant systems. From Fig. 2a and b, it is observed that the agglomeration phenomena of ZnS nanoparticle prepared without surfactant is very obvious. ZnS nanoparticle prepared in composite surfactant system is monodisperse. The uniformity of nanoparticle size with an average diameter of 10 nm is demonstrated. The shape of each nanoparticle is close to spherical and the mean diameter is 10 nm, which is in good agreement with calculated results from XRD patterns. The edges of nanoparticles are extremely clear. The selected area electron diffraction (SAED) pattern in Fig. 2c indicates that nanoparticles are of high crystalline and it is typical for the cubic ZnS phase. The three diffraction rings correspond to the (111), (220) and (311) reflections, which are fully according with the XRD results. The PL spectra are shown in Fig. 3, a strong peak centered at 450 nm (blue) in PL spectrum belongs to a violet defected-related which is assigned to recombination at sulfur vacancies in the materials. It is found that the PL intensity increases with the surfactant addition. For comparison with ZnS prepared in the monosurfactant, ZnS nanoparticles prepared in composite surfactant system exhibit stronger PL properties at the same measurement. The PL spectrum shows an emission peak
Fig. 2. TEM images of ZnS prepared in different surfactant systems (a) without surfactant; (b) in stearic acid and sodium dodecyl sulfate; and (c) SAED image.
Fig. 3. PL spectra of ZnS prepared in different surfactant systems (a) without surfactant; (b) in stearic acid; and (c) in stearic acid and sodium dodecyl sulfate.
Y. Zhang et al. / Materials Letters 64 (2010) 1521–1523
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operative effect of two surfactants improves the coordination ability of the monosurfactant. As a result, ZnS nanoparticles prepared in composite surfactant system have excellent dispersity and uniformity of nanoparticles size (see Fig. 2a and b). Generally, it is known that the PL properties of particles are impacted by many factors, such as particle shape, size, size distribution and so on. Therefore, the emission intensities can be enhanced. The composite surfactant system has an effect on improving the brightness of nanoparticles. Fig. 4 gives the photos of the contact angle experiment to obtain the hydrophilicity of ZnS nanoparticles. It is seen that ZnS nanoparticles prepared in composite surfactant system have smaller contact angle for comparison with ZnS prepared without surfactant. It means that water solubility of ZnS nanoparticles is improved by composite surfactant. It is known that the hydrophilicity and lipophilicity of surfactant are attributed by hydrophile–lipophile balance (HLB) value. The HLB value of stearic acid and sodium dodecyl sulfate is 17 and 40, respectively. As a result, the hydrophilicity of ZnS nanoparticles is enhanced greatly. 4. Conclusions
Fig. 4. Images of the contact angle experiment for ZnS (a) in stearic acid and sodium dodecyl sulfate; and (b) without surfactant.
centered at around 450 nm, which is at a shorter wavelength than 470 nm for bulk ZnS. In monosurfactant stearic acid or sodium dodecyl sulfate system, stearic acid or sodium dodecyl sulfate can be used as surfactant because they have an effect on complex formation by interacting with the metal ions to hinder nanoparticles agglomeration. Due to the coordination ability of the surfactant, they can interact with the zinc ions by coordination reaction to form surfactant–zinc complex. In other words, zinc ions are firstly separated each other by the surfactant. Then the independent nucleation and growth of each zinc ion prevent the agglomeration of nanoparticles. In composite surfactant system, the co-
In summary, ZnS nanoparticles with an average diameter of 10 nm were synthesized in composite surfactant system, which is easily controllable, safe and convenient route. The symmetric photoluminescence emissions were achieved at 450 nm. For comparison with ZnS prepared in the monosurfactant surfactant, not only the photoluminescence brightness of ZnS nanoparticles prepared in composite surfactant system has been enhanced but also the hydrophilicity has been improved greatly. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
Huang CP, Wi Liu S, Chen TM, Li YK. Sen Act B: Chem 2008;130:338–42. Murray CB, Kagan CR, Bawendi MG. Annu Rev Mater Sci 2000;30:545–610. Vossmeyer T, Katsikas L, Giersig M. J Phys Chem 1994;98:7665–73. Bowen Katari JE, Colvin VL, Alivisatos AP. J Phys Chem 1994;98:4109–17. Jiang CL, Zhang WQ, Zou GF, Yu WC, Qian YT. Mater Chem Phys 2007;103:24–7. Kang XH, Wang B, Zhu L, Zhu H. Wear 2008;265:150–4. Saleema N, Farzaneh M. Appl Surf Sci 2008;254:2690–5. Chen S, Liu WM. Mater Res Bull 2001;36:137–43. Lu SW, Burtrand IL, Wang ZL. J Lum 2001;92:73–8. Michael JM, David LS, Eric C. Opt Comm 2008;281:1771–80.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
Synthesis and photoluminescence properties of hydrophilic ZnS nanoparticles Yue Zhang ⁎, Xihui Liang, Langchen Li Institute of Material Science and engineering, Ocean University of China, Qingdao 266100, Shandong Province, PR China
a r t i c l e
i n f o
Article history: Received 18 January 2010 Accepted 6 April 2010 Available online 10 April 2010 Keywords: ZnS nanoparticles Nanomaterials Surfactant Luminescence Hydrophilic
a b s t r a c t ZnS nanoparticles with an average diameter of 10 nm were synthesized by a solvothermal method under easily controlled and mild conditions. A composite surfactant for the preparation of ZnS nanoparticles was reported in order to improve the hydrophilicity. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize ZnS nanoparticles. The selected area electron diffraction (SAED) pattern indicated that ZnS was of high crystalline. The photoluminescence (PL) properties and water solubility of ZnS were investigated too. The photoluminescence characteristics indicated that ZnS nanoparticles exhibited a strong luminescent at 450 nm. Results of the contact angle demonstrated that the hydrophilicity has been improved greatly. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Nanomaterials find many applications in nanobiotechnology because the mere change of their diameters significantly shifts their emission spectra [1]. As now well recognized, besides their narrow, tunable, and symmetric emission spectra, nanomaterials have much greater temporal stability and resistance to photobleaching than fluorescent dyes do. Semiconductor nanomaterials have attracted widespread attention because of their special optical and electronic properties arising from the quantum confinement of electrons and large surface area [2–4]. Consequently, semiconductor nanomaterials might be ideal probes for spectrally multiplexed, time-gated cellular detection with enhanced selectivity and sensitivity. However, the agglomeration phenomena of nanomaterials impact many applications in nanobiotechnology. In order to overcome this drawback, the capping/stabilizing agents have recently been extensively applied to synthesis and design of materials with new structures and properties [5–7]. But, water solubility of nanomaterials has not been improved. Usually, the nanomaterials require good water solubility in order to meet the needs in nanobiotechnology [8–10]. The use of the coating is known to yield excellent results with respect to stability of phosphor in applying environments. In all these studies the coating was precipitated onto particles dispersed in an aqueous solution. However, this method is too complicated. Now, a composite surfactant for the preparation of ZnS nanoparticles is reported in order to obtain nanoparticles with good dispersity and hydrophilicity. The photoluminescence (PL) properties and hydrophilicity of ZnS nanoparticles are investigated too. The hydrophilicity of ZnS nanoparticles is recorded by the contact angle experiment. There are few of literatures to report about
⁎ Corresponding author. E-mail address: [email protected] (Y. Zhang). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.04.009
this method. However, the contact angle experiment is effective and easy for studying surface properties. 2. Experimental section 2.1. Synthesis of ZnS nanoparticles The analytical grade regents of ZnAc2, Na2S were used as starting materials. Stearic acid and sodium dodecyl sulfate were used as the capping agent. In typical procedure, firstly, stearic acid was dissolved in alcohol under stirring at 40 °C. 15 ml 0.3 M ZnAc2 aqueous solution was added into 15 ml stearic acid alcoholic solution. Subsequently, 15 ml Na2S and 5 ml sodium dodecyl sulfate aqueous solution were added into
Fig. 1. XRD patterns of ZnS prepared in different surfactant systems (a) without surfactant; (b) in stearic acid; and (c) in stearic acid and sodium dodecyl sulfate.
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Y. Zhang et al. / Materials Letters 64 (2010) 1521–1523
the above mixture. Finally, the above resulting reactants were sealed in a 90 ml Teflon-lined autoclave and placed in an air oven at 200 °C for 6 h. After the reaction was completed, the autoclave was taken out of the oven and allowed to cool to room temperature. Then the resulting particles were separated by centrifugation, washed with distilled water and ethanol and then dried at 60 °C. 2.2. Property characterizations of ZnS nanoparticles The XRD patterns of nanoparticles were obtained on a Bruker D8 Advanced X-ray diffractometer with Cu–Kα radiation (λ = 1.5418 Å). The observation of the morphology and electron diffraction patterns was performed on a Hitachi Model 800 transmission electron
microscopy at an acceleration voltage 200 kV. The samples for TEM were prepared by making clear dispersion of the nanoparticles in ethanol and putting a drop of it on a carbon coated copper grid. The photoluminescence and photoluminescence excitation spectra were taken by a Jobin Yvon INC Flurolog-3-21spectrofluorometer at room temperature. The measurement of contact angle was performed on a JC2000C1 powder contact angle measuring instrument by pressed disc method. Firstly, the samples for contact angle were pushed into the tablet by 769yb-24b tablet machine at 5 MPa pressure for 5 min, then put a drop of water on a tablet. 3. Results and discussions Powder XRD patterns of the various ZnS nanoparticles prepared in different surfactant systems are shown in Fig. 1. The broadening of peaks in the XRD pattern compared to those of bulk ZnS indicates the nanocrystalline nature of the samples. These diffraction features appearing at 28.5°, 47.5°, and 56.3° correspond to the (111), (220), and (311) planes of the cubic zinc blende structure, which is very consistent with the values in the standard card (JCPDS No. 5-0566). The mean nanoparticle size is obtained from full-width at half-maximum of the (111) zinc blende reflection according to the Debye–Scherrer equation L=0.9λ/βcosθ. The nanoparticle size of ZnS prepared in different surfactant systems is not similar. The nanoparticle sizes of three samples estimated from the Debye–Scherrer formula are 20 nm, 15 nm and 10 nm. The size of ZnS nanoparticle prepared in composite surfactant system is the smallest. Fig. 2 shows the TEM images of ZnS nanoparticle prepared in different surfactant systems. From Fig. 2a and b, it is observed that the agglomeration phenomena of ZnS nanoparticle prepared without surfactant is very obvious. ZnS nanoparticle prepared in composite surfactant system is monodisperse. The uniformity of nanoparticle size with an average diameter of 10 nm is demonstrated. The shape of each nanoparticle is close to spherical and the mean diameter is 10 nm, which is in good agreement with calculated results from XRD patterns. The edges of nanoparticles are extremely clear. The selected area electron diffraction (SAED) pattern in Fig. 2c indicates that nanoparticles are of high crystalline and it is typical for the cubic ZnS phase. The three diffraction rings correspond to the (111), (220) and (311) reflections, which are fully according with the XRD results. The PL spectra are shown in Fig. 3, a strong peak centered at 450 nm (blue) in PL spectrum belongs to a violet defected-related which is assigned to recombination at sulfur vacancies in the materials. It is found that the PL intensity increases with the surfactant addition. For comparison with ZnS prepared in the monosurfactant, ZnS nanoparticles prepared in composite surfactant system exhibit stronger PL properties at the same measurement. The PL spectrum shows an emission peak
Fig. 2. TEM images of ZnS prepared in different surfactant systems (a) without surfactant; (b) in stearic acid and sodium dodecyl sulfate; and (c) SAED image.
Fig. 3. PL spectra of ZnS prepared in different surfactant systems (a) without surfactant; (b) in stearic acid; and (c) in stearic acid and sodium dodecyl sulfate.
Y. Zhang et al. / Materials Letters 64 (2010) 1521–1523
1523
operative effect of two surfactants improves the coordination ability of the monosurfactant. As a result, ZnS nanoparticles prepared in composite surfactant system have excellent dispersity and uniformity of nanoparticles size (see Fig. 2a and b). Generally, it is known that the PL properties of particles are impacted by many factors, such as particle shape, size, size distribution and so on. Therefore, the emission intensities can be enhanced. The composite surfactant system has an effect on improving the brightness of nanoparticles. Fig. 4 gives the photos of the contact angle experiment to obtain the hydrophilicity of ZnS nanoparticles. It is seen that ZnS nanoparticles prepared in composite surfactant system have smaller contact angle for comparison with ZnS prepared without surfactant. It means that water solubility of ZnS nanoparticles is improved by composite surfactant. It is known that the hydrophilicity and lipophilicity of surfactant are attributed by hydrophile–lipophile balance (HLB) value. The HLB value of stearic acid and sodium dodecyl sulfate is 17 and 40, respectively. As a result, the hydrophilicity of ZnS nanoparticles is enhanced greatly. 4. Conclusions
Fig. 4. Images of the contact angle experiment for ZnS (a) in stearic acid and sodium dodecyl sulfate; and (b) without surfactant.
centered at around 450 nm, which is at a shorter wavelength than 470 nm for bulk ZnS. In monosurfactant stearic acid or sodium dodecyl sulfate system, stearic acid or sodium dodecyl sulfate can be used as surfactant because they have an effect on complex formation by interacting with the metal ions to hinder nanoparticles agglomeration. Due to the coordination ability of the surfactant, they can interact with the zinc ions by coordination reaction to form surfactant–zinc complex. In other words, zinc ions are firstly separated each other by the surfactant. Then the independent nucleation and growth of each zinc ion prevent the agglomeration of nanoparticles. In composite surfactant system, the co-
In summary, ZnS nanoparticles with an average diameter of 10 nm were synthesized in composite surfactant system, which is easily controllable, safe and convenient route. The symmetric photoluminescence emissions were achieved at 450 nm. For comparison with ZnS prepared in the monosurfactant surfactant, not only the photoluminescence brightness of ZnS nanoparticles prepared in composite surfactant system has been enhanced but also the hydrophilicity has been improved greatly. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
Huang CP, Wi Liu S, Chen TM, Li YK. Sen Act B: Chem 2008;130:338–42. Murray CB, Kagan CR, Bawendi MG. Annu Rev Mater Sci 2000;30:545–610. Vossmeyer T, Katsikas L, Giersig M. J Phys Chem 1994;98:7665–73. Bowen Katari JE, Colvin VL, Alivisatos AP. J Phys Chem 1994;98:4109–17. Jiang CL, Zhang WQ, Zou GF, Yu WC, Qian YT. Mater Chem Phys 2007;103:24–7. Kang XH, Wang B, Zhu L, Zhu H. Wear 2008;265:150–4. Saleema N, Farzaneh M. Appl Surf Sci 2008;254:2690–5. Chen S, Liu WM. Mater Res Bull 2001;36:137–43. Lu SW, Burtrand IL, Wang ZL. J Lum 2001;92:73–8. Michael JM, David LS, Eric C. Opt Comm 2008;281:1771–80.