Article pubs.acs.org/IECR
Interfacial Self-assembly of NixCd1−xS/ODA Hybrids with Photoluminescent and Superhydrophobic Performance Yan Zhang, Qiang Zhang, Cai-Feng Wang, and Su Chen* State Key Laboratory of Materials-Oriented Chemical Engineering and College of Chemistry and Chemical Engineering, Nanjing University of Technology, No. 5 Xin Mofan Road, Nanjing 210009, People’s Republic of China ABSTRACT: We report herein a simple strategy for fabricating two-dimensional (2D) petal-like NixCd1−xS/octadecylamine (ODA) hybrids exhibiting both photoluminescent and superhydrophobic properties via a facile liquid−liquid interfacial selfassembly technique. First, thioglycolic acid stabilized CdS quantum dots (QDs) doped with nickel were synthesized in aqueous solution. Then, relying on the facile H2O/CHCl3 interfacial platform, through the electrostatic interactions between positively charged amino groups of ODA and negatively charged carboxyl groups of a QD surface, we have successfully fabricated petal-like NixCd1−xS/ODA hybrids. These NixCd1−xS/ODA hybrids present enhanced photoluminescence compared with NixCd1−xS QDs, especially in high quantum yield, which is enhanced from 3% to 50%. Moreover, the NixCd1−xS/ODA hybrid film has a water contact angle of 152.7°, leading to its excellent hydrophobic property. Finally, by virtue of their excellent polymer compatibility and optical properties, we extended the robust QDs as “fluorescent ink” to print elegant photoluminescent patterns by silk-screen printing.
1. INTRODUCTION Doped semiconductor quantum dots (QDs) have attracted extensive research interest in recent years because of their wide applications in diverse fields including solar cells,1 biolabeling,2 electroluminescent devices,3 photocatalysis,4 and diagnostics.5 Notably, the interaction of excitons and dopant ions causes the doped semiconductor QDs to exhibit new optical, electronic, and magnetic properties that are markedly different from those of the undoped ones.6,7 Cadmium sulfide (CdS), with a direct band gap of 2.43 eV at room temperature, is one of the best host materials used for the preparation of transition metal (TM)-doped semiconducting materials.8,9 To date, various methods for fabricating TM (Mn, Co, Fe, Cu, Cr, etc.)-doped CdS QDs have been widely investigated, such as hot injection, cluster thermolysis, solvothermal techniques, and ion-beam synthesis.10−15 However, most of the reported methods employed either expensive raw materials or tough experimental conditions, thereby limiting the extensive applications of doped QDs. Therefore, a couple of facile and efficient strategies are in great demand to fabricate doped semiconductor QDs with better performance and ideal versatility. Recently, liquid−liquid interfacial self-assembly has become a hot research topic because it can be an effective method for the fabrication of homogeneous QD networks with desirable properties and applications. Compared with previous methods, the creative interfacial method displays obvious advantages, for example, low reaction temperature, moderate and controllable experimental conditions, simple equipment, and a high quantum yield (QY) of the resulting QDs.25 The plane liquid−liquid interface can provide a favorable environment for the chemical reaction between capping ligands and reagents in the liquid phase, taking advantage of this plane, the QDs can be further modified by organic molecules with functional surface groups. Because the functional organic surface ligands can serve to heal QD surface defects and allow QDs to organize into hierarchical structures with size-dependent properties, QD © 2013 American Chemical Society
hybrids with better photostability, enhanced photoluminescence (PL), and hierarchical nano/microstructure are simply available.16,17 Illuminatingly, hierarchical structures constructed on the micro/nanoscale with low surface energy may pose a potential possibility to achieving superhydrophobic surfaces where the water contact angles (CAs) ≥150°.18,19 In general, superhydrophobic surfaces can be prepared either by tailoring the chemical composition of the solid surfaces or by building coarse micro/nanostructures on them. Until now, a large number of methods have been proposed to fabricate artificial superhydrophobic surfaces with such properties as transparence, responsiveness, and conductance, such as layer-bylayer processing,20 sol−gel processing,21 electrospinning,22 the creation of a rough surface covered with low surface energy molecules,23,24 and so forth. To the best of our knowledge, although great progress has been achieved, there are sparse examples on the fabrication of superhydrophobic films with optical properties using this facile liquid−liquid interfacial selfassembly method.25−28 Herein, we first demonstrated a facile route for the fabrication of nickel-doped CdS QDs at room temperature and studied the effects of nickel doping on the structural and optical properties of CdS QDs. Then, with the as-prepared thioglycolic acid (TGA)-stabilized NixCd1−xS QDs in water as the water phase and ODA dissolved in CHCl3 as the oil phase, we successfully transferred TGA-stabilized NixCd1−xS QDs from the water phase to the oil phase by simply adjusting the pH of the water phase to an optimal acidic range. Meanwhile, the QDs can be assembled into petal-like microstructures under the direction of ODA, with increasing assembly time. To our Received: Revised: Accepted: Published: 11590
April 28, 2013 July 11, 2013 July 19, 2013 July 19, 2013 dx.doi.org/10.1021/ie401354f | Ind. Eng. Chem. Res. 2013, 52, 11590−11596
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Figure 1. Illustration of the route for the synthesis of petal-like NixCd1−xS/ODA hybrids.
was dissolved in 5 mL of chloroform as the oil phase, and the above-synthesized water-soluble NixCd1−xS QDs (5 mL) were used as the water phase, along with adjustment of the pH value to 5.8. Then the water phase was carefully layered on top of the oil phase in a vessel, which was sealed and maintained at room temperature. As shown, aqueous synthetic QDs possess negatively charged carboxyl groups, thus providing a driving force for assembling themselves with positively charged ligands of ODA via electrostatic attraction, which slowly transport the NixCd1−xS QDs from water to the oil phase in several days. Last, the chloroform phase containing NixCd1−xS/ODA hybrids was precipitated by absolute ethanol, washed with it twice, isolated by centrifugation, and then dried under vacuum. 2.4. Preparation of a Ni0.02Cd0.98S/ODA Hybrid Film. The oil solution of Ni0.02Cd0.98S/ODA hybrids was dropped slowly on a clean glass slide at room temperature. A thin film was formed when the residual solvent fully evaporated, and then the solution was dripped onto the glass continually until the thickness reached ca. 0.3 mm. 2.5. Fluorescent Patterns from Ni0.02Cd0.98S QDs and Ni0.02Cd0.98S/ODA Hybrids. A 2 g aqueous solution of Ni0.02Cd0.98S QDs was magnetically blended with an SA solution (8 g, 2 wt %) to form a homogeneous solution. Also a 2 g oil solution of Ni0.02Cd0.98S/ODA hybrids was also blended with PLA, which is dissolved in CHCl3 (8 g, 2 wt %). The solution was cast on the printing mask of a silk-screenprinting device and was penetrated through the pattern screen (140 mesh) onto the filter paper. 2.6. Characterization. X-ray diffraction (XRD) patterns were conducted on a Bruker-AXS D8 ADVANCE X-ray diffractometer with Cu Kα radiation (λ = 0.1542 nm) at a scanning speed of 60 rpm over a 2θ range of 10−80°. Ultraviolet-visible (UV-vis) spectra were recorded on a PerkinElmer Lambda 900 UV-vis spectrometer. PL spectra were measured on a Varian Cary Eclipse spectrophotometer at room temperature, and the QY was calculated by comparison with quinine with the QY at 55%. The fluorescence images of the corresponding samples were all taken under irradiation with a 365 nm UV light. Fourier transform infrared (FT-IR) were
excitement, the obtained small organic-ligand-functionalized QD hybrids exhibited better optical properties, a higher QY, which increased from 3% to 50% after the interfacial assembly, and a hierarchical nano/microstructure. Most importantly, the NixCd1−xS/ODA hybrid films displayed excellent superhydrophobic properties. Finally, taking advantage of the asprepared QDs, we extended the robust QDs as “fluorescent ink” to print elegant PL patterns, which may find application in anticounterfeit field.
2. EXPERIMENTAL SECTION 2.1. Chemicals. Cadmium chloride (CdCl2·2.5H2O), nickel chloride (NiCl2·6H2O), thioglycolic acid (TGA), sodium sulfide (Na2S·9H2O), sodium hydroxide (NaOH), octadecylamine (ODA), and chloroform (CHCl3) were of analytical grade. Poly(lactic acid) (PLA), sodium alginate (SA), and quinine were purchased from standard sources. All of the materials were used as received without further purification. 2.2. Synthesis of Carboxyl-Coated NixCd1−xS QDs. The reaction was carried out in open-air environment. As shown in Figure 1a, for the synthesis of Ni0.02Cd0.98S QDs (x = 0.02), CdCl2·2.5H2O (0.3357 g, 1.47 mmol) and NiCl2·6H2O (0.0071 g, 0.03 mmol) were simultaneously dissolved in 20 mL of deionized water. Then, TGA (0.2764 g, 3 mmol) dissolved in 20 mL of deionized water was added under vigorous stirring, followed by an adjustment of the pH to 8 using a 5 M solution of NaOH. Subsequently, 20 mL of an aqueous solution of Na2S·9H2O (0.2162 g, 0.9 mmol) was added slowly into the above mixed solution with stirring. Finally, the mixture was stirred for an additional 6 h at room temperature. Similarly, through changes in the value of x, namely, x = 0.00, 0.01, 0.04, and 0.06, we can obtain NixCd1−xS QDs with different compositions, keeping the total molar weight of [Cd2+ + Ni2+] = 1.5 mmol and (Cd2+ + Ni2+)/TGA/S2− = 1/2/0.6 mol/ mol/mol. 2.3. Synthesis of NixCd1−xS/ODA Hybrids. The interfacial assembly of NixCd1−xS QDs with ODA via an interfacial diffusion process was performed according to a modified literature method.25 As depicted in Figure 1b, 0.1010 g of ODA 11591
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Figure 2. (a) TEM image and size-distribution diagram (inset) and (b) HRTEM micrograph of Ni0.02Cd0.98S QDs.
recorded on a Nicolet 6700 FT-IR spectrometer. The samples were ground with KBr crystals, and the mixture was pressed into a flake for IR measurement with 32 scans from 4000 to 500 cm−1 at a resolution of 4 cm−1. Transmission electron microscopy (TEM) observation was performed with a JEOL JEM-2010 transmission electron microscope. The microstructures of the NixCd1−xS/ODA hybrids were observed by scanning electron microscopy (SEM) with a Quanta 200 (Philips-FEI, Holland) instrument at 30.0 kV. The CA of a 5 μL water droplet and the sliding angle on the surface were measured with a Krüss DSA100 (Krüss, Germany) contact angle system at ambient temperature.
Figure 3. XRD patterns of TGA-stabilized NixCd1−xS QDs.
3. RESULTS AND DISCUSSION The synthesis of carboxyl-coated NixCd1−xS QDs involves the reaction between CdCl2, NiCl2, and S ions in the presence of TGA as the capping ligand. The electron-deficient atoms of cadmium serve as binding sites to anchor organic ligands and to hinder the further growth of crystal grains, which results in the formation of nanosized crystals.29 Simultaneously, the carboxyl functional groups of TGA provide a good access to surface modification and composite assembly for QDs.30 3.1. Effects of the Nickel Dopant on the Morphology, Size, Crystal Structure, and Optical Properties of CdS QDs. The water-phase QDs can be well scattered in the water mainly through a mutual electrostatic repulsive force, as shown in Figure 2a; the as-prepared nickel-doped CdS QDs are relatively uniform and well-dispersed without obvious aggregation. The mean size of the Ni0.02Cd0.98S QDs was measured to be about 4 nm, corresponding to the standards of QDs. The size-distribution diagram (inset) further indicates that the QDs have relatively narrow size distribution. Moreover, the highresolution TEM (HRTEM) image of the Ni0.02Cd0.98S nanoparticles (Figure 2b) demonstrates that the QDs are highly crystalline through the observation of lattice planes. To investigate the effect of nickel on the CdS crystal structure, we characterized NixCd1−xS QDs with various x values (x = 0.00−0.06) by XRD (shown in Figure 3). It can be seen from Figure 3 that the diffraction peaks at 2θ (degree) values of 28.20°, 47.50°, and 56.93° of CdS (x = 0) correspond to the (111), (220), and (311) planes, which are in very good agreement with the CdS cubic structure,31 and all of the peaks in the diffraction patterns of the alloyed QDs with different nickel molar fractions are found to be characteristic of CdS, indicating that the incorporation of nickel in the sample does not introduce appreciable changes in the crystal structure of CdS. However, the diffraction peaks of NixCd1−xS QDs gradually broadened with an increase in the nickel molar
fractions, indicating that the grain sizes of the crystal samples become smaller.32,33 Figure 4 shows the UV−vis absorption and PL spectra of the TGA-stabilized NixCd1−xS QDs with various x values (x = 0.00−0.06). It is clearly seen from the spectrum that the positions of peaks have a gradual blue shift with an increase in the nickel molar fractions in the QDs. The blue shift in the absorption spectra can be ascribed to the quantum confinement effect of an electron−hole pair (exciton), which is indicative of the formation of alloyed NixCd1−xS QDs.14,34 From Figure 4b, we have found that the PL intensity of QDs is strongly influenced by the nickel molar fraction, in which the PL intensity decreases gradually with an increase in the nickel molar fraction. Also the PL spectrum of NixCd1−xS QDs shows a broad peak in the range of 450−750 nm centered at about 565 nm, mainly originating from a recombination of the surface electrons and holes.35 To decrease the surface defects of the synthesized QDs and to improve their PL properties, herein, we utilized a simple liquid−liquid interfacial method under room temperature, allowing the ODA to tailor the surface structure of the QDs, where the initial TGA-stabilized Ni0.02Cd0.98S QD solution (QY ca. 3%) with pH 5.8 was applied as the water phase and ODA in CHCl3 served as the oil phase ([ODA] = 0.075 M). After several days, the NixCd1−xS QDs were slowly transformed from the water phase to the chloroform phase, and then we obtain the end products containing NixCd1−xS/ODA hybrids. 3.2. FT-IR Characterization. To confirm the phase transfer of NixCd1−xS QDs between the water and chloroform phases and clarify how the Ni0.02Cd0.98S QDs to react with ODA, the FT-IR spectra of the Ni0.02Cd0.98S, Ni0.02Cd0.98S/ODA hybrids, and ODA are shown in Figure 5, respectively. As depicted in the FT-IR spectrum of TGA-stabilized Ni0.02Cd0.98S (Figure 5a), strong absorption peaks at 1384 and 1570 cm−1 (νCOO−) are indicative of the presence of carboxyl groups on the surfaces 11592
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Figure 4. (a) UV−vis absorption and (b) PL spectra of TGA-stabilized NixCd1−xS QDs.
showing excellent dispersion without obvious aggregation. The well-resolved lattice fringes in the HRTEM picture (Figure 6b) and clear diffuse rings in the selected-area electron diffraction (SAED) pattern (Figure 6c) further indicate excellent monodispersion and finely preserved crystalline structures of QDs in Ni0.02Cd0.98S/ODA hybrids during the reaction of the ligand on the QD surface. In addition, the XRD pattern of the Ni0.02Cd0.98S/ODA hybrids (seen in Figure 6d) shows broad peaks, which are assigned to the (111), (220), and (311) planes of the cubic structure of a bulk CdS crystal, suggesting that surface modification of Ni0.02Cd0.98S QDs with ODA does not affect the structure of the Ni0.02Cd0.98S crystal. Also the size of the Ni0.02Cd0.98S QDs in the hybrids can be calculated as approximately 4 nm from the major diffraction peak (111) (2θ = 28.2°) by Scherrer’s equation,38 which is in good agreement with the result of TEM measurement. 3.4. Effect of the Interfacial Reaction Time on the Optical Properties of Ni0.02Cd0.98S/ODA Hybrids. The UV−vis absorption and PL properties of Ni0.02Cd0.98S/ODA hybrids with respect to different interfacial reaction times are shown in Figure 7. As demonstrated in UV−vis absorption spectra (Figure 7a), the positions of the absorption peaks remain almost unchanged with different reaction times, indicating that the size of the QDs does not change during the interfacial self-assembly process. Figure 7b presents the temporal evolution of PL spectra of Ni0.02Cd0.98S/ODA during the phase-transfer process. It can be seen from Figure 7b that the PL intensity of Ni0.02Cd0.98S/ODA hybrids is a function of the reaction time. At the beginning of the reaction, there is only a small amount of Ni0.02Cd0.98S QDs transferring from the water phase to the chloroform phase, so the PL intensity at 1−3 days is very weak. The ODA organic ligands are favorable for the surface ordering and reconstruction of Ni0.02Cd0.98S QDs, which is beneficial to the PL enhancement of QDs.39,40 As a
Figure 5. FT-IR spectra of (a) TGA-stabilized Ni0.02Cd0.98S, (b) Ni0.02Cd0.98S/ODA hybrids, and (c) pure ODA.
of Ni0.02Cd0.98S QDs, and there is no characteristic peak of the mercapto group ranging from 2500 to 2600 cm−1, suggesting the formation of robust bonding between Cd2+ and TGA.36 Figure 5c shows the FT-IR spectrum of pure ODA. The characteristic peak at 1471 cm−1 is assigned to the N−H unit of ODA, while two other absorption peaks situated at 2918 and 2850 cm−1 are identified as the −NH2 group of ODA. In the FT-IR spectrum of Ni0.02Cd0.98S/ODA hybrids (Figure 5b), the characteristic absorption peaks at 1384 and 1584 cm−1 (νCOO−), 1468 cm−1 (νNH), and 2850 and 2918 cm−1 (νNH2) are all observed, indicating that ODA molecules have been successfully grafted to the surface of QDs.37 Moreover, there are no characteristic peaks (from 1680 to 1670 cm−1) of the acrylamide, which confirms electrostatic interactions rather than a covalent bond between the carboxyl of Ni0.02Cd0.98S QDs and the amino of ODA. 3.3. TEM and XRD Patterns of Ni0.02Cd0.98S/ODA Hybrids. Figure 6 shows the TEM and XRD patterns of the as-prepared Ni0.02Cd0.98S/ODA hybrids. In a low-magnification TEM image (Figure 6a), the QDs appear as spherical particles
Figure 6. (a) TEM image, (b) HRTEM image, (c) SAED pattern, and (d) XRD pattern of Ni0.02Cd0.98S/ODA hybrids. 11593
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Figure 7. (a) UV−vis absorption and (b) PL spectra of Ni0.02Cd0.98S/ODA hybrids at different interfacial reaction times (pH 5.8; [ODA] = 0.075 M).
Figure 8. SEM images of the Ni0.02Cd0.98S/ODA hybrids with different reaction times: (a) 1 days; (b) 3 days; (c) 5 days; (d) 7 days; (e) 11 days; (f) 7 days with higher magnification.
of the petal flakes are about 1 μm and 20 μm from the highermagnification SEM image (Figure 8f), respectively. This welldefined and ordered structure is ascribed to the reduction of the total free energy in the whole system.42,43 After the reaction time was over 11 days, maybe because of the influence of the external environment, the petal-like structure disappeared and the structure of the Ni0.02Cd0.98S/ODA hybrids became sticklike micro/nanostructures. 3.6. Superhydrophobic Property. The parent TGAstabilized Ni0.02Cd0.98S QDs present obvious hydrophilic properties because of the carboxyl groups on the surface. Interestingly, through the aid of ODA with hydrophobic nature and low surface energy, the Ni0.02Cd0.98S/ODA hybrids with micro/nanostructure display good hydrophobic properties after interfacial self-assembly. Figure 9a shows a photograph of the water drops placed on the Ni0.02Cd0.98S/ODA hybrid film, which visually demonstrates the bifunctional photoluminescent−superhydrophobic properties of the synthesized QDs/ ODA hybrids. The film displays blue-green color under 365 nm UV light. Further evidence for the superhydrophobicity of the surface is given in Figure 9b: the wettability of the films was evaluated by water CA measurements as 152.7°. Moreover, the sliding angle is less than 9° (Figure 9c) and a 10 μL water droplet can roll off the film, showing low surface adhesion and its potential in fundamental research and industrial applications. Therefore, the present interfacial self-assembly through electro-
result, the PL intensity of the Ni0.02Cd0.98S/ODA hybrids increases with prolonged reaction time and achieves a maximum value (QY ca. 50%) at a reaction time of 9 days. Later, with a large number of Ni0.02Cd0.98S QDs transferred to the chloroform phase, the amount of ODA in the oil phase gradually decreased. Due to the absence of ODA, it is unfavorable to passivate the surface defects of the QDs, so new surface traps of the QDs are emerging in the end products, resulting in a decrease of the PL intensity after 9 days. On the other hand, the reduction of surface traps with the use of ODA modification during the interfacial assembly process also makes the maximum PL emission peak position of Ni0.02Cd0.98S/ODA hybrids transfer from 565 to 520 nm in comparison with the PL spectra of Ni0.02Cd0.98S QDs (seen in Figure 4b).38,41 3.5. Effect of the Interfacial Reaction Time on the Morphology of Ni0.02Cd0.98S/ODA Hybrids. In order to better understand the interfacial self-assembly process, we also observed the morphology of Ni0.02Cd0.98S/ODA hybrids with different reaction times by SEM. Parts a−e of Figure 8 show the SEM images of the samples with different reaction times. At a reaction time of 1 day, the structure of the Ni0.02Cd0.98S/ODA hybrid is disordered. Then it gradually becomes much more regular with an increase in the reaction time. When the reaction proceeds up to 7 days, we can obviously observe from Figure 8d that the well-defined and ordered petal-like flake nano/ microstructures are well-preserved and the thickness and width 11594
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(c) is blue-green and its PL intensity increases greatly compared with Ni0.02Cd0.98S QDs. Making QDs combine with silk-screen printing to form beautiful fluorescent patterns may be useful in the photoelectric and anticounterfeit fields.
4. CONCLUSIONS In summary, we have successfully prepared petal-like NixCd1−xS/ODA hybrids via a facile liquid−liquid interfacial self-assembly process. The TGA-stabilized nickel-doped CdS QDs were transferred from an aqueous phase to a chloroform phase in the presence of ODA, resulting in the formation of NixCd1−xS/ODA hybrids with highly enhanced PL. In addition, the fluorescent films of NixCd1−xS/ODA hybrids were also fabricated, and the CA measurement shows that NixCd1−xS/ ODA hybrid films exhibit superhydrophobic properties. This relatively simple method presented here provides a promising way to prepare superhydrophobic films with good optical properties. We have extended the use of QDs as fluorescent inks for multicolor patterns using silk-screen printing, which may offer further development for the optoelectric and anticounterfeit fields.
Figure 9. (a) Digital photographs of the water drops on the film of Ni0.02Cd0.98S/ODA hybrids under irradiation with a 365 nm UV light and a SEM image of the Ni0.02Cd0.98S/ODA hybrid film (the top right corner). (b and c) CA of a 5 μL water droplet and the sliding angle on the Ni0.02Cd0.98S/ODA hybrid film surface, respectively.
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AUTHOR INFORMATION
Corresponding Author
*Tel: 86-25-83172258. Fax: 86-25-83172258. E-mail: chensu@ njut.edu.cn.
static interaction provides a convenient and inexpensive approach to fabricating superhydrophobic surfaces. 3.7. Photographs of the Fluorescent Patterns by SilkScreen Printing. Finally, we applied these QDs as fluorescent inks for printing versatile fluorescent patterns by silk-screen printing, a cheap and easily handled method. Typically, a Ni0.02Cd0.98S QD aqueous solution was blended with an SA solution to form a homogeneous solution with a suitable viscosity. Similarly, we chose PLA as the matrix because of its benign affinity to the Ni0.02Cd0.98S/ODA hybrids. Fluorescent Ni0.02Cd0.98S QDs/SA and Ni0.02Cd0.98S/ODA/PLA solutions as printing inks can simply be obtained because of their good compatibility. The “inks” were screened through the woven meshes onto filter papers by extruding the scraper blade. As seen in Figure 10, under 365 nm UV light, the photographs of the fluorescent patterns of Ni0.02Cd0.98S QDs (b) displays yellow-green, which is consistent with the corresponding PL spectra (Figure 10a). Also, because of the influence of ODA on Ni0.02Cd0.98S QDs, the pattern of Ni0.02Cd0.98S/ODA hybrids
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the National High Technology Research and Development Program of China (863 Program; Grant 2012AA030313), National Natural Science Foundation of China (Grants 21076103 and 21006046), Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant 20103221110001), Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and Colleges and Universities in Jiangsu Province Plans to Graduate Research and Innovation (Grant CXZZ12_0449).
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REFERENCES
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Figure 10. (a) PL spectra of Ni0.02Cd0.98S QDs and Ni0.02Cd0.98S/ ODA hybrids. Photographs of the fluorescent patterns by silk-screen printing from different mixtures of QDs: (b) Ni0.02Cd0.98S/SA; (c) Ni0.02Cd0.98S/ODA/PLA under UV light. Inset of part a: digital images of Ni0.02Cd0.98S QDs and Ni0.02Cd0.98S/ODA hybrids under UV irradiation (λex = 365 nm). 11595
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dx.doi.org/10.1021/ie401354f | Ind. Eng. Chem. Res. 2013, 52, 11590−11596
