- Email: [email protected]
Layer-by-layer assembly of luminescent multilayer thin films by MMT, anionic chromophores and magnetic CoAl-LDHs nanosheets
Materials Letters 153 (2015) 40–43
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Layer-by-layer assembly of luminescent multilayer thin films by MMT, anionic chromophores and magnetic CoAl-LDHs nanosheets Meitang Liu 1, Tianlei Wang, Hongwen Ma, Yu Fu, Kunran Hu, Chao Guan Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, School of Materials Science and Technology, China University of Geosciences, Beijing 100083, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 1 December 2014 Accepted 1 April 2015 Available online 8 April 2015
In this report, luminescent multilayer thin films (MTFs) based on oppositely-charged montmorillonite (MMT) and transition metal-bearing layered double hydroxides (LDHs) nanosheets were fabricated via a layer-by-layer assembly method. Oppositely-charged inorganic nanosheets can be expected to assemble an electronic microenvironment (EME), and transition metal-bearing LDHs nanosheets can offer an additional magnetic field (MF) for the chromophores at the same time. Surprisingly, the luminescent lifetimes of MTFs with EME and MF are significantly prolonged compared with that of the pristine chromophores, even much longer than those of MTFs without oppositely-charged and magnetic architecture. Therefore, it is highly expected that the EME and MF formed by oppositely-charged and transition metal-bearing inorganic nanosheets have remarkable influence on enhancing the luminescent lifetimes of chromophores, which suggest a new potential way to manipulate, control and develop the novel light-emitting materials and optical devices at molecular level. & 2015 Elsevier B.V. All rights reserved.
Keywords: Layered double hydroxides Montmorillonite Luminescence Magnetic Electronic microenvironment
1. Introduction Layered materials are attractive targets for their rich fundamental physics and potential applications in future multifunctional devices, and the nanosheets of those have been used as building units for making new designed nanomaterials due to their intrinsic unique two-dimensional structure [1–4]. As for LDHs and MMT, several groups have just done many profound researches by using naonosheets with two-dimensional arrays which can provide a rigid and stable environment [5–10]. However, various different inorganic nanosheets possibly have certain natural features, such as LDHs exhibit permanent positive charge and MMT' nanosheets are evolved as permanent negative charge that can be delocalized over the entire layer surface, due to an isomorphic substitution [10,11]. But there was no relational report about taking full advantage of the nanosheets' charge, until our group [12] successfully confirmed that electronic microenvironment, which is assembled by oppositely-charged nanosheets between the interlayer, is fairly beneficial for enhancing the lifetimes of MTFs containing luminescent cations. On the other hand, transition metal-bearing LDHs' nanosheets can act as nanoscale ferromagnetic layers, and their multilayer assemblies exhibit significant magneto-optical response [9,10,13]. And then, our present work confirmed that MF also can improve the optical property in
E-mail address: [email protected] (M. Liu). Tel./fax: þ 86 10 8232 2759.
1
http://dx.doi.org/10.1016/j.matlet.2015.04.002 0167-577X/& 2015 Elsevier B.V. All rights reserved.
coordination with EME, especially the lifetimes of MTFs [14]. Herein, in this paper, what we are most interested in are whether anionic luminescent polymers can be designed for intercalating into EME and MF environments, and whether they can be affected by the different ferromagnetic inorganic nanosheets on the optical properties. In this work, a luminescent π-conjugated anionic polymer poly [5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene] potassium (APPV) was assembled with the CoAl-LDHs nanosheets and MMT nanosheets to fabricate multilayer thin films (MTFs), respectively. In the nano-system, as the assembled nano-architecture can provide an EME and the CoAl-LDHs can offer a constant MF to the chromophores (Fig. 1), the MTFs exhibit remarkable optical properties with reasonably longer luminescent lifetimes. Herein, this work successfully fabricates the MTFs with EME and MF0 , which can promote the hybrid systems with various functions, and confirm the concept about the EME and MF effecting chromophores simultaneously.
2. Results and discussion We selected the luminescent π-conjugated anionic polymer to assemble with different ferromagnetic inorganic nanosheets, in order to confirm the universality of the novel concept about EME and MF effecting the more series chromophores. The UV–visible absorption spectra of (CoAl-LDHs/APPV@PVA)n MTFs with varying numbers of assembly steps are shown in Fig. 2a, and the intensity of absorption
M. Liu et al. / Materials Letters 153 (2015) 40–43
peaks exhibit correlate linearly with the deposition cycles (Fig. 2a, inset), demonstrating a stepwise and regular growth procedure. Furthermore, the fluorescence emission intensity also displays a consistent increase with the layer growing, as shown in Fig. 2b. This can also be visualized by irradiating MTFs under daylight and UV light (365 nm), respectively (Fig. 2c), where these films exhibit uniform enhanced luminescence with increasing number of deposition cycles. Above all, the MTFs exhibit an ordered and regular film growth procedure and uniformly enhanced yellow luminescence as the layer number increases. Wondrously, it is remarkable that the luminescent lifetimes of (CoAl-LDHs/APPV@PVA)n MTFs (1.30–1.44 ns) are more than 2 times as long as the pristine APPV solution (0.6 ns) (Fig. 2d), and are also
Fig. 1. Schematic of APPV in EME and MF between the MMT and CoAl-LDHs nanosheets.
41
nearly 2 times the length of (MgAl-LDHs/APPV)n MTFs (0.66–0.81 ns) [7]. The profound increasing is partially due to the positive-charged CoAl-LDHs nanosheets' electrostatic attraction and isolation effect, preventing the formation of APPV aggregation. But most importantly, CoAl-LDHs can offer a constant MF, thus apparently affecting the vibration of the valence electron of the chromophores which will definitely prolong their lifetimes. According to this remarkable increase, it is confirmed that MF can definitely prolong anionic chromophores' lifetimes. At the same time, in order to verify the EME being able to affect the luminescent lifetimes of anionic chromophores, (MMT/APPV@PVA/ CoAl-LDHs/APPV@PVA)n MTFs were also fabricated via the same layerby-layer assembly method. In accordance with UV–visible absorption spectra, photoluminescence spectra and the photos under daylight and UV light (365 nm) of (MMT/APPV@PVA/CoAl-LDHs/APPV@PVA)n MTFs (Fig. 3a–c), MTFs, which exhibit ordered and regular enhanced yellow luminescent as the layer number increases, are obtained. Surprisingly, it is amazing that the luminescent lifetimes of (MMT/ APPV@PVA/CoAl-LDHs/APPV@PVA)n MTFs (1.75–1.86 ns) are prolonged more than 2.5-fold compared with the (MgAl-LDHs/APPV)n MTFs (0.66–0.81 ns), and are also amazingly prolonged 3-fold compared with the pristine APPV solution (0.60 ns) (Fig. 3d) [7]. Importantly, the luminescent lifetimes of (MMT/APPV@PVA/CoAl-LDHs/ APPV@PVA)n MTFs are startlingly extended to about 1.3-fold compared with those of (CoAl-LDHs/APPV@PVA)n MTFs. Above all, EME is benefitted for the luminescent lifetimes of anionic chromophores. According to this remarkable increase, the theory, as mentioned above, that EME and MF can definitely prolong chromophores'
Fig. 2. Characterization of (CoAl-LDHs/APPV@PVA)n MTFs (a) UV–visible absorption spectra, the inset shows the absorbance increasing linear relationship in 295.0 nm. (b) Photoluminescence spectra. (c) Photographs of MTFs with different layer numbers under daylight and UV light, respectively. (d) Fluorescence decay profiles.
42
M. Liu et al. / Materials Letters 153 (2015) 40–43
Fig. 3. Characterization of (MMT/APPV@PVA/CoAl-LDHs/APPV@PVA)n MTFs (a) UV–visible absorption spectra, the inset shows the absorbance increasing linear relationship in 295.0 nm and 425.5 nm. (b) Photoluminescence spectra. (c) Photographs of MTFs with different layer numbers under daylight and UV light, respectively. (d) Fluorescence decay profiles.
3. Conclusions To sum up, this work successfully confined anionic chromophores in the oppositely-charged and magnetic inorganic layer hosts. Importantly, it successfully demonstrates that the EME and MF formed by the different ferromagnetic inorganic nanosheets are fairly beneficial for enhancing the luminescent lifetimes of MTFs containing anionic chromophores. Therefore, the as-fabricated MTFs are expected to have much flexibility and be potential for manipulating, controlling and developing novel optoelectrical, optomagnetic, even photomagnetoelectric devices. Further work is ongoing with the research on lifetime of various luminescent guests imbedded in series of different layered inorganic nanosheets with EME and MF. Acknowledgments Fig. 4. The comparison of chromophores' lifetimes in the different states under the different environments. Black dot represents the APPV's lifetime, the red stands for the lifetimes of (MgAl-LDHs/APPV)n MTFs, the blue stands for the (CoAl-LDHs/ APPV@PVA)n MTFs, and the purple shows the lifetimes of (MMT/APPV@PVA/CoAlLDHs/APPV@PVA)n MTFs. (n=8, 16, 24). The folds stand for the different kinds of LMFs' luminescent lifetimes compared with the pristine APPV solution. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
luminescent lifetimes is verified. Then, Fig. 4 illustrates the comparison of APPV0 luminescent lifetimes in different states under different environments, and it is obvious that the chromophores under EME and MF have amazingly ultra-prolonged luminescent lifetimes.
This work was supported partially by the National Natural Science Foundation of China (Grant no. 40802013), Key Projects in the National Science & Technology Pillar Program (Grant no. 2006BAD10B04), the Fundamental Research Funds for the Central Universities (Grant no. 2011YXL058).
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.04.002.
M. Liu et al. / Materials Letters 153 (2015) 40–43
References [1] Park DH, Hwang SJ, Oh JM, Yang JH, Choy JH. Polymer–inorganic supramolecular nanohybrids for red, white, green, and blue applications. Prog Polym Sci 2013;38:1442. [2] Butt FK, Cao CB, Wanb Q, Li P, Idrees F, Tahir M, et al. Synthesis, evolution and hydrogen storage properties of ZnV2O4 glomerulus nano/microspheres: a prospective material for energy storage. Int J Hydrogen Energy 2014;39:7842. [3] Butt FK, Tahir M, Cao CB, Idrees F, Ahmed R, Khan WS, et al. Synthesis of novel ZnV2O4 hierarchical nanospheres and their applications as electrochemical supercapacitor and hydrogen storage material. ACS Appl Mater Interfaces 2014;6:13635. [4] Butt FK, Cao CB, Ahmed R, Khan WS, Cao T, Bidin N, et al. Synthesis of novel ZnV2O4 spinel oxide nanosheets and their hydrogen storage properties. CrystEngComm 2014;16:894. [5] Podsiadlo P, Kaushik AK, Arruda EM, Waas AM, Shim BS, Xu JD, et al. Ultrastrong and stiff layered polymer nanocomposites. Science 2007;318:80. [6] Wang Q, O’Hare D. Recent advances in the synthesis and application of layered double hydroxide (LDH) nanosheets. Chem Rev 2011;112:4124. [7] Yan DP, Lu J, Ma J, Wei M, Wang XR, Evans DG, et al. Anionic poly(pphenylenevinylene)/layered double hydroxide ordered ultrathin films with multiple quantum well structure: a combined experimental and theoretical study. Langmuir 2010;26:7007. [8] Huang S, Cen X, Peng HD, Guo SZ, Wang WZ, Liu TX. Heterogeneous ultrathin films of poly (vinyl alcohol)/layered double hydroxide and montmorillonite nanosheets via layer-by-layer assembly. J Phys Chem B 2009;113:15225. [9] Chen D, Wang XY, Liu TX, Wang XD, Li J. Electrically conductive poly(vinyl alcohol) hybrid films containing graphene and layered double hydroxide fabricated via layer-by-layer self-assembly. ACS Appl Mater Interfaces 2010;2:2005.
43
[10] Chen H, Hu LF, Chen M, Yan Y, Wu LM. Nickel–cobalt layered double hydroxide nanosheets for high-performance supercapacitor electrode materials. Adv Funct Mater 2014;24:934. [11] Ikeda M, Yoshii T, Matsui T, Tanida T, Komatsu H, Hamachi I. Montmorillonitesupramolecular hydrogel hybrid for fluorocolorimetric sensing of polyamines. J Am Chem Soc 2011;133:1670. [12] Wang TL, Liu MT, Ma HW, Liu XJ, Fu Y, Hu KR. Lifetime-ultra-prolonged luminescent multilayer thin films with electronic microenvironment. RSC Adv 2014;4:40748. [13] Liu ZP, Ma RZ, Osada M, Iyi N, Ebina Y, Takada KK, et al. Synthesis, anion exchange, and delamination of Co-Al layered double hydroxide: assembly of the exfoliated nanosheet/polyanion composite films and magneto-optical studies. J Am Chem Soc 2006;128:4872. [14] Liu MT, Wang TL, Ma HW, Fu Y, Hu KR, Guan C. Assembly of luminescent ordered multilayer thin-films based on oppositely-charged MMT and magnetic NiFe-LDHS nanosheets with ultra-long lifetimes. Sci Rep 2014. http://dx. doi.org/10.1038/srep07147.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Layer-by-layer assembly of luminescent multilayer thin films by MMT, anionic chromophores and magnetic CoAl-LDHs nanosheets Meitang Liu 1, Tianlei Wang, Hongwen Ma, Yu Fu, Kunran Hu, Chao Guan Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, School of Materials Science and Technology, China University of Geosciences, Beijing 100083, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 1 December 2014 Accepted 1 April 2015 Available online 8 April 2015
In this report, luminescent multilayer thin films (MTFs) based on oppositely-charged montmorillonite (MMT) and transition metal-bearing layered double hydroxides (LDHs) nanosheets were fabricated via a layer-by-layer assembly method. Oppositely-charged inorganic nanosheets can be expected to assemble an electronic microenvironment (EME), and transition metal-bearing LDHs nanosheets can offer an additional magnetic field (MF) for the chromophores at the same time. Surprisingly, the luminescent lifetimes of MTFs with EME and MF are significantly prolonged compared with that of the pristine chromophores, even much longer than those of MTFs without oppositely-charged and magnetic architecture. Therefore, it is highly expected that the EME and MF formed by oppositely-charged and transition metal-bearing inorganic nanosheets have remarkable influence on enhancing the luminescent lifetimes of chromophores, which suggest a new potential way to manipulate, control and develop the novel light-emitting materials and optical devices at molecular level. & 2015 Elsevier B.V. All rights reserved.
Keywords: Layered double hydroxides Montmorillonite Luminescence Magnetic Electronic microenvironment
1. Introduction Layered materials are attractive targets for their rich fundamental physics and potential applications in future multifunctional devices, and the nanosheets of those have been used as building units for making new designed nanomaterials due to their intrinsic unique two-dimensional structure [1–4]. As for LDHs and MMT, several groups have just done many profound researches by using naonosheets with two-dimensional arrays which can provide a rigid and stable environment [5–10]. However, various different inorganic nanosheets possibly have certain natural features, such as LDHs exhibit permanent positive charge and MMT' nanosheets are evolved as permanent negative charge that can be delocalized over the entire layer surface, due to an isomorphic substitution [10,11]. But there was no relational report about taking full advantage of the nanosheets' charge, until our group [12] successfully confirmed that electronic microenvironment, which is assembled by oppositely-charged nanosheets between the interlayer, is fairly beneficial for enhancing the lifetimes of MTFs containing luminescent cations. On the other hand, transition metal-bearing LDHs' nanosheets can act as nanoscale ferromagnetic layers, and their multilayer assemblies exhibit significant magneto-optical response [9,10,13]. And then, our present work confirmed that MF also can improve the optical property in
E-mail address: [email protected] (M. Liu). Tel./fax: þ 86 10 8232 2759.
1
http://dx.doi.org/10.1016/j.matlet.2015.04.002 0167-577X/& 2015 Elsevier B.V. All rights reserved.
coordination with EME, especially the lifetimes of MTFs [14]. Herein, in this paper, what we are most interested in are whether anionic luminescent polymers can be designed for intercalating into EME and MF environments, and whether they can be affected by the different ferromagnetic inorganic nanosheets on the optical properties. In this work, a luminescent π-conjugated anionic polymer poly [5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene] potassium (APPV) was assembled with the CoAl-LDHs nanosheets and MMT nanosheets to fabricate multilayer thin films (MTFs), respectively. In the nano-system, as the assembled nano-architecture can provide an EME and the CoAl-LDHs can offer a constant MF to the chromophores (Fig. 1), the MTFs exhibit remarkable optical properties with reasonably longer luminescent lifetimes. Herein, this work successfully fabricates the MTFs with EME and MF0 , which can promote the hybrid systems with various functions, and confirm the concept about the EME and MF effecting chromophores simultaneously.
2. Results and discussion We selected the luminescent π-conjugated anionic polymer to assemble with different ferromagnetic inorganic nanosheets, in order to confirm the universality of the novel concept about EME and MF effecting the more series chromophores. The UV–visible absorption spectra of (CoAl-LDHs/APPV@PVA)n MTFs with varying numbers of assembly steps are shown in Fig. 2a, and the intensity of absorption
M. Liu et al. / Materials Letters 153 (2015) 40–43
peaks exhibit correlate linearly with the deposition cycles (Fig. 2a, inset), demonstrating a stepwise and regular growth procedure. Furthermore, the fluorescence emission intensity also displays a consistent increase with the layer growing, as shown in Fig. 2b. This can also be visualized by irradiating MTFs under daylight and UV light (365 nm), respectively (Fig. 2c), where these films exhibit uniform enhanced luminescence with increasing number of deposition cycles. Above all, the MTFs exhibit an ordered and regular film growth procedure and uniformly enhanced yellow luminescence as the layer number increases. Wondrously, it is remarkable that the luminescent lifetimes of (CoAl-LDHs/APPV@PVA)n MTFs (1.30–1.44 ns) are more than 2 times as long as the pristine APPV solution (0.6 ns) (Fig. 2d), and are also
Fig. 1. Schematic of APPV in EME and MF between the MMT and CoAl-LDHs nanosheets.
41
nearly 2 times the length of (MgAl-LDHs/APPV)n MTFs (0.66–0.81 ns) [7]. The profound increasing is partially due to the positive-charged CoAl-LDHs nanosheets' electrostatic attraction and isolation effect, preventing the formation of APPV aggregation. But most importantly, CoAl-LDHs can offer a constant MF, thus apparently affecting the vibration of the valence electron of the chromophores which will definitely prolong their lifetimes. According to this remarkable increase, it is confirmed that MF can definitely prolong anionic chromophores' lifetimes. At the same time, in order to verify the EME being able to affect the luminescent lifetimes of anionic chromophores, (MMT/APPV@PVA/ CoAl-LDHs/APPV@PVA)n MTFs were also fabricated via the same layerby-layer assembly method. In accordance with UV–visible absorption spectra, photoluminescence spectra and the photos under daylight and UV light (365 nm) of (MMT/APPV@PVA/CoAl-LDHs/APPV@PVA)n MTFs (Fig. 3a–c), MTFs, which exhibit ordered and regular enhanced yellow luminescent as the layer number increases, are obtained. Surprisingly, it is amazing that the luminescent lifetimes of (MMT/ APPV@PVA/CoAl-LDHs/APPV@PVA)n MTFs (1.75–1.86 ns) are prolonged more than 2.5-fold compared with the (MgAl-LDHs/APPV)n MTFs (0.66–0.81 ns), and are also amazingly prolonged 3-fold compared with the pristine APPV solution (0.60 ns) (Fig. 3d) [7]. Importantly, the luminescent lifetimes of (MMT/APPV@PVA/CoAl-LDHs/ APPV@PVA)n MTFs are startlingly extended to about 1.3-fold compared with those of (CoAl-LDHs/APPV@PVA)n MTFs. Above all, EME is benefitted for the luminescent lifetimes of anionic chromophores. According to this remarkable increase, the theory, as mentioned above, that EME and MF can definitely prolong chromophores'
Fig. 2. Characterization of (CoAl-LDHs/APPV@PVA)n MTFs (a) UV–visible absorption spectra, the inset shows the absorbance increasing linear relationship in 295.0 nm. (b) Photoluminescence spectra. (c) Photographs of MTFs with different layer numbers under daylight and UV light, respectively. (d) Fluorescence decay profiles.
42
M. Liu et al. / Materials Letters 153 (2015) 40–43
Fig. 3. Characterization of (MMT/APPV@PVA/CoAl-LDHs/APPV@PVA)n MTFs (a) UV–visible absorption spectra, the inset shows the absorbance increasing linear relationship in 295.0 nm and 425.5 nm. (b) Photoluminescence spectra. (c) Photographs of MTFs with different layer numbers under daylight and UV light, respectively. (d) Fluorescence decay profiles.
3. Conclusions To sum up, this work successfully confined anionic chromophores in the oppositely-charged and magnetic inorganic layer hosts. Importantly, it successfully demonstrates that the EME and MF formed by the different ferromagnetic inorganic nanosheets are fairly beneficial for enhancing the luminescent lifetimes of MTFs containing anionic chromophores. Therefore, the as-fabricated MTFs are expected to have much flexibility and be potential for manipulating, controlling and developing novel optoelectrical, optomagnetic, even photomagnetoelectric devices. Further work is ongoing with the research on lifetime of various luminescent guests imbedded in series of different layered inorganic nanosheets with EME and MF. Acknowledgments Fig. 4. The comparison of chromophores' lifetimes in the different states under the different environments. Black dot represents the APPV's lifetime, the red stands for the lifetimes of (MgAl-LDHs/APPV)n MTFs, the blue stands for the (CoAl-LDHs/ APPV@PVA)n MTFs, and the purple shows the lifetimes of (MMT/APPV@PVA/CoAlLDHs/APPV@PVA)n MTFs. (n=8, 16, 24). The folds stand for the different kinds of LMFs' luminescent lifetimes compared with the pristine APPV solution. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
luminescent lifetimes is verified. Then, Fig. 4 illustrates the comparison of APPV0 luminescent lifetimes in different states under different environments, and it is obvious that the chromophores under EME and MF have amazingly ultra-prolonged luminescent lifetimes.
This work was supported partially by the National Natural Science Foundation of China (Grant no. 40802013), Key Projects in the National Science & Technology Pillar Program (Grant no. 2006BAD10B04), the Fundamental Research Funds for the Central Universities (Grant no. 2011YXL058).
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.04.002.
M. Liu et al. / Materials Letters 153 (2015) 40–43
References [1] Park DH, Hwang SJ, Oh JM, Yang JH, Choy JH. Polymer–inorganic supramolecular nanohybrids for red, white, green, and blue applications. Prog Polym Sci 2013;38:1442. [2] Butt FK, Cao CB, Wanb Q, Li P, Idrees F, Tahir M, et al. Synthesis, evolution and hydrogen storage properties of ZnV2O4 glomerulus nano/microspheres: a prospective material for energy storage. Int J Hydrogen Energy 2014;39:7842. [3] Butt FK, Tahir M, Cao CB, Idrees F, Ahmed R, Khan WS, et al. Synthesis of novel ZnV2O4 hierarchical nanospheres and their applications as electrochemical supercapacitor and hydrogen storage material. ACS Appl Mater Interfaces 2014;6:13635. [4] Butt FK, Cao CB, Ahmed R, Khan WS, Cao T, Bidin N, et al. Synthesis of novel ZnV2O4 spinel oxide nanosheets and their hydrogen storage properties. CrystEngComm 2014;16:894. [5] Podsiadlo P, Kaushik AK, Arruda EM, Waas AM, Shim BS, Xu JD, et al. Ultrastrong and stiff layered polymer nanocomposites. Science 2007;318:80. [6] Wang Q, O’Hare D. Recent advances in the synthesis and application of layered double hydroxide (LDH) nanosheets. Chem Rev 2011;112:4124. [7] Yan DP, Lu J, Ma J, Wei M, Wang XR, Evans DG, et al. Anionic poly(pphenylenevinylene)/layered double hydroxide ordered ultrathin films with multiple quantum well structure: a combined experimental and theoretical study. Langmuir 2010;26:7007. [8] Huang S, Cen X, Peng HD, Guo SZ, Wang WZ, Liu TX. Heterogeneous ultrathin films of poly (vinyl alcohol)/layered double hydroxide and montmorillonite nanosheets via layer-by-layer assembly. J Phys Chem B 2009;113:15225. [9] Chen D, Wang XY, Liu TX, Wang XD, Li J. Electrically conductive poly(vinyl alcohol) hybrid films containing graphene and layered double hydroxide fabricated via layer-by-layer self-assembly. ACS Appl Mater Interfaces 2010;2:2005.
43
[10] Chen H, Hu LF, Chen M, Yan Y, Wu LM. Nickel–cobalt layered double hydroxide nanosheets for high-performance supercapacitor electrode materials. Adv Funct Mater 2014;24:934. [11] Ikeda M, Yoshii T, Matsui T, Tanida T, Komatsu H, Hamachi I. Montmorillonitesupramolecular hydrogel hybrid for fluorocolorimetric sensing of polyamines. J Am Chem Soc 2011;133:1670. [12] Wang TL, Liu MT, Ma HW, Liu XJ, Fu Y, Hu KR. Lifetime-ultra-prolonged luminescent multilayer thin films with electronic microenvironment. RSC Adv 2014;4:40748. [13] Liu ZP, Ma RZ, Osada M, Iyi N, Ebina Y, Takada KK, et al. Synthesis, anion exchange, and delamination of Co-Al layered double hydroxide: assembly of the exfoliated nanosheet/polyanion composite films and magneto-optical studies. J Am Chem Soc 2006;128:4872. [14] Liu MT, Wang TL, Ma HW, Fu Y, Hu KR, Guan C. Assembly of luminescent ordered multilayer thin-films based on oppositely-charged MMT and magnetic NiFe-LDHS nanosheets with ultra-long lifetimes. Sci Rep 2014. http://dx. doi.org/10.1038/srep07147.