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γ-Radiation synthesis of poly(acrylic acid)–metal nanocomposites
1 December 1998
Materials Letters 37 Ž1998. 354–358
g-Radiation synthesis of poly žacrylic acid / –metal nanocomposites Xiangling Xu ) , Yadong Yin, Xuewu Ge, Hongkai Wu, Zhicheng Zhang Department of Applied Chemistry, UniÕersity of Science and Technology of China, Hefei, Anhui 230026, China Received 29 January 1998; revised 9 June 1998; accepted 15 June 1998
Abstract PolyŽacrylic acid. –metal nanocomposites were synthesized by irradiating the solutions of metal ions ŽAgq, Cu2q, Ni 2q . in acrylic acid monomer with g-ray. The products are characterized by XRD and TEM. It was found that the nanometer metal particles are well dispersed in polyŽacrylic acid. with a narrow-size distribution. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Composites; g-Radiation; Metal nanoparticles; PolyŽacrylic acid.
1. Introduction Nanometer metal particle–organic polymer composites have attracted considerable interests in recent years. These composites not only combine the advantageous properties of metals and polymers but also exhibit many new characters that single-phase materials do not have. They have a wide range of applications including electromagnetic inferences shielding, heat conduction, discharging static electricity, conversion of mechanical to electrical signals, and the like w1–3x. Generally, nanometer metal particle–polymer composites are prepared by homogenizing polymer and nanometer metal powder w3x, postheating or calcining metal ion containing polymers w4,5x, migrating the vapor of particles of noble metals into polymer )
Corresponding author.
matrices w6,7x, and reducing metal ions in polymer gels w8,9x. In these methods, the polymerization of organic monomer and the formation of nanometer metal particles are performed separately. So the metal particles in polymer matrix are not well homodispersed. And further, a heat treatment or high pressure is necessary in these methods. In this report, we attempted the preparation of nanometer silver, copper and nickel particle– polyŽacrylic acid. ŽPAA. composites by using a novel method. Organic monomers and metal compounds were mixed homogeneously at molecular level. When the solution was irradiated in the field of 60 Co g-ray source under normal pressure at room temperature, the formation of nanocrystal metal particles and the polymerization of monomers were performed in one step. The characteristics of the polyŽacrylic acid. metal nanocomposites are reported in the present paper.
00167-577Xr98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 9 8 . 0 0 1 1 9 - 0
X. Xu et al.r Materials Letters 37 (1998) 354–358
2. Experimental 2.1. Material All compounds used in the experiments were analytically pure and were used without further purification. Water was used after distillation throughout the experiments.
355
sion electron microscope ŽTEM. and X-ray diffraction ŽXRD. analysis. TEM observation was conducted by using a Hitachi H-800 transmission electron microscope with an accelerating voltage of 200 kV. XRD analysis was performed in a Rigaku Dmax gA X-ray diffractometer using graphite-monochromatic Cu-K a radiation Ž l s 0.154178 nm..
2.2. Preparation of solutions
3. Results and discussion
Because of their different oxidation–reduction potentials, the silver, copper and nickel metal ions were reduced in different environments ŽpH value, complexing agent.. The AgNO 3racrylic acid ŽAA. solution was simply prepared by dissolving AgNO 3 in distilled water at a concentration of 0.07 molrl, and then addition of the same volume of AA in the aqueous solution. To prepare CuSO4rAA solution, CuSO4 was dissolved in water to get a 0.1 molrl aqueous solution of Cu2q ions. EDTA was added as a complexing agent at the mole ratio of CuSO4 :EDTAs 1:1.5. Then the solution was mixed homogeneously with the same volume of AA, which was neutralized by NaOH aqueous solution first. The NiSO4rAA solution was prepared according to the following procedure: NiSO4 was dispersed in water at a concentration of 0.1 molrl. NH 3 P H 2 O was added as a complexing agent for Ni 2q ions until the pH value was between 10 and 11. After that, the solution was well mixed with the same volume of neutralized AA solution.
Silver ions are easy to be reduced to zero valent state, so the preparation of PAA–Ag nanocomposites is simply performed by irradiating the aqueous solution containing silver ions and AA monomers. The radiolysis of monomer solution results in the formation of radicals, which then initiate the polymerization to form polymer chains. On the other hand, the homodispersed silver ions are reduced by reductive particles Žfor example, solvated electrons.. The primary reduction products are silver atoms. Then these silver atoms undergo further aggregation to progressively larger clusters and at last nanometer silver particles are obtained w10,11x. Because the polymerization of monomers is quicker than the reduction of silver ions, the increase of system viscosity, which results from the formation of polymer chains, can limit the aggregation of silver particles and make them dispersed in polymer matrix homogeneously. Fig. 1 shows the XRD pattern and the TEM micrograph of PAA–Ag nanocomposites. In Fig. 1a, the wide peak whose 2 u value is about 198 is assigned to the diffraction of PAA. Three other peaks can also been seen at 2 u s 38, 44.5 and 648, which are characteristic diffraction peaks of metallic silver. These peaks correspond to the three d-spacings Ž111., Ž200. and Ž220., respectively. As estimated by the Scherrer formula w12x, the average particle size of silver is 21 nm. From Fig. 1b, it was found that the silver particles are spherical and their size ranges from 10 to 80 nm. The PAA–Cu nanocomposites are obtained by irradiating the CuSO4rAA solution, adding EDTA as complexing agent. As shown in Fig. 2a, XRD analysis of nanometer copper particles in PAA exhibits two characteristic peaks Ž2 u s 438, 518., which correspond to the Ž111. and Ž200. d-spacings. Copper particle size calculated from XRD pattern is
2.3. Irradiation and final treatment The solutions were deaerated by bubbling with nitrogen for about 20 min to remove oxygen solvated in them, then irradiated in the field of 2.59 = 10 15 Bq 60 Co g-ray source. After irradiation, three kinds of transparent, elastic gel like materials were obtained. All of these products were dried and then ground into powders. 2.4. Characterization The size and morphology of nanometer metal particles in polymer were investigated by transmis-
356
X. Xu et al.r Materials Letters 37 (1998) 354–358
Fig. 1. XRD pattern Ža. and TEM micrograph Žb. of PAA–Ag nanocomposites: AgNO 3 rAA s 0.07 mmolrml; absorbed dose: 1.8 = 10 4 Gy.
22 nm. The distribution of metallic copper particle size is shown in Fig. 2b, from which we can see that copper particle size ranges from 7 to 55 nm. The experiments showed that in the absence of EDTA in solution, neither the PAA matrices nor the copper particles could be obtained after g-radiation. As reported earlier w13x, the complexation of copper ions with EDTA is favorable for preparing nanocrystalline particles. The presence of complexant may decrease the reduction reaction rate. Also, the ligand on the copper ions may act as bridges for electron transfer from the solvent to the copper ions, thus possibly favouring the nucleation of crystallites and limiting the size of copper particles. On the other hand, the addition of Cu2q ions can also suppress the polymerization of monomers. So
the complexation of copper ions with EDTA may lower the inhibition effect. Reactive metals like nickel are hard to get as fine nanocrystalline particles by common methods because of their negative oxidation–reduction potentials. In this study, nickel ions were reduced by hydrated electrons, which have extremely negative reduction potentials. So, stable nickel particles with small dimensions were obtained. The XRD pattern and TEM micrograph of PAA–Ni nanocomposites are shown in Fig. 3. Fig. 3a also shows a wide diffraction peak of PAA Ž2 u s 198.. The 2 u value of two characteristic diffraction peaks of metallic nickel are 448 and 528. They correspond respectively to the d-spacings Ž111. and Ž200.. The broadening of these peaks indicates that the nickel particles in PAA are
Fig. 2. XRD pattern Ža. and TEM micrograph Žb. of PAA–Cu nanocomposites: CuSO4 rEDTArAAs 0.1 mmolrml; absorbed dose: 3.6 = 10 4 Gy.
X. Xu et al.r Materials Letters 37 (1998) 354–358
357
Fig. 3. XRD pattern Ža. and TEM micrograph Žb. of PAA–Ni nanocomposites: NiSO4rAA s 0.1 mmolrml; absorbed dose: 6.0 = 10 4 Gy.
very small. The average particle size is 19 nm calculated from the XRD pattern by using Scherrer formula. The TEM photograph shows a very narrow size distribution of nickel particles, ranging from 10 to 40 nm. Other than the functions of EDTA as a complexing agent for Cu2q, NH 3 P H 2 O also acts as an alkalizing agent to decrease the H 3 Oq concentration greatly w14x. When the concentration of H 3 Oq is high, the zero valency nickel may undergo reoxidation: Ni n q H 3 Oq™ Ni ny1 q Niqq 1r2H 2 q H 2 O. So the addition of NH 3 P H 2 O can suppress the occurrence of the reoxidation of nickel and increase the yield of crystalline nickel. XRD analyses of three samples indicate that the inorganics in PAA are pure metal particles. The dimensions of metal particle obtained from TEM are consistent with those obtained from XRD patterns. TEM observations show that these metal particles are well dispersed in PAA matrices. The electron diffraction patterns of the composites indicate that these nanometer particles are polycrystalline aggregates. From the results of XRD analysis, one can see that the average particle sizes of the three kinds of nanocomposites are nearly equal, but their TEM images are different in size distribution obviously. The more difficult metal ions are reduced, the lower the size polydispersity is. This phenomenon is in agreement with the supposed production or precipitation mechanism. Silver ions are easy to be reduced and at the early stage of irradiation many aggrega-
tion centers are formed when the polymerization is not completely finished. So the solution is not very viscous and the silver particles can undergo further aggregation to some extent. Many of silver particles observed in TEM image maybe the secondary aggregates. Copper ions and nickel ions are not reduced until the polymerization is performed almost completely and the solution is very viscous. The small particles have difficulty in undergoing further aggregation because the hindrance of polymer chains. So the polydispersity of these particles is lower than that of silver particles.
4. Conclusion A new method by using g-radiation for preparing PAA–metal nanocomposites is presented. This method can be applied under normal pressure at room temperature and is relatively simple and fast, because the reduction of metal ions and the polymerization of monomer AA are in one step. The metal particles are well dispersed in nanocomposites and their average size is comparatively small. This method is considered a promising way to prepare inorganic–polymer nanocomposites.
References w1x D.M. Bigg, Polym. Compos. 7 Ž1986. 125. w2x T.A. Skotheim, Handbook of Conductive Polymers, vol. 1, Marcel Dekker, New York, 1986. w3x K. Ghosh, S.N. Maiti, J. Appl. Polym. Sci. 60 Ž1996. 323.
358
X. Xu et al.r Materials Letters 37 (1998) 354–358
w4x A.K.St. Clair, L.T. Taylor, J. Appl. Polym. Sci. 28 Ž1983. 2393. w5x Y. Nakao, J. Colloid Interface Sci. 171 Ž1995. 386. w6x A.W. Olsen, Z.H. Kafari, J. Am. Chem. Soc. 113 Ž1991. 7758. w7x M.S. Kunz, K.R. Shull, A.J. Kellock, J. Colloid Interface Sci. 156 Ž1993. 240. w8x R. Saito, S. Okamoto, K. Ishizu, Polymer 33 Ž1992. 1099. w9x R. Saito, S. Okamoto, K. Ishizu, Polymer 34 Ž1993. 1189.
w10x J.L. Marignier, J. Belloni, M.O. Delcourt, J.P. Chevalier, Nature 317 Ž1985. 344. w11x A. Henglein, E. Janata, A. Fojtik, J. Phys. Chem. 96 Ž1992. 4734. w12x C.N.J. Wagner, E.N. Aqua, Adv. X-ray Anal. 7 Ž1964. 46. w13x Y. Zhu, Y. Qian, M. Zhang, Z. Chen, M. Chen, G. Zhou, J. Mater. Sci. Lett. 13 Ž1994. 1243. w14x Y. Zhu, Y. Qian, M. Zhang, Z. Chen, B. Lu, G. Zhou, Mater. Sci. Eng. B23 Ž1994. 116.
Materials Letters 37 Ž1998. 354–358
g-Radiation synthesis of poly žacrylic acid / –metal nanocomposites Xiangling Xu ) , Yadong Yin, Xuewu Ge, Hongkai Wu, Zhicheng Zhang Department of Applied Chemistry, UniÕersity of Science and Technology of China, Hefei, Anhui 230026, China Received 29 January 1998; revised 9 June 1998; accepted 15 June 1998
Abstract PolyŽacrylic acid. –metal nanocomposites were synthesized by irradiating the solutions of metal ions ŽAgq, Cu2q, Ni 2q . in acrylic acid monomer with g-ray. The products are characterized by XRD and TEM. It was found that the nanometer metal particles are well dispersed in polyŽacrylic acid. with a narrow-size distribution. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Composites; g-Radiation; Metal nanoparticles; PolyŽacrylic acid.
1. Introduction Nanometer metal particle–organic polymer composites have attracted considerable interests in recent years. These composites not only combine the advantageous properties of metals and polymers but also exhibit many new characters that single-phase materials do not have. They have a wide range of applications including electromagnetic inferences shielding, heat conduction, discharging static electricity, conversion of mechanical to electrical signals, and the like w1–3x. Generally, nanometer metal particle–polymer composites are prepared by homogenizing polymer and nanometer metal powder w3x, postheating or calcining metal ion containing polymers w4,5x, migrating the vapor of particles of noble metals into polymer )
Corresponding author.
matrices w6,7x, and reducing metal ions in polymer gels w8,9x. In these methods, the polymerization of organic monomer and the formation of nanometer metal particles are performed separately. So the metal particles in polymer matrix are not well homodispersed. And further, a heat treatment or high pressure is necessary in these methods. In this report, we attempted the preparation of nanometer silver, copper and nickel particle– polyŽacrylic acid. ŽPAA. composites by using a novel method. Organic monomers and metal compounds were mixed homogeneously at molecular level. When the solution was irradiated in the field of 60 Co g-ray source under normal pressure at room temperature, the formation of nanocrystal metal particles and the polymerization of monomers were performed in one step. The characteristics of the polyŽacrylic acid. metal nanocomposites are reported in the present paper.
00167-577Xr98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 9 8 . 0 0 1 1 9 - 0
X. Xu et al.r Materials Letters 37 (1998) 354–358
2. Experimental 2.1. Material All compounds used in the experiments were analytically pure and were used without further purification. Water was used after distillation throughout the experiments.
355
sion electron microscope ŽTEM. and X-ray diffraction ŽXRD. analysis. TEM observation was conducted by using a Hitachi H-800 transmission electron microscope with an accelerating voltage of 200 kV. XRD analysis was performed in a Rigaku Dmax gA X-ray diffractometer using graphite-monochromatic Cu-K a radiation Ž l s 0.154178 nm..
2.2. Preparation of solutions
3. Results and discussion
Because of their different oxidation–reduction potentials, the silver, copper and nickel metal ions were reduced in different environments ŽpH value, complexing agent.. The AgNO 3racrylic acid ŽAA. solution was simply prepared by dissolving AgNO 3 in distilled water at a concentration of 0.07 molrl, and then addition of the same volume of AA in the aqueous solution. To prepare CuSO4rAA solution, CuSO4 was dissolved in water to get a 0.1 molrl aqueous solution of Cu2q ions. EDTA was added as a complexing agent at the mole ratio of CuSO4 :EDTAs 1:1.5. Then the solution was mixed homogeneously with the same volume of AA, which was neutralized by NaOH aqueous solution first. The NiSO4rAA solution was prepared according to the following procedure: NiSO4 was dispersed in water at a concentration of 0.1 molrl. NH 3 P H 2 O was added as a complexing agent for Ni 2q ions until the pH value was between 10 and 11. After that, the solution was well mixed with the same volume of neutralized AA solution.
Silver ions are easy to be reduced to zero valent state, so the preparation of PAA–Ag nanocomposites is simply performed by irradiating the aqueous solution containing silver ions and AA monomers. The radiolysis of monomer solution results in the formation of radicals, which then initiate the polymerization to form polymer chains. On the other hand, the homodispersed silver ions are reduced by reductive particles Žfor example, solvated electrons.. The primary reduction products are silver atoms. Then these silver atoms undergo further aggregation to progressively larger clusters and at last nanometer silver particles are obtained w10,11x. Because the polymerization of monomers is quicker than the reduction of silver ions, the increase of system viscosity, which results from the formation of polymer chains, can limit the aggregation of silver particles and make them dispersed in polymer matrix homogeneously. Fig. 1 shows the XRD pattern and the TEM micrograph of PAA–Ag nanocomposites. In Fig. 1a, the wide peak whose 2 u value is about 198 is assigned to the diffraction of PAA. Three other peaks can also been seen at 2 u s 38, 44.5 and 648, which are characteristic diffraction peaks of metallic silver. These peaks correspond to the three d-spacings Ž111., Ž200. and Ž220., respectively. As estimated by the Scherrer formula w12x, the average particle size of silver is 21 nm. From Fig. 1b, it was found that the silver particles are spherical and their size ranges from 10 to 80 nm. The PAA–Cu nanocomposites are obtained by irradiating the CuSO4rAA solution, adding EDTA as complexing agent. As shown in Fig. 2a, XRD analysis of nanometer copper particles in PAA exhibits two characteristic peaks Ž2 u s 438, 518., which correspond to the Ž111. and Ž200. d-spacings. Copper particle size calculated from XRD pattern is
2.3. Irradiation and final treatment The solutions were deaerated by bubbling with nitrogen for about 20 min to remove oxygen solvated in them, then irradiated in the field of 2.59 = 10 15 Bq 60 Co g-ray source. After irradiation, three kinds of transparent, elastic gel like materials were obtained. All of these products were dried and then ground into powders. 2.4. Characterization The size and morphology of nanometer metal particles in polymer were investigated by transmis-
356
X. Xu et al.r Materials Letters 37 (1998) 354–358
Fig. 1. XRD pattern Ža. and TEM micrograph Žb. of PAA–Ag nanocomposites: AgNO 3 rAA s 0.07 mmolrml; absorbed dose: 1.8 = 10 4 Gy.
22 nm. The distribution of metallic copper particle size is shown in Fig. 2b, from which we can see that copper particle size ranges from 7 to 55 nm. The experiments showed that in the absence of EDTA in solution, neither the PAA matrices nor the copper particles could be obtained after g-radiation. As reported earlier w13x, the complexation of copper ions with EDTA is favorable for preparing nanocrystalline particles. The presence of complexant may decrease the reduction reaction rate. Also, the ligand on the copper ions may act as bridges for electron transfer from the solvent to the copper ions, thus possibly favouring the nucleation of crystallites and limiting the size of copper particles. On the other hand, the addition of Cu2q ions can also suppress the polymerization of monomers. So
the complexation of copper ions with EDTA may lower the inhibition effect. Reactive metals like nickel are hard to get as fine nanocrystalline particles by common methods because of their negative oxidation–reduction potentials. In this study, nickel ions were reduced by hydrated electrons, which have extremely negative reduction potentials. So, stable nickel particles with small dimensions were obtained. The XRD pattern and TEM micrograph of PAA–Ni nanocomposites are shown in Fig. 3. Fig. 3a also shows a wide diffraction peak of PAA Ž2 u s 198.. The 2 u value of two characteristic diffraction peaks of metallic nickel are 448 and 528. They correspond respectively to the d-spacings Ž111. and Ž200.. The broadening of these peaks indicates that the nickel particles in PAA are
Fig. 2. XRD pattern Ža. and TEM micrograph Žb. of PAA–Cu nanocomposites: CuSO4 rEDTArAAs 0.1 mmolrml; absorbed dose: 3.6 = 10 4 Gy.
X. Xu et al.r Materials Letters 37 (1998) 354–358
357
Fig. 3. XRD pattern Ža. and TEM micrograph Žb. of PAA–Ni nanocomposites: NiSO4rAA s 0.1 mmolrml; absorbed dose: 6.0 = 10 4 Gy.
very small. The average particle size is 19 nm calculated from the XRD pattern by using Scherrer formula. The TEM photograph shows a very narrow size distribution of nickel particles, ranging from 10 to 40 nm. Other than the functions of EDTA as a complexing agent for Cu2q, NH 3 P H 2 O also acts as an alkalizing agent to decrease the H 3 Oq concentration greatly w14x. When the concentration of H 3 Oq is high, the zero valency nickel may undergo reoxidation: Ni n q H 3 Oq™ Ni ny1 q Niqq 1r2H 2 q H 2 O. So the addition of NH 3 P H 2 O can suppress the occurrence of the reoxidation of nickel and increase the yield of crystalline nickel. XRD analyses of three samples indicate that the inorganics in PAA are pure metal particles. The dimensions of metal particle obtained from TEM are consistent with those obtained from XRD patterns. TEM observations show that these metal particles are well dispersed in PAA matrices. The electron diffraction patterns of the composites indicate that these nanometer particles are polycrystalline aggregates. From the results of XRD analysis, one can see that the average particle sizes of the three kinds of nanocomposites are nearly equal, but their TEM images are different in size distribution obviously. The more difficult metal ions are reduced, the lower the size polydispersity is. This phenomenon is in agreement with the supposed production or precipitation mechanism. Silver ions are easy to be reduced and at the early stage of irradiation many aggrega-
tion centers are formed when the polymerization is not completely finished. So the solution is not very viscous and the silver particles can undergo further aggregation to some extent. Many of silver particles observed in TEM image maybe the secondary aggregates. Copper ions and nickel ions are not reduced until the polymerization is performed almost completely and the solution is very viscous. The small particles have difficulty in undergoing further aggregation because the hindrance of polymer chains. So the polydispersity of these particles is lower than that of silver particles.
4. Conclusion A new method by using g-radiation for preparing PAA–metal nanocomposites is presented. This method can be applied under normal pressure at room temperature and is relatively simple and fast, because the reduction of metal ions and the polymerization of monomer AA are in one step. The metal particles are well dispersed in nanocomposites and their average size is comparatively small. This method is considered a promising way to prepare inorganic–polymer nanocomposites.
References w1x D.M. Bigg, Polym. Compos. 7 Ž1986. 125. w2x T.A. Skotheim, Handbook of Conductive Polymers, vol. 1, Marcel Dekker, New York, 1986. w3x K. Ghosh, S.N. Maiti, J. Appl. Polym. Sci. 60 Ž1996. 323.
358
X. Xu et al.r Materials Letters 37 (1998) 354–358
w4x A.K.St. Clair, L.T. Taylor, J. Appl. Polym. Sci. 28 Ž1983. 2393. w5x Y. Nakao, J. Colloid Interface Sci. 171 Ž1995. 386. w6x A.W. Olsen, Z.H. Kafari, J. Am. Chem. Soc. 113 Ž1991. 7758. w7x M.S. Kunz, K.R. Shull, A.J. Kellock, J. Colloid Interface Sci. 156 Ž1993. 240. w8x R. Saito, S. Okamoto, K. Ishizu, Polymer 33 Ž1992. 1099. w9x R. Saito, S. Okamoto, K. Ishizu, Polymer 34 Ž1993. 1189.
w10x J.L. Marignier, J. Belloni, M.O. Delcourt, J.P. Chevalier, Nature 317 Ž1985. 344. w11x A. Henglein, E. Janata, A. Fojtik, J. Phys. Chem. 96 Ž1992. 4734. w12x C.N.J. Wagner, E.N. Aqua, Adv. X-ray Anal. 7 Ž1964. 46. w13x Y. Zhu, Y. Qian, M. Zhang, Z. Chen, M. Chen, G. Zhou, J. Mater. Sci. Lett. 13 Ž1994. 1243. w14x Y. Zhu, Y. Qian, M. Zhang, Z. Chen, B. Lu, G. Zhou, Mater. Sci. Eng. B23 Ž1994. 116.