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Carbon composites from sucrose-assisted synthesis for highly efficient dehydrochlorination process
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Materials Letters 62 (2008) 1887 – 1889 www.elsevier.com/locate/matlet
Preparation of nano-MgO/Carbon composites from sucrose-assisted synthesis for highly efficient dehydrochlorination process Qian Zhou ⁎, Jia-Wei Yang, Yu-Zhong Wang ⁎, Yan-Hui Wu, De-Zhi Wang Centre for Degradable and Flame-Retardant Polymeric Material, College of Chemistry, Sichuan University, Chengdu 610064, China Received 10 July 2007; accepted 17 October 2007 Available online 24 October 2007
Abstract A carbon-coated nano-MgO has been prepared with the assistance of sucrose and characterized by adsorption methods, X-ray diffraction method (XRD) and Scanning electron microscopy (SEM). Sucrose can both prevent the agglomeration of the synthesized Mg(OH)2 and act as the carbon source for surface coating of the MgO nanoparticles, and both crystallite sizes and carbon contents of the composites can be delicately adjusted by simply changing the sucrose to magnesium molar ratio. The MgO/C obtained in controlled synthesis has been proved to be a highly efficient chemisorbent for the dehydrochlorination of a PVC-containing mixture (Polypropylene/Polyvinyl Chloride). © 2007 Elsevier B.V. All rights reserved. Keywords: MgO/Carbon; Nanocomposites; Dehydrochlorination; Sucrose; Polymer; Recycling
1. Introduction Polymer pyrolysis, aiming to degrade waste plastics to fuel oil or valuable chemicals, is regarded as the most promising technology for resource recovery from waste polymer materials [1]. However, during pyrolysis polyvinylchloride (PVC) in waste plastics generates HCl that causes corrosion problems and a contamination of all product streams with chlorinated organics. Therefore the dechlorination of waste plastics is very necessary. Different sorbents were used and investigated [2,3], among them alkaline earth oxides such as MgO attracted significant attention as effective dehydrochlorination catalysts and chemisorbents for dealing with the PVC-containing waste plastics. However, the limited dechlorination degree is far from the requirement of realizing commercial use of this process. MgO nanoparticles have been shown to be highly efficient dehalogenation catalysts because of the small average particle size and high surface area [4]. However, the high active surface of nano-MgO is prone to be deactivated by water and CO2 in the environment, leading to the decreased dehydrohalogenation ability. In order to increase the stability of nano-MgO, carbon-coated MgO was prepared by various methods such as decomposition of dry magnesium methoxide or resorcinol ⁎ Corresponding authors. Tel./fax: +86 28 85410259. E-mail address: [email protected] (Y.-Z. Wang). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.10.031
modified magnesium methoxide [5], reaction between Mg and Mo(CO)6 [6], and chemical vapor deposition method (CVD) with carbon precursors such as propylene [7], or butadiene [8]. However, the sol–gel method deals with the costly and hazardous metalorganic precursors, which is inconvenient and economically unacceptable, and the CVD method is essentially a kind of “postsynthesis” process in which nanoparticles should be prepared in advance. In this paper, a simple and economic “couple synthesis” method is developed for preparing the carbon-coated nano-MgO through coprecipitation magnesium nitrate with sucrose. Sucrose is served as carbon precursors because of the carbon rich character and the ability of complexation with metal ions [9] that it not only prevents the agglomeration of the synthesized Mg(OH)2 but also acts as the carbon source for surface coating of the MgO nanoparticles. With the assistance of sucrose, the obtained carbon-coated nano-MgO has been proved to be a highly efficient chemisorbent for the dechlorination process, which will be very useful in the recycling of chloride-containing waste plastics. 2. Experimental 2.1. Preparation and characterization of MgO/Carbon MgO/Carbon was synthesized as follows: sucrose and magnesium nitrate were dissolved in deionized water and precipitated by
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Q. Zhou et al. / Materials Letters 62 (2008) 1887–1889
ammonium hydroxide until the pH value reached 9.5, then the precipitation was dried under air at 90 °C for 12 h to obtain Mg (OH)2/Sucrose precursors. The precursors were heated from room temperature to 500 °C at a rate of 2 °C/min and kept at this temperature for 2 h. The Powder X-ray Diffraction Pattern (XRD) was recorded on a Philips X'Pert Pro X-ray instrument with a CuKα X-ray. Surface areas of the catalysts were calculated using the BET equation from adsorption isotherms of nitrogen measured at liquid nitrogen temperature (AUTOSORP ZXF-4, China). The particle morphology was observed by a Hitachi 4800 field emission gun (FEG) scanning electron microscopy (SEM), and transmission electron microscopic (TEM) images were obtained on a JEOL 100CX microscope. 2.2. Degradation procedure and product analysis The pyrolysis of PP/PVC was carried out in a glass reactor by batch operation. Experimental details and product analyses have been described previously [3]. In a typical catalytic run, sorbents (2 g) were mixed with PP/PVC (10 g, in a weight ratio of PP/PVC/sorbents = 4/1/1), and reacted at 400 °C until no liquid was produced. The chlorine contents in products were analyzed by oxygen bomb combustion and the chlorine ion selective electrode method (ISE). The components of pyrolysis oils were analyzed using an Agilent HP 6890N gas chromatography equipped with an Agilent HP 5973 N mass selective detector (GC/MS) and a 30 m × 0.25 mm × 0.25 μm DB-5 capillary column.
Table 1 Physichemical properties of MgO and MgO/C composites Sorbents
Crystallite size a (nm, XRD)
Carbon content (wt.%)
SBET (m2 g− 1)
MgO MgO/C(0.1) MgO/C(0.5) MgO/C(0.75) MgO/C(1) MgO/C(2)
18.2 15.9 13.1 – 11.6 8.8
– – 3.1 7.1 11.1 27.2
48.6 55.5 203 143 88.5 –
a
Based on (200) plane.
precursors preserve the lamellar shape, i.e., the crystals of the precursor (Sucrose: Mg = 0.5) randomly pile up and present a thin platelet shape with a more or less circular contour, and the individual platelet shows a thickness of about 30 nm and lateral dimensions of about 500 nm. Moreover, for the crystallite sizes of the samples calculated using the Scherrer equation, it can be seen that with the increase of the sucrose contents the crystallite sizes in the direction of (001) planes decrease, while those along (110) planes only slightly decrease so as to lead to a higher aspect ratio (width to height), suggesting sucrose molecules have the ability to slow the growth of (001) crystal planes to obtain a thinner Mg(OH)2 plate.
3. Results and discussion The powder XRD patterns of the as-prepared Mg(OH)2/sucrose precursors showed diffraction peaks of the hexagonal Mg(OH)2 phase, and the significant broadening peak could be easily detected, indicating that the as-synthesized Mg(OH)2 has very small crystallite sizes. Moreover, no sucrose diffraction peaks are detected even when the molar ratio of sucrose to magnesium ion is as high as 1:1, proving that sucrose owns a high dispersion capacity in Mg(OH)2 phase. From SEM observations shown in Fig. 1, it can be seen that the Mg(OH)2/sucrose
Fig. 1. A typical SEM image of Mg(OH)2/Sucrose precursor (Sucrose: Mg = 0.5).
Fig. 2. Typical SEM images of MgO/Carbon (Sucrose: Mg = 0.5) at a low magnification (a) and at high magnification (b).
Q. Zhou et al. / Materials Letters 62 (2008) 1887–1889
Fig. 3. Chlorine distribution from pyrolysis of PP/PVC at 400 °C.
X-ray diffraction (XRD) patterns of the MgO/C composite oxide prove that all peaks can be indexed as the cubic MgO phase. Moreover, no characteristic peaks of carbon are detected even when sucrose/Mg molar ratio is as high as 2, indicating that the carbon coating is amorphous in nature. The mean crystallite sizes calculated from Scherrer equation (Table 1) indicate that processing the Mg(OH)2 sample at 500 °C lead to collapse of the lamellar crystals to form smaller MgO crystals. On the other hand, a typical SEM image of the obtained MgO/C at low magnification clearly shows that the platelike feature is partly retained in the final MgO/C samples after calcinations (Fig. 2). However, the sample exhibits a coarse morphology compared to its original Mg(OH)2 precursor. A higher magnification SEM image shows that the coarse platelets are composed of nanocrystals with average crystallite size in the range of 20–40 nm connected with each other, which is in line with the results from XRD measurements. Furthermore, it is found that the crystallite sizes of the as-synthesized MgO/C composite oxide decrease with the increase of the sucrose contents according to Scherrer equation, and this observation is further confirmed by TEM measurements. Table 1 illustrates that the carbon contents of the synthesized MgO/C composite oxides almost linearly increase with the increase of sucrose contents in the precursor. Moreover, as we have ever mentioned above, the crystallite sizes of Mg (OH)2/Sucrose precursor decrease with the increase of sucrose/magnesium molar ratio. Therefore, we can conclude that the carbon deposited on the surface of MgO nanocrystals effectively retards sintering of the latter. In order to further illustrate the role of carbon coating, the Mg (OH)2/Sucrose precursors were calcinated under air flow (MgO/C-Air) and the physichemical properties of the MgO/Cair were compared with the MgO/C–N2. It can be seen that all XRD peaks are indexed as pure cubic MgO phases regardless of the calcination atmosphere, but the MgO calcinated under nitrogen shows smaller crystallite size (13.1 nm) and higher surface area (203 m2 g− 1) compared with those calcined under air (D: 15.8 nm, SBET: 59.4 m2 g− 1). These results further prove the importance of carbon in protecting the MgO nanocrystals from sintering. The MgO/Carbon composite oxide (Sucrose: Mg =0.5) was adopted for pyrolysis of a typical PVC-containing plastics (polypropylene/ polyvinyl chloride). For chlorine distribution (Fig. 3), the carbon-coated MgO from sucrose-assisted synthesis shows prominently superior dechlorination ability than MgO: the evolved chlorine is sharply decreased to 2.1 wt.% (MgO: 15.7 wt.%), including 1.1 wt.% as HCl, and 1.0 wt.% in the organic liquid phase with the chlorinated hydrocarbons mainly composed of 2-chloro-2-methylpropane, 2-chloro-2-methylbutane, 2-
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chloro-2-methylpentane, and 3-chloro-3-methylpentane. In fact, a higher SBET of MgO/C (203 m2 g− 1) than that of MgO (48.6 m2 g− 1) is observed. Therefore, the increased interactions between sorbents and the produced HCl due to the higher surface area of the MgO/C composite oxides may account for the superior dechlorination ability. On the other hand, it was found that the structural characteristics of carbon substantially influence hydrodechlorination performance [10]. Therefore, it is reasonable to hypothesize that the carbon deposited on MgO nanocrystals is able to promote the decomposition of organochlorine. The role of carbon coating is further demonstrated by comparing the dechlorination ability of MgO/Cair with MgO/C–N2. For the MgO/C-air system, the organic chlorine contents in liquid (5.0 wt.%) and HCl amounts in gas phase (2.6 wt.%) are much higher than those for MgO/C–N2 system, suggesting that carbon coatings effectively enhance the dechlorination ability of the MgO/C composite oxides. A systematic investigation such as the effects of carbon properties as well as carbon contents of the composite oxides on the decomposition behaviors of organochlorine is in progress.
4. Conclusions In summary, a simple and economic “couple synthesis” method is developed to synthesize the carbon-coated nanoMgO for dechlorination, and it has the following advantages: by simply changing the molar ratio of sucrose to magnesium we can adjust not only the crystallite sizes of the synthesized MgO/ C but also the carbon contents coated on the surface of the composite oxides; the MgO/C obtained in controlled synthesis shows prominent higher dechlorination ability for a PVCcontaining mixture (PP/PVC) than that of MgO. The simplicity and low cost of the process would be favorable to scaling-up industrial manufacture, and this method may be extended to synthesize other highly efficient carbon-coated dechlorination sorbents. Acknowledgement The authors wish to acknowledge the financial support of the National Science Foundation of China (20306019) and the National Science Fund for Distinguished Young Scholars (50525309). References [1] W. Kaminsky, F. Hartmann, Angew. Chem. Int. Ed. 39 (2000) 331–332. [2] T. Bhaskar, T. Matsui, J. Kaneko, M.A. Uddin, A. Muto, Y. Sakata, Green Chem. 4 (2002) 372–375. [3] Q. Zhou, C. Tang, Y.Z. Wang, L. Zheng, Fuel 83 (2004) 1727–1732. [4] J. Roggenbuck, G. Koch, M. Tiemann, Chem. Mater. 18 (2006) 4151–4156. [5] A.F. Bedilo, M.J. Sigel, O.B. Koper, M.S. Melgunov, K.J. Klabunde, J. Mater. Chem. 12 (2002) 3599–3604. [6] M. Motiei, J. Calderon-Moreno, A. Gedanken, Adv. Mater. 14 (2002) 1169–1172. [7] M.S. Mel'gunov, E.A. Mel'gunova, V.I. Zaikovskii, V.B. Fenelonov, A.F. Bedilo, K.J. Klabunde, Langmuir 19 (2003) 10426–10433. [8] D.S. Heroux, A.M. Volodin, V.I. Zaikovski, V.V. Chesnokov, A.F. Bedilo, K.J. Klabunde, J. Phys. Chem., B 108 (2004) 3140–3144. [9] P. Rondeau, D. Jhurry, S. Sers, F. Cadet, Appl. Spectrosc. 58 (2004) 816–822. [10] C. Amorim, G. Yuan, P.M. Patterson, M.A. Keane, J. Catal. 234 (2005) 268–281.
Materials Letters 62 (2008) 1887 – 1889 www.elsevier.com/locate/matlet
Preparation of nano-MgO/Carbon composites from sucrose-assisted synthesis for highly efficient dehydrochlorination process Qian Zhou ⁎, Jia-Wei Yang, Yu-Zhong Wang ⁎, Yan-Hui Wu, De-Zhi Wang Centre for Degradable and Flame-Retardant Polymeric Material, College of Chemistry, Sichuan University, Chengdu 610064, China Received 10 July 2007; accepted 17 October 2007 Available online 24 October 2007
Abstract A carbon-coated nano-MgO has been prepared with the assistance of sucrose and characterized by adsorption methods, X-ray diffraction method (XRD) and Scanning electron microscopy (SEM). Sucrose can both prevent the agglomeration of the synthesized Mg(OH)2 and act as the carbon source for surface coating of the MgO nanoparticles, and both crystallite sizes and carbon contents of the composites can be delicately adjusted by simply changing the sucrose to magnesium molar ratio. The MgO/C obtained in controlled synthesis has been proved to be a highly efficient chemisorbent for the dehydrochlorination of a PVC-containing mixture (Polypropylene/Polyvinyl Chloride). © 2007 Elsevier B.V. All rights reserved. Keywords: MgO/Carbon; Nanocomposites; Dehydrochlorination; Sucrose; Polymer; Recycling
1. Introduction Polymer pyrolysis, aiming to degrade waste plastics to fuel oil or valuable chemicals, is regarded as the most promising technology for resource recovery from waste polymer materials [1]. However, during pyrolysis polyvinylchloride (PVC) in waste plastics generates HCl that causes corrosion problems and a contamination of all product streams with chlorinated organics. Therefore the dechlorination of waste plastics is very necessary. Different sorbents were used and investigated [2,3], among them alkaline earth oxides such as MgO attracted significant attention as effective dehydrochlorination catalysts and chemisorbents for dealing with the PVC-containing waste plastics. However, the limited dechlorination degree is far from the requirement of realizing commercial use of this process. MgO nanoparticles have been shown to be highly efficient dehalogenation catalysts because of the small average particle size and high surface area [4]. However, the high active surface of nano-MgO is prone to be deactivated by water and CO2 in the environment, leading to the decreased dehydrohalogenation ability. In order to increase the stability of nano-MgO, carbon-coated MgO was prepared by various methods such as decomposition of dry magnesium methoxide or resorcinol ⁎ Corresponding authors. Tel./fax: +86 28 85410259. E-mail address: [email protected] (Y.-Z. Wang). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.10.031
modified magnesium methoxide [5], reaction between Mg and Mo(CO)6 [6], and chemical vapor deposition method (CVD) with carbon precursors such as propylene [7], or butadiene [8]. However, the sol–gel method deals with the costly and hazardous metalorganic precursors, which is inconvenient and economically unacceptable, and the CVD method is essentially a kind of “postsynthesis” process in which nanoparticles should be prepared in advance. In this paper, a simple and economic “couple synthesis” method is developed for preparing the carbon-coated nano-MgO through coprecipitation magnesium nitrate with sucrose. Sucrose is served as carbon precursors because of the carbon rich character and the ability of complexation with metal ions [9] that it not only prevents the agglomeration of the synthesized Mg(OH)2 but also acts as the carbon source for surface coating of the MgO nanoparticles. With the assistance of sucrose, the obtained carbon-coated nano-MgO has been proved to be a highly efficient chemisorbent for the dechlorination process, which will be very useful in the recycling of chloride-containing waste plastics. 2. Experimental 2.1. Preparation and characterization of MgO/Carbon MgO/Carbon was synthesized as follows: sucrose and magnesium nitrate were dissolved in deionized water and precipitated by
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Q. Zhou et al. / Materials Letters 62 (2008) 1887–1889
ammonium hydroxide until the pH value reached 9.5, then the precipitation was dried under air at 90 °C for 12 h to obtain Mg (OH)2/Sucrose precursors. The precursors were heated from room temperature to 500 °C at a rate of 2 °C/min and kept at this temperature for 2 h. The Powder X-ray Diffraction Pattern (XRD) was recorded on a Philips X'Pert Pro X-ray instrument with a CuKα X-ray. Surface areas of the catalysts were calculated using the BET equation from adsorption isotherms of nitrogen measured at liquid nitrogen temperature (AUTOSORP ZXF-4, China). The particle morphology was observed by a Hitachi 4800 field emission gun (FEG) scanning electron microscopy (SEM), and transmission electron microscopic (TEM) images were obtained on a JEOL 100CX microscope. 2.2. Degradation procedure and product analysis The pyrolysis of PP/PVC was carried out in a glass reactor by batch operation. Experimental details and product analyses have been described previously [3]. In a typical catalytic run, sorbents (2 g) were mixed with PP/PVC (10 g, in a weight ratio of PP/PVC/sorbents = 4/1/1), and reacted at 400 °C until no liquid was produced. The chlorine contents in products were analyzed by oxygen bomb combustion and the chlorine ion selective electrode method (ISE). The components of pyrolysis oils were analyzed using an Agilent HP 6890N gas chromatography equipped with an Agilent HP 5973 N mass selective detector (GC/MS) and a 30 m × 0.25 mm × 0.25 μm DB-5 capillary column.
Table 1 Physichemical properties of MgO and MgO/C composites Sorbents
Crystallite size a (nm, XRD)
Carbon content (wt.%)
SBET (m2 g− 1)
MgO MgO/C(0.1) MgO/C(0.5) MgO/C(0.75) MgO/C(1) MgO/C(2)
18.2 15.9 13.1 – 11.6 8.8
– – 3.1 7.1 11.1 27.2
48.6 55.5 203 143 88.5 –
a
Based on (200) plane.
precursors preserve the lamellar shape, i.e., the crystals of the precursor (Sucrose: Mg = 0.5) randomly pile up and present a thin platelet shape with a more or less circular contour, and the individual platelet shows a thickness of about 30 nm and lateral dimensions of about 500 nm. Moreover, for the crystallite sizes of the samples calculated using the Scherrer equation, it can be seen that with the increase of the sucrose contents the crystallite sizes in the direction of (001) planes decrease, while those along (110) planes only slightly decrease so as to lead to a higher aspect ratio (width to height), suggesting sucrose molecules have the ability to slow the growth of (001) crystal planes to obtain a thinner Mg(OH)2 plate.
3. Results and discussion The powder XRD patterns of the as-prepared Mg(OH)2/sucrose precursors showed diffraction peaks of the hexagonal Mg(OH)2 phase, and the significant broadening peak could be easily detected, indicating that the as-synthesized Mg(OH)2 has very small crystallite sizes. Moreover, no sucrose diffraction peaks are detected even when the molar ratio of sucrose to magnesium ion is as high as 1:1, proving that sucrose owns a high dispersion capacity in Mg(OH)2 phase. From SEM observations shown in Fig. 1, it can be seen that the Mg(OH)2/sucrose
Fig. 1. A typical SEM image of Mg(OH)2/Sucrose precursor (Sucrose: Mg = 0.5).
Fig. 2. Typical SEM images of MgO/Carbon (Sucrose: Mg = 0.5) at a low magnification (a) and at high magnification (b).
Q. Zhou et al. / Materials Letters 62 (2008) 1887–1889
Fig. 3. Chlorine distribution from pyrolysis of PP/PVC at 400 °C.
X-ray diffraction (XRD) patterns of the MgO/C composite oxide prove that all peaks can be indexed as the cubic MgO phase. Moreover, no characteristic peaks of carbon are detected even when sucrose/Mg molar ratio is as high as 2, indicating that the carbon coating is amorphous in nature. The mean crystallite sizes calculated from Scherrer equation (Table 1) indicate that processing the Mg(OH)2 sample at 500 °C lead to collapse of the lamellar crystals to form smaller MgO crystals. On the other hand, a typical SEM image of the obtained MgO/C at low magnification clearly shows that the platelike feature is partly retained in the final MgO/C samples after calcinations (Fig. 2). However, the sample exhibits a coarse morphology compared to its original Mg(OH)2 precursor. A higher magnification SEM image shows that the coarse platelets are composed of nanocrystals with average crystallite size in the range of 20–40 nm connected with each other, which is in line with the results from XRD measurements. Furthermore, it is found that the crystallite sizes of the as-synthesized MgO/C composite oxide decrease with the increase of the sucrose contents according to Scherrer equation, and this observation is further confirmed by TEM measurements. Table 1 illustrates that the carbon contents of the synthesized MgO/C composite oxides almost linearly increase with the increase of sucrose contents in the precursor. Moreover, as we have ever mentioned above, the crystallite sizes of Mg (OH)2/Sucrose precursor decrease with the increase of sucrose/magnesium molar ratio. Therefore, we can conclude that the carbon deposited on the surface of MgO nanocrystals effectively retards sintering of the latter. In order to further illustrate the role of carbon coating, the Mg (OH)2/Sucrose precursors were calcinated under air flow (MgO/C-Air) and the physichemical properties of the MgO/Cair were compared with the MgO/C–N2. It can be seen that all XRD peaks are indexed as pure cubic MgO phases regardless of the calcination atmosphere, but the MgO calcinated under nitrogen shows smaller crystallite size (13.1 nm) and higher surface area (203 m2 g− 1) compared with those calcined under air (D: 15.8 nm, SBET: 59.4 m2 g− 1). These results further prove the importance of carbon in protecting the MgO nanocrystals from sintering. The MgO/Carbon composite oxide (Sucrose: Mg =0.5) was adopted for pyrolysis of a typical PVC-containing plastics (polypropylene/ polyvinyl chloride). For chlorine distribution (Fig. 3), the carbon-coated MgO from sucrose-assisted synthesis shows prominently superior dechlorination ability than MgO: the evolved chlorine is sharply decreased to 2.1 wt.% (MgO: 15.7 wt.%), including 1.1 wt.% as HCl, and 1.0 wt.% in the organic liquid phase with the chlorinated hydrocarbons mainly composed of 2-chloro-2-methylpropane, 2-chloro-2-methylbutane, 2-
1889
chloro-2-methylpentane, and 3-chloro-3-methylpentane. In fact, a higher SBET of MgO/C (203 m2 g− 1) than that of MgO (48.6 m2 g− 1) is observed. Therefore, the increased interactions between sorbents and the produced HCl due to the higher surface area of the MgO/C composite oxides may account for the superior dechlorination ability. On the other hand, it was found that the structural characteristics of carbon substantially influence hydrodechlorination performance [10]. Therefore, it is reasonable to hypothesize that the carbon deposited on MgO nanocrystals is able to promote the decomposition of organochlorine. The role of carbon coating is further demonstrated by comparing the dechlorination ability of MgO/Cair with MgO/C–N2. For the MgO/C-air system, the organic chlorine contents in liquid (5.0 wt.%) and HCl amounts in gas phase (2.6 wt.%) are much higher than those for MgO/C–N2 system, suggesting that carbon coatings effectively enhance the dechlorination ability of the MgO/C composite oxides. A systematic investigation such as the effects of carbon properties as well as carbon contents of the composite oxides on the decomposition behaviors of organochlorine is in progress.
4. Conclusions In summary, a simple and economic “couple synthesis” method is developed to synthesize the carbon-coated nanoMgO for dechlorination, and it has the following advantages: by simply changing the molar ratio of sucrose to magnesium we can adjust not only the crystallite sizes of the synthesized MgO/ C but also the carbon contents coated on the surface of the composite oxides; the MgO/C obtained in controlled synthesis shows prominent higher dechlorination ability for a PVCcontaining mixture (PP/PVC) than that of MgO. The simplicity and low cost of the process would be favorable to scaling-up industrial manufacture, and this method may be extended to synthesize other highly efficient carbon-coated dechlorination sorbents. Acknowledgement The authors wish to acknowledge the financial support of the National Science Foundation of China (20306019) and the National Science Fund for Distinguished Young Scholars (50525309). References [1] W. Kaminsky, F. Hartmann, Angew. Chem. Int. Ed. 39 (2000) 331–332. [2] T. Bhaskar, T. Matsui, J. Kaneko, M.A. Uddin, A. Muto, Y. Sakata, Green Chem. 4 (2002) 372–375. [3] Q. Zhou, C. Tang, Y.Z. Wang, L. Zheng, Fuel 83 (2004) 1727–1732. [4] J. Roggenbuck, G. Koch, M. Tiemann, Chem. Mater. 18 (2006) 4151–4156. [5] A.F. Bedilo, M.J. Sigel, O.B. Koper, M.S. Melgunov, K.J. Klabunde, J. Mater. Chem. 12 (2002) 3599–3604. [6] M. Motiei, J. Calderon-Moreno, A. Gedanken, Adv. Mater. 14 (2002) 1169–1172. [7] M.S. Mel'gunov, E.A. Mel'gunova, V.I. Zaikovskii, V.B. Fenelonov, A.F. Bedilo, K.J. Klabunde, Langmuir 19 (2003) 10426–10433. [8] D.S. Heroux, A.M. Volodin, V.I. Zaikovski, V.V. Chesnokov, A.F. Bedilo, K.J. Klabunde, J. Phys. Chem., B 108 (2004) 3140–3144. [9] P. Rondeau, D. Jhurry, S. Sers, F. Cadet, Appl. Spectrosc. 58 (2004) 816–822. [10] C. Amorim, G. Yuan, P.M. Patterson, M.A. Keane, J. Catal. 234 (2005) 268–281.