- Email: [email protected]
A novel solvothermal route to benzene ring-capped oxide nanocrystals
Materials Letters 61 (2007) 4807 – 4810 www.elsevier.com/locate/matlet
A novel solvothermal route to benzene ring-capped oxide nanocrystals Meilan Wan a , Yanfei Pan a , Guoqun Liu b , Tao He c,⁎, Zhicai Zhou c , Tao Zhang a , Ruiming Zhao a b
a School of Chemical and Biological Science and Engineering, Yantai University, China School of Materials and Chemical Engineering, Zhongyuan University of Technology, Zhengzhou 450007, China c Institute of Applied catalysts, Yantai University, Yantai 264005, China
Received 13 November 2006; accepted 8 March 2007 Available online 15 March 2007
Abstract A novel solvothermal synthesis based on the reaction between nitrate and benzene for metal oxide nanocrystals including ZrO2 and SnO2 is introduced. The as-prepared nanocrystals are characterized by TEM, XRD and IR techniques in detail, and the possible mechanism of this solvothermal reaction is discussed. Benzene molecules used as capping agent, instead of long-carbon chain molecules, are chemically adsorbed to the surface of the as-prepared oxide nanocrystals, making nanocrystals with long-term stability and good dispersibility in hydrocarbons. © 2007 Published by Elsevier B.V. Keywords: Nanomaterials; Powder technology
1. Introduction Metal oxide nanocrystals exhibit a variety of structures and properties and significant application prospects in magnet, optics, batteries, electronics, precursors of ceramics, etc. [1]. However, nanocrystals readily grow during preparation, storage and application due to coarsening [2] or aggregating [3]. This consequently destroys their properties and debases their usability. The stability of oxide nanocrystals is therefore crucial to their application. So far, monodispersed and stable oxide nanocrystals with controlled particle size and shape have been prepared mostly by thermo-decomposition of metallorganics in high-boiling point hydrocarbons, into which a large quantity of capping agents such as surfactants are usually added to prevent them from aggregation [4]. The high cost and complication of the synthetic process, however, confine the production of oxide nanocrystals in a large scale, and a mass of capping agent molecules with long-carbon chains are chemically adsorbed to ⁎ Corresponding author. Tel.: +86 535 6902743 (O); fax: +86 535 6902063. E-mail addresses: [email protected] (M. Wan), [email protected] (Y. Pan), [email protected] (G. Liu), [email protected] (T. He), [email protected] (Z. Zhou), [email protected] (T. Zhang), [email protected] (R. Zhao). 0167-577X/$ - see front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.matlet.2007.03.039
the nanocrystals' surface, limiting their application in some fields such as catalysts, sensors, precursors for advanced nanoceramics and so on. Therefore, a novel synthetic route, through which monodispersed and stable nanocrystals can be cheaply prepared and long-carbon chain capping agents are no longer needed, is strongly desirable. In this paper, a facile solvothermal route to metal oxide nanocrystals including ZrO2 and SnO2, which is based on the reaction of metal nitrate and benzene, is introduced, and the mechanism of the solvothermal reaction is also discussed. The as-prepared nanocrystals with a particle size smaller than 10 nm and benzene molecules chemically adsorbed to their surface show good dispersibility in hydrocarbons, which might improve the application in many fields. 2. Experimental All reagents are of analytical grade and used as received. Typical experiments were conducted in a steel autoclave with a cubage of 15 ml and Teflon lining and described as below. The products were dried at 80 °C in air after washing. Zirconium nitrates (5 mmol) and benzene (12 ml) were put into an autoclave and heated at 180 °C for 4 h. After cooling to room temperature, the solid product was isolated by distillation
4808
M. Wan et al. / Materials Letters 61 (2007) 4807–4810
under vacuum and subsequently washed with absolute ethanol. Finally, a primrose powder was collected after drying. The mixture of SnCl4 (5 mmol), NaNO3 (20 mmol) and benzene (12 ml) was heated in an autoclave at 180 °C for 4 h, and then cooled to room temperature. The aimed product was extracted by benzene. After benzene distilled, the fawn solid was then washed with absolute ethanol supersonically and followed by centrifugation and drying. X-ray diffraction patterns were recorded on a Rigaku D/Max 2200-PC diffractometer with Cu-Kα radiation (λ = 0.15418 nm) and graphite monochromator at ambient temperature. The morphologies and dispersibility of the as-prepared nanocrystals were observed with a transmission electron microscope (TEM, JEM100-CXII) and high resolution transmission electron microscope (HRTEM, JEOL 2010). The aromatic molecules adsorbed to the surface of the as-prepared nanoparticles and the liquid product was characterized with a Nicolet 5DX FT-IR instrument using KBr pellet technique and GC-MSD Agilent 6890N-5973N (temperature range: 50 ∼ 250 °C, increasing rate: 5 °C/min). 3. Results and discussion The XRD patterns of the products indicate that pure monoclinic ZrO2 and tetragonal SnO2 are obtained (Fig. 1). Their average grain sizes based on the Scherrer equation are respectively 7.3 nm and 4.6 nm, and close to the sizes of the individual nanoparticles observed in TEM images, confirming that every individual nanoparticle is a nanocrystal. Since no capping agent molecules with long-carbon chains exists in their surface, most of the nanocrystals on the TEM grid are close to each other due to weak steric hindrance (Fig. 2). On the other hand, clear-cut boundaries between nanocrystals can be seen in TEM images (Fig. 2a for ZrO2 nanocrystals) and HRTEM images (Fig. 2c for SnO2 nanocrystals). The nanocrystals show good dispersibility in ethanol, benzene, cyclohexane. Dispersions of the as-prepared powders (ca. 50 mg) in the above solvents (100 ml) keep transparency for more than 1 h, and then flocculation occurs to form a loose precipitate, while Fig. 2. TEM images of the as-prepared powders: (a) ZrO2; (b) SnO2; (c) HRTEM image of the SnO2 nanocrystals, the clear-cut boundaries between nanocrystals are marked with black arrows.
Fig. 1. X-ray diffractograms of the as-prepared powders: (a) ZrO2 and (b) SnO2.
transparent dispersion will be recovered by gently shaking the bottle. The flocculation–redispersion can be repeated even when the precipitates are placed for 6 months at room temperature. Their size and morphology don't change, which is confirmed by XRD and TEM analysis. All of the above facts strongly prove that no aggregating or coarsening growth occurs among the as-prepared nanocrystals in hydrocarbons, although they are close to each other and have no longcarbon chain capping molecules in their surface. As discussed in the following text, the high stability of the fine nanocrystals against growth is attributed to their surface, which is chemically adsorbed by benzene rings. Aromatics tend to cover a parallel specific surface of oxide crystal particles through its electronic ring by chemical adsorption [5], and fine nanoparticles of metal oxides are full of oxyanion vacancy [6]. The chemical adsorption could be much stronger because of the electronic abundant character of benzene ring and the electron deficiency of oxide nanoparticles. Moreover, it is reasonable that the finer the nanoparticles, the stronger this kind of interaction. In order to identify the
M. Wan et al. / Materials Letters 61 (2007) 4807–4810
components adsorbed to the surface of the nanocrystals, both the asprepared powders and the powders after heat-treatment in vacuum at 220 °C for 2 h are characterized by IR technique. Besides the strong absorptions of metal–oxygen vibrations in ZrO2 and SnO2 nanocrystals below 800 cm− 1, the as-prepared powders also show a few absorption bands (Fig. 3). The bands centered at 3400 cm− 1 and 1627 cm− 1, assigned to the O–H stretching and bending modes of adsorbed water molecules [7], are greatly weakened, while the intensities of other absorption bands change little after the heat-treatment (Fig. 3). The strong and characteristic absorption band attributed to C–O stretching vibration of alcohol molecules usually at ca. 1050 cm− 1 [8] does not exist, because the dry vacuum can entirely eliminate the ethanol that was used as a solvent in the preparation. In the absence of benzene, metal oxide micro-powders can also be prepared under the same reaction conditions (in autoclave at 180 °C for 4 h). While, only one sharp and strong absorption band at ca. 1380 cm− 1, which is attributed to the absorption of NO−3 [9] was observed in their IR spectra in the same wavenumber range (from 2000 to 800 cm− 1). It was greatly weakened when the micro-powders were heated in vacuum at 220 °C for 2 h. The characteristic absorptions of benzene molecules are mainly located at 3100 ∼ 3000 cm− 1 for _C–H in-plane stretching vibration mode, at 1650 ∼ 1450 cm− 1 for C_C stretching vibration mode, and at 1250 ∼ 1000 cm− 1 for _C–H out-plane stretching vibration mode. And nitrobenzene shows two additional absorptions at ca. 1540 and 1350 cm− 1 attributing to the dissymmetric and symmetric stretching vibration modes of –NO2 [8]. It can be seen that most of the absorption bands are located in the wavenumber ranges of characteristic absorption of aromatic molecules. Since no other hydrocarbons exist in the reaction system, these absorption bands in Fig. 3 (a (2) and b (2)) can be assigned to the characteristic vibration modes of benzene and nitrobenzene molecules adsorbed to the nanocrystals' surface. The heat-treatment in vacuum at 220 °C for 2 h did not desorb the aromatic molecules, indicating a strong chemical interaction between the nanocrystals and the adsorbed benzene rings. As the particle surface is covered with aromatics such as benzene and nitrobenzene, two immediate results are induced: the surface energy and, then as a result, the growth of the coated nanoparticles became slow; the surface of the nanocrystals turned to hydrophobic.
4809
IR spectrum and mass spectrum system–total ion chromatography analysis prove that the reaction supernatant includes benzene, nitrobenzene and water. A nitration reaction, therefore, probably takes place in the solvothermal processes to form oxide nanoparticles. The following formulation could explain the synthesis reaction of ZrO2 nanocrystals: ZrðNO3 Þ4 þ 4C6 H6 →ZrO2 þ 4C6 H5 NO2 þ 2H2 O
ð1Þ
As many transition metal nitrates are essential covalent molecules and dissolve into hydrocarbon solvents [10], this solvothermal route might be applicable to the fabrication of many metal oxide nanoparticles. Our experiments indicate that metal chloride SnCl4 does not react with benzene without nitrate anions. However, the reaction occurs to give oxide nanocrystals, nitrobenzene and sodium chlorides, when introducing sodium nitrate (Eq. (2)): SnCl4 þ 4C6 H6 þ 4NaNO3 →SnO2 þ 4C6 H5 NO2 þ 4NaCl þ 2H2 O (2) Thus the whole process in fact includes two reactions: the first is the replacement reaction between SnCl4 and NaNO3: SnCl4 þ 4NaNO3 →SnðNO3 Þ4 þ 4NaCl
ð3Þ
The second is the nitration reaction of benzene with the formed metal nitrate Sn(NO3)4 (similar to Eq. (1)), and the equilibrium Eq. (3) would move to the right side with time onstream. Experiments prove that sodium nitrate doesn't react with benzene under the same reaction conditions, indicating that the formation of metal oxide that abided by the following reaction scheme is impossible. C6 H6 þ NO−3 →C6 H5 NO2 þ OH−
ð4Þ
4OH− þ MðNO3 Þ4 or MCl4 →MO2 þ 2H2 O þ 4NO−3 or 4Cl−
ð5Þ
Except for IA and IIA metals, other metal nitrates decompose to produce metal oxides or metal simple substances with liberation of oxygen and nitric oxide: MðNO3 Þx →MOx=2 þ xNO2 þ x=4O2
ð6Þ
NO2 as a nitrating agent can react with benzene to form nitrobenzene. Oxides may catalyze this reaction [11]: C6 H6 þ NO2 þ 1=4O2 →C6 H5 NO2 þ 1=2H2 O
ð7Þ
Based on the above information, the process in Eq. (1) actually includes two processes: the decomposition of metal nitrates (Eq. (6)) and the nitration of benzene with NO2 (Eq. (7)). The decomposed product NO2 and O2 could be consumed by reacting with benzene, implying the decomposition of metal nitrates proceeded thoroughly. As a result, the oxides are produced.
4. Conclusions The important conclusions of the experiments are summarized as follows:
Fig. 3. IR spectra of ZrO2 (a) and SnO2 (b) nanocrystals: (1) dried in room temperature and (2) after being heat-treated in vacuum at 220 °C for 2 h.
(1) A novel solvothermal synthesis based on the reaction between metal nitrate and benzene is introduced, through which ZrO2 and SnO2 nanocrystals with particle sizes smaller than 10 nm are prepared.
4810
M. Wan et al. / Materials Letters 61 (2007) 4807–4810
(2) The surface of the as-prepared nanocrystals is chemically adsorbed with benzene rings, endowing them with good dispersibility in hydrocarbons and long-time stability without coarsening and aggregating. Acknowledgements This work was supported by the Doctor Foundation of Yantai University. The authors thank Prof. Caixia Qi for editing the English of the manuscript. References [1] C.N.R. Rao, J. Mater. Chem. 9 (1999) 1. [2] E.M. Wong, J.E. Bonevich, P.C. Searson, J. Phys. Chem., B 102 (1998) 7770.
[3] J.F. Banfield, S.A. Welch, H. Zhang, T.T. Ebert, R.L. Penn, Science 289 (2000) 751. [4] J. Rockenberger, E.C. Scher, A.P. Alivisators, J. Am. Chem. Soc. 121 (1999) 11595. [5] A. Gutiérrez Sosa, T.M. Evans, S.C. Parker, C.T. Campbell, G. Thornton, J. Phys. Chem., B 105 (2001) 3783. [6] L.D. Zhang, J.M. Mou, Nanostruct. and Nanomater, Science Press, Beijing, 2000. [7] K. Nakamoto, in: D. Huang, R. Wang (Eds.), Infrared Spectra of Inorganic and Coordination Compound, 4th, Chemical Industry Press, Beijing, 1991, p. 251. [8] L.J. Bellamy, The Infrared Spectra of Complex Molecules, 2nd edn., Chapman and Hall, London, 1980. [9] T. He, D.R. Chen, X.L. Jiao, Chem. Mater. 16 (2004) 737. [10] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic Chemistry, John Wiley & Sons, 1999, p. 884. [11] H. Sato, K. Hirose, Appl. Catal., A Gen. 174 (1998) 77.
A novel solvothermal route to benzene ring-capped oxide nanocrystals Meilan Wan a , Yanfei Pan a , Guoqun Liu b , Tao He c,⁎, Zhicai Zhou c , Tao Zhang a , Ruiming Zhao a b
a School of Chemical and Biological Science and Engineering, Yantai University, China School of Materials and Chemical Engineering, Zhongyuan University of Technology, Zhengzhou 450007, China c Institute of Applied catalysts, Yantai University, Yantai 264005, China
Received 13 November 2006; accepted 8 March 2007 Available online 15 March 2007
Abstract A novel solvothermal synthesis based on the reaction between nitrate and benzene for metal oxide nanocrystals including ZrO2 and SnO2 is introduced. The as-prepared nanocrystals are characterized by TEM, XRD and IR techniques in detail, and the possible mechanism of this solvothermal reaction is discussed. Benzene molecules used as capping agent, instead of long-carbon chain molecules, are chemically adsorbed to the surface of the as-prepared oxide nanocrystals, making nanocrystals with long-term stability and good dispersibility in hydrocarbons. © 2007 Published by Elsevier B.V. Keywords: Nanomaterials; Powder technology
1. Introduction Metal oxide nanocrystals exhibit a variety of structures and properties and significant application prospects in magnet, optics, batteries, electronics, precursors of ceramics, etc. [1]. However, nanocrystals readily grow during preparation, storage and application due to coarsening [2] or aggregating [3]. This consequently destroys their properties and debases their usability. The stability of oxide nanocrystals is therefore crucial to their application. So far, monodispersed and stable oxide nanocrystals with controlled particle size and shape have been prepared mostly by thermo-decomposition of metallorganics in high-boiling point hydrocarbons, into which a large quantity of capping agents such as surfactants are usually added to prevent them from aggregation [4]. The high cost and complication of the synthetic process, however, confine the production of oxide nanocrystals in a large scale, and a mass of capping agent molecules with long-carbon chains are chemically adsorbed to ⁎ Corresponding author. Tel.: +86 535 6902743 (O); fax: +86 535 6902063. E-mail addresses: [email protected] (M. Wan), [email protected] (Y. Pan), [email protected] (G. Liu), [email protected] (T. He), [email protected] (Z. Zhou), [email protected] (T. Zhang), [email protected] (R. Zhao). 0167-577X/$ - see front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.matlet.2007.03.039
the nanocrystals' surface, limiting their application in some fields such as catalysts, sensors, precursors for advanced nanoceramics and so on. Therefore, a novel synthetic route, through which monodispersed and stable nanocrystals can be cheaply prepared and long-carbon chain capping agents are no longer needed, is strongly desirable. In this paper, a facile solvothermal route to metal oxide nanocrystals including ZrO2 and SnO2, which is based on the reaction of metal nitrate and benzene, is introduced, and the mechanism of the solvothermal reaction is also discussed. The as-prepared nanocrystals with a particle size smaller than 10 nm and benzene molecules chemically adsorbed to their surface show good dispersibility in hydrocarbons, which might improve the application in many fields. 2. Experimental All reagents are of analytical grade and used as received. Typical experiments were conducted in a steel autoclave with a cubage of 15 ml and Teflon lining and described as below. The products were dried at 80 °C in air after washing. Zirconium nitrates (5 mmol) and benzene (12 ml) were put into an autoclave and heated at 180 °C for 4 h. After cooling to room temperature, the solid product was isolated by distillation
4808
M. Wan et al. / Materials Letters 61 (2007) 4807–4810
under vacuum and subsequently washed with absolute ethanol. Finally, a primrose powder was collected after drying. The mixture of SnCl4 (5 mmol), NaNO3 (20 mmol) and benzene (12 ml) was heated in an autoclave at 180 °C for 4 h, and then cooled to room temperature. The aimed product was extracted by benzene. After benzene distilled, the fawn solid was then washed with absolute ethanol supersonically and followed by centrifugation and drying. X-ray diffraction patterns were recorded on a Rigaku D/Max 2200-PC diffractometer with Cu-Kα radiation (λ = 0.15418 nm) and graphite monochromator at ambient temperature. The morphologies and dispersibility of the as-prepared nanocrystals were observed with a transmission electron microscope (TEM, JEM100-CXII) and high resolution transmission electron microscope (HRTEM, JEOL 2010). The aromatic molecules adsorbed to the surface of the as-prepared nanoparticles and the liquid product was characterized with a Nicolet 5DX FT-IR instrument using KBr pellet technique and GC-MSD Agilent 6890N-5973N (temperature range: 50 ∼ 250 °C, increasing rate: 5 °C/min). 3. Results and discussion The XRD patterns of the products indicate that pure monoclinic ZrO2 and tetragonal SnO2 are obtained (Fig. 1). Their average grain sizes based on the Scherrer equation are respectively 7.3 nm and 4.6 nm, and close to the sizes of the individual nanoparticles observed in TEM images, confirming that every individual nanoparticle is a nanocrystal. Since no capping agent molecules with long-carbon chains exists in their surface, most of the nanocrystals on the TEM grid are close to each other due to weak steric hindrance (Fig. 2). On the other hand, clear-cut boundaries between nanocrystals can be seen in TEM images (Fig. 2a for ZrO2 nanocrystals) and HRTEM images (Fig. 2c for SnO2 nanocrystals). The nanocrystals show good dispersibility in ethanol, benzene, cyclohexane. Dispersions of the as-prepared powders (ca. 50 mg) in the above solvents (100 ml) keep transparency for more than 1 h, and then flocculation occurs to form a loose precipitate, while Fig. 2. TEM images of the as-prepared powders: (a) ZrO2; (b) SnO2; (c) HRTEM image of the SnO2 nanocrystals, the clear-cut boundaries between nanocrystals are marked with black arrows.
Fig. 1. X-ray diffractograms of the as-prepared powders: (a) ZrO2 and (b) SnO2.
transparent dispersion will be recovered by gently shaking the bottle. The flocculation–redispersion can be repeated even when the precipitates are placed for 6 months at room temperature. Their size and morphology don't change, which is confirmed by XRD and TEM analysis. All of the above facts strongly prove that no aggregating or coarsening growth occurs among the as-prepared nanocrystals in hydrocarbons, although they are close to each other and have no longcarbon chain capping molecules in their surface. As discussed in the following text, the high stability of the fine nanocrystals against growth is attributed to their surface, which is chemically adsorbed by benzene rings. Aromatics tend to cover a parallel specific surface of oxide crystal particles through its electronic ring by chemical adsorption [5], and fine nanoparticles of metal oxides are full of oxyanion vacancy [6]. The chemical adsorption could be much stronger because of the electronic abundant character of benzene ring and the electron deficiency of oxide nanoparticles. Moreover, it is reasonable that the finer the nanoparticles, the stronger this kind of interaction. In order to identify the
M. Wan et al. / Materials Letters 61 (2007) 4807–4810
components adsorbed to the surface of the nanocrystals, both the asprepared powders and the powders after heat-treatment in vacuum at 220 °C for 2 h are characterized by IR technique. Besides the strong absorptions of metal–oxygen vibrations in ZrO2 and SnO2 nanocrystals below 800 cm− 1, the as-prepared powders also show a few absorption bands (Fig. 3). The bands centered at 3400 cm− 1 and 1627 cm− 1, assigned to the O–H stretching and bending modes of adsorbed water molecules [7], are greatly weakened, while the intensities of other absorption bands change little after the heat-treatment (Fig. 3). The strong and characteristic absorption band attributed to C–O stretching vibration of alcohol molecules usually at ca. 1050 cm− 1 [8] does not exist, because the dry vacuum can entirely eliminate the ethanol that was used as a solvent in the preparation. In the absence of benzene, metal oxide micro-powders can also be prepared under the same reaction conditions (in autoclave at 180 °C for 4 h). While, only one sharp and strong absorption band at ca. 1380 cm− 1, which is attributed to the absorption of NO−3 [9] was observed in their IR spectra in the same wavenumber range (from 2000 to 800 cm− 1). It was greatly weakened when the micro-powders were heated in vacuum at 220 °C for 2 h. The characteristic absorptions of benzene molecules are mainly located at 3100 ∼ 3000 cm− 1 for _C–H in-plane stretching vibration mode, at 1650 ∼ 1450 cm− 1 for C_C stretching vibration mode, and at 1250 ∼ 1000 cm− 1 for _C–H out-plane stretching vibration mode. And nitrobenzene shows two additional absorptions at ca. 1540 and 1350 cm− 1 attributing to the dissymmetric and symmetric stretching vibration modes of –NO2 [8]. It can be seen that most of the absorption bands are located in the wavenumber ranges of characteristic absorption of aromatic molecules. Since no other hydrocarbons exist in the reaction system, these absorption bands in Fig. 3 (a (2) and b (2)) can be assigned to the characteristic vibration modes of benzene and nitrobenzene molecules adsorbed to the nanocrystals' surface. The heat-treatment in vacuum at 220 °C for 2 h did not desorb the aromatic molecules, indicating a strong chemical interaction between the nanocrystals and the adsorbed benzene rings. As the particle surface is covered with aromatics such as benzene and nitrobenzene, two immediate results are induced: the surface energy and, then as a result, the growth of the coated nanoparticles became slow; the surface of the nanocrystals turned to hydrophobic.
4809
IR spectrum and mass spectrum system–total ion chromatography analysis prove that the reaction supernatant includes benzene, nitrobenzene and water. A nitration reaction, therefore, probably takes place in the solvothermal processes to form oxide nanoparticles. The following formulation could explain the synthesis reaction of ZrO2 nanocrystals: ZrðNO3 Þ4 þ 4C6 H6 →ZrO2 þ 4C6 H5 NO2 þ 2H2 O
ð1Þ
As many transition metal nitrates are essential covalent molecules and dissolve into hydrocarbon solvents [10], this solvothermal route might be applicable to the fabrication of many metal oxide nanoparticles. Our experiments indicate that metal chloride SnCl4 does not react with benzene without nitrate anions. However, the reaction occurs to give oxide nanocrystals, nitrobenzene and sodium chlorides, when introducing sodium nitrate (Eq. (2)): SnCl4 þ 4C6 H6 þ 4NaNO3 →SnO2 þ 4C6 H5 NO2 þ 4NaCl þ 2H2 O (2) Thus the whole process in fact includes two reactions: the first is the replacement reaction between SnCl4 and NaNO3: SnCl4 þ 4NaNO3 →SnðNO3 Þ4 þ 4NaCl
ð3Þ
The second is the nitration reaction of benzene with the formed metal nitrate Sn(NO3)4 (similar to Eq. (1)), and the equilibrium Eq. (3) would move to the right side with time onstream. Experiments prove that sodium nitrate doesn't react with benzene under the same reaction conditions, indicating that the formation of metal oxide that abided by the following reaction scheme is impossible. C6 H6 þ NO−3 →C6 H5 NO2 þ OH−
ð4Þ
4OH− þ MðNO3 Þ4 or MCl4 →MO2 þ 2H2 O þ 4NO−3 or 4Cl−
ð5Þ
Except for IA and IIA metals, other metal nitrates decompose to produce metal oxides or metal simple substances with liberation of oxygen and nitric oxide: MðNO3 Þx →MOx=2 þ xNO2 þ x=4O2
ð6Þ
NO2 as a nitrating agent can react with benzene to form nitrobenzene. Oxides may catalyze this reaction [11]: C6 H6 þ NO2 þ 1=4O2 →C6 H5 NO2 þ 1=2H2 O
ð7Þ
Based on the above information, the process in Eq. (1) actually includes two processes: the decomposition of metal nitrates (Eq. (6)) and the nitration of benzene with NO2 (Eq. (7)). The decomposed product NO2 and O2 could be consumed by reacting with benzene, implying the decomposition of metal nitrates proceeded thoroughly. As a result, the oxides are produced.
4. Conclusions The important conclusions of the experiments are summarized as follows:
Fig. 3. IR spectra of ZrO2 (a) and SnO2 (b) nanocrystals: (1) dried in room temperature and (2) after being heat-treated in vacuum at 220 °C for 2 h.
(1) A novel solvothermal synthesis based on the reaction between metal nitrate and benzene is introduced, through which ZrO2 and SnO2 nanocrystals with particle sizes smaller than 10 nm are prepared.
4810
M. Wan et al. / Materials Letters 61 (2007) 4807–4810
(2) The surface of the as-prepared nanocrystals is chemically adsorbed with benzene rings, endowing them with good dispersibility in hydrocarbons and long-time stability without coarsening and aggregating. Acknowledgements This work was supported by the Doctor Foundation of Yantai University. The authors thank Prof. Caixia Qi for editing the English of the manuscript. References [1] C.N.R. Rao, J. Mater. Chem. 9 (1999) 1. [2] E.M. Wong, J.E. Bonevich, P.C. Searson, J. Phys. Chem., B 102 (1998) 7770.
[3] J.F. Banfield, S.A. Welch, H. Zhang, T.T. Ebert, R.L. Penn, Science 289 (2000) 751. [4] J. Rockenberger, E.C. Scher, A.P. Alivisators, J. Am. Chem. Soc. 121 (1999) 11595. [5] A. Gutiérrez Sosa, T.M. Evans, S.C. Parker, C.T. Campbell, G. Thornton, J. Phys. Chem., B 105 (2001) 3783. [6] L.D. Zhang, J.M. Mou, Nanostruct. and Nanomater, Science Press, Beijing, 2000. [7] K. Nakamoto, in: D. Huang, R. Wang (Eds.), Infrared Spectra of Inorganic and Coordination Compound, 4th, Chemical Industry Press, Beijing, 1991, p. 251. [8] L.J. Bellamy, The Infrared Spectra of Complex Molecules, 2nd edn., Chapman and Hall, London, 1980. [9] T. He, D.R. Chen, X.L. Jiao, Chem. Mater. 16 (2004) 737. [10] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic Chemistry, John Wiley & Sons, 1999, p. 884. [11] H. Sato, K. Hirose, Appl. Catal., A Gen. 174 (1998) 77.