Abstract:
The osmium (Os) cluster-functionalized CNT of the present invention formed from a triosmium derivative having one or more amine groups and a functionalized carbon nanotube having a plurality of COOH groups through zwitterionic interactions between the COOH and amine groups has high solubilities in water and various organic solvents.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a novel carbon nanotube functionalized with osmium clusters, and a process for preparing the same. 
     DESCRIPTION OF THE PRIOR ART 
     Carbon nanotubes (CNTs) are classified into single walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs) and rope nanotubes, and possess outstanding physical, chemical and mechanical properties, such as lightweight, excellent electrical and thermal conductivity and high tensile force. 
     In particular, CNTs exhibit either condutivity or semiconductivity depending on their surroundings through selective reactions with specific target molecules and thus are suitable for nanoscale sensing materials or nano-bioelectronic device applications. In this regards, in order to enhance such selectivities of CNTs, there have been developed functionalization or bio-immobilization techniques to anchor functional groups to CNTs so that the functionalized CNTs can selectively react with specific target molecules (H. Dai,  Acc. Chem. Res.,  35, 1035 (2002)). 
     Osmium (Os) clusters having good electrochemical properties are often used in nuclear energy, sensing system and molecular electronic applications. Recently, the synthesis of an Os cluster derivative comprising a specific DNA binding site has been reported (E. Roseberg et al.,  J. Organometal Chem.,  668, 51(2003)). Also, there have been numerous attempts to combine a CNT with such a specific Os cluster; for example, osmylation of SWNT by photoactivation reaction using OsO 4  (Cui, J. at al.,  Nano Lett.,  3, 615 (2003)); osmate esterification of SWNT (Lu, X. et al.,  Nano Lett.,  2, 1325 (2002)); and interaction of liquid-phase OsO 4  with SWNT under UV irradiation (Banerjee, S. et al.,  J. Am. Chem. Soc.,  126, 2073-2081 (2004)). However, such Os-CNT complexes all have low solubilities in water and organic solvents, to limit their industrial applications. 
     The present inventors have endeavored to develop a CNT-Os cluster complex having high solubilities in water and organic solvents; and have unexpectedly found that a new kind of Os cluster-functionalized CNT has high solubilities in organic solvents as well as water. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a primary object of the present invention to provide a functionalized carbon nanotube (CNT) which is highly soluble in water and various organic solvents. 
     It is another object of the present invention to provide an efficient process for the preparation of said CNT. 
     In accordance with one aspect of the present invention, there is provided an Os cluster-functionalized CNT complex formed from a triosmium derivative having one or more amine groups and a functionalized carbon nanotube having a plurality of COOH groups through zwitterionic interactions between the COOH and amine groups. 
     In accordance with another aspect of the present invention, there is provided a method for preparing said Os cluster-functionalized CNT, which comprises reacting the carboxyl (COOH)-functionalized CNT with the amino-functionalized triosmium derivative in an organic solvent. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and features of the present invention will become apparent from the following description of the invention, when taken in conjunction with the accompanying drawings, which respectively show: 
         FIG. 1 : Infrared (IR) spectra of the oxidized CNT (a), triosmium derivative (b) and osmium cluster-CNT prepared in Example 1 (c); 
         FIG. 2 : Mid-IR spectra of the triosmium derivative (b) and osmium cluster-CNT prepared in Example 1 (c); 
         FIG. 3 : UV-Vis-NIR spectra of the triosmium derivative (a), oxidized CNT (b) and osmium cluster-CNT prepared in Example 1 (c); 
         FIGS. 4A to 4D : Scanning electron microscopy (SEM) images of the osmium cluster-CNT prepared in Example 1 ( FIGS. 4A to 4C ) and CNT ( FIG. 4D ); 
         FIGS. 5A and 5B : Transmission electron microscopy (TEM) images of the osmium cluster-CNT prepared in Example 1; and 
         FIG. 6 : Energy dispersive X-ray spectrum (EDX) of the osmium cluster-CNT prepared in Example 1. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The inventive osmium cluster-functionalized CNT is a zwitterion complex formed between the CNT and Os cluster through ammonium-carboxylate bond (—CO 2   −+ NH 3 —). 
     The inventive osmium cluster-functionalized CNT may be prepared by the method comprising the step of reacting the carboxyl-functionalized CNT with the amino-functionalized triosmium derivative in an organic solvent under a nitrogen atmosphere. 
     The carboxyl-functionalized CNT used in the present invention may be obtained by oxidizing a CNT with a concentrated inorganic acid according to a conventional method (J. Liu et al.,  Science,  280, 1253-1256 (1998); and the amino-functionalized triosmium derivative, by reacting a triosmium cluster with an aminated benzoquinoline in accordance with a conventional method (R. Smith et al.,  Organometallics,  18, 3519-3527 (1999)). 
     The inorganic acid suitable for use in the oxidation of CNT include nitric acid, hydrochloric acid and a mixture of sulfuric acid and nitric acid, which may be employed in an amount ranging from 1 to 10 ml based on 10 mg of CNT. The oxidation of CNT may be conducted at a temperature ranging from 40 to 90° C. for 2 to 8 hours. 
     In the inventive method, the amino-functionalized triosmium derivative may be used in an amount ranging from 1 to 2 times, preferably 2 times the weight of the carboxyl-functionalized CNT, and the organic solvent may be selected from the group consisting of N,N-dimethyl formamide (DMF), dimethylsulfoxide (DMSO), acetone and octane. The reaction may be carried out at a temperature ranging from 70 to 140° C. for 3 to 7 days. 
     The inventive osmium cluster-functionalized CNT thus prepared has high solubilities in water and various organic solvents, and is easy to handle. Therefore, the inventive CNT can be advantageously used in CNT-based catalytic processes and next-generation electronic devices including nanobioelectronic devices. 
     The following Examples are given for the purpose of illustration only and are not intended to limit the scope of the invention. 
     Preparation of Inventive Compounds 
     EXAMPLE 1 
     Preparation of an Osmium Cluster-functionalized CNT 
     A purified single walled nanotube (SWNT; Ilzin, KR) was grown on a silicon substrate by pulsed laser deposition (PLD) according to the Fe catalyst-CNT growing method described in [Sohn, J. I. et al.,  App. Phy. Let.,  78, 901-903 (2001)], to obtain a multi-walled nanotube (MWNT) having a high purity of 95%. 10 mg of the MWNT was treated with 10 ml of concentrated HNO 3  at 80° C. for 6 hours, and the resulting oxidized MWNT was washed and dried. 20 mg of an aminated compound of the following formula obtained by the method described in [R. Smith et al.,  Organometallics,  18, 3519-3527 (1999)] was added dropwise thereto under a nitrogen atmosphere, and the mixture was continuously stirred at 140° C. for 7 days. 
     
       
                 
         
             
             
         
      
     
     After the color of the reaction mixture changed from green to brown, the reaction mixture was centrifuged and the liquid phase was removed. The resulting solid was sequentially washed several times with water and acetone, and dried in a vacuum oven to obtain 5 mg (yield 50%) of the title compound. 
     EXAMPLE 2 
     Preparation of an Osmium Cluster-functionalized CNT 
     The procedure of Example 1 was repeated except for using concentrated HCl instead of concentrated HNO 3 , to obtain 5 mg (yield 50%) of the title compound. 
     Characteristics of Inventive Compounds 
     (1) IR and Mid-IR Spectra 
     IR and Mid-IR spectra of the oxidized CNT (a), amino-functionalized triosmium derivative (b) and osmium cluster-functionalized CNT prepared in Example 1 (c) are shown in  FIGS. 1 and 2 , respectively. The wavenumbers of characteristic peaks observed in  FIGS. 1 and 2  are listed in Table 1, respectively. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 CNT-COOH 
                 Os derivative 
                 CNT-Os complex 
               
               
                   
                 (a) 
                 (b) 
                 (c) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 ν OH (carboxyl group) 
                 3228 cm −1   
                   
                   
               
               
                 Y C═O 
                 1712 cm −1   
               
               
                 ν C—O 
                 1233 cm −1   
               
               
                 ν N—H 
                   
                 1625 cm −1   
                 1629, 
               
               
                   
                   
                   
                 1550 cm −1   
               
               
                 ν C—N 
                   
                 1274 cm −1   
                 1278 cm −1   
               
               
                 C═O (carboxylic acid) 
                   
                   
                 1585 cm −1   
               
               
                   
               
             
          
         
       
     
     The results in Table 1 show that the preparations of the desired oxidized CNT, amino-functionalized triosmium derivative and Os cluster-functionalized CNT were indeed achieved, as is supported by the following discussion. 
     Referring to  FIGS. 1 and 2 , the strong peaks at 1712 cm −1  (C═O) and 1233 cm −1  (C—O) observed for the oxidized CNT were absent in the spectrum of the Os cluster-functionalized CNT, and broad strong peaks representing N—H bond were detected at 1625 cm −1  in the spectrum of the triosmium derivative and at 1629 cm −1  in the spectrum of the Os cluster-functionalized CNT. Further, a strong symmetrical COO −  peak at 1585 cm −1 , a broad peak corresponding to C—N bond at 1278 cm −1  (in case of triosmium derivative at 1274 cm −1 ), and osmium peaks at 1933 cm −1  and 2023 cm −1  were observed in the spectrum of the Os cluster-functionalized CNT. 
     Accordingly, it can be deduced that the Os cluster-functionalized CNT prepared above is a zwitterion complex formed between the CNT and Os cluster through ammonium-carboxylate bond (—CO 2   −+ NH 3 —). 
     (2) UV-Vis-NIR Spectra 
     UV-Vis-NIR spectra of the amino-functionalized triosmium derivative (a), oxidized CNT (b) and osmium cluster-functionalized CNT prepared in Example 1 (c) are shown in  FIG. 3  (the inset shows partially enlarged portion of the spectrum). 
     Referring to the results in  FIG. 3 , two main peaks at 1414 nm (1.14 eV) and 1554 nm (1.24 eV) in the spectrum of Os cluster-functionalized CNT are similar to those observed in the spectrum of oxidized CNT, which suggests that the inventive Os cluster-functionalized CNT has an intact carboxylate group of the CNT moiety linked to the Os cluster through an ionic ammonium-carboxylate bond. Further, the small peak observed at 859 nm (1.44 eV) in the spectrum of amino-functionalized tri-Os derivative is red-shifted 890 nm in the spectrum of Os cluster-functionalized CNT, which means that the conjugation length between the Os and amino group has increased due to the formation of the ammonium-carboxylate bond. 
     (3) SEM, TEM and EDX Spectra 
     The detail morphological properties of the Os cluster-functionalized CNT obtained in Example 1 and pristine CNT were evaluated by SEM ( FIGS. 4A to 4D ) and TEM ( FIGS. 5A and 5B ). 
       FIGS. 4A to 4D  clearly show that bulky groups are attached on the tips of the tubes having lengths of 30 nm to 1.5 μm of the Os cluster-functionalized CNT ( 4 A to  4 C), unlike in the pristine CNT ( 4 D), which demonstrates the zwitterion formation between CNT and Os derivative. Further, the bulky groups are not formed on the sidewalls of the same tubes because COOH groups mainly exist on the tips rather than sidewalls. 
       FIG. 6  shows EDX spectra of the Os cluster-functionalized CNT obtained in Example 1, which suggests that Os groups occupy about 1.4% of the functional moieties in the Os cluster-functionalized CNT. 
     (4) Measurement of Solubility 
     The solubilities of the oxidized and Os cluster-functionalized CNTs in water, DMF, THF and DMSO were measured. 
     It was found that the Os cluster-functionalized CNT had the solubilities of 150 mg/L in water, 250 mg/L in DMF, 50 mg/L in THF and 250 mg/L in DMSO. While the pristine CNT was hardly soluble in any of the solvents, the oxidized CNT had the solubilities of 7 mg/L in DMF, 7 mg/L in DMSO and 4 mg/L in THF. Thus, it can be seen that the inventive Os cluster-functionalized CNT has high solubilities in industrially useful organic solvents as well as in water due to the characteristic zwitterion bond. 
     Accordingly, the novel CNT functionalized with Os cluster of the present invention can be advantageously used in various fields including CNT-based catalytic processes and nanobioelectronic devices. 
     While the invention has been described with respect to the specific embodiments, it should be recognized that various modifications and changes may be made by those skilled in the art to the invention which also fall within the scope of the invention as defined by the appended claims.