Gas sensor and member using metal oxide semiconductor nanofibers including nanoparticle catalyst functionalized by bifunctional nano-catalyst included within apoferritin, and manufacturing method thereof

Abstract

According to embodiments of the inventive concepts, apo-ferritins containing hetero nanoparticle catalysts are mixed with an electrospinning solution, the mixture solution is electrospun to form complex nanofibers, and then a high-temperature thermal treatment process is performed to remove the apo-ferritins. Thus, the hetero nanoparticle catalysts are uniformly fastened to an inside and a surface of one-dimensional metal oxide nanofibers to form a member for a gas sensor. As a result, the member for a gas sensor has a high-sensitivity characteristic capable of sensing a very small amount of a gas and excellent selectivity capable of sensing various gases. In addition, a catalyst effect is maximized by the hetero nanoparticle catalysts uniformly distributed without aggregation. Furthermore, the member for a gas sensor and the gas sensor using the same can be mass-produced by a process method capable of effectively forming pores and of fastening high-performance catalysts.

What is claimed is: 
     
         1 . A method of manufacturing a sensing material for a gas sensor, the method comprising:
 synthesizing hetero nanoparticle catalysts using apo-ferritins made of protein;   mixing the apo-ferritins including the synthesized hetero nanoparticle catalysts with an electrospinning solution in which a metal precursor and a polymer are dissolved, thereby manufacturing a complex spinning solution;   applying an electrospinning process to the complex spinning solution to manufacture complex nanofibers in which the apo-ferritins including the hetero nanoparticle catalysts are fastened in an inside and/or on a surface of metal precursor/polymer complex nanofibers; and   performing a thermal treatment process to manufacture metal oxide nanofibers complex to which the hetero nanoparticle catalysts are fastened.   
     
     
         2 . The method of  claim 1 , wherein performing the thermal treatment process comprises: performing the thermal treatment process to remove the polymer and the protein of the apo-ferritins and to oxidize the metal precursor, thereby forming the meal oxide nanofibers complex which has a one-dimensional structure and includes fine pores, and
 wherein the hetero nanoparticle catalysts are fastened in an inside and on a surface of the metal oxide nanofibers complex.   
     
     
         3 . The method of  claim 1 , wherein synthesizing the hetero nanoparticle catalysts using the apo-ferritins made of the protein comprises:
 providing two or more different kinds of metal ions into the apo-ferritin by a substitution process; and   performing a reduction process to form a metal alloy catalyst including two or more different kinds of metals.   
     
     
         4 . The method of  claim 1 , wherein the hetero nanoparticle catalysts are fastened to the metal oxide nanofibers complex such that a concentration of the hetero nanoparticle catalysts in the metal oxide nanofibers complex is in a range of 0.00001% to 50%. 
     
     
         5 . The method of  claim 1 , wherein, in synthesizing the hetero nanoparticle catalysts using apo-ferritins, a reductant for reducing metal salts provided in the apo-ferritins includes at least one of sodium borohydride (NaBH 4 ), lithium aluminum hydride (LiAlH 4 ), nascent (atomic) hydrogen, zinc-mercury amalgam (Zn(Hg)), oxalic acid (C 2 H 2 O 4 ), formic acid (HCOOH), ascorbic acid (C 6 H 8 O 6 ), sodium amalgam, diborane, or iron(II) sulfate. 
     
     
         6 . The method of  claim 1 , wherein, in mixing the apo-ferritins including the synthesized hetero nanoparticle catalysts with the electrospinning solution, the hetero nanoparticle catalysts are uniformly dispersed in the electrospinning solution, in which the metal precursor and the polymer are dissolved, without aggregation between the hetero nanoparticle catalysts by the protein of the apo-ferritins. 
     
     
         7 . The method of  claim 1 , wherein, in mixing the apo-ferritins including the synthesized hetero nanoparticle catalysts with the electrospinning solution, a weight ratio of the polymer: the hetero nanoparticle catalysts, which are used in synthesis of the electrospinning solution, is in a range of 1:0.000001 to 1:0.5, and the apo-ferritins including the hetero nanoparticle catalysts, which have a concentration ranging from 0.001 wt % to 50 wt %, are added into the electrospinning solution. 
     
     
         8 . The method of  claim 1 , wherein, in performing the thermal treatment process, the polymer constituting the complex nanofibers and the protein of shell portions of the apo-ferritins including the hetero nanoparticle catalysts are pyrolyzed and removed by the thermal treatment process, the metal precursor is, oxidized and crystallized to form a poly-crystalline metal oxide nanofibers, fine pores are further formed in the metal oxide nanofiber complex by the removal of the protein, and sizes of nano-grains adjacent to an outer surface of the metal oxide nanofiber complex are greater than that of nano-grains disposed in a central portion of the metal oxide nanofiber complex by inhibition of grain growth caused by the hetero nanoparticle catalysts. 
     
     
         9 . The method of  claim 1 , further comprising:
 pulverizing the metal oxide nanofiber complex to which the hetero nanoparticle catalysts are fastened;   providing the pulverized metal oxide nanofiber complex onto an electrode for semiconductor-type gas sensor measurement which is capable of detecting a harmful environment gas and a biomarker gas (oxidation gas: NO 2 , NO, reduction gas: H 2 , CO, C 2 H 5 OH, H 2 S, CH 4 ) for diagnosis of a disease, by a coating method; and   manufacturing a plurality of gas sensor arrays using a plurality of the metal oxide nanofiber complexes.