Nanofibers, nanotubes and nanofiber mats comrpising crystalline metal oxides and methods of making the same

Abstract

Inorganic nanofibers comprise an inorganic matrix material surface functionalized with at least one metal oxide in crystalline form. Crystal growth on external surfaces may occur in substantial alignment with a longitudinal axis of the nanofibers, and the crystals are typically between about 10.0 nm and 30.0 nm in size. The nanofibers may be hollow (i.e., nanotubes) or they may be randomly dispersed together in the form of a nanofiber mat. Methods for making the nanofibers comprise spinning a dispersion comprising linear polymers and metal oxide precursors.

What is claimed is: 
     
         1 . An inorganic nanofiber comprising:
 (a) an inorganic matrix material having an external surface, the inorganic matrix material comprising calcium phosphate; and   (b) a plurality of metal oxide crystals, the metal oxide crystals positioned within the inorganic matrix material and/or on the external surface.   
     
     
         2 . The inorganic nanofiber of  claim 1 , wherein at least one of the metal oxide crystals is positioned in substantial alignment with a longitudinal axis of the inorganic nanofiber. 
     
     
         3 . The inorganic nanofiber of  claim 2 , wherein between about 25% and about 50% of the crystals are positioned in substantial alignment with the longitudinal axis. 
     
     
         4 . The inorganic nanofiber of  claim 1 , wherein at least a portion of the metal oxide crystals is oriented at an acute angle relative to the external surface. 
     
     
         5 . The inorganic nanofiber of  claim 1 , wherein at least a portion of the metal oxide crystals is oriented randomly in a variety of directions. 
     
     
         6 . The inorganic nanofiber of  claim 1 , wherein between about 8% and about 20% of the external surface comprises the metal oxide crystals. 
     
     
         7 . The inorganic nanofiber of  claim 1 , wherein the metal oxide crystals comprise a metal oxide selected from the group consisting of V 2 O 5 , VO 2 , TiO 2 , Fe 2 O 3 , Fe 3 O 4 , SnO 2 , ZrO 2 , BaTiO 3 , SrTiO 3  and combinations thereof. 
     
     
         8 . The inorganic nanofiber of  claim 1 , wherein the metal oxide crystals are physically entrapped on the external surface. 
     
     
         9 . The inorganic nanofiber of  claim 1 , wherein the nanofiber is a nanotube. 
     
     
         10 . The inorganic nanofiber of  claim 1 , wherein the nanofiber comprises a plurality of nanofibers that collectively form a nanofiber mat. 
     
     
         11 . The inorganic nanofiber of  claim 10 , wherein the nanofiber mat comprises a specific surface area between about 800.0 m 2 /g and 1,000.0 m 2 /g. 
     
     
         12 . The inorganic nanofiber of  claim 10 , wherein the nanofiber mat comprises a plurality of pores. 
     
     
         13 . The inorganic nanofiber of  claim 1 , further comprising amorphous metal oxide physically entrapped within the inorganic matrix material. 
     
     
         14 . The inorganic nanofiber of  claim 1 , wherein the metal oxide crystals do not comprise titania. 
     
     
         15 . The inorganic nanofiber of  claim 1 , further comprising metal oxide precursor. 
     
     
         16 . An inorganic nanofiber comprising: a calcium phosphate-based matrix material comprising an external surface; and a plurality of metal oxide crystals positioned on the external surface of the inorganic matrix material, with at least about 25% of the metal oxide crystals positioned in substantial alignment with a longitudinal axis of the nanofiber. 
     
     
         17 . A method for making a plurality of nanofibers comprising:
 providing a dispersion comprising at least one linear polymer;   subjecting the dispersion to electrospinning; and   collecting the plurality of nanofibers.   
     
     
         18 . The method of  claim 17 , wherein the linear polymer comprises the general formula: wherein R n -R m  are the same or different and independently comprise O, H, a lower alkyl group comprising C x  where x=1-4 or a lower hydroxy alkyl group comprising C x  where x=1-4 and where n and m range from 0 and 3, wherein X and Y are the same or different and independently comprise a metal, oxygen, nitrogen, selenium, sulfur, phosphorous or phosphate, and y=an integer between 1 and 1,000. 
     
     
         19 . The method of  claim 18 , wherein the metal is a transition metal. 
     
     
         20 . The method of  claim 18 , wherein the metal is an alkali earth metal. 
     
     
         21 . The method of  claim 18 , wherein X and Y are the same or different and independently comprise silicon and oxygen. 
     
     
         22 . The method of  claim 18 , wherein X and Y are the same or different and independently comprise Ti, V, Fe, Si, Sn, Ba, Zr, Sr, Ca, O or phosphate. 
     
     
         23 . The method of  claim 17 , wherein the linear polymer comprises an elongational viscosity between about 1,000 poise and 3,000 poise. 
     
     
         24 . The method of  claim 17 , wherein the linear polymer comprises a molecular weight between about 100,000 amu to about 300,000 amu. 
     
     
         25 . The method of  claim 17 , further comprising forming the dispersion through sol-gel synthesis and the dispersion does not comprise a gel or a three dimensional network. 
     
     
         26 . The method of  claim 17 , wherein the dispersion comprises a metal oxide precursor. 
     
     
         27 . The method of  claim 17 , wherein the dispersion does not comprise a polymeric binder. 
     
     
         28 . The method of  claim 17 , wherein the plurality of nanofibers comprise metal oxide crystals positioned on an external surface thereof. 
     
     
         29 . The method of  claim 28 , wherein about 8.0% to about 50% of the external surface comprises the metal oxide crystals. 
     
     
         30 . The method of  claim 28 , wherein the metal oxide crystals are selected from the group consisting of V 2 O 5 , VO 2 , TiO 2 , Fe 2 O 3 , Fe 3 O 4 , SnO 2 , ZrO 2 , BaTiO 3 , SrTiO 3  and combinations thereof. 
     
     
         31 . The method of  claim 17 , wherein the plurality of nanofibers comprise at least one of silica, calcium phosphate and titanium dioxide. 
     
     
         32 . The method of  claim 17 , wherein the plurality of nanofibers form a nanofiber mat comprising a plurality of pores. 
     
     
         33 . The method of  claim 17 , wherein the collected nanofibers are nanotubes. 
     
     
         34 . The method of  claim 17 , wherein the spinning step comprises co-axial electrospinning. 
     
     
         35 . The method of  claim 17 , further comprising calcining the plurality of nanofibers after the collecting step. 
     
     
         36 . The method of  claim 35 , wherein the calcining step is carried out for about 2.0 hours to about 12.0 hours at temperatures ranging from about 500° C. to about 1,200° C. 
     
     
         37 . The method of  claim 35 , further comprising exposing the collected nanofibers to deionized water prior to the calcining step.