Thermally stable crystalline mesoporous metal oxides with substantially uniform pores
Highly crystalline metal oxide-carbon composites, as precursors to thermally stable mesoporous metal oxides, are coated with a layer of amorphous carbon. Using a ‘one-pot’ method, highly crystalline metal oxide-carbon composites are converted to thermally stable mesoporous metal oxides, having highly crystalline mesopore walls, without causing the concomitant collapse of the mesostructure. The ‘one-pot’ method uses block copolymers with an sp or sp 2 hybridized carbon containing hydrophobic block as structure directing agents which converts to a sturdy, amorphous carbon material under appropriate heating conditions, providing an in-situ rigid support which maintains the pores of the oxides intact while crystallizing at temperatures as high as 1000 deg C. A highly crystalline metal oxide-carbon composite can be heated to produce a thermally stable mesoporous metal oxide consisting of a single polymorph.
1. A method for preparing a thermally stable crystalline mesoporous metal oxide comprising the steps of:
(a) providing a block copolymer/metal oxide solution, wherein the block copolymer comprises a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit, or
providing a colloidal assembly of polystyrene beads/metal oxide, wherein the polystyrene beads comprise a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit;
(b) casting the solution or the colloidal assembly in air resulting in the formation of a polymer metal oxide hybrid;
(c) heating the polymer metal oxide hybrid in an inert atmosphere to a temperature of about 700° C. for at least 2 hours resulting in the formation of a porous crystalline metal oxide-carbon composite; and
(d) following the heating step, removing the carbon by heating the composite in air, resulting in the formation of a thermally stable mesoporous metal oxide.
2. A thermally stable mesoporous metal oxide produced by the method of claim 1 .
3. A method for preparing a thermally stable crystalline mesoporous metal oxide comprising the steps of:
(a) providing a block copolymer/metal oxide solution, wherein the block copolymer comprises a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit, or
providing a colloidal assembly of polystyrene beads/metal oxide, wherein the polystyrene beads comprise a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit;
(b) casting the solution or the colloidal assembly in air resulting in the formation of a polymer-metal oxide hybrid;
(c) heating the polymer metal oxide hybrid in an inert atmosphere to a temperature of about 700° C. for at least 2 hours resulting in the formation of a porous crystalline metal oxide-carbon composite; and
(d) following the heating step, removing the carbon by heating the composite in air at a temperature in the range of about 400° C. to 700° C. for a time sufficient to result in the formation of a thermally stable mesoporous metal oxide.
4. A method for preparing thermally stable crystalline mesoporous metal oxide comprising the steps of:
(a) providing a block copolymer/metal oxide solution, wherein the block copolymer comprises a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit, or
providing a colloidal assembly of polystyrene beads/metal oxide, wherein the polystyrene beads comprise a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit;
wherein the metal oxide comprises a metal oxide selected from the group consisting of a Group IV oxide and a Group V oxide;
(b) casting the solution or the colloidal assembly in air resulting in the formation of a polymer-metal oxide hybrid;
(c) heating the polymer metal oxide hybrid in an inert atmosphere to a temperature of about 700° C. for at least 2 hours resulting in the formation of a porous crystalline metal oxide-carbon composite; and
(d) following the heating step, removing the carbon by heating the composite in air, resulting in the formation of a thermally stable mesoporous metal oxide.
5. The method of claim 4 in which the metal oxide is selected from the group consisting of TiO 2 and Nb 2 O 5 .
6. The method of claim 4 in which the resulting thermally stable mesoporous metal oxide consists of a single polymorph.
7. A method for preparing thermally stable crystalline mesoporous metal oxide comprising the steps of:
(a) providing a block copolymer/metal oxide solution, wherein the block copolymer comprises a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit, or
providing a colloidal assembly of polystyrene beads/metal oxide, wherein the polystyrene beads comprise a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit;
(b) casting the solution or the colloidal assembly in air resulting in the formation of a polymer-metal oxide hybrid;
(c) heating the polymer-metal oxide hybrid in an inert atmosphere to a temperature of about 700° C. for at least 2 hours resulting in the formation of a porous crystalline metal oxide-carbon composite; and
(d) following the heating step, removing the carbon by heating the composite in air at a temperature in the range of about 400° C. to 700° C. for a time sufficient to result in the formation of a thermally stable mesoporous metal oxide.
8. A method for preparing a thermally stable mesoporous titanium oxide comprising the steps of:
(a) providing a block copolymer/titanium oxide solvent solution, wherein the block copolymer comprises a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit, or
providing a colloidal assembly of polystyrene beads/titanium oxide, wherein the polystyrene beads comprise a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit;
(b) casting the solution or the colloidal assembly in air resulting in the formation of a polymer-titanium oxide hybrid;
(c) heating the polymer-titanium oxide hybrid in an inert atmosphere at a temperature of about 700° C. for at least 2 hours resulting in crystallization of the titanium oxide and conversion of the block copolymer to amorphous carbon; and
(d) following the heating step, removing the carbon by heating in air at about 400° C. to 700° C. resulting in the formation of a thermally stable mesoporous titanium oxide.
9. The method of claim 8 in which the resulting thermally stable mesoporous metal oxide consists of a single polymorph.
10. A thermally stable mesoporous titanium oxide produced by the method of claim 8 .
11. A method for preparing a thermally stable mesoporous niobium oxide comprising the steps of:
(a) providing a block copolymer/niobium oxide solution, wherein the block copolymer comprises a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit, or
providing a colloidal assembly of polystyrene beads/niobium oxide, wherein the polystyrene beads comprise a hydrophobic portion comprising sp or sp 2 hybridized carbon atoms in each monomer unit;
(b) casting the solution or the colloidal assembly in air resulting in the formation of a polymer-metal niobium oxide hybrid;
(c) heating the polymer-niobium oxide hybrid in an inert atmosphere at a temperature of about 700° C. for at least 2 hours resulting in crystallization of the niobium oxide and conversion of the block copolymer to amorphous carbon; and
(d) following the heating step, removing the carbon by heating in air at about 400° C. to 700° C. resulting in the formation of a thermally stable mesoporous niobium oxide.
12. The method of claim 11 in which the resulting thermally stable mesoporous metal oxide consists of a single polymorph.
13. A thermally stable mesoporous niobium oxide produced by the method of claim 11 .
14. A method for preparing a thermally stable crystalline mesoporous transition metal oxide comprising the steps of:
(a) providing a block copolymer/transition metal oxide solution , wherein the block copolymer comprises a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit, or
providing a colloidal assembly of polystyrene beads/transition metal oxide, wherein the polystyrene beads comprise a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit;
(b) casting the solution or the colloidal assembly in air resulting in the formation of a polymer-transition metal oxide hybrid;
(c) heating the polymer-transition metal oxide hybrid in an inert atmosphere to a temperature of about 700° C. for at least 2 hours resulting in the formation of a porous crystalline transition metal oxide-carbon composite; and
(d) following the heating step, removing the carbon by heating the composite in air, resulting in the formation of a thermally stable mesoporous transition metal oxide.
15. A thermally stable mesoporous transition metal oxide produced by the method of claim 14 .
16. A method for preparing a crystalline metal oxide-carbon composite comprising the steps of:
(a) providing a block copolymer/metal oxide solution wherein the block copolymer comprises a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit, or
providing a colloidal assembly of polystyrene beads/metal oxide, wherein the polystyrene beads comprise a hydrophobic portion comprising sp or sp2 hybridized carbon atoms in each monomer unit;
(b) casting the solution or the colloidal assembly in air resulting in the formation of a polymer-metal oxide hybrid; and
(c) heating the polymer metal oxide hybrid in an inert atmosphere to a temperature of about 700° C. for at least 2 hours resulting in the formation of a porous crystalline metal oxide-carbon composite in which an amorphous carbonaceous material lines the walls of the resulting mesopores.
17. The product formed by the method of claim 16 .
18. A method for preparing a nanostructured inorganic/ceramic-transition metal oxide composite comprising the steps of:
(a) providing a block copolymer/metal oxide solution wherein the block copolymer comprises a hydrophobic portion which transforms upon heating into an inorganic/ceramic, or
providing a colloidal assembly of polystyrene beads/metal oxide, wherein the polystyrene beads comprise a hydrophobic portion which transforms upon heating into an inorganic/ceramic;
(b) casting the solution or the colloidal assembly in air resulting in the formation of a polymer-metal oxide hybrid; and
(c) heating the polymer metal oxide hybrid in an inert atmosphere to a temperature of about 700° C. for at least 2 hours resulting in the formation of a nanostructured inorganic/ceramic-transition metal oxide composite.
19. The product formed by the method of claim 18 .