Nanosorbents and methods of use thereof

1. A selenium core-sheath composition comprising:

a selenium nanostructure core comprising a selenium nanowire; and

a melt-resistant sheath enveloping at least a portion of the selenium nanostructure core.

2. The composition of claim 1 , wherein the melt-resistant sheath has a melting point greater than that of selenium, and comprises a metal-selenide, a metal oxide, a silica-sol, or mixtures thereof.

3. The composition of claim 1 , wherein the melt-resistant sheath is porous.

4. The composition of claim 1 , wherein the melt-resistant sheath comprises at least one metal selected from the group consisting of Zn, Ni, Ag, Cu, Pd, Hg, Cd, and Fe.

5. The composition of claim 1 , wherein the melt-resistant sheath comprises at least one metal cation selected from the group consisting of Zn cation, Ni cation, Ag cation, Cu cation, Pd cation, Hg cation, Cd cation, and Fe cation.

6. The composition of claim 1 , wherein the melt-resistant sheath comprises at least one metal cation selected from the group consisting of Zn 2+ , Hg 2+ , Cd 2+ , Fe 2+ , Fe 3+ , Cu 2+ , Ni 2+ , Ag 2+ , and Pd 2+ .

7. The composition of claim 1 , further comprising a support structure in contact with the selenium core-sheath composition.

8. The composition of claim 7 , wherein the support structure is selected from filter paper, activated carbon, expanded graphite, silica, alumina, or any combination thereof.

9. The composition of claim 1 , wherein the melt-resistant sheath fully envelops the selenium nanostructure core.

10. A method of preparing a selenium core-sheath material, the method comprising:

contacting a selenium nanostructure with a metal salt, a metal oxide, or a silica-sol to form a composition, wherein the selenium nanostructure comprises a selenium nanowire; and

maintaining the composition under conditions effective to form a selenium core-sheath material comprising a selenium nanostructure core and a melt-resistant sheath enveloping at least a portion of the selenium nanostructure core.

11. The method of claim 10 , wherein the contacting comprises mixing the selenium nanostructure with a metal salt.

12. The method of claim 10 , wherein the contacting comprises heating and mixing the selenium nanostructure with a metal salt.

13. The method of claim 10 , wherein the contacting comprises mixing the selenium nanostructure with a metal oxide.

14. The method of claim 10 , wherein the contacting comprises mixing the selenium nanostructure with a silica-sol to form a selenium-silica-sol composition.

15. The method of claim 14 , wherein the selenium-silica-sol composition is an emulsion.

16. The method of claim 10 , the method further comprising absorbing the selenium core-sheath material onto a support structure.

17. The method of claim 16 , wherein the support structure is selected from the group consisting of filter paper, activated carbon, and expanded graphite.

18. A method of removing mercury and/or cadmium from a sample, the method comprising:

providing an untreated sample suspected of containing mercury and/or cadmium; and

contacting the untreated sample and a composition to form a treated sample, wherein the composition comprises a selenium core-sheath material comprising a selenium nanostructure core and a melt-resistant sheath enveloping at least a portion of the selenium nanostructure core.

19. The method of claim 18 , wherein the concentration of mercury and/or cadmium in the untreated sample is higher than the concentration of the mercury and/or cadmium in the treated sample.

20. The method of claim 18 , wherein the untreated sample has a temperature greater than the melting point of a selenium nanostructure core.

21. The method of claim 18 , wherein the untreated sample has a temperature greater than about 200 degrees Celsius.

22. The method of claim 18 , wherein the untreated sample is coal flue gas.

23. The method of claim 18 , wherein the selenium core-sheath material absorbs the mercury and/or cadmium in the untreated sample.