Photoswitchable graphene membranes

1. A graphene composite, comprising:

a photoswitchable layer configured to reversibly change between a state wherein the photoswitchable layer exhibits a first level of hydrophobicity and a state wherein the photoswitchable layer exhibits a second level of hydrophobicity different from the first level, the photoswitchable layer including at least one azobenzene compound and an electrospun nanofiber;

a graphene layer disposed on the photoswitchable layer; and

a substrate,

wherein the photoswitchable layer is disposed between the substrate and the graphene layer.

2. The graphene composite of claim 1 , wherein the at least one azobenzene compound is represented by a formula:

wherein R 1 is a first functional group, R 2 is a spacer group, and R 3 is a second functional group.

3. The graphene composite of claim 2 , wherein the first functional group includes an alkyl, a haloalkyl, an alkoxy, a haloalkoxy, or a halogen.

4. The graphene composite of claim 2 , wherein the spacer group includes a C 1-20 -alkylene.

5. The graphene composite of claim 2 , wherein the second functional group includes an amine, a carboxylic acid, a thiol, or a silane coupling group.

6. The graphene composite of claim 1 , wherein the photoswitchable layer further comprises a polymer, wherein the at least one azobenzene compound is conjugated to the polymer.

7. The graphene composite of claim 6 , wherein the polymer includes a brush copolymer.

8. The graphene composite of claim 1 , wherein one or more of:

the photoswitchable layer has a thickness in the range of about 1 nm to about 20 nm;

the graphene layer has a thickness in the range of about 0.3 nm to about 2 nm; or

the graphene layer has a thickness of one to six graphene sheets.

9. The graphene composite of claim 1 , wherein the graphene layer exhibits one or more of:

a water contact angle in the range of about 80° to about 120° when the photoswitchable layer is in the state wherein the photoswitchable layer exhibits the first level of hydrophobicity;

a water contact angle in the range of about 10° to about 60° when the photoswitchable layer is in the state wherein the photoswitchable layer exhibits the second level of hydrophobicity; or

the graphene layer exhibits a first water contact angle when the photoswitchable layer is in the state wherein the photoswitchable layer exhibits the first level of hydrophobicity, and the graphene layer exhibits a second water contact angle when the photoswitchable layer is in the state wherein the photoswitchable layer exhibits the second level of hydrophobicity, and wherein a difference between the first water contact angle and the second water contact angle is within a range of 5° to 150°.

10. The graphene composite of claim 1 , wherein the graphene layer is disposed within 3.0 nm, 2.5 nm, 2.0 nm, or 1.5 nm of the photoswitchable layer; or directly on the photoswitchable layer.

11. The graphene composite of claim 1 , wherein the substrate comprises silicon or silica.

12. A method to make a graphene composite, the method comprising:

providing a substrate;

forming a photoswitchable layer on the substrate, the photoswitchable layer being configured to reversibly change between a state wherein the photoswitchable layer exhibits a first level of hydrophobicity and a state wherein the photoswitchable layer exhibits a second level of hydrophobicity different from the first level, the photoswitchable layer including at least one azobenzene compound and an electrospun nanofiber; and

applying graphene to the photoswitchable layer.

13. The method of claim 12 , wherein forming the photoswitchable layer on the substrate comprises applying a polymer on the substrate, wherein the polymer comprises the at least one azobenzene compound conjugated to the polymer.

14. The method of claim 12 , wherein forming the photoswitchable layer on the substrate comprises:

applying a polymer on the substrate; and

conjugating the at least one azobenzene compound to the polymer.

15. The method of claim 12 , wherein forming the photoswitchable layer on the substrate comprises conjugating the at least one azobenzene compound with the substrate, wherein the at least one azobenzene compound comprises a silane coupling agent.

16. The method of claim 12 , wherein forming the photoswitchable layer on the substrate comprises:

conjugating an amine-containing silane coupling agent with a surface of the substrate; and

reacting the at least one azobenzene compound with the amine-containing silane coupling agent conjugated to the surface of the substrate.

17. A method, comprising:

providing a graphene composite comprising:

a photoswitchable layer configured to reversibly change between a state wherein the photoswitchable layer exhibits a first level of hydrophobicity and a state wherein the photoswitchable layer exhibits a second level of hydrophobicity different from the first level, the photoswitchable layer including at least one azobenzene compound and an electrospun nanofiber;

a graphene layer disposed on the photoswitchable layer; and

a substrate, wherein the photoswitchable layer is disposed between the substrate and the graphene layer;

applying a first radiation to the photoswitchable layer effective to cause at least a portion of the photoswitchable layer to be in the state wherein the photoswitchable layer exhibits the first level of hydrophobicity; and

applying a second radiation to the photoswitchable layer effective to cause at least a portion of the photoswitchable layer to be in the state wherein the photoswitchable layer exhibits the second level of hydrophobicity.

18. The method of claim 17 , wherein the first radiation has a wavelength of peak emission greater than 400 nm and the second radiation has a wavelength of peak emission less than 400 nm.

19. The method of claim 17 , wherein at least one of:

applying the first radiation to the photoswitchable layer comprises applying the first radiation to the photoswitchable layer such that the graphene layer has a water contact angle of at least about 80°;

applying the second radiation to the photoswitchable layer comprises applying the second radiation to the photoswitchable layer such that the graphene layer has a water contact angle of less than or equal to about 60°; or

wherein the graphene layer exhibits a first water contact angle when the photoswitchable layer is in the state wherein the photoswitchable layer exhibits a first level of hydrophobicity, and the graphene layer exhibits a second water contact angle when the photoswitchable layer is in the state wherein the photoswitchable layer exhibits a second level of hydrophobicity, and wherein a difference between the first water contact angle and the second water contact angle is within a range of 5° to 150°.

20. The method of claim 17 , further comprising:

prior to applying the second radiation to the photoswitchable layer,

contacting a sample having one or more analytes with the graphene layer while the photoswitchable layer is in the state wherein the photoswitchable layer exhibits a first level of hydrophobicity;

applying a first voltage to the graphene layer such that a first current flows in the graphene layer; and

measuring the first current in the graphene layer while the first voltage is applied.

21. The method of claim 20 , further comprising:

after applying the second radiation to the photoswitchable layer, applying a second voltage to the graphene layer such that a second current flows in the graphene layer; and

measuring the second current in the graphene layer while the second voltage is applied.