Water vapor harvesting materials and devices

1. An atmospheric water harvesting material, comprising:

a deliquescent salt;

a photothermal agent; and

a polymeric hydrogel matrix containing the deliquescent salt and photothermal agent.

2. The atmospheric water harvesting material of claim 1 , wherein the deliquescent salt is in a liquid phase but held in a solid form in the polymeric hydrogel matrix.

3. The atmospheric water harvesting material of claim 1 , wherein the deliquescent salt is a chloride salt or a nitrate salt.

4. The atmospheric water harvesting material of claim 3 , wherein the deliquescent salt is a chloride salt comprising lithium chloride, LiCl, calcium chloride, CaCl 2 , magnesium chloride, MgCl 2 , zinc chloride, ZnCl 2 , iron (III) chloride, FeCl 3 , or zinc nitrate, Zn(NO 3 ) 2 .

5. The atmospheric water harvesting material of claim 3 , wherein the deliquescent salt is a nitrate salt comprising copper (II) nitrate, Cu(NO 3 ) 2 , nickel (II) nitrate, Ni(NO 3 ) 2 , or manganese (II) nitrate, Mn(NO 3 ) 2 .

6. The atmospheric water harvesting material of claim 1 , wherein the polymeric hydrogel matrix comprises at least one of the following polymers:

poly(acrylic acid), PAA;

poly(vinyl pyrrolidone), PVP;

poly(acrylamide), PAM;

poly(ethylene oxide), PEO;

poly(vinyl methyl ether), PVME;

poly(vinyl alcohol), PVA;

hydroxypropylcellulose, HPC;

hydroxyethylcellulose, HEC;

poly(2-hydroxyethyl vinyl ether), PHEVE; and

poly(N-isopropylacrylamide) PNIPAM.

7. The atmospheric water harvesting material of claim 1 , wherein the photothermal agent comprises one or more of the following:

a carbon material;

a two-dimensional metal carbide;

a two-dimensional metal nitride;

phosphorus;

titanium oxide;

metal nanomaterial;

iron oxide;

a polymer; and

a metal oxide.

8. The atmospheric water harvesting material of claim 1 , wherein the photothermal agent comprises one or more of the following:

carbon black;

graphite;

graphene;

graphene oxide, GO;

carbon nanotubes, CNTs;

an MXene;

black phosphorous;

black titanium oxide;

metal nanorods;

metal nanoparticles;

metal nanowire;

ferrous ferric oxide;

polypyrrole;

dopamine; and

a metal oxide.

9. The atmospheric water harvesting material of claim 1 , wherein the atmospheric water harvesting material captures atmospheric water having a relative humidity in a range of 15%-100%.

10. The atmospheric water harvesting material of claim 1 , wherein the polymeric hydrogel matrix comprises a cross-linked and flexible hydrogel network.

11. A method for forming an atmospheric water harvesting material, the method comprising:

forming a polymeric hydrogel matrix comprising a photothermal agent;

freeze-drying the polymeric hydrogel matrix comprising the photothermal agent; and

immersing the freeze-dried polymeric hydrogel matrix comprising the photothermal agent in a solution containing deliquescent salt to form a polymeric hydrogel matrix comprising the photothermal agent and the deliquescent salt; and

drying the polymeric hydrogel matrix comprising the photothermal agent and the deliquescent salt.

12. The method of claim 11 , wherein the formation of the polymeric hydrogel matrix comprising the photothermal agent comprises:

dissolving a polymer precursor in a dispersion of the photothermal agent to form a dispersion of the polymer precursor and the photothermal agent;

eliminating dissolved oxygen in the dispersion of the polymer precursor and the photothermal agent; and

adding a hydrogelling initiator and a hydrogelling agent to the dispersion of the polymer precursor and the photothermal agent.

13. The method of claim 12 , further comprising:

adding a hydrogelling accelerator to the composition of the polymer precursor, photothermal agent, hydrogelling initiator, and hydrogelling agent.

14. The method of claim 12 , wherein the elimination of dissolved oxygen comprises:

purging the dispersion of the polymer precursor and the photothermal agent with nitrogen.

15. A method for generating water from water vapor, the method comprising:

absorbing water vapor by an atmospheric water harvesting material arranged on an outer surface of a cylinder, wherein the atmospheric water harvesting material comprises a deliquescent salt, a photothermal agent, and a polymeric hydrogel matrix containing the deliquescent salt and photothermal agent;

rotating the cylinder so that a portion of the atmospheric water harvesting material that has absorbed the water vapor is facing a condensation chamber, which is arranged above the cylinder and has a light-admitting upper surface;

exposing the portion of the atmospheric water harvesting material facing the condensation chamber to solar energy passing through the light-admitting upper surface;

releasing, due to the solar energy, the water vapor from the portion of the atmospheric water harvesting material facing the condensation chamber into the condensation chamber; and

condensing in the condensation chamber, the released water vapor into water,

wherein the condensed water is pure water or the water vapor is released exclusively due to the solar energy.

16. The method of claim 15 , wherein when the portion of the atmospheric water harvesting material is facing the condensation chamber, a second portion of the atmospheric water harvesting material is not directly exposed to the solar energy, the method further comprising: absorbing water vapor by the second portion of the atmospheric water harvesting material.

17. The method of claim 15 , wherein the atmospheric water harvesting material does not change phase from hydrophilic to hydrophobic while releasing the water vapor.

18. The method of claim 15 , wherein the condensed water is pure water.

19. The method of claim 15 , wherein the water vapor is released exclusively due to the solar energy.