Draw solutions and methods of treating an aqueous liquid

1. A method of treating an aqueous liquid, the method comprising:

delivering an aqueous feed liquid comprising water and at least one solute to a first side of a membrane;

delivering a draw solution comprising water and a draw solute comprising one or more of a phosphazene compound and a triazine compound to a second side of the membrane;

osmosing at least a portion of the water of the aqueous feed liquid across the membrane and into the draw solution to form a diluted draw solution comprising water and the draw solute; and

separating the water of the diluted draw solution from the draw solute of the diluted draw solution to form a purified water product.

2. The method of claim 1 , wherein delivering the aqueous feed liquid comprises delivering at least one of an aqueous saline solution, ocean water, brine, brackish water, mineralized water, and industrial waste water.

3. The method of claim 1 , wherein delivering a draw solution comprises selecting the draw solute of the draw solution to comprise a cyclic phosphazene compound having a plurality of salt-terminated pendant groups bonded to phosphorus atoms of a plurality of phosphorus-nitrogen units.

4. The method of claim 1 , wherein delivering a draw solution comprises selecting the draw solute of the draw solution to comprise a triazine compound having a plurality of salt-terminated pendant groups bonded to carbon atoms of a triazine ring.

5. The method of claim 1 , wherein delivering a draw solution comprises selecting the draw solute to at least partially dissociate in water to produce from about three particles of the draw solute to about seven particles of the draw solute.

6. The method of claim 1 , wherein delivering a draw solution further comprises adjusting at least one of an amount of the water in the draw solution and an amount of the draw solute in the draw solution such that the draw solution comprises a greater number of particles than a total number of particles in the aqueous feed liquid.

7. The method of claim 1 , wherein separating the water of the diluted draw solution from the draw solute of the diluted draw solution comprises filtering the diluted draw solution.

8. The method of claim 7 , wherein filtering the diluted draw solution comprises subjecting the diluted draw solution to at least one of microfiltration, ultrafiltration, and nanofiltration.

9. A method of treating an aqueous liquid, the method comprising:

delivering an aqueous feed liquid comprising water and one or more of a homogenous material and a heterogeneous material to a first side of a semi-permeable membrane;

delivering a draw solution comprising water and at least one draw solute comprising one or more of at least one cyclic phosphazene compound and at least one triazine compound to a second side of the semi-permeable membrane;

drawing at least a portion of the water of the aqueous feed liquid across the semi-permeable membrane and into the draw solution to form a diluted draw solution comprising water and the at least one draw solute; and

separating the water of the diluted draw solution from the at least one draw solute of the diluted draw solution to form a purified water product.

10. The method of claim 9 , wherein delivering a draw solution comprises selecting the at least one draw solute of the draw solution to comprise one or more compounds independently having one of the following chemical structures:

where each X 1 is independently —O—, —S—, or —NH—;

each X 2 is independently —N—, —P—, —CH—, or —SiH—;

each G is independently an alkylene group, an alkenylene group, an alkynylene group, an alicyclic group, an arylene group, —CO—, —SO 2 —, —SO—, —PO—, —O—, —S—, or —NH—; and

each R is independently a sulfonate salt group, a phosphonate salt group, a quaternary ammonium salt group, or a quaternary phosphorous salt group.

11. The method of claim 10 , wherein each R is independently one of the following structures:

where each M 1 is independently a mono-valent cationic counterion or a multi-valent cationic counterion.

12. The method of claim 11 , wherein each M 1 is independently Li + , Na + , K + , NH 4 + , Ca 2 + , Mg 2 + , Zn 2+ , (R 1 ) 4 N + , or (R 1 ) 4 P + , wherein each R is independently H, a substituted alkyl group having from 1 carbon atom to 8 carbon atoms, an unsubstituted alkyl group having from 1 carbon atom to 8 carbon atoms, a substituted aryl group having from 5 carbon atoms to 8 carbon atoms, or an unsubstituted aryl group having from 5 carbon atoms to 8 carbon atoms.

13. The method of claim 10 , wherein each R is independently one of the following structures:

where each R 1 is independently H, a substituted alkyl group having from 1 carbon atom to 8 carbon atoms, an unsubstituted alkyl group having from 1 carbon atom to 8 carbon atoms, a substituted aryl group having from 5 carbon atoms to 8 carbon atoms, or an unsubstituted aryl group having from 5 carbon atoms to 8 carbon atoms; and

each M 2 is independently a mono-valent anionic counterion or a multi-valent anionic counterion.