Crosslinked polymers and a method for heavy metal ion removal

1. A crosslinked polymer, in the form of a Mannich polycondensation product comprising reacted units of

a first monomer of formula (I)

or a salt thereof, a solvate thereof, a stereoisomer thereof, or a mixture thereof;

a second monomer, which is at least one selected from the group consisting of melamine and a bisphenol-S compound represented by formula (II)

or a salt thereof, a solvate thereof, a tautomer thereof, a stereoisomer thereof, or a mixture thereof; and

an aldehyde of formula (III)

or a salt thereof, a solvate thereof, a stereoisomer thereof, or a mixture thereof, wherein:

m is 2 or 3; and

n is 2 or 3;

wherein when the second monomer is melamine the crosslinked polymer has X number of repeating units of formula (IV);

wherein X is 2 to 10,000;

wherein * represents an amino site of an additional melamine ring;

wherein when the second monomer is the bisphenol-S compound represented by formula (II) the crosslinked polymer has Y number of repeating units of formula (V);

wherein Y is 2 to 10,000;

wherein the crosslinked polymer has a BET surface area in the range of 10-80 m 2 /g.

2. The crosslinked polymer of claim 1 , wherein the second monomer is melamine, the molar ratio of the first monomer to melamine is in the range of 1.5:1 to 5:1, and the molar ratio of the aldehyde to melamine is in the range of 2:1 to 10:1.

3. The crosslinked polymer of claim 1 , wherein the second monomer is the bisphenol-S compound represented by formula (II), the molar ratio of the first monomer to the bisphenol-S compound is in the range of 1.2:1 to 4:1, and the molar ratio of the aldehyde to the bisphenol-S compound is in the range of 2:1 to 6:1.

4. The crosslinked polymer of claim 1 , wherein m and n are 2.

5. The crosslinked polymer of claim 1 , wherein the first monomer is piperazine.

6. The crosslinked polymer of claim 1 , wherein the second monomer is melamine, and the crosslinked polymer exhibits a semi-crystalline structure.

7. The crosslinked polymer of claim 1 , consisting of,

the first monomer of formula (I);

the second monomer which is at least one selected from the group consisting of melamine and the bisphenol-S compound represented by formula (II); and

the aldehyde of formula (III).

8. A method for removing a heavy metal from an aqueous solution, comprising:

contacting the aqueous solution having an initial concentration of the heavy metal with the crosslinked polymer of claim 1 to form a mixture; and

filtering the mixture to obtain the aqueous solution having a reduced concentration of the heavy metal compared to the initial concentration.

9. The method of claim 8 , wherein the crosslinked polymer has an average particle size of 1-10 μm in diameter.

10. The method of claim 8 , wherein the heavy metal is an ion of at least one heavy metal selected from the group consisting of Pb, Cd, As, Zn, Cu, Ni, Co, Mn, and Cr.

11. The method of claim 8 , wherein the heavy metal is Pb(II).

12. The method of claim 8 , wherein the aqueous solution has a pH in the range of 1 to 7.

13. The method of claim 8 , wherein the initial concentration of the heavy metal in the aqueous solution ranges from 0.1 mg L −1 to 50 mg L −1 .

14. The method of claim 8 , wherein the crosslinked polymer is present at a concentration in the range of 0.1-10 g per liter of the aqueous solution during the contacting.

15. The method of claim 8 , wherein the crosslinked polymer is contacted with the aqueous solution for 0.1-12 hours; and

the aqueous solution has a temperature in the range of 10° C. to 80° C.

16. The method of claim 8 , wherein greater than 40% of a total mass of the heavy metal is removed from the aqueous solution.

17. The method of claim 8 , wherein the first monomer is piperazine, the second monomer is bisphenol S, and the aldehyde is formaldehyde;

wherein the aqueous solution comprises Pb(II) and at least one additional heavy metal ion, which is an ion of at least one heavy metal selected from the group consisting of Cd, As, Zn, Cu, Ni, Co, Mn, and Cr; and

wherein greater than 95% of a total mass of Pb(II) is removed from the aqueous solution.

18. The method of claim 8 , wherein during the contacting the heavy metal is physisorbed by the crosslinked polymer.