Composite polyamide membrane treated with dihyroxyaryl compounds and nitrous acid

1. A method for making a composite polyamide membrane comprising a porous support and a polyamide layer, wherein the method comprises:

i) applying a polar solution comprising a polyfunctional amine monomer and a non-polar solution comprising a polyfunctional acyl halide monomer to a surface of a porous support and interfacially polymerizing the monomers to form a polyamide layer;

ii) applying a dihydroxyaryl compound to the polyamide layer, wherein the dihydroxyaryl compound is represented by

 wherein D, D′, D″ and D′″ are independently selected from: alkyl, alkoxy, hydrogen, halogen, hydroxyl and amine, E and E′ are independently selected from: amide, amine, azo, ether and ester, and L′ is selected from at least one of: aliphatic and arylene, and

iii) exposing the thin film polyamide layer to nitrous acid;

wherein step ii) is performed before, during or after step iii).

2. The method of claim 1 wherein steps i), ii) and iii) are performed sequentially.

3. The method of claim 1 wherein D, D′, D″, and D′″ are hydrogen.

4. The method of claim 1 wherein E and E′ are independently selected from: amide and ether.

5. The method of claim 1 wherein the non-polar solution further comprises an acid-containing monomer comprising a C 2 -C 20 hydrocarbon moiety substituted with at least one carboxylic acid functional group or salt thereof and at least one amine-reactive functional group selected from: acyl halide, sulfonyl halide and anhydride, wherein the acid-containing monomer is distinct from the polyfunctional acyl halide monomer.

6. The method of claim 1 wherein the thin film polyamide layer has a dissociated carboxylic acid content of at least 0.18 moles/kg at pH 9.5 as measured by RBS prior to the step of exposing the thin film polyamide layer to nitrous acid.

7. The method of claim 1 wherein at least one of the polar and non-polar solutions further comprises a tri-hydrocarbyl phosphate compound represented by Formula (I):

wherein R 1 , R 2 and R 3 are independently selected from hydrogen and hydrocarbyl groups comprising from 1 to 10 carbon atoms, with the proviso that no more than one of R 1 , R 2 and R 3 are hydrogen.

8. The method of claim 1 wherein the dihydroxyaryl compound is selected from at least one of:

N,N′-(benzene-1,3-diyldimethanediyl)bis(3,5-dihydroxybenzamide)

N,N′-(1,4-phenylenebis(methylene))bis(3,5-dihydroxybenzamide)

N,N′-[5-(trifluoromethyl)benzene-1,3-diyl]bis(3,5-dihydroxybenzamide)

N,N′-biphenyl-4,4′-diylbis(3,5-dihydroxybenzamide)

N,N′-ethane-1,2-diylbis(3,5-dihydroxybenzamide)

3,5-bis[(3,5-dihydroxybenzoyl)amino]benzoic acid.

9. The method of claim 1 wherein the dihydroxyaryl compound is represented by at least one of:

wherein Y is selected from the aliphatic and arylene.

10. The method of claim 1 wherein the dihydroxyaryl compound is represented by at least one of: