A method of making a membrane, the method comprising: (a) casting a first solution comprising a dissolvable silica nanoparticle-containing polymer solution comprising a negatively charged polymer onto a substrate, said negatively charged polymer bearing carboxyl, sulfonic, or phosphonic groups; (b) casting a second solution comprising a dissolvable silica nanoparticle-containing polymer solution comprising a positively charged polymer onto the casted first solution, said positively charged polymer bearing amino, imino, ammonium, or phosphonium groups; (c) carrying out phase inversion of the first and second nanoparticle-containing polymer solutions to provide a membrane; (d) dissolving the nanoparticles and obtaining a nanoparticle-depleted membrane comprising a first negatively charged zone comprising a negatively charged bulk and a first microporous surface, and a second positively charged zone comprising a positively charged second porous bulk and a microporosus surface; wherein the first porous bulk comprises a first set of pores having outer rims, the first set of pores having a first controlled pore size, and a second set of pores connecting the outer rims of the first set of pores, the second set of pores having a second controlled pore size, and a polymer matrix supporting the first set of pores, wherein the first controlled pore size is greater than the second controlled pore size; and wherein the second porous bulk comprises a third set of pores having outer rims, the third set of pores having a third controlled pore size, and a fourth set of pores connecting the outer rims of the third set of pores, the fourth set of pores having a fourth controlled pore size, and a second polymer matrix supporting the third set of pores, wherein the third controlled pore size is greater than the fourth controlled pore size, and wherein said membrane comprises a hexagonal packing of said first and third set of pores; and (e) washing the nanoparticle-depleted membrane. (a) casting a first solution comprising a dissolvable silica nanoparticle-containing polymer solution comprising a negatively charged polymer onto a substrate, said negatively charged polymer bearing carboxyl, sulfonic, or phosphonic groups; (b) casting a second solution comprising a dissolvable silica nanoparticle-containing polymer solution comprising a positively charged polymer onto the casted first solution, said positively charged polymer bearing amino, imino, ammonium, or phosphonium groups; (c) carrying out phase inversion of the first and second nanoparticle-containing polymer solutions to provide a membrane; (d) dissolving the nanoparticles and obtaining a nanoparticle-depleted membrane comprising a first negatively charged zone comprising a negatively charged bulk and a first microporous surface, and a second positively charged zone comprising a positively charged second porous bulk and a microporosus surface; wherein the first porous bulk comprises a first set of pores having outer rims, the first set of pores having a first controlled pore size, and a second set of pores connecting the outer rims of the first set of pores, the second set of pores having a second controlled pore size, and a polymer matrix supporting the first set of pores, wherein the first controlled pore size is greater than the second controlled pore size; and wherein the second porous bulk comprises a third set of pores having outer rims, the third set of pores having a third controlled pore size, and a fourth set of pores connecting the outer rims of the third set of pores, the fourth set of pores having a fourth controlled pore size, and a second polymer matrix supporting the third set of pores, wherein the third controlled pore size is greater than the fourth controlled pore size, and wherein said membrane comprises a hexagonal packing of said first and third set of pores; and wherein the first porous bulk comprises a first set of pores having outer rims, the first set of pores having a first controlled pore size, and a second set of pores connecting the outer rims of the first set of pores, the second set of pores having a second controlled pore size, and a polymer matrix supporting the first set of pores, wherein the first controlled pore size is greater than the second controlled pore size; and wherein the second porous bulk comprises a third set of pores having outer rims, the third set of pores having a third controlled pore size, and a fourth set of pores connecting the outer rims of the third set of pores, the fourth set of pores having a fourth controlled pore size, and a second polymer matrix supporting the third set of pores, wherein the third controlled pore size is greater than the fourth controlled pore size, and wherein said membrane comprises a hexagonal packing of said first and third set of pores; and (e) washing the nanoparticle-depleted membrane.