Elimination of surfactants and small dyes from water with silica-supported dendritic amphiphiles

Silica-supported branched polyethylenimine (Sil@PEI) is a conventional adsorbent and shows a limited affinity to anionic surfactants and small dyes ( K = 10 6 –10 7 L/mol). If the PEI is alkylated with cetyl groups (C16), the K of the resulting adsorbents (Sil@PEI@C16- x , where x is the fraction of PEI units being alkylated) is significantly improved. Optimization shows that Sil@PEI@C16-0.15 can best reduce aqueous surfactants to a residue around 10 −10 mol/L; while Sil@PEI@C16-0.6 can reduce even small aqueous dyes to a residue below 10 −10 mol/L, nearly 10 5 -fold lower than that by Sil@PEI. The adsorbents are well recyclable. It is believed that in the case of dyes, the dense cetyl shell can isolate the PEI from the bulky water and thus suppress the competitive binding by water; while in the case of surfactants, the semiclosed cetyl shell can simultaneously meet electrostatic complement and hydrophobic complement to the surfactants.