LAUSR

Abstract The present work represents the first attempt to apply a polyoxometalates (POMs) type heptamolybdate [Mo 7 O 24 ] 6− as a complexing agent for the removal of toluidine blue (TB) dye by ultrafiltration. Before ultrafiltration study, the interaction between heptamolybdate and dye was investigated using spectrophotometry UV–visible. It was shown that a metachromatic complex dye/POMs type 1:6 was formed with a blue shift from 623 to 550 nm indicating the formation of dye H-aggregates. The ultrafiltration process shows that the addition of heptamolybdate to dye solution greatly improved TB retention from 10 to 97%. The heptamolybdate concentration (0–1 mM), NaCl concentration (0.001–1500 mM), CTAB concentration (0.001–10 mM), pH (2–12) and applied pressure ∆P (2–4 bar) on the dye retention and permeate flux have been investigated. A 2 5 full factorial design shows that the main influenced factors are CTAB surfactant following by heptamolybdate and salt concentrations. Graphic abstract Schematic of the process of TB removal by PAUF method