Commercial polyurethane foam (PUF) was coupled with magnetite nanoparticles (MNPs) through isothiouronium groups (IT) to prepare a new porous sorbent (PUF@IT@MNPs) with improved ionic character and better sorption affinity towards ionic molecules. PUF@IT@MNPs was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), thermal analysis (TGA), Brunauer-Emmett-Teller (BET) and FT-IR studies. PUF@IT@MNPs had an electrical conductivity (σ) value of 1.0 × 10−5 Ω−1m−1 and maximum ΔpH values of +0.3 and −3.5 at pH 1.4 and 9.7, pointing to the acidic character of the sorbent. FT-IR and TGA studies demonstrated that PUF@IT@MNPs contained different surface-active groups and had a composition of 40.90 wt % of Fe3O4. PUF@IT@MNPs had an improved stability in both acidic and alkaline solutions and high sorption efficiency for anionic (brilliant yellow, BY) and cationic (brilliant green, BG) dyes. The sorption capacities of PUF@IT@MNPs were 330, 328, 225 and 221 mg/g for I2, BY, BG, and MB. The average pore radius values of PUF@IT@MNPs were found to be 1.5 and 8.0 nm and the particle size was 21.4 nm. The sorption of BY was an exothermic process (ΔH = −15.51 kJ mol−1) while that of BG was endothermic (ΔH = 59.19 kJ mol−1).