Fig. 5. Contact time as a function of the adsorption capacity for IC onto APAN/Fe₃O₄–MPA. The solid and dashed lines represent non-linear pseudo-first order model and pseudo-second order model fitting to the experimental data. Experimental conditions: dye initial concentration = 20 mg L⁻¹, adsorbent amount = 10 mg, pH = 5. The relative standard deviations of all measurements were less than 5%.