High effective adsorption/removal of illegal food dyes from contaminated aqueous solution by Zr-MOFs (UiO-67)

UiO-67, a bifunctional adsorbent, was successfully applied to remove illegal food dyes (Congo red and Malachite green) from aqueous solution. The relevant adsorption conditions were optimized: pH 6, 120 min for contact time, and 10.0 mg L^-1 adsorbent dose for Congo red. Adsorption behavior of UiO-67 exhibits a better fitting to pseudo-second-order kinetic model and Langmuir model. Moreover, the maximum adsorption capacities of Congo red (1236.9 mg g^-1) and Malachite green (357.3 mg g^-1) are higher than that of the most reported adsorbents. Thermodynamic analysis reveals that adsorption processes are spontaneous and endothermic in nature. Powder X-ray diffraction patterns, Fourier-transform infrared spectra and the X-ray photoelectron spectroscopy analysis indicates Zr-OH groups have positive influence on binding of target molecules. What's more, UiO-67 could be reused without significant loss of its capacity after seven cycles. These results prefigure the promising potentials of UiO-67 in food safety risk management.