Adsorption performance and mechanism of g-C3N4/UiO-66 composite for U(VI) from aqueous solution

The uranium (VI) adsorption performance of g-C3N4/UiO-66 composite (CNUIO) was evaluated under different solution pH values, adsorbent dosages, coexisting ions, contact times, initial U(VI) concentrations, and temperatures. The surface properties and the interaction mechanism between U(VI) and CNUIO were analyzed via SEM-EDS, BET, FT-IR and XPS. CNUIO exhibited the maximum adsorption rate of 95.01% under the conditions of C-U(VI) = 10 mg/L, pH = 6, M/V = 0.4 g/L, t = 120 min, and T = 298 K, which was about 25% and 33.73% higher than that of g-C3N4 and UiO-66, respectively. The adsorption process was found to be a spontaneous endothermic process and conformed to the pseudo-second-order kinetic model and the Langmuir isothermal adsorption model. SEM-EDS and BET analysis revealed that increasing the specific surface area effectively improved the adsorption capacity of CNUIO. FT-IR spectroscopy and XPS indicated that the removal of U(VI) was attributed to the coordination complexation between the nitrogen-containing and the oxygen-containing functional groups of CNUIO and U(VI). Adsorption-desorption experiment demonstrated that CNUIO has a good reusability.