Synergistic immobilization of UO22+ by novel graphitic carbon nitride @ layered double hydroxide nanocomposites from wastewater

Cotton-like graphitic carbon nitride @ layered double hydroxides nanocomposites (g-C3N4@Ni-Mg-Al-LDH) was fabricated using lamellar g-C3N4 and rod-like Ni-Mg-Al-LDH as monomer molecules by one-step hydrothermal synthesis strategy, and it exhibited superior adsorption performance to U(VI) from wastewater based on strong synergistic effects among metal–oxygen functional groups (Mg O, Al O and Ni O) and free-metal functional groups (O C O, C O C, C O, C C and NH2/ NH /= N ). The adsorption of U(VI) on g-C3N4@Ni-Mg-Al-LDH was controlled by outer-sphere surface complexation or ion exchange, which was evidenced with batch adsorption experiments and SEM, EDS, elemental mapping, FT-IR, XRD and XPS characterizations. Moreover, the maximum adsorption capacity of U(VI) on g-C3N4@Ni-Mg-Al-LDH (99.7 mg·g−1) was approximately 1.5 times higher than that of U(VI) on Ni-Mg-Al-LDH (59.8 mg·g−1) and approximately 3.0 times higher than that of U(VI) on g-C3N4 (31.1 mg·g−1) at 298.15 K, and a multilayer adsorption was existed in a low concentration of UO22+, while a monolayer adsorption was appeared in a high concentration of UO22+. The results also showed that the adsorption reaction of U(VI) was a typical endothermic and spontaneous process because of ΔHθ > 0, ΔSθ > 0 and ΔGθ