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-/= = Ne-). 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 Delta H-theta > 0 Delta S-theta > 0 and Delta G(theta) < 0. Thus, it can provide new highlights to improve the physicochemical properties of low efficiency adsorbents based on synergistic effect through polymerization reaction, and it can be selected as superior synthetic route for the synthesis of excellent adsorbents in environmental remediation.