Search

Cotton-like graphitic carbon nitride @ layered double hydroxides nanocomposites (g-C 3 N 4 @Ni-Mg-Al-LDH) was fabricated using lamellar g-C 3 N 4 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 NH 2 / NH /= N ). The adsorption of U(VI) on g-C 3 N 4 @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-C 3 N 4 @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-C 3 N 4 (31.1 mg·g −1 ) at 298.15 K, and a multilayer adsorption was existed in a low concentration of UO 2 2+ , while a monolayer adsorption was appeared in a high concentration of UO 2 2+ . The results also showed that the adsorption reaction of U(VI) was a typical endothermic and spontaneous process because of ΔH θ > 0, ΔS θ > 0 and ΔG θ < 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. [ABSTRACT FROM AUTHOR]

Herein the novel natural bimetallic oxides of perovskite oxides (CaTiO x ) and calcium aluminum oxides (CaAlO x ) were fabricated by one-step calcination-oxidation process under air conditions and were characterized using zeta potential, FT-IR, SEM, TEM, XRD, and XPS techniques. Porous and cotton-shaped irregular surface morphologies of CaTiO x and CaAlO x could provide excellent active sites and large specific surface area for the removal of U(VI) from wastewater. Based on FT-IR, XRD and XPS analyses, the enrichment of U(VI) was attributed to the abundant adsorption sites (e.g., M-O groups) of CaTiO x and CaAlO x . The consequences demonstrated that the sorption of U(VI) on CaTiO x and CaAlO x were strongly dependent on pH and weakly dependent on ionic strength at pH < 4.0, while strongly dependent on pH and ionic strength at pH > 4.0. The accordance of sorption kinetic data with the pseudo-second order model suggested that the sorption reaction was multi-stage controlled chemical process. The sorption isotherms of U(VI) can be satisfactorily simulated by the Langmuir model and the maximum monolayer sorption capacities of U(VI) were 241.71 mg·g −1 on CaTiO x and 258.29 mg·g −1 on CaAlO x at 298.15 K. In addition, the thermodynamic results pointed out that the sorption reaction was spontaneous and endothermic process. The sorption mechanism was interpreted as surface complexation and electrostatic interactions. The results demonstrated that CaTiO x and CaAlO x could be widely used as promising and cost-effective materials for the treatment of U(VI) of aqueous solutions in environmental management and pollution prevention and cure. [ABSTRACT FROM AUTHOR]