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

Abstract

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 (MgO, AlO and NiO) and free-metal functional groups (OCO, COC, CO, CC 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 (99.7mg·g−1) was approximately 1.5 times higher than that of U(VI) on Ni-Mg-Al-LDH (59.8mg·g−1) and approximately 3.0 times higher than that of U(VI) on g-C3N4 (31.1mg·g−1) at 298.15K, 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<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.