Superior coagulation of graphene oxides on nanoscale layered double hydroxides and layered double oxides

With the development and application of graphene oxides (GO), the potential toxicity and environmental behavior of GO has become one of the most forefront environmental problems. Herein, a novel nanoscale layered double hydroxides (glycerinum-modified nanocrystallined Mg/Al layered double hydroxides, LDH-Gl), layered double oxides (calcined LDH-Gl, LDO-Gl) and metallic oxide (TiO₂) were synthesized and applied as superior coagulants for the efficient removal of GO from aqueous solutions. Coagulation of GO as a function of coagulant contents, pH, ionic strength, GO contents, temperature and co-existing ions were studied and compared, and the results showed that the maximum coagulation capacities of GO were LDO-Gl (448.3 mg g^-1) > TiO₂ (365.7 mg g^-1) > LDH-Gl (339.1 mg g^-1) at pH 5.5, which were significantly higher than those of bentonite, Al₂O₃, CaCl₂ or other natural materials due to their stronger reaction active and interfacial effect. The presence of SO₃^2- and HCO₃^- inhibited the coagulation of GO on LDH-Gl and LDO-Gl significantly, while other cations (K⁺, Mg²⁺, Ca²⁺, Ni²⁺, Al³⁺) or anion (Cl^-) had slightly effect on GO coagulation. The interaction mechanism of GO coagulation on LDO-Gl and TiO₂ might due to the electrostatic interactions and strong surface complexation, while the main driving force of GO coagulation on LDH-Gl might be attributed to electrostatic interaction and hydrogen bond, which were further evidenced by TEM, SEM, FT-IR and XRD analysis. The results of natural environmental simulation showed that LDO-Gl, TiO₂ or other kinds of natural metallic oxides could be superior coagulants for the efficient elimination of GO or other toxic nanomaterials from aqueous solutions in real environmental pollution cleanup.