Calcined Mg/Al layered double hydroxides as efficient adsorbents for polyhydroxy fullerenes

The environmental behaviors and pollution control of engineered nanomaterials are drawing increasing interests nowadays. This work showed that the calcined layered double hydroxides (LDH), i.e., layered double oxides (LDO), could effectively adsorb polyhydroxy fullerenes (PHF) from aqueous solution. The maximum adsorption capacity of LDO reached similar to 476 mg/g, much higher than that on LDH (similar to 47 mg/g) and activated carbon (similar to 28 mg/g). All of the three equilibrium adsorption isotherms could be well fitted with the Langmuir equation. The high adsorption capacity of PHF on LDO can be attributed to the enhanced accessibility to the adsorption sites for PHF during structural reconstruction of LDO. In addition, the rehydrated LDH, with a net positive surface charge, has high affinity for negatively charged PHF through an electrostatic interaction. Cl-, CO32-, and SO42- could slightly enhance the adsorption of the PHF on LDO, while HPO42- showed an evident inhibiting effect in the whole concentration range of PHF. The adsorbents before and after the adsorption of PHF were characterized by XRD, FT-IR, and TG. The obtained results indicated that the adsorbed PHF could not intercalate into the interlayer spaces of the reconstructed LDH, but could effectively compete with CO32- during the adsorption process.