Ultrathin layered double hydroxide nanosheets prepared from a water-in-ionic liquid surfactant-free microemulsion for phosphate removal from aquatic systems

• Ultrathin LDH nanosheets are prepared in a surfactant-free microemulsion system.
• LDH nanosheets display larger surface areas with smaller pore size and uniform size.
• LDH nanosheets perform the superior removal ability for low concentration phosphate.

A water-in-(ionic liquid) surfactant-free reverse microemulsion were used for the controllable preparation of the small sized Mg2Al-layered double hydroxide (LDH) nanosheets. The metallic salts and alkali aqueous solutions were respectively employed as water phase for preparation of BmimPF6-dimethylformamide-water reverse microemulsions. Then the uncontaminated LDH sheets (LDH-M) have been afforded with a narrow diameter distribution (∼10–35 nm). The LDH nanoplatelets present a uniform lateral dimension (∼31 nm) and a small thickness (∼0.71 nm), which may probably be composed of single brucite-like layer. They display larger surface areas (110–291 m2/g) and smaller pore sizes (17.57 nm and ∼3.83 nm) than LDH based on traditional co-precipitation technique. The treatment of its calcined product (LDO) in water results in the flower-like LDH nanosheets with obvious aggregation and larger size. The phosphate adsorption experiments show that the small sized LDH nanosheets perform superior removal ability toward low concentration phosphate to the large sized LDH sheets. However, the LDO product exhibits further excellent adsorption efficiency due to losing the interaction of carbonate with metal hydroxide layers. After five recycle usage, the ultrathin LDH-M nanoflakes and the calcined product LDO keep about 88.7–93.5% uptake efficiency of the original adsorbents, indicating a good reusability.