Liquid exfoliation of Zn-Al layered double hydroxide using NaOH/urea aqueous solution at low temperature

The present study provides a new simple but efficient method for preparation of layered double hydroxide (LDH) nanosheets. The exfoliation of Zn-Al LDH is demonstrated in NaOH/urea aqueous solution at low temperature below zero Celsius (-10 degrees C) to form stable transparent colloidal suspensions. The successful exfoliation of LDH is proved by XRD, SEM, TEM and AFM measurements. Typically, the thickness of exfoliated LDH nanosheets is around 0.6 nm while the pristine Zn-Al LDH is about 300 nm. The further study of the mechanism indicates that the NaOH hydrates formed at low temperature below zero Celsius could easily intercalate into the interlayer galleries of LDH and attach to the host layers and the urea hydrates formed at low temperature below zero Celsius play a key role in aggregation prevention and nanosheets stabilization. These two hydrates result in breakage of the original hydrogen bonding network between the adjacent LDH layers and the buildup of a new hydrogen bonding network between the hydrates and LDH host layers. The approach adopted to exfoliate LDH in this paper is a completely novel method, which is extremely convenient, highly efficient and eco-friendly.