Controlled synthesis and investigation of the mechanism of formation of hollow hemispherical protrusions on laurate anion-intercalated Zn/Al layered double hydroxide hybrid films

Films of laurate (La) anion-intercalated zinc–aluminum layered double hydroxides (ZnAl–La–LDHs) with hollow hemispherical protrusions on the surface of the hybrid film have been conveniently prepared by an ion-exchange reaction of a nitrate-containing LDH film previously grown in situ on a porous anodic alumina/aluminum (PAO/Al) substrate. No template is required to form the hemispherical protrusions, thus avoiding a complicated template removal process. The dimensions, morphology, and resistance to bursting of the hollow hemispherical protrusions can be easily tuned by varying the experimental conditions such as sodium laurate concentration, reaction time, and reaction temperature. The evolution of the hollow protrusions was investigated by scanning electron microscopy (SEM), and a “bubble template-reconfiguration assembly” mechanism, in which air bubbles on the film surface act as a template, has been proposed to explain their formation. When the ion-exchange reaction was carried out on a film that had been treated by ultrasound to eliminate surface air bubbles, no hemispherical protrusions were formed, which is consistent with the proposed mechanism.

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► Hemispherical hollow protrusions composed of ZnAl–La–LDH crystals were fabricated without the aid of a template.
► It provides an economic way to prepare hollow nanostructured LDH materials.
► A “bubble template-reconfiguration assembly” mechanism has been proposed to explain the formation process.