Studies On Synthesis And Wettability Of Layered Double Hydroxides Films

Layered double hydroxides (LDHs), also known as anionic or hydrotalcite-like clays, are currently of intense academic and industrial research interests, in part, because of their properties as catalysis and catalyst precursors, adsorption, separation, biology and medicine materials. Filming or immobilizing LDHs materials will enlarge their usability in optic, electrical, magnetical fields. In our work, LDHs films were prepared by in situ crystallization on porous anodic alumina/aluminium (AAO/A1) substrates. The growth mechanism of the LDHs films was also discussed. With ZnAl-NO₃^--LDHs as the precursor, lauric-intercalated ZnAl-LDHs hybrid film was prepared by one step anion-exchange reaction.The ZnAl-NO₃^--LDHs and ZnAl-Cl^--LDHs films were synthesized on AAO/Al substrate under mild conditions. By changing reaction conditions, such as Zn²⁺ ions concentration, pH value and the reaction time, the growth mechanism of the LDHs film was investigated. It was concluded that the synthesis process of the LDHs films was heterogeneous nucleation. The layered basic salts of zinc (BSZ) minicrystals were firstly crystallized from the solution, then adsorbed onto the substrate and reacted with the Al(III) on it. The replacement Al III) by Zn (II) in the BSZ made the layered positively charged and turned into the LDHs. The coordination bonding of the BSZ made it possible to let the NO₃^- or Cl^- spections insert into the layers with priority.Highly sticky superhydrophobic lauric-intercalated ZnAl-La-LDHs hybrid film had been prepared by one step anion-exchange with ZnAl-NO₃^--LDHs film precursor. The observation with SEM and AFM showed that the structure of hybrid film was lotus-like structure. Numbers of hemispherical protrusions located on the surface of the hybrid film were obtained. The experiment revealed that the anion-exchange reaction was the results of cooperation with thermodynamics and dynamics. The number and dimension of the protrusions were related to the LDHs particles conditions.The wettability of the hybrid film was measured by using contact angle method. These hybrid films performed both excellent sticky and superhydrophobic properties. The hybrid film was characterized by using a high-sensitivity micro-electro-mechanical balance and the Force Curves of Atomic Force microscope. The macro- (high-sensitivity micro-electro-mechanical balance) and the micro- (AFM) observation results concluded that the sticky character of the hybrid film was decided by both the morphology structure and chemical properties of material.