Synthesis, Anion Exchange, and Delamination of Co−Al Layered Double Hydroxide:  Assembly of the Exfoliated Nanosheet/Polyanion Composite Films and Magneto-Optical Studies

This paper describes a systematic study on the synthesis, anion exchange, and delamination of Co−Al layered double hydroxide (LDH), with the aim of achieving fabrication and clarifying the properties of LDH nanosheet/polyanion composite films. Co−Al−CO3 LDH hexagonal platelets of 4 μm in lateral size were synthesized by the urea method under optimized reaction conditions. The as-prepared CO32--LDH was converted to Cl--LDH by treating with a NaCl−HCl mixed solution, retaining its high crystallinity and hexagonal platelike morphology. LDHs intercalated with a variety of anions (such as NO3-, ClO4-, acetate, lactate, dodecyl sulfate, and oleate) were further prepared from Cl--LDH via an anion-exchange process employing corresponding salts. Exchanged products in various anion forms were found to show different delamination behaviors in formamide. Among them, best results were observed for NO3--LDH in terms of the exfoliating degree and the quality of the exfoliated nanosheets. The delamination gave a pink transparent suspension containing well-defined nanosheets with lateral sizes of up to 2 μm. The resulting nanosheets were assembled layer-by-layer with an anionic polymer, poly(sodium styrene 4-sulfonate) (PSS), onto quartz glass substrates to produce composite films. Magnetic circular dichroism (MCD) measurements revealed that the assembled multilayer films exhibited an interesting magneto-optical response.