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

摘要

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-AI-CO_3 LDH hexagonal platelets of 4mum in lateral size were synthesized by the urea method under optimized reaction conditions.The as-prepared CO_3~(2-)-LDH was converted to CI~-LDH by treating with a NaCI-HCI mixed solution,retaining its high crystallinity and hexagonal platelike morphology.LDHs intercalated with a variety of anions (such as NO_3~-,CIO_4~-,acetate,lactate,dodecyl sulfate,and oleate) were further prepared from CI~--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 NO_3~--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 mum.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.