Nucleation and growth of cobalt hydroxide crystallites in organized polymeric multilayers

In this paper, we report the hydrolysis of Co2+ ions absorbed in organized, multilayered polymer films to form cobalt hydroxide nanocrystals. Polymer films were prepared using the layer-by-layer deposition technique that cons ists of adsorbing polycations and polyanions alternately on a quartz substr ate. By monitoring the UV-vis absorbance of the polymer films as a function of the number of absorption-hydrolysis cycles, it was shown that the cryst als continued to grow with additional cycles. It is also found in this stud y that using more polymer layer pairs results in more crystal growth. Hydro lysis of the Co2+ ions in a nitrogen-rich environment gives rise to mainly needlelike crystallites of alpha-Co(OH)(2) that are initially about 100 nm in length and th en increase in size with the number of absorption-hydrolys is cycles. However, in an oxygen-rich microenvironment, hexagonal crystalli tes were found to be predominant. X-ray diffraction and transmission electr onmicroscopic studies revealed that these hexagonal crystallites mainly con sist of beta-Co(OH)(2) with a contribution of CoOOH. Our studies suggest th at by varying the nitrogen-to-oxygen ratio the formation of alpha-Co(OH)(2) and beta-Co(OH)(2) can be controlled.