A thin film sorbent of layered organo-MnO sub(2) for the extraction of p-aminoazobenzene from aqueous solution

An electrochemically grown thin film sorbent, consisting of layered manganese dioxide (MnO sub(2)) intercalated with cetyltrimethylammonium (CTA) cations, was employed to remove p-aminoazobenzene (p-AAB), a neutral organic dye, from aqueous solution. The CTA super(+)-intercalated MnO sub(2) (CTA/MnO sub(2)) film sorbed approximately six times more p-AAB than a film of K super(+)-intercalated MnO sub(2) (K/MnO sub(2)). The equilibrium p-AAB sorption data obtained for the CTA/MnO sub(2) film exhibited a better fit to the Langmuir isotherm than the Freundlich isotherm. The maximum sorption capacity of the film was determined to be 781 mg p-AAB per gram of electrodeposited MnO sub(2). The sorption of p-AAB was not affected by the presence of an excess of small ions such as Na super(+) and SO sub(4) super(2-). XRD and FTIR analyses demonstrated that the p-AAB molecules were accommodated in large, surfactant-filled interlayer spaces between MnO sub(2) layers, and that the layered structure was maintained during sorption. The versatility of this sorbent was verified by its high sorption capacities for cationic (methylene blue) and anionic (Congo red) dyes. The sorption kinetics were well described by an intra-particle diffusion model, rather than by pseudo-first-order or pseudo-second-order models, and diffusion into the interlayer spaces was found to be the rate controlling step over a wide range of contact times, where a rate constant of 73.6 mg g super(-1) min super(-1/2) was estimated. The p-AAB molecules sorbed in the interlayer spaces were gradually expelled after immersing the film in a solution containing solely the supporting electrolyte. When the film was polarized at 0 V vs.Ag/AgCl, the p-AAB desorption was remarkably accelerated as the result of the expulsion of intercalated CTA molecules upon reduction of the MnO sub(2) layers due to charge compensation.