A thin film sorbent of layered organo-MnO₂ for the extraction of p-aminoazobenzene from aqueous solution

Abstract

An electrochemically grown thin film sorbent, consisting of layered manganese dioxide (MnO 2 ) intercalated with cetyltrimethylammonium (CTA) cations, was employed to remove p-aminoazobenzene (p-AAB), a neutral organic dye, from aqueous solution. The CTA + -intercalated MnO 2 (CTA/MnO 2 ) film sorbed approximately six times more p-AAB than a film of K + -intercalated MnO 2 (K/MnO 2 ). The equilibrium p-AAB sorption data obtained for the CTA/MnO 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 2 . The sorption of p-AAB was not affected by the presence of an excess of small ions such as Na + and SO 4 2À. XRD and FTIR analyses demonstrated that the p-AAB molecules were accommodated in large, surfactant-filled interlayer spaces between MnO 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 À1 min À1/2 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 2 layers due to charge compensation. 85-9201 † Electronic supplementary information (ESI) available: Sorption capacities of various materials towards organic species, FTIR and XRD data of MB-and CR-sorbed CTA/MnO 2 lms, MnO 2 lms on carbon cloth, time courses of p-AAB absorption spectra during desorption with and without polarization, XRD patterns of the p-AAB-sorbed CTA/MnO 2 lm before and aer polarization, and sorption quantities on a K/MnO 2 lm with and without polarization. See

Electrosynthesis of Layered Organo-Manganese Dioxide Framework-Doped with Cobalt for Iodide Sensing

“…Their structure is similar to that of organoclays because it is composed of a two-dimensional, inorganic host (MnO 2 ) and an organic guest species, and therefore, the composite materials can be termed “organo-MnO 2 ”. An electrochemical approach to build layered organo-MnO 2 was first demonstrated by Nakayama et al The process involves potentiostatic oxidation of aqueous Mn 2+ ions in the presence of organic cations such as tetra-alkylammonium, cationic polymers, , and cationic surfactants, , yielding a transparent thin film adhered well to an electrode substrate. The thus-obtained films were applied to the sorption of organic dyes and the electrooxidation of hydroquinone …”

“…An electrochemical approach to build layered organo-MnO 2 was first demonstrated by Nakayama et al The process involves potentiostatic oxidation of aqueous Mn 2+ ions in the presence of organic cations such as tetra-alkylammonium, cationic polymers, , and cationic surfactants, , yielding a transparent thin film adhered well to an electrode substrate. The thus-obtained films were applied to the sorption of organic dyes and the electrooxidation of hydroquinone …”