Cr(VI) removal from the aqueous solutions by the samples of polyanyline doped with phosphoric acid

Abstract

Samples of polyaniline (PAn) were synthesized by oxidative polycondensation of aniline in the presence ammonium peroxydisulfate in the aqueous solutions of phosphoric acid (PA) of different concentrations (0.16–3.30 M). Produced polyaniline was in the form of the emeraldine salt of phosphoric acid (PAn–PA). The prepared samples were used to study in the static conditions of their adsorption properties with regard to Cr(VI) from the aqueous solutions of different concentrations, namely 50, 100, 150, 200 and 300 mg/L, accordingly to the following technique: the 10 ml of the K 2 Cr 2 O 7 solution with appropriate concentration has been added to the portion of adsorbent sample, recorded time and at certain intervals took samples with a volume of 500 μl. These selected samples have been placed into the quartz cuvette with 2 mm thick and has been photometered. The amount of adsorpted substance was determined by the calibration plot. The adsorption experiments were carried out under the temperature 20±1°С. It is shown that the percentage of Cr(VI) removal by PAn samples reaches 94–99 %. It was found that the sorption capacity of all PAn–PA samples increases with increasing phosphoric acid concentration in the reaction mixture during synthesis. Analysis of the IR-FT spectra of PAn–PA samples shown that the partial oxidation of the emeraldine salt to pernigraniline takes place in the result of Cr(VI) adsorption. It was demonstrated that this process can be described sufficiently good by Langmuir or Freundlich adsorption isotherms, while the kinetics of process is in good agreement with model of pseudo second order. As a result of research, the possibility of the using of PAn samples, where polymer is doped with phosphoric acid during synthesis, for sorption of Cr(VI) from aqueous solutions without their additional acidification, has been determined. Keywords : polyaniline, Cr(VI) sorption, kinetics.