Birnessite-type manganese oxides (MnO2) are environment-friendly and inexpensive compounds. They have recently received close attention because of their unique adsorption and catalytic properties. However, because birnessite-type manganese oxides are usually synthesized as fine-grained aggregates their technological application are limited due to nanoparticles agglomeration and difficulties in separation of the fine particles from aqueous solution.
In this study we propose novel nanocomposite material based on birnessite-coated polyacrylonitrile (PAN) fibers, which was prepared by in situ formation of birnessitenano-sized aggregates within andon the fibers’ surface. The original PAN fibers have cream color, but composite (PAN-MnO2) fibers became black. Microanalysis results of composite fibers showed presence of elements corresponding to the birnessite composition (Na, K, Mn, O). The SEM images of fibers’ surface revealed the formation of the birnessite nanoaggragates (~100 nm). XRD and FT-IR analyses also confirmed the formation of composite fibers with the birnessite phase.
The synthesized PAN-MnO2 fibers were tested for the removal of Mn2+ from the model solutions in batch mode, and the influence of contact time, pH, and salt content in the multicomponent solutions was investigated. The experimental results showed that PAN-MnO2 fibers demonstrate fast adsorption kinetics. The major fraction (~ 75%) of Mn2+ presented in the solution was adsorbed within the first 15 min, while pure synthetic birnessite could adsorb only 15% during the same time. The adsorption of Mn2+ is pH dependent process, and the maximal removal was observed within the pH range of 6-8. Removal of Mn2+ from multicomponent solutions (mainly Na+, K+, Mg2+, Cl-, SO42-, HCO3- and heavy metals as microcomponents) with high and low salt content (22 and 2,2 g/l, respectively) was carried out. It was found that the adsorption from the single component solution (water solution of Mn2+ salt) is 98 % and it is 30 and 68% under removal of Mn2+ from multicomponent solutions with high and low salt content, respectively. The obtained results showed that the composite material based on birnessite-coated PAN fibers can be used as an effective adsorbent for manganese ions.