Development of a starch assisted facile method for the preparartion of nano iron-manganese based binary oxides

Abstract

In the present study, attempt was taken to develop a facile method for the preparation of binary oxide of Fe‒Mn in nanodimension using starch and metal salts for the removal of total arsenic of ground water. Arsenic contaminated groundwater is a serious health issue worldwide especially in Bangladesh. Arsenic is naturally present in groundwater in the forms of arsenite (AsO33-) and arsenate (AsO43-). As (III) is more toxic and more difficult to remove from groundwater than As (V). Oxidation of As(III) to As(V) always benefits to attain higher removal of arsenic from arsenic contaminant water in sorption process. However, this leads to a complicated operation and is not cost-effective. To overcome these disadvantages, a novel Fe–Mn binary oxide material which combined the oxidation property of manganese dioxide (oxidation of As(III) to As(V))and the high sorption features of iron oxides to As(V), were developed from low cost materials viz. starch and metal salt via a gel formation route. The samples of different Fe:Mn ratio were prepared using Fe(NO3)3, KMnO4 and starch at 80oC in aqueous media. The mixed oxide-starch gel was heat treated at 650oC in air. The phase identification, chemical composition, crystal structure, crystallinity and surface morphology were analyzed using powder X-ray Diffraction (XRD), Energy Dispersive X-ray (EDX), Fourier Transform Infra-Red (FTIR) and Field Emission Scanning Electron Microscopy (FESEM) techniques. The FESEM shows that the dimensions of the synthesized particles of the mixed oxide matrix were around 5-50 nm which was agreement with XRD data. The mixing ratio of Fe(NO3)3 and KMnO4 had profound effect on the size and shape of the nanoparticles. When Fe(NO3)3 treated with starch in absence of KMnO4 the prepared iron oxide nanoparticles was α−Fe2O3 (Lattice structure: Rhombohedral) but in the presence of KMnO4 it form Fe3O4 (Lattice structure : Face-centered cubic). The surface morphology of the particles also vary with the mixing ratio of Fe:Mn. Small spherical (around 5 nm) Fe‒Mn binary oxide nanoparticles were obtained, when the mixing ratio was 1:2.55 (Fe:Mn). Also, the material was arranged in high order looks as like as a wall made of rock on the surface of Fe‒Mn binary oxide found at mixing ratio 1:0.64 (Fe:Mn). The simultaneous oxidation and sorption capacity of the sorbents were carried out at neutral media (pH 7.0). Batch experimental results shows that the sorbents could oxidize As(III) to As(V) and was effective for the simultaneous removal of both As(V) and As(III). The maximal sorption capacity was 79.675 mg/g for solution containing equimolar As(III) and As(V) species at pH 7.0 which was moderately high. MnO2 nanoparticles has high oxidation ability to As(III) but cannot be absorbed As(III) and As(V) from arsenic contaminant water. Thus in As sorption process MnO2 works as oxidizing agent. The Fe‒Mn binary oxides could be a promising sorbent for both As(V) and As(III) removal because of its excellent performance, facile and low-cost synthesis process.