Abstract:
Nanotechnology is an emerging interdisciplinary subject that has been booming in
many areas during the recent decade. Looking into this aspect, black MnO2
nanoparticles (nps) have been synthesized, via a facile one stop solution phase
approach, by co-precipitation method by the reduction from a system containing
KMnO4 and MnSO4 solutions. Pure phase, spherical, uniformly dispersed brown
Mn3O4 nps powder was synthesized successfully by forced hydrolysis of Mn(II)
acetate by heating its aqueous solution at 800C. Blackish brown γ−MnOOH nps was
synthesized by a simple route using Mn(II) acetate as precursor by hydrothermal
treatment.
The evidence of MnO2, Mn3O4 and γ−MnOOH nps formation under the synthesis
conditions were confirmed by UV–vis spectra, FT-IR, XRD, SEM, EDX, DLS, TG-DTA,
pHpzc and Specific Surface Area (SSA) analysis. FT-IR spectra of MnO2 nps showed
the occurrence of O–Mn–O vibrational mode at around 571 and 535 cm-1. The
selected area electron diffraction patterns revealed that the MnO2 was crystalline
and rod like in nature. Elemental analysis exhibited the presence of Mn and oxygen
elements in the MnO2, Mn3O4 and γ−MnOOH and no foreign elements in them. The
average crystallite size was calculated from the XRD data for MnO2, Mn3O4 and
γ−MnOOH nps were approximately 7.0 nm, 10.0 nm and 11.0 nm respectively. The
specific surface area of γ−MnOOH nps was found to be 142.962 and 195.747 (m2 g-
1) respectively.
Oxidative decolorization of MB and OG were studied at different pH,
concentration, adsorbent dose and contact time by UV-Vis spectroscopy. From
kinetic analysis, it was found that decolorization is dependent on parameters such as
dye concentration, Mn-oxide doses, pH and other parameters. The observed results
were in good agreement with experimental data.
The decolorization data showed that both MB and OG could be decolorized by Mnoxide
surface. But the extent of MB decolorization was much higher than OG,
suggesting the present γ−MnOOH nps can be used as a highly efficient material for
oxidative decolorization of MB. MB decolorization was through a surface mechanism,
that is, formation of surface precursor complex between MB and surface bound
MnOOH center, followed by electron transfer within the surface complex. Kinetic
study demonstrated that both MB and OG decolorization followed pseudo-secondorder
kinetic.
The experimental isotherm results were fitted using Langmuir, Freundlich, Temkin
and Sips isotherm. The Freundlich model agreed very well with experimental data.
The pathogenic experiment was performed following the standard conventional
method by treating the Mn-oxides nps in 7.5% (v/v) DMSO suspension to various
pathogenic organisms. The experiments were performed duplicate and triplicate.
From the experimental evidence it was clear that Mn-oxides did not have potential
antibacterial activity.
