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The aggregates of carbon nanotubes in aqueous solution limit their potential application as effective adsorbents for organic contaminants. In the present study, Manganese dioxide coated on multi-walled carbon nanotubes (MnO²/MWNT) was prepared by redox reaction. Adsorption properties of two dyes (malachite green and rhodamine B) on MnO²/MWNT were examined to explore the potential of MnO²/MWNT for the removal of dyes from aqueous solutions. Compared with MWNT, MnO²/MWNT showed extraordinarily high adsorption affinity for both tested dyes, adsorption of the test dyes was enhanced 3-10 times. It was proposed that the strong adsorption mechanisms were π−π electron donor-acceptor interaction and Lewis acid-base interaction. The effecst of pH and dissolved humic acids on adsorption were also assessed. For two dyes, similar patterns of pH-dependent adsorption were observed, implying the predominance of graphene structures for the adsorption to MnO²/MWNT. The presence of humic acids suppressed the adsorption of two dyes on MnO²/MWNT.

The optimum condition and the specific energy consumption of ozone generation in a coaxial cylindrical ozonizer under dielectric barrier discharge were studied. In addition, we investigated the efficiency and the specific energy consumption of organic compound degradation in ZnO photocatalytic ozonation system. We have found that the optimum conditions in pilot ozone generator for the synthesis of ozone correspond to voltage of 6.2 kV and pressure of 0.5 psi. The specific energy consumptions of ozone generation and dye degradation are decreases to less than 100 kWh/kg and 0.1 kWh/ppm for high dye concentrations, respectively.