Fabrication of One Dimensional MnO₂‐TiO₂ Nano‐Heterostructures for Enhanced Hole Mediated Oxidation of As(III) in Potable Water

Abstract

The conversion of the toxic As(III) from drinking water is a challenging task and it becomes more difficult when As(III) is present in low concentrations (50-200 ppb). Considering this, the present article demonstrates an easy and cost effective wet chemical synthesis of MnO 2 ÀTiO 2 nanoheterostructures (NHs) and its application as the electrode for the oxidation and subsequent conversion of the comparatively low concentration of As(III) from drinking water. The MnO 2 ÀTiO 2 NHs have been employed as the anode to enhance the hole mediated fast and effective oxidation and subsequent conversion of As(III) from water under the applied bias of 1 V vs. Ag/AgCl at room temperature (30 8C) with the water pH~7 in a three-electrode electrochemical cell. The nano-interfacial electronic band engi-neering at MnO 2 -TiO 2 heterointerface is found to be very effective to boost the hole mediated oxidation of As(III). The same NHs also exhibit enhanced photo-electrochemical oxidation of As(III) under the illumination of low-intensity white light. The photo-oxidation in assistance with the applied bias has considerably improved the overall conversion efficiency of As(III) to As(V) in water with a treatment time of just five minutes. The study shows that the material and the method described here is an easy and effective strategy for the enhanced preoxidation and subsequent elimination of As(III) from the drinking water with a low arsenic concentration in the typical weather of Indian subcontinent.

Designing of Functionalized MWCNTs/Anodized Stainless Steel Heterostructure Electrode for Anodic Oxidation of Low Concentration As(III) in Drinking Water

“…Where, n=0 to 3 for As(III) and 0 to 4 for As(V). Alongside, another possible route for the oxidation of As(III) to As(V) could be its interaction with the reactive hydroxyl group as given below: …”

“…This also indicates that the anchoring of f‐MWCNTs on the surface of anodized SS foil enhances the charge transfer process of the electrode compared to the bare anodized SS foil. The linearity of the LSV plots in both cases, probably indicates that no pinning of Fermi level occurs in the semiconducting materials used within the range of applied voltage . The Nyquist plots of the as‐prepared electrodes (Figure (b)) obtained by performing electrochemical impedance spectroscopy (EIS) study shows that the equivalent series resistance ( R s ) of the pristine anodized SS foil and f‐MWCNTs/anodized SS foil is 6.96 and 5.5 ohm.cm 2 , respectively.…”

“…This is probably happening due to the enhanced rate of adsorption of arsenic (mostly As(V)) on the electrode surface as a consequence of an increased temperature, which is believed to be a favouring condition for the adsorption of arsenic on the materials the working electrode is made of . The adsorption of arsenic on the electrode might not reach equilibrium at a lower temperature (20 °C), which is perhaps not sufficient to provide the required thermal energy to overcome the barrier of diffusion . Whereas, a higher temperature (above 40 °C, here) provides the required energy to the oxyanions of arsenic to overcome the diffusion barrier to get adsorbed on the electrode surface.…”

MnO2/TiO2 Nanotube Array-Coated Titanium Substrates as Anodes for Electrocatalytic Oxidation of As(III) in Aqueous Solution

“…In addition, the TiO 2 nanotube arrays can provide a stable framework and large surface area to support MnO 2 , and the Ti substrate with a high conductivity can facilitate the electron transfer, further promoting the electrochemical oxidation efficiency. Recently, Sarkar et al used MnO 2 to fabricate one dimensional MnO 2 –TiO 2 nano-heterostructures and demonstrated a good effectiveness of 76% in the electrocatalytic oxidation of As­(III) at a concentration of 200 ppb, which illustrated the great potential of TiO 2 –MnO 2 nano-heterostructures in boosting the oxidation and conversion As­(III) to As­(V) at relatively low concentration . The hetero-interface of MnO 2 –TiO 2 will strengthen the migration/transportation of the charge carriers.…”

“…Recently, Sarkar et al used MnO 2 to fabricate one dimensional MnO 2 −TiO 2 nanoheterostructures and demonstrated a good effectiveness of 76% in the electrocatalytic oxidation of As(III) at a concentration of 200 ppb, which illustrated the great potential of TiO 2 −MnO 2 nano-heterostructures in boosting the oxidation and conversion As(III) to As(V) at relatively low concentration. 32 The hetero-interface of MnO 2 −TiO 2 will strengthen the migration/transportation of the charge carriers. However, this study as yet has only focused on the electrocatalytic oxidation effect of MnO 2 −TiO 2 nanostructures on comparatively low-concentration As(III), while there are still knowledge gaps regarding the effect of the morphology and preparation conditions of MnO 2 −TiO 2 nanostructures on electrocatalytic oxidation performance.…”