Enhanced arsenic removal at neutral pH using functionalized multiwalled carbon nanotubes

• Preparation and characterization of zerovalent iron functionalized multiwalled carbon nanotubes for the first time.
• Removal of both As(III) and As(V) over the wide range of pH values.
• High adsorption capacity of 111.1 ± 4.8 and 166.7 ± 5.8 mg g−1 for As(III) and As(V) respectively.
• Recyclability up to 5 cycles.
• Applied successfully to high hard and highly alkaline arsenic contaminated groundwater.

In this study, zerovalent iron nano-particles were immobilized on oxidized multiwalled carbon nanotubes (MWCNT) using EDTA as chelating agent (ZCNT). In addition to zerovalent iron (ZVI), the prepared composite had various surface functional groups including hydroxyl, amino and carboxyl groups. Presence of EDTA in the composite preserved the zerovalent state of iron. The prepared composite was characterized with various spectral techniques like Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDAX), Brunauer, Emmett, and Teller (BET) surface area analyzer, Fourier Transform Infra-red (FTIR) and Raman Spectroscopy. The equilibrium data were fitted to Langmuir model and maximum adsorption capacities at neutral pH were found to be 111.1 ± 4.8 and 166.7 ± 5.8 mg g−1 for As(III) and As(V) respectively. Thermodynamic parameters such as ΔS, ΔH and ΔG indicated the suitability of ZCNT for the removal of As(III) and As(V). Recycling studies indicated the performance of ZCNT up to 5 cycles without appreciable depreciation in the capacity. The effect of commonly existing anions such as silicate, phosphate, sulfate, and humic acid were also tested. Finally, the adsorbent was successfully applied to the removal of total inorganic arsenic from arsenic contaminated ground water without resorting to any pretreatment.

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