Tuning electrochemical behavior and band gap energy of ammonium phosphomolybdate/polymer composite and facilitate reduction of Cr(VI) in contaminated water

Binary composites of ammonium phosphomolybdate (APM) with polyaniline and poly(N-methylaniline) namely APM/PAni and APM/PNMAni were synthesized respectively in situ by exploiting the oxidizing ability of APM. The composites were characterized using fourier transform infrared spectroscopy, powder X-ray diffraction, and scanning electron microscopy. Further, the electrochemical behavior of these composites was investigated using cyclic voltammetry. The redox peaks obtained for APM, APM/PAni and APM/PNMAni at 0.302, 0.228 and 0.298 V respectively could be attributed to MoV/MoVI electron process. The appreciable shift in the peak could be attributed to the electron donating behavior of methyl groups in APM/PNMAni. Additionally, the band gap energy was calculated using diffuse reflectance spectroscopy data. The optical band gap of the composites increased considerably as compared to APM. A higher band gap was observed for APM/PNMAni as compared to APM/PAni, indicating the influence of methyl substitution in tuning the band gap energy. In addition, the role of these composites and its constituents in the removal of hexavalent chromium ions from aqueous solution was also explored. The removal of Cr(VI) from aqueous solution was monitored using UV-Visible spectroscopy. While removal of Cr(VI) as high as 96.3 % could be achieved using polymers, composites exhibited the ability to reduce toxic Cr(VI) moieties to environmentally benign Cr(III) ions.