Selective reduction of nitrite to nitrogen by polyaniline-carbon nanotubes composite at neutral pH

Abstract

The selective reduction of nitrite (NO2−) to nitrogen by chemical reductant is a desirable strategy to remove NO2− from polluted water and wastewater. However, the residue and reuse of chemical reductant are two main issues to be addressed. Herein, a novel polyaniline-carbon nanotubes composite (PANI-CNTs) was developed by in-situ polymerization to selectively reduce NO2− to nitrogen gas (N2). The used PANI-CNTs could be reused after regeneration with NaBH4. The PANI-CNTs could reduce NO2− with 93.9% N2 selectivity at initial pH of 6.8. The NO2− removal efficiency only decreased by 12.08% after five cycles of reduction/regeneration. The interconversion between imine nitrogen (–N) and amine nitrogen (–NH–) groups induced the chemical reduction of NO2− and regeneration of PANI-CNTs. PANI-CNTs exhibited an excellent performance for the removal of NO2− in the presence of competitive ions and in actual water and wastewater samples. This new PANI-CNTs composite may have great potential for water purification and wastewater denitrification.