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

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.