Nitrate reduction using Fe₃O₄-MWCNTs@PEI-Ag nanocomposite as a reusable catalyst

Abstract

In this work, Multi-walled carbon nanotubes (MWNTs) were modified with carboxylic acid functional groups, and then were decorated with Fe₃O₄ nanoparticles. In the next step, polyethyleneimine (PEI) was loaded on Fe₃O₄-MWCNTs to supply an appropriate platform for coordination and in situ reduction in silver ions to create Fe₃O₄-MWCNTs@PEI-Ag nanocomposite. The morphology and structural features of the Fe₃O₄-MWCNTs@PEI-Ag hybrid material was characterized by various techniques such as Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and thermogravimetric analysis (TGA). Fe₃O₄-MWCNTs@PEI-Ag was used as an efficient catalyst for nitrate reduction in water. Effects of the catalyst dosage, pH, temperature, and reaction time were studied on the reduction in nitrate by Taguchi orthogonal array design. Under the optimized conditions including 0.02 mg of catalyst at pH 7.0, 85% of nitrate reduction was achieved at 35 °C after 45 min. The catalyst was magnetically recoverable and recycled up to five runs without considerable loss of its efficiency.

Graphical abstract

Fe₃O₄-MWCNTs@PEI-Ag was used as a heterogeneous catalyst for reduction in nitrate to nitrite in aqueous solution. The nanocatalyst showed high efficiency, because the MWCNTs were functionalized by PEI, which supplied a suitable platform for coordination and in situ reduction in silver ions. Under the optimized conditions including 0.02 mg of catalyst at pH 7.0, 85% of nitrate reduction was achieved at 35 °C after 45 min.