Functionalized carbon nanotubes based filters for chromium removal from aqueous solutions.

This investigation examines the filtration efficiency of chromium from aqueous solution using two types of commercial multiwalled carbon nanotubes (MWCNTs) (Taunit-M (TM) and Taunit-MD (TMD)). These MWCNTs were modified using two complementary treatments, purification (using a mixture of hydrochloric acid and hydrogen peroxide) and functionalization (using nitric acid). The effect of these treatments on the morphology of MWCNT Taunit filters was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy to estimate the outer diameter distribution and element content deposited on filters. Effects of different parameters, i.e., carbon nanotube filter mass, concentration of chromium in aqueous solution, and pH of aqueous solution, on removal of this heavy metal were determined. From these investigations, the removal efficiency of chromium could reach 97% for modified TM and 70% for modified TMD at concentration of 10 ppm, suggesting that modified TM is an excellent adsorbent for chromium removal from aqueous solutions and more efficient than modified TMD. A significant increase in chromium removal by modified TM at pH = 2 has been observed compared with higher pH values. It was found that modified TM filters can be reused through many cycles of regeneration with high performance. Modified TM filters may be a promising candidate for heavy metal ion removal from industrial wastewater.