Enhanced Removal of Cr (VI) ions from Industrial Wastewater using Functionalized HNTs

Abstract

The surface of raw halloysite nanotubes (HNTs) were functionalized with four different kinds of groups to produce four different functionalized halloysite nanotubes (f-HNTs) namely H1, H2, H3 and H4. The prepared f-HNTs were characterized using various techniques like FTIR, XRD, EDS and SEM. FTIR results confirmed that grafting has been accomplished successfully on the external surface of HNTs. SEM and XRD also verified that only outer surface has been modified rather than interlayer or lumen. These f-HNTs were used as adsorbents for Cr (VI) ions uptake present in wastewater. Batch adsorption was employed to optimize conditions like pH, contact time and metal ions concentration. Functionalized HNTs displayed excellent adsorption and adsorption efficiency of more than 90% was noticed within first 10-15 minutes for H1 and H2 and 66% and 58% for H3 and H4 respectively. Maximum % removal falls in broader pH range of 3-5. The model of Langmuir isotherm provided the nearest fit to the data suggesting the monolayer adsorption of Cr (VI) ions. Langmuir isotherm suggests that adsorption process was favorable (RL between 0 and 1). The adsorption mechanisms involved are quite complicated.Yet possible mechanism involved may be the electrostatic interaction of negatively charged Cr (VI) ions and positively charged amine groups on the surface of f-HNTs. All these results testified that functionalized HNTs may be used as highly efficient and cost-effective adsorbent for wastewater treatment.