Enhanced hexavalent chromium adsorption from aqueous solutions onto amine functionalized MWCNTs synthesized using iron(0)/egg-shell as an efficient catalyst

摘要

Multiwall carbon nanotubes (MWCNTs) were synthesized using chemical vapor deposition method by iron impregnation onto the natural egg-shell support. The employed support has a low cost and the iron fragment induces superparamagnetic property on as-synthesized MWCNTs which were then functionalized with ethylenediamine (En) as well as triethylenetetramine (TTA). The prepared materials were characterized by XRD, TGA/DTA, VSM,FT-IR and Raman techniques. Effect of iron percentage on the MWCNT yield and influence of temperature on the product quality were investigated. The as-synthesized MWCNTs, oxidized MWCNTs and amine functionalized MWCNTs were employed for Cr(VI) removal from aqueous solution. Effective parameters on adsorption efficiency such as pH, contact time, adsorbent dosage and temperature were optimized. Kinetic and isotherm studies revealed that chromium adsorption by modified adsorbents followed second order and Langmuir adsorption model with the equilibrium time of 30 min and adsorption capacities of 125 and 166.6 mg g(-1) using MWCNTs and oxidized CNTs, respectively, while 333.3 mg g(-1) using both amine functionalized MWCNTs. Thermodynamic experiments illustrated that chromium adsorption was spontaneous as well as followed an exothermic path. Regeneration of the sorbents using NaOH solution exhibited that the sorbents have appropriate reusabilities after six cycles of sorption and desorption.