Removal of Cr(VI) from Aqueous Solutions Using Amino-Functionalized Carbon Nanospheres Adsorbents

Carbon nanospheres were prepared and functionalized with carboxyl acid groups (CNS-CA), then reacted with 3-aminopropyltriethoxysilane to introduce amino groups onto the surface (CNS-NH2) by post-synthesis grafting. CNS-NH2 was acidified in order to convert the amino groups (-NH2) into ammonium moieties (-NH3+). Various techniques such as N-2 physisorption, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetry, X-ray photoelectron spectroscopy, and transmission electron microscopy were used to characterize the nanospheres. The removal of chromium ions from aqueous solution using CNS-NH3+ was investigated. Factors influencing the uptake of Cr(VI) ions such as solution pH, adsorbent dose, and initial Cr(VI) ion concentration were investigated. Equilibrium adsorption data fitted the Langmuir model very well. The adsorption maximum capacity of Cr(VI) was found to be 52.38 mg/g. The reusability of CNS-NH3+ results indicated that it can be reused five times successfully without loss of adsorption capacity.