Adsorption, Chitosan, Hexavalent chromium, Carbon nanotubes, Encapsulation H, eavy metal contamination
This work demonstrates the performance of a composite adsorbent encapsulated with chitosan (CS) and maghemite-doped multiwall carbon nanotubes (MWCNTs). Hexavalent chromium (CrVI) was used as the representative hazardous heavy metal to characterize the adsorption behavior of the composite beads. The chromium speciation chemistry combined with the chitosan surface chemistry rendered pH at 4 to be the optimized condition in which the uptake of CrVI was quantitatively most effective. The Langmuir isotherm with a maximum adsorption capacity of 119 mg g−1 at 298 K was observed. The CrVI adsorption studies using partial compositions of the beads further demonstrated the synergistic role of combining the surface properties of CS and MWCNTs. The CrVI removal efficiency increased from 82 % to 96 % as the CS contents doubled in the CS/MWCNTs/Fe beads. Kinetically, the pseudo-second-order model showed the best regression fit (r2 > 0.99) with the experimental data. The intra-particle diffusion model further elucidated that the multiphasic rate-limiting steps during CrVI adsorption included external mass transfer resistance and intra-particle diffusion. The thermodynamic parameters (ΔG, ΔH, ΔS) indicated the adsorption process was spontaneous and endothermic in the tested temperature range (298–313 K). The weak negative Gibbs free energy (ΔG < −20 kJ mol−1) suggested a spontaneous adsorption process governed by electrostatic adsorption. The evolution of CrIII indicates a possible charge transfer effect of Fe2+/Fe3+ mediated through conductive carbon nanotubes, leading to the reduction of CrVI. In five adsorption-desorption cycles, the CrVI removal efficiency of CS/MWCNTs/Fe beads remained about 80 % in adsorption capacity.
Digital Object Identifier (DOI)
Aslam, Mian Muhammad-Ahson; Den, Walter; and Kuo, Hsion-Wen, "Encapsulated Chitosan-Modified Magnetic Carbon Nanotubes for Aqueous-Phase CrVI Uptake" (2021). Water Resources Science and Technology Faculty Publications. 20.
Available for download on Wednesday, March 15, 2023