Activated carbons from agricultural byproducts (pine tree and coconut shell), coal, and carbon nanotubes as adsorbents for removal of sulfamethoxazole from spiked aqueous solutions: Kinetic and thermodynamic studies

In this study, four different adsorbent materials: commercial powdered activated carbon (PAC) from pine tree (PAC-I) and coconut shell (PAC-III) agricultural crop wastes, coal (PAC-II), and carbon nanotubes (CNT) were tested and compared for the removal of sulfamethoxazole (SMX) from spiked aqueous solutions. The kinetic, extrathermodynamic, and thermodynamic parameters for the adsorption of SMX on PACs and CNT were also determined. The results indicate that PAC-I was the best adsorbent for SMX adsorption. SMX adsorption was only favorable with PAC-I and CNT, leading to Gibbs free energies in the range of -39 to -44 kJ mol(-1) and showing that the adsorption process was spontaneous in all temperature ranges (15-45 degrees C) tested. Langmuir model best described SMX adsorption on PAC-I and led to maximum adsorption capacity of similar to 131 mg g(-1) (at 25 degrees C), which was similar to 4.6 times higher than that observed for CNT. The mechanism of SMX adsorption on PAC-I and CNT was suggested with basis on thermodynamic and extrathermodynamic parameters. The kinetic studies showed the pseudo-second-order model best described SMX adsorption, yielding k(2) values of 0.0035 and 0.0016 g mg(-1) min(-1) for PAC-I and CNT, respectively. (C) 2015 Elsevier B.V. All rights reserved.