Tetracycline and sulfamethoxazole adsorption onto nanomagnetic walnut shell-rice husk: isotherm, kinetic, mechanistic and thermodynamic studies.

Nanomagnetic walnut shell-rice husk prepared via calcination and chemical co-deposition was applied as adsorbent for tetracycline (TC) and sulfamethoxazole (SMX) removal from aqueous solution. Various factors (solution pH, nanomagnetic walnut shell-rice husk activated carbon dosage, contact time and initial concentration) influencing adsorption process were examined. Kinetic data were well-fitted into pseudo second-order model for both TC and SMX adsorption with complex diffusion mechanism. Isotherm study revealed equilibrium data well-fitted into Langmuir model with maximum adsorption capacities of 476.2 and 495.8 mg g⁻¹ at pH 6.0 and 323K for TC and SMX sorption onto nanomagnetic walnut shell-rice husk activated carbon (NM-WS-RH-AC), respectively. Spontaneous, exothermic and high degree of disorderliness were revealed by thermodynamic study within the examined temperature ranges (303, 313 and 323K). SEM, FTIR and EDS exhibited randomly-distributed particles of NM-WS-RH-AC with high magnetite deposition, presence of active functional groups and electrostatic attraction of H⁺ and OH⁻ at adsorbent surface, respectively. BET and CHN analysis revealed increase in adsorbent surface area, total pore volume and average pore diameter due to calcination; and presence of larger carbon percentage, respectively. In conclusion, NM-WS-RH-AC served as effective adsorbent for TC and SMX removal from aqueous solution [ABSTRACT FROM AUTHOR]