Gemifloxacin removal from aqueous solution by rice-straw based activated carbon: Batch adsorption and thermal regeneration

Due to the worldwide concern about emerging contaminants in aqueous systems, the main objective of the present study is the adsorption of gemifloxacin (GMF), a fluoroquinolone-type antibiotic, by rice straw-based activated carbon. The rice straw chemically activated with K2CO3 (RSAC) had very high carbon content (>80%) and low silica content (due to the extraction step after activation), high specific surface area (1668 m(2)/g), and oxygenated functional groups. The GMF adsorption capacity of RSAC was relatively dependent on the initial pH of the solution and highly dependent on the adsorbent dose. The pseudo-second order model and the BET isotherm models were the best models for predicting adsorption's kinetic and equilibrium behaviors. The maximum monolayer adsorption capacities of RSAC at 25, 35, and 45 degrees C were 565.6, 552.4, and 525.8 mg/g, respectively. The thermodynamic parameters indicated a spontaneous and exothermic character of the GMF adsorption process. n-pi, pi-pi, electrostatic interactions, and hydrogen bonding were demonstrated as probable mechanisms involved. Thermal regeneration of GMF-saturated RSAC at 550 degrees C resulted in perfect adsorbent regeneration in the second cycle and reasonable performance in the third cycle.