Biochars’ adsorption performance towards moxifloxacin and ofloxacin in aqueous solution: Role of pyrolysis temperature and biomass type

Three different biomass wastes (rice husk, sawdust, and municipal organic waste) were thermally converted to value-added biochars at two pyrolytic temperatures of 300 °C and 700 °C. Resulted biochars were evaluated for their adsorption potential for the two most widely used fluoroquinolone antibiotics, i.e. moxifloxacin and ofloxacin, through sorption experiments. The results showed that biochars pyrolyzed at 300 °C removed a higher percentage of tested antibiotics (up to 96.18%) than those produced at 700 °C (up to 38.74 %). The Langmuir and Freundlich isotherm models fitted well to the sorption data of the antibiotics indicating monolayer to multilayer adsorption onto the biochars. The adsorption kinetics data of both moxifloxacin and ofloxacin was well fitted to the pseudo-second-order model, suggesting that chemisorption could be the dominant mechanism of adsorption of antibiotics onto different biochars. Among all the biochars, the organic waste-derived biochar (synthesized at 300 °C) was the best adsorbent, with an adsorption potential of 39.10 and 57.10 mg g−1 for moxifloxacin and ofloxacin, respectively. Relatively greater adsorption of moxifloxacin than ofloxacin was due to its high polar surface area. The possible cause of chemisorption of antibiotics onto low-temperature (300 °C) biochars was hydrogen bonding and polar interactions. On the whole, the results indicated that biochar produced from organic waste has significant adsorption potential to remove moxifloxacin and ofloxacin from an aqueous solution.