Modification of bio-char derived from fast pyrolysis of biomass and its application in removal of tetracycline from aqueous solution

► Bio-char, a by-product of pyrolysis, can remove TC in wastewater effectively. ► Alkali modification could enhance the bio-char adsorption capacity. ► The TC adsorption is attributed mainly to π–π interactions and hydrogen bonding. In this work, bio-char, a mass productive by-product of biomass fast pyrolysis, was adopted as an adsorbent to remove tetracycline (TC) from aqueous solution. To enhance the adsorption capacity, a simple modification of bio-char with acid and alkali was carried out. Bio-char samples were characterized by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption isotherm. The results show that the alkali treated bio-char possesses larger surface area than those of raw and acid treated bio-chars, and accordingly exhibits a more excellent adsorption performance (58.8mg/g) than the other two bio-chars and other adsorbents reported previously. The graphite-like structure of bio-char facilitates the formation of π–π interactions between ring structure in tetracycline molecule and graphite-like sheets. The surface area showed significant effects on TC adsorption as well as O-containing functional groups, whereas the initial pH of solution has small effects on TC adsorption under the experimental conditions.