Single-step H3PO4 activation of chitosan for efficient adsorption of amoxicillin and doxycycline antibiotic pollutants

An efficient activated carbon adsorbent was directly prepared through activation of phosphoric acid-impregnated chitosan and used to remove amoxicillin (AMX) and doxycycline (DOC) antibiotics. In the batch process, the adsorption efficiency of the adsorbent for removal of AMX and DOC was evaluated within 30 °C–50 °C, with initial antibiotic concentration ranging from 50 to 400 mg/L and initial pH of 3–13. The phosphoric acid activation modified the topological and textural properties of the obtained activated carbon, leading to a relatively large surface area of 918.79 m²/g and pores with a volume of 0.461 cm³/g and an average size of 2.05 nm. The experimental data of antibiotics uptake over time best fitted the pseudo-first-order model. The adsorption isotherms of the studied systems were well analyzed by the Langmuir equation, and the adsorbent showed the maximum uptakes of 229.82 and 295.43 mg/g for AMX and DOC, respectively, at 50 °C. The thermodynamic results showed positive enthalpy changes of 28.53 and 24.88 kJ/mol for both AMX and DOC antibiotics. Hence, the activated carbon derived from inexpensive chitosan can be effectively used for adsorption of different antibiotics pollutants.