Activated carbons derived from hydrothermal impregnation of sucrose with phosphoric acid: remarkable adsorbents for sulfamethoxazole removal

Abstract

A series of activated carbons with surface areas of 925–1929 m² g⁻¹ were synthesized by in situ hydrothermal impregnation of sucrose with H₃PO₄ and subsequent calcination at 500–900 °C. The prepared various types of activated carbons were utilized for the removal of sulfamethoxazole (SMX) from its solution by adsorption, and the effects of contact time, adsorbent dosage, initial concentration, adsorption temperature and pH on SMX adsorption were studied. The pseudo-second-order and the intra-particle diffusion model were used to analyze the adsorption kinetic data. The adsorption isotherm studies showed that the activated carbon prepared at 900 °C (C-900) showed the highest Langmuir maximum adsorption capacity of 808.7 mg g⁻¹ among them, much higher than that of C-500 (274.0 mg g⁻¹). Adsorption thermodynamic results showed that the adsorption of SMX was a spontaneous exothermic process, with a standard enthalpy change of −6.59 kJ mol⁻¹ and a standard entropy change of 47.7 J mol⁻¹ K⁻¹. It was deduced that hydrophobic, electron donor–acceptor and electrostatic interactions were involved in the adsorption mechanism. Finally, regeneration experiments showed that more than 90% of the adsorption capacity could be recovered after four cycles through ethanol washing. Considering the remarkable and regenerable adsorption ability as well as the economic and environmental merits, these activated carbons are considered as promising candidates for potential practical applications in adsorptive removal of SMX.