Adsorption of tetracycline and ciprofloxacin on activated carbon prepared from lignin with H3PO4 activation

Adsorption of tetracycline (TC) and ciprofloxacin (CPX) onto activated carbon prepared from lignin by H3PO4 impregnated was investigated. Lignin-activated carbon (LGAC) was carbonized at 450°C in a muffle furnace for 1 h. Scanning electron microscope, N2 adsorption–desorption isotherms, X-ray diffraction, pH at the point of zero charge and Boehm titration analysis need to characterize the properties of LGAC. Batched adsorption experiments were performed to study the adsorption properties and interaction mechanisms between TC/CPX and LGAC. The prepared activated carbon was found to have a porous structure with surface area of 931.53 m2/g and many functional groups (acidic groups, basic groups). The adsorption kinetics for the two adsorbates both well fitted the pseudo-second-order model (R2 > 0.99). Compared with Temkin isotherm and Freundlich isotherm, the adsorption equilibrium data were very well represented by the Langmuir isotherm. The maximum adsorption capacities for the TC and CPX calculated by the Langmuir isotherm model were high at 475.48 and 418.60 mg/g, respectively. Thermodynamics study showed that the adsorption was spontaneous and favorable. These results suggested that LGAC could be an effective adsorbent for removal of TC and CPX.