Adsorption mechanism and performance of tetracycline on different biochar-based amphoteric clays

Abstract

The adsorption characteristics and mechanism of tetracycline (TC) on biochar-based amphoteric clay was explored by modifying bentonite (B) with different proportions (50%, 100%) of dodecyl dimethyl betaine (BS) to prepare BS modified-B (BS-B). Then, BS-B was loaded on the xerophyte (X) and hydrophyte (H) Alternanthera philoxeroides biochar (named as XAp-C and HAp-C) to form XAp-C/50BS-B (50%BS-B loaded XAp-C, the same below), XAp-C/100BS-B, HAp-C/50BS-B, and HAp-C/100BS-B. Batch method was used to study the adsorption differences of TC under different pH, ionic strength, and temperature, and the isothermal adsorption and thermodynamic characteristics of TC on different Ap-C/BS-Bs were compared. In addition, the regeneration properties of the materials were tested. The following results were obtained: (1) The amount of TC adsorbed by the test materials decreased with increasing pH (3–6) and ionic strength (0.01–0.5 mol/L). (2) TC adsorption capacity was positively correlated with increasing temperature, the adsorption process was a spontaneous and endothermic, and entropy-increasing process. (3) The maximum adsorption capacity (qm) of TC on the tested materials changed from 17.19 mmol/kg to 40.93 mmol/kg, and showed the trend of Ap-C/100BS-B > Ap-C/50BS-B > Ap-C/B > Ap-C. The adsorption effect of XAp-C/BS-B was better than HAp-C/BS-B under the same BS modification ratio. (4) With increased regeneration time, the mass loss of materials gradually decreased, and the loss rate of the third regeneration was only approximately 4.0%. XAp-C/100BS-B was a good cyclic-adsorption material, and its adsorption effect can still reach 60.2% of the original material after three times of regeneration.