Adsorptive and photocatalytic performance of cobalt-doped ZnTiO₃/Ti₃C₂T_x MXene nanohybrids towards tetracycline: Kinetics and mechanistic insight

Tetracycline (TC) antibiotics are widely used in animal husbandry and can cause environmental risk due to its high ecological toxicity and persistence. In this study, cobalt doped/ZnTiO₃ (ZTO)/Ti₃C₂T_x MXene (ZCxTM, x indicates wt% of Co loading) was synthesized and explored to remove TC by adsorption and photocatalysis under visible light irradiation. The as-prepared ZC5TM was characterized using various analytical techniques, and key operating parameters such as solution pH, background ions, and temperature were systematically investigated. Interestingly, ZC5TM (14.9 mg/g) showed excellent adsorption capacity for TC, which was higher than activated carbon (7.7 mg/g), ZTO (4.9 mg/g), ZC3T (5.2 mg/g), ZC5T (5.3 mg/g), MXene (12.1 mg/g), ZTOM (12.5 mg/g), and ZC3TM (12.9 mg/g). The pseudo-second-order kinetics and Langmuir isotherm models well explained the effect of contact time and initial concentrations on the adsorption of TC. The adsorption process was primarily through the electrostatic attraction, surface complexation, and hydrogen bonding. In addition, MXene and Co doped on ZTO served as co-catalyst and reduced recombination rate of photo-generated e^–-h⁺ pairs by the intimate interface of its heterojunction. Thus, ZC5TM was highly effective for the photocatalytic degradation of residual TC after adsorption by showing 18% TC degradation rate, compared to 8% and 9% degradation rate for ZTO and MXene, respectively. There results finally support the feasible use of ZC5TM as efficient adsorbent and photocatalyst in removal of TC in wastewater.