ZIF-67 derived hollow cobalt sulfide as superior adsorbent for effective adsorption removal of ciprofloxacin antibiotics

The hollow nanostructures receive increasing attention in recent years. In particular, the confined cavity in the hollow nanostructures can function as a carrier for loading target molecules, whereas the porous walls are beneficial for shortening the transport distance of target molecules from solution to surface of adsorbent, making it possible to achieve high adsorption capacity with short adsorption time. Here, the hollow Co3S4 was synthesized by using ZIF-67 as template and thioacetamide as sulfide reagent through a simple solvothermal method, and characterized by SEM, TEM, HRTEM, XRD, FT-IR, zeta potential measurement, TG, N2 adsorption-desorption and XPS analysis. The adsorption performance of hollow Co3S4 for ciprofloxacin (CIP) antibiotics was evaluated in neutral aqueous solution. The equilibrium adsorption data were well fitted by Langmuir model, and a high maximum CIP adsorption capacity of 471.7 mg g−1 was obtained. The relatively high correlation coefficient of Tempkin model (r2 = 0.960) indicated a stronger electrostatic interaction between CIP and hollow Co3S4, which was consistent with the observation from the effects of pH and ionic strength. Result of adsorption kinetic investigation indicated fast CIP adsorption by hollow Co3S4. The adsorption kinetics follows the pseudo-second-order kinetic model and liquid-film diffusion model. CIP adsorption by hollow Co3S4 was hardly affected by humic acid. Further, the hollow Co3S4 exhibited no obvious loss in CIP removal after recycling for five times. The result displays an important environmental significance of hollow Co3S4 for CIP sequestration, in particular in wastewater, where CIP antibiotics are only slightly transformed or even unchanged.