Adsorption of Ba2+ and Sr2+ on Ti3C2Tx MXene in model fracking wastewater

Wastewater from hydraulic fracking contains both organic and inorganic pollutants; the latter include radioactive nuclides such as Ba2+ and Sr2+. We explored whether MXene (Ti3C2Tx), a novel adsorbent, could remove Ba2+ and Sr2+ from model wastewater. Zeta potential analysis showed that MXene had a high negative surface charge. MXene adsorbed Ba2+ and Sr2+ via electrostatic attraction, as confirmed by the adsorption at different solution pH values and in the presence of various concentrations of other ions (NaCl and CaCl2). MXene exhibited outstanding adsorption of Ba2+ and Sr2+, to approximately 180 and 225 mg g(-1), respectively, when 1 g L-1 MXene was admixed with adsorbates at 2 g L-1. MXene exhibited very rapid adsorption kinetics, attaining equilibrium within 1 h. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy revealed that MXene adsorbed Ba2+ and Sr2+, respectively, via ion exchange and inner-sphere complex formation. Finally, we performed MXene reusability tests; reusability was excellent over at least four cycles. Thus, MXene removed Ba2+ and Sr2+ from model fracking wastewater.