Simultaneous adsorption of uranium(VI) and 2-chlorophenol by activated carbon fiber supported/modified titanate nanotubes (TNTs/ACF): Effectiveness and synergistic effects

Mixtures of U(VI) and chlorinated compounds have been detected at many radionuclides-contaminated sites. Yet, simultaneous removal of the two classes of contaminants is still challenging. Herein, we prepared a new type of composite material (TNTs/ACF) based on commercial TiO2 and activated carbon fiber (ACF) through a hydrothermal approach and tested it for simultaneous removal of U(VI) and 2-Chlorophenol (2-CP). The hydrothermal treatment converted TiO2 into titanate nanotubes (TNTs), a cation exchanger, which are not only supported by bulk ACF, but also modified by carbon nanoparticles. TNTs/ACF exhibited fast sorption kinetics and high adsorption capacities for both U(VI) (Langmuir O-max = 188.0 mg/g) and 2-CP (Q(max)= 122.1 mg/g). Moreover, higher adsorption was observed when both solutes are co-present than in the single-solute systems. An extended dual-mode model, which considers adsorption and other specific mechanisms well interpreted the adsorption isotherms. The optimal working pH for U(VI) ranged from 6.0 to 8.0, while the sorption of 2-CP remained high over a broader pH range. The presence of 1.0-10.0 mg/L humic acid as TOC increased the adsorption of both chemicals. The key adsorption mechanism for U(VI) is ion-exchange at the -O- functional sites in the interlayers of TNTs, while 2-CP was taken up via hydrophobic interactions with ACF and capillary condensation. The adsorption synergy of U(VI) and 2-CP in the binary systems resulted from the complexation between U(VI) ions and phenolic groups of 2-CP and the cation-A interactions. TNTs/ACF appears promising for simultaneous removal of radionuclides and chlorinated chemicals from contaminated water.