Simultaneous removal of Cd(II) and 2-chlorophenol from aqueous solution using activated carbon supported titanate nanotubes

Abstract

Combined heavy metals and chlorinated organic compounds have been widely reported in industrial wastewater. Yet, simultaneous removal of these contaminants remains challenging. In this study, a bi-functional composite (TNTs@AC) was prepared based on commercial titanium dioxide (TiO2) and activated carbon (AC) and tested for simultaneous removal of Cd(II) and 2-chlorophenol (2-CP). Under the action of high temperature and pressure, TiO2 was transformed into titanate nanotubes (TNTs) and bound to AC, and in the meanwhile, nanoscale AC particles were patched on the TNTs. In the mixed TNTs and AC phases, TNTs was responsible for taking up Cd(II), whereas AC for 2-CP. As such, the relative adsorption capacities of the composite for Cd(II) and 2-CP varied with the mass ratio of TiO2:AC, with decent uptakes for both chemicals in the mass ratio rage of 1:3 ∼1:1. TNTs@AC (prepared at TiO2:AC = 1:1) demonstrated fast sorption kinetics and high sorption capacities for both Cd(II) and 2-CP, with a maximum Langmuir adsorption capacity of 109 and 52 mg/g, respectively, in the single solute systems. In the binary systems, the adsorption capacity of Cd(II) was not affected by the presence of 2-CP, whereas the presence of Cd(II) slightly increased the uptake of 2-CP in the low Cd concentration domain (final Cd < 7 mg/L) but mildly inhibited the uptake at Cd > 7 mg/L. The dominant adsorption mechanism of Cd(II) was ion exchange between Cd(II) and Na+/H+ of the -ONa/H group of TNTs; while AC served as the primary sink for 2-CP via hydrophobic interaction along with some other possible mechanisms such as surface complexation and hole filling. TNTs@AC also performed well under common environmental conditions (pH, common co-ions, and dissolved organic matter). The formation of mixed TNTs and AC microphases appears promising for simultaneous removal of heavy metals and organic compounds from contaminated water.