Selective Removal of Technetium from Water Using Graphene Oxide Membranes

The effective removal of radioactive technetium (Tc-99) from contaminated water is of enormous importance from an environmental and public health perspective, yet many current methodologies are highly ineffective. In this work, however, we demonstrate that graphene oxide membranes may remove Tc-99, present in the form of pertechnetate (TcO4-), from water with a high degree of selectivity, suggesting they provide a cost-effective and efficient means of achieving Tc-99 decontamination. The results were Obtained by quantifying and comparing the free energy changes associated with the entry of the ions into the membrane capillaries (Delta F-perm), using molecular dynamics simulations. Initially, three capillary widths were investigated (0.35, 0.68, and 1.02 nm). In each case, the entry of TcO4- from aqueous solution into the capillary is associated with a decrease in free energy, unlike the other anions (SO42-, I- and Cl-) investigated. For example, in the model with a capillary width of 0.68 nm, Delta F-perm(TcO4-) = -6.3 kJ mol(-1), compared to Delta F-perm(SO42-) = +22.4 kJ mol(-1). We suggest an optimum capillary width (0.48 nm) and show that a capillary with this width results in a difference between Delta F-perm(TcO4-) and Delta F-perm(SO42-) of 89 kJ mol(-1). The observed preference for TcO4- is due to its weakly hydrating nature, reflected in its low experimental hydration free energy.