Insight into the effect of surface carboxyl and amino groups on the adsorption of titanium dioxide for acid red G

In this study, TiO2 functionalized with organic groups were prepared to study the effect of carboxyl and amino groups on the adsorption behavior of TiO2 for the removal of acid red G (ARG) as an anionic dye from aqueous solution. TiO2 was successfully modified with carboxyl and amino groups by using the hydrolysis method with oxalic acid (OAD, with two carboxyl groups), ethylenediamine (EDA, with two amino groups) and DL-alanine (DLA, with one carboxyl group and one amino group) at low temperature (65 °C) and labeled as OAD-TiO2, EDA-TiO2 and DLA-TiO2, respectively. The ARG uptake by the functionalized TiO2 samples was largely dependent on the functional groups. The interaction between ARG and the functional organic groups on the TiO2 samples plays an important role in the adsorption process, which leads to the excellent adsorption performance (higher capacity and faster adsorption rate) of the functionalized TiO2 samples than that of P25 (commercial TiO2 without modification). Furthermore, there is no obvious loss of the adsorption capacity for the functionalized TiO2 even after 5 adsorption-desorption cycles, which indicated the good reusability of the modified TiO2 samples for anionic dye removal from aqueous solution.