Enhanced aqueous adsorption and photodecomposition of anionic organic target by amino group-modified TiO2 as anionic adsorptive photocatalyst

Abstract

Photocatalysts are promising materials for the photo-oxidation of organic pollutants in air and water. For practical applications in water purification, the contact efficiency between the photocatalyst and organic pollutants must be maximized. Here, we developed an amino functional-based spacer (3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane, DETA), and used it to modify TiO2. In the modified catalyst (DT), the protonated amino functional groups could carry a positive charge in the range of pH 3–9. As a result, it electrostatically adsorbs indigo carmine (INC) as a target model anionic organic compound, depending on a number of amino groups attached to the TiO2 surface. Furthermore, when coated on a glass plate to prevent its aggregation in solution, DT demonstrated higher adsorption than plate coated with unmodified TiO2. Especially, the plate with the highest DETA-to-TiO2 ratio (4.85 × 10−4) of the prepared photocatalysts in this study had the highest photodecomposition rate among all plates tested at pH 3, as well as the highest adsorptivity. During the photodecomposition of INC by the DT-coated glass plate, isatin-5-sulfonate is first generated as the main byproduct, and then it is decomposed to produce sulfate under UV irradiation. These data demonstrate that the modification of TiO2 by positively charged amino groups could enhance the adsorption and photodecomposition of anionic organic targets, and glass plates coated with these photocatalysts can have practical use in water purification.