Amine-stabilized boronate groups at the surface of modified TiO2 under circumneutral pH conditions: Application to selective photocatalytic degradations

TiO2 has been functionalized by using 3-aminopropyltrimethoxy silane (APTMS) and 4-carboxyphenylboronic acid (CPBA). Solid state NMR indicated that ca. 50% of the amino groups did not react with CPBA, and stabilized vicinal boronate groups even at circumneutral pH, i.e. outside the stability range of isolated boronate ions (pH > 8.8). The as demonstrated existence of stabilized boronate groups at circumneutral pH has been used to carry out the proof of concept for selective photocatalytic degradations. In particular, irradiating bare TiO2 induced the expected oxidation of two model pollutants (alizarin red, AR and methylene blue, MB) dissolved in the reacting medium. Instead, the presence of boronate groups at the surface of TiO2 prevented the photocatalytic degradation of adsorbed AR, while simultaneously allowing oxidation of MB. Results are of environmental interest, and pave the way to processes enabling recovery of valuable compounds and simultaneous photocatalytic degradation of other noxious and/or useless species present in the same stream.