Adsorption behavior of terephthalic acid on Au(1 0 0), Au(1 1 1) and Au(1 1 0) electrodes in neutral solution

Adsorption of terephthalic acid on Au(1 0 0), Au(1 1 1) and Au(1 1 0) electrodes in neutral solution has been investigated using in situ Fourier transform infrared (FT-IR) spectroscopy, differential capacity measurements and scanning tunneling microscopy (STM). At negative potentials, the terephthalate anions in solution adsorb in a flat orientation onto the electrode via the π electrons of the aromatic ring. At positive potentials, the terephthalate anions adsorb in a vertical orientation via the oxygen atoms of one of the carboxyl groups as a form of dianion. At more positive potentials, the anions adsorb in a vertical orientation as a form of hydrogen terephthalate. For the three electrodes examined, the overtone and/or combination bands, due to vertically oriented hydrogen terephthalate, were observed at 2642 and 2517 cm−1, respectively. For the Au(1 1 1) electrode, STM observations indicated a flat orientation in the form of terephthalic acid.