Photocatalytic reduction of cadmium on TiO2 nanoparticles modified with amino acids

The photocatalytic reduction of cadmium ions was investigated using TiO2 nanoparticles (45 Å in diameter) surface-modified with histidine (His) or alanine (Ala). The X-ray diffraction measurements indicated that illumination of suspension consisting of His- or Ala-modified TiO2 nanoparticles in the presence of cadmium ions under an anoxic atmosphere lead to the formation of metallic cadmium. The TiO2 Fermi level upon surface modification with His or Ala must be shifted towards negative potentials at least 400 mV in order to achieve efficient photoreduction of cadmium ions. The surface structure of His- or Ala-modified TiO2 nanoparticles was proposed based on the changes in the vibration spectrum of His or Ala after adsorption on TiO2 and after addition of cadmium ions.