Surface Modification of Small Particle TiO2 Colloids with Cysteine for Enhanced Photochemical Reduction: An EPR Study

• DOI: 10.1021/jp952002p
• Publication Date: 2002-07-26T04:43:17Z
• Authors: Tijana Rajh; Agnes E. Ostafin; Olga I. Micic; David M. Tiede; Marion C. Thurnauer
• Keywords: Unpaired electron

Surface complexation of colloidal titanium dioxide nanoparticles (40−60 Å) with cysteine was investigated by electron paramagnetic resonance (EPR) and infrared (diffuse reflectance Fourier transform−DRIFT) spectroscopies. Cysteine found to bind strongly the TiO2 surface, resulting in formation new trapping sites where photogenerated electrons holes are localized. Illumination cysteine-modified at 77 K resulted radicals unpaired localized on carboxyl group. Upon warming 150 K, these transformed into sulfur-centered as observed EPR spectroscopy. We have demonstrated existence two surface Ti(III) centers particles having different extents tetragonal distortion octahedral crystal field. addition lead ions, a complex that bridges atoms ions detected IR lead/cysteine-modified did not result radicals. Instead, symmetrical, lattice defect type signal for trapped observed. Addition methanol this system ·CH2OH radical 8.2 K. After temperature raised 120 doubling associated particle (Ti(III)surf) On further increase 200 disappeared due reduction Pb2+ metallic precipitated room temperature. Conversion presence can doubled quantum efficiency precipitation.