Tailoring the surface and solubility properties of nanocrystalline titania by a nonaqueous in situ functionalization process

The reaction between titanium tetrachloride and benzyl alcohol in the presence of enediol ligands such as dopamine and 4-tert-butylcatechol provides a simple nonaqueous route to in situ surface functionalization of titania nanoparticles. The as-prepared precipitates are resoluble either in water or in organic solvents, depending on the ligand used. The surface chemistry of the 4-tert-butylcatechol-functionalized particles dissolved in dimethylformamide was analyzed by H-1 NMR measurements revealing the presence of adsorbed 4-tert-butylcatechol, in addition to benzyl alcohol and water. Although the reaction temperatures of 70 or 80 degreesC are relatively low, XRD and HRTEM investigations give evidence that the as-synthesized nanoparticles are highly crystalline. Ultracentrifugation analysis of dopamine-functionalized titania nanoparticles dissolved in water shows a particle size distribution of approximately 3.5-8 nm with the peak maximum at 5.5 nm. Furthermore, the UV-vis detector system of the ultracentrifuge allows the measurement of the absorption spectra dependent on the particle size, showing an unusual red shift with decreasing particle size.