Influence of substituted acetic acids on “bridge” synthesis of highly photocatalytic active heterophase TiO 2 in hydrogen production

Anatase/brookite nanoparticles were prepared by low-temperature hydrolysis and polycondensation of titanium isopropoxide in the presence of low concentrations of acetic acid substituted in the α−position with Cl, F, NH 2 or OH groups. A bridging mechanism described the formation of TiO 2 with heterophase junctions between anatase and brookite. Substituted acetic acids formed short Ti---X-CH 2 -COO---Ti bridges that held neighboring Ti species close together and facilitated their condensation and the formation of Ti-O-Ti bonds. The structure of the anatase-brookite heterophase junctions was located and fully characterized by HR-TEM. The most acidic acetic acids substituted with groups with a strongly negative inductive effect, monochloroacetic, dichloroacetic, trichloroacetic, trifluoroacetic and amino acetic acids, supported the formation of TiO 2 , which in cooperation with the Pt cocatalyst had photocatalytic activity, 144.6–165.6 μmol H 2 /min. g, in the production of hydrogen. All photocatalysts had a pronounced mesoporous structure and a large specific surface area (212.6 to 247.2 m 2 /g), which contributed to the high photocatalytic activity. Graphical Abstract Heterophase anatase-brookite photocatalysts were prepared by hydrolysis and polycondensation of titanium isoproproxide in a solution of substituted acetic acids. Bridges between substituted acetic acids and Ti atoms supported the formation of heterophase anatase-brookite junctions, which formed highly active photocatalysts in hydrogen production.