Hierarchically Porous, Biphasic, and C-Doped TiO2 for Solar Photocatalytic Degradation of Dyes and Selective Oxidation of Benzyl Alcohol.

Macroporous TiO2 monoliths were synthesized by self-sustained combustion reactions of molded pellets made up of a mixture of TiCl4 as a precursor, urea as a fuel, ammonium nitrate as an oxidizer, and starch as a binder. The porous TiO2 monoliths were found to be a heterostructure of anatase and rutile phases, in addition to being doped with carbon. Variation in the amount of starch yielded porous monoliths of different anatase-rutile ratios (increasing rutile component from 0 to 40%) but comparable Brunauer-Emmett-Teller (BET) surface area (∼30 m2 g-1). The porous monoliths obtained, where the TiCl4/starch mass ratio was 2.17, exhibit exceptional photocatalytic activity in the degradation of dyes (methylene blue and methyl orange) and selective oxidation of benzyl alcohol to benzaldehyde under natural sunlight. The synergistic combination of high surface area, porous network, lowered band gap due to heterostructured anatase-rutile polymorphs, and the presence of doped carbon renders the macroporous TiO2 an efficient photocatalyst.