Hybrid Templating Approach for the Synthesis of Hierarchical Oxides: Titania Heterojunctions for Photodegradation of Organic Dyes

Hierarchical titania with anatase/rutile crystalline phases were obtained by a hybrid hard/soft templating approach. Three sets of conditions were chosen including absolute ethanol, ethanol: water and absolute ethanol with the addition of microcrystalline cellulose as a hard template; in all of the experiments P123 three block co-polymer was utilized as the soft template. Crystallite sizes, porosity and surface acidity were found to change drastically by modifying the initial synthesis conditions. The obtained samples were characterized using powder XRD, FESEM, SEM, TEM, DRS, EDS, N2-physisorption, DLS and zeta potential meter. Methyl violet, methyl orange and malachite green were chosen as representative organic pollutants with different chemistries and a series of experiments were performed under a high-pressure mercury lamp equipped with UV filter. It was found that the hierarchical titania sample works best to remove methyl violet from aqueous media while simpler nanostructures obtained with soft templating work better for methyl orange and malachite green. Based on the characterization results, possible enhancement mechanisms were proposed to explain the drastic differences between the performance of different samples for removing different organic dyes.