Tailoring the Selectivity of Ti-Based Photocatalysts (TiO₂ and Microporous ETS-10 and ETS-4) by Playing with Surface Morphology and Electronic Structure

Abstract

In the first part of this work we report an exhaustive characterization of the bulk and surface properties of ETS-4 and ETS-10 microporous titanosilicates by means of combined N 2 volumetric measurements, SEM, IR, Raman, and UV-Vis techniques. The structure of the surface titanols, derived from literature XRD studies, is shown using a molecular graphic approach. UV-Vis titration experiments using H 2 O 2 , and catechol molecules, allowed us to directly measure the total number of available titanols (both in the channels and on the crystal external surface) and the surface titanols, respectively. In the second part of the paper, the ability of ETS-4 and ETS-10 (and of the standard P25) in the photodegradation of phenol (P), 4-chlorophenol (CP), 2,5-dichlorophenol (DCP), 2,4,5-trichlorophenol (TCP), 1,3,5-trihydroxybenzene (THB), and 2,3-dihydroxynaphthalene (DHN) is investigated, using both UV and visible lights, exciting above and below the materials energy gap, respectively. While microporous ETS-4 and ETS-10 exhibit a significant selectivity in the photodegradation of the above-mentioned molecules using both lights, P25 selectivity is observed with visible light only. This means that besides the inverse shape selectivity effect already observed for the microporous materials [Xamena et al. J. Am. Chem. Soc. 2003, 125, 2264, selectivity may be achieved also by selecting the excitation light in accordance with the electronic transition of the adsorbed molecule (determined by a previous systematic UV-Vis study). In such a case the photodegradation may occur if the conduction band of the Ti-based material is opportunely matched with the LUMO level of the adsorbed molecule so that it can receive the electron of the excited adsorbate. The concept of band alignment, well-established in the field of solid-state physics applied to semiconductor heterostructures [Margaritondo, G.

Carbon-Doped TiO2 and Carbon, Tungsten-Codoped TiO2 through Sol–Gel Processes in the Presence of Melamine Borate: Reflections through Photocatalysis

“…The smaller crystalline particle size and increased surface area of the material calcined only for 1 h appear to have enhanced the photocatalytic activity. Furthermore, even though neither TiO 2 nor Chlorophenol (CP) absorb visible light it has been reported that the TiO 2 -CP ads system has charge transfer bands that can absorb such radiation [54][55][56][57]. Kim and Choi have shown that charge carriers can be generated from the excitation of these charge transfer states and that there remains the possibility for a variety of photochemistries to result from reaction of these charge carriers.…”

Probing Photocatalytic Active Sites on a Single Titanosilicate Zeolite with a Redox‐Responsive Fluorescent Dye

“…Single-crystal Raman spectroscopy measurements also support the hypothesis that the partial dissociation of titania wires in ETS-10 by HF treatment produces the surface active sites ( Figure S8 in the Supporting Information). [3] Experiments on a single crystal provide useful information for elucidating the inherent heterogeneity of reaction processes occurring at the solid-liquid interface. Figure 3 shows an example of the influence of crystal defects on the photocatalytic oxidation of APF molecules.…”

“…[1][2][3] In a defect-free crystal, charge carriers, that is, electrons and holes, are generated by the irradiation with photons with an energy corresponding to the band gap of approximately 4 eV. These carriers migrate in the crystal through the wires.…”

“…However, the wires are broken at random points in the crystal because of inherent defects; these defects form active centers for molecular adsorption and redox reactions. [3][4][5][6] To date, the influences of structural defects in ETS-10 on the adsorption and reaction dynamics of organic compounds have not been well characterized, possibly because of the heterogeneous distribution of active sites in the material.…”

Oriented TiO2 Nanostructured Pillar Arrays: Synthesis and Characterization

“…The first centers on tailoring of the size, shape, and threedimensional organization of TiO 2 particles [1,2,11,12] or of Ti-O-Ti wires with semiconductor character. [5,[13][14][15][16] The second strategy focuses on improving the photocatalytic properties: i) by incorporating metal cations and anions (mainly nitrogen, sulphur, iodine, and other elements) into the bulk; [6,14,[17][18][19][20][21][22][23] ii) by supporting metal particles (mainly Au, Ag, Pt, Ni). [1,3,[24][25][26][27][28][29][30][31] Interesting results are obtained when the two abovementioned research directions are combined to benefit from the sum of their advantages.…”