María S. Galletero

Tuning the photocatalytic activity of titanium dioxide by encapsulation inside zeolites exemplified by the cases of thianthrene photooxygenation and horseradish peroxidase photodeactivation

A series of Y, Beta, mordenite and ZSM-5 zeolites containing different amounts of nanosized TiO2 clusters have been prepared by TiO2+ exchange followed by condensation. The presence of TiO2+ and its subsequent oligomerization can be followed in Raman spectroscopy by the appearance of the band at ca. 530 cm−1 and its replacement by others at 394, 460 and 637 nm. X-ray diffractograms of the solids show a considerable intensity decrease as the amount of TiO2 present increases. High-resolution transmission electron microscopy (HRTEM) shows that no isolated TiO2 particles are present in the case of zeolite Y, while the sample of mordenite at the highest Ti loading contains isolated TiO2 particles distinguishable by HRTEM. Diffuse reflectance UV-Vis spectroscopy indicates that the bandgap and the apparent extinction coefficient depend remarkably on the Ti content as well as on the zeolite crystal structure. Quantum chemical calculations at the semiempirical level also predict large variations in the HOMO–LUMO energies as a function of the number of Ti atoms. It has been found that the photoactivity of TiO2@Y and TiO2@mordenite is higher than that of commercial anatase for the photooxygenation of thianthrene to thianthrene oxide (λex>200 nm), but smaller for the hoseradish peroxidase photodeactivation in aqueous buffer (λex=350 nm). These variations in the photocatalytic activity of TiO2 illustrate the potential that inclusion of TiO2 nanoclusters within zeolites has to modulate its photoactivity.

Pyrene covalently anchored on a large external surface area zeolite as a selective heterogeneous sensor for iodide

Pyrene as a fluorophore has been covalently anchored on a delaminated ITQ-2 zeolite having a large external surface area (730 m2 g-1) and the resulting solid found to have a selective response as a heterogeneous sensor for I- in the presence of other halides.

Prevalence of the external surface over the internal pores in the spontaneous generation of tetrathiafulvalene radical cation incorporated in the novel delaminated ITQ-2 zeolite

ITQ-2 is a novel delaminated zeolite whose crystalline sheets (2.5 nm depth) define a large external surface (∽720 m2 g−1) having 12-membered ring (MR) open cups together with a reduced microporosity due to a 10 MR channel system. This feature is the reverse of that of classical zeolites (i.e., much larger internal area compared to the external surface). Herein, we have used tetrathiafulvalene and triphenylamine to probe the capability of layered ITQ-2 zeolite to generate persistent organic radical cations compared to conventional Y, mordenite and ZSM-5 zeolites as well as to Al/MCM-41 (3.2 nm diameter) and amorphous silica–alumina. By selective silylation of the external cups, it has been found that formation of a significant concentration of persistent organic radical cations in ITQ-2 is a property that occurs within the open cups of the external surface rather than inside the 10 MR pores.

Dramatic persistence (minutes) of the triplet excited state and efficient singlet oxygen generation for C60 incorporated in Y zeolite and MCM-41 silicate

Abstract The triplet excited state of C 60 ( λ max =780 nm) lives minutes and can be monitored by conventional spectrophotometers when this fullerene is incorporated inside LiY, as opposed to C 60 @HY and C 60 @MCM-41 wherein C 60 triplet lives in the submillisecond time scale. C 60 adsorbed in LiY or MCM-41 efficiently generates 1 O 2 that was detected by its characteristic NIR emission (λ em =1270 nm ) .

Spontaneous doping and magnetic properties of polyacetylene and polypropyne synthesized in situ in Ni-exchanged mordenite and mesoporous MCM-41

Upon polymerisation of acetylene and propyne inside the channels of Ni2+-exchanged mordenite and mesoporous MCM-41 spontaneous doping and formation of antiferromagnetic NiO clusters are observed to various extents. The population of polarons present in the final polymer/zeolite composite: (i) is higher for polyacetylene than for polypropyne; (ii) increases with polymerisation temperature in the range 100 to 335 °C; (iii) increases with the C content; and (iv) is higher for mordenite than for MCM-41 under the same conditions. The use of Ni(0),H+-mordenite for polymer formation enhances the polaron population of the resulting polymer by over one order of magnitude. Doped polyacetylene encapsulated in mordenite or MCM-41 was found to be persistent for periods of over three months after its preparation.

Photophysical properties and fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene in zeolites

Abstract 2,3-Diazabicyclo[2.2.2]oct-2-ene (DBO) was used as a long-lived fluorescent probe in zeolites (NaY, Na-mordenite, Na-ZSM-5, H-ZSM-5) and related oxide materials (all silica MCM-41, silica, silica–alumina, γ-alumina). The photophysical properties are dominated by a hydroxylic environment, caused by the inorganic framework and co-adsorbed water. The quenching of DBO by oxygen was strongly dependent on the type of zeolite. In ZSM-5 zeolites, the fluorescence decays were not monoexponential in the presence of oxygen (air).

Electrocatalysis of neurotransmitter catecholamines by 2,4,6-triphenylpyrylium ion immobilized inside zeolite Y supercages

2,4,6-Triphenylpyrylium ions entrapped inside the supercages of Y zeolite exert a remarkable catalytic effect toward the electrochemical oxidation of dopamine and norepinephrine (neurotrasmitter catecholamines) in neutral aqueous media.

Evidence for through-framework electron transfer in intrazeolite photochemistry. Case of Ru(bpy)32+ and methylviologen in novel delaminated ITQ-2 zeolite

A sample of novel delaminated zeolite ITQ-2 containing Ru(bpy)3(2+) on the external cups and MV2+ included in the independent and not connected channels has been prepared; emission and time-resolved laser flash photolysis has shown unambigously that photoinduced electron transfer from Ru(bpy)3(2+) to MV2+ occurs through the zeolite framework.