(I₂)<i>_n</i> Encapsulation inside TiO₂: A Way To Tune Photoactivity in the Visible Region

We report on the synthesis of nanovoid-structured TiO2 material via a sol−gel route using titanium isopropoxide as precursor. The nanovoids are formed during the thermal treatment in air at 773 K. The surfaces of internal cavities are populated by the partial oxidation products of the organic part of the Ti precursor (CO2, hydrogen carbonates, and residual isopropoxide groups). The thermal treatment in air at 773 K allows the maintainence, in the internal voids, of the encapsulated species. Addition of iodine in the synthesis procedure results in a new nanovoid-structured titanium oxide able to absorb light in the whole visible part of the electromagnetic spectrum. The origin of this absorption is attributed to the presence of (I2)n adducts encapsulated in the nanocavities. These species coexist with partial combustion products of isopropoxide groups. Due to the protection of the TiO2 walls, the (I2)n adducts are not destroyed by thermal treatments in air. We have investigated whether the electron promoted in the excited state of the dye* molecule (upon absorption of visible light from the (I2)n adducts) can be injected into either the TiO2 conduction band or some titanium-localized acceptor, followed by migration of the injected electron to the surface where it reduces adsorbed organic molecules. Preliminarily experiments conducted with sunlight show that the surface-specific efficiency of this process, tested by following the degradation of methylene blue, is about 10 times higher than that of the P25 commercial TiO2 photocatalyst

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

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 N2 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 H2O2, 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. Rep. Prog. Phys. 1999, 62, 765; Lamberti, C. Surf. Sci. Rep. 2004, 53, 1], is transferred to the field of photocatalysis for the first time

Zwitterion-Coated Iron Oxide Nanoparticles: Surface Chemistry and Intracellular Uptake by Hepatocarcinoma (HepG2) Cells

Nanoparticles (NPs) have received much attention in recent years for their diverse potential biomedical applications. However, the synthesis of NPs with desired biodistribution and pharmacokinetics is still a major challenge, with NP size and surface chemistry being the main factors determining the behavior of NPs in vivo. Here we report on the surface chemistry and in vitro cellular uptake of magnetic iron oxide NPs coated with zwitterionic dopamine sulfonate (ZDS). ZDS-coated NPs were compared to similar iron oxide NPs coated with PEG-like 2-[2-(2-methoxyethoxy)­ethoxy]­acetic acid (MEEA) to investigate how surface chemistry affects their in vitro behavior. ZDS-coated NPs had a very dense coating, guaranteeing high colloidal stability in several aqueous media and negligible interaction with proteins. Treatment of HepG2 cells with increasing doses (2.5–100 μg Fe/mL) of ZDS-coated iron oxide NPs had no effect on cell viability and resulted in a low, dose-dependent NP uptake, inferior than most reported data for the internalization of iron oxide NPs by HepG2 cells. MEEA-coated NPs were scarcely stable and formed micrometer-sized aggregates in aqueous media. They decreased cell viability for dose ≥50 μg Fe/mL, and were more efficiently internalized than ZDS-coated NPs. In conclusion, our data indicate that the ZDS layer prevented both aggregation and sedimentation of iron oxide NPs and formed a biocompatible coating that did not display any biocorona effect. The very low cellular uptake of ZDS-coated iron NPs can be useful to achieve highly selective targeting upon specific functionalization

Synthesis and Stability of Tagged UiO-66 Zr-MOFs

The development in the field MOF materials is moving from the discovery of new structures toward applications of the most promising materials. In most cases, specialized applications require incorporation of functional chemical groups. This work is a systematic investigation of the effect that simple substituents attached to the aromatic linker have on the stability and property to the parent MOF. A family of isoreticular MOFs, based on the UiO-66 structure was obtained from the three different linker ligands H2N−H2BDC, O2N−H2BDC, and Br−H2BDC. The physicochemical and chemical investigation of these materials demonstrate that this class of MOFs retains high thermal and chemical stabilities, even with functional groups present at the linker units. The results demonstrate the possibility of incorporating active functional groups into the UiO-66 structure almost without losing its exceptionally high thermal and chemical stability. It has been established that the functional groups, at least in the amino functionalized UiO-66 sample, are chemically available as evidenced by the H/D exchange experiment, making the tagged UiO series MOFs very interesting for further studies within the field of catalysis