Herme G. Baldoví

Visible‐Light Photoresponse of Gold Nanoparticles Supported on TiO2: A Combined Photocatalytic, Photoelectrochemical, and Transient Spectroscopy Study

In the context of gaining understanding on the origin of the visible-light photoresponse of TiO2 containing gold nanoparticles, the photocurrent spectra and photocatalytic H2 evolution of titania (P25) and Au-P25 were compared. Whereas no photocurrent was detected upon visible-light irradiation for either of the two photocatalysts, Au-P25 exhibited photocatalytic H2 evolution for wavelengths between 400 and 575 nm. This contradictory behavior under visible-light irradiation of Au-P25 was rationalized by transient absorption spectroscopy. It was suggested that photocatalytic H2 generation results from methanol quenching of the charge-separation state in each semiconductor nanoparticle, but the lack of photocurrent is due to the short lifetime of the charge separation, which makes interparticle charge migration for micrometric distances unlikely.

Transient absorption spectroscopy and photochemical reactivity of CAU-8

CAU-8 is a metal organic framework with the composition [Al(OH)(BPDC)] (BPDC: 4,4′-benzophenone dicarboxylate) whose structure is constituted by chains of corner-sharing AlO6 octahedra connected by BPDC linkers, giving rise to an array of non-intersecting channels. According to the well known photochemical behavior of benzophenone, in the present study we have been able to obtain spectroscopic evidence of the photochemical reactivity of CAU-8, including the generation of short-lived triplet excited states that react with either electron donors (triethylamine) or hydrogen donors (isopropanol) and lead to the corresponding radical anions or ketyl radicals, respectively. These two species have long half live times in CAU-8 and their decay is not complete hundreds of microseconds after the laser pulse. The photochemical activity of the BPDC linker in CAU-8 has been used to promote the radical-induced (co)polymerization of styrene and the coupling of BPDC and ethanol has been followed with IR spectroscopy.

Photoinduced Charge Separation on the Microsecond Timescale in Graphene Oxide and Reduced Graphene Oxide Suspensions

Transient absorption spectroscopy of graphene oxide (GO) and reduced graphene oxide (rGO) suspensions provides evidence for the photochemical generation of a charge-separated state on the microsecond timescale upon laser excitation. The lifetime and quantum yield of charge separation in suspended rGO were found to be higher than for GO. This could be advantageous for optoelectronic and photocatalytic applications, where graphene-based materials act as charge (electron) carriers. The electron-transfer quenching of the rGO charge-separated state by different amines is more efficient when the amine is a better electron donor and more easily oxidized.

Phthalocyanine-Gold Nanoparticle Hybrids: Modulating Quenching with a Silica Matrix Shell.

An asymmetrically substituted zinc phthalocyanine (ZnPc) with a terminal dithiolane group is anchored to Au nanoparticles (NPs) directly or through an interposed silica matrix. Transient absorption spectroscopy shows that the quenching of the ZnPc excited state by AuNPs occurs through a photoinduced electron transfer, the efficiency of which is modulated by the presence of the insulating silica matrix.

Gas-Phase Photochemical Overall H2S Splitting by UV Light Irradiation

Splitting of hydrogen sulfide is achieved to produce value-added chemicals. Upon irradiation at 254 nm in the gas phase and in the absence of catalysts or photocatalysts at near room temperature, H2 S splits into stoichiometric amounts of H2 and S with a quantum efficiency close to 50 %. No influence of the presence of CH4 and CO2 (typical components in natural gas and biogas in which H2 S is an unwanted component) on the efficiency of overall H2 S splitting was observed. A mechanism for the H2 and S formation is proposed.

Ceria nanoparticles with rhodamine B as a powerful theranostic agent against intracellular oxidative stress

Ceria nanoparticles with rhodamine B groups covalently attached on their surface (RhB-CeNPs) were successfully prepared to simultaneously exhibit antioxidant activity and the ability to detect oxidant species. In order to use them for biomedical purposes, the nanoparticles were internalized in two human cell lines (HeLa and Hep3B), confirmed by confocal microscopy. In addition, their biocompatibility was assessed by performing proliferation, viability and apoptosis assays, in which they showed a remarkable lack of toxicity. Thereafter, the antioxidant activity of RhB-CeNPs against reactive oxygen species (ROS) in a model of oxidative stress was demonstrated in HeLa cells using the dichloro-dihydro-fluorescein diacetate (DCFH-DA) assay. RhB-CeNPs exhibited higher cytosolic antioxidant activity than the well-established ceria nanoparticles. Surprisingly, the antioxidant capacity of RhB-CeNPs was evident when the ROS content of the cells increased notably (and was, therefore, harmful for those cells). Furthermore, the ability of RhB-CeNPs as ROS-content sensors was evaluated by measuring oxidative stress in HeLa cells using the intrinsic fluorescence of the rhodamine B groups present on the nanoparticles. The results with respect to the detection and quantification of ROS were similar to those obtained with DCFH-DA, a typical method of quantifying intracellular ROS. Our results demonstrate the potential of RhB-CeNPs as remarkably biocompatible theranostic agents with application in the field of oxidative stress.

Toxicological properties of two fluorescent carbon quantum dots with onion ring morphology and their usefulness as bioimaging agents

In the present work, two carbon quantum dots with onion ring morphology, C-NOR and C-NOR(Eu) with an average size of 40 nm differing in the absence or presence of Eu3+ as Lewis acids during their preparation were synthesized and fully characterized by several techniques. These nanoparticles can be internalized into human HeLa and Hep3B carcinoma cells where they exhibit interesting photoluminescent properties, in the same manner as in solution, confirming their utility as bioimaging agents. To address this possibility, a complete in vitro toxicological study has been performed here. Viability, proliferation, apoptosis and oxidative stress assessments upon limited or continuous exposure were done. It was observed that both nanoparticles did not show toxicity in both situations at low concentration, although some toxicity has been determined at higher concentrations under continuous exposure. These results support the possible use of C-NOR and C-NOR(Eu) nanoparticles as bioimaging agents.