“Soft” Confinement of Graphene in Hydrogel Matrixes

Graphene plays as protagonist among the newly discovered carbon nanomaterials on the laboratory bench. Confinement of graphene, combined with enhanced exchange properties within aqueous environment, is key for the development of biosensors, biomedicine devices, and water remediation applications. Such confinement is possible using hydrogels as soft matrixes. Many entrapment methods focused on the modification of the graphene structure. In this paper, however, we address a confinement method that leaves unchanged the graphene structure, although intimately participating in the buildup of a network of polyvinyl alcohol (PVA) chains. PVA is a polymer known as biomaterial for its hydrophilicity, biocompatibility, and chemical versatility. A robust hybrid PVA – graphene construct was obtained starting from a surfactant-assisted sonication of an aqueous dispersion of graphite. Stable graphene sheets suspension was photopolymerized in a methacryloyl-grafted PVA, using the vinyl moiety present on the surfactant scaffold. This method can allow the incorporation in the polymer network of oligomers of <i>N-</i>(isopropylacrylammide), p­(NiPAAm). These chains display in aqueous solution a low critical solution temperature, LCST, around 33 °C and trigger a volume phase transition when incorporated in a hydrophilic network around the physiological temperature. Raman analysis was used to characterize the state of hydrogel embedded graphene single sheets. Evidence for an intimate interaction of graphene sheets and polymer matrix was collected. Release of the anticancer drug doxorubicin showed the active role of the graphene/PVA/p­(NiPAAm) construct in the drug delivery

Effects of Dopant Ionic Radius on Cerium Reduction in Epitaxial Cerium Oxide Thin Films

The role of trivalent rare-earth dopants on the cerium oxidation state has been systematically studied by in situ photoemission spectroscopy with synchrotron radiation for 10 mol % rare-earth doped epitaxial ceria films. It was found that dopant rare-earths with smaller ionic radius foster the formation of Ce³⁺ by releasing the stress strength induced by the cation substitution. With a decrease of the dopant ionic radius from La³⁺ to Yb³⁺, the out-of-plane axis parameter of the crystal lattice decreases without introducing macroscopic defects. The high crystal quality of our films allowed us to comparatively study both the ionic conductivity and surface reactivity ruling out the influence of structural defects. The measured increase in the activation energy of films and their enhanced surface reactivity can be explained in terms of the dopant ionic radius effects on the Ce⁴⁺ → Ce³⁺ reduction as a result of lattice relaxation. Such findings open new perspectives in designing ceria-based materials with tailored properties by choosing suitable cation substitution

Phenyl Derivative of Iron 5,10,15-Tritolylcorrole

The phenyl–iron complex of 5,10,15-tritolylcorrole was prepared by reaction of the starting chloro–iron complex with phenylmagnesium bromide in dichloromethane. The organometallic complex was fully characterized by a combination of spectroscopic methods, X-ray crystallography, and density functional theory (DFT) calculations. All of these techniques support the description of the electronic structure of this phenyl–iron derivative as a low-spin iron­(IV) coordinated to a closed-shell corrolate trianion and to a phenyl monoanion. Complete assignments of the ¹H and ¹³C NMR spectra of the phenyl–iron derivative and the starting chloro–iron complex were performed on the basis of the NMR spectra of the regioselectively β-substituted bromo derivatives and the DFT calculations

Vertical TiO₂ Nanorods as a Medium for Stable and High-Efficiency Perovskite Solar Modules

Perovskite solar cells employing CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> active layers show power conversion efficiency (PCE) as high as 20% in single cells and 13% in large area modules. However, their operational stability has often been limited due to degradation of the CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> active layer. Here, we report a perovskite solar module (PSM, best and av. PCE 10.5 and 8.1%), employing solution-grown TiO₂ nanorods (NRs) as the electron transport layer, which showed an increase in performance (∼5%) even after shelf-life investigation for 2500 h. A crucial issue on the module fabrication was the patterning of the TiO₂ NRs, which was solved by interfacial engineering during the growth process and using an optimized laser pulse for patterning. A shelf-life comparison with PSMs built on TiO₂ nanoparticles (NPs, best and av. PCE 7.9 and 5.5%) of similar thickness and on a compact TiO₂ layer (CL, best and av. PCE 5.8 and 4.9%) shows, in contrast to that observed for NR PSMs, that PCE in NPs and CL PSMs dropped by ∼50 and ∼90%, respectively. This is due to the fact that the CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> active layer shows superior phase stability when incorporated in devices with TiO₂ NR scaffolds