Peptide based low molecular weight gelators

Over the last 12 months a number of papers have been published which shed light on the processes that control the self-assembly of peptides into fibrous hydrogel networks. A number of new properties of dipeptide hydrogels have also been reported. This article highlights recent activity in the area of peptide self-assembly, with a particular focus on tri-peptides, di-peptides and protected amino acids

Cs⁺ incorporation into CH₃NH₃PbI₃ perovskite:substitution limit and stability enhancement

In this study we systematically explored the mixed cation perovskite Csx(CH3NH3)1-xPbI3. We exchanged the A-site cation by dipping MAPbI3 films into a CsI solution, thereby incrementally replacing the MA+ in a time-resolved dipping process and analysed the resulting thin-films with UV-Vis, XRD, EDAX, SEM and optical depth-analysis in a high-throughput fashion. Additional in situ UV-Vis and time-resolved XRD measurements allowed us to look at the kinetics of the formation process. The results showed a discontinuity during the conversion. Firstly, small amounts of Cs+ are incorporated into the structure. After a few minutes, the Cs content approaches a limit and grains of δ-CsPbI3 occur, indicating a substitution limit. We compared this cation exchange to a one-step crystallisation approach and found the same effect of phase segregation, which shows that the substitution limit is an intrinsic feature rather than a kinetic effect. Optical and structural properties changed continuously for small Cs incorporations. Larger amounts of Cs result in phase segregation. We estimate the substitution limit of CsxMA1-xPbI3 to start at a Cs ratio x = 0.13, based on combined measurements of EDAX, UV-Vis and XRD. The photovoltaic performance of the mixed cation perovskite shows a large increase in device stability from days to weeks. The initial efficiency of mixed CsxMA1-xPbI3 devices decreases slightly, which is compensated by stability after a few days.</p

Sulfur-Doped Cubic Mesostructured Titania Films for Use as a Solar Photocatalyst

Sulfur-doped titania thin films with cubic mesostructures were prepared by dip coating via the evaporation induced self-assembly route. The effect of sulfur doping on structure, morphology, porosity, optical properties, and photocatalytic activity of the mesoporous films was studied. Compared to undoped titania films, the S-doped films showed better long-range ordering, bigger pore size, higher porosity, less shrinkage of the structure during calcination, a red-shift of the band gap, and a more hydrophilic surface. These characteristics led to an improved photocatalytic activity when the S-doped and undoped titania films were tested for degradation of methylene blue in aqueous solutions under the irradiation of 1 sun from a solar simulator. The photocatalytic activity of the sulfur doped titania film was stable during three consecutive experiments under solar light irradiation, confirming the mechanical stability and reusability of the doped nanostructured thin film photocatalysts

Ordered mesoporous particles in titania films with hierarchical structure as scattering layers in dye-sensitized solar cells

This work aimed to understand the relationship between the physical properties of scattering particle layers in dye-sensitized solar cells (DSSCs) and their performance, to assist optimization of this component of the DSSC. Highly ordered anatase 2D-hexagonal mesoporous titania (meso-TiO₂) nanoparticles with a high surface area and large pore size were fabricated. Meso-TiO₂ was used as scattering particles and mixed with titania nanocrystallites at weight proportions ranging from 0 to 100%. Films made from the composites were used as scattering layers in DSSCs. The influence of meso-TiO₂ proportion on the structure, morphology, and optical properties of the films were investigated. The results show that the films became more porous, with a larger surface roughness, and had higher surface areas and greater light-scattering effects when meso-TiO₂ was incorporated. The performance of these scattering layers in relatively large, 1 cm² area, DSSCs was studied to link cell performance to the detailed physical properties of the meso-TiO₂/nanoparticle films. The optimum composition of scattering layers was obtained by mixing 50 wt % meso-TiO₂ with titania nanoparticles

Halogen effects on ordering and bonding of CH₃NH₃ ⁺ in CH₃NH₃PbX₃ (X = Cl, Br, I) hybrid perovskites:a vibrational spectroscopic study

This study reports Raman and infrared spectra of hybrid organic-inorganic MAPbX3 perovskites (MA = CH3NH3, X = Cl, Br, I) and their mixed-halide derivatives. Raman spectra were recorded at three laser wavelengths (514, 785, and 1064 nm) under on- and off-resonance conditions, as well as at room temperature and 100 K. The use of different excitation wavelengths allowed the unambiguous acquisition of "true" Raman spectra from the perovskites, without degradation or photoinduced structural changes. Low-frequency PbX vibrational modes were thoroughly identified by comparison of Raman and far-IR results. Red Raman frequency shifts for almost all MA vibrations from 200 to 3200 cm-1, and particularly intense for the torsional mode, were observed toward heavy halide derivatives, indicative of strengthening the interaction between halides and the organic cation inside the inorganic cage. Different MA-X bonding schemes are evidenced by torsional mode pairs emerging in the orthorhombic phase. MAPbBr3 was further characterized by variable temperature Raman measurements (100-295 K). Broadening of the MA rocking mode slightly above the tetragonal I to II phase transition is connected with disorder of the MA cation. Our results advance the understanding of perovksite materials properties (ferroelectric domain formation, anomalous hysteresis) and their use as efficient light absorbers in solar cells.</p

Azulene – Thiophene – Cyanoacrylic acid dyes with donor-π-acceptor structures. Synthesis, characterisation and evaluation in dye-sensitized solar cells

We report the synthesis of five new azulene containing dyes, having D-π-A type structures. These dyes are synthesised using a sulfonium salt cross-coupling reaction. The dyes have been evaluated spectroscopically, electrochemically, crystallographically, and as sensitizers in dye-sensitized solar cells. We propose a rationale for the dyes’ spectroscopic properties and performance in cells, based on conformational data derived from their crystal structures.</p

Nanostructured WO₃ photoanodes for efficient water splitting via anodisation in citric acid

We report the production of nanostructured WO3 photoanodes for solar water splitting produced via anodisation using for the first time citric acid, a safer and more environmentally friendly alternative to fluoride-based electrolytes.</p