The conclusions reached by a diverse group of scientists who attended an intense 2-day workshop on hybrid organic-inorganic perovskites are presented, including their thoughts on the most burning fundamental and practical questions regarding this unique class of materials, and their suggestions on various approaches to resolve these issues.

In the context of studying the feasibility of photocatalytically self-cleaning windows and windshields, clear, abrasion resistant, photocatalytic films of TiO2 were formed on soda lime glass and on fused quartz by a sol-gel process. The rate of photooxidation of contaminant deposits was estimated by measuring the rate of decrease in the integrated IR absorbance associated with the C-H stretching vibrations of a thin solution-cast film of stearic acid under 365 nm (2.4 mW/cm2) or 254 nm (0.8 mW/cm2) irradiation. Approximately 3 X 1 0 " * stearic acid molecules were stripped per 365 nm photon in either front-or back-illuminated soda lime glass, and 6 X 10"* molecules when the films were coated on fused quartz. For thin TiO2 films on fused quartz, the rate of photooxidation, normalized by the number of photons absorbed per unit area, was independent of the wavelength. In contrast, for films on soda lime glass, the rate of photooxidation, when similarly normalized, was higher for the less penetrating wavelength. The reduced photoactivity on glass at the deeply penetrating wavelength (365 nm), as well as the greater photoefficiency on quartz than on glass, are attributed to diffusion of sodium oxide from the glass into the inner glass-contacting zone of the T1O2 layer.

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This brief review aims at analyzing the use of dyestuffs for evaluating the photocatalytic properties of novel photocatalysts. It is shown that the use of dyes as predictors for photocatalytic activity has its roots in the pre visible-light activity era, when the aim was to treat effluents streams containing hazardous dyes. The main conclusion of this review is that, in general, dyes are inappropriate as model compounds for the evaluation of photocatalytic activity of novel photocatalysts claimed to operate under visible light. Their main advantage, the ability to use UV-Vis spectroscopy, is severely limited by a variety of factors, most of which are related to the presence of other species. The presence of a second mechanism, sensitization, diminishes the generality required from a model contaminant used for testing a novel photocatalyst. While it is recommended not to use dyes for general testing of novel photocatalysts, it is still understandable that a model system consisting of a dye and a semiconductor can be of large importance if the degradation of a specific dye is the main aim of the research, or, alternatively, if the abilities of a specific dye to induce the degradation of a different type of contaminant are under study.

Composite nanofibers containing nanometric TiO2 particles and multiwalled carbon nanotubes dispersed in poly(acrylonitrile) (PAN) were prepared by the electrospinning technique. The structure and quality of the precursor dispersions were evaluated by cryo-transmission electron microscopy. The fabricated nanofibers, the diameters of which were in the 20-200 nm range, contained well-oriented nanotubes and spherical TiO2 nanoparticles in close proximity. Such nanofibers are under investigation as new photocatalytic reactor elements.

In the context of photocatalytically self-cleaning windows and windshields, clear, abrasion resistant, thin (60 ± 10 nm) photocatalytic films of TiO2 were formed by a sol-gel process on (a) soda lime glass, (b) the proton-exchanged surface of soda lime glass, and (c) fused silica. The hypothesis that diffusion of sodium oxide from the soda lime glass into the titanium dioxide layer during the calcination step causes the lower photoefficiency in films on glass was tested and proven. At high concentration sodium prevented formation of the photoactive anatase phase and, at low concentration, introduced surface and bulk recombination centers. Sodium transport was efficiently blocked by a thin layer at the interface of proton-exchanged (“hydrogen”) glass and nascent TiO2, formed at 400 °C of a poly(titanyl acetylacetonate) TiO2 precursor. The sodium transport blocking layer did not form and the highly photocatalytic film was not obtained when the TiO2-precursor film was applied to glass that was not proton exchanged. Furthermore, only a much less effective sodium transport blocking layer was formed on glass that was proton-exchanged, but was calcined at 400 °C prior to application of the TiO2 precursor layer, showing that the sodium depleted glass surface, by itself, was a less effective barrier against sodium transport than the interfacial product of hydrogen glass and the TiO2 precursor.

The LCST phase-transition of aqueous PNIPA solutions in rising concentrations of the strong chaotropic salt KSCN was studied microcalorimetrically by DSC and apparently for the first time by ITC. An endothermic (entropy driven) binding of KSCN onto PNIPA was observed, explained by electrostatic perturbation of hydrophobic hydration by adsorbed ions. A good fit was found for the one-typeof-sites binding model, and the binding affinity increased with rising temperature from 15 to 20 °C but decreased at 25 °C. DSC measurements emphasized the lowering and broadening of the endothermic peak of PNIPA phase-transition with rising KSCN concentration, explained by reduced cooperativity of coil-toglobule collapse with increased heterogeneity along the polymer chain, caused by salt adsorption. A hysteresis was observed between heating and cooling DSC peaks, which decreased asymptotically with rising KSCN concentration, further supporting that binding occurs. This work provides new insights into the mechanisms of chaotropic salt effects on polymers and biopolymers in aqueous solutions.

A cross-linked self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) was chemisorbed on well-defined structures, comprised of alternating microstripes of TiO2 and silicon. The kinetics of the photodegradation of the anchored SAM on the hybrid structure was then measured in situ by FTIR under controlled humidity and surface temperature. It was found that mineralization of the aliphatic chains anchored to the inert silicon domains can occur, even when these chains are located as far as 20 μm away from the photocatalytic titanium dioxide microdomains. An apparent first-order kinetics was found for each of the two domain types. Apparent activation energies were calculated on the basis of the temperature-dependent measurements. The observation that the oxidizing species can induce mineralization far from the locus of their formation may have large effect on the design and modeling of porous photocatalysts having “dark” pores and on the developing of hybrid photocatalysts.