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Despite the increasing demand for enantiopure drugs in the pharmaceutical industry, currently available chiral separation technologies are still lagging behind, whether due to throughput or to operability considerations. This paper presents a new kinetic resolution method, based on the specific adsorption of a target enantiomer onto a molecularly imprinted surface of a photocatalyst and its subsequent degradation through a photocatalytic mechanism. The current model system is composed of an active TiO2 layer, on which the target enantiomer is adsorbed. A photocatalytic suppression layer of Al2O3 is then grown around the adsorbed target molecules by atomic layer deposition. Following the removal of the templating molecules, molecularly imprinted cavities that correspond to the adsorbed species are formed. The stereospecific nature of these pores encourages enantioselective degradation of the undesired species through its enhanced adsorption on the photocatalyst surface, while dampening nonselective photocatalytic activity around the imprinted sites. The method, demonstrated with the dipeptide leucylglycine as a model system, revealed a selectivity factor of up to 7 and an enrichment of a single enantiomer to 85% from an initially racemic mixture. The wide range of parameters that can be optimized (photocatalyst, concentration of imprinted sites, type of passivating layer, etc.) points to the great potential of this method for obtaining enantiomerically pure compounds, beginning from racemic mixtures.

Surface chemistry plays a major role in photocatalytic and photoelectrochemical processes taking place with the participation of TiO2. The synthesis methods, surface characterizations, theoretical research methods, and hardware over the last decade generated opportunities for progress in the surface science of this photocatalyst. Very recently, attention was paid to the design of photocatalysts at the nanoscale level by adjusting the types of exposed surfaces and their ratio, the composition and the surface structure of nanoparticles, and that of individual surfaces. The current theoretical methods provide highly detailed designs that can be embodied experimentally. The present review article describes the progress in the surface science of TiO2 and TiO2-based photocatalysts obtained over the last three years. Such aspects including the properties of macro- and nano-scale surfaces, noble-metal-loaded surfaces, doping with Mg and S, intrinsic defects (oxygen vacancies), adsorption, and photoreactions are considered. The main focus of the article is on the anatase phase of TiO2.

Transient FTIR measurements were performed on graphitic carbon nitride using a step-scan method, facilitating temporal resolution of a few nanoseconds. Variations in the location and the intensity of specific peaks and emerging of new peaks were observed during the first 170 nanoseconds after excitation. A comparison was made between graphitic carbon nitride prepared at two temperatures: 510 °C and 650 °C. The material prepared at 650 °C revealed very strong non-specific absorption beginning 35 nanoseconds after excitation and lasting for 20 nanoseconds. This phenomenon, termed “IR-blackening” was observed neither in g-C3N4 prepared at 510 °C nor in g-C3N4 prepared at 650 °C that was exposed to hole scavengers (ethanol and benzyl alcohol). In contrast, exposure of material prepared at 650 °C to an electron scavenger (methyl viologen) hardly alter the “IR-blackening” phenomenon. The results were explained by a mechanism, predicting higher reductive activity for materials having imperfect heptazine polymerization, as indeed was found in the photocatalytic degradation of 4-nitrophenol.

Background: Recent years have seen the increased use of antibiotics and hormones in domestic, agricultural and healthcare applications. As a result, waste streams contain more and more of these compounds, which eventually end up in the environment, where they might cause serious damage to flora and fauna, even in miniscule amounts. This issue is currently not resolved by conventional waste treatment plants, as their adequacy for handling these compounds, many of which are non-polar, is quite limited. Objective: This work studies the effect of modifying the hydrophilic photocatalyst TiO2 with various rare earth oxides (REOs), of the lanthanide family (Er, La, Gd, Ce), on the photocatalytic activity toward degrading non-polar compounds. Ciprofloxacin, a widely used antibiotic, was chosen as a model hydrophobic compound. Its degradation rate was compared with that of caffeine, used as a model hydrophilic compound. Methods: Fused silica plates were coated with REO-containing films comprising TiO2 and silica. The latter was used as a binder to assure high integrity and strong adherence of the films to their substrates. The plates were characterized by SEM, EDS, XPS, and scratch-resistance measurements. The photocatalytic kinetics were determined with UV-Vis spectroscopy (caffeine) or fluorescence spectroscopy (ciprofloxacin). Further information was obtained by measuring the kinetics in the presence of charge scavengers and by SEM-EDS mapping of the surface following photodeposition of platinum. Results: Most REOs-modified TiO2 coatings showed increased activity and selectivity towards ciprofloxacin compared to coatings that did not contain REOs. A study on the silica binder's role suggests that the binder's hydrophobicity plays an important role in promoting ciprofloxacin degradation. With respect to REOs contribution, SEM-EDS mapping of REOs-containing films indicated that the REOs act as electron sinks, despite the position of their conduction bands. This charge accumulation is likely responsible for the contribution of the REOs to the enhanced degradation of ciprofloxacin. The hydrophobicity of lanthanide oxides, while affecting the adsorption of the non-polar ciprofloxacin, cannot explain the observed effects. Conclusion: Oxides of erbium, gadolinium and lanthanum may be used to increase photocatalytic rates via electron accumulation, despite the location of their conduction bands. This is in parallel to their effect as adsorption promotors of hydrophobic compounds

Hydrogen sulfide is a hazardous contaminant that may appear in well-water and in sewage streams. Here we present a very efficient way for the removal of H2S from well-water, based on combining UVC light and oxygen. The method was tested with H2S-enriched tap water as well as with natural well water, both of which containing up to 20 mg/L of H2S. A conversion of up to 90% was obtained within a residence time of no more than a few minutes. The quantum efficiency, defined as the ratio between the number of removed H2S molecules to the number of impinging photons, was found to be as high as 70%, depending on conditions. The main product was found to be sulfate, without the appearance of elemental sulfur, i.e. with no major change in turbidity. The absence of sulfur in the outlet stream in of large importance when treating H2S-containing well-water, since it omits the need for posttreatment removal of particles. Results are explained by the excitation of HS− species, following by formation of polysulfide anions that readily react with any formed elemental sulfur, eventually yielding sulfate ions.

BACKGROUND: Understanding the structures and properties of photocatalysts requires the developing of computational quantum models. The present study is devoted to calculating structures, bands positions and location of the HOMO/LUMO orbitals in anatase titanium dioxide (TiO₂) nanoparticles comprising of exposed (001) and (100) surfaces of various sizes having different extent of hydroxylation at their edges. The (001) surface was left intact or was reconstructed by introducing an additional row of atoms every four unit cells. Two computational approaches were compared: self‐consistent charge density‐functional tight‐binding (SCC‐DFTB) and PM6. RESULTS: The SCC‐DFTB method was found to be, for most cases, superior to the PM6 method in terms of structure, band positions and electronic orbitals. Based on the SCC‐DFTB approach it was concluded that the presence of the (1 × 4) reconstruction was essential for keeping the (001) surface flat. Otherwise the surface undergoes anisotropic shrinking and bending, which contradicts experimental data. The band gap of the de‐hydroxylated or partially hydroxylated nanoparticles was always smaller than that of nanoparticles with hydroxylated edges. No clear quantum size effects were found for these nanoparticles. Photogenerated non‐thermalized holes were found to localize around (001) facets and at their edges, while electrons tended to concentrate over the central parts of the (100) facets. CONCLUSION: Efficient separation of charge carriers is predicted for anatase nanoparticles having (001) and (100) external surfaces. This conclusion, and moreover, the approach of using SCC‐DFTB calculations to study faceting effects, is likely to be relevant to the developing of new, highly active, photocatalysts as well as for fundamental studies of adsorption. © 2020 Society of Chemical Industry

A unique structure of a thin layer consisting of cesium iodine, manifested by a “ladder-like” fractal structure formed by spin-coating is reported herein. The ladder-like structure is made of mm-size domains, each comprising of a highly correlated, perpendicularly interconnected, network of CsI lines. Each line served as the growth origin of 2–3 levels of short, perpendicularly-oriented CsI crystals, yielding a fractal dimension of 1.53. The observed structure differs from common Diffusion Limited Aggregation (DLA) shapes by the absence of any morphological indicators that may point on the origin of growth. Furthermore, the perfect orthogonal alignment of all junctions in the CsI structure is very rare in DLA type of growth. A formation mechanism is presented, based on studying the evolution of this structure at different spinning rates and on a variety of substrates. It is proposed that this unique structure originates from a rare combination of conditions: strong anisotropy in surface energy between different facets arising from the primitive ionic crystal of CsI, the strong water-breaking property of cesium ions and an unusual effect of mesoporous substrates in preventing premature nucleation.

Nanostructured TiO2 is the most widely studied photocatalytic material and is used in self-cleaning coatings in buildings and for Cultural Heritage applications. To extend the photocatalytic activity of nanocrystalline titania into the visible spectral range, doping of titania by non-metal elements as N, C, F and S is currently widely investigated. Here we report tests on carbonatic Travertine stones coated with two self-cleaning coatings based on N-doped TiO2 nanoparticles. The two coatings, both obtained by sol-gel synthesis, differ by their titanium precursors and nitrogen sources. The obtained nanoparticles were characterized by X-ray diffraction, UV–VIS absorption, Raman and X-ray photoelectron spectroscopies. The harmlessness of the coatings is demonstrated by colorimetric analysis and by capillary absorption measurements. The self-cleaning properties of the treated stones were evaluated by the measurement of water contact angle and of organic dyes degradation as a function of UV–VIS light irradiation time. The results confirm that the synthesized nanoparticles were successfully doped with nitrogen, allowing a photocatalytic activity, even in the visible range, comparable or better than that shown by P25 Evonik commercial product. A comparison between coating where the dopants are introduced by an acidic process and coating doped using urea as the nitrogen source revealed higher activity for the former. The importance of the nature of the dye in the evaluation of the self cleaning properties is discussed.

BACKGROUND Water purification is challenged by the co-presence of contaminants, some of which are too toxic for bacteria or too opaque for photocatalytic processes. This challenge may be overcome by utilizing two types of reactors (for example biological and photocatalytic) operating in sequence. Realization of this approach should be based on a steady state model for calculating the optimal design under nominal conditions, a non-steady state responding to fluctuating conditions and fast measurement of toxicity and turbidity. RESULTS A steady-state model, examining the effect of coexisting toxicity and turbidity on the optimal sequence, on the relative retention times in the two reactors and on the effect of recycling, under an estimated cost function constraint is presented. It was found that the optimal sequence depends on the relative importance of toxicity and turbidity, that a single branch operation is likely to be more cost effective than dual branch (Bio→photocatalytic in parallel with photocatalytic→Bio) system. CONCLUSION It is recommended to add the possibility for altering flow direction to account for operation under non-nominal conditions. To decrease instability during flow-direction switching, a recycling option should be added. Recycling may also be beneficial in particular when the activated biological medium has sluggish kinetics. © 2017 Society of Chemical Industry

Nanocrystalline nitrogen-doped TiO2 photocatalysts were applied as surface coatings to three typical Israeli limestones, Maccabim, Halila and Hebron, widely used for historic buildings. Two different N-doped TiO2 sols were synthesised by sol-gel method starting from titanium oxysulfate ( TiOSO4 as Ti precursor: a new N-doped TiO2 coating (N-TiF), obtained in neutral conditions, was developed and compared to a N-doped TiO2 (N-TiA), obtained in acidic medium. XRD and Raman spectroscopy confirm the nanocrystalline nature of N-doped TiO2, mainly in anatase phase, with size similar to 4 nm as revealed by TEM analysis. Diffuse Reflectance Spectroscopy indicates a red-shift in the absorption spectra for both nanopowders, even if the X-ray Photoelectron spectroscopy results are not conclusive on the state and location of the N doping ions. The self-cleaning efficiency of the two TiO2 coatings was assessed on the three Israeli carbonate stones and compared to commercial TiO2 (Evonik P25) by the photoinduced degradation of two organic dyes (Methyl orange and Rhodamine B) and by following hydrophilicity changes, through static contact angle measurements. The harmlessness of these coatings was confirmed by colorimetric and water capillary absorption measurements.

Graphitic carbon nitride (g-C3N4) is a fascinating visible-light-responsive conjugated polymer with appealing characteristics for applications in the solar to fuel conversion arena. Specifically, the morphology of hollow nanoscale spheres decorated with metal cocatalyst attracts attention for the water splitting reaction. Here, we reveal general challenges relating to proper conjugation of this layered material with Pt, with regards to both efficiency of charge separation and long-term stability. We correlate photocatalytic activity towards water splitting and the oxidation half-reaction with transient IR measurements, which provide indirect information on the whereabouts of photoinduced charge carriers. These transient spectral changes were found to be as long as 100 ns in g-C3N4 hollow spheres. The addition of Pt nanoparticles as cocatalysts resulted in nearly 3-fold improvement in activity towards water oxidation half-reaction. Yet, this improvement was short lived. It seems that the Pt domains, which likely grow on primary and secondary amino sites, provide an avenue for trapping holes in shallow traps for a time that is sufficient for them to participate in redox reactions, while still maintaining enough oxidative power. The benevolent effect of platinum was found to be hampered by insufficient stability of the Pt attachment to the surface of the g-C3N4.

Bismuth vanadate is an appealing candidate for photocatalysis. In a quest to clarify the effect of phase and shape on its photocatalytic activity, four types of particles, differing in phase and shape, were prepared, characterized and studied. Monoclinic particles having a prismatic shape as well as tetragonal particles were found to be more active towards Cr(VI) reduction than a mixed phase or octahedron-shaped monoclinic particles. A negative correlation was found between the activity and the concentration of oxygen vacancies near the surface. Transient IR measurements following pulsed excitation revealed temporal changes in the spectra, prevailing for dozens of nanoseconds. A negative correlation between the duration of the IR transient signal and the photocatalytic activity was found. The observations made by the transient step-scan FTIR technique clearly demonstrate the potential of this technique as a tool for understanding, rationalizing, or even predicting the activity of photocatalytic materials.

Synthetic derivatives of flavins were covalently attached to the surfaces of BiOCl particles as photosensitizers for facilitating the heterogeneous photocatalytic degradation of organic molecules under visible light. The anchored flavins, tethered through their N3 position, were found to significantly (up to more than 6 times) increase the ability of BiOCl to oxidize salicylic acid upon exposure to visible light. The extent of rate enhancement was found to depend on the type of synthetic flavin, where a compound having a conjugated linker was found to be more active than flavins with nonconjugated linkers. Two competing mechanisms are discussed: One is based on flavin photoexcitation followed by charge transport from the excited flavin to the BiOCl solid support phase. A second (parallel) mechanism hinges on BiOCl photoexcitation instead, followed by charge injection in the opposite direction.

BiYWO 6 is considered to be a promising visible light-active photocatalyst, however, so far there were no reports on its preparation by low-temperature routes. In this work, BiYWO 6 was synthesized by sol–gel and by hydrothermal routes for the first time. Its photocatalytic visible light activity was evaluated by following the degradation of resazurin (Rz) while decoupling between photocatalysis, photosensitization and photolysis. The various preparation routes yielded different morphologies which resulted not only in different optical properties but also in different tendencies to form the stable intermediate product resorufin. These low-temperature methods pave the way for the fabrication of well-adhered Bi 2− x Y x WO 6 electrodes.

Si–SiO2 interface plays an important role in the performance of VLSI devices. Minor changes in interfaces, which cannot be detected by direct measurements, can alter the electrical performance of sensitive devices, for example CMOS Image Sensors (CIS). In such cases, there is a significant time delay (up to several months) between the processing of the interface and the monitoring of its quality. In what follows, we describe herein a method for analyzing the quality of Shallow Trench Isolation (STI) interface based on analyzing the performance of a simple STI interface named as Sensitive High Resistance Structure (SSHR). This testing device can be introduced in the production line as a “short loop” monitoring device. The method was demonstrated by comparing various cleaning treatments while analyzing the resistivity and breakdown voltage of the SSHR device. Results were correlated with STI-sensitive final products such as CIS and Lateral Diffused Metal Oxide Semiconductor (LDMOS) transistors.

During recent years there has been a growing tendency to study new photocatalysts for water and air treatment. To large extent this endeavor is part of a more general effort searching for efficient conversion of solar energy into electricity and into chemical energy stored in hydrogen. Yet, despite the so many man-years invested in this search titanium dioxide is still considered to be the photocatalyst of choice. This paper discusses the current status of research with non-TiO2 photocatalysts for water decontamination. It suggests that developing of new, highly photoactive photocatalysts for water and air treatment is hindered by a combination of reasons, reflecting the tendency of the scientific community to “search under the streetlight”. This includes the overemphasis on bandgap values while overlooking the importance of band positions, the use of dyes as model contaminants under visible light, the ignoring of the importance of transient phenomena, the under-emphasis of the role of surface area and the lack of implementation of theoretical tools in the developing of new photocatalysts. Stepping out of the comfort zone is not only possible but essential.

Synthetic flavin molecules were anchored on Degussa P25 titanium dioxide (TiO2). The effect of their presence on the photocatalytic (PC) activity of TiO2 was studied. Under UV light, an increase in the degradation rate of ethanol was observed. This increase was accompanied by stabilization of the anchored flavin against self-degradation. The unprecedented stabilization effect was found also in the absence of a reducing agent such as ethanol. In contrast, under the less energetic visible light, fast degradation of the anchored flavin was observed. These rather surprising observations were attributed to the propensity for charge transport from excited flavin molecules to the semiconductor and to the role that such charge transfer may play in stabilizing the overall assembly. Anchored flavins excited by UV light to their S2, S3 electronic states were able to transfer the excited electrons to the TiO2 phase whereas anchored flavin molecules that were excited by visible light to the S1 state were less likely to transfer the photo-excited electrons and therefore were destabilized. These findings may be relevant not only to anchored flavins in general but to other functionalized photocatalysts, and may open up new vistas in the implementation of sensitizers in PC systems.

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.

Bismuth oxychloride (BiOCl) is well known for its photocatalytic activity. Here, we report on a study aimed at the effects of co-doping on photocatalysis. More BiOCl, co-doped with niobium and iron/indium/lanthanum was prepared by a low temperature procedure. The materials revealed high activity in the photocatalytic degradation of rhodamine B under both UV light and visible light. This high activity originated from their high specific surface areas, which more than compensated for their less-than optimal crystallinity. Of particular interest is BiOCl co-doped with niobium and iron, where a strong synergistic effect was found in the degradation of the dye. In contrast to the common experience with doping effects, the synergistic effect was not due to changes in the optical properties of the BiOCl, but due to specific interaction between the dye molecules and the co-doped photocatalyst, as manifested by the adsorption tendency of the dye. Hence, the study demonstrates that doping can be used for designing photocatalysts with high specificity.

Over the years, a considerable amount of attention has been given to the thermodynamics of photocatalysts, i.e. to the location of their valence and conduction bands on the energy scale. The kinetics of the photoinduced charge carriers at short times (i.e. prior to their surface redox reactions) is no less important. While significant work on the transient electronic spectra of photocatalysts has been performed, the transient vibrational spectra of this class of materials was hardly studied. This manuscript aims to increase the scientific awareness to the potential of transient IR spectroscopy (TRIR) as a complementary tool for understanding the first, crucial, steps of photocatalytic processes in solid photocatalysts. This was done herein first by describing the various techniques currently in use for measuring transient IR signals of photo-excited systems and discussing their pros and cons. Then, a variety of examples is given, representing different types of photocatalysts such as oxides (TiO2, NaTaO3, BiOCl, BiVO4), photosensitized oxides (dye-sensitized TiO2), organic polymers (graphitic carbon nitride) and organo-metalic photocatalysts (rhenium bipyridyl complexes). These examples span from materials with no IR fingerprint signals (TiO2) to materials having a distinct spectrum showing well-defined, localized, relatively narrow, vibrational bands (carbon nitride). In choosing the given-above examples, care was made to represent the several pump & probe techniques that are applied when studying transient IR spectroscopy, namely dispersive, transient 2D-IR spectroscopy and step-scan IR spectroscopy. It is hoped that this short review will contribute to expanding the use of TRIR as a viable and important technique among the arsenal of tools struggling to solve the mysteries behind photocatalysis.

Composite particles comprised of titanium dioxide strongly coupled to various types of carbon nanotubes (CNTs) were prepared by low temperature hydrothermal synthesis. A significant enhancing effect on the photocatalytic reduction rate of Cr(VI) was observed, as a consequence of Cr(VI) adsorption on the CNTs. This rate-enhancing effect was shown to depend on the type of the CNTs and on their functionalization. While evidence for the presence of a synergistic effect is well documented, the comparison between the effects of the various types of CNTs enables to present a new phenomenon., connected to the fact that for this specific model system both reduction and oxidation occur mainly on the CNTs. Here, the extent by which the reduction rate will be enhanced depends not only upon the tendency of the CNTs to adsorb the Cr(VI), but also on the ability of the system to shuttle both holes and electrons to the CNTs, namely whether the CNTs are metallic or not.

The last four decades have shown a remarkable increase in scientific interest in photocatalysis as a tool for tackling the world's energy and waste problems. The apparent similarity between photocatalytic water splitting and photocatalytic degradation of pollutants, which have been studied so far by two different scientific communities, raises the question regarding the extent to which one may utilize knowledge obtained in one field for the benefit of the other. This review examines the common features and differences between the two areas. The main similarities stem from the common dependence on the absorption of photons and on subsequent charge-carrier dynamics. The main dissimilarities are linked to thermodynamics, the type of reactants and end products, and to the role of adsorption and desorption. At present the fundamental differences between storing energy and using it to solve environmental issues affect practical solutions. Yet, easy transfer of knowledge, research resources, and personnel between the two is not only possible but should be encouraged.

Electrospinning was used to prepare polyacrylonitrile (PAN)-based nanofibrous mats. The mats were processed at an elevated temperature. It was found that the heat-treated polyacrylonitrile was able, under UV light, to reduce toxic Cr(VI) species to the less toxic Cr(III) very efficiently. The reduction rates were found to depend strongly on the temperature of the heat-treatment process, with hardly any correlation with the specific surface area of the polymer. Optimal performance was obtained with mats that had been heated in air to 250 °C and then were held under nitrogen at 350 °C. This photoinduced activity was significantly superior to similar means of Cr(VI) removal. Good correlation was found between the ability to adsorb the Cr(VI) species and reduction kinetics. The results are explained by a mechanism comprising of charge injection from the polymer to photo-excited Cr(VI) species. This injection is, in particular, efficient whenever the preparation conditions are such that in-chain charge delocalization and good coupling between the polymer and the Cr(VI) ions are formed. The authors do not negate the possibility that the observed phenomena, most likely originating from intra-chain charge conduction may be utilized in other areas, in particular photovoltaics.

This study establishes structure-property relationships for four synthetic flavin molecules as bioinspired redox mediators in electro- and photocatalysis applications. The studied flavin compounds were disubstituted with polar substituents at the N1 and N3 positions (alloxazine) or at the N3 and N10 positions (isoalloxazines). The electrochemical behavior of one such synthetic flavin analogue was examined in detail in aqueous solutions of varying pH in the range from 1 to 10. Cyclic voltammetry, used in conjunction with hydrodynamic (rotating disk electrode) voltammetry, showed quasi-reversible behavior consistent with freely diffusing molecules and an overall global 2e(-) , 2H(+) proton-coupled electron transfer scheme. UV/Vis spectroelectrochemical data was also employed to study the pH-dependent electrochemical behavior of this derivative. Substituent effects on the redox behavior were compared and contrasted for all the four compounds, and visualized within a scatter plot framework to afford comparison with prior knowledge on mostly natural flavins in aqueous media. Finally, a preliminary assessment of one of the synthetic flavins was performed of its electrocatalytic activity toward dioxygen reduction as a prelude to further (quantitative) studies of both freely diffusing and tethered molecules on various electrode surfaces.

There is a common notion in the field of photocatalysis that the same requirements for air purification hold also for self-cleaning surfaces, and that the same product may be adequate for the two purposes. This notion was tested on cementitious objects by comparing the activity of a series of commercially available TiO

Catalysts that are made of composite particles may comprise several compounds, where each compound utilizes its own specific properties, thus providing synergistic effects that cannot be found when the constituents are used separately. Developing and quality control of such particles require measuring the shape of the domains and the length of the contact line between domains made from different compounds. In what follows, the feasibility of using Fluorescence Resonance Energy Transfer (FRET) in order to gain information on the length of contour lines between neighboring domains is demonstrated. The principle of the method is to selectively adsorb the donor on one type of domain while selectively adsorbing the acceptor on the second type of domain. The requirement for a short distance between the acceptor dye molecule and the donor dye molecule in order to obtain fluorescence is then translated into a linear dependence between the emission intensity and the contour line length. This facilitates, upon using calibrated standards, the calculation of the average length of the contour between domains.

The preparation, characterization, and performance of an electrophotocatalytic cell, made of low-cost, planar interdigitated electrodes is reported hereby. The operation of the cell under small positive bias was demonstrated by photocatalytically degrading the dye rhodamine 6G in solution as well as by monitoring the degradation of self-assembled monolayer chemisorbed on the TiO2electrode. Results point out to the importance of activated oxygen species formed in the process and suggest that the short distance between the two electrodes provides a way to utilize the activated oxygen species formed at the negatively biased electrode.

To illuminate the impacts of sugar concentration and stereochemistry on protein protection we used attenuated-total-reflectance Fourier-transform infrared-spectroscopy (ATR-FTIR) to study the effects of four aldohexoses on poly-N-isopropylacrylamide (PNIPA) phase transition. Protein stability in aqueous solutions is essential in numerous fields, predominantly biotechnology and food science. Saccharides protect proteins against thermal denaturation, but the mechanisms are still debatable. We therefore studied the effect of sugar concentration and stereochemistry on the LCST phase transition of PNIPA as a model for protein cold renaturation, using ATR-FTIR. The transition temperature of PNIPA, as observed by both the shift in amide II peak and its area, revealed the following order: galactose > glucose > mannose > talose, i.e., galactose is the most kosmotropic of the four isomers and talose is the least. We concluded that the soluting-out effect exerted on the polymer by these sugars positively correlates with the sugar hydration number governed by sugar stereochemistry.

Polymeric nanofibers containing both carbon nanotubes and titanium dioxide were produced by electrospinning and used to photocatalytically reduce Cr(VI) ions. A comparison was made between multiwall carbon nanotubes (CNTs) and single-wall CNTs, as well as between OH-functionalized and nonfunctionalized CNTs. The reduction rate was found to decrease upon using OH-functionalized CNTs, whereas the opposite phenomenon was observed with nonfunctionalized CNTs. The systems under study demonstrate the counterintuitive possibility that charge separation for specific target species can be quite deleterious for photocatalysis. Whether enhanced charge separation is benevolent or deleterious depends on the type of reaction (oxidation or reduction) as well as the location of the reaction (the photocatalyst or the inert electron sink) and the adsorpticity of both the photocatalyst and the inert partner.

A review of patents on the application of titanium dioxide photocatalysis for air treatment is presented. A comparison between water treatment and air treatment reveals that the number of scientific publications dedicated to photocatalytic air treatment is significantly lower than the number of scientific manuscripts dedicated to photocatalytic water treatment, yet the situation is reversed upon comparing relevant patents. This indicates a growing interest in the implementation of photocatalysis for air treatment purposes, which surpasses that of water treatment. This manuscript analyzes the various patents in the area of air treatment, while differentiating between indoor air treatment and outdoor air treatment. Specific efforts were made to characterize the main challenges and achievements en-route for successful implementation, which were categorized according to mass transport, adsorption of contaminants, quantum efficiency, deactivation, and, no less important, the adherence and the long term stability of the photocatalyst.

Composite photocatalysts, made of titanium dioxide and high surface area adsorbents become more and more common. To large extent, this is due to the phenomenon of "Adsorb & Shuttle", i.e. the adsorption of molecules on the inert, adsorptive, domains, followed by diffusion to the photocatalytic domains. This manuscript reviews the published literature on composite photocatalysts, and analyzes the various aspects affecting their performance. One of these aspects is the enhancement of the degradation rate of pollutants, which is governed by a variety of factors including surface area, adsorpticity, strength of interaction, the loading of photocatalyst in the composite, and operation parameters (such as temperature, humidity and pH). Other aspects include a reduction in the emission of intermediate products and a different distribution of end-products. Care was taken to describe the possibility of using the inert adsorptive domains to enhance the degradation of specific species, as well as to discuss the effect of composite photocatalysts on deactivation phenomena, and the interrelation between "Adsorb & Shuttle" phenomena and out- diffusion of oxidizing species from the TiO2 domains, known as the "remote degradation" phenomenon.

The photocatalytic degradation of organic contaminants on titanium dioxide is basically non-selective. While this seems at first glance to be an advantage, this is not the case when a stream containing low concentrations of highly toxic substances together with high concentrations of low toxic organics has to be treated. A method for obtaining preferential degradation by means of preparation of molecularly imprinted photocatalyst is presented hereby. The method is demonstrated with two model compounds simulating the nerve gas sarin: diisopropyl methylphosphonate (DIMP) and diethylhydroxy methylphosphonate (DEHMP). An improvement by a factor of 3–4 in the mineralization rates was observed upon using the imprinted substrates. This enhancement in photocatalytic rates cannot be explained by the modest growth in the surface area (not more than 20–30%), hence it can be concluded that the enhancement resulted from the conformity between the target molecules and the molecular cavities on the imprinted sites. This conclusion is further supported by the lower extent of enhancement upon degrading benzene and heptane. Of particular interest is the fact that substrates that were imprinted with DEHMP were found to be very effective in the degradation of the homolog DIMP. This observation suggests the use of molecules having good affinity to the matrix as a means to obtain high surface concentration of molecular active sites, thus detouring the problem of aggregation that might arise in cases where the target contaminants have low affinity to the matrix. Another benefit is the possibility of using non-toxic homolog molecules for constructing the imprinted photocatalyst. This benefit is in particular important when designing a photocatalyst for WMD warfare agents, as in the case of sarin.

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-type-of-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-to-globule 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 c...

Composite poly(acrylonitrile) nanofibers containing nanometric TiO2 particles and multiwalled carbon nanotubes have been prepared by the electrospinning technique. The photocatalytic activity of th...

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.

Titanium dioxide is a well-known photocatalyst for the treatment of air and water. The use of structures comprised of photocatalytic sites and high capacity adsorption sites may improve the TiO2 photoefficiency, in cases where the contaminnants do not adsorb well onto the photocatalyst. In this work, composite particles composed of activated carbon, partially coated with sol-gel-made titanium dioxide, were prepared and characterized. It was found that chelating the titanium tetraiso-propoxide, used as a precursor, with acetylacetone is crucial for obtaining reasonable loading (up to 12–15% in weight). High content of water or humidity tends to form thick films that might bridge over the pores of the activated carbon, thus reducing the available surface area. The photocatalytic activity of the composite particles was tested by following the rate of production of carbon dioxide during the photodegradation of Rhodamine 6G in an aqueous solution. Enhanced mineralization rates relative to sol-gel-made titanium dioxide particles (by ˜30%) were observed. This enhancement is attributed to the adsorption of the contaminants in the vicinity of the photoactive sites. It was further found that the composite particles produced relatively less of the toxic by-product carbon monoxide, than sol-gel-made titanium dioxide or the commercially available Degussa P25. The reason for this effect is yet to be determined.

Nous discutons la necessite d'augmenter les vitesses de photodegradation de substances toxiques qui peuvent coexister dans des effluents, a cote de produits contaminants moins dangereux. Malgre le nombre relativement limite de donnees sur ce sujet, il est possible d'indiquer plusieurs parametres du procede, tels que le pH, le dopage et le type de solvant qui peuvent influencer les vitesses de photodegradation avec une certaine specificite. La plupart des parametres agissent en controlant le transfert de matiere des reactifs vers les surfaces photoactives. Le controle du transfert de matiere est aussi a la base de plusieurs filieres permettant de projeter une photodegradation preferentielle. Nous devrions considerer, entre autres, la modification de la surface par impression des contaminants et l'approche par "adsorption et navette", comme des methodes pouvant donner une grande specificite.