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Objective: There is a research gap on the impact of payment, reimbursement, and academic productivity in career decision-making for early-career (EC) attendings in gynecologic oncology. We sought to assess gynecologic oncology fellows and EC attendings on their knowledge and perceptions regarding the business of medicine. Methods: An anonymous survey was electronically disseminated to fellow and EC SGO members. Key themes were the business of medicine, productivity, and compensation/negotiation. A 5-point Likert scale was utilized; descriptive statistics were calculated using SPSS. Results: There was a 29 % response rate: 82 fellows and 102 EC attendings. Most were white (n = 143, 78 %) and female (n = 138, 75 %.) Most fellows (n = 67, 82 %) were interested in, and most EC (n = 82, 82 %) were employed in, academic/non-private practice. Fellows and EC attendings reported insufficient education on RVUs (relative value units) and reimbursement (80 %, n = 66; 81 %, n = 83) and did not feel prepared for the business aspect of practice (80 %, n = 66; 73 %, n = 75). Over 40 % of fellows did not understand how RVUs relate to practice. Thirty-three percent of EC attendings did not understand RVU assignments; 29 % were satisfied with methods used to determine productivity, and 17 % did not understand their compensation. Over 60 % of fellows felt unprepared to negotiate clinical productivity expectations. For EC attendings, 47 % were uncomfortable negotiating clinical expectations, 32 % negotiating academic expectations, and 52 % negotiating compensation changes. Female EC felt less prepared than male EC regarding the business of medicine (p = 0.02), RVU assignments (p

In the presented work, the structure dependence as well as luminescence features of a wide range of hybrid crystals based on lead halides and a homologous series of alkyl diamines from 1,4-diaminobutane to 1,8-diaminooctane are investigated. The structure of several previously undescribed hybrid crystals has been established. The even-odd effect of alkanes and its influence on the structure of such hybrid crystals have been demonstrated for the first time. The luminescence properties of the crystals and their dependence on the type of anion as well as the length and oddity of the organic cation are described in detail. The obtained data expand our knowledge of the relationship between the structure of the organic cation, including its parity and structure, and the electronic and optical properties of the hybrid crystals.

This work reports on hybrid hexamethylenediaminium lead halide perovskites. The materials were prepared using wet synthesis and the subsequent precipitation from aqueous solution. Structural and morphological charactarization studies show their high degree of crystallinity and phase purity. The determined perovskites' structural parameters agree well with the literature reports. The recorded XPS and DRS data allowed for the first schematic representation of the perovskite band structures. The latter match well the results of DFT modeling. It is shown for the first time that the increase in the perovskite bandgaps is solely due to the increase in the anion electronegativity. Namely, as the anion electronegativity increases, the corresponding valence band energy decreases. In contrast, the electronegativity of the anions has no effect on the perovskite conduction band energies. The presented study deepens our understanding of the relationship between the crystal and electronic structures of low-dimensional hybrid halide perovskites.

In this work, we apply polarized Raman spectroscopy for study of internal vibrations of the 3-cyanopyridinium cation in the halide post-perovskite (3cp)PbBr 3 (3cp = 3-CN-C 5 H 5 NH + ). For a single cation, the vibrational frequencies and intensities of the Raman signal were calculated using the density functional theory. Selection rules were established for vibrations of cations in the crystal. These rules together with modeling results were used to identify the internal vibrations of the cation in the Raman spectrum of the crystal. Narrow and isolated internal vibrations of cations could be used as spectators of the crystalline environment.

Halide perovskites and their low-dimensional analogs are promising semiconductor materials for solar cells, LEDs, lasers, detectors and other applications in the area of photonics. The most informative optical property of semiconductor photonics materials is the absorption spectrum enabling observation of the fundamental absorption edge, exciton structure, defect-related bands, etc. Traditionally, in the study of halide perovskites, this spectrum is obtained by absorption spectroscopy of thin films or diffuse reflectance spectroscopy of powders. The first method is applicable only to compounds with the developed thin film deposition technology, and in the second case, a large absorption coefficient narrows the observations down to the sample transparency region. In this paper, we suggest the diffuse reflectance spectroscopy with dilution as a method for obtaining the full-range absorption spectrum from halide perovskite powders, and demonstrate its application to practically important cases.

The effect of a Cu 2 O substrate on the photoinduced alteration of the hydrophilicity of TiO 2 and ZnO surfaces was studied. It was demonstrated that the formation of heterostructures Cu 2 O/TiO 2 and Cu 2 O/ZnO strongly changed the direction of the photoinduced alteration of surface hydrophilicity: while both TiO 2 and ZnO demonstrate surface transition to superhydrophilic state under UV irradiation and no significant alteration of the surface hydrophilicity under visible light irradiation, the formation of Cu 2 O/TiO 2 and Cu 2 O/ZnO heterostructures resulted in photoinduced decay of the surface hydrophilicity caused by both UV and visible light irradiation. All observed photoinduced changes of the surface hydrophilicity were compared and analyzed in terms of photoinduced alteration of the surface free energy and its polar and dispersive components. Alteration of the photoinduced hydrophilic behavior of TiO 2 and ZnO surfaces caused by formation of the corresponding heterostructures with Cu 2 O are explained within the mechanism of electron transfer and increasing of the electron concentration on the TiO 2 and ZnO surfaces.

Compared to lead-based solar cells whose power conversion efficiency is 25.2%, the highest power conversion efficiency of a halide double Cs 2 AgBiBr 6 -based perovskite solar cell is less than 3%. It was therefore relevant to unravel the inherent reason(s) for such a low efficiency in the latter that may be related to trapping/detrapping of photocarriers. Accordingly, photocoloration and photobleaching phenomena occurring in the Cs 2 AgBiBr 6 photochromic perovskite were examined from 100 to 450 K by diffuse reflectance spectroscopy (DRS). The separation and recombination of photogenerated charge carriers implicated both color centers and optically silent trap states within the bandgap. The processes were reversible subsequent to heating after illumination at 100 K but were mostly irreversible at 290 K. DRS spectral and kinetic measurements at T = 100-450 K were carried out after visible light illumination that further revealed the nature of the various charge carrier traps in Cs 2 AgBiBr 6 . Results confirmed the separation of photogenerated electrons and holes, with formation of the color centers identified as deep electron traps. Three different photoinduced color centers were responsible for the absorption bands observed at 1.78 ( ab1 ), 1.39 ( ab2 ), and 1.10 eV ( ab3 ) at 100 K. Annealing of these electron-type color centers occurred in the temperature range of 100-450 K via recombination with holes in the valence band following their thermal release from the several hole traps. Application of a first-order kinetic model to the thermoprogrammed annealing (TPA) of the color centers' spectra yielded estimates of the activation energies of hole detrapping and lifetimes of trapped holes at room temperature. The irreversibility of photocoloration at 290 K was caused by the formation of new deep hole trap states.

We present a structural and optoelectronic study of 1D piperidinium, pyridinium, and 3-hydroxypyridinium lead trihalides. In contrast to the piperidinium and pyridinium species whose single inorganic chains [PbX31-]n are separated by organic cations, the 3-hydroxypyridinium compound is characterized by double inorganic chains. According to DFT the valence and conduction bands of the piperidinium lead trihalides are composed of occupied p-orbitals of the halogen anions and unoccupied p-orbitals of the Pb2+ cations. In contrast, the pyridinium species feature low-lying cationic energy levels formed from the cation's π*-orbitals. Thus, electronic transitions between the cationic energy levels and valence bands require less energy than valence to conduction band transitions in the case of piperidinium lead trihalides. The presence of an OH group in the pyridinium ring leads to a bathochromic shift of the cationic energy levels resulting in a decreased energy of transitions from the cationic energy levels to the valence band. Electronic transitions predicted by DFT are observable in experimental optical absorption and luminescence spectra. This study paves the way for creation of 1D perovskite-like structures with desired optoelectronic properties.

Two novel hybrid organic-inorganic perovskites, pyridinium lead tribromide and pyridinium lead triiodide, are prepared. Based on the XRD data, we find that the compounds are quasi-one-dimensional crystals of Pna21 symmetry. DFT calculations demonstrate that the valence band of the new compounds is comprised of the occupied p-orbitals of the halogen anions, while their conduction bands CB and CB + 1 are composed mainly of the unoccupied π-orbitals of the aromatic pyridinium rings. The computed DOS matches well with the recorded XPS spectra. The pyridinium lead tribromide and pyridinium lead triiodide absorption peaks derived from the experimental DRS are located at ∼3.1 eV and ∼2.4 eV, respectively. An agreement between the experimentally and theoretically predicted absorption spectra is found. The synthesized compounds extend the range of quasi-one-dimensional organometallic perovskites suitable for optical and possibly electronic applications.

Heterovalent CsPbBr 3 doping with Bi results in a significant red shift of the optical absorption of both single-crystal and powdered samples. The results of low-temperature (3.6 K) photoluminescence studies of perovskite single crystals indicate that the position of the excitonic luminescence peak remains unaffected by Bi doping that, in turn, infers that the band gap of Bi-doped perovskite is not changed as well. The position and state density distribution of the valence band and Fermi level of single-crystal perovskites were determined by another direct method of ultraviolet photoelectron spectroscopy. The obtained results show that Bi 3+ doping causes no changes in the valence band structure but an increase in the Fermi level by 0.6 eV. The summary of the obtained results directly demonstrates that the concept of the band-gap engineering in Bi 3+ -doped CsPbBr 3 halide perovskite is not valid.

We present an optical study of MAPbBr 3 single crystal grown from solution. The crystal Pm3m symmetry was confirmed by electron backscatter diffraction. Our major attention was focused on optical effects related to the excitonic states in MAPbBr 3 . Photoluminescence temperature dependence of narrow exciton resonance showed encouragingly low inhomogeneous broadening Γ ≈ 0.5 meV that allows one to distinguish the signals from free excitons and those arising from recombination of excitons localized on defects. Excitonic origin of the resonance was proved by its superlinear pump intensity dependence, in contrast to the linear behavior of the defect-assisted recombination bands. For the first time, the phonon replicas originating from free exciton recombination accompanied by partial energy transfer to the phonons were observed in high-resolution PL spectra and confirmed by independent low-temperature Raman scattering experiments. In turn, low-temperature, low-frequency Raman scattering studies let us resolve the structure of the low-frequency phonon spectrum.

This article evokes the futuristic visions of two giants, one a writer, Jules Verne , who foresaw water as the coal of the future, and the other a scientist, Giacomo Ciamician , who foresaw the utilization of solar energy as an energy source with which to drive photochemical and photocatalytic reactions for the betterment of mankind. Specifically, we examine briefly the early work of the 1960s and 1970s on the photosplitting of free water and water adsorbed on solid supports, based mostly on metal oxides, from which both hydrogen and oxygen evolve in the expected stoichiometric ratio of 2 to 1. The two oil crises of the 1970s (1973 and 1979) spurred the interest of researchers from various disciplines (photochemistry, photo-catalysis and photoelectrochemistry) in search of a Holy Grail photocatalyst, process, or strategy to achieve efficient water splitting so as to provide an energy source alternative to fossil fuels. Some approaches to the photosplitting of water adsorbed on solid insulators (high bandgap materials; E bg ≥ 5 eV) and semiconductor photocatalysts (metal oxides) are described from which we deduce that metal oxides with bandgap energies around 5 eV (e.g., ZrO₂) are more promising materials to achieve significant water splitting on the basis of quantum yields than narrower bandgap photocatalysts (e.g., TiO₂; E bg ≈ 3.0-3.2 eV), which tend to be relatively inactive by comparison. Although proof of concept of the photosplitting of water has been demonstrated repeatedly in the last four decades, much remains to be done to find the Holy Grail photocatalyst and/or strategy to achieve significant yields of hydrogen.

Modified Pt-TiO 2 NPs/decorated carbon nanotubes were synthesized utilizing sonochemical/hydration-dehydration techniques. Pt was loaded on TiO 2 by a photodeposition method keeping in mind the end goal to achieve electron-hole pair separation and promote the surface reaction. The morphological and basic properties of Pt-TiO 2 /fCNTs were investigated by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) and Raman spectroscopy. The selected area electron diffraction (SAED) patterns of Pt-TiO 2 /fCNTs were obtained utilizing TEM-based energy dispersive X-ray spectroscopy (EDXS) analysis. It was found that the TiO 2 nanoparticles were uniformly distributed on the fCNTs, and the Pt particles were decorated on the surface of TiO 2 /fCNTs. The photocatalytic hydrogen production activity of the Pt (0.5%) -TiO 2 /fCNTs (0.5%) nanoparticle composites was investigated using a sacrificial agent methanol solution. Pt-loaded TiO 2 demonstrated a hydrogen evolution rate around 20 times that of TiO 2 /fCNTs (0.5%) (fSWCNTs, fMWCNTs). When compared with platinized TiO 2 in methanol, which was utilized as a control material, Pt-TiO 2 /fCNTs demonstrated an almost 2-fold increment in hydrogen generation.

In recent years many works are aimed at finding a method of controllable switching between hydrophilicity and hydrophobicity of a surface. The hydrophilic surface state is generally determined by its energy. Change in the surface energy can be realized in several different ways. Here we report the ability to control the surface wettability of zirconium dioxide nano-coatings by changing the composition of actinic light. Such unique photoinduced hydrophilic behavior of ZrO 2 surface is ascribed to the formation of different active surface states under photoexcitation in intrinsic and extrinsic ZrO 2 absorption regions. The sequential effect of different actinic lights on the surface hydrophilicity of zirconia is found to be repeatable and reversibly switchable from a highly hydrophilic state to a more hydrophobic state. The observed light-controllable reversible and reproducible switching of hydrophilicity opens new possible ways for the application of ZrO 2 based materials.

Here we focused on the study of the effect of the zinc oxide nano-coatings surface acidity on the surface hydrophilicity and photoinduced hydrophilic conversion. A three-step procedure was used to have the initial state of the ZnO surface free of organics and to control the conditions during the water wetting and the irradiation steps. The kinetics of photoinduced hydrophilic conversions for ZnO films were obtained and demonstrated a dependence on the initial hydrophilic state. No conversion into the superhydrophilic state was observed for ZnO nano-films independently of the surface acidity. Irradiation in the ultraviolet and visible spectral regions showed the existence of "slow" and "fast" processes in the photoinduced hydrophilic conversion of the ZnO surface. A multi-layered model of hydroxyl-hydrated coverage of the surface is proposed to explain the experimental results., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Introduction: Transition from first- to second-generation photocatalysts has followed the notion that greater absorption of light in the visible region would yield greater spectral sensitivity and greater photoactivity. Though a promising strategy, in practice, it did not meet expectation because of various side issues, which in many cases has led to loss of photoactivity and chemical reactivity. This article examines some earlier notions that arose from applications of different metal oxides (e.g., TiO(2), ZnO, MgO among others) that made these oxides good photocatalysts in many processes., Discussion: Phenomena that proved relevant in developing next generation photoactive materials are considered: the dependence of the activity of photocatalysts on the band gap energy, the spectral variations of the activity of photoactive materials, and the spectral variations of selectivity of photoactive materials. The tendency to decrease the energy of actinic photons through doping in forming second-generation photocatalysts is completely opposite the fundamental observation in first-generation photocatalysts whereby the activity increased with increasing band gap energy. Extension of spectral sensitivity of second-generation photoactive materials also caused a decrease of their photoactivity; hence, some notions are reconsidered to produce next(third) generation photoactive materials. The article proposes the following concepts to develop next generation photocatalysts: (1) multi(two)-photon excitation of photoactive materials with lower energy photons to achieve the same excited state as with higher energy photons, (2) utilization of heterojunctions to drive electronic processes in the desired direction, and (3) selective photoexcitation of localized electronic states to gain better selectivity.

The concept Photocatalysis and, of greater import here, Heterogeneous Photocatalysis were first introduced in the second decade (1910-1920) of the 20th century according to the CAPLUS and MEDLINE databases (SciFinder). This review reports a brief historical perspective on the origins of the two concepts, whether implied or explicitly stated, in some detail up to about the mid-1980s when heterogeneous photocatalysis witnessed the beginning of an exponential growth, with particular emphasis on the use of nanosized TiO(2) particles in powdered form as the (so-called) photocatalyst of choice in environmental applications because of its inherent properties of abundance and chemical stability in acidic and alkaline aqueous media (in the dark), in contrast to ZnO that had been the metal oxide of choice in the early days. The early workers in this area often used the term photosensitization rather than the current popular term photocatalysis, used since the early 1980s. The term Photocatalysis appeared in the literature as early as 1910 in a book by Plotnikow (Russia) and a few years later it was introduced in France by Landau. The review also reports on contributions during the early years by Terenin at the University of St. Petersburg (previously Leningrad, Soviet Union), and in the decade spanning 1975-1985 contributions by Bard's group at the University of Texas at Austin (USA) as well as those of other groups. Some activities into the conversion of light energy to chemical fuels (e.g. H(2)) during the 1975-1985 decade are also considered.

The present study explored photoinduced radical processes caused by interaction of CH(4) and NH(3) with a photoexcited surface of a complex metal oxide: magnesium-aluminum spinel (MgAl(2)O(4); MAS). UV irradiation of MAS in vacuo yielded V-type color centers as evidenced by the 360 nm band in difference diffuse reflectance spectra. Interaction of these H-bearing molecules with photogenerated surface-active hole states (O(S)(-)•) yielded radical species which on recombination produced more complex molecules (including heteroatomic species) relative to the initial molecules. For the MAS/CH(4) system, photoinduced dissociative adsorption of CH(4) on surface-active hole centers produced •CH(3) radicals that recombined to yield CH(3)CH(3). For MAS/NH(3), a similar dissociative adsorption process led to formation of •NH(2) radicals with formation of NH(2)NH(2) as an intermediate product; continued UV irradiation ultimately yielded N(2). For the mixed MAS/CH(4)/NH(3) system, however, interaction of adsorbed NH(3) and CH(4) on the UV-activated surface of MAS yielded •NH(2) and •CH(3) radicals, respectively, which produced CH(3)-NH(2) followed by loss of the remaining hydrogens to form a surface-adsorbed cyanide, CN(S), species. Recombination of photochemically produced radicals released sufficient energy to re-excite the solid spinel, generating new surface-active sites and a flash luminescence (emission decay time at 520 nm, τ ~ 6 s for the MAS/NH(3) case) referred to as the PhICL effect.

Photodegradation of phenol and 4-chlorophenol over six different TiO(2) samples was tested in order to establish whether an interconnection between the activity and selectivity of photocatalysts exists. The obtained experimental data were analyzed using correlation analysis. Some correlations between the activity in phenol(s) photodegradation and selectivity toward formation of primary intermediate products were established. The type of correlations depends on the type of studied photoreactions. The discussion of the observed correlations between the activity and selectivity of photocatalysts is given in terms of the difference of surface concentrations of electrons and holes and corresponding surface active sites which might be dependent on the types of dominating surface faces. On the basis of the obtained results of correlation analysis it was assumed that a higher activity of photocatalysts could be achieved provided that both reduction and oxidation reaction pathways occur with equally high efficiency., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Dual function of self-cleaning and antireflection can be created in double-layered TiO2-SiO2 nanostructured films. The film were prepared by (1) layer-by-layer deposition of multilayered SiO2 nanoparticles with polydiallyldimethylammonium (PDDA) cations, (2) layer-by-layer deposition of multilayered titanate nanosheets with polications on PDDA/SiO2 multilayer films, and (3) burning out the polymer and converting titanate nanosheets into TiO2 by hearing at 500 degrees C. The as-prepared films, consisting of a porous SiO2 bottom layer and a dense TiO2 top layer, improved the transmittance of glass or quartz substrates, as demonstrated by transmission spectra collected at normal incidence. The photocatalytic properties of the films were studied by the change of the water contact angle together with the decay of the IR absorption of the hydrocarbon chain of octadecylphosphonic-acid-modified films under 2.6 mW cm-2 UV illumination. Both the antireflective and the photocatalytic properties of the films were dependent on the number of PDDA/nanosheet bilayers deposited. however, excellent surface wettability of the films for water was obtained, independent of the preparation conditions. The experimental findings are discussed in terms of the special structure of the double-layered nanostructured film.

The electrospinning method is employed to prepare a fibrous TiO2-SiO2 (Ti : Si = 1 : 2) nanocomposite photocatalyst, in which Degussa P25 T i O2 nanoparticles are embedded inthe body of SiO2 fibers and which shows good photocatalytic activity due to its 3-D open structure, as evidenced by photocatalytic reduction of silver ions and decomposition of acetaldehyde.

We report for the first time an experimental application of the concept of a "black body" like reactor to measure quantum yields (Phi) of photochemical reactions in liquid-solid heterogeneous systems. A major advantage of this new method is its simplicity since the fractions of reflected and transmitted light are negligible due to reactor geometry and high optical density of the heterogeneous systems. The average quantum yield of a test reaction (phenol photodegradation) over TiO(2) (Degussa P25) as determined by this method was 0.14, identical to the quantum yield measured earlier for this same reaction under similar conditions by Salinaro and Serpone. We also report the quantum yield of phenol photodegradation over N-doped TiO(2) during photoexcitation at the fundamental absorption band (lambda = 365 nm; Phi = 0.12) and at the N-doping induced extrinsic absorption band (lambda = 436 nm; Phi = 0.08) of the photocatalyst.

The photoelectrochemical behavior of degenerate Nb-doped TiO2 (Ti(1-x)Nb(x)O2: x = 0, 0.01, 0.03, 0.06, 0.1) electrodes prepared by pulsed laser deposition on LaAlO3 (LAO) and SrTiO3 (STO) was examined, revealing that an increase in Nb concentration causes a significant decay of titania photoactivity. One reason for such behavior may be a Burstein-Moss effect, which leads to a blue shift of the spectral limit of photoactivity. Another reason typical for metal-doped photocatalysts is the increase of the efficiency of charge carrier recombination.

In a recent article, Ollis analyzed heretofore reported photocatalyst kinetics of surface photochemical reactions that take place in heterogeneous systems and that rely heavily on the Langmuir-Hinshelwood (LH) kinetic model to interpret the experimental observations. This model assumes a fast adsorption/desorption equilibrium step and a subsequent slow surface step. His interesting analysis of the experimental results reported in 2000 by Emeline and co-workers, Xu and Langford, and Martyanov and Savinov prompted our reexamination of the LH kinetic model along with several other dogmas that continue to propagate in the heterogeneous photocatalytic landscape. This short article discusses some of these issues and reexamines certain misinterpretations. Specifically, we reexamine (1) the a priori assumed validity of the LH kinetic model in heterogeneous photocatalysis, (2) the recombination of photogenerated free charge carriers on the solid (metal oxide) photocatalyst by the band-to-band recombination pathway, and (3) the mistaken assertion that the kinetics of a heterogeneous photoreaction are either only first-order dependent or half-order dependent on photon flow (i.e., light irradiance).

A nonphotocatalytic reaction occurring on the surface of an irradiated wide band gap metal oxide, such as ZrO2, can affect the process of photoinduced formation of Zr3+, F- and V-type color centers. The effect of such reactions is seen as the influence of photostimulated adsorption on the photocoloration of the metal oxide specimen. In particular, photoadsorption of electron donor molecules leads to an increase of electron color centers, whereas photoadsorption of electron acceptor molecules leads to an increase of hole color centers. Monitoring the photocoloration of a metal oxide during a surface photochemical reaction probes whether the reaction is photocatalytic: accordingly, the influence of simple photoreactions on the photocoloration of ZrO2, reactions that involved the photoreduction of molecular oxygen, the photooxidation of molecular hydrogen, the photooxidation of hydrogen by adsorbed oxygen, and the photoinduced transformation of ammonia and carbon dioxide. Kinetics of the photoprocesses are reported, as well as the photoinduced chesorluminscence (PhICL effect) of ammonia. Thermoprogrammed desorption and mass spectral monitoring of the photoreaction involving NH3 identified hydrazine as an intermediate and molecular nitrogen as the final product. The photoreactions involving NH3 and CO2 are nonphotocatalytic processes, in contrast to the photooxidation of hydrogen which is photocatalytic. Carbon dioxide and carbonate radical anions are formed by interaction of CO2 with Zr3+ centers and hole states (OS-*), respectively. Mechanistic implications are discussed.

The photoadsorption of oxygen (photoreduction on electron surface-active centers) and the photoadsorption of hydrogen (photooxidation on hole surface-active centers) as well as the photooxidation of hydrogen in the presence of oxygen were examined over irradiated zirconia (ZrO2) specimens by thermoprogrammed desorption spectroscopy (TPD) and kinetically to assess the states (forms) of oxygen species formed on the surface of zirconia. The three TPD spectral maxima observed inferred three oxygen species of varying activity in the photooxidation of hydrogen. The number of surface-active sites on the zirconia surface were quantitatively estimated (ca. 1 x 10(16) centers), thereby permitting an estimate of the turnover numbers (TON) for the photooxidation of hydrogen (TON > 14.5) and for the photoreduction of oxygen (TON > 6.6). These demonstrate for the first time that a photoreaction occurring on the surface of a metal-oxide photocatalyst is truly photocatalytic.

Adsorption of hydrogen and methane on a preirradiated surface of gamma-Al2O3 produces an afterglow, which has been described as a photoinduced chesorluminescence (PhICL), whose spectral features identify with the intrinsic photoluminescence of alumina. The emission spectrum consists of at least four overlapping single emission bands. For methane adsorption, the PhICL phenomenon is seen only if the solid is preirradiated in the presence of oxygen. Emission decay kinetics of the PhICL effect for gamma-Al2O3 reveal two wavelength regimes: a short wavelength regime at lambda = 300-370 nm (decay time tau = 1.1 +/- 0.2 s; signal width = 2.8 s), and a longer wavelength regime at lambda = 380-700 nm (decay time tau = 2.1 +/- 0.1 s; signal width = 4.3 s). A model is proposed in which there exist two different emission centers and, thus, two different pathways for emission decay. In the first, emission originates with electron trapping by such deep energy traps as anion vacancies {e- + Va --> F+ + hv1} to yield electron F-type color centers, whereas in the second, emission originates from electron/trapped hole recombination {e- + Os*- --> Os2- + hv2}. The first common step of the pathways is homolytic dissociative chemisorption of hydrogen and methane upon interaction with surface-active hole centers Os*-, produced upon preirradiation of alumina, to give atomic hydrogen H* and methyl radicals CH3*. Thermoprogrammed desorption spectra of photoadsorbed or postsorbed oxygen show that adsorbed oxygen interacts with atomic hydrogen and methyl radicals. The products of thermodesorption were H2O for hydrogen and H2O, CO2, and CH3CH3 for methane. The Solonitsyn memory effect coefficient was also evaluated for oxygen photoadsorption.

The photostabilities of a random set of commercially available sunscreen lotions and their active ingredients are examined spectroscopically subsequent to simulated sunlight UV exposure. Loss of filtering efficacy can occur because of possible photochemical modifications of the sunscreen active agents. Changes in absorption of UVA/ UVB sunlight by agents in sunscreen lotions also leads to a reduction of the expected photoprotection of human skin and DNA against the harmful UV radiation. The active ingredients were investigated in aqueous media and in organic solvents of various polarities (methanol, acetonitrile, and n-hexane) under aerobic and anaerobic conditions The UV absorption features are affected by the nature of the solvents with properties closely related to oil-in-water (o/w) or water-in-oil (w/o) emulsions actually used in sunscreen formulations, and by the presence of molecular oxygen. The photostabilities of two combined chemical ingredients (oxybenzone and octyl methoxycinnamate) and the combination oxybenzone/titanium dioxide were also explored. In the latter case, oxybenzone undergoes significant photodegradation in the presence of the physical filter TiO2.