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The continuity equation revisited, including a subsurface electric field (E) in the space charge region of the semiconductor photocatalyst is used to assess the effect that the electric field has on the activity and selectivity of the photocatalyst. A mismatch between the experimental spectral dependence of the quantum yield and the corresponding absorption band may be an indicator of the existence of a space charge region in the solid photocatalyst.

Polarization deficiency and excess ion hydration free energy at an electric field E (ion hydration free energy at the field E subtracted by the ion hydration free energy at zero field) of hydrated calcium, sodium, and chloride ions is determined by Monte Carlo simulations. A primitive polarization model of electrolyte solution near charged interfaces is proposed.

A development of a microscopic model based on a novel generalization of the Becker-Doring equations of nucleation, which describes the stepwise growth of vesicles is shown. A preexisting vesicle provides a catalytic surface on which vesicle fragment can grow at an accelerated rate as per assumption and involves aggregation and fragmentation rate coefficients, which together determine an equilibrium solution.

Self-assembled monolayers (SAMs) of alkanethiols, HS(CH2)(sub n-1)CH3 absorbed on gold is used to explore the dynamics of energy exchange and thermalization in high-energy gas-surface collisions. The results suggest that long-range molecular motions involving up to 6 carbon atoms play the dominate role in controlling the dynamics of the gas-surface impact.

A study was conducted to analyze the spectral dependencies of the quantum yields of photoadsorption of donor molecules on the surfaces of Sc2O3 particulates during excitation in the spectral absorption area of photogenerated hole color centers. Results indicated that the quantum yields of photoadsorption correlated with the efficiency of the photophysical processes associated with carrier photogeneration and carrier transport toward the particle surface.

Research was conducted to examine the photoluminescence and transient spectroscopy of free base porphyrin aggregates. Four different types of aggregates whose absorption spectra were characterized by invariant Soret bands with bandwidths that were independent of the preparative approach were studied. Results demonstrate that the aggregates differ in their time-resolved absorption and fluorescence decay properties which may be attributed to differences in aggregate structures.

Utilization of water as an inexhaustible supply of a fuel (hydrogen) was predicted over a century ago by Jules Verne in The Mysterious Island. Since the oil crisis of 1973, considerable progress has been made in the search for alternative energy supplies. Although the water splitting process to generate simultaneously hydrogen and oxygen has been demonstrated (albeit the process is inefficient) by utilization of light energy, the technology is not mature enough to seriously bring it to pilot-plant demonstration. Much fundamental research remains to be done. The present paper examines the present status and looks at the perspectives of the technological progress, particularly in the high temperature thermochemical and photochemical fields with emphasis in the utilization of solar quantum and thermal photons.

A number of calcium bismuthates were synthesized (25 to 50 mol% in Ca) and characterized by XRD, SEM, EDX, XPS and DRS techniques; the latter provided an estimate of the bandgap energies (Ebg=2.41 to 3.29 eV) via Tauc plots for indirect transitions, whereas XPS established the potentials (vs NHE) of their respective valence bands (and thus the conduction bands). Linear correlations existed between EVB/ECB and Ebg that when compared with those of strontium bismuthates (reported earlier) showed that differences in energies at Ebg=0 eV are related to the difference in the absolute electronegativities of Ca and Sr, from which the following empirical phenomenological rule is postulated: replacing one alkaline earth metal in bismuthates by another causes the points of intersection of the linear correlations ECB(Ebg) and EVB(Ebg) to be displaced by an amount equal to twice the difference in absolute electronegativities of these metals. [ABSTRACT FROM AUTHOR]

A perovskite-like barium bismuthate of the BaBi2O4 class, Ba1.264(4)Bi1.971(4)O4, has been prepared by solid-state synthesis and subsequently characterized by a number of experimental techniques (XPS, DRS, SEM, EDX and Raman spectroscopy), as well as by a DFT computational approach using the GGA Perdew–Burke–Ernzerhof (PBE) density functional to determine the energy band structure. XRD peaks were indexed to a rhombohedral cell (R3¯m) with parameters close to Ba0.156Bi0.844O1.422 (i.e., to Ba0.439Bi2.374O4), which upon Rietveld refinement gave Ba1.264(4)Bi1.971(4)O4. The Bi–O bond lengths determined from this refinement (1.86 and 2.31 Å) accorded with the bond lengths estimated from Raman spectra (1.97 and 2.26 Å). DFT calculations revealed the bismuthate to display two bandgaps that correspond to lower-energy indirect (2.28 eV) and to higher-energy direct (2.36 eV) electronic transitions in good agreement with the experimental bandgaps of 2.26 eV and 2.43 eV, respectively, from Tauc plots of DRS spectra. Relative to the indirect bandgap energy of 2.26 eV, the energies of the valence band and of the conduction band were, respectively, +1.14 eV and −1.12 eV. The photoactivity of Ba1.264(4)Bi1.971(4)O4 was examined toward the photoreduction of the greenhouse gas CO2 in aqueous media photoelectrochemically yielding alcohols and alkanes, while in the gas phase in an infrared cell reactor the products were carbon monoxide and alkanes. [ABSTRACT FROM AUTHOR]

The reexamination of the Langmuir-Hinshelwood (LH) kinetic model along with several other dogmas that continue to propagate in the heterogeneous photocatalytic landscape is presented. The priori assumed validity of the LH kinetic model in heterogenous photocataylsis and the recombination of photogenerated free charge carriers on the solid photocataylsis by the band-to-band recombination pathway is reexamined.

The study was aimed at examining the effect(s) of surface photochemical reactions involving H(sub 2), O(sub 2), NH(sub 3), and CO(sub 2) on the photocoloration of ZrO(sub 2) in particular, and metal oxides in general. The effect of a nonphotocatalytic reaction occurring on the surface of an irradiated wide band gap metal oxide is seen as the influence of photosimulated adsorption on the photocoloration of the metal oxide specimen.

The results of a mechanistic study into the formation of various states of oxygen produced over irradiated zirconia (ZrO2) under various conditions. The photooxiodation of hydrogen in the presence of molecular oxygen over irradiated powdered ZrO2 as a model reaction is examined.

The results of studies on the solonitsyn memory effect in gas-solid heterogeneous systems with respect to photo-stimulated adsorption of molecular hydrogen, oxygen and methane on a dielectric metal oxide surface are mentioned. The experimental data is explained using a simple model.

Electron transfer quenching of the fluorescence of rhodamine-6G in polyvinyl acetate and poly-α-methylstyrene films by aromatic amine quenchers has been examined, using both steady-state and time-resolved methods. Observed quencher concentration dependences do not conform to expectations from either the simple Perrin or Stern–Volmer models. The steady-state quenching results are consistent with long-range electron (tunnel) transfer, with collective quenching at higher quencher concentration, but existing models of this process do not quantitatively rationalize our results. Some potential difficulties with these models are accordingly discussed. Time-resolved (streak camera) experiments confirm that all the quenching events are of dynamic origin, to the exclusion of the involvement of a fractional population of fluorescence-inactive absorbers owing to ground-state complex formation. [ABSTRACT FROM AUTHOR]

The studies on photoinduced processes that take place in gas-solid heterogeneous systems are reported. It is found that the introduction of H2 yields an after-glow that is caused by chemical interaction between the photoactivated surface of the photocatalyst and the H-containing molecules in the heterogeneous gas-solid system. Further, a mechanism is proposed that involves shallow traps and deep energy traps for electrons to explain the photophysical events triggered by the surface chemical reaction.

The photocatalyzed transformation of phenol and 4-chloropphenol in air-equilibrated TiO(sub 2) dispersions are used to examine the spectral behavior of the quantum yields phi of loss of theses two substrates at various wavelengths.

This article reports an in situ UV–Vis–NIR diffuse reflectance (DR) spectroscopic and kinetic study of the photoformation and thermal annealing of light absorbing electronic point defects (color centers) in photochromic TiO2 in the temperature range 90–720 K using a simple laboratory-made cryostat-type accessory (for a Cary 5000 spectrophotometer equipped with an integrating sphere). The accessory also allowed for UV–Vis–NIR DR studies to be undertaken either in vacuum or in an oxygen atmosphere at significantly high temperatures (to 720 K) to assess dark chemical events occurring in photochromic titania with the participation of color centers. The DR spectral and kinetic measurements provided the opportunity to examine the separation of photoinduced charge carriers at traps and thermally stimulated carrier detrapping and recombination, as well as the response of color centers to oxidative/reductive treatments of photochromic TiO2. Kinetic results also demonstrate the applicability of the fabricated DR accessory as a high-temperature reaction cell in the systematic study of the principal regularities in the formation and destruction of color centers in titania at various temperatures and gaseous atmospheres. [ABSTRACT FROM AUTHOR]

A new study seeks to establish whether spectral sensitization of metal oxides by UV illumination is a phenomenon more general than previously thought and whether it includes photostimulated adsorption of molecules and photochemical reactions.

Research was conducted to examine the photostimulated reactions at the surface of wide band-gap metal oxides such as TiO2 and ZrO2. Specifically, the photostimulated adsorption of oxygen on ZrO2 upon illumination with UV light and its postphotostimulated photoadsorption on irradiation with visible light were investigated. Results indicate that the proposed photoadsorption mechanism can be expanded to photocatalyzed oxidative reactions of phenol in irradiated aqueous TiO2 dispersions.