Charles Kutal

Synthesis and photocatalytic oxidation properties of iron doped titanium dioxide nanosemiconductor particles

The structure, physical characteristics and selective photocatalytic oxidation properties of quantum confined nanosize iron doped TiO2 (Q-TiO2/Fe3+) particles were studied by TG-DSC, XRD, DRS, EPR and Selective Oxidation Photocatalytic Measurements. It is shown that the solubility of iron in the obtained Q-TiO2/Fe3+ nanoparticles is 1.0 atom% and the iron doping level has a great influence on the transformation of anatase to rutile (A-R). The quantum confined effect was observed for Q-TiO2/Fe3+ nanoparticles. All of the samples have EPR Bulk-Fe3+ and Surf-Fe3+ signals, which are located in the bulk and surface of TiO2 nanoparticles respectively. Quantitative EPR results indicate that the relative EPR intensity of these paramagnetic centers shows regular change with varying corresponding iron modification level. In situ EPR indicates that the photo-generated charge carrier (h+, e−) could be trapped by different Fe3+ sites simultaneously, i.e., trapping of h+ is due to Surf-Fe3+ sites at g = 4.30, whereas that of e− is attributed to Bulk-Fe3+ sites at g = 1.99. Selective photocatalytic oxidation of cyclohexane into cyclohexanol with higher selectivity has been obtained by molecular oxygen activation over Q-TiO2/Fe3+ nanoparticles under mild conditions. It is thought that the optical surface state of Q-TiO2/Fe3+ nanoparticles play a key role in the selective photocatalytic oxidations.

Synthesis and characterization of superparamagnetic CoxFe3−xO4 nanoparticles

Abstract CoxFe3−xO4 nanoparticles having dimensions varying from 6.3 to 10.5 nm have been synthesized by a micelle chemical control method, which is capable of producing large quantities of nanocomposite materials at rather low temperature. The average diameter of cobalt ferrite particles ranged from several nanometers to tens of nanometers, which can be controlled by the value of x. For the fine particle, a diffused electron pattern is observed. The Mossbauer absorption patterns consist of a ferromagnetic component superposed on a superparamagnetic doublet. The intensity of the superparamagnetic doublet is found to be larger for particles having small average diameter. The magnetic hyperfine field shows size dependence and is bigger for very fine particle. They decrease with increasing particle size for all the two sublattice sites. For the SPM particles, the quadruple splitting at A sites are generally bigger than those at B sites. Whereas the thing is reversible for isomer shift. The cation distribution and saturation magnetic moment for the obtained powders were presented.

Photocatalytic mineralization of 2,4,6-trinitrotoluene in aqueous suspensions of titanium dioxide

Abstract The photocatalytic destruction of 2,4,6-trinitrotoluene (TNT) in aqueous suspensions of titanium dioxide (TiO2, Degussa type P25) was investigated. Under aerobic conditions, irradiation with the Pyrex-filtered output of a 200-W high pressure mercury-arc lamp resulted in complete (95 ± 5%) mineralization of 50 ppm of TNT within a few hours. Rapid photodegradation of TNT also occurred under anaerobic conditions but without appreciable mineralization. In the absence of TiO2, direct photolysis of TNT yielded a complex mixture of colored organic products in both aerobic and anaerobic environments.

Use of transition metal compounds to sensitize a photochemical energy storage reaction

Abstract A solar energy storage system based upon the valence isomerization of norbornadiene to quadricyclene possesses several attractive features, including high specific energy storage capacity, kinetic stability of the energy rich photo-product in the absence of suitable catalysts, and relatively inexpensive reactants. An inherent difficulty with the system is the lack of absorption of solar energy by norbornadiene. Attempts to overcome this shortcoming have focused upon the use of transition metal compounds to sensitize the desired energy storage step. Results to date indicate that complexation of norbornadiene to the metal provides a potentially useful route to sensitization. Several copper(I) compounds have thus far been found to be effective. The facors which affect the ability of a transition metal compound to function as a sensitizer via a complexation mechanism are discussed.

Photochemistry of transition metal-organic systems

Abstract Irradiation of an organic substrate in the presence of a transition metal compound offers a convenient and often highly-selective route to a variety of interesting and useful products. In this article we seek to identify the key ground- and excited-state interactions between the metal and substrate, and thereby gain insight about the factors that predispose the system to a particular reaction path. Such information, in turn, can be of value in the design of new or improved applications based upon this type of process.

Generation of bases and anions from inorganic and organometallic photoinitiators

Abstract Photosensitive materials composed of a substrate (monomer, oligomer or polymer) and a photoinitiator play a central role in numerous commercial processes. Most photoinitiators in common use are organic compounds that, upon irradiation, produce radicals and/or acids. The desire to expand the scope of photoinitiated chemistry has led to the recent discovery of several classes of inorganic and organometallic photoinitiators that photochemically release neutral Lewis bases and/or anions. This article provides an overview of the authors research program to develop novel photobase and photoanion generators. Fundamental studies of these systems and examples of their potential applications are described.

Substitutional photochemistry of sandwich and half-sandwich complexes of ruthenium(II)

Abstract Ruthenium(II) sandwich complexes of the type Ru( η 6 -arene) 2 2+ (arene is benzene or 1,3,5-trimethylbenzene) undergo photosubstitution of one arene ring by solvent (S) to yield Ru( η 6 -arene)(S) 3 2+ . Reaction occurs from the lowest ligand field triplet state of the complex with a quantum efficiency that decreases with increasing methylation of the arene. Half-sandwich complexes of general formula Ru( η 6 -arene)(L) 3 2+ (L is CH 3 CN or NH 3 ) undergo competitive photosubstitution of arene and L by solvent. The relative importance of these pathways depends upon a number of factors, including excitation wavelength, solvent, and the nature of L. Mechanisms for these photoreactions are discussed and comparisons to earlier studies are presented.

Charge-transfer spectroscopy and photochemistry of alkylamine cobalt(III) complexes

Abstract Spectroscopic and photochemical studies are reported for Co(NH2R)63+, Co(NH2R)5OH23+, and Co(NH2R)5X2+ (where R is methyl, ethyl, or n-propyl, and X is Cl− or Br−). These complexes absorb strongly in the ultraviolet region owing to the presence of one or more ligand-to-metal charge transfer (LMCT) band(s). Irradiation into this charge transfer region results in redox decomposition of the complex with the release of Co2+, alkylamine, and a radical. Photoredox quantum yields measured in fluid solution are generally high and dependent upon excitation wavelength, oxygen concentration, temperature, and solution viscosity. In contrast to their well-studied ammine analogues, the alkylamine complexes (1) possess a N → Co charge transfer band at wavelengths well above 200 nm, (2) undergo redox decomposition from the X → Co and N → Co charge transfer excited states, and (3) avoid an intermolecular decomposition pathway involving photooxidation of the solvent. Reasons for these differences between the two families of complexes are discussed.

Electrochemical catalysis of the valence isomerization of quadricyclene

Abstract Electrochemical oxidation of quadricyclene results in its isomerization to norbornadiene by a redox chain mechanism.

Ground- and excited-state reactivities of cationic sandwich and half-sandwich complexes of iron(II)

Abstract Irradiation of cationic complexes belonging to the [CpFe(η 6 -arene)] + family (Cp is η 5 -C 5 H 5 ) results in the substitution of arene by solvent or other potential ligands present in solution. In solutions containing an epoxide monomer, this photochemical reaction generates a species that initiates polymerization. While several studies of this commercially important process have been reported, the nature of the active initiating species has remained largely conjectural. We have undertaken an investigation that employs two powerful techniques—ion cyclotron resonance Fourier transform mass spectrometry and electrospray ionization mass spectrometry—to elucidate the mechanism of photoinitiated polymerization in systems containing [CpFe(η 6 -arene)] + complexes. These techniques have led to the first direct observation of several cationic photoproducts that can serve as initiators for epoxide polymerization. Our results and their mechanistic implications form the subjects of this article.