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Abstract: Characteristic microwave effects on the TiO2 behavior in photoassisted processes have been examined for surface affinity, electric surface charge, size of aggregated TiO2 particles, and not least the number of ls formed using in situ observation techniques. Novel microwave and UV radiation components were assembled to investigate the microwave effects. Microwave radiation can influence analytical instruments. Hence, the assembled components were designed so as to microwave irradiate only the sample solution containing the TiO2 photomediator particles. Peculiar microwave effects implicated in photoassisted reactions involve both thermal and non-thermal factors. [Copyright &y& Elsevier]

Abstract: A microwave discharge electrodeless lamp (MDEL) filled with low pressure mercury gas has been developed for the photocatalytic treatment of organic air pollutants over anatase TiO2 pellets. The benefit of the combination of MDEL and TiO2 pellets under microwave radiation was assessed by examining the degradation of acetaldehyde in humidified synthetic air. The effect of microwave irradiation was quantified by the decomposition rate of acetaldehyde and the desorption rate of acetaldehyde on the TiO2 surface. It is shown that acetaldehyde is readily transformed at the surface of the TiO2 pellets by the combined action of UV light and microwave irradiation coupling homogeneous and heterogeneous photoreactions. [Copyright &y& Elsevier]

Abstract: The microwave-assisted photodegradation of bisphenol-A (BPA) in the presence of TiO2 was examined at ambient temperature to unravel some details on the importance of the microwave non-thermal effect. Normally, bisphenol-A photodegrades under microwave irradiation as a result of a thermal effect emanating from the microwave radiation which sees increase in temperature in the aqueous TiO2 dispersion. However, on cooling the dispersion with circulating silicone oil at −20°C, the temperature of the dispersion could be maintained constant at 21°C. Under the latter irradiation conditions, the microwave-assisted photodegradation of BPA was shown to be not only due to a microwave thermal effect, but also to a significant non-thermal effect that might implicate hot-spots on the TiO2 particle surface leading to enhanced photodegradation under constant ambient temperature. Other origins of the microwave non-thermal effect may include additional formation of charge carriers on the photomediator TiO2 and formation of additional trap sites that may otherwise prolong the lifetimes of the charge carriers through diminished recombination and ultimately increase process kinetics. [Copyright &y& Elsevier]

Abstract: Microwave frequency (2.45GHz and 5.8GHz) effects on the photoactivity of P-25 TiO2 were examined for the photodecomposition of 4-chlorophenol (4-CP), bisphenol A (BPA) and methylene blue (MB), and by the characterization of dielectric properties. Changes in microwave (MW) irradiation efficiency between water and the TiO2 particulates were examined at two MW frequencies on the basis of penetration depth of the microwaves and the dielectric loss factor. TiO2 particles in aqueous media were less photoactive under 5.8-GHz microwave radiation in degrading the organic substrates than under 2.45-GHz microwaves for otherwise identical temperature conditions. Factors that affect the photoactivity of TiO2 at the two frequencies are briefly discussed. [Copyright &y& Elsevier]

The electrochemical behavior of the S,S′-bridged adducts of square planar metalladithiolene complexes was investigated by using cyclic voltammetry and electrochemical spectroscopies (visible, near-IR, and ESR). The norbornene-bridged S,S′-adduct [Ni(S2C2Ph2)2(C7H8)] (2a; C7H8=norbornene) formed by [Ni(S2C2Ph2)2] (1a) and quadricyclane (Q) was dissociated by an electrochemical reduction, and anion 1a- and norbornadiene (NBD) were formed. Q was isomerized to NBD in the overall reaction. The o-xylyl-bridged S,S′-adduct [Ni(S2C2Ph2)2(CH2)2(C6H4)] (3a; (CH2)2(C6H4)=o-xylyl) was also dissociated by an electrochemical reduction, and this reaction gave the o-xylyl radical (o-quinodimethane). The reduction of complex 3a in the presence of excess o-xylylene dibromide underwent the catalytic formation of o-quinodimethane. The butylene-bridged S,S′-adduct [Ni(S2C2Ph2)2(CH2)4] (4a; (CH2)4=butylene) was stable on an electrochemical reduction. The lifetimes of reduced species of these adducts 2a–4a were influenced by the stability of the eliminated group (stability: NBD > o-xylyl radical (o-quinodimethane) > butylene radical). Therefore, the reduced species are stable in the sequence 4a- > 3a- > 2a-. Although the palladium complex [Pd(S2C2Ph2)2] (1b) was easier to reduce than the nickel complex 1a or the platinum complex [Pt(S2C2Ph2)2] (1c), their S,S′-adducts were easier to reduce in the order of Ni adduct > Pd adduct > Pt adduct. [Copyright &y& Elsevier]

Abstract: The square-planar metal dithiolene complexes of o-xylenediyldithioethylene-1,2-dithiolate (oxddt) ligand, (Et4P)[Ni(oxddt)2] (1), (Ph4P)[Ni(oxddt)2] (2) and (Ph4P)[Au(oxddt)2] (3), were prepared and characterized. Among them, the Ni complexes 1 and 2 showed cis-anti-form structures, whose two benzene rings of the Ni(oxddt)2 molecule are closely located to the dithiolene rings but located on the opposite side with respect to the dithiolene ring. In contrast to these Ni complexes, the Au complex 3 has a trans-anti form, suggesting that a Ni/Au substitution in the [M(oxddt)2] modifies those molecular structures in the crystals. An intramolecular π orbital overlap at the α-LUMO+5 level between benzene and dithiolene rings was observed in the [Ni(oxddt)2] complex with the cis-anti-form. Redox behavior of 1 and 3 were investigated by cyclic voltammetry measurements. [Copyright &y& Elsevier]

Abstract: Azido coordinated dithiolene complexes [CpCo(N3){S2C2(CO2Me)2}(S-CHR1R2)], where R1, R2 =H (4a); R1 =H, R2 =SiMe3 (4b); R1 =H, R2 =CO2Et (4c), were synthesized by the reactions of the corresponding Cl− coordinated precursors [CpCo(Cl){S2C2(CO2Me)2}(S-CHR1R2)] (3a–3c) with sodium azide. The Cl− coordinated complex 3d (R1, R2 =CO2Me) did not produce any N3 − coordinated complexes but formed the CR1R2-bridged alkylidene adduct [CpCo{S2C2(CO2Me)2}(CR1R2)] (2d; R1, R2 =CO2Me). The structure of 4a was determined by X-ray diffraction study. In the molecular structure of 4a, the coordinated N3 − ligand and CHR1R2 group were located at the same side with respect to the dithiolene ring (syn form), although the corresponding Cl− precursor (3a; R1, R2 =H) was anti form. A structural conversion of syn/anti was conceivable during the Cl−/N3 − ligand exchange. Thermal (80°C) and photochemical reactions (Hg lamp) of 4a–4c were performed. Among them, 4c was relatively well reacted compared with the others to form the CR1R2-bridged alkylidene adduct (2c; R1 =H, R2 =CO2Et), followed by a formal HN3 elimination, and the reaction also produced non-adduct of the cobalt dithiolene complex [CpCo{S2C2(CO2Me)2}] (1). The electrochemical 1e− reduction of 4c underwent a formal N3 − ligand elimination, and successive second reduction caused the CHR1R2 group elimination or reformed the CR1R2-bridged alkylidene adduct 2c. [Copyright &y& Elsevier]

The rhodiadithiolene complexes [Rh(Cp)(S2C2Z2)] (Z=Ph (1a) and COOMe (1b)) reacted with quadricyclane (Q) to give 1:1 adducts [Rh(Cp)(S2C2Z2) (C7H8)] (Z=Ph (2a) and COOMe (2b)) in which Rh and S of the complexes are bridged by C(7) (bridge carbons) and C(5) (edge carbons) of norbornene (C7H8), respectively. The structure of the adduct 2a was re-investigated and determined by X-ray structural analysis. The rhodiadithiolene complexes and those adducts showed the catalytic activities for the thermal isomerization from Q to norbornadiene (NBD). Adduct 2a photochemically dissociated to give the original complex 1a and NBD upon irradiation with a high-pressure mercury lamp. Skeletal rearrangements of the hydrocarbon moiety were confirmed in the formation of these adducts and in their photo-dissociation, according to deuterium labeling experiments. [Copyright &y& Elsevier]