堀越 智

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The present study examines carbon microcoils (CMCs) as a novel support for Pt and Pd nanocatalysts and compares it with activated carbon nanoparticles as support for Pt and Pd metal deposits in two model microwave-assisted organic syntheses: (i) the Suzuki-Miyaura coupling reaction between phenylboronic acid and 1-bromo-4-methylbenzene in toluene solvent to produce 4-methyl-biphenyl and (ii) the dehydrogenation of tetralin (1,2,3,4-tetrahydronaphthalene) in solvent-free conditions. The microwave absorption capacity of the CMCs was more effective than the ACs support from the viewpoint of dielectric parameters (dielectric constant, dielectric loss, and loss tangent). Possible generation of microplasma (i.e., hot spots) on both supports that can impact on the progress of the reactions was monitored visually and photographed with a high-speed camera. Conventional heating (oil bath or heating mantles) of the Pd(Pt)/CMCs and Pd(Pt)/ACs system led to significantly lower product yields. (C) 2012 Elsevier Inc. All rights reserved.

The present study examines carbon microcoils (CMCs) as a novel support for Pt and Pd nanocatalysts and compares it with activated carbon nanoparticles as support for Pt and Pd metal deposits in two model microwave-assisted organic syntheses: (i) the Suzuki-Miyaura coupling reaction between phenylboronic acid and 1-bromo-4-methylbenzene in toluene solvent to produce 4-methyl-biphenyl and (ii) the dehydrogenation of tetralin (1,2,3,4-tetrahydronaphthalene) in solvent-free conditions. The microwave absorption capacity of the CMCs was more effective than the ACs support from the viewpoint of dielectric parameters (dielectric constant, dielectric loss, and loss tangent). Possible generation of microplasma (i.e., hot spots) on both supports that can impact on the progress of the reactions was monitored visually and photographed with a high-speed camera. Conventional heating (oil bath or heating mantles) of the Pd(Pt)/CMCs and Pd(Pt)/ACs system led to significantly lower product yields. © 2012 Elsevier Inc. All rights reserved.

Effects of temperature variation in microwave-induced system of tetralin dehydrogenation on the enhancement of reactivity were investigated. The enhancement of heating ability of Pt-supported activated carbon catalyst (Pt/AC) particle and decreasing of an existing temperature gradient (non-uniformed heat distribution) in tetralin solution under microwave heating and boiling-reflux condition were examined by three methodologies: an employment of Dewar-like insulation reactor (DIR), addition of an ionic liquid as an optional microwave absorber in the system, and optimization of the catalyst to the reactant in the reaction system. The Dewar-like insulation reactor was used to prevent heat loss in the heterogeneous solution. Under microwave heating with DIR, the reaction can be heated approximately 3 degrees C above the normal boiling point of tetralin. In comparison to the reaction carried out in a conventional reactor, tetralin conversion increased from 31% to 56% under 190 W microwave irradiation. Addition of an ionic liquid to the system to function as a heating promoter remarkably enhanced the heating rate of tetralin. However, the ionic liquid deactivated the activity of the catalyst in the reaction. Optimization of tetralin to Pt/AC catalyst in the reaction system improved heat distribution and showed an interesting result. It was found that the reaction performed under the liquid film state showed the highest tetralin conversion, 69% with the microwave irradiation for 60 min. (C) 2011 Elsevier B.V. All rights reserved.

This study investigates the effect of microwaves on the dehydrogenation of decalin and tetralin. The reactions were studied in a fixed-bed reactor under microwave heating (MWH), and the results were compared with those under conventional heating (electrical heating) (CH). The result of this investigation showed that under the same operating conditions, increase in the conversion of tetralin in the microwave-heated system was more than that in the conventional heated system. This demonstrated the microwave effect appeared in the dehydrogenation of tetralin. In addition, the activity and stability of the catalyst also improved under MWH. The microwave effect resulted in increase in the conversion reaction of tetralin dehydrogenation by generation of a large temperature gradient from the catalyst surface to surrounding species and the subsequent mass transfer in which both vectors have direction inverted from that of CH. Such a phenomenon induced faster molecule desorption (product species) or enhancement of species transport in the system. In addition, the contiguous strong adsorption of hydrocarbon can be reduced, leading to decrease in coke deposition. Conditionally, this benefit issue particularly resulted in increase in the reaction rate in which species transport or mass diffusion is the rate-limiting step. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

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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 TiO2 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.

This article examines the generation of hot-spots and their impact in the heterogeneous Suzuki-Miyaura coupling reaction for the synthesis of 4-methylbiphenyl in toluene solvent in the presence of Pd/AC. Hot-spots easily formed on the surface of the activated carbon (AC) catalyst support under high electric field conditions; they were recorded in real time using a high-speed camera. Chemical yields of 4-methylbiphenyl under the microwaves' magnetic field (H-field) were 2-fold greater than those under electric field (E-field) conditions at identical temperatures and reaction times (120 min). Microwave E-field irradiation with a high accuracy device enhanced generation of hot-spots. Excessive formation of hot-spots impacted negatively on this coupling reaction.

A simplified and energy-saving integrated device consisting of a microwave applicator and an ultrasonic homogenizer has been fabricated to generate liquid plasma in a medium possessing high dielectric factors, for example water. The microwave waveguide and the ultrasonic transducer were interconnected through a tungsten/titanium alloy stick acting both as the microwave antenna and as the horn of the ultrasonic homogenizer. Both microwaves and ultrasonic waves are simultaneously transmitted to the aqueous media through the tungsten tip of the antenna. The microwave discharge liquid plasma was easily generated in solution during ultrasonic cavitation. The simple device was evaluated by carrying out the degradation of the perfluorooctanoic acid (PFOA), a system highly recalcitrant to degradation by conventional advanced oxidation processes (AOPs). PFOA is 59% degraded in an aqueous medium after only 90 s of irradiation by the plasma. Intermediates were identified by electrospray mass spectral techniques in the negative ion mode. (C) 2011 Elsevier B.V. All rights reserved.

This brief article reviews the behavior of microwaves in organic syntheses from the viewpoint of the frequency effect, which has been examined on various common solvents with a newly fabricated 5.80-GHz microwave organic synthesis apparatus, whose features are compared with a similar 2.45-GHz microwave apparatus. Results from usage of the 5.80-GHz microwaves are also compared to the more frequently used MW frequency of 2.45 GHz. The frequency effect was examined for various organic reactions such as the Diels-Alder reaction, the synthesis of benzimidazole-based room-temperature ionic liquids, and the Suzuki-Miyaura coupling reaction. Non-polar solvents can prove particularly useful in organic reactions with the higher frequency microwaves. In this regard, further experiments on microwave-assisted organic syntheses will extend our understanding of the microwave frequency effect(s).

The influence of moisture content (15% w/w) on the remediation (vaporization) of trichloroethylene (TCE) present in natural sands, chosen as a TCE-polluted model system for soils, was investigated with regard to applied microwave power levels, the depth of the sand sample, and the dielectric factors. The heating process occurring in the sand samples arises through the microwave conduction loss heating and dielectric loss heating mechanisms. The characteristic relevance of the electric and magnetic microwave radiation fields to the heating mechanisms was also examined. Heating by the magnetic microwave radiation field was considerable when magnetite was added to the dry and wet sand samples as the microwave absorber. Optimal microwave conditions are reported for a single-mode microwave applicator. Near-quantitative elimination of the TCE contaminant was achieved for sandy soils within a very short time.

Novel microwave discharge granulated electrodeless lamps (MDGELs: 5 mm x 10 mm), fabricated using vacuum-UV (VUV) transparent quartz envelopes, have been examined for the treatment of model contaminated wastewaters. Evaluation of these MDGELs was performed through the self-ignition of the lamps at low microwave power levels and by the photoassisted decomposition and defluorination of trifluoroacetic acid (TFA), heptafluorobutyric acid (HFBA) and perfluorooctanoic acid (PFOA) in aqueous solutions in a flow-through microwave photoreactor (MW/Photo) containing 20 such MDGELs. A conventional single rod-shaped microwave discharge electrodeless lamp (MDEL) and a low-pressure electrode Hg lamp were also used to compare the performance of these novel MDGELs. The dominant performance of the MDGELs was established by the defluorination kinetics per surface area of the light source immersed in the solutions and by the applied electric power of the lamps. At pH 10, the kinetics correlated with the carbon chain length and with the number of C-F bonds in the three fluorinated acids. Microwave irradiation of the single rod-shaped MDEL device achieved a defluorination level of 51% (TFA), 67% (HFBA), and 37% (PFOA) for a 240-min VUV/UV irradiation of solutions at initial pHs = 4.7-5.2, whereas at pH = 10 defluorination of TFA and HFBA was 100% complete within 120-135 min of irradiation: defluorination of PFOA was ca. 80% complete after 200 min. With the 20 MDGEL system, 100% defluorination of TFA and HFBA was achieved after 105 min, whereas 100% defluorination of PFOA required ca. 400 min of irradiation. A decomposition/defluorination pathway is described for PFOA on the basis of intermediates identified by LC-MS techniques that involved initial VUV/UV irradiation (185 nm and 254 nm) of the PFOA contaminant followed by subsequent losses of CO2 and -CF2 units to complete defluorination and degradation. (C) 2011 Elsevier B.V. All rights reserved.

The aromatic [CpCo(S2C2(R)(H))] (R = Ph, Me, 9-phenanthryl, H) complexes reacted with N-halosuccinimides (NXS; X - Cl, Br, I) in carbon tetrachloride at room temperature to undergo the N-succinimide substitution reaction on the dithiolene ring, but no halogenated dithiolene complex was obtained. The imidation products [CpCo(S2C2(R)(N-sccinimide))] were yielded up to 64% where X I and R 9-phenanthryl. The reaction of [CpCo(S2C2(Ph)(H))] with N-bromophthalimide (NBP) also gave the imidation product [CpCo(S2C2(Ph)(N-phthalimide))]. This is the rare direct imidation reaction to an aromatic metallacycle by NXS. The reaction of [CpCo(S2C2H2)] (R = H) with NIS afforded the double imidation product. One by-product in this reaction was the dithiolene-dithiolene homo-coupling product [CpCo(S2C2(R))](2) (R= Ph, Me, 9-phenanthryl). The microwave-enhanced (MW) reactions were attempted in the carbon tetrachloride solution. Although the solution temperature increased up to only 43 degrees C by MW irradiation, the imidation reaction worked with short reaction time. (C) 2010 Elsevier B.V. All rights reserved.

The effects of 2.45-GHz microwave radiation on the Raman-active lattice phonons of two selected (Wako) anatase and rutile specimens and on Degussa P-25 TiO2 nanoparticles were probed by in situ microscopic Raman spectroscopy in the solid phase with samples subjected to microwave irradiation (MW) or in combination with UV illumination (UV/MW). Significant changes were seen in the Raman band intensities for the pure anatase E-g mode at 143 cm(-1) and for the rutile vibration at 446 cm(-1), whereas only negligible changes in intensity were observed for the 144 cm(-1) band of P-25 nanoparticles exposed to MW and UV/MW radiation. It is deduced that microwaves have a negligible impact on the lattice vibrational modes (phonons) of P-25 titania, even though this specimen was thermally heated by the microwaves. The photodegradation of phenol was re-visited to examine the photoactivity of the TiO2 specimens selected for the in situ Raman study, as attested by the number of center dot OH radicals produced (DMPO spin trap ESR) under UV versus UV/MW irradiations, and by the related enhanced dynamics under UV/MW irradiation relative to UV alone or UV/CH. (C) 2011 Elsevier B.V. All rights reserved.

疎水性の単層カーボンナノチューブ（SWNTs）表面への界面活性剤分子の吸着挙動を分子動力学法および濁度，分散率測定による実験的手法により検討した。本論文では，一般的な界面活性剤分子であるドデシル硫酸ナトリウム（SDS）およびセチルトリメチルアンモニウムブロミド（CTAB）をモデルとして用い，その構造による吸着挙動の違いとそれが疎水性粒子の分散率に与える影響について議論した。SWNTsの分散率の違いが界面活性剤分子の構造によって異なることを実験的に見いだした。SDS分子の親水基は吸着の初期において疎水性表面に吸着し，疎水基は疎水性表面において吸着度脱着を繰り返した。SDSと比較して，CTAB分子は疎水性表面に安定な吸着層を形成した。結果として，SDSおよびCTABのSWNTs表面への吸着挙動がまったく異なりこれが分散率の違いに大きく影響していることが示唆された。

マイクロ波をエネルギー源とする粒状の無電極紫外線ランプ（microwave discharge electrodeless lamp：MDEL）を試作し，マイクロ波によるランプの自己点灯効率や1，4－ジオキサン水溶液の光分解速度から，水処理の性能評価を行った。粒状MDELを20個入れた循環式反応容器を用いて，ジオキサン水溶液を循環させながら分解し，濃度や全有機炭素量の減少から分解効率を検討した。比較実験として，棒状MDELや有電極低圧水銀ランプを用いた分解実験も同様に行い，MDELの表面積や消費電力の観点から，粒状MDELの優位性を明らかにした。一方，反応容器の通過回数に対するジオキサン水溶液の分解率を求めた結果，3回の流通で93％の分解率が観測された。分解時間に対するジオキサン水溶液のLC-MS測定から，分解中間生成物の分析を行った結果，初期分解メカニズムとして，^·OHラジカルによる攻撃と，それに伴う環状構造の分解が進行することを明らかにした。

Characteristics of 2.45-GHz microwave radiation were examined on two second generation nitrogen-doped TiO2 nanomaterials prepared by annealing Degussa P-25 TiO2 and Ishihara ST-01 TiO2 at 400 degrees C and 500 degrees C, respectively, in air in the presence of urea, and for comparison on the undoped pristine samples. Band gaps of all four samples were determined by diffuse reflectance spectroscopy. Both the sizes and the BET specific surface areas of the TiO2 particles were determined, together with dielectric constants and dielectric loss factors. Nitrogen doping caused the size to increase and surface area to decrease. Temperature-time profiles showed that the heating efficiency of the N-doped specimens by the microwaves was greater, particularly significant for the N-doped P25 sample, but rather small for the N-ST01 sample. The effect of microwaves on the surface optical phonons of the samples, with and without UV-vis irradiation, was examined by an in situ Raman spectroscopic technique: for the undoped P-25 and nitrogen-doped N-P25 TiO2 systems the effect was negligible. By contrast, microwave irradiation of Ishihara ST-01 and nitrogen-doped N-ST01 TiO2 samples showed significant changes in the 144-cm(-1) optical phonons. Results infer a microwave thermal effect on the Ishihara ST-01 and N-ST01 specimens, whereas for the Degussa P-25 samples the microwaves also imparted a specific effect as the microwaves influenced the N-dopant sites in contrast to the ST-01 systems where the dopant sites were unaffected as evidenced by temperature-time profiles. The microwave-/photo-assisted degradation of 4-chlorophenol under various conditions of UV-vis irradiation and conventional heating, as opposed to microwave heating, confirms the specific microwave effect for the P-25 systems. (C) 2010 Elsevier B.V. All rights reserved.

Molecular dynamics simulations have been carried out to assess event details in the adsorption of the hydrophobic substrate 1,2,4-trichlorobenzene (TCB) on the hydrophilic TiO2 particle surface in the presence of the biosurfactant 4-O-(4',6'-di-O-acetyl-2',3'-di-O-alkanoyl-beta-D-mannopyranosyl)-D-erythritol (MEL) and the SDS (sodium dodecylsulfate) surfactant in aqueous media at ambient temperature with interaction forces between organic molecules and TiO2 calculated from Lennard-Jones and Coulomb potential models. The surfactant and the TCB substrate were arranged in the vicinity of TiO2 using 768 water molecules in the simulations. Results indicate that the MEL molecules adsorb on the TiO2 surface in ca. 5 Ps (k = 2 x 10(11) s(-1)) through the oxygen atoms of the hydrophilic functions. Contact distance between the MEL and the TiO2 surface shortened further after 10 ps with adsorption controlled mostly by van der Waals' forces. The TCB molecules are trapped within the alkyl chains of the MEL system, which subsumes TCB to a greater extent by the repulsion of water, thereby facilitating the TCB molecules to approach the highly hydrophilic and positively charged TiO2 particle surface. Along with the simulations, also examined was the photodegradation of this hydrophobic TCB substrate that takes place at the TiO2/water interface in the presence of the MEL biosurfactant. For comparison, the advantages of the MEL in this task and of the commonly used SDS surfactant were determined under otherwise identical experimental conditions (200 mg L-1 of surfactants) by examining the dynamics of the photo-induced degradation and dechlorination of TCB. The photodegradation of TCB was nearly quantitative in MEL/TiO2 in contrast to only ca. 22% complete in SDS/TiO2 dispersions. It is deduced that wastewater treatments with the highly hydrophilic TiO2 are seriously limited in their photodegradation of hydrophobic pollutants, an issue easily resolvable by the presence of biodegradable surfactants. (C) 2010 Elsevier B.V. All rights reserved.

Given earlier observations that microwave frequencies can have a substantial effect on the photoactivity of a well-known photocatalyst (TiO(2)), in the synthesis of 3,6-diphenyl-4-n-butylpyridazine through a Diels-Alder process, and in the one-pot solvent-free synthesis of a room-temperature ionic liquid, we proceeded to examine the frequency effects of the 5.8 and 2.45 GHz microwave (MW) radiation in the synthesis of gold nanoparticles in non-polar media, such as oleylamine, which have a low dielectric constant (epsilon'), and we further examine differences in shape and size under otherwise identical temperature conditions when the synthesis of the gold nanoparticles was carried out in an ethylene glycol polar medium in the presence of polyvinylpyrrolidone. Whereas a change in microwave frequency from 2.45 to 5.8 GHz at equal microwave power levels led to the synthesis of gold nanoparticles in the non-polar media, a change in the microwave frequency had no effect on the size and shape of the gold nanoparticles synthesized in polar media for identical microwave power levels.

A novel mercury-free Dewar-like (double-walled structure) microwave discharge thermally-insulated electrodeless lamp (MDTIEL) was fabricated and its performance evaluated using the photo-isomerization of trans-urocanic acid (trans-UA) in aqueous media as a test process driven by the emitted UV light when ignited with microwave radiation. The photo-isomerization processes trans-UA -> cis-UA and cis-UA -> trans-UA were re-visited using light emitted from a conventional high-pressure Hg light source and examined for the influence of UV light irradiance and solution temperature; the temperature dependence of the trans -> cis process displayed a negative activation energy, E(a) = -1.3 cal mol(-1). To control the photo-isomerization of urocanic acid from the heat usually dissipated by a microwave discharge electrodeless lamp (single-walled MDEL), it was necessary to suppress the microwave-initiated heat. For comparison, the gas-fill in the MDEL lamp, which typically consists of a mixture of Hg and Ar, was changed to the more eco-friendly N(2) gas in the novel MDTIEL device. The dynamics of the photo-isomerization of urocanic acid driven by the UV wavelengths of the N(2)-MDTIEL light source were compared to those from the more conventional single-walled N(2)-MDEL and Hg/Ar-MDEL light sources, and with those from the Hg lamp used to irradiate, via a fiber optic, the photoreactor located in the wave-guide of the microwave apparatus. The heating efficiency of a solution with the double-walled N(2)-MDTIEL was compared to the efficiency from the single-walled N(2)-MDEL device. Advantages of N(2)-MDTIEL are described from a comparison of the dynamics of the trans-UA. cis-UA process on the basis of unit surface area of the lamp and unit power consumption. The considerably lower temperature on the external surface of the N(2)-MDTIEL light source should make it attractive in carrying out photochemical reactions that may be heat-sensitive such as the photothermochromic urocanic acid system.

The adsorption and aggregation behaviors of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) on a hydrophobic graphite surface were examined using a novel molecular dynamics (MD) simulation with the periodic-shell boundary condition (PSBC). Differences in the adsorption behavior of SDS and CTAB molecules were clearly shown on the hydrophobic surface. Unexpectedly, the SDS molecules approached the graphite surface with their hydrophilic head groups. This unexpected approach mode was thought to be due to the aqueous layer on the graphite surface. The hydrophobic moiety of SDS molecules repeatedly adsorbed and desorbed on the graphite surface. In addition, SDS molecules kept moving on the graphite surface thus, they did not form a stable adsorption layer. In contrast to SDS, the hydrophobic moiety of CTAB molecules approached the graphite surface at the primary step of adsorption. The hydrophobic moieties of CTAB molecules came close to each other, whereas the hydrophilic groups separated from one another. This result suggests that the CTAB molecules form molecular assemblies with a curved structure. The simulation results were consistent with the experimental observations. A clear difference between the adsorption behavior of SDS and CTAB molecules was revealed by MD simulations with PSBC. © 2011 by Japan Oil Chemists' Society.

This article examines the relative stability of five surfactant-free water-in-oil (w/o) emulsions produced by 1-min irradiation of the mixture with 42-kHz ultrasounds; it also reports on the synthesis of hollow silica nanospheres in such emulsions. The oily phase in these w/o emulsions consisted of cyclohexane, dodecane, benzene, octane, and hexane, whereas the dispersed phase consisted of aqueous ammonia at pH 11. Light scattering experiments revealed that the size of the dispersed phase in the cyclohexane emulsion was fairly constant with time (ca. 0.97 mu m) and was the most stable emulsion, whereas for the least stable dodecane w/o emulsion the dispersed phase particles increased in size from ca. 1.5 mu m to 7.3 mu m after 48 min. The stability of the w/o emulsions decreased in the order cyclohexane > octane > benzene > hexane > dodecane. Hollow silica nanospheres were synthesized by a soft template method involving the five surfactant-free water-in-oil emulsions by hydrolysis of tetraethoxysilane (TEOS) at the water/oil interface (pH 11). Formation of these hollow SiO2 nanospheres is described in terms of the stability of the various emulsions and characterized by transmission electron microscopy, which showed well-defined hollow silica nanospheres of relatively uniform sizes (100 +/- 20 nm) in the cyclohexane emulsion. The latter w/o emulsion was further examined for the pH dependence of the formation of the silica nanospheres. At pHs 6 and 7, respectively, highly aggregated hollow silica nanoparticles of ill-defined structure formed with relatively thin skin, whereas well-structured silica nanospheres were obtained at pHs 8 and 9 although the nanospheres also tended to aggregate. By contrast, at pH 10 well-defined hollow silica nanospheres were produced with a silica skin 3 times thinner (5 nm) than that of nanospheres produced at pH 11 (ca. 14 nm). Various stages in the overall process are described. (C) 2010 Elsevier B.V. All rights reserved.

A novel microwave reaction vessel is herein proposed for maintaining constant heat during microwave-assisted organic syntheses. The structure of the vessel is Dewar-like in that it prevents conduction of microwave-generated heat in dielectric substrates into the surroundings. The potential of the double-walled vacuum-filled vessel has been examined for the absence of thermal gradients in aqueous media (homogeneous media) and in the synthesis of biphenyl in a nonpolar solvent (heterogeneous media) involving the Suzuki-Miyaura coupling reaction. The efficiency of the microwave-assisted organic synthesis was enhanced significantly (6- to 7-fold) with this double-walled vessel relative to the conventional single-walled reactor vessel currently used in commercial microwave chemical devices.

The microwave specific effect(s) that can impact a microwave-assisted and photo-assisted reaction occurring on the surface of ZnO or TiO2 (P-25) particles was (were) examined by comparing the process occurring under rich magnetic field conditions and under magnetic/electric field conditions. The features of the photo-assisted process in the presence of microwaves rich in a magnetic field (H) and an electric field (E) are described on the basis of (i) the degradation dynamics of 4-chlorophenol (4-CP) at ambient temperatures, (ii) the number of (OH)-O-center dot radicals produced, and (iii) the dielectric properties of the metal oxides (in pellet form). For ZnO, the photoactivity is enhanced by a microwave specific non-thermal (i.e. non-caloric) effect originating from the microwaves' magnetic field, but decreased by the thermal (i.e. caloric) factor originating from the microwaves' electric field. Contrary to ZnO, the photoactivity of TiO2 (P-25) was enhanced by the synergistic effect between the magnetic and electric fields of the microwave radiation. Photocorrosion of ZnO in the aqueous dispersions was negligibly small (<0.05%) under UV, MW-EH, and UV/MW-EH irradiation conditions. (C) 2009 Elsevier B.V. All rights reserved.

This review article focuses, albeit non-exhaustively, on the influence of microwave radiation on photoassisted processes often referred to as Advanced Oxidation Processes. In particular, we describe and illustrate the possible advantages of microwaves in TiO(2)-assisted photodegradations and photomineralizations of various organic pollutants such as herbicides and endocrine disruptors, among others. Described are also various reactor configurations involving UV/visible radiation and microwaves, with the former being supplied either by traditional Hg lamps or alternatively by electrodeless lamps activated by microwaves. To place the use of microwaves on processes occurring in aqueous TiO(2) dispersions in perspective regarding environmental applications, we first introduce the various sources of pollutants and subsequently describe in brief the various advanced oxidation processes such as UV/peroxidation, UV/ozonation and the photo-Fenton process(es) in addition to direct photolysis either by sunlight or by artificial light sources. (C) 2010 Elsevier B.V. All rights reserved.

The hydrogen production from tetralin was carried out under microwave heating compared with conventional heating. Pt-supported activated carbon was used as a catalyst and microwave receptor in the reaction. Microwave heating increased the conversion of tetralin dehydrogenation as compared with conventional heating up to 19% at the same condition (207 degrees C). Moreover, the microwave reaction exhibited the lower retardation constant resulting from naphthalene adsorption on the surface of heterogeneous catalyst. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Monoglycerylcetyldimethylammonium chloride was synthesized from 3-chloro-1,2-propanediol (CP) and N,N-dimethylhexadecylamine (DMHA) in 2-propanol solvent and in solvent-free conditions to examine microwave specific effects. None were evident in homogeneous 2-propanol media under temperature conditions identical to conventional heating. In contrast, heterogeneous solvent-free conditions brought out specific microwave effects as evidenced by variant product yields (130 degrees C; 30 min): 62% by microwave and 47% by conventional heating. This variance is attributed to thermal conduction and localized hot spots formed under microwave irradiation. The model proposed for the solvent-free synthesis considers hydrophilic 3-chloro-1,2-propanediol molecules form H-bonded domains (size, 2-20 mu m) preferentially heated by the microwaves and dispersed in a sea of hydrophobic N, N-dimethylhexadecylamine molecules. (C) 2010 Elsevier B. V. All rights reserved.

This short article examines the microwave-assisted photolytic disinfection of aqueous solutions contaminated by Bacillus subtilis microorganisms using UV and vacuum-UV radiation emitted from a microwave discharge electrodeless lamp (MDEL), a device containing a Hg/Ar gas-fill that was proposed recently for use in Advanced Oxidation Processes (AOPs). Results of the disinfection are compared with those obtained from UV radiation emitted by a low-pressure electrode Hg lamp and by an excimer lamp. Also examined is the disinfection of B. subtilis aqueous media that contained Au3+ or Ni2+ ions, species often found in the treatment of electroplating wash wastewaters.

The photooxidative mineralizations of two microorganisms-produced glycolipid biosurfactants 4-O-(4',6'-di-O-acetyl-2',3'-di-O-alkanoyl-beta-D-mannopyranosyl)-D-erythritol (MEL-A) and 1-O-(6'-O-acetyl-2',3'-di-O-alkanoyi-beta-D-mannopyranosyl)-D-erythritol (MEL-B) were examined by monitoring the temporal changes in UV absorption, the time profiles of CO2 evolution and the changes in interfacial tension occurring by an advanced oxidation process in the presence of a metal-oxide (TiO2). Features of their mineralization are compared to the photomineralization of the anionic dodecylbenzene sulfonate (DBS) surfactant carried out under otherwise identical conditions. The adsorption of surfactants on the TiO2 surface and the positions of attack of the photogenerated (OH)-O-center dot radicals on the surfactants' structure were assessed by molecular orbital (MO) calculations of partial charges and frontier orbital electron densities, respectively. The photodegradation of DBS was faster than the MELs as also evidenced by surface tension measurements, whereas the photomineralization of the anionic DBS surfactant was definitely slower than that of the MEL biosurfactants due to the hydrophobic alkyl chain in the DBS structure. Possible initial mechanistic stages of the photooxidation of MEL-A and MEL-B are proposed based on experimental data and comparison with MO calculations. (C) 2009 Elsevier B.V. All rights reserved.

This article examines the effect(s) of the 2.45-GHz microwave (MW) radiation in the synthesis of silver nanoparticles in aqueous media by reduction of the diaminesilver(I) complex, [Ag(NH(3))(2)](+), with carboxymethylcellulose (CMC) in both batch-type and continuous-flow reactor systems with a particular emphasis on the characteristics of the microwaves in this process and the size distributions. This microwave thermally-assisted synthesis is compared to a conventional heating (CH) method, both requiring a reaction temperature of 100 degrees C to produce the nanoparticles, in both cases leading to the formation of silver colloids with different size distributions. Reduction of the diaminesilver(I) precursor complex, [Ag(NH(3))(2)](+), by CMC depended on the solution temperature. Cooling the reactor during the heating process driven with 390-Watt microwaves (MW-390W/Cool protocol) yielded silver nanoparticles with sizes spanning the range 1-2 nm. By contrast, the size distribution of Ag nanoparticles with 170-Watt microwaves (no cooling; MW-170W protocol) was in the range 1.4-3.6 nm (average size similar to 3 nm). The overall results suggest the potential for a scale-up process in the microwave-assisted synthesis of nanoparticles. Based on the present data, a flow-through microwave reactor system is herein proposed for the continuous production of silver nanoparticles. The novel flow reactor system (flow rate, 600 mL min(-1)) coupled to 1200-Watt microwave radiation generated silver nanoparticles with a size distribution 0.7-2.8 nm (average size ca. 1.5 nm).

The microwave specific effect(s) that can impact a microwave-assisted and photo-assisted reaction occurring on the surface of ZnO or TiO2 (P-25) particles was (were) examined by comparing the process occurring under rich magnetic field conditions and under magnetic/electric field conditions. The features of the photo-assisted process in the presence of microwaves rich in a magnetic field (H) and an electric field (E) are described on the basis of (i) the degradation dynamics of 4-chlorophenol (4-CP) at ambient temperatures, (ii) the number of (OH)-O-center dot radicals produced, and (iii) the dielectric properties of the metal oxides (in pellet form). For ZnO, the photoactivity is enhanced by a microwave specific non-thermal (i.e. non-caloric) effect originating from the microwaves' magnetic field, but decreased by the thermal (i.e. caloric) factor originating from the microwaves' electric field. Contrary to ZnO, the photoactivity of TiO2 (P-25) was enhanced by the synergistic effect between the magnetic and electric fields of the microwave radiation. Photocorrosion of ZnO in the aqueous dispersions was negligibly small (less than 0.05%) under UV, MW-EH, and UV/MW-EH irradiation conditions. (C) 2009 Elsevier B.V. All rights reserved.

The microwave specific effect(s) that can impact a microwave-assisted and photo-assisted reaction occurring on the surface of ZnO or TiO2 (P-25) particles was (were) examined by comparing the process occurring under rich magnetic field conditions and under magnetic/electric field conditions. The features of the photo-assisted process in the presence of microwaves rich in a magnetic field (H) and an electric field (E) are described on the basis of (i) the degradation dynamics of 4-chlorophenol (4-CP) at ambient temperatures, (ii) the number of (OH)-O-center dot radicals produced, and (iii) the dielectric properties of the metal oxides (in pellet form). For ZnO, the photoactivity is enhanced by a microwave specific non-thermal (i.e. non-caloric) effect originating from the microwaves' magnetic field, but decreased by the thermal (i.e. caloric) factor originating from the microwaves' electric field. Contrary to ZnO, the photoactivity of TiO2 (P-25) was enhanced by the synergistic effect between the magnetic and electric fields of the microwave radiation. Photocorrosion of ZnO in the aqueous dispersions was negligibly small (less than 0.05%) under UV, MW-EH, and UV/MW-EH irradiation conditions. (C) 2009 Elsevier B.V. All rights reserved.

The tendency of water-soluble organics to be photomineralized under microwave and UV irradiation was examined using model substrates bearing alcoholic (methanol, ethanol 1-propanol, ethylene glycol and glycerin) and carbonyl functions (acetone, formic acid and acetic acid). Trends were seen from the decrease of the kinetics of loss of total organic carbon (TOC) with irradiation time. Microwave thermal and specific (non-thermal) effects were probed for the photomineralization process on irradiation of TiO(2) suspensions with 2.45-GHz microwaves and UV irradiation with conventional heating under otherwise identical temperatures, and relative to UV irradiation alone to assess the thermal (TH) and microwave (MW) factors. Dielectric properties of each substrate were also determined under the experimental conditions used. (C) 2009 Elsevier B.V. All rights reserved.

Microwave radiation has recently become an active source of thermal energy in numerous chemical reactions. As such, the microwave energy is not ordinarily and is not likely to be used to drive photochemical reactions. Accordingly, is the role of microwaves then relegated solely to be a source of heat? They do not have to be since photochemical reactions can be activated indirectly by microwaves using the UV light emitted from certain gas-fills excited by microwave radiation. This article examines the microwave radiation not only as a dielectric heat source but also a source of vacuum-UV radiation and UV light through microwave discharge electrodeless lamp devices, which in some cases (depending on design) can also serve as photoreactors. (C) 2009 Elsevier B.V. All rights reserved.

Microwave specific effects on various potential TiO2 photocatalyst specimens were examined for the photodecomposition of 4-chlorophenol (4-CP) with regard to physical and chemical properties and by the characterization of dielectric properties such as the dielectric loss factor (epsilon ''), the dielectric constant (epsilon'), and the dielectric loss tangent (tan delta = epsilon ''/epsilon'). Dielectric properties were measured in both dispersed TiO2 particles in a 4-CP aqueous solution and in TiO2 pellets prepared from the specimens' powders. The irradiation efficiency of the microwave for the TiO2 particles in aqueous media is discussed on the basis of the changes in the dielectric loss factor and penetration depth from the increase in the temperature of water. Changes in crystalline shape and the estimated band gap energies were analyzed before and after irradiation by the microwaves. Of particular significance, the band gap energies were estimated by an in situ observation method under UV and microwave irradiation conditions.

Microwave frequency (2.45 GHz and 5.8 GHz) 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. (C) 2009 Elsevier B.V. All rights reserved.