堀越 智

Attempts to generate plasma in liquids have been successful and various devices have been proposed. Many reports have described the optimal conditions needed to generate plasma, and mechanisms have been inferred, together with the composition of the plasma. Elucidation of a stable method ( and mechanism) to generate plasma in liquids has led to various active investigations into applications of this new energy source. This review article describes the generator and the generation mechanism of in-liquid plasma, and pays attention to the evolving technology. The characteristics of submerged plasma are summarized and examples of nanomaterials syntheses and wastewater treatment are given, both of which have attracted significant attention. Extreme reaction fields can be produced conveniently using electrical power even without the use of chemical substances and high-temperature high-pressure vessels. Chemical reactions can be carried out and environmental remediation processes achieved with high efficiency and operability with the use of in-liquid plasma. Suggestions for introducing in-liquid plasma to chemical processes are discussed.

Water splitting occurring on a semiconductor photocatalyst has become the Holy Grail process to produce a solar fuel, hydrogen, on irradiation with sunlight (or simulated sunlight) in heterogeneous media. Authors often claim highly efficient evolution of hydrogen and oxygen from water through water splitting or efficient hydrogen evolution in the presence of some sacrificial electron donor, whether photocatalytically or photo electrochemically. Perusal of the scientific and patent literature reveals that yields of hydrogen are disappointingly low even after decades of remarkable advances in materials science and in strategies to achieve significant progress in water splitting. This Review identifies and discusses intrinsic and extrinsic factors (e.g., Phi(h nu) = fn{beta, k(r), S, D, d, s, tau, alpha(h nu)}; photostability; back reactions) that impact redox reactions in general and water splitting in particular. The lack of control and handling of these various factors present a challenging, if not an impossible task in improving process efficiencies to achieve significant practical evolution of hydrogen from water splitting.

Continuous hydrogen evolution occurred in near-quantitative yields from the dehydrogenation of an organic hydride (methylcyclohexane; MCH) through a microwave-assisted catalyzed process taking place in a fixed-bed reactor in the presence of Pd catalyst particles supported on activated carbon particulates (Pd/AC). Unlike conventional heating, the microwave heating method displayed a large temperature distribution experimentally observed along the vertical catalyst fixed-bed reactor attributed to the distribution of the microwave electric field, among other factors. A principal feature of the microwave-assisted method was the rapid heating response of the catalyst at low microwave power with considerable energy saving relative to conventional heating with a ceramics heater (2 min versus ca. 35-40 min; 33 W versus 139 W). A more uniform distribution of the microwave-generated heat and introduction of warmer liquid organic hydride (greater than ambient) should lead to significant improvement in process efficiency. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

<p>Continuous hydrogen evolution occurred in near-quantitative yields from the dehydrogenation of an organic hydride (methylcyclohexane; MCH) through a microwave-assisted catalyzed process taking place in a fixed-bed reactor in the presence of Pd catalyst particles supported on activated carbon particulates (Pd/AC). Unlike conventional heating, the microwave heating method displayed a large temperature distribution experimentally observed along the vertical catalyst fixed-bed reactor attributed to the distribution of the microwave electric field, among other factors. A principal feature of the microwave-assisted method was the rapid heating response of the catalyst at low microwave power with considerable energy saving relative to conventional heating with a ceramics heater (2 min versus ca. 35‒40 min; 27W versus 139 W). A more uniform distribution of the microwave-generated heat and introduction of warmer liquid organic hydride (greater than ambient) should lead to significant improvement in process efficiency.</p>

Microwave discharge electrodeless lamps (MDELs) have been examined for continuous on-site field treatment of contaminated water using solar cells to provide the necessary electrical power. The equipment aimed to decontaminate water in areas impacted by natural disasters such as the extensive earthquake that hit Eastern Japan in 2011. An energy-saving semiconductor microwave generator provided the microwaves to activate the MDELs in a microwave/UV reactor setup operated using a single-mode applicator and an E/H tuner. The herbicide 2,4-dichlorophenoxyacetic acid degraded within a shorter time compared to methylene blue at a defined flow rate through the microwave/UV reactor. Sterilization of natural water contaminated with the bacterial microorganism Escherichia coli was complete within 20min. Microwave discharge electrodeless lamps activated by microwaves from a semiconductor generator were used on-site to treat contaminated water with solar cells providing the electrical power. Such a system is able to degrade relatively high concentrations of organic pollutants and sterilize water contaminated with bacteria on-site in relatively short time.

Microwave discharge electrodeless lamps (MDELs) have been examined for continuous on-site field treatment of contaminated water using solar cells to provide the necessary electrical power. The equipment aimed to decontaminate water in areas impacted by natural disasters such as the extensive earthquake that hit Eastern Japan in 2011. An energy-saving semiconductor microwave generator provided the microwaves to activate the MDELs in a microwave/UVreactor setup operated using a single-mode applicator and an E/H tuner. The herbicide 2,4-dichlorophenoxyacetic acid degraded within a shorter time compared to methylene blue at a defined flow rate through the microwave/UV reactor. Sterilization of natural water contaminated with the bacterial microorganism Escherichia coli was complete within 20 min.

The effect of microwave heating (MW) on the activity of a well-known enzyme (catalase) was elucidated by examining the catalase-assisted decomposition of hydrogen peroxide (H2O2 at various heating times (0 to 12 min)). For comparison, conventional water bath heating (WB) was also examined under identical temperature conditions. Microwave radiation had a positive effect on the activity of catalase only over a very short time (less than 3 min), presumably because of the possible disruption of the catalase structural integrity under microwave irradiation at longer times (a negative influence) as evidenced by Gel Permeation Chromatographic (GPC) and MALDI Time-Of-Flight-Mass-Spectrometric (MALDI-TOFMS) analyses. The effect of temperature on the catalase activity was also probed at 39, 37, and 25 degrees C. Results indicate that utilizing a hybrid heating approach with conventional heating (water bath) coupled to microwaves was more effective provided microwave irradiation was carried out for a short time (also less than 3 min). Moreover, it is demonstrated that microwave heating in degrading hydrogen peroxide was most effective when the enzymatic reaction was carried out at a lower temperature, particularly at 25 degrees C.

To date syntheses of nitrogen-doped TiO2 photocatalysts (TiO2-xNx) have been carried out under high temperatures and high pressures with either NH3 or urea as the nitrogen sources. This article reports for the first time the facile preparation of N-doped TiO2 (P25 titania) in aqueous media at ambient temperature and pressure under inert conditions (Ar- and N-2-purged dispersions) with 4-nitrophenol (or 4-nitro-benzaldehyde) as the nitrogen source. The resulting N-doped P25 TiO2 materials were characterized by UV/Vis and X-ray photoelectron spectroscopies (XPS) that confirmed the presence of nitrogen within the photocatalyst; X-ray diffraction (XRD) techniques confirmed the crystalline phases of the doped material. The photocatalytic activity of N-doped TiO2 was assessed through examining the photodegradation of 4-chlorophenol in aqueous media and iso-propanol as a volatile pollutant under UV/Vis and visible-light irradiation. Under visible light irradiation, undoped P25 was inactive contrary to N-doped P25 that successfully degraded 95% of the 4-chlorophenol (after 10 h) and 23% of iso-propanol (after 2.5 h).

A novel phased array antenna systemwas tested for use inmicrowaveassisted organic syntheses under waveguideless and applicatorless setup conditions with the synthesis of the ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM] Cl) as an example; 5.8 GHz microwaves were used to irradiate the sample through free space a distance of 5 m from the antenna system.

A solution containing ethanol as polar material and either benzene or n-dodecane as nonpolar solvent was heated by microwave irradiation employing a single-mode resonance microwave device. Although the microwave heating efficiency was expected from the just value of the relative dielectric constant (εr′) or relative dielectric loss (εr″) for liquid system, it was revealed that the clustering structure of alcohol molecules expected from the excess parameter such as the excess relative dielectric loss is the important factor in the decision for efficiency of the microwave heating for the solution. This assumption and novel theory were strongly supported from the thermodynamic data such as vapor pressure and the partial enthalpy.

A stable water/oil (W/O) emulsion was prepared by adjustment with sorbitan fatty acid monoester surfactants. The prepared W/O emulsion was stable for 60 min in the atmosphere; however, the formation of non-uniform water droplets in the height of the emulsion in the quartz tube reactor were observed by the backscattering measurements with an infrared laser at 850 nm. The increase of temperature under microwave irradiation was influenced sensitively by the position of those water droplets. Those results were caused from the size and concentration of water droplets in the W/O emulsion. On the other hand, selective heating of the water droplets caused heating of the entire W/O emulsion, although the temperature difference between the water droplets and the oil phase was 20 degrees C. (C) 2015 Elsevier Ltd. All rights reserved.

© 2014 American Society of Civil Engineers. There is a need for a detoxification system that is capable of processing debris in the aftermath of urban disasters into less-harmful waste, quickly and efficiently. The research reported in this paper investigated the potential for transforming asbestos-cement into harmless waste using microwave heating, in small-scale and full-scale experiments. The small-scale setup investigated the relationship between temperature and the number of asbestos fibers in cement slates at various microwave treatment times, during which both the internal and surface temperatures were measured for the samples. Subsequently, the full-size apparatus, which was capable of processing 2 t/day of asbestos-contaminated debris, was constructed at a location affected by the Tohoku earthquake in 2011. This system could successfully process 80 kg/h of asbestos-contaminated material and 80-160 kg/h of wood waste. The test results demonstrate that compact asbestos-treatment systems possess efficiency advantages and can operate in full compliance with applicable legal restrictions.

The present article examined the advantages of 5.8-GHz microwaves versus the more commonly used 2.45-GHz microwaves using a modular non-commercial apparatus on the proteolysis of the Arg-Arg-Leu-Ile-Glu-Asp-Ala-Glu-Tyr-Ala-Ala-Arg-Gly peptide at the amino side of the aspartic acid (Asp) using the Asp-N metallo-endoproteinase enzyme. The microscale sample was subjected to microwaves' electric field (E-field) and magnetic field (H-field) radiation: good temperature control for samples at the mu L scale was achieved using an apparatus that emitted microwaves at a precise frequency (5.800000 GHz). Temperature-dependent experiments with the Asp-N metallo-enzyme confirmed the activity of this enzyme to be greatest at 37 degrees C reached within 15 s on irradiation with the 5.8-GHz microwaves' H-field component with an input power of 1.7W under air cooling conditions. Enzymatic activity decreased significantly above and below this temperature by a slight temperature change of 1 degrees C. Proteolysis yields of the peptide by the Asp-N enzyme at 30-42 degrees C under microwave E-field and H-field heating and under conventional heating revealed that enhancement of the proteolysis of the peptide at 37 degrees C by E-field irradiation (42.6%) was 1.5 times greater than by conventional heating (27.5%), whereas under microwave H-field irradiation (63.5%) it was 2.3 times greater than conventional heating. The relative dielectric loss factors (epsilon(r)'') of the sample solution (peptide + enzyme) were also determined: 22.19 (5.8 GHz) and 12.78 (2.45 GHz) at 22 degrees C, which decreased with increasing temperature (faster for the 5.8-GHz microwaves) so that the initial heating efficiency of 5.8-GHz microwaves was nearly twofold greater than for 2.45-GHz microwaves. Results indicated that in addition to a thermal factor, microwave non-thermal factors also had a significant influence as the microwaves considerably enhanced the proteolytic process relative to traditional heating. (C) 2015 Elsevier B.V. All rights reserved.

© 2014 Elsevier B.V. The detoxification mechanism of asbestos materials was investigated through simulations and experiments. The permittivities of pure CaO and Mg3Si4O12, as quasi-asbestos materials, were measured using the cavity perturbation method. The real and imaginary parts of the relative permittivity (e{open}r' and e{open}r″) of CaO are functions of temperature, and numerical simulations revealed the thermal distributions in an electromagnetic field with respect to both asbestos shape and material configuration based on permittivity. Optical microscopic observation revealed that the thickness of chrysotile fibers decreased as a result of CaO heating. The heating mechanism of asbestos materials has been determined using CaO phase, and the detoxification mechanism of asbestos materials was discussed based on the heating mechanism.

The wet synthesis of mono-disperse Ag, Ag-Ni, and Pd-Ag nanoparticles has been performed employing glycol solutions containing [Ag(NH3)(2)](+) and a second metal cation Mn+ (M = Ag, Na, Al, Ni or Pd) under microwave irradiation in a predominately electric (E-) or a predominately magnetic (H-) field. No specific effects of the microwave E-field and H-field on the rate of product formation have been observed. But the synthesis of Ag-Ni alloy particles in the E-field and the H-field resulted in products with different particle size distribution, thus possibly indicating specific field effects.

We report a picosecond transient diffuse reflectance study of commercially available pristine Ishihara ST01 titania, which upon treatment with hydrogen gas yields an oxygen-vacancy rich V-O-ST01 system. For comparison, a nitrogen-doped N-ST01 sample was also prepared using urea as the nitrogen donor. These were characterized by XRD and by diffuse reflectance spectroscopy. Transient decay kinetics at 550 nm for all three samples were determined in situ using a 150 ps Nd-YAG pulsed laser system (10 Hz) and a Xe flash lamp (2 mu s pulses) probe while samples were being microwave-irradiated (2.45 GHz). The transient(s) absorbing at the probe wavelength displayed double exponential decay kinetics: a fast decay that occurred within ca. 5-12 ns ascribed to recombination of photogenerated shallow-trapped or free conduction band electrons with valence band holes, and a slower decay that occurred from hundreds of nanoseconds to several microseconds attributable to recombination of electrons trapped in deep traps (e.g., either as Ti3+ or as F color centers) with free holes. Significant differences were observed for the wet pristine ST01/H2O and V-O-ST01/H2O systems when subjected to microwave irradiation; results concurred with those from the degradation of the 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide in aqueous TiO2 dispersions at 100 degrees C under UV/microwave irradiation (UV/MW) and UV irradiation with conventional heating (UV/CH).

This article reports on the fabrication and enhanced performance of a novel microwave discharge electrodeless lamp (MDEL) consisting of a three layered cylindrical structure that was effective in the remediation of wastewater containing the 2,4-D herbicide and the near total sterilization of bacteria-contaminated pond water (E. coli and other microorganisms) through photolysis with the emitted vacuum-UV (185 nm) and UVC (254 nm) light from the MDEL and through chemical oxidation with reactive oxygen species (ROS) produced by the photolysis of dioxygen and air oxygen through one of the photoreactors. The flow rates of the 1.0 L contaminated waters were 0.6 and 1.2 L min(-1). The integrated UV/ROSO2 and UV/ROSair methods used to carry out the degradation of 2,4-D and sterilization processes were more effective than either the UV method alone or the ROSO2 and ROSair methods for short time periods (5 or 8 min). At a lower flow rate, 79% of 2,4-D was degraded by the UV/ROSO2 method and 55% by UV/ROSair after 8 min. At a faster flow rate of 1.2 L min(-1), degradation of 2,4-D in 1.0 L volume of water was 84% and 77% complete by the UV/ROSO2 and the UV/ROSair method, respectively, after 8 min of irradiation. The number of kills of E. coli bacteria was nearly quantitative (98 and 99%) by the UV/ROSO2 and UV/ROSair methods after treating the contaminated water for 5 min. The decrease of total viable microorganisms in pond water was 90% and 80% after 5 min of microwave irradiation at a flow rate of 1.2 L min(-1) by the integrated methods UV/ROSO2 and UV/ROSair, respectively. The rate of flow of oxygen gas through the photo-reactor impacted the extent of degradation and the related dynamics of the 2,4-D herbicide.

The microwave-induced acceleration of photocatalytic reactions was discovered serendipitously in the late 1990s. The activity of photocatalysts is enhanced significantly by both microwave radiation and UV light. Particularly relevant, other than as a heat source, was the enigmatic phenomenon of the non-thermal effect(s) of the microwave radiation that facilitated photocatalyzed reactions, as evidenced when examining various model contaminants in aqueous media. Results led to an examination of the possible mechanism(s) of the microwave effect(s). In the present article we contend that the microwaves' non-thermal effect(s) is an important factor in the enhancement of TiO2-photoassisted reactions involving the decomposition of organic pollutants in model wastewaters by an integrated (coupled) microwave-/UV-illumination method (UV/MW). Moreover, such coupling of no less than two irradiation methods led to the fabrication and ultimate investigation of microwave discharged electrodeless lamps (MDELs) as optimal light sources; their use is also described. The review focuses on the enhanced activity of photocatalytic reactions when subjected to microwave radiation and concentrates on the authors' research of the past few years.

This article revisits the formation of 4-methylbiphenyl by the Suzuki-Miyaura reaction to examine the formation of hot spots and the factors impacting product yields, such as (i) mass transfer of reactants to the Pd/AC catalyst, (ii) continuous versus pulsed microwave irradiation, (iii) presence of a standing wave versus a nonstanding wave, and (iv) microwave input power levels. Present results indicate that mass transfer and hot spots impact the catalytic process. The rate of stirring of the heterogeneous mixture impinges on the formation of hot spots and product yields. Continuous and pulsed microwave have little effect, whereas both mass transfer and the presence or a absence of a standing wave do affect the yields. Beyond a certain stirring rate (1500 rpm), mass transfer is no longer an issue as yields remain constant; below this value, however, mass transfer, hot spots, and microwave input power levels play a role in the extent of products formed.

This article revisits the formation of 4-methylbiphenyl by the Suzuki-Miyaura reaction to examine the formation of hot spots and the factors impacting product yields, such as (i) mass transfer of reactants to the Pd/AC catalyst, (ii) continuous versus pulsed microwave irradiation, (iii) presence of a standing wave versus a nonstanding wave, and (iv) microwave input power levels. Present results indicate that mass transfer and hot spots impact the catalytic process. The rate of stirring of the heterogeneous mixture impinges on the formation of hot spots and product yields. Continuous and pulsed microwaves have little effect, whereas both mass transfer and the presence or absence of a standing wave do affect the yields. Beyond a certain stirring rate (1500 rpm), mass transfer is no longer an issue as yields remain constant below this value, however, mass transfer, hot spots, and microwave input power levels play a role in the extent of products formed.

Asbestos-containing debris generated by the tsunami after the Great East Japan Earthquake of March 11, 2011, was processed by microwave heating. The analysis of the treated samples employing thermo gravimetry, differential thermal analysis, X-ray diffractometry, scanning electron microscopy, and phase-contrast microscopy revealed the rapid detoxification of the waste by conversion of the asbestos fibers to a nonfibrous glassy material. The detoxification by the microwave method occurred at a significantly lower processing temperature than the thermal methods actually established for the treatment of asbestos-containing waste. The lower treatment temperature is considered to be a consequence of the microwave penetration depth into the waste material and the increased intensity of the microwave electric field in the gaps between the asbestos fibers resulting in a rapid heating of the fibers inside the debris. A continuous treatment plant having a capacity of 2000 kg day-1 of asbestos-containing waste was built in the area affected by the earthquake disaster. This treatment plant consists of a rotary kiln to burn the combustible waste (wood) and a microwave rotary kiln to treat asbestos-containing inorganic materials. The hot flue gas produced by the combustion of wood is introduced into the connected microwave rotary kiln to increase the energy efficiency of the combined process. Successful operation of this combined device with regard to asbestos decomposition is demonstrated. © 2014 American Chemical Society.

This article reviews, albeit non-exhaustively, recent research of chemical reactions induced by microwave radiation in heterogeneous catalytic systems, a field that has been rather active since the 1990s. Results have shown that acceleration of chemical reactions by the microwave method cannot be achieved with conventional heating under otherwise identical temperature conditions. The interaction(s) between the microwave radiation fields and the catalyst appears to be at the origin of such a facilitator effect. Accordingly, the article examines process enhancement in heterogeneous catalytic systems exposed to microwave radiation, particularly on such reactions as the dehydrogenation of methane and other hydrocarbons, and the synthesis of 4-methylbiphenyl by the Suzuki-Miyaura cross-coupling reaction. Also examined are the usage of suitable reactors for carrying out microwave-assisted heterogeneous catalysis, and the role of hot spots that are sometimes encountered in microwave chemistry.

This article reports on a microreactor/microwave high-pressure flow hybrid apparatus of a novel concept design, which includes both the microreactor and a spiral reactor, and its efficient use in the synthesis of silver nanoparticles of relatively uniform sizes (4.3 +/- 0.7 nm) under microwave irradiation. By contrast, under otherwise identical experimental conditions but with conventional heating, the nanoparticle size was non-uniform (8.3 +/- 2.7 nm) and the spiral reactor walls were covered with a silver mirror deposit. Formation of the nanoparticles was monitored by UV-visible spectroscopy (plasmonic absorption band; LSPR), TEM and by small-angle X-ray scattering (SAXS). Both the spiral microreactor and the spiral quartz reactor of the hybrid system played an important role in the synthesis, with the microreactor providing the environment wherein mixing of the aqueous solution of [Ag(NH3)(2)](+) and the solution of glucose (the reducing agent) and poly(N-vinyl-2-pyrrolidone) (PVP; stabilizer/dispersing agent) occurred. The microwaves provided the thermal energy to effect a uniform growth of the silver nanoparticles at temperatures above 120 C. Mixing the two solutions by conventional methods (no microreactor) failed to yield such nanoparticles even under microwave irradiation and no formation of a silver mirror occurred in the inner walls of the spiral reactor. (c) 2013 Elsevier BY. All rights reserved.

This article reports on the preparation and characterization (SEM, SEM-EDX, XRD, diffuse reflectance spectroscopy, and BET surface area) of TiO2 particles supported on activated carbon (AC) particulates using a titanium oxysulphate precursor and subjecting the aqueous dispersion to microwave (MW) heating and to a more traditional heating method with an oil bath. The TiO2/AC composites were subsequently tested for their photoactivity through an examination of the transformation of a volatile organic pollutant (VOC) in air: iso-propanol. Under MW irradiation at 70 degrees C the synthesis resulted in the formation of a thin coating about the AC support, while TiO2 particles formed at higher temperatures; the average particle size of TiO2 tended to decrease with increase in reaction temperature from 426 nm at 80 degrees C to 243 nm at 180 degrees C. The accelerated heating of the AC-dispersed solution above 80 degrees C was confirmed by determining the dielectric loss (epsilon '') of the dispersion at various temperatures at the microwave frequency of 2.45 GHz. Subjecting the dispersion to oil-bath heating only led to formation of a thin film about the AC particulates. In the absence of the AC support TiO2 particle sizes averaged ca. 460 nm for the MW method, while they averaged around 682 nm with the oil-bath method. The BET specific surface area of the TiO2/AC composites was significantly greater for the MW heating method (ca. 990 m(2) g(-1) versus 848 m(2) g(-1) for the oil-bath method). Both UV-vis spectroscopy (estimated band-gap energy of TiO2/AC composites was 3.3 eV) and XRD spectra confirmed the anatase nature of the TiO2 specimens. The MW-produced TiO2/AC particulates proved to be nearly six-fold more photoactive in the photoinduced degradation of the VOC pollutant than those produced by the oil-bath method. A possible growth mechanism of the TiO2/AC composites is proposed. (C) 2013 Elsevier B.V. All rights reserved.

This review article summarizes research directed toward microwave heating in the oil chemistry. Topics to be discussed include microwave synthesis of surfactants, extraction methods, modification of crude oil properties, and degradation of surfactants. The specific effects of microwave heating, which cannot be obtained by conventional heating in particular, are explained. © 2013 by Japan Oil Chemists' Society.

The influence of lattice distortions on TiO2 photocatalysis produced by subjecting commercially available P25 titania samples to a heat treatment in the temperature range 645-800 °C was examined it caused the initial anatase-to-rutile ratio of 81/19 to decrease to 1/99 at the highest temperature. The photoactivities of these heat-treated samples were established through the photodegradation of 4-chlorophenol (4-CP) exposed to UV irradiation alone, UV/microwave irradiation (2.45 GHz), and to UV irradiation accompanied with conventional heating at a temperature otherwise identical to that under UV/MW irradiation. Raman band intensities of pure anatase (143 cm-1), pure rutile (446 cm-1) and of the heat-treated P25 specimens were examined in situ after being exposed to microwave irradiation for about 4 min. Changes are attributed to a microwave non-thermal effect involving oxygen vacancies that affect the specimens' photoactivities as determined by subjecting samples of Evonik P25 titania (AEROXIDE® TiO2 P25) and Ishihara ST-01 TiO2 to a heat treatment in the presence of molecular hydrogen. Such treatment caused lattice distortions of both systems that affected the kinetics of degradation of the chlorophenol under various irradiation conditions. UV/visible absorption spectra of the heat/H2-treated specimens displayed a broad unresolved absorption envelope at wavelengths above 400 nm that has been attributed to oxygen vacancies and thus to F-type color centers in accord with an earlier study by Kuznetsov and Serpone. The presence of such defects, particularly in the heat/H2-treated samples, and the influence of the microwaves caused the photodegradation kinetics for the 4-CP to be enhanced significantly. © 2013 Elsevier B.V.