Development of a microwave-discharge light-emitting diode (MDLED): a novel UV source for the UV-driven microwave-assisted TiO2 photocatalytic treatment of contaminated wastewaters.

This brief article reports on the fabrication of a prototype novel semiconductor digital device, a microwave-discharge light-emitting diode (MDLED), consisting of an LED and a Schottky barrier diode encapsulated in a quartz ampoule. Coating the surface of this ampoule with TiO2 yielded a new photocatalytic TiO2 unit (MDLED-TiO2) for use in treating contaminated wastewaters. To the extent that this MDLED-TiO2 is driven only by microwave energy, there is no need for electric wires or electrical AC power. As much of the activity of TiO2 photocatalyst is enhanced and ultraviolet light emission is generated only by irradiating with microwaves, the MDLED-TiO2 affords a simple water treatment device as demonstrated in the present study. The digital device consisted of 14 pieces of MDLED-TiO2  units immersed into a model contaminated wastewater toward the decomposition of organic pollutants and sterilization of natural bacteria-contaminated wastewaters performed in an energy-saving manner simply by irradiating the wastewaters with microwaves.

Uptake of nanoparticles from sunscreen physical filters into cells arising from increased environmental microwave radiation: increased potential risk of the use of sunscreens to human health.

This study examines the microwave chemical risks posed by photocatalysts present in sunscreens (physical filters) against the increasing use of microwaves (radio waves) in the environment, sometimes referred to as electronic smog. Specifically, the study assesses the damage caused by silica-coated physical filters (photocatalysts, TiO2⋅ and/or ZnO) contained in commercially available sunscreens and fresh silica-coated ZnO for sunscreens to mouse skin fibroblasts cells (NIH/3T3) evaluated in vitro by the life/death of cells using two types of electromagnetic waves: UV light and microwave radiation, and under simultaneous irradiation with both UV light and microwaves. Conditions of the electromagnetic waves were such as to be of lower light irradiance than that of UVA/UVB radiation from incident sunlight, and with microwaves near the threshold power levels that affect human health. The photocatalytic activity of the physical filters was investigated by examining the degradation of the rhodamine B (RhB) dye in aqueous media and by the damage caused to DNA plasmids from E. coli. Compared to the photocatalytic activity of ZnO and TiO2 when irradiated with UV light alone, a clear enhanced photocatalytic activity was confirmed upon irradiating these physical filters concurrently with UV and microwaves. Moreover, the uptake of these metal oxides into the NIH/3T3 cells led to the death of these cells as a result of the enhanced photocatalytic activity of the metal oxides on exposure to microwave radiation.

Photoluminescent Carbon Quantum Dots: Synthetic Approaches and Photophysical Properties.

A number of synthetic methodologies and applications of carbon quantum dots (CQDs) have been reported since they were first discovered nearly two decades ago. Unlike metal-based or semiconductor-based (e. g., metal chalcogenides) quantum dots (MSQDs), CQDs have the unique feature of being prepared through a variety of synthetic protocols, which are typically understood from considerations of reaction models and photoluminescence mechanisms. Consequently, this brief review article describes quantum dots, in general, and CQDs, in particular, from various viewpoints: (i) their definition, (ii) their photophysical properties, and (iii) the superiority of CQDs over MSQDs. Where possible, comparisons are made between CQDs and MSQDs. First, however, the review begins with a general brief description of quantum dots (QDs) as nanomaterials (sizes≤10 nm), followed by a short description of MSQDs and CQDs. Described subsequently are the various top-down and bottom-up approaches to synthesize CQDs followed by their distinctive photophysical properties (emission spectra; quantum yields, Φs).

Sunscreens and their usefulness: have we made any progress in the last two decades?

Sunscreens have now been around for decades to mitigate the Sun's damaging ultraviolet (UV) radiation which, although essential for the existence of life, is a recognized prime carcinogen. Accordingly, have suncreams achieved their intended purposes towards protection against sunburns, skin photo-ageing and the like? Most importantly, however, have they provided the expected protection against skin cancers that current sunscreen products claim to do? In the last two decades, there have been tens, if not hundreds of studies on sunscreens with respect to skin protection against UVB (280‒320 nm)-traditionally sunscreens with rather low sun protection factors (SPF) were intended to protect against this type of radiation-and UVA (320‒400 nm) radiation; a distinction between SPF and UVA protection factor (UVA-PF) is made. Many of the studies of the last two decades have focused on protection against the more skin-penetrating UVA radiation. This non-exhaustive article reviews some of the important facets of what is currently known about sunscreens with regard (i) to the physical UV filters titanium dioxide (TiO2) and zinc oxide (ZnO) and the mostly photo-unstable chemical UVB/UVA filters (e.g., octinoxate (OMC) and avobenzone (AVO), among others), (ii) to novel chemical sunscreen agents, (iii) to means that minimize the breakdown of chemical filters and improve their stability when exposed to UV sunlight, (iv) to SPF factors, and (v) to a short discussion on non-melanoma skin cancers and melanoma. Importantly, throughout the article we allude to the safety aspects of sunscreens and at the end ask the question: do active ingredients in sunscreen products pose a risk to human health, and what else can be done to enhance protection? Significant loss of skin protection from two well-known commercial suncreams when exposed to simulated UV sunlight. Cream I: titanium dioxide, ethylhexyl triazone, avobenzone, and octinoxate; Cream II: octyl salicylate, oxybenzone, avobenzone, and octinoxate.

Development of a Hg-free UV light source incorporating a Kr/Br2 gas, and its application for wastewater treatments.

Mercury lamps are typically the major light sources in water treatments. However, the use of mercury has raised some concerns with regard to the Minamata Convention on Mercury. As such, Hg-free microwave discharged electrodeless lamps (MDELs) that incorporate a rare gas and a halogen gas (R/H-MDEL) have been investigated with such Hg-free mixture filler gases as Kr/Cl2, Xe/Cl2, and Kr/Br2 (R/H). Of these, only the Kr/Br2-MDEL lamp is self-ignited at an inner pressure of 15 Torr when irradiated with microwave radiation. Accordingly, a novel Kr/Br2 three-layer MDEL (Kr/Br2-MDEL) photoreactor was fabricated to assess the optimal gas composition and gas pressure toward its performance vis-à-vis the treatment of model wastewaters contaminated with the tartrazine dye in aqueous media and with Escherichia coli (E. coli) bacteria. The extent of degradation of the tartrazine dye and sterilization of E. coli increased with irradiation time, with microwave radiation power (100, 200, and 300 W), and with increased sample flow rate 0.4 L min‒1 to 0.8 L min‒1. The tartrazine-contaminated wastewater was treated at a flow rate of 0.4 L min‒1 for 60 min of microwave irradiation by three different protocols that resulted in UV (62%) >> UV/ROS (24%) > ROS (0%); ROS denotes reactive oxygen species. After 5 min irradiation of the E.coli wastewater, also at 0.4 L min‒1, the order was UV (99.5%) ≈ UV/ROS (99.3%) >> ROS (14.5%). For comparison, the photosterilization of E. coli with an equivalent Hg/Ar-MDEL light source was also nearly complete (99.7%). Thus, the suitability of the environmentally friendlier Kr/Br2 gas fill to replace Hg/Ar filler gas in MDELs for the photoelimination of organic pollutants and microbial disinfection in aqueous media has been demonstrated.

Revisiting the BaBiO3 semiconductor photocatalyst: synthesis, characterization, electronic structure, and photocatalytic activity.

This article revisits the properties of BaBiO3 examined extensively in the last two decades because of its electronic properties as a superconductor and as a semiconductor photocatalyst. Solid-state syntheses of this bismuthate have often involved BaCO3 as the barium source, which may lead to the formation of BaBiO3/BaCO3 heterostructures that could have an impact on the electronic properties and, more importantly, on the photocatalytic activity of this bismuthate. Accordingly, we synthesized BaBiO3 by a solid-state route to avoid the use of a carbonate; it was characterized by XRD, SEM, and EDX, while elemental mapping characterized the composition and the morphology of the crystalline BaBiO3 and its thin films with respect to structure, optoelectronic, and photocatalytic properties. XPS, periodic DFT calculations, and electrochemical impedance spectroscopy ascertained the electronic and electrical properties, while Raman and DRS spectroscopies assessed the relevant optical properties. The photocatalytic activity was determined via the degradation of phenol in aqueous media. Although some results accorded with earlier studies, the newer electronic structural data on this bismuthate, together with the photocatalytic experiments carried out in the presence of selective radical trapping agents, led to elucidating some of the mechanistic details of the photocatalytic processes that previous views of the BaBiO3 band structure failed to address or clarify. Analytical refinement of the XRD data inferred the as-synthesized BaBiO3 adopted the C2/m symmetry rather than the I2/m structure reported earlier, while Tauc plots from DRS spectra yielded a bandgap of 2.05 eV versus the range of 1.1-2.25 eV reported by others; the corresponding flatband potentials were 1.61 eV (EVB) and - 0.44 eV (ECB). The photocatalytic activity of BaBiO3 was somewhat greater than that of the well-known Evonik P25 TiO2 photocatalyst under comparable experimental conditions.

In Search of the Driving Factor for the Microwave Curing of Epoxy Adhesives and for the Protection of the Base Substrate against Thermal Damage.

This study used controlled microwaves to elucidate the response of adhesive components to microwaves and examined the advantages of microwave radiation in curing epoxy adhesives. Curing of adhesives with microwaves proceeded very rapidly, even though each component of the adhesive was not efficiently heated by the microwaves. The reason the adhesive cured rapidly is that microwave heating was enhanced by the electrically charged (ionic) intermediates produced by the curing reaction. In contrast, the cured adhesive displayed lower microwave absorption and lower heating efficiency, suggesting that the cured adhesive stopped heating even if it continued to be exposed to microwaves. This is a definite advantage in the curing of adhesives with microwaves, as, for example, adhesives dropped onto polystyrene could be cured using microwave heating without degrading the polystyrene base substrate.

Microwave Flow Chemistry as a Methodology in Organic Syntheses, Enzymatic Reactions, and Nanoparticle Syntheses.

Several studies have used microwaves as a heat source for carrying out various types of reactions employing circulation reaction vessels. The microwave flow chemical synthesis methodology is most appropriate in the use of microwaves in chemical syntheses. It can attenuate the problem of microwave heating (non-uniform heating and penetration depth) and maximize the benefits (rapid heating and first temperature adjustments). In this brief review, we examine and explain some of the relevant features of microwave heating with applicative examples of the usage of microwave flow chemistry equipment in carrying out organic syntheses, enzymatic reactions, and (not least) nanoparticle syntheses.

Development of a Hg-free UV light source and its performance in photolytic and photocatalytic applications.

Constraints on light sources that use mercury (arc lamps) are evolving with the establishment of the Minamata Convention, which has led to the proliferation of LEDs. However, no LED light source emits intense ultraviolet radiation at wavelengths below 300 nm for photolytic applications. Thus, it is necessary to develop suitable UV light sources for the decontamination of wastewater and water sterilization processing. Herein, we explore various substitute gases (e.g., N2, Ar, He and SF6) to replace mercury, which is commonly employed in arc lamps, using an EL (electroluminescence) quartz assembly platform similar to microwave-discharge electrodeless lamps. Although nitrogen is an inexpensive and safe gas, it cannot generate significant UV radiation in the UVC region of 200-300 nm. This problem in the Hg-free light source was resolved by mixing a very small quantity of sulfur hexafluoride (SF6) as an additive filler gas in a nitrogen-, argon- or helium-filled assembly. The low-pressure mercury lamp consisting of Hg/Ar filler gases is ca. 25% more efficient than the novel N2/SF6 lamp toward the photolytic decomposition of Rhodamine-B (RhB) dye-contaminated wastewater (1.66 × 10-4 mM min-1versus 1.22 × 10-4 mM min-1). Nonetheless, the latter has proven far more efficient than an LED source emitting 365 nm radiation (0.057 × 10-4 mM min-1). The addition of TiO2 to RhB-contaminated wastewater demonstrated that this Hg-free N2/SF6 light source is as efficient as the corresponding Hg/Ar electroluminescent lamp toward the photocatalytic decomposition of the RhB dye pollutant.

Facile preparation of N-doped TiO2 at ambient temperature and pressure under UV light with 4-nitrophenol as the nitrogen source and its photocatalytic activities.

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 N2-purged dispersions) with 4-nitrophenol (or 4-nitrobenzaldehyde) 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).

Formation of Hexamethylenetetramine (HMT) from HCHO and NH3--Relevance to Prebiotic Chemistry and B3LYP Consideration.

Despite its importance in the prebiotic and biochemical fields, a complete theoretical study of the formation of hexamethylenetetramine (HMT) starting from its precursors ammonia and formaldehyde has not received due considerations in the literature with regard to the thermodynamic feasibility of many of the mechanistically proposed intermediates in its formation. Most of the studies in this area have been mostly concerned with the initial steps of the reaction between formaldehyde and ammonia, while poor attention is dedicated to successive steps. In this article, different results from published literature were critically considered and the most probable hypothesis regarding the mechanism of HMT formation is discussed on the basis of B3LYP calculations of free energies.

Water Will Be the Coal of the Future-The Untamed Dream of Jules Verne for a Solar Fuel.

This article evokes the futuristic visions of two giants, one a writer, Jules Verne, who foresaw water as the coal of the future, and the other a scientist, Giacomo Ciamician, who foresaw the utilization of solar energy as an energy source with which to drive photochemical and photocatalytic reactions for the betterment of mankind. Specifically, we examine briefly the early work of the 1960s and 1970s on the photosplitting of free water and water adsorbed on solid supports, based mostly on metal oxides, from which both hydrogen and oxygen evolve in the expected stoichiometric ratio of 2 to 1. The two oil crises of the 1970s (1973 and 1979) spurred the interest of researchers from various disciplines (photochemistry, photo-catalysis and photoelectrochemistry) in search of a Holy Grail photocatalyst, process, or strategy to achieve efficient water splitting so as to provide an energy source alternative to fossil fuels. Some approaches to the photosplitting of water adsorbed on solid insulators (high bandgap materials; Ebg ≥ 5 eV) and semiconductor photocatalysts (metal oxides) are described from which we deduce that metal oxides with bandgap energies around 5 eV (e.g., ZrO2) are more promising materials to achieve significant water splitting on the basis of quantum yields than narrower bandgap photocatalysts (e.g., TiO2; Ebg ≈ 3.0-3.2 eV), which tend to be relatively inactive by comparison. Although proof of concept of the photosplitting of water has been demonstrated repeatedly in the last four decades, much remains to be done to find the Holy Grail photocatalyst and/or strategy to achieve significant yields of hydrogen.

Epitaxial Bi2 FeCrO6 Multiferroic Thin Film as a New Visible Light Absorbing Photocathode Material.

Ferroelectric materials have been studied increasingly for solar energy conversion technologies due to the efficient charge separation driven by the polarization induced internal electric field. However, their insufficient conversion efficiency is still a major challenge. Here, a photocathode material of epitaxial double perovskite Bi(2) FeCrO(6) multiferroic thin film is reported with a suitable conduction band position and small bandgap (1.9-2.1 eV), for visible-light-driven reduction of water to hydrogen. Photoelectrochemical measurements show that the highest photocurrent density up to -1.02 mA cm(-2) at a potential of -0.97 V versus reversible hydrogen electrode is obtained in p-type Bi(2) FeCrO(6) thin film photocathode grown on SrTiO(3) substrate under AM 1.5G simulated sunlight. In addition, a twofold enhancement of photocurrent density is obtained after negatively poling the Bi(2) FeCrO(6) thin film, as a result of modulation of the band structure by suitable control of the internal electric field gradient originating from the ferroelectric polarization in the Bi(2) FeCrO(6) films. The findings validate the use of multiferroic Bi(2) FeCrO(6) thin films as photocathode materials, and also prove that the manipulation of internal fields through polarization in ferroelectric materials is a promising strategy for the design of improved photoelectrodes and smart devices for solar energy conversion.

Enhanced Ga2O3-photocatalyzed and photochemical degradation of the Fipronil insecticide by UVC irradiation in mixed aqueous/organic media under an inert atmosphere.

Agrochemicals such as the insecticide Fipronil that bear fluoro groups are generally fat-soluble and nearly insoluble in water, so that their photodegradation in a heterogeneous aqueous gallium oxide dispersion presents some challenges. This article examined the photodegradation of this insecticide by solubilizing it through the addition of organic solvents (EtOH, MeOH, THF, 1,4-dioxane and ethylene glycol) to an aqueous medium and then subjecting the insecticide to 254 nm UVC radiation under photocatalytically inert (Ga2O3/N2) and air-equilibrated (Ga2O3/O2) conditions, as well as photochemically in the absence of Ga2O3 but also under inert and air-equilibrated conditions. Defluorination, dechlorination, desulfonation and denitridation of Fipronil were examined in mixed aqueous/organic media (10, 25 and 50 vol% in organic solvent). After 3 h of UVC irradiation (50 vol% mixed media) defluorination with Ga2O3/N2 was ∼65% greater than in aqueous media, and ca. 80% greater than the direct photolysis of Fipronil under inert (N2) conditions; under air-equilibrated conditions both Ga2O3-photocatalyzed and photochemical defluorination were significantly lower than in aqueous media. Dechlorination of Fipronil was ∼160% (Ga2O3/N2) and 140% (photochemically, N2) greater than in aqueous media; under air-equilibrated conditions, both photocatalyzed and photochemical formation of Cl(-) ions in mixed media fell rather short relative to aqueous media. The photocatalyzed (Ga2O3/N2) and photochemical (N2) conversion of the sulfur group in Fipronil to SO4(2(-)) ions was ca. 20% and 30% greater, respectively, in mixed media, while under air-equilibrated conditions photocatalyzed desulfonation was nearly twofold less than in the aqueous phase; direct photolysis showed little variations in mixed media. Denitridation of the nitrogens in Fipronil occurred mostly through the formation of ammonia (as NH4(+)) under all conditions with negligible quantities of NO3(-); again mixed media offered enhanced denitridation, particularly under inert N2 conditions. Time-of-flight electrospray (TOF-MS/ESI(-)) mass spectrometry revealed a fairly large number of intermediates formed in the degradation of Fipronil, particularly under photocatalytic conditions. Only a couple of intermediates were identified in the photodegradation and the presence of Ga2O3 enhanced the complexity of an already cumbersome problem owing to the involvement of organic solvents.

Microwave discharge electrodeless lamps (MDELs). Part IX. A novel MDEL photoreactor for the photolytic and chemical oxidation treatment of contaminated wastewaters.

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 photoreactor impacted the extent of degradation and the related dynamics of the 2,4-D herbicide.

Photocatalytic generation of solar fuels from the reduction of H2O and CO2: a look at the patent literature.

The application of photocatalysis in environment remediation as well as in the generation of useful fuels from the reduction of water (hydrogen) and of carbon dioxide (methanol, carbon monoxide and/or methane) has been investigated largely in the last four decades. A significant part (12-13%) of the literature on the generation of such fuels is found in patents. Accordingly, the present article presents a selection of the patent literature on the theme. Photocatalysts, whether pure or doped, solid solutions or composites, reported in patents are reviewed along with the corresponding preparative methods and the photocatalytic performance. The absorption of light by such materials has been extended toward the red side of the spectrum, so that a better use of solar irradiation has been obtained, but the expected improvement of the catalytic effect has not always been achieved. The causes of these results and the way for improving the performance in the various steps of the process (e.g. avoiding charge recombination or catalyst corrosion) have been documented. The correct use of the term water splitting and the fundamentals of photochemical hydrogen evolution in the presence of a sacrificial electron donor (e.g., alcohols) are discussed. Quantitative data about the amount of hydrogen evolved or carbon-based fuels produced are indicated whenever available.

Coupled microwave/photoassisted methods for environmental remediation.

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.

Photoassisted defluorination of fluorinated substrates and pharmaceuticals by a wide bandgap metal oxide in aqueous media.

Persistent fluorinated substances, such as the fluorine-bearing pharmaceutical drugs Fluoxetine (FLX; Prozac) and Fluvoxamine maleate (FOM) together with several other substrates (fluorobenzoic acid and fluoroaliphatic model compounds), were photochemically defluorinated and degraded under UVC illumination in relatively good yields in the presence of a wide band gap metal oxide (ß-Ga2O3) in heterogeneous aqueous media. The formation of fluoride ions increased with increasing illumination time under an inert nitrogen atmosphere, the transformation of the aromatic moiety was slower under these conditions, but nonetheless it did occur. The optimal amount of ß-Ga2O3 loading for defluorination was 50 mg in aqueous media (0.10 mM, 100 mL); the optimal pH to defluorinate FLX was pH 6. Platinization (1 wt%) of the gallium oxide particles enhanced defluorination under an inert nitrogen atmosphere, but was decreased under an oxygen atmosphere; however, in the latter case the degradation of the substrates was facilitated as witnessed by loss of the aromatic moiety. The Ames test on the intermediate products from the photodegradation of FLX and 4-(trifluoromethyl)benzoic acid after long illumination times revealed that none were mutagenic.

Three-dimensional observations of the electric field distribution of variable frequency microwaves, and scaling-up organic syntheses.

Variable Frequency Microwave (VFM) radiation provides a solution to the inhomogeneity of the electric field in the cavity, which has long led to a decline in the reliability of microwave chemical data and its industrial utilization. Herein, we report in-situ three-dimensional experimental measurements of the electric field's uniform distribution of VFMs within a multimode cavity under high power conditions, and their subsequent comparison to Fixed Frequency Microwaves (FFM) that could only be assessed earlier through theoretical analysis. We also examine the consequences of changes in VFM irradiation conditions and elucidate the threshold at which VFM irradiation might prove beneficial in syntheses. With an ultimate focus on the use of VFM microwave radiation toward industrial applications, we carried out an effective synthesis of 4-methylbyphenyl (4-MBP) in the presence of palladium (the catalyst) supported on activated carbon particulates (Pd/AC), and revisited two principal objectives: (a) the effective suppression of discharge phenomena (formation of hot spots), and (b) synthesis scale-up using a 5-fold increase in sample quantity and a 7.5-fold larger reactor size (diameter) than otherwise used in earlier studies.

Chemical reaction networks as a model to describe UVC- and radiolytically-induced reactions of simple compounds.

When a chemical system is submitted to high energy sources (UV, ionizing radiation, plasma sparks, etc.), as is expected to be the case of prebiotic chemistry studies, a plethora of reactive intermediates could form. If oxygen is present in excess, carbon dioxide and water are the major products. More interesting is the case of reducing conditions where synthetic pathways are also possible. This article examines the theoretical modeling of such systems with random-generated chemical networks. Four types of random-generated chemical networks were considered that originated from a combination of two connection topologies (viz., Poisson and scale-free) with reversible and irreversible chemical reactions. The results were analyzed taking into account the number of the most abundant products required for reaching 50% of the total number of moles of compounds at equilibrium, as this may be related to an actual problem of complex mixture analysis. The model accounts for multi-component reaction systems with no a priori knowledge of reacting species and the intermediates involved if system components are sufficiently interconnected. The approach taken is relevant to an earlier study on reactions that may have occurred in prebiotic systems where only a few compounds were detected. A validation of the model was attained on the basis of results of UVC and radiolytic reactions of prebiotic mixtures of low molecular weight compounds likely present on the primeval Earth.