Photochemical Route Research Articles

In situ loading amorphous CoSx on N-doped g-C3N4 through light assisted synthesis for enhanced photocatalytic hydrogen generation

Loading co-catalysts are an effective strategy to break the confinement of bulk carbon nitride in photocatalysis. Employing this strategy, N-doped g-C3N4 decorated with CoSx was successfully prepared through a photochemical synthesis route. The optimum hydrogen evolution performance of N-CN-CoSx-4 was 1757 μmol g−1 h−1 under visible light irradiation. Superior interfacial carrier transfer properties and improved light absorption of N-CN-CoSx-4 could elucidate its better photocatalytic activity. This research offers a reference for the construction of high-efficiency, stable and low-priced photocatalysts.

Photochemical Degradation of the UV Filter Octyl Methoxy Cinnamate Probed via Laser-Interfaced Mass Spectrometry.

Octyl methoxycinnamate (OMC) is a common UVA and UVB filter molecule that is widely used in commercial sunscreens. Here, we used gas-phase laser photodissociation spectroscopy to characterise the intrinsic photostability and photodegradation products of OMC by studying the system in its protonated form, i.e., [OMC·H]+. The major photofragments observed were m/z 179, 161, and 133, corresponding to fragmentation on either side of the ether oxygen of the ester group (m/z 179 and 161) or the C-C bond adjacent to the ester carbonyl group. Additional measurements were obtained using higher-energy collisional dissociation mass spectrometry (HCD-MS) to identify fragments that resulted from the breakdown of the vibrationally hot electronic ground state. We found that the m/z 179 and 161 ions were the main fragments produced by this route. Notably, the m/z 133 ion was not observed through HCD-MS, revealing that this product ion is only produced through a photochemical route. Our results demonstrate that UV photoexcitation of OMC is able to access a dissociative excited-state surface that uniquely leads to the rupture of the C-C bond adjacent to the key ester carbonyl group.

One-Step Photochemical Immobilization of Aptamer on Graphene for Label-Free Detection of NT-proBNP

A novel photochemical technological route for one-step functionalization of a graphene surface with an azide-modified DNA aptamer for biomarkers is developed. The methodology is demonstrated for the functionalization of a DNA aptamer for an N-terminal B-type natriuretic peptide (NT-proBNP) heart failure biomarker on the surface of a graphene channel within a system based on a liquid-gated graphene field effect transistor (GFET). The limit of detection (LOD) of the aptamer-functionalized sensor is 0.01 pg/mL with short response time (75 s) for clinically relevant concentrations of the cardiac biomarker, which could be of relevance for point-of-care (POC) applications. The novel methodology could be applicable for the development of different graphene-based biosensors for fast, stable, real-time, and highly sensitive detection of disease markers.

Synthesis, spectral characterization and fluorescence study of functional [5]Helicene derivatives: Experimental and theoretical investigation

Two D–π–A structured [5]Helicene derivatives, labeled HL1 and HL2, were synthesized in a high overall yield through a short synthetic photochemical route using mild conditions. Structural analyses, photophysical and electrochemical properties and theoretical studies were investigated in a comparative manner. These compounds show deep green color in both solution and solid state and they are highly soluble in common organic solvents and even in non-polar solvents such as toluene and cyclohexane. The shapes of experimental and calculated absorption spectra of these helical scaffolds in a dichloromethane solution were found to be approximately the same, indicating that the alkoxy groups could efficiently prevent intermolecular contact and aggregation. These Helicene derivatives were found to emit a green light in the fluorescence process inducing a Stokes shift of 0.39–0.41 eV (3200–3303 cm−1). They exhibit an irreversible one-electron oxidation and one-electron reduction and their HOMO and LUMO energy levels were electrochemically estimated to be, respectively, -5.88 and -3.20 eV for HL1 and -5.76 and -3.26 eV for HL2. Complementary density functional theory (DFT) calculations have also been performed in order to rationalize the different behaviors in the target [5]Helicenes and to gain insight into their geometric, electronic and spectroscopic properties. The corresponding calculated results were found to be in good agreement with the experimental data.

A Photochemical Macrocyclization Route to Asymmetric Strained [3.2] Paracyclophanes.

The intricate frameworks of paracyclophanes are an important target for synthesis since they are found in various chiral auxiliaries, solar cells, high-performance plastics, pharmaceuticals, and molecular machines. Whereas numerous methods exist for the preparation of symmetric paracyclophanes, protocols for the efficient synthesis of strained asymmetric scaffolds are limited. Here we report a remarkably simple photochemical route to strained [3.2]paracyclophanes starting from readily available educts. By way of NMR and X-ray analyses, we discovered that UV-irradiation of an aromatic carboxylic ester tethered to a toluene moiety leads to the intramolecular formation of a new C-C bond, with loss of an alcohol. A systematic evaluation of the reaction conditions and substituents, as well as radical starter and triplet quenching experiments, point to a reaction mechanism involving an excited triplet state and hydrogen atom transfer. The new method proved to be robust and versatile enabling the synthesis of a range of cyclophanes with different substitutions, including an unusual diastereoisomer with two planar chiral centers, and thus proved to be a valuable addition to the synthetic toolbox.

Redox Cycles, Active Materials, and Reactors Applied to Water and Carbon Dioxide Splitting for Solar Thermochemical Fuel Production: A Review

The solar thermochemical two-step splitting of H2O and CO2 based on metal oxide compounds is a promising path for clean and efficient generation of hydrogen and renewable synthetic fuels. The two-step process is based on the endothermic solar thermal reduction of a metal oxide releasing O2 using a high-temperature concentrated solar heat source, followed by the exothermic oxidation of the reduced oxide with H2O and/or CO2 to generate pure H2 and/or CO. This pathway relates to one of the emerging and most promising processes for solar thermochemical fuel production encompassing green H2 and the recycling/valorization of anthropogenic greenhouse gas emissions. It represents an efficient route for solar energy conversion and storage into renewable and dispatchable fuels, by directly converting the whole solar spectrum using heat delivered by concentrating systems. This eliminates the need for photocatalysts or intermediate electricity production, thus bypassing the main limitations of the low-efficient photochemical and electrochemical routes currently seen as the main green methods for solar fuel production. In this context, among the relevant potential redox materials, thermochemical cycles based on volatile and non-volatile metal oxides are particularly attractive. Most redox pairs in two-step cycles proceed with a phase change (solid-to-gas or solid-to-liquid) during the reduction step, which can be avoided by using non-stoichiometric oxides (chiefly, spinel, fluorite, or perovskite-structured materials) through the creation of oxygen vacancies in the lattice. The oxygen sub-stoichiometry determines the oxygen exchange capacity, thus determining the fuel production output per mass of redox-active material. This paper provides an overview of the most advanced cycles involving ZnO/Zn, SnO2/SnO, Fe3O4/FeO, ferrites, ceria, and perovskites redox systems by focusing on their ability to perform H2O and CO2 splitting during two-step thermochemical cycles with high fuel production yields, rapid reaction rates, and performance stability. Furthermore, the possible routes for redox-active material integration and processing in various solar reactor technologies are also described.

Plasmon-promoted oxygen evolution catalysis with Ag nanocrystals loaded α-Co(OH)2 nanosheets

Exploration of low-cost and high efficiency oxygen evolution reaction (OER) electrocatalysts is very important for the large-scale industrial application of alkaline water splitting driven by electricity. The present promising cobalt-based catalysts still leave room to meet the activity requirement. Here, a composite catalyst of α-Co(OH)2/Ag was synthesized by a simple photochemical deposition route, which was designed to improve the electrocatalytic activity for OER. Moreover, a photoinduced surface plasmon on Ag particles was found to further enhance the catalytic performance under low power of laser irradiation. Loading of silver nanocrystals on α-Co(OH)2 nanosheets can decrease the overpotential towards OER for 10 mA cm−2 from 320 to 288 mV, this value can be further decreased of 45 mV under 1000 mW of laser irradiation with a wavelength of 532 nm. The derivation of the catalyst during the OER process was examined, which indicates the structural transformation from α-Co(OH)2 to CoOOH. The photoinduced surface plasmon modulates the electronic structure of cobalt sites, facilitates the formation of active cobalt species, and induces the enhancement of catalytic activity. These findings may give some hints for plasmon-induced electrocatalysis and the design of advanced electrocatalysts.

Tide-Triggered Production of Reactive Oxygen Species in Coastal Soils.

We report an unrecognized, tidal source of reactive oxygen species (ROS). Using a newly developed ROS-trapping gel film, we observed hot spots for ROS generation within ∼2.5 mm of coastal surface soil. Kinetic analyses showed rapid production of hydroxyl radicals (•OH), superoxide (O2•-), and hydrogen peroxide (H2O2) upon a shift from high tide to low tide. The ROS production exhibited a distinct rhythmic fluctuation. The oscillations of the redox potential and dissolved oxygen concentration followed the same pattern as the •OH production, suggesting the alternating oxic-anoxic conditions as the main geochemical drive for ROS production. Nationwide coastal field investigations confirmed the widespread and sustainable production of ROS via tidal processes (22.1-117.4 μmol/m2/day), which was 5- to 36-fold more efficient than those via classical photochemical routes (1.5-7.6 μmol/m2/day). Analyses of soil physicochemical properties demonstrated that soil redox-metastable components such as redox-active iron minerals and organic matter played a key role in storing electrons at high tide and shuttling electrons to infiltrated oxygen at low tide for ROS production. Our work sheds light on a ubiquitous but previously overlooked tidal source of ROS, which may accelerate carbon and metal cycles as well as pollutant degradation in coastal soils.

Silver nanoparticle-deposited whey protein isolate amyloid fibrils as catalysts for the reduction of methylene blue

The unique structural characteristics and superior biocompatibility make the protein nanofibers promising immobilization platforms/substrates for catalysts/enzymes. Metal nanoparticles have been employed as the catalysts in industries due to their excellent catalytic activity and stability, whereas their high surface energy leads to nanoparticle aggregation, thereby hampering their catalytic performance. Here, amyloid fibril (AF) derived from whey protein isolate (WPI) was chosen as the support of silver nanoparticles (AgNP) and utilized for the catalytic reduction of methylene blue (MB). The one-dimensional amyloid-based hybrid materials (AgNP/WPI-AF) were first synthesized via chemical or photochemical route. The characterization of AgNP/WPI-AF by UV–vis spectrophotometry and electron microscopy revealed that the sizes of AgNP on WPI-AF's surface ranged from 2 to 30 nm. Next, the catalytic performances of AgNP/WPI-AF prepared by various routes for MB degradation were investigated. Additionally, the kinetic data were analyzed using two different models and the apparent rate constants and thermodynamic parameters were further determined accordingly. Moreover, the reusability of AgNP/WPI-AF was assessed by monitoring the percentage removal of MB over consecutive filtering cycles. Our results indicated that Langmuir-Hinshelwood-type mechanism better described the catalytic MB reduction using AgNP/WPI-AF. This work provides a nice example of application of nanoparticle-amyloid fibril composite materials for catalysis.

Diel Fluctuation of Extracellular Reactive Oxygen Species Production in the Rhizosphere of Rice.

Reactive oxygen species (ROS) are ubiquitous on earth and drive numerous redox-centered biogeochemical processes. The rhizosphere of wetland plants is a highly dynamic interface for the exchange of oxygen and electrons, presenting the basis of the precedent for ROS production, yet whether extracellular ROS are produced in the rhizosphere remains unknown. Here, we designed a microfluidic chip setup to detect in-situ ROS productions in the rhizosphere of rice with spatial and temporal resolutions. Fluorescence imaging clearly displayed the hot spots of ROS generation in the rhizosphere. The formation concentration of the hydroxyl radical (•OH, a representative ROS, 10-6 M) was comparable to those by the classical photochemical route (10-6-10-7 M) in aquatic systems, therefore highlighting the rhizosphere as an unrecognized hotspot for ROS production. Moreover, the rhizosphere ROS production exhibits diel fluctuation, which simultaneously fluctuated with dissolved oxygen, redox potential, and pH, all driven by radial oxygen loss near the root in the daytime. The production and diel fluctuation of ROS were confirmed in the rhizosphere of rice root incubated in natural soils. We demonstrated that the extracellular ROS production was triggered by the interplay between root-released oxygen and microbial respiration released extracellular electrons, while iron mineral and organic matter might play key roles in storing and shuttling electrons. Our results highlight the rhizosphere as a widespread but previously unappreciated hotspot for ROS production, which may affect pollutant redox dynamics and biogeochemical processes in soils.

Plasmonic silica-gold core-shell nanoparticles: Interaction with organic dyes for light-induced applications

The interaction of plasmonic nanoparticles with ground- and excited states of dyes can strongly affect the fluorescence of the organic molecules, as well as the generation of reactive oxygen species (ROS). This interaction can be exploited in bioimaging and photodynamic therapy (PDT) of tumors. In this line, we prepare here gold-decorated silica nanoparticles (SiO2@Au NPs) via a novel method, which combines the synthesis of gold nuclei through reduction of a Au3+ salt, with a photochemical route driving the growth of the metallic nuclei. In this hybrid nanomaterial, the surface groups of the silica particle can potentially act as adsorption sites for the dyes in a range close to the gold nanoparticles, favoring the interaction. The ability of SiO2@Au NPs to enhance fluorescence and generation of ROS upon irradiation of riboflavin and Rose Bengal is evaluated. SiO2@Au enhance the fluorescence emission of both dyes, although through different mechanisms. The excitation of the flavin is enhanced, whereas for Rose Bengal the radiative decay rate is increased by the nanoparticles.For neither of the two dyes, SiO2@Au affect ROS generation as measured by Electron Paramagnetic Resonance (EPR) spectroscopy. However, the increase in fluorescence emission observed for both dyes demonstrates the potential application of SiO2@Au in fluorescence-sensing methods and bioimaging.

Assignment of the Vibrational Spectra of Diiron Nonacarbonyl, Fe2(CO)9

Diiron nonacarbonyl, Fe2(CO)9, was discovered in 1905 and was the third metal carbonyl to be found. It was the first to be synthesized by a photochemical route. This is a challenging material to study: it is insoluble in virtually all solvents and decomposes at 373 K before melting. This means that only solid-state spectroscopic data are available. New infrared, Raman and inelastic neutron scattering (INS) spectra have been measured and used to generate a complete assignment of the vibrational spectra of Fe2(CO)9. Density functional theory (DFT) calculations are used to support the assignments; however, for this material, they are much less useful than expected, although the calculated intensities provide crucial information.

Selective hydroboration of terminal alkynes catalyzed by heterometallic clusters with uranium–metal triple bonds

Selective hydroboration of terminal alkynes catalyzed by heterometallic clusters with uranium–metal triple bonds

Hydrogen Utilization in the Sustainable Manufacture of CO2-Based Methanol

Production of alternative CO2-based products may play a major role in decoupling fossil resources to the economy’s needs. CO2 hydrogenation is one of the most readily operational CO2 conversion pathways to produce chemicals. Beyond this, electrochemical, photoelectrochemical, and photochemical CO2 conversion routes have gained attention as long-term direct conversion routes. This work analyzes under what conditions H2 could be a sustainable intermediate vector in producing renewable hydrogen-based methanol (hMeOH) and compares it with the fossil-based (fMeOH) and the emerging electrochemical-based (eMeOH) routes. The technological and exogenous drivers are identified, and the trade-offs between alternatives are assessed under an integrated life cycle approach. The deployment of low carbon hMeOH is locally conditioned to use electricity with carbon intensities of 150 kg of CO2e/MWh or lower. Higher electrolysis efficiency (>70%) and product concentration (>40 wt %) are needed in the eMeOH route to be competitive with the H2-based path. Substitution of fMeOH by wind-powered hMeOH could avoid substantial CO2 emissions (−1.57 kg of CO2e/kg) and fossil resources (−0.61 kg of oileq/kg) but at the cost of almost triple the impact of land use.

Nitrile grafted thia[5]Helicenes through a photocyclization pathway of styrylnaphtho[2,1-b]thiophenes: Synthesis and photophysical properties

Six nitrile grafted pentacyclic π-conjugated systems have been designed and synthesized, in 44–68% overall yields, through a photochemical route under mild conditions and using a suitable phenanthrene-like derivative as a basic molecular skeleton. Their structural characterization has been performed using various spectroscopic techniques among them X-ray diffraction, which indicated the presence of pair of P and M helical enantiomers in the crystal structure. These helical compounds were found readily soluble in a variety of organic solvents and exhibit a good thermal stability. The UV–vis absorption and photoluminescence properties of these π-conjugated helical scaffolds have been experimentally examined indicating an absorption maxima around 281–284 nm and a remarkable dual emissions in the blue region as their characteristic. All compounds exhibited irreversible redox-active characteristics. HOMO and LUMO energy level have been evaluated experimentally by cyclic voltammetry showing an electrochemical band gap (Eg-el) ranging from 2.87 eV to 3.01 eV.

Tuning the photophysical properties of luminescent lanthanide complexes through regioselective antenna fluorination.

Carbostyrils monofluorinated in the 3, 5, or 6 positions were synthesised from olefinic precursors via a photochemical isomerisation-cyclisation route, and incorporated into octadentate cyclen triacetate ligands that formed luminescent complexes with Tb(III) and Eu(III). The photophysical properties of the emitters were strongly dependent on the position of the fluorination.

A combined photobiological–photochemical route to C10 cycloalkane jet fuels from carbon dioxide via isoprene

A photobiological–photochemical process, where sunlight can be used, is shown to convert CO2 to C10 cycloalkane jet fuels. The properties are comparable to commercial aviation fuels and LCA indicates the potential sustainability of the process.

Direct photochemical route to azoxybenzenes via nitroarene homocoupling.

We report on a direct photochemical method for the one-pot, catalyst- and additive-free synthesis of azoxybenzene and substituted azoxy derivatives from nitrobenzene building blocks. This reaction is conducted at room temperature and under air, and can be applied to substrates with a wide range of substituents. Yields of products derived from para- and meta-substituted nitrobenzenes are typically good, while sterically encumbered ortho-substituted substrates are not as fruitful. Photochemical Wallach rearrangement of generated azoxybenzenes to ortho-hydroxyazoxybenzenes was observed in some cases, most markedly in selected ortho-halogenated nitrobenzenes. Overall, this method provides an efficient, green pathway to highly value-added azoxybenzene products.

Plastic-free silica-titania-polyphenol heterojunction hybrids for efficient UV-to-blue light blocking and suppressed photochemical reactivity

The photocatalytic activity of ultraviolet (UV) filters, generating reactive oxygen species (ROS), must be minimized in skincare products to avoid adverse biological and chemical effects. Unfortunately, the screening effect of UV filters is intrinsically correlated with their photocatalytic activity in the presence of oxygen and water. Polymeric encapsulation has been widely employed to inhibit photochemical ROS generation; however, it can cause serious microplastic issues because UV filters act as photocatalysts under sunlight irradiation. Here we present plastic-free silica-titania-tannin (SiO2-TiO2-TA) heterojunction hybrids to increase UV-to-blue light blocking effects while suppressing UV-induced ROS generation by altering their photochemical routes. Mesoporous SiO2-TiO2 particles were prepared through the in situ synthesis of TiO2 nanocrystals within SiO2 particles, followed by the spontaneous deposition of TA via Ti-pyrogallol and Ti-catechol coordination. Ligand-to-metal charge transfer (LMCT) from TA to the conduction band of TiO2, demonstrated by theoretical calculations, extends the absorption spectrum of TiO2 over the blue wavelength regime, increasing a specific sun protection factor ∼ 1.8 times. The TA layer efficiently suppressed the UV-induced ROS generation: the SiO2-TiO2-TA produced only < 1 % hydroxyl radical ions compared to pristine TiO2 under simulated solar irradiation. Accordingly, the UV and blue light-induced cytotoxicity of fibroblasts was significantly alleviated by the ROS stabilization effect of TA complexed with TiO2, while pristine TiO2 exacerbated the cytotoxic effect via ROS generation in the cytoplasm. This work demonstrates that polyphenol coatings are a promising method to suppress the ROS generation by inorganic UV filters while increasing their screening effects through LMCT.

Rational design of palladium single-atoms and clusters supported on silicoaluminophosphate-31 by a photochemical route for chemoselective hydrodeoxygenation of vanillin

Rational design of palladium single-atoms and clusters supported on silicoaluminophosphate-31 by a photochemical route for chemoselective hydrodeoxygenation of vanillin