At a distance of 1.295 parsecs, the red dwarf Proxima Centauri (α Centauri C, GL 551, HIP 70890 or simply Proxima) is the Sun's closest stellar neighbour and one of the best-studied low-mass stars. ...It has an effective temperature of only around 3,050 kelvin, a luminosity of 0.15 per cent of that of the Sun, a measured radius of 14 per cent of the radius of the Sun and a mass of about 12 per cent of the mass of the Sun. Although Proxima is considered a moderately active star, its rotation period is about 83 days (ref. 3) and its quiescent activity levels and X-ray luminosity are comparable to those of the Sun. Here we report observations that reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. Its equilibrium temperature is within the range where water could be liquid on its surface.
Display omitted
•Photocatalytic decomposition of PFOA using a TiO2-rGO catalyst was studied.•TiO2-rGO catalyst (0.1gL−1) allowed 93±7% PFOA removal under UV–vis irradiation.•Formation of intermediate ...PFCAs and F− elucidated the PFOA degradation mechanism.•Faster degradation kinetics were observed for shorter carbon-chain PFCAs.
The inherent resistance of perfluoroalkyl substances (PFASs) to biological degradation makes necessary to develop advanced technologies for the abatement of this group of hazardous substances. The present work investigated the photocatalytic decomposition of perfluorooctanoic acid (PFOA) using a composite catalyst based on TiO2 and reduced graphene oxide (95% TiO2/5% rGO) that was synthesized using a facile hydrothermal method. The efficient photoactivity of the TiO2-rGO (0.1gL−1) composite was confirmed for PFOA (0.24mmolL−1) degradation that reached 93±7% after 12h of UV–vis irradiation using a medium pressure mercury lamp, a great improvement compared to the TiO2 photocatalysis (24±11% PFOA removal) and direct photolysis (58±9%). These findings indicate that rGO provided the suited properties of TiO2-rGO, possibly as a result of acting as electron acceptor and avoiding the high recombination electron/hole pairs. The release of fluoride and the formation of shorter-chain perfluorocarboxilyc acids, that were progressively eliminated in a good match with the analysed reduction of total organic carbon, is consistent with a step-by-step PFOA decomposition via photogenerated hydroxyl radicals. Finally, the apparent first order rate constants of the TiO2-rGO UV–vis PFOA decompositions, and the intermediate perfluorcarboxylic acids were found to increase as the length of the carbon chain was shorter.
Display omitted
•The potential carcinogenic disinfection by-product DCA is removed by photocatalysis.•DCA degradation was achieved using TiO2/Pt 0.5 wt% photocatalyst.•Role of O2−, OHads, OHfree and ...h+VB radicals is determined in DCA abatement.•DCA decomposition is conducted mainly by OHfree radicals using TiO2 as catalyst.•OHfree radicals from O2− play a key role in DCA removal using TiO2/NM catalysts.
Modified TiO2 catalysts are of interest in environmental water remediation since they can lead to efficient electron-hole separation and greatly enhance the photocatalytic properties of TiO2. Reactive oxygen species (ROS), such as the superoxide radical (O2−), hydroxyl radical (OH), and positive valence band holes (h+VB), have been reported as the main oxidative species involved in photocatalytic degradation processes. In this work, the role of these species using TiO2, TiO2/Pt 0.5 wt%, and TiO2/Ag 10 wt% has been examined in order to clarify the oxidation pathways. For this purpose, the contribution of the main oxidative species was analyzed in the photocatalytic degradation of dichloroacetic acid (DCA) solutions using specific scavengers (benzoquinone, tert-butyl alcohol, and formic acid). Moreover, the hydroxyl radicals were quantitatively determined in order better understand the results. Regardless of the catalyst used, it is concluded that OH radicals are the major reactive species responsible for DCA degradation and no significant degradation is due to O2− radicals. Nevertheless, different OH generation pathways were found, depending on the nature of the catalysts. Degradation using TiO2 was conducted mainly via OH radicals generated in the positive holes, while noble metal-doped TiO2 catalysts generated OH radicals through the transformation of O2− radicals.
This article aims to show the identity of “circularly polarized luminescent active simple organic molecules” as a new concept in organic chemistry due to the potential interest of these molecules, as ...availed by the exponentially growing number of research articles related to them. In particular, it describes and highlights the interest and difficulty in developing chiral simple (small and non‐aggregated) organic molecules able to emit left‐ or right‐circularly polarized light efficiently, the efforts realized up to now to reach this challenging objective, and the most significant milestones achieved to date. General guidelines for the preparation of these interesting molecules are also presented.
Will it be possible to generate circularly polarized luminescence (CPL) efficiently from simple organic molecules (SOM) in solution? This Concept article highlights the interest of this difficult question, the efforts realized up to now to solve it, and the most significant milestones achieved to date. The article postulates the important role that molecular designs based on helical structures could play in overcoming limiting factors.
Noble metals have been used to improve the photocatalytic activity of TiO
2
. Noble metal nanoparticles prevent charge recombination, facilitating electron transport due to the equilibration of the ...Fermi levels. Furthermore, noble metal nanoparticles show an absorption band in the visible region due to a high localized surface plasmon resonance (LSPR) effect, which contributes to additional electron movements. Moreover, systems based on graphene, titanium dioxide, and noble metals have been used, considering that graphene sheets can carry charges, thereby reducing electron-hole recombination, and can be used as substrates of atomic thickness. In this work, TiO
2
-based nanocomposites were prepared by blending TiO
2
with noble metals (Pt and Ag) and/or graphene oxide (GO). The nanocomposites were mainly characterized via transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transformed infrared (FTIR), Raman spectroscopy, and photocurrent analysis. Here, the photocatalytic performance of the composites was analyzed via oxidizing dichloroacetic acid (DCA) model solutions. The influence of the noble metal load on the composite and the ability of the graphene sheets to improve the photocatalytic activity were studied, and the composites doped with different noble metals were compared. The results indicated that the platinum structures show the best photocatalytic degradation, and, although the presence of graphene oxide in the composites is supposed to enhance their photocatalytic performance, graphene oxide does not always improve the photocatalytic process.
Graphical abstract
It is a schematic diagram. Where NM is Noble Metal and LSPR means Localized Surface Plasmon Resonance
Display omitted
•Recent progress on the use of magnetic nanophotocatalysts (MNPCs).•MNPCs synthesis and applications for water treatment technologies.•Evaluation of TiO2 based- and alternative ...MNPCs.•Magnetic separation of the MNPCs and their reusability are highlighted.•Future trends and challenges associated with the applications of MNPCs.
The integration of magnetic nanophotocatalysts (MNPCs) in water treatment technologies has recently received great attention due to the enhanced physical and chemical properties of these materials. Thanks to the introduction of a magnetic material into the nanocomposite, its separation can be easily performed through the application of external magnetic fields, thus obtaining more efficient, economic and environmentally friendly water purification processes. However, the successful implementation of the MNPCs-based water treatment technology needs the evaluation of several steps that are involved in the process. Therefore, this work presents a comprehensive review on the use of MNPCs in the treatment of polluted wastewaters with several organic pollutants including Contaminants of Emerging Concern (CECs). The study of the specific photocatalytic properties of these materials, which are related to the synthesis methods employed in their formulation and determine their photocatalytic performance, are particularly analyzed. Moreover, the potential use of these materials as visible light photocatalysts is described and their magnetic recovery is highlighted. In addition, several guidelines and possible challenges that this technology might face in the near future are discussed.
Among the different alternatives to generate hydrogen, photocatalysis can play an important role since it is based on the use of solar radiation and a suitable semiconductor. Starting from the most ...commonly researched TiO2 catalyst, many efforts have been devoted to improve its efficacy. This work, based on the potential of reduced graphene oxide (rGO) to carry charges and platinum nanoparticles to act as efficient traps for photogenerated electrons, assesses the performance of synthesized binary and ternary photocatalysts (TiO2/rGO, TiO2/Pt and TiO2/rGO/Pt) for hydrogen generation. The addition of rGO to TiO2 almost duplicates (1.95 factor) the hydrogen production rate compared to bare TiO2. Moreover, the binary TiO2/Pt photocatalyst reported the best performance, with an increase in the hydrogen production rate by a factor of 15.26 compared to TiO2. However, the ternary catalyst performed worse than the binary TiO2/Pt probably due to the use of non-optimized co-catalyst ratios. Since the addition of rGO reduces the cost of the catalyst, the trade-off between the catalyst performance and cost is worth of future research.
•The TiO2/rGO/Pt materials are successfully synthesized.•rGO is an alternative to reduce catalysts cost in photocatalytic hydrogen generation.•Comparative performance of photocatalysts in the rmax,H2 is developed.•Optimum loads of rGO and Pt co-catalyst on TiO2 are required.
Abscisic acid (ABA) is a major phytohormone involved in important stress‐related and developmental plant processes. Recent phosphoproteomic analyses revealed a large set of ABA‐triggered ...phosphoproteins as putative mitogen‐activated protein kinase (MAPK) targets, although the evidence for MAPKs involved in ABA signalling is still scarce. Here, we identified and reconstituted in vivo a complete ABA‐activated MAPK cascade, composed of the MAP3Ks MAP3K17/18, the MAP2K MKK3 and the four C group MAPKs MPK1/2/7/14. In planta, we show that ABA activation of MPK7 is blocked in mkk3‐1 and map3k17mapk3k18 plants. Coherently, both mutants exhibit hypersensitivity to ABA and altered expression of a set of ABA‐dependent genes. A genetic analysis further reveals that this MAPK cascade is activated by the PYR/PYL/RCAR‐SnRK2‐PP2C ABA core signalling module through protein synthesis of the MAP3Ks, unveiling an atypical mechanism for MAPK activation in eukaryotes. Our work provides evidence for a role of an ABA‐induced MAPK pathway in plant stress signalling.
Circularly polarized luminescence (CPL) in simple (small, nonaggregated, nonpolymeric) O-BODIPYs (R)-1 and (S)-1 by irradiation with visible light is first detected as proof of the ability of a new ...structural design to achieve CPL from inherently achiral monochromophore systems in simple organic molecules. The measured level of CPL (|g lum|) in solution falls into the usual range of that obtained from other simple organic molecules (10–5–10–2 range), but the latter having more complex architectures since axially chiral chromophores or multichromophore systems are usually required. The new design is based on chirally perturbing the acting achiral chromophore by orthogonally tethering a single axially chiral 1,1′-binaphtyl moiety to it. The latter does not participate as a chromophore in the light-absorption/emission phenomenon. This simple design opens up new perspectives for the future development of new small-sized CPL organic dyes (e.g., those based on other highly luminescent achiral chromophores and/or chirally perturbing moieties), as well as for the improvement of the CPL properties of the organic molecules spanning their use in photonic applications.
Proxima Centauri, the star closest to our Sun, is known to host at least one terrestrial planet candidate in a temperate orbit. Here we report the Atacama Large Millimeter/submillimeter Array (ALMA) ...detection of the star at 1.3 mm wavelength and the discovery of a belt of dust orbiting around it at distances ranging between 1 and 4 au, approximately. Given the low luminosity of the Proxima Centauri star, we estimate a characteristic temperature of about 40 K for this dust, which might constitute the dust component of a small-scale analog to our solar system's Kuiper Belt. The estimated total mass, including dust and bodies up to 50 km in size, is of the order of 0.01 Earth masses, which is similar to that of the solar Kuiper Belt. Our data also show a hint of warmer dust closer to the star. We also find signs of two additional features that might be associated with the Proxima Centauri system that still require further observations to be confirmed: an outer extremely cold (about 10 K) belt around the star at about 30 au, with an orbital plane that is tilted about 45° with respect to the plane of the sky; additionally, we marginally detect a compact 1.3 mm emission source at a projected distance of about 1.2 arcsec from the star, the nature of which is still unknown.
PDF
