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crystal structure on the stability of polymer composites exposed to vacuum ultraviolet radiation
摘要： Vacuum ultraviolet (VUV) radiation produced by the Sun in the space environment can cause degradation to thermoregulating coatings producing changes in optical, mechanical, and chemical properties. These effects are particularly important for polymers. The purpose of this study was to study the effect of VUV radiation on polymeric composites based on polyalkaneimide. Amorphous and crystalline SiO2 were used as the filler. A comparative characterization of physico-mechanical properties of composites is presented depending on the polymorphic structure of the filler being introduced. According to the microhardness of the surface of composites with amorphous and crystalline SiO2, an optimum filler content of 60–65 wt% is established. The exposure of VUV radiation to polymeric composites with SiO2 leads to a mass loss and a change in their near-surface layers, which leads to a deterioration in the optical properties. At an elevated temperature (125oC), the mass loss of all composites with amorphous crystalline SiO2 does not exceed 1.33%, and with crystalline SiO2, the maximum mass loss is 0.52%. The mass loss of composites with crystalline SiO2 of all compositions did not exceed the allowable value for spacecraft products of 1%. For high-filled (50 wt% filler or more) composites with amorphous SiO2, mass loss after VUV treatment is more than 1%, which does not allow them to be used in outer space. The change in the main optical characteristics of thermoregulating coatings after VUV treatment was studied. The smoothing of the surface of composites after VUV treatment is established.
关键词： Spacecraft coverings,Deep vacuum,Optical characteristics,Gas evolution,Vacuum ultraviolet,Cosmic radiation
更新于2025-09-10 09:29:36
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Facile synthesis of rod-like g-C3N4 by decorating Mo2C co-catalyst for enhanced visible-light photocatalytic activity
摘要： Designing and optimizing visible-light-driven photocatalyst with cost-efficiency and high performance is very imperative and highly challenging for photocatalytic hydrogen evolution reaction. Herein, g-C3N4/Mo2C hybrid photocatalyst with one dimensional (1D) heterostructure for highly enhanced photocatalytic H2 generation activity were obtained by a facile two step processing, in which Mo2C nanoparticles were highly dispersed on rod-like g-C3N4 surface. Attributed to the synergistic effect of 1D structure and Mo2C co-catalyst, the resultant g-C3N4/Mo2C sample exhibits an impressive visible-light photocatalytic H2 production rate of up to 507 μmol?h-1?g-1 and quantum efficiencies of 3.74% at 420 nm, which is 9.8 times higher than that of bulk g-C3N4, indicating that decorating Mo2C as co-catalysts on the surface of g-C3N4 leads to the improved visible light absorption, promoted charge separation and enhanced the following H2-evolution rate. Moreover, the mechanism for the photocatalytic activity enhancement was also discussed. This study provides a guide for researchers to design efficient g-C3N4-based hybrid photocatalysts with excellent stability and photocatalytic activity during the photoreaction process.
关键词： Photocatalytic H2 evolution,1D heterostructure,g-C3N4,Mo2C co-catalyst
更新于2025-09-10 09:29:36
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Direct Z-scheme 2D/2D MnIn2S4/g-C3N4 architectures with highly efficient photocatalytic activities towards treatment of pharmaceutical wastewater and hydrogen evolution
摘要： Semiconductor photocatalysis has been regarded as an environmentally friendly technology in wastewater treatment and energy production. Here, a series of direct Z-scheme MnIn2S4/g-C3N4 (MnISCN) photocatalysts without electron mediators were fabricated by a simple hydrothermal route on the basis of in-situ loading of MnIn2S4 (MnIS) nanoflakes on the surface of g-C3N4 (CN) nanosheets. Photocatalytic performances evaluated under visible light irradiation revealed these Z-scheme heterostructured photocatalysts exhibited higher photocatalytic activities than single-component samples. The effect of weight ratio between MnIn2S4 nanoflakes and mesoporous CN nanosheets on photocatalytic activity towards treatment of pharmaceutical wastewater was optimized to achieve highly efficient photocatalytic activities for both degradation of pharmaceutical wastewater and hydrogen generation compared with alone MnIS nanoflakes and isolated mesoporous CN nanosheets. The significant enhancement in photocatalytic activity could be primarily ascribed to the construction of Z-scheme MnISCN architectures, which effectively accelerated the transfer and separation of photogenerated charge carriers via tight interface contacts built among these two components. The recycling experiments for pharmaceutical wastewater treatment revealed the excellent stability of MnISCN nanocomposites. The advantages of highly efficient photocatalytic activity and excellent stability endowed a promising potential for MnISCN nanocomposites to apply in photocatalytic fields.
关键词： pharmaceutical wastewater,g-C3N4,hydrogen evolution,Z-scheme,MnIn2S4
更新于2025-09-10 09:29:36
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ROLE OF CYCLIC AND PSEUDO-CYCLIC ELECTRON TRANSPORT IN RESPONSE TO DYNAMIC LIGHT CHANGES IN PHYSCOMITRELLA PATENS
摘要： Photosynthetic organisms support cell metabolism by harvesting sunlight and driving the electron transport chain at the level of thylakoid membranes. Excitation energy and electron flow in the photosynthetic apparatus is continuously modulated in response to dynamic environmental conditions. Alternative electron flow around photosystem I plays a seminal role in this regulation contributing to photo-protection by mitigating over-reduction of the electron carriers. Different pathways of alternative electron flow coexist in the moss Physcomitrella patens, including cyclic electron flow mediated by the PGRL1/PGR5 complex and pseudo-cyclic electron flow mediated by the flavodiiron proteins FLV. In this work we generated P. patens plants carrying both pgrl1 and flva knock-out (KO) mutations. A comparative analysis of the WT, pgrl1, flva and pgrl1 flva lines suggests that cyclic and pseudo-cyclic processes have a synergic role in the regulation of photosynthetic electron transport. However, while both contribute to photosystem I protection from over-reduction by modulating electron flow following changes in environmental conditions, FLV activity is particularly relevant in the first seconds after a light change while PGRL1 has a major role upon sustained strong illumination.
关键词： Photosynthetic Reaction Center Complex Proteins,Photosynthesis,photoprotection,Energy metabolism,Evolution, Molecular,Bryophyta
更新于2025-09-10 09:29:36
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Effect of Linking Pattern of Dibenzothiophene- <i>S</i> , <i>S</i> -dioxide-Containing Conjugated Microporous Polymers on the Photocatalytic Performance
摘要： Conjugated microporous polymers (CMPs) exhibit great potential for photocatalytic hydrogen generation due to their tunable electronic structure. The rational molecular design is a key point for developing an efficient CMP photocatalyst. Herein, we developed two CMPs photocatalysts via the copolymerization from pyrene and dibenzothiophene-S,S-dioxide building blocks. The effect of the linking pattern of the building block of dibenzothiophene-S,S-dioxide on the photocatalytic hydrogen evolution was explored. The polymer of PyDOBT-1 with 3,7-linking pattern shows a superior photocatalytic performance to PyDOBT-2 with 2,8-linking pattern because the 3,7-linking pattern enhances the conjugation chain length and improves the coplanarity of the polymeric backbone, which facilitate the charges migration along the polymer chain. As a result, the bare PyDOBT-1 shows an impressive visible light activity with a hydrogen evolution rate (HER) of 5697 μmol h?1 g?1. Notably, an outstanding HER of 12986 μmol h?1 g?1 was also obtained by the Pt-modified PyDOBT-1 under the full-arc spectrum (λ > 300 nm), which lies toward the upper end compared to that of the reported organic photocatalysts.
关键词： Conjugated microporous polymers,Dibenzothiophene-S,S-dioxide,Photocatalytic hydrogen generation,Linking pattern,Hydrogen evolution rate
更新于2025-09-10 09:29:36
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PVP assisted hydrothermal synthesis of CuCoO2 nanoplates with enhanced oxygen evolution reaction performance
摘要： Tuning size and morphology and exploiting new catalytic materials are several important strategies commonly used to develop highly efficient oxygen evolution reaction (OER) electrocatalysts. In this work, we report the synthesis of CuCoO2 (CCO) nanoplates through a facile one-step PVP assisted hydrothermal process. The influence of hydrothermal reaction parameters, including the precursor composition, reaction temperature and duration, on the morphology, size and crystal phase of CCO crystals has been investigated in detail. In addition, X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have been used to comprehensively characterize CCO’s crystal structure, morphology, composition and chemical states of elements. Furthermore, the electrocatalytic performance of CCO nanoplates towards the OER is studied and compared to that of CCO micrometer-sized crystals. The CCO nanoplates only require a low overpotential of 390 mV to attain an anodic current density 10 mA cm-2 in alkaline solution, and show comparatively fast OER kinetics with a Tafel slope of 70 mV dec-1 and reasonably good long-term catalytic stability, substantially outperforming CCO micro-crystals, which highlights the importance of size and morphology of CCO for use in OER electrocatalysis.
关键词： Water splitting,Oxygen evolution reaction,CuCoO2,Delafossite,Electrocatalyst
更新于2025-09-10 09:29:36
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Channel Estimation and Equalization for SS-OOFDM System with High Mobility
摘要： When orthogonal frequency division multiplexing (OFDM) is used in high-speed mobile scenarios, the traditional implementation of the OFDM receiver causes signi?cant performance degradation. This letter proposes a subband superposed oversampled OFDM (SS-OOFDM) scheme for accommodating the diverse scenarios, including the scenarios with high mobility. To track the fast-varying mobile channel, a time-domain channel estimation method is developed to ?rstly obtain the channel impulse response (CIR) values at pilots by means of the basis expansion model. Subsequently, by utilizing Slepian sequences-based interpolation, the CIR values at data symbols are reconstructed. Furthermore, we design a subband decision feedback and feedforward equalizer (SDFFE) for exploiting the Doppler and multipath diversity gains. Simulation results show that the SS-OOFDM, especially in high-speed mobile channels, outperforms the traditional OFDM receiver in terms of the bit-error-rate (BER) performance.
关键词： Mobile Channel,SS-OOFDM,OFDM,Channel Estimation and Equalization,Long Term Evolution (LTE)
更新于2025-09-10 09:29:36
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Enhanced Electron Separation on in-Plane Benzene-Ring Doped g-C3N4 Nanosheets for Visible Light Photocatalytic Hydrogen Evolution
摘要： Solar-to-chemical energy conversion by photocatalytic hydrogen evolution (PHE) is critical for reduction of the pollution and storage of clean energy. To improve the solar conversion efficiency, it is highly imperative to accelerate the photocarrier separation and transportation through materials design. Herein, we describe a highly effective PHE catalyst based on in-plane benzene-ring doped g-C3N4 nanosheets heterostructure through the thermal co-polymerization of urea and 4, 4'-sulfonyldiphenol (BPS) followed by a controlled heat-etching step. The solid-state 13C NMR confirms the existence of benzene-ring structure in g-C3N4 nanosheets. Experimental results and theoretical calculations show that the energy and electronic structure of the catalyst are optimally regulated, inducing increased light absorption and effectively accelerated separation of the photo-driven charge carriers. It exhibits enhanced photocatalytic hydrogen evolution efficiency with a PHE rate of 12.3 mmol h-1 g-1 (almost 12 times higher than that of pure g-C3N4 nanosheets) and the quantum efficiency of 17.7 % at 420 nm.
关键词： g-C3N4,hydrogen evolution,in-plane,benzene-ring doping,photocatalysis
更新于2025-09-10 09:29:36
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Multi-mode photocatalytic performances of CdS QDs modified CdIn2S4/CdWO4 nanocomposites with high electron transfer ability
摘要： In general, quantum dots have the property of generating a plurality of charge carriers using hot electrons or using a single high-energy photon to improve the photocatalytic properties of the material. In this paper, CdS QDs@CdIn2S4/CdWO4 modified by CdS QDs was synthesized by the microwave-assisted hydrothermal method, and its composition, crystal structure, morphology, and surface physicochemical properties were well characterized. Electron microscopy results showed that CdS QDs@CdIn2S4/CdWO4 composite material exhibited a sheet structure with a length of ca. 350 nm and a width of ca. 50 nm, and CdS QDs uniformly distributes with a diameter of about 5 nm on the sheet structure. UV-visible diffuse reflectance tests showed that the combination of CdS QDs and CdIn2S4 can extend the light absorption range of CdWO4 to the visible region. Photoluminescence spectroscopy confirmed that CdS QDs had efficient electron transport capabilities. The multi-mode photocatalytic activity of CdS QDs@CdIn2S4/CdWO4 showed an excellent ability to degrade organic pollutants. Under the conditions of no co-catalyst and Na2S-Na2SO3 as the sacrificial agent, the hydrogen production of CdS QDs@CdIn2S4/CdWO4 can reach 221.3 μmol g?1 when exposed to visible light (λ > 420 nm) for 8 h.
关键词： CdS QDs,Quantum dots,Microwave-assisted hydrothermal method,CdWO4,Multimode photocatalysis,H2 evolution,CdIn2S4
更新于2025-09-10 09:29:36
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Comparative activity of aqueous dispersions of CdS nanocrystals stabilized by cationic and anionic polyelectrolytes in photocatalytic hydrogen production from water
摘要： The results of a study on the photocatalytic activity of aqueous dispersions of Ni-doped CdS nanocrystals (NCs) covered with an amphiphilic polyelectrolyte (PE) shell, i.e., a polycation (NC-PC) or polyanion (NC-PA), are presented for the first time. The H2 evolution rate measured under identical conditions served as a measure of activity. The NC-PC and NC-PA samples were characterized by similar PE content (~40%) and monomodal size distribution. According to our calculations based on the NC dimensions and lattice parameters, about one macromolecule of the PE is required to stabilize one NC. The average hydrodynamic diameter of the NC-PC was found to be 1.5 times larger than that of the NC-PA due to the difference between their chemical structures and different abilities of ionogenic groups to dissociate. The photocatalytic activity of the PE-stabilized CdS nanocrystals was significantly influenced by the type of the PE, while the H2 evolution rate depended on the reducing medium used during the process. When the medium contained Na2S or when the PE-stabilized NCs were pre-treated with Na2S, the effect of the shell type was more pronounced and the activity of NC-PA was 2 to 14 times higher than that of NC-PC.
关键词： polyelectrolytes,nanocrystals,photocatalysis,cadmium sulfide,hydrogen evolution reactions,nickel
更新于2025-09-10 09:29:36