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Intrinsic correlation between electronic structure and degradation: from few layers to bulk black phosphorus
摘要： Black phosphorus (BP) has received much attention due to its fascinating properties, such as a high mobility and tunable band gap which covers the band gap lacuna between graphene and transition metal dichalcogenides. However, these advantages have been overshadowed due to the fast degradation of BP in ambient conditions. To overcome this obstacle, the degradation mechanisms should be unveiled with direct observation followed by a thorough analysis. Here, we reveal two sequential degradation processes and layer-dependent degradation rates of BP under dark conditions by scanning Kelvin probe microscopy (SKPM) measurements and theoretical modeling. The layer-dependent degradation is successfully interpreted with the oxidation model based on the Marcus-Gerischer theory (MGT). Under dark conditions, the electron transfer rate from BP to oxygen molecule depends on the number of layers that give different carrier concentrations. The oxidation rate is strongly dependent on the number of layers, and thus carrier concentrations. This suggests the possibility of stability improvement by carrier modulation. This work not only provides a deeper understanding of the degradation mechanism itself but also suggest new strategies for stable BP-based electronics design.
关键词： oxidation model,degradation,work function,Marcus-Gerischer theory,black phosphorus
更新于2025-09-04 15:30:14
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Switching on efficient photocatalytic water oxidation reactions over CaNbO2N by Mg modifications under visible light illumination
摘要： In spite of a strong visible light absorbance as far as 600 nm, CaNbO2N generally exhibits poor photocatalytic activity under normal conditions because of various structural defects and poor charge mobility. In this work, we have synthesized a series of Mg-modified CaNbO2N, i.e. CaNb1-xMgxO2+yN1-y (0 ≤ x ≤ 0.2), and performed a detailed investigation on their crystal structures, optical absorption and other physicochemical properties. Our results show that there is a slight shrinkage of the unit cell and a blue-shift of absorption edges upon Mg incorporation into CaNbO2N. The nitrogen contents as well as defects levels can be effectively tuned by altering the content of Mg. More strikingly, photocatalytic oxygen productions are much improved after Mg modifications under visible light irradiation (λ ≥ 420 nm). An average oxygen production rate as much as ~126.8 umol h?1 and an apparent quantum efficiency as high as ~3.4 % at 420 ± 20 nm is achieved for CaNb0.9Mg0.1O2+yN1-y (x = 0.1). These improvements probably stem from a substantial decrease of Nb4+ defects in CaNbO2N as well as slight positive shift of valence band maximum (VBM) after Mg modifications. Meanwhile, photoelectrochemical analysis suggests charge migration is somewhat enhanced in response to Mg modifications.
关键词： water oxidation,CaNbO2N,photocatalyst,water splitting,Mg modification
更新于2025-09-04 15:30:14
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Exploration of charge carrier delocalization in the iron oxide/CdS type-II heterojunction band alignment for enhanced solar-driven photocatalytic and antibacterial applications
摘要： Recyclable magnetic photocatalysts of iron oxide (IO)/CdS core/shell nanocrystals (CSNCs) were prepared by a facile sequential one-pot method using 3, 3'-thiobispropanoic acid (TDP) as a bridge. The CSNCs showed redshift in absorption edge, decrease in the optical band gap, reduced exciton decay rates and increment in particle size. Quenching studies have been employed to understand the position of the electron/hole wave-functions at the IO/CdS interface. Antimicrobial tests have also been performed using broth tube dilution and disc diffusion methods against S. aureus. Additionally, photocatalytic properties of IO/CdS CSNCs have been evaluated for the decomposition of xylenol blue. In comparison with CdS quantum dots (QDs) and iron oxide nanoparticles (IONPs), the IO/CdS CSNCs showed improved photocatalytic and bactericidal activities. Finally, levels of oxidative damage to proteins and lipids were evaluated.
关键词： Photocatalysis,Wave-function engineering,Advanced oxidation process,Iron oxide/CdS nanocrystals,Photocatalytic bacterial inactivation
更新于2025-09-04 15:30:14
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Advanced oxidation of formaldehyde in aqueous solution using the chemical-less UVC/VUV process: Kinetics and mechanism evaluation
摘要： This study was conducted to evaluate the degradation of high concentrations of formaldehyde in the chemical-less UVC/VUV photo-reactor. 99.5% degradation and 94% chemical oxygen demand (COD) removal of 200 mg/L formaldehyde was achieved in the UVC/VUV photo-reactor at reaction time of 60 min and solution pH of 7. The effect of water anions such as carbonate, bicarbonate, nitrate, chloride, sulfate and phosphate was examined on degradation and COD removal of formaldehyde; nitrate and carbonate exhibited the highest inhibitory effects on the process. Besides, treatment of formaldehyde-contaminated tap water was also investigated and formaldehyde removal was decreased from 99.5% is aqueous solution to 86.2% in tap water. The findings of radical scavenging tests revealed that hydroxyl radical was the most predominant oxidizing agent contributed in degradation of formaldehyde. It is concluded therefore that the UVC/VUV process as a unique chemical-less process efficient for advanced degradation of high concentrations of formaldehyde.
关键词： Hydroxyl radical,COD removal,Vacuum UV,Formaldehyde degradation,Advanced photo-oxidation
更新于2025-09-04 15:30:14
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Spectro-electrochemical Studies on [Ru(TAP) <sub/>2</sub> (dppz)] <sup>2+</sup> —Insights into the Mechanism of its Photosensitized Oxidation of Oligonucleotides
摘要： [Ru(TAP)2(dppz)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene; dppz = dipyrido[3,2-a:2′,3′-c]phenazine) is known to photo-oxidize guanine in DNA. Whether this oxidation proceeds by direct photoelectron transfer or by proton-coupled electron transfer is still unknown. To help distinguish between these mechanisms, spectro-electrochemical experiments have been carried out with [Ru(TAP)2(dppz)]2+ in acetonitrile. The UV?vis and mid-IR spectra obtained for the one-electron reduced product were compared to those obtained by picosecond transient absorption and time-resolved infrared experiments of [Ru(TAP)2(dppz)]2+ bound to guanine-containing DNA. An interesting feature of the singly reduced species is an electronic transition in the near-IR region (with λmax at 1970 and 2820 nm). Density functional and time-dependent density functional theory simulations of the vibrational and electronic spectra of [Ru(TAP)2(dppz)]2+, the reduced complex [Ru(TAP)2(dppz)]+, and four isomers of [Ru(TAP)(TAPH)(dppz)]2+ (a possible product of proton-coupled electron transfer) were performed. Significantly, these predict absorption bands at λ > 1900 nm (attributed to a ligand-to-metal charge-transfer transition) for [Ru(TAP)2(dppz)]+ but not for [Ru(TAP)(TAPH)(dppz)]2+. Both the UV?vis and mid-IR difference absorption spectra of the electrochemically generated singly reduced species [Ru(TAP)2(dppz)]+ agree well with the transient absorption and time-resolved infrared spectra previously determined for the transient species formed by photoexcitation of [Ru(TAP)2(dppz)]2+ intercalated in guanine-containing DNA. This suggests that the photochemical process in DNA proceeds by photoelectron transfer and not by a proton-coupled electron transfer process involving formation of [Ru(TAP)(TAPH)(dppz)]2+, as is proposed for the reaction with 5′-guanosine monophosphate. Additional infrared spectro-electrochemical measurements and density functional calculations have also been carried out on the free TAP ligand. These show that the TAP radical anion in acetonitrile also exhibits strong broad near-IR electronic absorption (λmax at 1750 and 2360 nm).
关键词： proton-coupled electron transfer,DNA oxidation,photoelectron transfer,Ruthenium complexes,spectro-electrochemistry
更新于2025-09-04 15:30:14
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Highly transparent conductive reduced graphene oxide/silver nanowires/silver grid electrodes for low-voltage electrochromic smart windows
摘要： Transparent conductive electrodes (TCEs) based on hybrid structures (silver nanowires) have been compressively reconnoitered in next-generation electronics such as flexible displays, artificial skins, smart windows, and sensors, owing to their admirable conductivity as well as flexibility, which make them favorable substitutes to replace ITO (Indium Tin Oxide) as a transparent conductor. Nevertheless, silver-based TCEs grieve from poor stability owing to the corrosion and oxidation of silver in electrolytes. To overcome these issues, a RGO (Reduced Graphene Oxide) layer on silver was promote to resolve the difficulties of corrosion and oxidation in the electrolyte. Moreover, we successfully designed and demonstrated low-voltage WO3-based electrochromic devices (ECDs) with fabricated hybrid TCEs. The hybrid electrodes with RGO/silver nanowires/metal grid/PET (RAM) electrode exhibited improvements in the switching stability and optoelectronic properties, such as the sheet resistance (0.714 ohm/sq), as well as optical transparency of 90.9%. The coloration and bleaching behavior of the ECD was observed in an applied low-voltage range of -1.0 to 0.0 V with a maximum optical difference of 72% at 700 nm, which yielded a coloration efficiency (η) of ~33.4 cm2/C. The highly conductive hybrid TCEs exhibit favorable features for numerous embryonic flexible electronics and optoelectronic devices.
关键词： Oxidation,Silver nanowires,Electrochromic devices,Reduced graphene oxide,Corrosion
更新于2025-09-04 15:30:14
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Synthesis of core–shell ZIF-67@Co-MOF-74 catalyst with controllable shell thickness and enhanced photocatalytic activity for visible light-driven water oxidation
摘要： In this paper, a core–shell ZIF-67@Co-MOF-74 catalyst was synthesized by coating 2,5-dihydroxyterephthalic acid (DHTP) molecules on the surface of ZIF-67 crystals via the ligand exchange method. Notably, the ZIF-67@Co-MOF-74 catalyst with shell thicknesses of 10 nm, 25 nm and 50 nm can be further obtained by adjusting the mass ratio of ZIF-67 and DHTP. Compared to individual ZIF-67 or Co-MOF-74 catalyst, the as-prepared core–shell MOF catalyst exhibited enhanced photocatalytic activities for light-driven water oxidation reaction. Furthermore, the content of oxygen evolution by water splitting increased gradually with the increase in shell thickness. The formation of crystal defects and the uncoordinated hydroxyl and carboxyl groups on the surface of core–shell MOFs facilitated the exposure of the metal catalytic center and the adsorption of water molecules through hydrogen bonding interactions to react with the catalytic active center effectively. In addition, the photogenerated holes and electrons could be excellently separated and rapidly transferred at the interface of ZIF-67 (core) and Co-MOF-74 (shell), resulting in effective increase in the interfacial charge transfer rate. Furthermore, this simple and novel method is also applicable to three other carboxylic acid ligands, which implies that it may be a general method that can be extended to other ligands for fabricating different core–shell ZIF-67@MOF crystals.
关键词： ZIF-67@Co-MOF-74,ligand exchange method,water oxidation,core–shell,photocatalytic activity
更新于2025-09-04 15:30:14
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Confocal Fluorescence Microscopy and Kinetics of the Cr3+-Chromate Ion Oxidation Equilibria at the Solid Liquid Interface
摘要： Silica-borax pearl samples impregnated with 0.17 and 0.64% Cr3+ were characterized by specific surface area measurements, UV-Vis spectroscopy, energy-dispersive X-ray fluorescence and laser-scanning confocal microscopy. Pearl stability against oxidizing conditions was tested by adding samples to an aqueous hydrogen peroxide solution. The reaction was examined by UV-Vis spectroscopic measurements of the supernatant and laser-scanning confocal microscopy images of the substrate. Overall, hydrogen peroxide-induced Cr3+ to Cr6+ oxidation across the solid-liquid interface promoted solid matrix cleavage pearl degradation and concomitant formation of multiple scattering centers was observed. A dual-detection scheme was employed in the confocal microscopy measurements allowing us to separate scattering and absorptive contributions to the observed signals. The confocal microscopy images indicate that Cr3+ oxidation induced by hydrogen peroxide solutions occurs throughout the entire pearl sample and indicate that oxidation reactions induce leakage of chromate ion into aqueous solutions.
关键词： energy dispersive X-ray fluorescence,confocal fluorescence microscopy,chromium mobility,H2O2 oxidation equilibria,mass transfer phenomena,solid liquid interfaces
更新于2025-09-04 15:30:14
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TiO2 Nanoparticles Catalyze Oxidation of Huntingtin Exon 1-Derived Peptides Impeding Aggregation: a Quantitative NMR Study of Binding and Kinetics
摘要： Polyglutamine expansion within the N-terminal region of the huntingtin protein results in the formation of intracellular aggregates responsible for Huntington’s disease, a fatal neurodegenerative condition. The interaction between TiO2 nanoparticles and huntingtin peptides comprising the N-terminal amphiphilic domain without (httNT) or with (httNTQ10) a ten-residue C-terminal polyglutamine tract, is investigated by NMR spectroscopy. TiO2 nanoparticles decrease aggregation of httNTQ10 by catalyzing the oxidation of Met7 to a sulfoxide, resulting in an aggregation-incompetent peptide. The oxidation agent is hydrogen peroxide generated on the surface of the TiO2 nanoparticles either by UV irradiation or at low steady-state levels in the dark. The binding kinetics of non-aggregating httNT to TiO2 nanoparticles is characterized by quantitative analysis of 15N dark state exchange saturation transfer and lifetime line broadening NMR data. Binding involves a sparsely-populated intermediate that experiences hindered rotational diffusion relative to the free state. Catalysis of methionine oxidation within the N-terminal domain of the huntingtin protein may potentially provide a strategy for delaying the onset of Huntington’s disease.
关键词： Huntingtin,TiO2 nanoparticles,aggregation,NMR spectroscopy,oxidation
更新于2025-09-04 15:30:14