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1.
Carcinogenesis ; 2024 Apr 04.
Artículo en Inglés | MEDLINE | ID: mdl-38573327

RESUMEN

Telomerase reactivation is implicated in approximately 85% of human cancers, yet its underlying mechanism remains elusive. In this study, we elucidate that the Cullin RING Ubiquitin Ligase 4 (CRL4) complex drives the reactivation of human telomerase reverse transcriptase (hTERT) in colorectal cancer (CRC) by degrading the tumor suppressor, menin 1 (MEN1). Our data show that, in noncancerous intestinal epithelial cells, the transcription factor specificity protein 1 (Sp1) recruits both the histone acetyltransferase p300 and MEN1 to suppress hTERT expression, thus maintaining telomere shortness post-cell division. Inflammation-induced microenvironments trigger an activation of the CRL4DCAF4 E3 ligase, leading to MEN1 ubiquitination and degradation in CRC cells. This process nullifies MEN1's inhibitory action, reactivates hTERT expression at the transcriptional level, interrupts telomere shortening, and spurs uncontrolled cellular proliferation. Notably, MEN1 overexpression in CRC cells partially counteracts these oncogenic phenotypes. NSC1517, an inhibitor of the CRL4DCAF4 complex identified through high-throughput screening from a plant-derived chemical pool, hinders MEN1 degradation, attenuates hTERT expression, and suppresses tumor growth in mouse xenograft models. Collectively, our research elucidates the transcriptional mechanism driving hTERT reactivation in CRC. Targeting the CRL4DCAF4 E3 ligase emerges as a promising strategy to counteract cancer cell immortalization and curb tumor progression.

2.
Environ Sci Technol ; 57(47): 18607-18616, 2023 Nov 28.
Artículo en Inglés | MEDLINE | ID: mdl-36745772

RESUMEN

In this study, novel light emitting diode (LED)-activated periodate (PI) advanced oxidation process (AOP) at an irradiation wavelength in the ultraviolet A range (UVA, UVA-LED/PI AOP) was developed and investigated using naproxen (NPX) as a model micropollutant. The UVA-LED/PI AOP remarkably enhanced the degradation of NPX and seven other selected micropollutants with the observed pseudo-first-order rate constants ranging from 0.069 ± 0.001 to 4.50 ± 0.145 min-1 at pH 7.0, demonstrating a broad-spectrum micropollutant degradation ability. Lines of evidence from experimental analysis and kinetic modeling confirmed that hydroxyl radical (•OH) and ozone (O3) were the dominant species generated in UVA-LED/PI AOP, and they contributed evenly to NPX degradation. Increasing the pH and irradiation wavelength negatively affected NPX degradation, and this could be well explained by the decreased quantum yield (ΦPI) of PI. The degradation kinetics of NPX by the UVA-LED/PI AOP in the presence of water matrices (i.e., chloride, bicarbonate, and humic acid) and in real waters were examined, and the underlying mechanisms were illustrated. A total of nine transformation products were identified from NPX oxidation by the UVA-LED/PI AOP, mainly via hydroxylation, dealkylation, and oxidation pathways. The UVA-LED/PI AOP proposed might be a promising technology for the treatment of micropollutants in aqueous solutions. The pivotal role of ΦPI during light photolysis of PI may guide the future design of light-assisted PI AOPs.


Asunto(s)
Ozono , Contaminantes Químicos del Agua , Purificación del Agua , Radical Hidroxilo , Contaminantes Químicos del Agua/análisis , Agua , Oxidación-Reducción , Cinética , Rayos Ultravioleta
3.
Environ Sci Technol ; 57(29): 10804-10815, 2023 07 25.
Artículo en Inglés | MEDLINE | ID: mdl-37431633

RESUMEN

Carbon nanotubes (CNTs) and their derivatives have been widely exploited to activate various oxidants for environmental remediation. However, the intrinsic mechanism of CNTs-driven periodate (PI) activation remains ambiguous, which significantly impedes their scientific progress toward practical application. Here, we found that CNTs can strongly boost PI activation for the oxidation of various phenols. Reactive oxygen species analysis, in situ Raman characterization, galvanic oxidation process experiments, and electrochemical tests revealed that CNTs could activate PI to form high-potential metastable intermediates (CNTs-PI*) rather than produce free radicals and 1O2, thereby facilitating direct electron transfer from the pollutants to PI. Additionally, we analyzed quantitative structure-activity relationships between rate constants of phenols oxidation and double descriptors (e.g., Hammett constants and logarithm of the octanol-water partition coefficient). The adsorption of phenols on CNT surfaces and their electronic properties are critical factors affecting the oxidation process. Besides, in the CNTs/PI system, phenol adsorbed the CNT surfaces was oxidized by the CNTs-PI* complexes, and products were mainly generated via the coupling reaction of phenoxyl radical. Most of the products adsorbed and accumulated on the CNT surfaces realized phenol removal from the bulk solution. Such a unique non-mineralization removal process achieved an extremely high apparent electron utilization efficiency of 378%. The activity evaluation and theoretical calculations of CNT derivatives confirmed that the carbonyl/ketonic functional groups and double-vacancy defects of the CNTs were the primary active sites, where high-oxidation-potential CNTs-PI* were formed. Further, the PI species could achieve a stoichiometric decomposition into iodate, a safe sink of iodine species, without the generation of typical iodinated byproducts. Our discovery provides new mechanistic insight into CNTs-driven PI activation for the green future of environmental remediation.


Asunto(s)
Nanotubos de Carbono , Nanotubos de Carbono/química , Fenol , Oxidación-Reducción , Fenoles
4.
Environ Sci Technol ; 57(8): 3334-3344, 2023 02 28.
Artículo en Inglés | MEDLINE | ID: mdl-36734031

RESUMEN

Accelerating the rate-limiting Fe3+/Fe2+ circulation in Fenton reactions through the addition of reducing agents (or co-catalysts) stands out as one of the most promising technologies for rapid water decontamination. However, conventional reducing agents such as hydroxylamine and metal sulfides are greatly restricted by three intractable challenges: (1) self-quenching effects, (2) heavy metal dissolution, and (3) irreversible capacity decline. To this end, we, for the first time, introduced redox-active polymers as electron shuttles to expedite the Fe3+/Fe2+ cycle and promote H2O2 activation. The reduction of Fe3+ mainly took place at active N-H or O-H bonds through a proton-coupled electron transfer process. As electron carriers, H atoms at the solid phase could effectively inhibit radical quenching, avoid metal dissolution, and maintain long-term reducing capacity via facile regeneration. Experimental and density functional theory (DFT) calculation results indicated that the activity of different polymers shows a volcano curve trend as a function of the energy barrier, highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap, and vertical ionization potential. Thanks to the appropriate redox ability, polyaniline outperforms other redox-active polymers (e.g., poypyrrole, hydroquinone resin, poly(2,6-diaminopyridine), and hexaazatrinaphthalene framework) with a highest iron reduction capacity up to 5.5 mmol/g, which corresponds to the state transformation from leucoemeraldine to emeraldine. Moreover, the proposed system exhibited high pollutant removal efficiency in a flow-through reactor for 8000 bed volumes without an obvious decline in performance. Overall, this work established a green and sustainable oxidation system, which offers great potential for practical organic wastewater remediation.


Asunto(s)
Peróxido de Hidrógeno , Hierro , Hierro/química , Peróxido de Hidrógeno/química , Sustancias Reductoras , Electrones , Oxidación-Reducción
5.
Phys Chem Chem Phys ; 25(44): 30670-30678, 2023 Nov 15.
Artículo en Inglés | MEDLINE | ID: mdl-37933752

RESUMEN

Previous research is predominantly in consensus on the reaction mechanism between formaldehyde (HCHO) and oxygen (O2) over catalysts. However, water vapor (H2O) always remains present during the reaction, and the intrinsic role of H2O in the oxidation of HCHO still needs to be fully understood. In this study, a single-atom catalyst, Al-doped C2N substrate, Al1/C2N, can be adopted as an example to investigate the relationship and interaction among O2, H2O, and HCHO. Density functional theory (DFT) calculations and microkinetic simulations were carried out to interpret the enhancement mechanism of H2O on HCHO oxidation over Al1/C2N. The outcome demonstrates that H2O directly breaks down a surface hydroxyl group on Al1/C2N, considerably lowering the energy required to form crucial intermediates, thus promoting oxidation. Without H2O, Al1/C2N cannot effectively oxidize HCHO at ambient temperature. During oxidation, H2O takes the major catalytic responsibility, delaying the entrance of O2 into the reaction, which is not only the product but also the crucial reactant to initiate catalysis, thereby sustaining the catalytic cycle. Moreover, this study predicts the catalytic behavior at various temperatures and presents feasible recommendations for regulating the reaction rates. The oxidation mechanism of HCHO is explained at the molecular level in this study, emphasizing the intrinsic role of water on Al1/C2N, which fills in the relevant studies for HCHO oxidation on two-dimensional carbon materials.

6.
J Am Chem Soc ; 144(39): 17865-17875, 2022 10 05.
Artículo en Inglés | MEDLINE | ID: mdl-36075889

RESUMEN

Enhancing the enzymatic activity inside metal-organic frameworks (MOFs) is a critical challenge in chemical technology and bio-technology, which, if addressed, will broaden their scope in energy, food, environmental, and pharmaceutical industries. Here, we report a simple yet versatile and effective strategy to optimize biocatalytic activity by using MOFs to rapidly "lock" the ultrasound (US)-activated but more fragile conformation of metalloenzymes. The results demonstrate that up to 5.3-fold and 9.3-fold biocatalytic activity enhancement of the free and MOF-immobilized enzymes could be achieved compared to those without US pretreatment, respectively. Using horseradish peroxidase as a model, molecular dynamics simulation demonstrates that the improved activity of the enzyme is driven by an opened gate conformation of the heme active site, which allows more efficient substrate binding to the enzyme. The intact heme active site is confirmed by solid-state UV-vis and electron paramagnetic resonance, while the US-induced enzyme conformation change is confirmed by circular dichroism spectroscopy and Fourier-transform infrared spectroscopy. In addition, the improved activity of the biocomposites does not compromise their stability upon heating or exposure to organic solvent and a digestion cocktail. This rapid locking and immobilization strategy of the US-induced active enzyme conformation in MOFs gives rise to new possibilities for the exploitation of highly efficient biocatalysts for diverse applications.


Asunto(s)
Estructuras Metalorgánicas , Metaloproteínas , Enzimas Inmovilizadas/química , Hemo , Peroxidasa de Rábano Silvestre , Estructuras Metalorgánicas/química , Solventes
7.
Small ; 18(2): e2105279, 2022 01.
Artículo en Inglés | MEDLINE | ID: mdl-34837320

RESUMEN

Water in motion presented in natural systems contains a rich source of renewable mechanical energy. Harvesting this water energy to trigger the generation of reactive oxygen species (ROS) for water purification is a desirable yet underexplored solution. Herein, the authors report a self-powered water motion triggered Fenton-like reaction system for wastewater treatment through the piezo-activation of peroxymonosulfate (PMS). Isolated protrudent Fe single atomic sites are immobilized on the surface of molybdenum disulfide (MoS2 ) nanosheet to improve piezoelectric polarization of MoS2 , to accelerate piezoelectric charge separation, and to enhance PMS activation for water purification. ROS (• OH, SO4•- , O2•- , and 1 O2 ) generation for PMS piezo-activation are observed, and different water contaminants, including antibiotic, industrial chemicals, and dyes are efficiently removed under the natural water fluid. Aimed at solving concurrent issues of environmental pollution and energy crisis, this study provides a pathway for single atomic-mediated piezo-activation of Fenton-like reactions through ambient self-powered water motion for water purification.


Asunto(s)
Hierro , Purificación del Agua , Agua
8.
Environ Sci Technol ; 56(14): 10372-10380, 2022 07 19.
Artículo en Inglés | MEDLINE | ID: mdl-35795970

RESUMEN

Although periodate-based advanced oxidation processes have been proven to be efficient in abating organic contaminants, the activation properties of different periodate species remain largely unclear. Herein, by highlighting the role of H4IO6-, we reinvestigated the pH effect on the decontamination performance of the H2O2/periodate process. Results revealed that elevating pH from 2.0 to 10.0 could markedly accelerate the rates of organic contaminant decay but decrease the amounts of organic contaminant removal. This pH-dependent trend of organic contaminant degradation corresponded well with the HO· yield and the variation of periodate species. Specifically, although 1O2 could be detected at pH 9.0, HO· was determined to be the major reactive oxidizing species in the H2O2/periodate process under all the tested pH levels. Furthermore, it was suggested that only H4IO6- and H2I2O104- could serve as the precursors of HO·. The second-order rate constant for the reaction of H2I2O104- species with H2O2 was determined to be ∼1199.5 M-1 s-1 at pH 9.0, which was two orders of magnitude greater than that of H4IO6- (∼2.2 M-1 s-1 at pH 3.0). Taken together, the reaction pathways of H2O2 with different periodate species were proposed. These fundamental findings could improve our understanding of the periodate-based advanced oxidation processes.


Asunto(s)
Peróxido de Hidrógeno , Contaminantes Químicos del Agua , Peróxido de Hidrógeno/química , Concentración de Iones de Hidrógeno , Cinética , Oxidación-Reducción , Ácido Peryódico , Rayos Ultravioleta , Contaminantes Químicos del Agua/química
9.
Environ Sci Technol ; 56(19): 13996-14007, 2022 10 04.
Artículo en Inglés | MEDLINE | ID: mdl-36083161

RESUMEN

In this study, a wet scrubber coupled with a persulfate-based advanced oxidation process [carbocatalysts/peroxymonosulfate (PMS)] was demonstrated to efficiently remove gaseous volatile organic compounds (VOCs). The removal efficiency of a representative VOC, styrene, was stable at above 98%, and an average mineralization rate was achieved at 76% during 2 h. The removal efficiency of the carbocatalysts/PMS wet scrubber for styrene was much higher than that of pure water, carbocatalysts/water, or PMS/water systems. Quenching experiments, electron spin resonance spectroscopy, in-situ Raman spectroscopy and density functional theory (DFT) calculations indicated that singlet oxygen (1O2) and oxidative complexes are the main reactive oxygen species and that both contributed to styrene removal. In particular, carbonyl groups (C═O) in the carbocatalyst were found to be the active sites for activating PMS during styrene oxidation. The role of 1O2 was discovered to be benzene ring breaking and a possible non-radical oxidation pathway of styrene was proposed based on time-of-flight mass spectroscopy which was further verified by DFT calculations. In particular, the electron transfer process of multi world carbon nanotubes-PMS* in styrene oxidation was further studied in-depth by experiments and DFT calculations. The unstable vinyl on styrene was simultaneously degraded by the oxidative complexes and 1O2 into benzene, and finally oxidized by 1O2 into H2O and CO2. This study provides an effective method for VOC removal and clearly illustrates the complete degradation mechanism of styrene in a nonradical PMS-based process by a wet scrubber.


Asunto(s)
Nanotubos de Carbono , Compuestos Orgánicos Volátiles , Benceno , Dióxido de Carbono , Gases , Peróxidos/química , Especies Reactivas de Oxígeno , Oxígeno Singlete , Estirenos , Agua
10.
Environ Sci Technol ; 55(10): 7034-7043, 2021 05 18.
Artículo en Inglés | MEDLINE | ID: mdl-33620197

RESUMEN

Recently, reactive iron species (RFeS) have shown great potential for the selective degradation of emerging organic contaminants (EOCs). However, the rapid generation of RFeS for the selective and efficient degradation of EOCs over a wide pH range is still challenging. Herein, we constructed FeN4 structures on a carbon nanotube (CNT) to obtain single-atom catalysts (FeSA-N-CNT) to generate RFeS in the presence of peroxymonosulfate (PMS). The obtained FeSA-N-CNT/PMS system exhibited outstanding and selective reactivity for oxidizing EOCs over a wide pH range (3.0-9.0). Several lines of evidences suggested that RFeS existing as an FeN4═O intermediate was the predominant oxidant, while SO4·- and HO· were the secondary oxidants. Density functional theory calculation results revealed that a CNT played a key role in optimizing the distribution of bonding and antibonding states in the Fe 3d orbital, resulting in the outstanding ability of FeSA-N-CNT for PMS chemical adsorption and activation. Moreover, CNT could significantly enhance the reactivity of the FeN4═O intermediate by increasing the overlap of electrons of the Fe 3d orbital, O 2p orbital, and bisphenol A near the Fermi level. The results of this study can advance the understanding of RFeS generation in a heterogeneous system over a wide pH range and the application of RFeS in real practice.


Asunto(s)
Hierro , Peróxidos , Catálisis , Oxidantes
11.
Environ Sci Technol ; 55(13): 9189-9198, 2021 07 06.
Artículo en Inglés | MEDLINE | ID: mdl-34048222

RESUMEN

Many reagents as electron sacrificers have been recently investigated to induce decomposition of permanganate (KMnO4) to produce highly reactive intermediate Mn species toward oxidation of organic contaminants; however, this strategy meanwhile causes low KMnO4 utilization efficiency. This study surprisingly found that graphite can mediate direct electron transfer from organics (e.g., sulfamethoxazole (SMX)) to KMnO4, resulting in high KMnO4 utilization efficiency, rather than reductive sites of graphite-induced conversion of KMnO4 to highly reactive intermediate Mn species. The galvanic oxidation process (GOP) and comparative experiments of different organic contaminants prove that the KMnO4/graphite system mainly extracts electrons from organic contaminants via a one-electron pathway instead of a two-electron pathway. More importantly, the KMnO4/graphite system has superior reusability, graphite can keep a long-lasting reactivity, and the KMnO4 utilization efficiency elevates significantly after each cycle of graphite. The transformation of SMX in the KMnO4/graphite system mainly includes self-coupling, hydroxylation, oxidation, and hydrolytic reaction. The work will improve insights into the electron-transfer mechanism and unveil the advantages of efficient KMnO4 utilization in the KMnO4-based technologies in environmental remediation.


Asunto(s)
Grafito , Contaminantes Químicos del Agua , Electrones , Compuestos de Manganeso , Oxidación-Reducción , Óxidos , Permanganato de Potasio , Sulfametoxazol , Contaminantes Químicos del Agua/análisis
12.
Phys Chem Chem Phys ; 22(25): 13981-13988, 2020 Jul 07.
Artículo en Inglés | MEDLINE | ID: mdl-32555843

RESUMEN

Designing effective electrocatalysts for N2 fixation to NH3 under mild conditions is important and challenging. In this work, we explored the feasibility of transition metal atom embedded stanene as an effective catalyst for the nitrogen reduction reaction (NRR) based on first-principles calculations. The results reveal that Mo atom embedded stanene possesses high stability and good electrical conductivity. Specifically, Mo atom embedded stanene exhibits excellent catalytic activity for NRR with an over-potential of only 0.50 V along the mixed pathway. This low over-potential is due to the acceptance and back donation of electrons between the transition metal and N2 molecules. Furthermore, due to the preferential adsorption of N2 relative to H, competition from the hydrogen evolution reaction (HER) can be inhibited effectively. The fairly low over-potential and high electrical conductivity make Mo-embedded stanene promising for NRR. Our theoretical results indicate that stanene could be a new and effective anchoring material for TM-based catalysts for NRR.

13.
Phys Chem Chem Phys ; 22(2): 615-623, 2020 Jan 02.
Artículo en Inglés | MEDLINE | ID: mdl-31822873

RESUMEN

An appropriate band structure and effective carrier separation are very important for the performance of a solar photocatalyst. In this paper, based on first-principles calculations, it was predicted that blue phosphorene (BlueP) and a C2N monolayer can form a promising metal-free type-II heterojunction. The electronic structure of the BlueP/C2N heterojunction facilitated the overall water splitting reactions well. The projected band structure showed that the conduction band edge was contributed by C2N and the valence band edge was dominated by BlueP. Under the combination of the driving force of the band offset and the built-in electric field between the two layers, the photo-generated electrons and holes were transferred spontaneously to the conduction band of C2N and the valence band of BlueP, respectively. An effective carrier separation in the heterostructure was thus achieved. More notably, the obtained light absorption of the BlueP/C2N junction showed an obvious red-shift, which greatly extended the area of light adsorption to the visible light region. We further proposed that strain could also be used to modulate the band gap and the band edge positions of the heterojunction. Our results not only provide a theoretical design, but also reveal the fundamental separation mechanism of the photo-generated carriers in the BlueP/C2N heterojunction.

14.
Environ Sci Technol ; 53(7): 3773-3781, 2019 04 02.
Artículo en Inglés | MEDLINE | ID: mdl-30865825

RESUMEN

The interactions between nanoparticles and humic acid (HA) are critical to understanding the environmental risks and applications of nanoparticles. However, the interactions between HA fractions and graphene oxide (GO, a popular carbon nanosheet) at the molecular level remain largely unclear. Four HA fractions with molecular weights ranging from 4.6 to 23.8 kDa were separated, and the large HA fractions presented low oxygen contents and many aromatic structures. The binding constants of the large HA fractions on GO were 2.6- to 3551-fold higher than those of the small HA fractions, while the maximum adsorption capacities of the larger HA fractions onto GO were much higher. Atomic force microscopy (AFM) found that the small and large HA fractions were spread over the center and the edge of the GO nanosheets, respectively. Density functional theory (DFT) simulation and nuclear magnetic resonance spectroscopy confirmed the above phenomena (three adsorption patterns, "vs", "ps", and "pea") and revealed that HA bonded to the GO nanosheets mainly through van der Waals force and π-π interactions. The integrating analysis of binding affinity, AFM, and DFT provides new insights into the environmental behavior of GO and the applications of GO in pollutant removal under exposure from HA.


Asunto(s)
Grafito , Adsorción , Teoría Funcional de la Densidad , Sustancias Húmicas , Interferometría , Microscopía de Fuerza Atómica , Óxidos
15.
Environ Sci Technol ; 53(19): 11391-11400, 2019 Oct 01.
Artículo en Inglés | MEDLINE | ID: mdl-31436973

RESUMEN

The maximization of the numbers of exposed active sites in supported metal catalysts is important to achieve high reaction activity. In this work, a simple strategy for anchoring single atom Fe on SBA-15 to expose utmost Fe active sites was proposed. Iron salts were introduced into the as-made SBA-15 containing the template and calcined for simultaneous decomposition of the iron precursor and the template, resulting in single atom Fe sites in the nanopores of SBA-15 catalysts (SAFe-SBA). X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and extended X-ray absorption fine structure (EXAFS) imply the presence of single atom Fe sites. Furthermore, EXAFS analysis suggests the structure of one Fe center with four O atoms, and density functional theory calculations (DFT) simulate this structure. The catalytic performances of SAFe-SBA were evaluated in Fenton-like catalytic oxidation of p-hydroxybenzoic acid (HBA) and phenol. It was found that the single atom SAFe-SBA catalysts displayed superior catalytic activity to aggregated iron sites (AGFe-SBA) in both HBA and phenol degradation, demonstrating the advantage of SAFe-SBA in catalysis.


Asunto(s)
Hierro , Fenol , Catálisis , Oxidación-Reducción , Difracción de Rayos X
16.
Phys Chem Chem Phys ; 17(8): 5586-93, 2015 Feb 28.
Artículo en Inglés | MEDLINE | ID: mdl-25588863

RESUMEN

In this work, the systems are constructed with the defect lines of B-B or N-N dimers embedded in a graphene matrix using density functional theory. It is found that the Dirac-cone dispersions appear at the Fermi level in the bands introduced by the B or N heteroatom, linear B-B or N-N dimers, demonstrating that the carrier mobility is ∼10(6) m s(-1) which is comparable with that of the pristine graphene. Most importantly, such dimer lines act as the quasi-1-D conducting nanowires whose charge carriers are confined around the linear defects in these dimers while the charge carriers in pristine graphene are dispersed two-dimensionally. Such systems suggest that heteroatoms in graphene can indeed contribute to the Dirac cone. In addition, the type of carriers (p-type or n-type) can be manipulated using the B or N heteroatoms, respectively. This will greatly enrich the electronic properties of Dirac semimetals.

17.
Phys Chem Chem Phys ; 17(14): 8692-8, 2015 Apr 14.
Artículo en Inglés | MEDLINE | ID: mdl-25735239

RESUMEN

Density-functional theory calculations are performed to investigate the effects of surface modifications and nanosheet thickness on the electronic and magnetic properties of gallium nitride (GaN) nanosheets (NSs). Unlike the bare GaN NSs terminating with polar surfaces, the systems with hydrogenated Ga (H-GaN), fluorinated Ga (F-GaN), and chlorinated Ga (Cl-GaN) preserve their initial wurtzite structures and exhibit ferromagnetic states. The abovementioned three different decorations on Ga atoms are energetically more favorable for thicker GaN NSs. Moreover, as the thickness increases, H-GaN and F-GaN NSs undergo semiconductor to metal and half-metal to metal transition, respectively, while Cl-GaN NSs remain completely metallic. The predicted diverse and tunable electronic and magnetic properties highlight the potential of GaN NSs for novel electronic and spintronic nanodevices.

18.
Phys Chem Chem Phys ; 17(14): 8994-9000, 2015 Apr 14.
Artículo en Inglés | MEDLINE | ID: mdl-25751702

RESUMEN

In order to reveal the origin of enhanced photocatalytic activity of N-doped La2Ti2O7 in both the visible light and ultraviolet light regions, its electronic structure has been studied using spin-polarized conventional density functional theory (DFT) and the Heyd-Scuseria-Ernzerhof (HSE06) hybrid approach. The results show that the deep localized states are formed in the forbidden band when nitrogen solely substitutes for oxygen. Introducing the interstitial Ti atom into the N-doped La2Ti2O7 photocatalyst still causes the formation of a localized energy state. Two nitrogen substitutions co-exist stably with one oxygen vacancy, creating a continuum energy band just above the valence band maximum. The formation of a continuum band instead of mid-gap states can extend the light absorption to the visible light region without increasing the charge recombination, explaining the enhanced visible light performance without deteriorating the ultraviolet light photocatalytic activity.

19.
Phys Chem Chem Phys ; 16(42): 23476-82, 2014 Nov 14.
Artículo en Inglés | MEDLINE | ID: mdl-25265892

RESUMEN

ß-Bi2O3 is an efficient visible-light photocatalyst, however, it is unable to split water to produce hydrogen because of the positive conduction band minimum (CBM). In this paper, using hybrid density functional theory (DFT) calculations, we demonstrated that by doping indium in ß-Bi2O3, the CBM shifts upward because of the orbital hybridization of Bi, In and O. In-doped ß-Bi2O3 photocatalysts synthesized using a precipitation method can photocatalytically split water to produce hydrogen in experiments. In-doping also causes the morphological change of ß-Bi2O3 from the hierarchical bulk assembled by nano-sheets to a spongy-like brick. Furthermore, In-doping induces the formation of electric dipoles along the tunnel in the crystal and decreases the effective mass of the electrons, favouring the separation of electron-hole pairs and electron mobility. Therefore, In-doped ß-Bi2O3 has much better performance than that of the pristine ß-Bi2O3 for photocatalytically decomposing methyl orange (MO) solution. This idea of simply incorporating an isovalent single element into photocatalysts to elevate the CBM and tune the local crystal structure is anticipated to be very useful for designing efficient photocatalysts.

20.
Phys Chem Chem Phys ; 16(31): 16588-94, 2014 Aug 21.
Artículo en Inglés | MEDLINE | ID: mdl-24988182

RESUMEN

An alternative approach for hydrogenation of silicene is proposed through applying an external electric field in order to reduce the reaction energy barrier based on density functional theory calculations. It is found that a positive perpendicular electric field F can act as a catalyst to reduce the energy barrier of H2 dissociative adsorption on silicene, which facilitates the hydrogenation of silicene. In addition, it is found that the barrier decreases as F increases, and when F is above 0.05 a.u. (1 a.u. = 5.14 × 10(11) V m(-1)), the barrier is quite low and hydrogenation of silicene can take place efficiently at room temperature. The catalytic effect of the electric field on hydrogenation of silicene is induced by the redistribution of atomic charge under the electric field, which would change the chemical activity of silicene significantly.

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