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1.
Nanoscale ; 2020 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-32129406

RESUMO

Efficient spatial charge separation and transfer that are critical factors for solar energy conversion primarily depend on the energetic alignment of the band edges at interfaces in heterojunctions. Herein, we first report that constructing a 0D/0D type-II(T-II)/T-II heterojunction is an effective strategy to ingeniously achieve long-range charge separation by taking a ternary heterojunction of TiO2 and graphitic carbon nitride (g-C3N4) as a proof-of-concept. Incorporating g-C3N4 quantum dots (QCN), as the third component, into the commercial P25 composed of anatase (a-TiO2) and rutile (r-TiO2) can be realized via simply mixing the commercially available Degussa P25 and QCN solution followed by heat treatment. The strong coupling and matching band structures among a-TiO2, r-TiO2 and QCN result in the construction of novel T-II/T-II heterojunctions, which would promote the spatial separation and transfer of photogenerated electrons and holes. Moreover, QCN plays a key role in reinforcing light absorption. Particularly, the unique 0D/0D architecture possesses the advantages of abundant active sites for the photocatalytic reaction. As a result, the optimized QCN/a-TiO2/r-TiO2 heterojunctions exhibit enhanced photocatalytic H2 and O2 evolution, especially the hydrogen evolution rate (49.3 µmol h-1) is 11.7 times that of bare P25 under visible light irradiation, and sufficient catalytic stability as evidenced by the recycling experiments. The remarkably enhanced photocatalytic activity can be attributed to the synergistic effects of the energy level alignment at interfaces, the dimensionality and component of the heterojunctions. This work provides a stepping stone towards the design of novel heterojunctions for photocatalytic water splitting.

2.
Adv Mater ; : e1906015, 2020 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-32027058

RESUMO

Developing low-cost, highly efficient, and durable electrocatalysts for oxygen evolution reaction (OER) is essential for the practical application of electrochemical water splitting. Herein, it is discovered that organic small molecule (hexabromobenzene, HBB) can activate commercial transition metal (Ni, Fe, and NiFe) foam by directly evolving metal nanomeshes embedded in graphene-like films (M-NM@G) through a facile Br-induced solid-phase migration process. Systematic investigations indicate that HBB can conformally generate graphene-like network on bulk metal foam substrate via the cleavage of CBr bonds and the formation of CC linkage. Simultaneously, the cleaved CBr fragments can efficiently extract metal atoms from bulk substrate, in situ producing transition metal nanomeshes embedded in the graphene-like films. As a result, such functional nanostructure can serve as an efficient OER electrocatalyst with a low overpotential and excellent long-term stability. Specifically, the overpotential at 100 mA cm-2 is only 208 mV for NiFe-NM@G, ranking the top-tier OER electrocatalysts. This work demonstrates an intriguing general strategy for directly transforming bulk transition metals into nanostructured functional electrocatalysts via the interaction with organic small molecules, opening up opportunities for bridging the application of organic small molecules in energy technologies.

3.
Phys Chem Chem Phys ; 22(5): 3037-3047, 2020 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-31960006

RESUMO

The energetic alignment of band edges at the interface plays a central role in determining the properties and applications of two-dimensional (2D) van der Waals (vdW) heterostructures. Generally, three conventional heterojunction types (type-I, type-II, and type-III) have widely been investigated and used in diverse fields. Unconventional band alignments (type-IV, type-V, and type-VI) are, however, hitherto unreported in the vdW heterostructures. We find that 2D binary semiconductors composed of group IV-V elements manifest a similar electronic structure, offering in principle the possibility of designing heterostructures with novel band alignments due to the hybridization of band-edge states. We first show here that a 2D SiAs/GeP heterostructure exhibits a type-VI band alignment, which is induced by the interlayer pz orbital hybridization, and a transition of band alignment from type-VI to type-V occurs when strain or electric field is applied over a critical value. The unconventional band alignments and their transition natures enable broad application of these vdW heterostructures in special opto-electronic devices and energy conversion.

4.
Nanoscale ; 12(5): 3135-3145, 2020 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-31965134

RESUMO

Steering charge kinetics at the interface is essential to improve the photocatalytic performance of two-dimensional (2D) material-based heterostructures. Herein, we developed a novel strategy-simultaneously building two kinds of heterojunctions- to modulate interfacial charge kinetics in polymeric carbon nitride (CN) for improving the photocatalytic activity. Using a simple one-step thermal condensation of carbon quantum dot (CQD)-contained supramolecular precursors formed in water, the controllable CQD embedded CN nanoframes possessed two kinds of heterogeneous interfaces within seamlessly stitched micro-area two-dimensional in-plane and out-of-plane domains. These two kinds of heterojunctions can effectively enhance its intrinsic driving force to accelerate the separation and transfer of charge along different directions. Furthermore, the hollow double-deck porous CN-CQD nanoframes with a high surface area (296.74 m2 g-1) endowed more exposed active sites. The remarkable visible-light photocatalytic activity of hollow porous CN-CQD nanoframes was demonstrated by degrading tetracycline (TC) and rhodamine (RhB) as the models, whose robust degradation rate constant is approximately 11 and 29 times higher than that of pristine CN, respectively. This work provides a novel strategy for the interfacial design of the heterophase junction with atomic precision.

5.
Nanoscale Res Lett ; 14(1): 306, 2019 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-31493117

RESUMO

Two-dimensional (2D) penta-graphene (PG) with unique properties that can even outperform graphene is attracting extensive attention because of its promising application in nanoelectronics. Herein, we investigate the electronic and transport properties of monolayer PG with typical small gas molecules, such as CO, CO2, NH3, NO and NO2, to explore the sensing capabilities of this monolayer by using first-principles and non-equilibrium Green's function (NEGF) calculations. The optimal position and mode of adsorbed molecules are determined, and the important role of charge transfer in adsorption stability and the influence of chemical bond formation on the electronic structure of the adsorption system are explored. It is demonstrated that monolayer PG is most preferred for the NOx (x = 1, 2) molecules with suitable adsorption strength and apparent charge transfer. Moreover, the current-voltage (I-V) curves of PG display a tremendous reduction of 88% (90%) in current after NO2 (NO) adsorption. The superior sensing performance of PG rivals or even surpasses that of other 2D materials such as graphene and phosphorene. Such ultrahigh sensitivity and selectivity to nitrogen oxides make PG a superior gas sensor that promises wide-ranging applications.

6.
Nanoscale ; 11(35): 16393-16405, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31436768

RESUMO

Polymeric carbon nitride (CN) is a promising metal-free catalyst plagued by a low intrinsic activity. Herein, a novel strategy based on controllable in situ surface engineering and morphology was developed to synergistically boost the catalytic activity of CN by tuning the hydroxyl groups on its surface and constructing a unique nanostructure. The controllable introduction of hydroxyl groups on CN nanoshells, prepared by the thermal condensation of oxygen-containing supramolecular precursors formed in water, led to spatial separation of the HOMO and LUMO, and effective exciton dissociation, as verified by experiments and ab initio calculations. Furthermore, the hollow hemispherical nanoshell endowed more exposed active sites, optimal mass transport, and dynamic modulations. The optimized hollow hemispherical CN nanoshells exhibited remarkable catalytic activity, with a photoelectrocatalytic OER overpotential of about 330 mV at a current density of 10 mA cm-2, outperforming state-of-the-art precious-metal catalyst IrO2. High activity for the visible-light photocatalytic HER and pollutant degradation were also observed. This study proposes that, through rational surface group modification, a polymer material with high catalytic activity can be practically realized, which is promising for the design of efficient metal-free catalysts.

7.
Nanoscale Res Lett ; 14(1): 233, 2019 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-31300919

RESUMO

One-dimensional (1D)/2D heterostructures have attracted great attention in electronic and optoelectronic fields because of their unique geometrical structures and rich physics. Here, we systematically explore electronic structure and optical performance of single-wall carbon nanotube (CNT)/phosphorene (BP) hybrids by large-scale density functional theory (DFT) computation. The results show that the interfacial interaction between CNT and BP is a weak van der Waals (vdW) force and correlates with tube diameter of CNTs. The CNT/BP hybrids have strong optical absorption compared with that of individual BP and CNT. A diameter-dependent type I or II heterojunction in CNT/BP hybrids is observed. Moreover, CNTs can not only significantly promote photogenerated carrier transfer, but also effectively improve the photocatalytic activities of BP as a co-catalyst. These findings would enrich our understanding of BP-based 1D/2D heterostructures, providing further insight into the design of highly efficient phosphorene-based or CNT-based nanophotocatalysts.

8.
Heliyon ; 5(3): e01442, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30976703

RESUMO

This paper gives the design of electromagnetically induced transparency effect using two U-shaped resonators with different opening directions (same direction and opposite direction). It is revealed that extremely similar transparency effect can be found for the two cases. The reason is that the two structures have the same sizes. However, the change in position of the two U-shaped resonators in the opposite opening has a significant effect on the transparent peak which is mainly reflected in the broadening of the broadband and the frequency shift of the working frequency, while there is almost no change in resonance performance for the same opening. We provide the field distributions for analyzing the causes of these different results. We believe these performance can guide future research.

9.
ACS Appl Mater Interfaces ; 11(19): 17341-17349, 2019 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-30964629

RESUMO

Unlike graphene, graphitic carbon nitride (CN) polymer contains a weak hydrogen bond and van der Waals (vdWs) interactions besides a strong covalent bond, which controls its final morphology and functionality. Herein, we propose a novel strategy, hydrogen-bond engineering, to tune hydrogen bonds in polymeric CN through nonmetal codoping. Incorporation of B and P dopants breaks partial hydrogen bonds within the layers and simultaneously weakens the vdWs interaction between neighboring layers, resulting in ultrathin codoped CN nanosheets. The two-dimensional structure of the ultrathin sheet, broken hydrogen bonds, and incorporated dopants endow them with efficient visible light harvesting, improved charge separation, and increased active edge sites that synergistically enhance the photocatalytic activity of doped CN. Specifically, the B/P-codoped CN exhibits an extremely high hydrogen-evolution rate of 10877.40 µmol h-1 g-1, much higher than most reported values of CN. This work demonstrates that hydrogen bond engineering is an effective strategy to modify the structure and properties of polymers for various applications.

10.
Nanoscale ; 11(14): 6876-6885, 2019 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-30912790

RESUMO

Structural defects can greatly inhibit electron transfer in two-dimensional (2D) layered polymeric carbon nitride (CN) unit, seriously lowering its utilization ratio of photogenerated charges during photocatalysis. Herein, we propose a new strategy based on intra-melon hydrogen bonding interactions in 2D CN frameworks to improve the crystallinity of CN. This concept was validated by removing some amino groups and connecting melon using codoped B and F atoms via a simple one-step sodium fluoroborate-assisted thermal treatment. The enhancement in crystallinity effectively promoted exciton dissociation and charge transfer in the CN nanosheets. Furthermore, the B/F dopants also improved the separation of photogenerated carriers by promoting charge capture. The highly efficient visible-light photocatalytic activity of the crystalline B/F-codoped CN nanosheets was demonstrated by degrading methyl orange, Rhodamine B, colorless phenol and tetracycline hydrochloride as models, where their degradation rate constant was more than 10, 5, 32 and 3 times higher than that of pure CN, respectively. Moreover, the B/F-codoped CN exhibited an excellent photoelectrocatalytic performance for the oxygen evolution reaction (OER), outperforming the precious-metal IrO2 catalyst. The simple and effective strategy proposed herein provides a direct route to engineer high crystallinity in 2D materials for tunable charge carrier separation and migration for electronic and optoelectronic applications.

11.
Nanoscale Res Lett ; 13(1): 294, 2018 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-30242559

RESUMO

We propose a planar metamaterial formed by four-strip metallic resonators, which can achieve high-Q Fano resonance in terahertz regime. This terahertz planar metamaterial supports a sharp Fano resonance at 0.81 THz with 25% transmission. The resonance bandwidth of the dip is 0.014 THz with the Q-factor of 58. The interference between the bright mode and dark mode leads to the Fano line shape. This sharp Fano profile is explained by the electromagnetic theory of Fano resonance. Moreover, multiple Fano resonances can be realized by adding more strips into the original structure. As an example, two Fano dips with Q-factors of 61 and 65 can be achieved via a five-strip structure.

12.
Nanoscale ; 10(30): 14667-14677, 2018 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-30039142

RESUMO

Silicene has shown great potential for applications as a versatile material in nanoelectronics and is particularly promising as a building block for spintronic applications. Unfortunately, despite its intriguing properties, such as a relatively large spin-orbit interaction, one of the greatest obstacles to the use of silicene as a host material in spintronics is its lack of magnetism or a topological phase transition owing to the silicene-substrate interaction, which influences its fundamental properties and has yet to be fully investigated. Here, we show that when silicene is grown on a CeO2 substrate, an appreciable robust magnetic moment appears in silicene covalently bonded to CeO2 (111), while a topological phase transition from a topological insulator to a band insulator occurs regardless of van der Waals (vdW) interactions or covalent bonding interactions at the interface. The induced magnetism of silicene is due to the breaking of Si-Si π-bonds, which also results in a trivial topological phase. The silicene-substrate interaction, and even weak vdW forces (equivalent to an electric field), can destroy the quantum spin Hall effect (QSHE) in silicene. We propose a viable strategy-the construction of an inverse symmetrical sandwich structure (protective layer/silicene/substrate)-to preserve the quantum spin Hall (QSH) state of silicene in a system with weak vdW interactions. This work takes a critical step towards the fundamental physics and realistic applications of silicene-based spintronic devices.

13.
Materials (Basel) ; 11(6)2018 Jun 06.
Artigo em Inglês | MEDLINE | ID: mdl-29882834

RESUMO

This paper presents a plasmon-induced transparency (PIT) using an easy-fabricating metamaterial composed of three pieces of metallic arc-rings on top of a dielectric substrate. The transmission of the transparent peak of 1.32 THz reaches approximately 93%. The utilization of the coupled Lorentzian oscillator model and the distribution of electromagnetic fields together explain the cause of the transparent peak. The simulation results further demonstrate that the bandwidth of the transmission peak can be narrowed by changing the sizes of the arc-rings. Moreover, an on/off effect based on the transparent peak is discussed by introducing photosensitive silicon into the air gaps of the suggested metamaterial structure.

14.
Nanoscale Res Lett ; 13(1): 137, 2018 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-29740712

RESUMO

Quad-band terahertz absorber with single-sized metamaterial design formed by a perforated rectangular resonator on a gold substrate with a dielectric gap in between is investigated. The designed metamaterial structure enables four absorption peaks, of which the first three peaks have large absorption coefficient while the last peak possesses a high Q (quality factor) value of 98.33. The underlying physical mechanisms of these peaks are explored; it is found that their near-field distributions are different. Moreover, the figure of merit (FOM) of the last absorption peak can reach 101.67, which is much higher than that of the first three absorption modes and even absorption bands of other works operated in the terahertz frequency. The designed device with multiple-band absorption and high FOM could provide numerous potential applications in terahertz technology-related fields.

15.
J Nanosci Nanotechnol ; 18(8): 5502-5510, 2018 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-29458603

RESUMO

Elimination of pollutants from water is one of the greatest challenges in resolving global environmental issues. Herein, we report a high-surface-area mesoporous g-C3N4 nanosheet with remarkable high adsorption capacity and photocatalytic performance, which is prepared through directly polycondensation of urea followed by a consecutive one-step thermal exfoliation strategy. This one-pot method to prepare mesoporous g-C3N4 nanosheet is facile and rapid in comparison with others. The superior adsorption capacity of the fabricated mesoporous g-C3N4 nanostructures is demonstrated by a model organic pollutant-methylene blue (MB), which is up to 72.2 mg/g, about 6 times as that of the largest value of various g-C3N4 adsorbents reported so far. Moreover, this kind of porous g-C3N4 nanosheet exhibits high photocatalytic activity to MB and phenol degradation. Particularly, the regenerated samples show excellent performance of pollutant removal after consecutive adsorption/degradation cycles. Therefore, this mesoporous g-C3N4 nanosheet may be an attractive robust metal-free material with great promise for organic pollutant elimination.

16.
Chemphyschem ; 19(3): 291-299, 2018 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-29178167

RESUMO

A high light-absorption coefficient and long-range hot-carrier transport of hybrid organic-inorganic perovskites give huge potential to their composites in solar energy conversion and environmental protection. Understanding interfacial interactions and their effects are paramount for designing perovskite-based heterostructures with desirable properties. Herein, we systematically investigated the interfacial interactions in monolayer and few-layer SnS/CH3 NH3 PbI3 heterostructures and their effects on the electronic and optical properties of these structures by density functional theory. It was found that the interfacial interactions in SnS/CH3 NH3 PbI3 heterostructures were van der Waals (vdW) interactions, and they were found to be insensitive to the layer number of 2D SnS sheets. Interestingly, although their band gap decreased upon increasing the layer number of SnS, the near-gap electronic states and optical absorption spectra of these heterostructures were found to be strikingly similar. This feature was determined to be critical for the design of 2D layered SnS-based heterostructures. Strong absorption in the ultraviolet and visible-light regions, type II staggered band alignment at the interface, and few-layer SnS as an active co-catalyst make 2D SnS/CH3 NH3 PbI3 heterostructures promising candidates for photocatalysis, photodetectors, and solar energy harvesting and conversion. These results provide first insight into the nature of interfacial interactions and are useful for designing hybrid organic-inorganic perovskite-based devices with novel properties.

17.
Phys Chem Chem Phys ; 19(11): 7955-7963, 2017 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-28262896

RESUMO

Understanding the interfacial interaction is of paramount importance for rationally designing carbon nanomaterial-based hybrids with optimal performance for electronics, optoelectronics, sensing, advanced energy conversion and storage. Here, we firstly reveal that both covalent and noncovalent interactions simultaneously exist in carbon nanotube (CNT)/Ag3PO4 hybrids by studying systematically the electronic and optical properties to elucidate the mechanism of their enhanced photocatalytic performance. Metallic CNT(9,0) may chemically or physically interact with the Ag3PO4(100) surface depending on its relative orientations, whereas semiconducting CNT(10,0) can only noncovalently functionalize Ag3PO4. The C-Ag bond in the covalently bonded hybrid and type-II, staggered, band alignment in noncovalent hybrids lead to a robust separation of photoexcited charge carriers between two constituents, thus enhancing the photocatalytic activity. The small band gap makes the CNT/Ag3PO4 hybrids absorb sunlight from the ultraviolet to infrared region. Moreover, CNTs are not only effective sensitizers, but also highly active co-catalysts in hybrids. The results can be rationalized by the available experiments, thereby partly resolving a debate on the interpretation of the experimental results, and paving the way for developing highly efficient carbon-based nanophotocatalysts.

18.
Nanoscale Res Lett ; 11(1): 495, 2016 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-27832524

RESUMO

The ability to strongly absorb light is central to solar energy conversion. We demonstrate here that the hybrid of monolayer ZrS2 and double-ring tubular B20 cluster exhibits dramatically enhanced light absorption in the entire visible spectrum. The unique near-gap electronic structure and large built-in potential at the interface will lead to the robust separation of photoexcited charge carriers in the hybrid. Interestingly, some Zr and S atoms, which are catalytically inert in isolated monolayer ZrS2, turn into catalytic active sites. The dramatically enhanced absorption in the entire visible light makes the ZrS2/B20 hybrid having great applications in photocatalysis or photodetection.

19.
Phys Chem Chem Phys ; 18(48): 33094-33102, 2016 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-27886313

RESUMO

Recent experiments have shown that the photocatalytic activity of g-C3N4 can be greatly enhanced by C60 modification, however, a fundamental understanding of its mechanistic operation is still lacking. Using first-principles calculations, the interfacial effects of C60/g-C3N4 nanocomposites on the electronic properties, charge transfer and optical response have been explored in detail. For different stacking patterns, the two constituents are always linked by van der Waals (vdW) forces without any exception, and form type-II heterojunctions in most cases. The valence band maximum and conduction band minimum of these heterostructures are dominated by the unsaturated nitrogen (N2) atoms and C60 molecule, respectively, which strongly interact with each other, resulting in strong charge transfer between the two involved constituents and an obvious bending of the g-C3N4 sheets. The unsaturated N2 atoms included in the interfaces have a significant influence on promoting the photocatalytic performance, while the existence of saturated nitrogen (N1 and N3) atoms lying in the interfaces will weaken the interfacial interactions between C60 molecules and the g-C3N4 monolayers. Moreover, the sensitive optical response and satisfactory type-II band alignment clearly show that the C60/g-C3N4 heterostructure is an outstanding photocatalyst for hydrogen production. We proposed a deep insight (the role of nitrogen) into understanding the improved photocatalytic ability of the C60/g-C3N4 nanocomposites, which may contribute to the rational design of both C60/g-C3N4 and g-C3N4-based nanocomposite photocatalysts.

20.
Dalton Trans ; 45(34): 13383-91, 2016 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-27483028

RESUMO

Atomically thin two-dimensional transition metal dichalcogenides (TMDCs) heterostructures have recently attracted growing interest due to their massive potential in solar energy applications due to their band gap in the visible spectral range and extremely strong light-matter interactions. Herein, heterostructures composed of WS2 and MoS2 monolayers, as representative TMDCs, with small fullerenes (B12 and C20) are investigated to explore their applications in solar energy conversion using first principles calculations based on density functional theory (DFT). The WS2 (MoS2) monolayer and fullerene form a van der Waals (vdW) heterostructure. Compared to pure monolayers, the heterostructures have a smaller band gap, which favours enhancing visible light absorption. The amount of charge transfer at the interface induced by vdW interactions depends on the type of fullerene. Most importantly, a type-II staggered band alignment is formed between WS2 (MoS2) and fullerene with the latter possessing the higher electron affinity which results in the robust separation of photoexcited charge carriers between them. These results indicate that the electronic properties and photoactivity of TMDCs monolayers can be tuned by non-covalent coupling with small fullerenes, thus meeting the needs of various applications.

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