Semiconductor-based photocatalysts have received extensive attention for their promising capacity in confronting global energy and environmental issues. In photocatalysis, a large band gap with ...suitable edge-position is necessary to warrant enough driving force for reaction, whereas a much smaller band gap is needed for visible-light response and high solar energy conversion efficiency. This paradox hinders the development of photocatalysts.
Via
state-of-the-art first-principles calculations, we find that the transition dipole moments (TDMs) are changed significantly in O-doped partly polymerized g-C
3
N
4
,
i.e.
, OH-terminated polymeric heptazine imide (PHI-OH), and concomitantly, an enhancement of visible-light absorption is achieved; meanwhile a large enough band gap can provide a powerful driving force in the photocatalytic watersplitting reaction. Furthermore, by using TDM analysis of the PHI-OH/BC
3
N heterostructure, direct light excited transition between two building layers can be confirmed, suggesting it as a candidate catalyst for hydrogen evolution. From TDM analysis of the PHI-OH/BCN heterostructure, we also verify a Z-scheme process, which involves simultaneous photoexcitations with strong reducibility and oxidizability. Thus, TDM could be a good referential descriptor for revealing photocatalytic mechanisms in semiconductor photocatalysts and interlayer photoexcitation behavior in layered heterostructures. Hopefully, more strategies
via
modification of TDMs would be proposed to enhance the visible-light response of a semiconductor without sacrificing its photocatalytic driving force.
Transition dipole moment is suggested as a bridge between band structure and optical absorption in semiconductor photocatalysts and as referential descriptor for interlayer photoexcitation in layered heterostructures.
Finding photocatalysts that fully utilize the visible solar light to split water into hydrogen and oxygen has been a challenging problem for a long time. In this regard, compared to traditional ...three-dimensional materials, graphene-like two-dimensional materials offer many advantages such as ultra-high surface area for photochemical reactions and minimal migration distance for carriers. Herein, using density functional theory (DFT), we examine the potential of a new series of two-dimensional boron chalcogenides, B2X3 (X = S, Se, Te) as candidates for such photocatalysts. We show that B2Se3 and B2Te3 possess the ideal energy levels for photon excitation for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Furthermore, a bilayer van der Waals heterostructure consisting of B2Te3/B2Se3 is found to have the greatest potential for two-step photo-excitation for water splitting reaction. Our results can stimulate the synthesis of new two dimensional materials for photocatalysis.
In order to improve the properties of AlCoCrFeNiNbx (x = 0, 0.1, and 0.5) high-entropy alloys (HEAs), the microstructure of the AlCoCrFeNiNbx is regulated by laser remelting (LR). By testing the ...microstructure and properties of alloys before and after LR treatment，the results indicate that the original AlCoCrFeNiNbx alloys have typical dendritic morphology, and the addition of the Nb element promoted the formation of Laves phase. The grains were significantly refined after LR treatment, and the dense remelting layers with thicknesses ranging from 1200 μm to 1650 μm were formed on the surface of the alloys. In addition, the hardness and wear resistance of the alloys were improved with the increase of Nb content and LR treatment due to the combined effect of fine grain strengthening, solid solution strengthening, and the second phase strengthening. At the same time, the corrosion resistance of the alloys before and after LR treatment in 3.5 wt% NaCl solution was significantly improved by the stable Nb2O5 passivation film for Nb0 and Nb1 alloys.
•LR treatment was conducted on the surface of as-cast AlCoCrFeNiNbx (x = 0.1,0.5 and 1) high entropy alloys.•AlCoCrFeNiNbx alloys have typical dendritic morphology, and the addition of the Nb element promoted the formation of Laves phase.•The grains were significantly refined after LR treatment, and the dense remelting layers with thicknesses ranging from 1200 μm to 1650 μm were formed on the surface of the alloys.•The hardness and wear resistance of the alloys were improved with the increase of Nb content and LR treatment due to the combined effect of fine grain strengthening, solid solution strengthening, and the second phase strengthening.•The corrosion resistance of the alloys before and after LR treatment in 3.5 wt% NaCl solution was significantly improved by the stable Nb2O5 passivation film for Nb0 and Nb1 alloys.
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GEOZS, IJS, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Atom‐by‐atom substitution is a promising strategy for designing new cluster‐based materials, which has been used to generate new gold‐ and silver‐containing clusters. Here, the first study ...focused on atom‐by‐atom substitution of Fe and Ni to the core of a well‐defined cobalt sulfide superatom Co
6
S
8
L
6
+
ligated with triethylphosphine (L = PEt
3
) to produce Co
5
MS
8
L
6
+
(M = Fe, Ni) is reported. Electrospray ionization mass spectrometry confirms the substitution of 1–6 Fe atoms with the single Fe‐substituted cluster being the dominant species. The Fe‐substituted clusters oxidize in solution to generate dicationic species. In contrast, only a single Ni‐substituted cluster is observed, which remains stable as a singly charged species. Collision‐induced dissociation experiments indicate the reduced stability of the Co
5
FeS
8
L
6
+
toward ligand loss in comparison with the unsubstituted and Ni‐substituted counterparts. Density functional theory calculations provide insights into the effect of metal atom substitution on the stability and electronic structures of the clusters. The results indicate that Fe and Ni have a different impact on the electronic structure, optical, and magnetic properties, as well as ligand‐core interaction of Co
6
S
8
L
6
. This study extends the atom‐by‐atom substitution strategy to the metal chalcogenide superatoms providing a direct path toward designing novel atomically precise core‐tailored superatoms.
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Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Finding photocatalysts that fully utilize the visible solar light to split water into hydrogen and oxygen has been a challenging problem for a long time. In this regard, compared to traditional ...three-dimensional materials, graphene-like two-dimensional materials offer many advantages such as ultra-high surface area for photochemical reactions and minimal migration distance for carriers. Herein, using density functional theory (DFT), we examine the potential of a new series of two-dimensional boron chalcogenides, B
2
X
3
(X = S, Se, Te) as candidates for such photocatalysts. We show that B
2
Se
3
and B
2
Te
3
possess the ideal energy levels for photon excitation for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Furthermore, a bilayer van der Waals heterostructure consisting of B
2
Te
3
/B
2
Se
3
is found to have the greatest potential for two-step photo-excitation for water splitting reaction. Our results can stimulate the synthesis of new two dimensional materials for photocatalysis.
Finding photocatalysts that fully utilize the visible solar light to split water into hydrogen and oxygen has been a challenging problem for a long time.
Finding photocatalysts that fully utilize the visible solar light to split water into hydrogen and oxygen has been a challenging problem for a long time. In this regard, compared to traditional ...three-dimensional materials, graphene-like two-dimensional materials offer many advantages such as ultra-high surface area for photochemical reactions and minimal migration distance for carriers. Herein, using density functional theory (DFT), we examine the potential of a new series of two-dimensional boron chalcogenides, B
X
(X = S, Se, Te) as candidates for such photocatalysts. We show that B
Se
and B
Te
possess the ideal energy levels for photon excitation for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Furthermore, a bilayer van der Waals heterostructure consisting of B
Te
/B
Se
is found to have the greatest potential for two-step photo-excitation for water splitting reaction. Our results can stimulate the synthesis of new two dimensional materials for photocatalysis.
High current pulsed electron beam (HCPEB) technology was applied to irradiate the surface of mono-crystalline Ge wafers (Ge (100) and Ge (111)) with different orientations, and the microstructure and ...properties of the irradiated surface were analyzed in detail. The results show that after HCPEB irradiation, numerous molten pits and local microcracks were produced on the surface of mono-crystalline Ge, and the pit density decreased with the increase of irradiation pulses. TEM observations indicated that after irradiation, the defects are mainly vacancy group defects and dislocation rings, and Ge nanocrystals with uniform size distribution are produced. HCPEB irradiation also formed self-assembled nanostructures on the surface of Ge. Cross section TEM indicated that the 250 nm deep defect channels were under the quantum dots, which confirms the formation mechanism of self-assembled nanostructures. The photoluminescence results indicated that the irradiated mono-crystalline Ge still has blue emission properties, and the luminescence mechanism is the quantum confinement effect of Ge nanocrystals embedded in slightly oxidized or nitrided amorphous structures.
•HCPEB irradiation can induce the proliferation of crystal defects and the formation of neatly arranged microcrack.•HCPEB irradiation induced numerous supersaturated vacancy defects in mono-crystalline Ge.•HCPEB irradiation induced the formation of nanocrystals on the Ge surface.•HCPEB irradiation induced the formation of self-assembled nanostructures on Ge surface.•After HCPEB irradiation, the blue light emission phenomenon of photoluminescence appeared in mono-crystalline Ge.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
