Interlayer interactions perturb the electronic structure of two-dimensional materials and lead to new physical phenomena, such as van Hove singularities and Hofstadter's butterfly pattern. Silicene, the recently discovered two-dimensional form of silicon, is quite unique, in that silicon atoms adopt competing sp2 and sp3 hybridization states leading to a low-buckled structure promising relatively strong interlayer interaction. In multilayer silicene, the stacking order provides an important yet rarely explored degree of freedom for tuning its electronic structures through manipulating interlayer coupling. Here, we report the emergence of van Hove singularities in the multilayer silicene created by an interlayer rotation. We demonstrate that even a large-angle rotation (>20°) between stacked silicene layers can generate a Moiré pattern and van Hove singularities due to the strong interlayer coupling in multilayer silicene. Our study suggests an intriguing method for expanding the tunability of the electronic structure for electronic applications in this two-dimensional material.
Abstract Both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are crucial to water splitting, but require alternative active sites. Now, a general π‐electron‐assisted strategy to anchor single‐atom sites (M=Ir, Pt, Ru, Pd, Fe, Ni) on a heterogeneous support is reported. The M atoms can simultaneously anchor on two distinct domains of the hybrid support, four‐fold N/C atoms (M@NC), and centers of Co octahedra (M@Co), which are expected to serve as bifunctional electrocatalysts towards the HER and the OER. The Ir catalyst exhibits the best water‐splitting performance, showing a low applied potential of 1.603 V to achieve 10 mA cm −2 in 1.0 m KOH solution with cycling over 5 h. DFT calculations indicate that the Ir@Co (Ir) sites can accelerate the OER, while the Ir@NC 3 sites are responsible for the enhanced HER, clarifying the unprecedented performance of this bifunctional catalyst towards full water splitting.
The technology integrating adsorption and photocatalysis is regarded as the most promising strategy for the elimination of low concentration antibiotic contaminant. In this study, we firstly prepared the mesoporous g-C3N4 nanosheets (CN) with the thickness of 4–5 nm by the thermal etching and ultrasonic techniques. Then perovskite ErFeO3 nanoparticles (EF) were incorporated into CN to construct the 3/g-C3N4 (EFC) heterojunction. The heterojunction with EF content of 2 wt% (2-EFC) had the optimal adsorption and photocatalytic performance. 87.8% of ciprofloxacin (CIP) was eliminated via the adsorption–photocatalysis synergistic process over 2-EFC. The CIP adsorption capability of 2-EFC was 11.7 times that of CN, and the zero-order degradation reaction rate constant (k0) was 25.2 times of CN. The ultrathin and porous structure of CN increased the specific surface area and reaction active sites, shorten the diffusion distance of photoinduced charge carriers. And the construction of EFC heterojunction further accelerated the separation of charge carriers and inhibited its recombination. These two strategies ameliorated the adsorption and photocatalytic activity of EFC in removal of CIP. The CIP adsorption on the samples followed pseudo second order kinetics model, and the adsorption isotherm data complied with Langmuir isotherm model. The photocatalytic degradation process of CIP on 2-EFC could be divided into two phases. Due to the CIP concentration change in the degradation solution, the kinetics curve followed the zero order rate equation at 0 to 40 min. After that, it deferred to the first order rate equation. The h+, ⋅ OH and ⋅ O2– were involved in the photocatalytic degradation process. The structures of degradation intermediates and possible degradation pathways of CIP were proposed according to the HPLC-MS results. This research provided an alternative with high efficient synergetic effect of adsorption and photocatalytic degradation for the treatment of antibiotic wastewater.
Abstract Zero‐dimensional (0D) hybrid manganese halides have gained wide attention for the various crystal structures, excellent optical performance and scintillation properties compared with 3D lead halide perovskite nanocrystals. In this work, a new family of 0D hybrid manganese halides of A 2 MnBr 4 (A = BzTPP, Br‐BzTPP, and F‐BzTPP) based on discrete [MnBr 4 ] 2− tetrahedral units is reported as highly efficient lead‐free scintillators. Excited by UV or blue light, these hybrids emit bright green light originating from the d – d transition of Mn 2+ with near‐unity PLQY (99.5%). Significantly, high PLQY and low self‐absorption render extraordinary radioluminescence properties with the highest light yield of 80,100 photons MeV −1 , which reached the climax of present hybrid manganese halides and surpassed most commercial scintillators. The radioluminescence intensity features a linear response to X‐ray doses with a detection limit of 30 nGy air s −1 , far lower than the requirement of medical diagnostic (5.5 µGy air s −1 ). X‐ray imaging demonstrates ultrahigh spatial resolution of 14.06 lp mm −1 and short afterglow of 0.3 ms showcasing promising application prospects in radiography. Overall, we demonstrated new hybrid manganese halides as promising scintillators for advanced applications in X‐ray imaging with multiple superiorities of nontoxicity, facile‐assembly process, high irradiation light yield, excellent resolution, and stability.
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