Visible-Light-Driven Selective Hydrogenation of Nitrostyrene over Layered Ternary Sulfide Nanostructures.

Selective hydrogenation of nitrostyrenes is a great challenge due to the competitive activation of the nitro groups (─NO2 ) and carbon-carbon (C═C) double bonds. Photocatalysis has emerged as an alternative to thermocatalysis for the selective hydrogenation reaction, bypassing the precious metal costs and harsh conditions. Herein, two crystalline phases of layered ternary sulfide Cu2 WS4 , that is, body-centered tetragonal I-Cu2 WS4 nanosheets and primitive tetragonal P-Cu2 WS4 nanoflowers, are controlled synthesized by adjusting the capping agents. Remarkably, these nanostructures show visible-light-driven photocatalytic performance for selective hydrogenation of 3-nitrostyrene under mild conditions. In detail, the I-Cu2 WS4 nanosheets show excellent conversion of 3-nitrostyrene (99.9%) and high selectivity for 3-vinylaniline (98.7%) with the assistance of Na2 S as a hole scavenger. They also can achieve good hydrogenation selectivity to 3-ethylnitrobenzene (88.5%) with conversion as high as 96.3% by using N2 H4 as a proton source. Mechanism studies reveal that the photogenerated electrons and in situ generated protons from water participate in the former hydrogenation pathway, while the latter requires the photogenerated holes and in situ generated reactive oxygen species to activate the N2 H4 to form cis-N2 H2 for further reduction. The present work expands the rational synthesis of ternary sulfide nanostructures and their potential application for solar-energy-driven organic transformations.

Accessible Tetrathiafulvalene Moieties in a 3D Covalent Organic Framework for Enhanced Near-Infrared Photo-Thermal Conversion and Photo-Electrical Response.

Redox-active tetrathiafulvalene (TTF)-based covalent organic frameworks (COFs) exhibit distinctive electrochemical and photoelectrical properties, but their prevalent two-dimensional (2D) structure with densely packed TTF moieties limits the accessibility of redox center and constrains their potential applications. To overcome this challenge, an 8-connected TTF linker (TTF-8CHO) is designed as a new building block for the construction of three-dimensional (3D) COFs. This approach led to the successful synthesis of a 3D COF with the bcu topology, designated as TTF-8CHO-COF. In comparison to its 2D counterpart employing a 4-connected TTF linker, the 3D COF design enhances access to redox sites, facilitating controlled oxidation by I2 or Au3+ to tune physical properties. When irradiated with a 0.7 W cm-2 808 nm laser, the oxidized 3D COF samples ( I X - ${\mathrm{I}}_{\mathrm{X}}^{-}$ @TTF-8CHO-COF and Au NPs@TTF-8CHO-COF) demonstrated rapid temperature increases of 239.3 and 146.1 °C, respectively, which surpassed those of pristine 3D COF (65.6 °C) and the 2D COF counterpart (6.4 °C increment after I2 treatment). Furthermore, the oxidation of the 3D COF heightened its photoelectrical responsiveness under 808 nm laser irradiation. This augmentation in photothermal and photoelectrical response can be attributed to the higher concentration of TTF·+ radicals generated through the oxidation of well-exposed TTF moieties.

Directly Imaging Dynamic Electronic Coupling during Electrochemical Oxidation of Single Silver Nanoparticles.

The electronic coupling between a metal electrode and single nano-entities is of unfading significance which impacts the heterogeneous electron transfer. Herein, we demonstrated a simple optical technique for directly imaging the transient interfacial electronic coupling events during electrochemical oxidation of single Ag nanoparticles on Au electrode. The electronic coupling brings out a dramatic dip behavior of bright field imaging traces, and is conductive to cross the energy barrier of oxidation for single silver nanoparticles. This dip behavior is further verified by in situ vis-transmission spectroscopy, and the heterogeneity of the Au-Ag electronic coupling down to single-nanoparticle level is uncovered by unifying the morphology and size of individual silver nanoparticles. These results suggest the interfacial electronic coupling facilitates electron transfer of single nanoparticles, and provide important insight into understanding detailed mechanism of nanoelectrochemistry.

Preparation of CdSy Se1- y -MoS2 Heterostructures via Cation Exchange of Pre-Epitaxially Synthesized Cu2- χ Sy Se1- y -MoS2 for Photocatalytic Hydrogen Evolution.

Construction of 2D transition metal dichalcogenide (TMD)-based epitaxial heterostructures with different compositions is important for various promising applications, including electronics, photonics, and catalysis. However, the rational design and controlled synthesis of such kind of heterostructures still remain challenge, especially for those consisting of layered TMDs and other non-layered materials. Here, a facile one-pot, wet-chemical method is reported to synthesize Cu2- χ Sy Se1- y -MoS2 heterostructures in which two types of different epitaxial configurations, i.e., vertical and lateral epitaxies, coexist. The chalcogen ratio (S/Se) in Cu2- χ Sy Se1- y and the loading amount of MoS2 in the heterostructures can be tuned. Impressively, the obtained Cu2- χ Sy Se1- y -MoS2 heterostructures can be transformed to CdSy Se1- y -MoS2 without morphological change via cation exchange. As a proof-of-concept application, the obtained CdSy Se1- y -MoS2 heterostructures with controllable compositions are used as photocatalysts, exhibiting distinctive catalytic activities toward the photocatalytic hydrogen evolution under visible light irradiation. The method paves the way for the synthesis of different TMD-based lateral epitaxial heterostructures with unique properties for various applications.

Simple Synthesis of Red Iridium(III) Complexes with Sulfur-Contained Four-Membered Ancillary Ligands for OLEDs.

Phosphorescent iridium(III) complexes have been widely researched for the fabrication of efficient organic light-emitting diodes (OLEDs). In this work, three red Ir(III) complexes named Ir-1, Ir-2, and Ir-3, with Ir-S-C-S four-membered framework rings, were synthesized efficiently at room temperature within 5 min using sulfur-containing ancillary ligands with electron-donating groups of 9,10-dihydro-9,9-dimethylacridine, phenoxazine, and phenothiazine, respectively. Due to the same main ligand of 4-(4-(trifluoromethyl)phenyl)quinazoline, all Ir(III) complexes showed similar photoluminescence emissions at 622, 619, and 622 nm with phosphorescence quantum yields of 35.4%, 50.4%, and 52.8%, respectively. OLEDs employing these complexes as emitters with the structure of ITO (indium tin oxide)/HAT-CN (dipyra-zino[2,3-f,2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile, 5 nm)/TAPC (4,4'-cyclohexylidenebis[N,N-bis-(4-methylphenyl)aniline], 40 nm)/TCTA (4,4″,4″-tris(carbazol-9-yl)triphenylamine, 10 nm)/Ir(III) complex (10 wt%): 2,6DCzPPy (2,6-bis-(3-(carbazol-9-yl)phenyl)pyridine, 10 nm)/TmPyPB (1,3,5-tri(mpyrid-3-yl-phenyl)benzene, 50 nm)/LiF (1 nm)/Al (100 nm) achieved good performance. In particular, the device based on complex Ir-3 with the phenothiazine unit showed the best performance with a maximum brightness of 22,480 cd m-2, a maximum current efficiency of 23.71 cd A-1, and a maximum external quantum efficiency of 18.1%. The research results suggest the Ir(III) complexes with a four-membered ring Ir-S-C-S backbone provide ideas for the rapid preparation of Ir(III) complexes for OLEDs.

Rational Synthesis of 1D Hyperbranched Heterostructures with Enhanced Optoelectronic Performance.

One-dimensional (1D) hyperbranched heterostructures (HBHSs) with abundant interfaces are rendered with various interfacial phenomena and functionalities. However, the rational synthesis of 1D HBHSs with desired spatial architecture and specific interface remains a great challenge. Here, we report a seeded growth method for controlled synthesis of two extraordinary types of HBHSs, in which high-intensity of CdS branches selectively grow on 1D nanowire (NW) trunks with different growth behaviors. The composition of the HBHSs can be further tuned by combining with cation exchange method, which enriches the variety of the HBHSs. The optoelectronic devices based on a single HBHS were fabricated and exhibit a better photoresponse performance compared with that of a single NW trunk. This advance provides a strategy for the controlled synthesis HBHSs with complex morphology and offers a platform for exploring their applications for photo harvesting and conversion.

Selective Epitaxial Growth of Oriented Hierarchical Metal-Organic Framework Heterostructures.

Metal-organic framework (MOF) heterostructures have shown promising applications in gas adsorption, gas separation, catalysis, and energy, arising from the synergistic effect of each component. However, owing to the difficulty in controlling the size, shape, nucleation, and growth of MOFs, it remains a great challenge to construct MOF heterostructures with precisely controlled orientation, morphology, dimensionality, and spatial distribution of each component. Here, we report a seeded epitaxial growth method to prepare a series of hierarchical MOF heterostructures by engineering the structures, sizes, dimensionalities, morphologies, and lattice parameters of both MOF seeds and the secondary MOFs. In these heterostructures, PCN-222 (also known as MOF-545) nanorods selectively grow along the major axis of the ellipsoid-like PCN-608 nanoparticles, on the two end facets of the hexagonal prism-like NU-1000 nanorods, and on the two basal planes of the hexagonal PCN-134 nanoplates, while Zr-BTB nanosheets selectively grow on the six edge facets of PCN-134 nanoplates. The selective epitaxial growth of MOFs opens the way to synthesize different hierarchical heterostructures with tunable architectures and dimensionalities, which could process various promising applications.

Ag@MoS2 Core-Shell Heterostructure as SERS Platform to Reveal the Hydrogen Evolution Active Sites of Single-Layer MoS2.

Understanding the reaction mechanism for the catalytic process is essential to the rational design and synthesis of highly efficient catalysts. MoS2 has been reported to be an efficient catalyst toward the electrochemical hydrogen evolution reaction (HER), but it still lacks direct experimental evidence to reveal the mechanism for MoS2-catalyzed electrochemical HER process at the atomic level. In this work, we develop a wet-chemical synthetic method to prepare the single-layer MoS2-coated polyhedral Ag core-shell heterostructure (Ag@MoS2) with tunable sizes as efficient catalysts for the electrochemical HER. The Ag@MoS2 core-shell heterostructures are used as ideal platforms for the real-time surface-enhanced Raman spectroscopy (SERS) study owing to the strong electromagnetic field generated in the plasmonic Ag core. The in situ SERS results provide solid Raman spectroscopic evidence proving the S-H bonding formation on the MoS2 surface during the HER process, suggesting that the S atom of MoS2 is the catalytic active site for the electrochemical HER. It paves the way on the design and synthesis of heterostructures for exploring their catalytic mechanism at atomic level based on the in situ SERS measurement.

Recent Advances in Ultrathin Two-Dimensional Nanomaterials.

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocatalysis, batteries, supercapacitors, solar cells, photocatalysis, and sensing platforms. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.

Edge Epitaxy of Two-Dimensional MoSe2 and MoS2 Nanosheets on One-Dimensional Nanowires.

Rational design and synthesis of heterostructures based on transition metal dichalcogenides (TMDs) have attracted increasing interests because of their promising applications in electronics, catalysis, etc. However, the construction of epitaxial heterostructures with an interface at the edges of TMD nanosheets (NSs) still remains a great challenge. Here, we report a strategy for controlled synthesis of a new type of heterostructure in which TMD NSs, including MoS2 and MoSe2, vertically grow along the longitudinal direction of one-dimensional (1D) Cu2-xS nanowires (NWs) in an epitaxial manner. The obtained Cu2-xS-TMD heterostructures with tunable loading amount and lateral size of TMD NSs are achieved by the consecutive growth of TMD NSs on Cu2-xS NWs through gradual injection of chalcogen precursors. After cation exchange of Cu in Cu2-xS-TMD heterostructures with Cd, the obtained CdS-MoS2 heterostructures retained their original architectures. Compared to the pure CdS NWs, the CdS-MoS2 heterostructures with 7.7 wt % loading of MoS2 NSs exhibit the best performance in the photocatalytic hydrogen evolution reaction with a H2 production rate up to 4647 µmol·h-1·g-1, about 58 times that catalyzed with pure CdS NWs. Our synthetic strategy opens up a new way for the controlled synthesis of TMD-based heterostructures, which could have various promising applications.

Anodized Aluminum Oxide Templated Synthesis of Metal-Organic Frameworks Used as Membrane Reactors.

The incorporation of metal-organic frameworks (MOFs) into membrane-shaped architectures is of great importance for practical applications. The currently synthesized MOF-based membranes show many disadvantages, such as poor compatibility, low dispersity, and instability, which severely limit their utility. Herein, we present a general, facile, and robust approach for the synthesis of MOF-based composite membranes through the in situ growth of MOF plates in the channels of anodized aluminum oxide (AAO) membranes. After being used as catalysis reactors, they exhibit high catalytic performance and stability in the Knoevenagel condensation reaction. The high catalytic performance might be attributed to the intrinsic structure of MOF-based composite membranes, which can remove the products from the reaction zone quickly, and prevent the aggregation and loss of catalysts during reaction and recycling process.

Preparation of Ultrathin Two-Dimensional Tix Ta1-x Sy Oz Nanosheets as Highly Efficient Photothermal Agents.

Although two-dimensional (2D) metal oxide/sulfide hybrid nanostructures have been synthesized, the facile preparation of ultrathin 2D nanosheets in high yield still remains a challenge. Herein, we report the first high-yield preparation of solution-processed ultrathin 2D metal oxide/sulfide hybrid nanosheets, that is, Tix Ta1-x Sy Oz (x=0.71, 0.49, and 0.30), from Tix Ta1-x S2 precursors. The nanosheet exhibits strong absorbance in the near-infrared region, giving a large extinction coefficient of 54.1 L g-1 cm-1 at 808 nm, and a high photothermal conversion efficiency of 39.2 %. After modification with lipoic acid-conjugated polyethylene glycol, the nanosheet is a suitable photothermal agent for treatment of cancer cells under 808 nm laser irradiation. This work provides a facile and general method for the preparation of 2D metal oxide/sulfide hybrid nanosheets.

In Situ Synthesis of Metal Sulfide Nanoparticles Based on 2D Metal-Organic Framework Nanosheets.

A facile in situ synthetic method is developed to synthesize metal sulfide nanoparticles based on 2D M-TCPP (M = Cu, Cd, or Co, TCPP = tetrakis(4-carboxyphenyl)porphyrin)) metal-organic framework nanosheets. The obtained CuS/Cu-TCPP composite nanosheet is used as the active material in photoelectrochemical cells, showing notably increased photocurrent due to the improved exciton separation and charge carrier transport.

Synthesis of 4H/fcc-Au@Metal Sulfide Core-Shell Nanoribbons.

Although great advances on the synthesis of Au-semiconductor heteronanostructures have been achieved, the crystal structure of Au components is limited to the common face-centered cubic (fcc) phase. Herein, we report the synthesis of 4H/fcc-Au@Ag2S core-shell nanoribbon (NRB) heterostructures from the 4H/fcc Au@Ag NRBs via the sulfurization of Ag. Remarkably, the obtained 4H/fcc-Au@Ag2S NRBs can be further converted to a novel class of 4H/fcc-Au@metal sulfide core-shell NRB heterostructures, referred to as 4H/fcc-Au@MS (M = Cd, Pb or Zn), through the cation exchange. We believe that these novel 4H/fcc-Au@metal sulfide NRB heteronanostructures may show some promising applications in catalysis, surface enhanced Raman scattering, solar cells, photothermal therapy, etc.

AuAg nanosheets assembled from ultrathin AuAg nanowires.

Assembly of noble metal nanocrystals into free-standing two-dimensional (2D) nanostructures with a regular shape is still a challenge. Here we report the preparation of a novel 2D AuAg nanosheet with length of 1.50 ± 0.30 µm, width of 510 ± 160 nm, and thickness of ∼100 nm via the assembly of ultrathin AuAg nanowires in the presence of the triblock copolymer Pluronic P123. The self-assembly of P123 and the fusion behavior of the nanowires during the assembly process are the key reasons for the formation of AuAg nanosheets in P123. Furthermore, the obtained AuAg nanosheet@P123 is used as the active material in a memory device that exhibits the write-once-read-many-times memory behavior.

One-pot synthesis of CdS nanocrystals hybridized with single-layer transition-metal dichalcogenide nanosheets for efficient photocatalytic hydrogen evolution.

Exploration of low-cost and earth-abundant photocatalysts for highly efficient solar photocatalytic water splitting is of great importance. Although transition-metal dichalcogenides (TMDs) showed outstanding performance as co-catalysts for the hydrogen evolution reaction (HER), designing TMD-hybridized photocatalysts with abundant active sites for the HER still remains challenge. Here, a facile one-pot wet-chemical method is developed to prepare MS2-CdS (M=W or Mo) nanohybrids. Surprisedly, in the obtained nanohybrids, single-layer MS2 nanosheets with lateral size of 4-10 nm selectively grow on the Cd-rich (0001) surface of wurtzite CdS nanocrystals. These MS2-CdS nanohybrids possess a large number of edge sites in the MS2 layers, which are active sites for the HER. The photocatalytic performances of WS2-CdS and MoS2-CdS nanohybrids towards the HER under visible light irradiation (>420 nm) are about 16 and 12 times that of pure CdS, respectively. Importantly, the MS2-CdS nanohybrids showed enhanced stability after a long-time test (16 h), and 70% of catalytic activity still remained.

Liquid-phase epitaxial growth of two-dimensional semiconductor hetero-nanostructures.

Although many two-dimensional (2D) hybrid nanostructures are being prepared, the engineering of epitaxial 2D semiconductor hetero-nanostructures in the liquid phase still remains a challenge. The preparation of 2D semiconductor hetero-nanostructures by epitaxial growth of metal sulfide nanocrystals, including CuS, ZnS and Ni3S2, is achieved on ultrathin TiS2 nanosheets by a simple electrochemical approach by using the TiS2 crystal and metal foils. Ultrathin CuS nanoplates that are 50-120 nm in size and have a triangular/hexagonal shape are epitaxially grown on TiS2 nanosheets with perfect epitaxial alignment. ZnS and Ni3S2 nanoplates can be also epitaxially grown on TiS2 nanosheets. As a proof-of-concept application, the obtained 2D CuS-TiS2 composite is used as the anode in a lithium ion battery, which exhibits a high capacity and excellent cycling stability.

Copper-based ternary and quaternary semiconductor nanoplates: templated synthesis, characterization, and photoelectrochemical properties.

Two-dimensional (2D) copper-based ternary and quaternary semiconductors are promising building blocks for the construction of efficient solution-processed photovoltaic devices at low cost. However, the facile synthesis of such 2D nanoplates with well-defined shape and uniform size remains a challenge. Reported herein is a universal template-mediated method for preparing copper-based ternary and quaternary chalcogenide nanoplates, that is, CuInS2, CuIn(x)Ga(1-x)S2, and Cu2ZnSnS4, by using a pre-synthesized CuS nanoplate as the starting template. The various synthesized nanoplates are monophasic with uniform thickness and lateral size. As a proof of concept, the Cu2ZnSnS4 nanoplates were immobilized on a Mo/glass substrate and used as semiconductor photoelectrode, thus showing stable photoelectrochemical response. The method is general and provides future opportunities for fabrication of cost-effective photovoltaic devices based on 2D semiconductors.

Two-dimensional CuSe nanosheets with microscale lateral size: synthesis and template-assisted phase transformation.

Semiconducting nanosheets with microscale lateral size are attractive building blocks for the fabrication of electronic and optoelectronic devices. The phase-controlled chemical synthesis of semiconducting nanosheets is of particular interest, because their intriguing properties are not only related to their size and shape, but also phase-dependent. Herein, a facile method for the synthesis of phase-pure, microsized, two-dimensional (2D) CuSe nanosheets with an average thickness of approximately 5 nm is demonstrated. These hexagonal-phased CuSe nanosheets were transformed into cubic-phased Cu(2-x)Se nanosheets with the same morphology simply by treatment with heat in the presence of Cu(I) cations. The phase transformation, proposed to be a template-assisted process, can be extended to other systems, such as CuS and Cu1.97 S nanoplates. Our study offers a new method for the phase-controlled preparation of 2D nanomaterials, which are not readily accessible by conventional wet-chemical methods.

A Multistate Thermoresponsive Smart Window Based on a Multifunctional Luminescent Solar Concentrator.

Conventional luminescent solar concentrators (LSCs) usually only have the ability to absorb solar energy and convert it to electricity but are not able to regulate the transmitted light. Herein, a multistate thermoresponsive smart window (SW) based on LSC has been fabricated, in which the stimuli-responsive host layer consists of polydimethylsiloxane (PDMS) and ethylene glycol solution (EGS) microdroplets stacking with LSC layer-based on near-infrared (NIR) CuInSe2-xSx/ZnS core/shell quantum dots (QDs) and PDMS matrix. As-synthesized CISSe/ZnS QDs with broad NIR absorption in LSC exhibit controllable emission spectra over 833-1088 nm and high photoluminescence (PL) quantum yield from 45 to 83%. Coupling with Si solar cells as a reference, optimized LSC-SW devices with dimensions of 5 × 5 × 0.9 cm3 exhibit higher power conversion efficiency (PCE) of 1.19-1.36% with increased temperature from 0 to 50 °C than those of sole LSC and SW devices. The corresponding visible light transmissions are regulated from 75.1 to 48.1% accordingly. The improvement of PCEs in an opaque state is mainly due to enhanced absorption of QDs originating from rescattered photons from the EGS/PDMS layer, leading to more emitted photons reaching photovoltaics. This work is expected to bring up new opportunities for applications in greenhouses, building facades, and energy-efficient smart windows.