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Our work indicates that the decoupling relationship and distinctive temperature dependence of thermoelectric parameters can be obtained by regulating molecular arrangements and electronic structures of charge-transfer salts.

The scarcity of two-dimensional (2D) magnetic nanostructures has hindered their applications in spintronics, which is attributed to that most magnetic materials exhibit non-van der Waals (nvdWs) structure and it is hard to reduce their thickness to 2D nanostructures. Thus it is eager to develop a promising strategy for free-standing 2D magnetic nvdWs nanostructures. We have achieved free-standing 2D nvdWs hexagonal FeSe with a thickness of 2.9 nm by the reaction between oleylamine-Se complex and Fe2+ with the assistance of Cl-, where the synergetic effects of Cl- and -NH2 lead to the anisotropic growth. Inspiringly, the 2D hexagonal FeSe exhibits intrinsic antiferromagnetic order rooted in Fe2+ and semiconductor nature. In addition, the temperature variation would result in the chemical environment changes of Fe2+, responsible for the temperature-dependent magnetic transitions. This work promotes the potential applications of 2D hexagonal FeSe and the preparation of other 2D nvdWs materials.

Interlayer interactions are proved to be essential in determining the accurate active site of metal–benzenehexathiol (M–BHT) for hydrogen evolution and Mo–BHT is predicted to be a new promising member of the family of highly active M–BHT catalysts.

Highly functionalized materials at the nanoscale on optical fibers offer notable opportunities to construct "lab-on-fiber" functional devices with unusual properties. However, it is extremely difficult to fabricate nanostructures with special morphology on a thin cylindrical optical fiber surface using the commonly used physical lithography techniques. Meanwhile, it is vital to maintain the plasmonic properties of Ag-riched particles while improving their stability. Herein, we design a facile strategy for the fabrication of Au-Ag bimetallic nanorings (Au-Ag NRs) immobilized on optical fibers for enhanced plasmonic properties. Ag NPs are first grownin situon an optical fiber surface through chelation and redox of polydopamine (PDA) to metal ions, and then are quickly converted into Au-Ag NRs by a galvanic replacement reaction and metal deposition. This conversion only takes 3.5 min, while the formed Au-Ag NRs exhibit outstanding localized surface plasmon resonance (LSPR) sensitivity (2204 nm per RIU) and oxidation resistance, and Au and Ag atoms are distributed uniformly in the nanorings. Furthermore, a novel and interesting formation process of the nanorings including deformation, spallation, growth in the gaps, and ring formation is studied. These findings provide a way to grow bimetallic nanorings on optical fibers, which are promising candidates for photoelectric "lab-on-fiber" devices. This work was supported by the Hainan Provincial Natural Science Foundation of China (No. 519QN179) and the National Natural Science Foundation of China (No. 21621004 and 51473115).

UiO-66(Ce)-encapsulated ruthenium nanoparticles (Ru@UiO-66(Ce)) was designed and used for dehydrogenation of primary amines to nitriles in water without any hydrogen acceptors and additives. Introduction of metal Ru to UiO-66(Ce) contributes to the formation of Lewis acid–base pairs on the catalyst owing to the metal–support interaction, acting as active sites for activation of amines and transfer of hydrogen. Ab initio calculation results further confirm the roles of Lewis acid–base pairs in the reaction.

We describe the design and modular synthesis of a library of substituted hexabenzoovalene derivatives (SHBO), along with the key precursor dinaphthopyrenes (3), highlighting the influence of a wide array of substituent variation on the photophysical properties via UV-vis absorption, fluorescence spectra and electrochemical methods. The results show that the cyclized hexabenzoovalenes present a stronger spectroscopic red-shift than the corresponding dinaphthopyrenes. X-ray diffraction analysis suggests that intermediate 3hx containing two nitro groups forms a trans-configuration with twisted structures. Our systematic investigation might provide a realistic design strategy to construct large one-dimensional and two-dimensional materials via bottom-up approaches.

Crystal phase engineering is a promising strategy to tune the catalytic performance of metal nanomaterials. Generally, the crystal phase effect on catalysis is ascribed to distinct surface atomic arrangements of catalysts with different crystal phases. Here we show that even for similar surfaces, such as the close-packed surfaces, different crystal phases have considerably different surface reactivities due to their distinct intrinsic surface strains. Using first-principles calculations, we find that the close-packed surfaces of hexagonal close-packed (HCP) and double HCP (4H) gold have significantly smaller intrinsic strains (∼1.3%) than those of face-centered cubic (FCC) gold (∼2.3%). These distinct intrinsic surface strains result in various oxygen adsorption energies and O2 dissociation barriers on these close-packed gold surfaces, and the dissociation of O2 on different crystal phases and surfaces follows the Bronsted–Evans–Polanyi principle.

Organic π-conjugated polymers (CPs) have been intensively explored for a variety of critical photocatalytic applications in the past few years. Nevertheless, CPs for efficient CO2 photoreduction have been rarely reported, which is mainly due to the lack of suitable polymers with sufficient solar light harvesting ability, appropriate energy level alignment and good activity and selectivity in multi-electron-transfer photoreduction of CO2 reaction. We report here the rational design and synthesis of two novel triphenylamine (TPA) based conjugated microporous polymers (CMPs), which can efficiently catalyze the reduction of CO2 to CO using water vapor as an electron donor under ambient conditions without adding any co-catalyst. Nearly 100% selectivity and a high CO production rate of 37.15 μmol h−1 g−1 are obtained for OXD-TPA, which is significantly better than that for BP-TPA (0.9 μmol h−1 g−1) as a result of co-monomer change from biphenyl to 2,5-diphenyl-1,3,4-oxadiazole. This difference could be mainly ascribed to the synergistic effect of a decreased optical band gap, improved interface charge transfer and increased CO2 uptake for OXD-TPA. This contribution is expected to spur further interest in the rational design of porous conjugated polymers for CO2 photoreduction. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

The description of surface-enhanced Raman scattering (SERS) as a molecular optomechanical process has provided new insights into the vibrational dynamics and nonlinearities of this inelastic scattering process. In earlier studies, molecular vibrations have typically been assumed to couple with a single plasmonic mode of a metallic nanostructure, ignoring the complexity of the plasmonic response in many configurations of practical interest such as in metallic nanojunctions. By describing the plasmonic fields as a continuum, we demonstrate here the importance of considering the full plasmonic response to properly address the molecule-cavity optomechanical interaction. We apply the continuum-field model to calculate the Raman signal from a single molecule in a plasmonic nanocavity formed by a nanoparticle-on-a-mirror configuration, and compare the results of optomechanical parameters, vibrational populations, and Stokes and anti-Stokes signals of the continuum-field model with those obtained from the single-mode model. Our results reveal that high-order non-radiative plasmonic modes significantly modify the optomechanical behavior under strong laser illumination. Moreover, Raman linewidths, lineshifts, vibrational populations, and parametric instabilities are found to be sensitive to the energy of the molecular vibrational modes. The implications of adopting the continuum-field model to describe the plasmonic cavity response in molecular optomechanics are relevant in many other nanoantenna and nanocavity configurations commonly used to enhance SERS., We acknowledge project Nr. 12004344 from the National Science Foundation of China, joint project Nr. 21961132023 from the NSFC-DPG, project PID2019-107432GB-I00 from the Spanish Ministry of Science and Innovation, project KK-2019/00101 from Eusko Jaurlaritza, project H2020-FET Open “THOR” Nr. 829067 from the European Commission, UK EPSRC EP/L027151/1, and grant IT1164-19 for consolidated groups of the Basque University, through the Department of Education, Research and Universities of the Basque Government.

In recent years, organic-based, especially carbonyl-based, Li-ion battery electrode materials have attracted great attention due to their low-cost, environmentally friendly nature and strong Li-ion bonding abilities. However, new research is required to further increase the electron mobility and cycling performance of organic materials. The performance of a high-carbonyl C6O6 molecule-functionalized graphene electrode for Li-ion batteries is investigated using the density functional theory. The binding energy calculations indicate that the C6O6 molecule is adsorbed on graphene via physisorption. C6O6@graphene maintains excellent electronic conductivity with 1 to 6 Li ions. By our statistical method, the reduced voltage of the C6O6@graphene cathode displays a voltage between 2.6 V and 1.5 V with 2 phases from 1 to 6 Li ions with energy density of approximately 155 mA h g−1. The results obtained reveal that C6O6@graphene is a promising electrode material for renewable Li-ion batteries.

Novel nitrogen-doped porous molybdenum carbide (α-MoC1−x and β-Mo2C) architectures were prepared using Mo-based metal–organic frameworks (MOFs) as the precursor. The synthesized molybdenum carbides consist of numerous nanocrystals organized into micro-sized rods with interpenetrating mesoporous-channels and macroporous-tunnels along the axial direction. When employed as the cathode catalyst for Li-O2 batteries, this dual pore configuration offers abundant active sites for the electrochemical reaction and many nucleation sites for the discharge product of Li2O2; hence, decent performances were obtained. Among the two synthesized molybdenum carbides, the α-MoC1−x electrode stands out as being better due to its lower charge transfer resistance (395.8 Ω compared to 627.9 Ω) and better O2 adsorption (binding energy of −1.87 eV of α-(111)-Mo compared to −0.72 eV of β-(101)-Mo). It delivered a high full discharge of 20 212 mA h g−1 with a discharge voltage of 2.62 V at 200 mA g−1. A good cycling stability was also obtained: i.e. 100 stable cycles with a fixed capacity of 1000 mA h g−1 (at a current density of 200 mA g−1) with a charging voltage of 4.24 V and maintaining a respectable round-trip efficiency of ∼70%. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore)

Shape-controlled polyhedral particles and their assembled structures have important applications in plasmonics and biosensing, but the interfacial configurations that will critically determine their resultant assembled structures are not well-understood. Hence, a reliable theory is desirable to predict the position and orientation of a polyhedron at the vicinity of a liquid/liquid interface. Here we demonstrate that the free energy change theory can quantitatively predict the position and orientation of an isolated octahedral nanoparticle at a liquid/liquid interface, whose vertices and facets can play crucial roles in biosensing. We focus on two limiting orientations of an octahedral nanoparticle, vertex up and facet up. Our proposed theory indicates that the surface wettability (hydrophilic/hydrophobic ratio) of the nanoparticle determines its most stable position and the preferred orientation at a water/oil interface. The surface wettability of an octahedron is adjusted from extremely hydrophobic to extremely hydrophilic by changing the amount of charge on the Ag surface in molecular dynamics (MD) simulations. The MD simulations results are in excellent agreement with our theoretical prediction for an Ag octahedral nanoparticle at a hexane/water interface. Our proposed theory bridges the gap between molecular-level simulations and equilibrium configurations of polyhedral nanoparticles in experiments, where insights from nanoparticle intrinsic wettability details can be used to predict macroscopic superlattice formation experimentally. This work advances our ability to precisely predict the final structures of the polyhedral nanoparticle assemblies at a liquid/liquid interface. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Photocatalytic solar energy conversion is a clean technology for producing renewable energy sources, but its efficiency is greatly hindered by the kinetically sluggish oxygen evolution reaction. Herein, confined defects in atomically-thin BiOCl nanosheets were created to serve as a remarkable platform to explore the relationship between defects and photocatalytic activity. Surface defects can be clearly observed on atomically-thin BiOCl nanosheets from scanning transmission electron microscopy images. Theoretical/experimental results suggest that defect engineering increased states of density and narrowed the band gap. With combined effects from defect induced shortened hole migratory paths and creation of coordination-unsaturated active atoms with dangling bonds, defect-rich BiOCl nanosheets displayed 3 and 8 times higher photocatalytic activity towards oxygen evolution compared with atomically-thin BiOCl nanosheets and bulk BiOCl, respectively. This successful application of defect engineering will pave a new pathway for improving photocatalytic oxygen evolution activity of other materials.

Label-free and real time far-field super-resolution imaging (hyperlensing) at the nanoscale is of significant interest where sub-λ imaging remains a constraint because of Abbe's diffraction limit. Though by utilizing anisotropic permittivities, metal-dielectric multilayers have been successful in reconstructing high-frequency components of sub-λ objects, yet they remain cumbersome and expensive to make. Most of the multilayer structures require multiple vacuum deposition cycles and are plagued by stringent requirements on the surface roughness of metallic layers. In contrast to the multilayer structure here we propose a 3D hyperbolic metamaterial model composed of metallic nanorods arranged in a sea-urchin geometry as a hyper-lensing device, which is capable of projecting and magnifying diffraction limited information into the far-field at Near-infrared (NIR) frequencies. The hyperlens generates a band of flat hyperbolic dispersions in spherical coordinates, which in turn supports the propagation of high wave-vector spatial harmonics leading to far-field super-resolution imaging. Using full-wave finite-difference time-domain (FDTD) simulations with diffraction limited trimer, quadrumer and ringed objects etched on thin perfect electric conductor (PEC) films, we show that the hyperlens model can achieve magnification factors of up to 10× in the far-field (∼4.5λ from the object's surface) under a light source with a wavelength of 1 μm, with successful resolution down to 220 nm (∼λ/5). The magnified image field distribution projected into the far-field is shown to follow the object under a reduction in the symmetry. These results are important for making progress in the realization of real-time biomolecular imaging systems, eliminating the need for near-field scanning, destructive electron microscopy and various image post-processing techniques.

In this work, we synthesized a series of core@shell Au2r@Agt nanoparticles (CS Au2r@Agt NPs) with defined but varied Au core diameter (2r) and Ag shell thickness (t) via overgrowth of Ag on preformed Au NPs at room temperature. We demonstrate that the surface enhanced Raman scattering (SERS) activity of as-prepared Au2r@Agt NPs is dependent on the Ag shell thickness (t). The critical t value (tc), above which Au2r@Agt NPs reach the maximal SERS activity, can be empirically correlated with the r values as tc = 0.301·r + 0.695 when the diameters of Au cores (2r) are smaller than 42 nm, the mean free path of bulk gold, while the tc is fixed at about 3 nm when 2r > 42 nm. The simple empirical rule should be very useful for the design of Au@Ag NPs for SERS applications, which is hardly discussed in the literature.

We developed a novel method for the real-time monitoring of the delicate change in refractive index (RI) when DNA or RNA hybridize near a DNA-capped silver nanocube (AgNC) surface. This method offers an alternative platform in the quantitative analysis of the trace lung cancer-associated miRNAs in label-free detection.

Direct evidence of plasmon-enhanced H2 generation is observed in photocatalytic water reduction by using TiO2 electrospun nanofibers co-decorated with Au and Pt nanoparticles through dual-beam irradiation. The Au/Pt/TiO2 nanofibers exhibit certain activity for H2 generation under single irradiation at 420 nm that excites the defect/impurity states of TiO2. Significantly, when secondary irradiation at 550 nm is introduced to simultaneously excite Au SPR, we observed 2.5 times higher activity for H2 generation. Further investigation by finely controlling the irradiation wavelengths reveals that the enhancement factor on the photocatalytic activity for H2 generation is directly correlated with the plasmon absorption band of the Au nanoparticles in the Au/Pt/TiO2 nanofibers. The control experiments with different sacrificial agents suggest that the hot plasmonic electrons of Au are responsible for the enhanced photocatalytic activity that can be magnified when TiO2 is simultaneously excited. Accepted version

Hot spots with a large electric field enhancement usually come in small volumes, limiting their applications in surface-enhanced spectroscopy. Using a finite-difference time-domain method, we demonstrate that spiky nanoparticle dimers (SNPD) can provide hot spots with both large electric field enhancement and large volumes because of the pronounced lightning rod effect of spiky nanoparticles. We find that the strongest electric fields lie in the gap region when SNPD is in a tip-to-tip (T-T) configuration. The enhancement of electric fields (|E|(2)/|E0|(2)) in T-T SNPD with a 2 nm gap can be as large as 1.21 × 10(6). And the hot spot volume in T-T SNPD is almost 7 times and 5 times larger than those in the spike dimer and sphere dimer with the same gap size of 2 nm, respectively. The hot spot volume in SNPD can be further improved by manipulating the arrangements of spiky nanoparticles, where crossed T-T SNPD provides the largest hot spot volume, which is 1.5 times that of T-T SNPD. Our results provide a strategy to obtain hot spots with both intense electric fields and large volume by adding a bulky core at one end of the spindly building block in dimers.

The morphologies/dimensions of Au nanostructures can be tailored by merely controlling the reduction degree of graphene oxide surface. Au nanoparticles, long Au nanowires, and semicircular-shaped Au nanoplates are in situ synthesized on slightly, moderately, and highly reduced graphene oxide films respectively, without the need of any templating agent.