Kinetic Controlled Chirality Transfer and Induction in 2D Hydrogen-Bonding Assemblies of Glycylglycine on Au(111).

Chirality transfer is of vital importance that dominates the structure and functionality of biological systems and living matters. External physical stimulations, e.g. polarized light and mechanical forces, can trigger the chirality symmetry breaking, leading to the appearance of the enantiomeric entities created from a chiral self-assembly of achiral molecule. Here, several 2D assemblies with different chirality, synthesized on Au(111) surface by using achiral building blocks - glycylglycine (digly), the simplest polypeptide are reported. By delicately tuning the kinetic factors, i.e., one-step slow/rapid deposition, or stepwise slow deposition with mild annealing, achiral square hydrogen-bond organic frameworks (HOF), homochiral rhombic HOF and racemic rectangular assembly are achieved, respectively. Chirality induction and related symmetry broken in assemblies are introduced by the handedness (H-bond configurations in principle) of the assembled motifs and then amplified to the entire assemblies via the interaction between motifs. The results show that the chirality transfer and induction of biological assemblies can be tuned by altering the kinetic factors instead of applying external forces, which may offer an in-depth understanding and practical approach to peptide chiral assembly on the surfaces and can further facilitate the design of desired complex biomolecular superstructures.

Growth of Mesoscale Ordered Two-Dimensional Hydrogen-Bond Organic Framework with the Observation of Flat Band.

Flat bands (FBs), presenting a strongly interacting quantum system, have drawn increasing interest recently. However, experimental growth and synthesis of FB materials have been challenging and have remained elusive for the ideal form of monolayer materials where the FB arises from destructive quantum interference as predicted in 2D lattice models. Here, we report surface growth of a self-assembled monolayer of 2D hydrogen-bond (H-bond) organic frameworks (HOFs) of 1,3,5-tris(4-hydroxyphenyl)benzene (THPB) on Au(111) substrate and the observation of FB. High-resolution scanning tunneling microscopy or spectroscopy shows mesoscale, highly ordered, and uniform THPB HOF domains, while angle-resolved photoemission spectroscopy highlights a FB over the whole Brillouin zone. Density-functional-theory calculations and analyses reveal that the observed topological FB arises from a hidden electronic breathing-kagome lattice without atomically breathing bonds. Our findings demonstrate that self-assembly of HOFs provides a viable approach for synthesis of 2D organic topological materials, paving the way to explore many-body quantum states of topological FBs.

Electronic Modulation of Hierarchical Spongy Nanosheets toward Efficient and Stable Water Electrolysis.

The energy conversion efficiency of water electrolysis is determined by the activity of selected catalysts. Ideal catalysts should possess not only porous architecture for high-density assembly of active sites but also a subtle electronic configuration for the optimized activity at each site. In this context, the development of stable porous hosting materials that allow the incorporation of various metal elements is highly desirable for both experimental optimization and theoretical comparison/prediction. Herein, MOF-derived spongy nanosheet arrays constructed by assembly of carbon encapsulated hetero-metal doped Ni2 P nanoparticles is presented as a superior bifunctional electrocatalyst for water splitting. This hierarchical structure can be stably retained when secondary metal dopants are introduced, providing a flexible platform for electronic modulation. The catalytic origin of activity enhancement via metal (Fe, Cr, and Mn) doping is deciphered through experimental and theoretical investigations. Combining the advantages in both morphological and electronic structures, the optimized catalyst NiMn-P exhibits remarkable activity in both hydrogen and oxygen evolution in the alkaline media, with an ultrasmall cell voltage of 1.49 V (at 10 mA cm-2 ) and high durability for at least 240 h.

TiO2 with exposed (001) facets/Bi4O5Br2 nanosheets heterojunction with enhanced photocatalytic for NO removal.

A TiO2 with exposed (001) facets/Bi4O5Br2 nanosheets heterojunction (TNS/BOB) was fabricated via a hydrothermal and electrostatic self-assembly method. The photocatalytic activity for NO removal was evaluated under simulated solar light irradiation. Through optimizing the content of TNS nanosheets, the photo-oxidative NO removal rate of 15% TNS/BOB was increased by up to 54.3%. This value is much higher than that of the individual components TNS (31.1%) and BOB (37.7%). Through capturing experiments and electron spin resonance (ESR) measurements, the main active species in the photocatalytic process were identified as ·[Formula: see text] and ·OH. Discrete Fourier transform computation results and ESR tests revealed that the photo-induced electrons in TNS should recombine with the holes in BOB, leading to effectively promoted charge separation at the TNS/BOB interface through the Z-type charge transfer. This work showed that with appropriate facet control and heterojunction design TiO2 can be used as an effective visible-light photocatalyst material.

Synergetic Effects of Pd0 Metal Nanoparticles and Pd2+ Ions on Enhanced Photocatalytic Activity of ZnWO4 Nanorods for Nitric Oxide Removal.

Doping and novel metallic nanoparticles loading on the photocatalyst are two effective means to enhance its photocatalytic activity. In our study, Pd0/Pd2+-co-modified ZnWO4 nanorods were fabricated by a two-step hydrothermal process and room-temperature reduction method. The performance of the as-prepared samples was evaluated through the photocatalytic nitric oxide (NOx) removal under simulated solar and visible-light irradiation. Pd0/Pd2+-co-modified ZnWO4 nanorods present a significantly enhanced photocatalytic activity for NOx removal compared with Pd0-loaded or Pd2+-doped ZnWO4 under simulated sunlight irradiation owing to a narrower band gap of Pd2+ doping compared with that of pure ZnWO4. The role of Pd0 nanoparticles is to act as an electron reservoir to restrain the recombination of e-/h+ pairs. According to the trapping measurements, the photoinduced holes and electrons play critical roles during the photocatalytic process. In addition, electron spin resonance (ESR) results further confirm that •O2- and •OH radicals are present and assist in the photocatalysis under simulated solar light irradiation. Stability test demonstrated that 1.5% Pd0/0.5% Pd2+-co-modified ZnWO4 nanorods as photocatalyst have high photocatalytic stability in NOx removal. This work proved that Pd0/Pd2+-co-modified ZnWO4 nanorods can be considered as an efficient photocatalyst for NOx removal.

Controlled Manipulation of Magic Number Gold-Fullerene Clusters Using Scanning Tunneling Microscopy.

We report controlled manipulation of magic number gold-fullerene clusters, (C60) m-(Au) n, on a Au(111) substrate at 110 K using scanning tunneling microscopy (STM). Each cluster consists of a two-dimensional gold island of nAu atoms confined by a frame of mC60 molecules. Using STM, C60 molecules are extracted from the molecular frame one at a time. The extraction is conducted by driving the STM tip into the cluster, leading to one of the molecules being squeezed out of the frame. Unlike at room temperature, the extracted molecules do not move away from the cluster because of the lack of thermal energy at 110 K; they are found to be attached to the outside of the frame. Reversible manipulation is also possible by pushing an extracted molecule back into the frame. This reversible manipulation is possible only for molecules from the edge of the cluster.

Bridge-bonded methylthiolate on Au(111) observed with the scanning tunneling microscope.

We report the discovery of bridge-bonded methylthiolate, SCH3, along the step edges of the Au(111) surface. Real-space imaging with a scanning tunnelling microscope reveals the presence of bridge-bonded SCH3 along both the [11[combining macron]0] and the [112[combining macron]] oriented step edges. The nearest neighbour distances of SCH3 along these steps are 2a and , respectively. The Au(111) terrace is covered with the usual CH3SAuSCH3 staples. The bridge-bonded alkanethiolate is expected to play a rather significant role in the formation of thiol-passivated Au nanoclusters because of the high fraction of atoms in similar low-coordination sites.

Achieving Molecular-Level Selective Detection of Volatile Organic Compounds through a Strong Coupling Effect of Ultrathin Nanosheets and Au Nanoparticles.

The high density of surface active sites, high efficiency of interfacial carrier transport, and molecular diffusion path determine the efficiency of the electrochemical sensors. The ultrathin structures have atomic-level thickness, carrier migration and heat diffusion are limited in the two-dimensional plane, resulting in excellent conductivity and high carrier concentration. A one-step chemical method is applied to synthesize defect-rich Au-SnO2 in an ultrathin nanosheet form (thickness of 2-3 nm). The strong interaction between Au and SnO2 via the Au-O-Sn bonding and the catalytic effect of Au can prolong the service life via decreasing the optimal operating temperature (55 °C) and promote the Au-SnO2 sensor to exclusively detect formaldehyde at the ppb level (300 ppb). The experimental findings along with theoretical study reveal that Au nanoparticles have a different effect on the competitive adsorption and chemical reaction over the surface of the Au-SnO2 with formaldehyde and other interfering VOC gases, such as methanol, ethanol, and acetone. This study provides mechanistic insights into the correlation between operating temperature and the performance of the Au-SnO2 chemiresistive sensor. This work allows the development of highly efficient and stable electrochemical sensors to detect VOC gases at room temperature in the future.

Mixed methyl- and propyl-thiolate monolayers on a Au(111) surface.

Mixed methyl- and propyl-thiolate self-assembled monolayers (SAMs) are prepared on a Au(111) surface by exposing the gold substrate to methyl-propyl-disulfide vapor at room temperature. Scanning tunneling microscopy imaging of such SAMs reveals a (3 × 4) phase consisting of CH3-S-Au-S-CH3, CH3-S-Au-S-(CH2)2CH3, and CH3-(CH2)2-S-Au-S-(CH2)2CH3. Partial desorption of methyl-thiolate occurs when samples are thermally annealed to 373 K, leading to the formation of a striped phase consisting of primarily CH3-(CH2)2-S-Au-S-(CH2)2CH3.

The striped phases of ethylthiolate monolayers on the Au(111) surface: a scanning tunneling microscopy study.

Striped phases of ethylthiolate monolayers, corresponding to surface coverage in between 0.2 ML and 0.27 ML, were studied using high-resolution scanning tunneling microscopy. Striped phases consist of rows of Au-adatom-diethythiolate (AAD) aligned along the [112] direction. In the perpendicular [110] direction, the AAD rows adjust their spacing according to the surface coverage. A (5√3 × âˆš3)-R30° striped phase with 0.27 ML thiolate and a (6√3 × âˆš3)-R30° striped phase with 0.23 ML thiolate, both with long-range order, are found. A localized (5 × âˆš3)-rect. phase is also found as a minority phase embedded in the 5√3 × âˆš3)-R30° phase. This (5 × âˆš3)-rect. phase can be constructed using di-Au-adatom-tri-thiolate species.

Reducing the vulnerability of network by inserting modular topologies.

In this paper, we present a strategy whose purpose is to reduce the vulnerability of a network via inserting modular topologies. The modular topologies are generated as WS small-world random network, which is relatively highly robust. Using betweenness and betweenness centrality as the vulnerability measurement, the strategy searches for remote nodes with low betweenness in the network and sets these nodes to be connected to the modular topologies. We test our strategy on some basis networks and the results show sufficient availability of our strategy. And by comparing with other methods of adding topologies into the network, we show that our strategy is especially efficient in reducing the vulnerability of the critical network components.

The expression and function of long noncoding RNAs in hepatocellular carcinoma.

With the deepening of the genome project study, attention on noncoding RNAs is increasing. Long noncoding RNAs (lncRNAs) have become a new research hotspot. A growing number of studies have revealed that lncRNAs are involved in tumorigenesis and tumor suppressor pathways. Aberrant expressions of lncRNAs have been found in a variety of human tumors including hepatocellular carcinoma (HCC). In this review, we provide a brief introduction to lncRNA and highlight recent research on the functions and clinical significance of lncRNAs in HCC.

Adsorption and electron-induced dissociation of ethanethiol on Au(111).

Dissociation of ethanethiol and the formation of Au-adatom-diethylthiolate rows on the Au(111) surface were investigated using scanning tunneling microscopy (STM) at low temperature. Ethanethiol molecules physisorb on Au(111) at 120 K by sequentially occupation of the elbow site, the fcc domain before covering the whole surface with a semiliquid layer without long-range order. Scanning the physisorbed layer with a sample bias higher than +1.2 V leads to dissociation via cleaving the H-S bond. One of the dissociation products, ethylthiolate, forms a double-row structure with the rows aligned in one of the [112(-)] directions. These double rows arise from the Au-adatom-dithiolate species: CH(3)CH(2)S-Au-SCH(2)CH(3).

Complex supramolecular tessellations with on-surface self-synthesized C60 tiles through van der Waals interaction.

Supramolecular tessellation with self-synthesized (C60)7 tiles is achieved based on a cooperative interaction between co-adsorbed C60 and octanethiol (OT) molecules. Tile synthesis and tiling take place simultaneously on a gold substrate leading to a two-dimensional lattice of (C60)7 tiles with OT as the binder molecule filling the gaps between the tiles. This supramolecular tessellation is featured with simultaneous on-site synthesis of tiles and self-organized tiling. In the absence of specific functional groups, the key to ordered tiling for the C60/OT system is the collective van der Waals (vdW) interaction among a large number of molecules. This bicomponent system herein offers a way for the artificial synthesis of 2D complex vdW supramolecular tessellations.

Bi selectively doped SrTiO3-x nanosheets enhance photocatalytic CO2 reduction under visible light.

Converting CO2 into chemical energy by using solar energy is an environmental strategy to achieve carbon neutrality. In this paper, two dimensionality (2D) SrTiO3-x nanosheets with oxygen vacancies were synthesized successfully. Oxygen vacancies will generate defect levels in the band structure of SrTiO3-x. So, SrTiO3-x nanosheets have good photocatalytic CO2 reduction performance under visible light. In order to further improve its photocatalytic efficiency, Bi was used to dope Sr site and Ti site in SrTiO3-x nanosheets respectively. It is found that Sr site is the adsorption site of CO2 molecules. When Bi replaced Sr, CO2 adsorption on the surface of SrTiO3-x nanosheets was weakened. When Bi replaced Ti, there has no effect on CO2 adsorption. Due to the synergistic effect of Bi doping, oxygen vacancies, and Sr active site, the 1.0% Bi-doped Ti site in SrTiO3-x (1.0% Bi-Ti-STO) had the best photocatalytic performance under visible light (λ ≥ 420 nm). CO and CH4 yields were 5.58 umol/g/h and 0.36 umol/g/h. Photocatalytic CO2 reduction path has always been the focus of exploration. The in-situ FTIR spectrum proved the step of photocatalytic CO2 reduction and COO- and COOH are important intermediates in the photocatalytic CO2 reaction.

Anchoring Platinum Clusters onto Oxygen Vacancy-Modified In2O3 for Ultraefficient, Low-Temperature, Highly Sensitive, and Stable Detection of Formaldehyde.

To avoid carcinogenicity, formaldehyde gas, currently being only detected at higher operating temperatures, should be selectively detected in time with ppb concentration sensitivity in a room-temperature indoor environment. This is achieved in this work through introducing oxygen vacancies and Pt clusters on the surface of In2O3 to reduce the optimal operating temperature from 120 to 40 °C. Previous studies have shown that only water participates in the competitive adsorption on the sensor surface. Here, we experimentally confirm that the adsorbed water on the fabricated sensor surface is consumed via a chemical reaction due to the strong interaction between the oxygen vacancies and Pt clusters. Therefore, the long-term stability of formaldehyde gas detection is improved. The results of theoretical calculations in this work reveal that the excellent formaldehyde gas detection of Pt/In2O3-x originates from the electron enrichment due to the surface oxygen vacancies and the molecular adsorption and activation ability of Pt clusters on the surface. The developed Pt/In2O3-x sensor has potential use in the ultraefficient, low-temperature, highly sensitive, and stable detection of indoor formaldehyde at an operating temperature as low as room temperature.

A Fullerene-Platinum Complex for Direct Functional Patterning of Single Metal Atom-Embedded Carbon Nanostructures.

The development of patterning materials ("resists") at the nanoscale involves two distinct trends: one is toward high sensitivity and resolution for miniaturization, the other aims at functionalization of the resists to realize bottom-up construction of distinct nanoarchitectures. Patterning of carbon nanostructures, a seemingly ideal application for organic functional resists, has been highly reliant on complicated pattern transfer processes because of a lack of patternable precursors. Herein, we present a fullerene-metal coordination complex as a fabrication material for direct functional patterning of sub-10 nm metal-containing carbon structures. The attachment of one platinum atom per fullerene molecule not only leads to significant improvement of sensitivity and resolution but also enables stable atomic dispersion of the platinum ions within the carbon matrix, which may gain fundamentally new interest in functional patterning of hierarchical carbon nanostructures.

Electronic modulation of oxygen evolution on metal doped NiFe layered double hydroxides.

The bottleneck of electrochemical water splitting is the sluggish kinetics of oxygen evolution reaction (OER). Layered double hydroxides (LDHs) have been proposed as active and affordable electrocatalysts in OER. It has been reported that the activity of LDHs can be effectively tuned by doping of other metals. Despite previous experimental synthesis and improved catalytic performance, the in-depth OER mechanism on metal doped LDHs remains ambiguous. In the present work, transition metals (Cr, Mn and Co) doped NiFe LDHs were designed to investigate the doping effect in OER by both experimental analysis and density functional theory calculations. Based on experimental results, the intrinsic OER activity is Cr-NiFe LDHs > Co-NiFe LDHs > Mn-NiFe LDHs > NiFe LDHs, while the enhanced catalytic performance upon doping can be attributed to the interface effect, which results in the tuning of the binding energies of the intermediate states in OER.

Computational Search for Better Thermoelectric Performance in Nickel-Based Half-Heusler Compounds.

Half-Heusler alloys have recently received extensive attention because of their promising thermoelectric (TE) properties and great potential for applications requiring efficient thermoelectricity. Although the conversion efficiency of these materials can be greatly improved by doping, it is still far away from the real-life applications. Therefore, search for better parent TE compounds is deemed urgent. Using a high-throughput search method based on first-principles calculations in newly proposed 378 half-Heusler alloys, we identify nine nickel-based half-Heusler semiconductors as candidates and systematically study their mechanical, electronic, and transport properties. Their mechanical and dynamical stabilities are verified based on the calculated elastic constants and phonon spectra. The electronic structure calculations indicate the existence of direct energy gaps in the NiVZ (Z = Al, Ga, and In) and indirect energy gaps in the NiTiZ (Z = Si, Ge, and Sn) and NiScZ (Z = P, As, and Sb) compounds. Among them, NiVAl, NiVGa, and NiVIn exhibit a sharp slope of density of states near the Fermi level, which is predicted to be essential for a high TE performance. Further investigation on carrier concentration and temperature dependence of TE properties shows the high power factors of NiVAl, NiVGa, and NiVIn, which are responsible for their high figure of merit values. The highest maximum power factor of 5.152 mW m-1 K-2 and figure of merit of 0.309 are predicted for pristine half-Heusler NiVIn, which are larger than the values of some known pristine and doped half-Heusler TE materials. Our work opens up new avenues for rationally searching better TE materials among half-Heusler alloys for applications in fields requiring efficient thermoelectricity.

In Situ Observation of Stepwise C-H Bond Scission: Deciphering the Catalytic Selectivity of Ethylbenzene-to-Styrene Conversion on TiO2.

The conversion of light alkanes to olefins is crucial to the chemical industry. The quest for improved catalytic performance for this conversion is motivated by current drawbacks including: expensive noble metal catalysts, poor conversion, low selectivity, and fast decay of efficiency. The in situ visualization of complex catalysis at the atomic level is therefore a major advance in the rational framework upon building the future catalysts. Herein, the catalytic C-H bond activations of ethylbenzene on TiO2(110)-(1 × 1) were explored with high-resolution scanning tunneling microscopy and first-principles calculations. We report that the first C-H bond scission is a two-step process that can be triggered by either heat or ultraviolet light at 80 K, with near 100% selectivity of ß-CH bond cleavage. This work provides fundamental understanding of C-H bonds cleavage of ethylbenzene on metal oxides, and it may promote the design of new catalysts for selective styrene production under mild conditions.