Blue phosphorus, a previously unknown phase of phosphorus, has been recently predicted by theoretical calculations and shares its layered structure and high stability with black phosphorus, a rapidly rising two-dimensional material. Here, we report a molecular beam epitaxial growth of single layer blue phosphorus on Au(111) by using black phosphorus as precursor, through the combination of in situ low temperature scanning tunneling microscopy and density functional theory calculation. The structure of the as-grown single layer blue phosphorus on Au(111) is explained with a (4 × 4) blue phosphorus unit cell coinciding with a (5 × 5) Au(111) unit cell, and this is verified by the theoretical calculations. The electronic bandgap of single layer blue phosphorus on Au(111) is determined to be 1.10 eV by scanning tunneling spectroscopy measurement. The realization of epitaxial growth of large-scale and high quality atomic-layered blue phosphorus can enable the rapid development of novel electronic and optoelectronic devices based on this emerging two-dimensional material.

This paper compares the kinetics of exchanges of phenylethanethiolate ligands (PhC2S-) of the monolayer-protected clusters (MPCs) Au(38)(SC2Ph)(24) and Au(140)(SC2Ph)(53) with p-substituted arylthiols (p-X-PhSH), where X = NO(2), Br, CH(3), OCH(3), and OH. First-order rate constants at 293 K for exchange of the first ca. 25% of the ligands on the molecule-like Au(38)(SC2Ph)(24) MPC, measured using (1)H NMR, vary linearly with the in-coming arythiol concentration; ligand exchange is an overall second-order reaction. Remarkably, the second-order rate constants for ligand exchange on Au(38)(SC2Ph)(24) are very close to those of corresponding exchange reactions on the larger nanoparticle Au(140)(SC2Ph)(53) MPCs. These are the first results that quantitatively show that the chemical reactivity of different sized nanocrystals is almost independent of size; presumably, this is because the locus of the initial ligand exchanges is a common kind of site, thought to be the nanocrystal vertexes. The rates of later stages of exchange (beyond ca. 25%) differ for Au(38) and Au(140) cores, the latter being much slower presumably due to its larger terrace-like surface atom content. The reverse exchange reaction was studied for Au(38)(p-X-arylthiolate)(24) MPCs (X = NO(2), Br, and CH(3)), where the in-coming ligand is now phenylethanethiol. Remarkably, the rate constants of both forward and reverse exchanges display identical substituent effects, which implies a concurrent bonding of both in-coming and leaving ligands to the Au core in the rate-determining step, as in an associative mechanism. X = NO(2) gives the fastest rates, and the ratio of forward and reverse rate constants gives an equilibrium constant of K(EQ,PE) = 4.0 that is independent of X.

The near-infrared photoluminescence of monolayer-protected Au38 and Au140 clusters (MPCs) is intensified with exchange of nonpolar ligands by more polar thiolate ligands. The effect is general and includes as more polar in-coming ligands: thiophenolates with a variety of p-substituents; alkanethiolates omega-terminated by alcohol, acid, or quaternary ammonium groups; and thio-amino acids. Remarkably, place exchanges of the initial phenylethanethiolates on Au38 MPCs by p-substituted thiophenolates and thio-amino acids and of hexanethiolates on Au140 MPCs by omega-quaternary ammonium terminated undecylthiolates result in increases in the near-infrared (NIR) luminescence intensities that are linear with the number of new polar ligands. The increased intensities are systematically larger for thiophenolate ligands having more electron-withdrawing substituents. Analogous effects on intensities are observed in the NIR emission of Au140 MPCs upon place exchange of alkanethiolates with thiolates having short connecting alkanethiolate chains to quaternary ammonium and to omega-carboxylic acid termini, and with oxidative charging of the Au cores. The observations are consistent with sensitivity of the luminescence mechanism to any factor that enhances the electronic polarization of the bonds between the Au core atoms and their thiolate ligands. The luminescence is discussed in terms of a surface electronic excitation, as opposed to a core volume excitation.

This paper describes the reaction of the phosphine-protected Au nanoparticle Au(55)(PPh(3))(12)Cl(6) (1, "Au55") with hexanethiol (2) and other thiols. The voltammetry of the reaction product 2 displays a well-defined pattern of peaks qualitatively reminiscent of Au(38) nanoparticles, but with quite different spacing (0.74 +/- 0.01 V) between the potentials of initial oxidation and reduction steps (electrochemical gap). Correction of this "molecule-like" gap for charging energy indicates a HOMO-LUMO gap energy of about 0.47 V. Voltammetry of the products (3 and 4) of reaction of 1 with C(3)H(7)SH and PhC(2)H(4)SH, respectively, is similar. Laser desorption/ionization mass spectrometry (LDI-MS) shows that 2 contains a high proportion of a core mass in the 14-15 kDa range, which is proposed to be Au(75). UV-vis spectra of 2-4 are relatively featureless, similar to previous reports of thiolate-protected Au(75) nanoparticles. HPLC analysis of 2 shows a Au(75) content of ca. 73%; the electrochemical purity estimate is also high, about 55%. Combining the mass spectrometric result with thermogravimetric analysis of 2 leads to a preliminary formulation Au(75)(SC(6)H(13))(40). This Au(75) synthesis complements a previous Brust-type synthesis and is unusual in the apparent provocation in the reaction of an increase in core size.

A molecule-like substituent effect on redox formal potentials in the nanoparticle series Au(38)(SPhX)(24) has been discovered. Electron-withdrawing "X" substituents energetically favor reduction and disfavor oxidation, and give formal potentials that correlate with Hammett substituent constants. The ligand monolayer of the nanoparticles is shown, thereby, to play a strong role in determining electronic energies of the nanoparticle core and is more than simply a protecting or capping layer. The substituent effect does not, however, detectably change the HOMO-LUMO gap energy, being identical for the HOMO and LUMO levels and presumably inductive in nature.

Among the multiple components of propolis, flavonoids contribute greatly to the antioxidant activities of propolis. Flavonoids mainly exist in the form of sugar-conjugated derivatives. Quercetin glycosides represent the predominant flavonoid fraction in propolis. In this work, density functional theory (DFT) calculations were applied to analyze the antioxidative properties of quercetin and its glucosides in the gas and in the liquid phase (ethanol, water). Three main antioxidant mechanisms, hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) were used to analyze the antioxidative capacity of the investigated compounds. Solvent effects dominantly affect SET-PT and SPLET. Thus, the thermodynamically preferred mechanism can be altered. HAT and SPLET are the thermodynamically dominant mechanisms in gas and solvent phases, respectively. Therefore, in the gas phase, the sequence of the antioxidative capacity is similar with the bond dissociation enthalpy values: quercetin > quercetin-5-O-glucoside > quercetin-7-O-glucoside > quercetin-3-O-glucoside > quercetin-3′-O-glucoside > quercetin-4′-O-glucoside. While, in the solvent phases, the sequence is similar with the proton affinity values: quercetin-4′-O-glucoside > quercetin-5-O-glucoside > quercetin > quercetin-3-O-glucoside > quercetin-7-O-glucoside > quercetin-3′-O-glucoside. OH groups in B-ring and C-ring contribute mainly to the antioxidative activities of quercetin and glucosides compared with A-ring.

Black phosphorus (BP) shows great potential in electronic and optoelectronic devices owing to its semiconducting properties, such as thickness-dependent direct bandgap and ambipolar transport characteristics. However, the poor stability of BP in air seriously limits its practical applications. To develop effective schemes to protect BP, it is crucial to reveal the degradation mechanism under various environments. To date, it is generally accepted that BP degrades in air via light-induced oxidation. Herein, we report a new degradation channel via water-catalyzed oxidation of BP in the dark. When oxygen co-adsorbs with highly polarized water molecules on BP surface, the polarization effect of water can significantly lower the energy levels of oxygen (i.e. enhanced electron affinity), thereby facilitating the electron transfer from BP to oxygen to trigger the BP oxidation even in the dark environment. This new degradation mechanism lays important foundation for the development of proper protecting schemes in black phosphorus-based devices.

Aprotic Li-O 2 batteries are promising candidates for next-generation energy storage technologies owing to their high theoretical energy densities. However, their practically achievable specific energy is largely limited by the need for porous conducting matrices as cathode support and the passivation of cathode surface by the insulating Li 2 O 2 product. Herein, a self-standing and hierarchically porous carbon framework is reported with Co nanoparticles embedded within developed by 3D-printing of cobalt-based metal-organic framework (Co-MOF) using an extrusion-based printer, followed by appropriate annealing. The novel self-standing framework possesses good conductivity and necessary mechanical stability, so that it can act as a porous conducting matrix. Moreover, the porous framework consists of abundant micrometer-sized pores formed between Co-MOF-derived carbon flakes and meso-and micropores formed within the flakes, which together significantly benefit the efficient deposition of Li 2 O 2 particles and facilitate their decomposition due to the confinement of insulating Li 2 O 2 within the pores and the presence of Co electrocatalysts. Therefore, the self-standing porous architecture significantly enhances the cell's practical specific energy, achieving a high value of 798 Wh kg −1 cell . This study provides an effective approach to increase the practical specific energy for Li-O 2 batteries by constructing 3D-printed framework cathodes.