Zhixun Luo

Facile preparation of N- and O-doped hollow carbon spheres derived from poly(o-phenylenediamine) for supercapacitors

Nitrogen and oxygen doped hollow carbon spheres (HCSs) have been prepared by pyrolysis of poly(o-phenylenediamine) (PoPD) submicrospheres, which were synthesized by a facile polymerization procedure with an environmental-friendly dopant glycine. Utilizing o-phenylenediamine (oPD) and glycine as the precursors, we are also motivated by the recognition that effective heteroatom doping increases the supercapacitor performance of carbon materials. The as-prepared N- and O- doped HCSs exhibit an enlarged specific surface area (∼355 m2 g−1) and pore volume (∼0.14 cm3 g−1), and they have superior performance in supercapacitors owing to the synergies gained from effective heteroatom doping, their hollow structures, and their good mesoporosity. The reasonable capacitance performance coupled with the facile synthesis procedure suggests supercapacitor applications.

Spin accommodation and reactivity of silver clusters with oxygen: the enhanced stability of Ag13(-).

Spin accommodation is demonstrated to play a determining role in the reactivity of silver cluster anions with oxygen. Odd-electron silver clusters are found to be especially reactive, while the anionic 13-atom cluster exhibits unexpected stability against reactivity with oxygen. Theoretical studies show that the odd-even selective behavior is correlated with the excitation needed to activate the O-O bond in O(2). Furthermore, by comparison with the reactivity of proximate even-electron clusters, we demonstrate that the inactivity of Ag(13)(-) is associated with its large spin excitation energy, ascribed to a crystal-field-like splitting of the orbitals caused by the bilayer atomic structure, which induces a large gap despite not having a magic number of valence electrons.

Probing the Magic Numbers of Aluminum–Magnesium Cluster Anions and Their Reactivity toward Oxygen

We report a joint experimental and theoretical investigation into the geometry, stability, and reactivity with oxygen of alloy metal clusters Al(n)Mg(m)(-) (4 ≤ n+m ≤ 15; 0 ≤ m ≤ 3). Considering that Al and Mg possess three and two valence electrons, respectively, clusters with all possible valence electron counts from 11 to 46 are studied to probe the magic numbers predicted by the spherical jellium model, and to determine whether enhanced stability and reduced reactivity may be found for some Al(n)Mg(m)(-) at non-magic numbers. Al5Mg2(-) and Al11Mg3(-) exhibit enhanced stability corresponding to the expected magic numbers of 20 and 40 electrons, respectively; while Al7Mg3(-), Al11Mg(-), and Al11Mg2(-) turn out to be unexpectedly stable at electron counts of 28, 36, and 38, respectively. The enhanced stability at non-magic numbers is explained through a crystal-field-like splitting of degenerate shells by the geometrical distortions of the clusters. Al(n)Mg(m)(-) clusters appear to display higher oxidation than pure Al(n)(-) clusters, suggesting that the addition of Mg atoms enhances the combustion of pure aluminum clusters.

Net-like Assembly of Au Nanoparticles as a Highly Active Substrate for Surface-Enhanced Raman and Infrared Spectroscopy

Anodic aluminum oxide (AAO) templates were employed to filtrate and assemble Au nanoparticles by the pressure difference method. It was found that the colloidal Au nanoparticles can be uniformly arranged as nanonet assembly on the AAO surface. The net-assembled Au nanoparticles are clean and closely packed with nanochains. Taking fullerene C60/C70 as probe molecules, high-quality surface-enhanced Raman scattering (SERS) spectra were observed. The net-assembled Au nanoparticles even synchronously support the observation of surface-enhanced infrared absorption (SEIRA) spectra of the fullerene C60/C70. These results indicate that the AAO template filtrated with net-assembled Au nanoparticles is a highly active substrate for surface-enhanced spectroscopy.

An application of AAO template: orderly assembled organic molecules for surface-enhanced Raman scattering

High-density ordered arrays of core–shell nano-pillars of Ag–perylene were fabricated using an anodic aluminium oxide (AAO) template which was first embedded with the perylene molecules, followed by an electrochemical deposition of Ag. The surface-enhanced Raman scattering (SERS) spectrum obtained from this system showed well-resolved Raman peaks with good signal-to-noise ratios and little fluorescence background. This is in sharp contrast to the SERS of the individual Ag–perylene nanorods removed from the same AAO template, and the SERS of perylene molecules adsorbed on Ag colloidal nanoparticles. In the latter two cases, the SERS spectra consisted of broad and not-so-well-resolved Raman peaks with a strong fluorescence background. It is believed that the orderly assembly of the perylene molecules on the inner walls of the pores of the AAO template along the Ag nano-pillars led to fluorescence quenching. The high-density ordered arrays of Ag nano-pillars brought forth a surface plasmon resonance for the SERS effect. The present AAO template system offers a new substrate for studying SERS of highly fluorescing molecules.

The fabrication of TiO2 nanorods from TiO2 nanoparticles by organic protection assisted template method

We report here the fabrication of TiO(2) nanorods from TiO(2) nanoparticles by using the organic protection assisted template method. After the deposition of perylene nanotubes in the pores of the porous alumina membranes, implantation of TiO(2) nanoparticles resulted in the formation of TiO(2)/perylene composite nanorods. The diameters and lengths of the nanorods correspond well to the diameter of the pores of the membrane and the thickness of the template used. After removing the perylene protection layer by calcination, the TiO(2) nanorods obtained have an anatase structure, the same as that of the original TiO(2) nanoparticles. It is supposed that the organic layers protected the TiO(2) rods from damage during removal of the template by alkaline etching. Such an organic layer protection method presents a new approach to fabricating one-dimensional nanostructures from the corresponding nanoparticles by an AAO template.

Stabilizing single-molecular Raman spectrum of a nonbonding molecule on Ag nanoparticles

The applicability of single-molecule surface-enhanced Raman spectroscopy to a nonbonding molecular system is demonstrated on a uniformly assembled colloidal Ag nanoparticle substrate.

Porous hydrogen-bonded organic–inorganic frameworks: weak interactions and selective dye filtration

Three hydrogen-bonded organic–inorganic frameworks (HOIFs) are synthesized. Along with full characterization and a comparison with similarly synthesized deuterated counterparts, we reveal that hydrogen-bond interactions of the HOIFs dominate the thermostability, porosity and selectivity in dye filtration on alumina membranes.

Core-shell nanopillars of fullerene C60/C70 loading with colloidal Au nanoparticles: a Raman scattering investigation.

High-density ordered core-sheath nanopillars of fullerene C60/C70 loading with colloidal Au nanoparticles were fabricated with a template method. The anodic aluminum oxide (AAO) template was first imbedded with the fullerene C60/C70 molecules and then followed by a pressure-difference approach for Au colloid. High-quality surface-enhanced Raman scattering (SERS) spectra of fullerene C60/C70 were obtained. The spectra show intense SERS signals with a fluorescence-free background, even with a 514 nm excitation at which the normal Raman of fullerene C60/C70 present poor signal-to-noise. The assembly of the fullerene C60/C70 on the inner walls of the AAO pores along the Au nanopillars lead to fluorescence quenching; meanwhile, the high-density and ordered arrays of Au nanopillars contribute to surface plasmon resonance for the SERS effect.

A theoretical study of weak interactions in phenylenediamine homodimer clusters

Weak intermolecular interactions in phenylenediamine dimer (pdd) clusters are studied by dispersion-corrected density functional theory (DFT) calculations. Along with the optimization of geometric structures and the calculation of interaction energies, we employ molecular electrostatic potential (MEP) mapping, natural bond orbital (NBO) analysis and quantum theory of atoms in molecule (AIM) to analyze the origin and relative energetic contributions of the weak interactions in these pdd systems. It is revealed that the most stable o-phenylenediamine dimer (opdd) cluster is dominated by N-HN hydrogen bonds, the p-phenylenediamine dimer (ppdd) cluster is largely stabilized by N-Hπ and ππ stacking interactions, while the m-phenylenediamine dimer (mpdd) cluster is mainly held by a combination of n → π*, C-Hπ and C-HN interactions. Energy decomposition analysis (EDA) of the total interaction energies of these clusters further demonstrates that the weak intermolecular interactions are associated with electrostatic and dispersion contributions. Structural spectroscopic analysis is also addressed depicting the coexistence of multiple intermolecular interactions which give rise to the spectral variation in wavenumbers of the infrared and Raman activities. Insights into the weak interactions of pdds help us to understand the molecular mechanisms involved in biochemistry and self-assembly materials.