The Journal of Physical Chemistry C (J PHYS CHEM C)

Publications in this journal

• Article: Surface Decoration of MgO Nanocubes with Sulfur Oxides: Experiment and Theory.

  Andreas Sternig, Oliver Diwald, Silvia Gross, Peter V Sushko
  [show abstract] [hide abstract]
  ABSTRACT: We investigated the effect of surface sulfate formation on the structure and spectroscopic properties of MgO nanocubes using X-ray diffraction, electron microscopy, several spectroscopic techniques, and ab initio calculations. After CS2 adsorption and oxidative treatment at elevated temperatures the MgO particles remain cubic and retain their average size of ∼6 nm. Their low coordinated surface elements (corners and edges) were found to bind sulfite and sulfate groups even after annealing up to 1173 K. The absence of MgO corner specific photoluminescence emission bands at 3.4 and 3.2 eV substantiates that sulfur modifies the electronic properties of characteristic surface structures, which we attribute to the formation of (SO3)(2-) and (SO4)(2-) groups at corners and edges. Ab initio calculations support these conclusions and provide insight into the local atomic structures and spectroscopic properties of these groups.
  The Journal of Physical Chemistry C 04/2013; 117(15):7727-7735.
• Article: A Systematic Investigation of p-Nitrophenol Reduction by Bimetallic Dendrimer Encapsulated Nanoparticles.

  Zachary D Pozun, Stacia E Rodenbusch, Emily Keller, Kelly Tran, Wenjie Tang, Keith J Stevenson, Graeme Henkelman
  [show abstract] [hide abstract]
  ABSTRACT: We demonstrate that the reduction of p-nitrophenol to p-aminophenol by NaBH4 is catalyzed by both monometallic and bimetallic nanoparticles (NPs). We also demonstrate a straightforward and precise method for the synthesis of bimetallic nanoparticles using poly(amido)amine dendrimers. The resulting dendrimer encapsulated nanoparticles (DENs) are monodisperse, and the size distribution does not vary with different elemental combinations. Random alloys of Pt/Cu, Pd/Cu, Pd/Au, Pt/Au, and Au/Cu DENs were synthesized and evaluated as catalysts for p-nitrophenol reduction. These combinations are chosen in order to selectively tune the binding energy of the p-nitrophenol adsorbate to the nanoparticle surface. Following the Brønsted-Evans-Polanyi (BEP) relation, we show that the binding energy can reasonably predict the reaction rates of p-nitrophenol reduction. We demonstrate that the measured reaction rate constants of the bimetallic DENs is not always a simple average of the properties of the constituent metals. In particular, DENs containing metals with similar lattice constants produce a binding energy close to the average of the two constituents, whereas DENs containing metals with a lattice mismatch show a bimodal distribution of binding energies. Overall, in this work we present a uniform method for synthesizing pure and bimetallic DENs and demonstrate that their catalytic properties are dependent on the adsorbate's binding energy.
  The Journal of Physical Chemistry C 04/2013; 117(15):7598-7604.
• Article: Computational Studies on SAMs of {Mn6} SMMs on Au(111): Do Properties Change upon Grafting?

  Federico Totti, Gopalan Rajaraman, Marcella Iannuzzi, Roberta Sessoli
  [show abstract] [hide abstract]
  ABSTRACT: Single molecule magnets (SMM) adsorbed on surfaces as magnetic building blocks represent a hot topic of research in the area of molecular magnetism. Indeed, the understanding the properties of molecules on surface is extremely challenging as atomistic structures are not readily available. In this regard, theoretical studies as reliable tool to reproduce and predict the structure and the magnetic ground state of a SMM in the bulk phase and adsorbed on a surface, should be considered very appealing. In this framework, we report a periodic density functional (DF) study on two {Mn6} SMM complexes of general formula [Mn(III)6O2(R-sao)6(O2C-th)2L], where HO2C-th=3-thiophene carboxylic acid, saoH2 = salicylaldoxime, R = H and L = (EtOH)4 (1) or R = Et and L = (EtOH)4(H2O)2 (2), performed to ascertain the structure of their self-assembled monolayers (SAM) on the Au(111) surface. Their magnetic properties in vacuum and in the adsorbed state have also been computed and our results clearly demonstrate that the grafting process is expected to not be a smooth one as it alters their bulk structure and, consequently, their magnetic properties.
  The Journal of Physical Chemistry C 04/2013; 117:7186.
• Article: Surface Defects: Possible Source of Room Temperature Ferromagnetism in Co Doped ZnO Nanorods

  Nadeem Tahir, Altaf Karim, Kristin Aslaug Persson, Syed Tajammul Hussain, Alejandro Gabrie Cruz Gonzalez, Muhammad Usman, Muhammad Naeem, Ruimin Qiao, Wanli Yang, Yi-De Chuang, Zahid Hussain
  [show abstract] [hide abstract]
  ABSTRACT: Contradicting results about the origin of RTFM from measurements on different forms of TM-doped ZnO nanostructured materials lead to strong debates on whether RTFM could be an intrinsic property to TM-doped ZnO or not. Through careful synthesis and extensive characterizations, we have excluded the extrinsic contaminations as the cause of RTFM. Our experimental study confirms that defects such as oxygen vacancies lie on surface of nanorods and are likely a source of RTFM. X-ray absorption and emission spectroscopy (XAS and XES) suggest that the doped Co ions, primarily in the divalent state, replace the Zn ions inside the tetrahedral without introducing Co clustering or Zn-related defects. Band gap narrowing upon Co doping is observed in both optical reflectance and O K-edge XAS/XES, and is in agreement with the presence of oxygen vacancies and strong sp-d hybridization. Furthermore, such trend can be nicely reproduced in GGA+U band structure calculations. Calculations also suggest that these oxygen vacancies are likely to congregate at low energy (101) and (100) surfaces, instead of inside the bulk. Our findings highlight the importance of using the nanocrystalline surfaces to enhance the impurity concentrations and stabilize the ferromagnetism without post sample annealing in oxygen-deficient environment.
  The Journal of Physical Chemistry C 04/2013;
• Article: Performance of Non-local Optics when Applied to Plasmonic Nanostructures

  Lorenzo Stella, Pu Zhang, Francisco J García-Vidal, Angel Rubio, Pablo Garcia-Gonzalez
  [show abstract] [hide abstract]
  ABSTRACT: Semi-classical non-local optics based on the hydrodynamic description of conduction electrons might be an adequate tool to study complex phenomena in the emerging field of nanoplasmonics. With the aim of confirming this idea, we obtain the local and non-local optical absorption spectra in a model nanoplasmonic device in which there are spatial gaps between the components at nanometric and sub-nanometric scales. After a comparison against time-dependent density functional calculations, we conclude that hydrodynamic non-local optics provides absorption spectra exhibiting qualitative agreement but not quantitative accuracy. This lack of accuracy, which is manifest even in the limit where induced electric currents are not established between the constituents of the device, is mainly due to the poor description of induced electron densities.
  The Journal of Physical Chemistry C 04/2013;
• Article: EQCM Investigation of Electrochemical Deposition and Stability of Co-Pi Oxygen Evolution Catalyst of Solar Energy Storage

  Ahamed Irshad, Nookala Munichandraiah
  [show abstract] [hide abstract]
  ABSTRACT: Photo assisted electrolysis of water is considered as an effective way of storing solar energy in the form of hydrogen fuel. This overall reaction involves the oxidation of water to oxygen at the anode and the reduction of protons to hydrogen at the cathode. Cobalt phosphate based catalyst (Co-Pi) is a potentially useful material for oxygen evolution reaction. In the present study, electrochemical deposition of Co-Pi catalyst is carried out on Au coated quartz crystal from 0.1 M phosphate buffer (pH 7) containing 0.5 mM Co2+ ion, along with the simultaneous measurement of mass changes at the electrode surface. Cyclic voltammograms and massograms are recorded during the course of deposition. A current peak is observed at 0.92 V vs. Ag/AgCl, 3 M KCl corresponding to oxidation of Co2+ ion. Mass of the electrode starts increasing at this potential suggesting the deposition of a Co (III)-based insoluble product on the electrode surface. The stability of the catalyst is also studied at several potentials
  The Journal of Physical Chemistry C 03/2013;
• Article: Surface-Supported Hydrocarbon π Radicals Show Kondo Behavior.

  Stefan Müllegger, Mohammad Rashidi, Michael Fattinger, Reinhold Koch
  [show abstract] [hide abstract]
  ABSTRACT: Stable hydrocarbon radicals are utilized as spin standards and prototype metal-free molecular magnets able to withstand ambient conditions. Our study presents experimental results obtained with submolecular resolution by scanning tunneling microscopy and spectroscopy from monomers and dimers of stable hydrocarbon π radicals adsorbed on the Au(111) surface at 7-50 K. We provide conclusive evidence of the preservation of the radical spin-1/2 state, aiming to establish α,γ-bisdiphenylene-β-phenylallyl (BDPA) on Au(111) as a novel Kondo system, where the impurity spin is localized in a metal-free π molecular orbital of a neutral radical state in gas phase preserved on a metal support.
  The Journal of Physical Chemistry C 03/2013; 117(11):5718-5721.
• Article: Deploying RNA and DNA with Functionalized Carbon Nanotubes.

  Simone Alidori, Karim Asqiriba, Pablo Londero, Magnus Bergkvist, Marco Leona, David A Scheinberg, Michael R McDevitt
  [show abstract] [hide abstract]
  ABSTRACT: Carbon nanotubes internalize into cells and are potential molecular platforms for siRNA and DNA delivery. A comprehensive understanding of the identity and stability of ammoniumfunctionalized carbon nanotube (f-CNT)-based nucleic acid constructs is critical to deploying them in vivo as gene delivery vehicles. This work explored the capability of f-CNT to bind single- and double-strand oligonucleotides by determining the thermodynamics and kinetics of assembly and the stoichiometric composition in aqueous solution. Surprisingly, the binding affinity of f-CNT and short oligonucleotide sequences was in the nanomolar range, kinetics of complexation were extremely rapid, and from one to five sequences were loaded per nanotube platform. Mechanistic evidence for an assembly process that involved electrostatic, hydrogen-bonding and π-stacking bonding interactions was obtained by varying nanotube functionalities, oligonucleotides, and reaction conditions. (31)P-NMR and spectrophotometric fluorescence emission data described the conditions required to assemble and stably bind a DNA or RNA cargo for delivery in vivo and the amount of oligonucleotide that could be transported. The soluble oligonucleic acid-f-CNT supramolecular assemblies were suitable for use in vivo. Importantly, key evidence in support of an elegant mechanism by which the bound nucleic acid material can be 'off-loaded' from the f-CNT was discovered.
  The Journal of Physical Chemistry C 03/2013; 117(11):5982-5992.
• Article: Synthesis, Photophysics, Electrochemistry and Electrogenerated Chemiluminescence of PEG-Modified BODIPY dyes in Organic and Aqueous Solutions.

  Alexander B Nepomnyashchii, Allen J Pistner, Allen J Bard, Joel Rosenthal
  [show abstract] [hide abstract]
  ABSTRACT: A set polyethylene glycol (PEG) appended BODIPY architectures (BOPEG1 - BOPEG3) have been prepared and studied in CH2Cl2, H2O:CH3CN (1:1) and aqueous solutions. BOPEG1 and BOPEG2 both contain a short PEG chain and differ in substitution about the BODIPY framework. BOPEG3 is comprised of a fully substituted BODIPY moiety linked to a PEG polymer that is roughly 13 units in length. The photophysics and electrochemical properties of these compounds have been thoroughly characterized in CH2Cl2 and aqueous CH3CN solutions. The behavior of BOPEG1 - BOPEG3 correlates with established rules of BODIPY stability based on substitution about the BODIPY moiety. ECL for each of these compounds was also monitored. BOPEG1, which is unsubstituted at the 2- and 6-positions dimerized upon electrochemical oxidation while BOPEG2, which contains ethyl groups at the 2- and 6-positions, was much more robust and served as an excellent ECL luminophore. BOPEG3 is highly soluble in water due to the long PEG tether and demonstrated modest ECL activity in aqueous solutions using tri-n-propylamine (TPrA) as a coreactant. As such, BOPEG3 represents the first BODIPY derivative that has been shown to display ECL in water without the need for an organic cosolvent, and marks an important step in the development of BODIPY based ECL probes for various biosensing applications.
  The Journal of Physical Chemistry C 03/2013; 117(11):5599-5609.