Efficient Mercury Capture Using Functionalized Porous Organic Polymer.

The primary challenge in materials design and synthesis is achieving the balance between performance and economy for real-world application. This issue is addressed by creating a thiol functionalized porous organic polymer (POP) using simple free radical polymerization techniques to prepare a cost-effective material with a high density of chelating sites designed for mercury capture and therefore environmental remediation. The resulting POP is able to remove aqueous and airborne mercury with uptake capacities of 1216 and 630 mg g-1 , respectively. The material demonstrates rapid kinetics, capable of dropping the mercury concentration from 5 ppm to 1 ppb, lower than the US Environmental Protection Agency's drinking water limit (2 ppb), within 10 min. Furthermore, the material has the added benefits of recyclability, stability in a broad pH range, and selectivity for toxic metals. These results are attributed to the material's physical properties, which include hierarchical porosity, a high density of chelating sites, and the material's robustness, which improve the thiol availability to bind with mercury as determined by X-ray photoelectron spectroscopy and X-ray absorption fine structure studies. The work provides promising results for POPs as an economical material for multiple environmental remediation applications.

A ZnO nanowire bio-hybrid solar cell.

Harvesting solar energy as a carbon free source can be a promising solution to the energy crisis and environmental pollution. Biophotovoltaics seek to mimic photosynthesis to harvest solar energy and to take advantage of the low material costs, negative carbon footprint, and material abundance. In the current study, we report on a combination of zinc oxide (ZnO) nanowires with monolayers of photosynthetic reaction centers which are self-assembled, via a cytochrome c linker, as photoactive electrode. In a three-probe biophotovoltaics cell, a photocurrent density of 5.5 µA cm-2 and photovoltage of 36 mV was achieved, using methyl viologen as a redox mediator in the electrolyte. Using ferrocene as a redox mediator a transient photocurrent density of 8.0 µA cm-2 was obtained, which stabilized at 6.4 µA cm-2 after 20 s. In-depth electronic structure characterization using photoemission spectroscopy in conjunction with electrochemical analysis suggests that the fabricated photoactive electrode can provide a proper electronic path for electron transport all the way from the conduction band of the ZnO nanowires, through the protein linker to the RC, and ultimately via redox mediator to the counter electrode.

Advanced Photoemission Spectroscopy Investigations Correlated with DFT Calculations on the Self-Assembly of 2D Metal Organic Frameworks Nano Thin Films.

Metal-organic frameworks (MOFs) deposited from solution have the potential to form 2-dimensional supramolecular thin films suitable for molecular electronic applications. However, the main challenges lie in achieving selective attachment to the substrate surface, and the integration of organic conductive ligands into the MOF structure to achieve conductivity. The presented results demonstrate that photoemission spectroscopy combined with preparation in a system-attached glovebox can be used to characterize the electronic structure of such systems. The presented results demonstrate that porphyrin-based 2D MOF structures can be produced and that they exhibit similar electronic structure to that of corresponding conventional porphyrin thin films. Porphyrin MOF multilayer thin films were grown on Au substrates prefunctionalized with 4-mercaptopyridine (MP) via incubation in a glovebox, which was connected to an ultrahigh vacuum system outfitted with photoelectron spectroscopy. The thin film growth process was carried out in several sequential steps. In between individual steps the surface was characterized by photoemission spectroscopy to determine the valence bands and evaluate the growth mode of the film. A comprehensive evaluation of X-ray photoemission spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and inverse photoemission spectroscopy (IPES) data was performed and correlated with density functional theory (DFT) calculations of the density of states (DOS) of the films involved to yield the molecular-level insights into the growth and the electronic properties of MOF-based 2D thin films.

Enhanced simulation of an RF ion funnel including gas turbulence.

Electrodynamic ion funnels are used to enhance the transmission of ions in electrospray-based ion injection systems in 0.1 to 30 Torr pressure range. Jet disrupters are commonly employed to prevent droplets and high pressure jets from entering subsequent vacuum regions. This study presents the simulation and testing of an ion funnel containing a jet disrupter using computational fluid dynamics (CFD) and SIMION ion trajectory simulations. Traditional modeling approaches have utilized approximations for the bulk fluid flow fields without including the time-varying nature of the turbulent flow present in the system, thus yielding idealized results. In this study, the fluid flow fields are calculated using CFD. In an effort to include time dependence, a random velocity vector, whose magnitude is proportional to the square root of the turbulence kinetic energy, was calculated at each time step and added to the velocity of the background gas. These simulations predicted that the transmitted ion current is effectively modulated by the variation of the jet disrupter voltage. The addition of the random velocity vector produced results that closely matched the experiments. The simulations yielded the dependence of the transmission on the jet disrupter voltage, and the voltage necessary for maximum ion throughput was accurately predicted. In addition, the magnitude of the predicted transmission closely matched that of the experimental results. This modeling approach could be extended to similar ion transport and filtering systems in which the effects of turbulent fluid flow cannot be ignored.

Orbital line-up at poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV)/poly(3-hexylthiophene) (P3HT) heterojunction.

The poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV)/poly(3-hexylthiophene) (P3HT) heterojunction was investigated by photoemission spectroscopy. The orbital line-up at the MEH-PPV/P3HT heterojunction was determined based on the data of X-ray and ultra-violet photoemission measurements. The results were discussed with reference to the Induced Density of Interface States (IDIS) and integer charge transfer models. The predicted interface orbital line-up by IDIS is in agreement with measured energy alignment of the investigated interface. This suggests the IDIS model is also valid for polymer/polymer heterojunctions.

Experimental determination of the charge neutrality level of poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV).

The charge neutrality level (CNL) of poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) was determined. This was achieved by measuring the hole injection barrier at the MEH-PPV/Al interface with X-ray and ultraviolet photoemission spectroscopies in combination with in situ multistep electrospray-based thin film deposition. This deposition technique allows the deposition of polymers into a vacuum environment from solution, preventing significant contamination of the interface. Hence, the hole injection barrier energy at the interface between MEH-PPV and Al could be determined without the presence of significant amounts of ambient contamination. The result of this measurement was combined with published barrier energies for Au and Ag measured with the same technique. This enabled the correlation between barrier heights and substrate work functions as prescribed by the "induced density of states" (IDIS) model. This yielded a CNL of MEH-PPV of 3.76 eV relative to the vacuum level. The corresponding "screening factor" was calculated to be 0.21. The results are discussed in light of the IDIS, which was initially developed for small molecular materials, as well as the integer charge transfer model (ICT). The ICT model was determined for contaminated polymer interfaces featuring only weak interaction.

Determination of the charge neutrality level of poly(3-hexylthiophene).

The Al/poly(3-hexylthiophene) (P3HT) and Ag/P3HT interfaces were investigated using photoemission spectroscopy in combination with in situ thin-film deposition. The P3HT thin films were deposited directly into high vacuum from solution on the two metal substrates using an electrospray system and characterized via photoemission spectroscopy. The electronic structure and charge injection barriers at these interfaces were determined from the evaluation of the resulting spectra sequences. A linear correlation between barrier heights and substrate work functions was observed from the collected data in combination with previously published results, suggesting that the "Induced Density of Interfaces States" model for small molecular materials is also valid for conjugated polymer interfaces. The corresponding P3HT "screening factor" as well as its charge neutrality level was determined to be 0.48 and 3.44 eV, respectively.

A one pot organic/CdSe nanoparticle hybrid material synthesis with in situ π-conjugated ligand functionalization.

A one pot method for organic/colloidal CdSe nanoparticle hybrid material synthesis is presented. Relative to traditional ligand exchange processes, these materials require smaller amounts of the desired capping ligand, shorter syntheses and fewer processing steps, while maintaining nanoparticle morphology.

Antibody immobilization using pneumatic spray: comparison with the avidin-biotin bridge immobilization method.

The formation of a thin antibody film on a glass surface using pneumatic spray was investigated as a potential immobilization technique for capturing pathogenic targets. Goat-Escherichia coli O157:H7 IgG films were made by pneumatic spray and compared against the avidin-biotin bridge immobilized films by assaying with green fluorescent protein (GFP) transformed E. coli O157:H7 cells and fluorescent reporter antibodies. Functionality, stability, and immobilization of the films were tested. The pneumatic spray films had lower fluorescence intensity values than the avidin-biotin bridge films but resulted in similar detection for E. coli O157:H7 at 10(5)-10(7)cells/ml sample concentrations with no detection of non-E. coli O157:H7 strains. Both methods also resulted in similar percent capture efficiencies. The results demonstrated that immobilization of antibody via pneumatic spray did not render the antibody non-functional and produced stable antibody films. The amount of time necessary for immobilization of the antibody was reduced significantly from 24h for the avidin-biotin bridge to 7 min using the pneumatic spray technique, with additional benefits of greatly reduced use of materials and chemicals. The pneumatic spray technique promises to be an alternative for the immobilization of antibodies on glass slides for capturing pathogenic targets and use in biosensor type devices.

Charge transfer through modified peptide nucleic acids.

We studied the charge transfer properties of bipyridine-modified peptide nucleic acid (PNA) in the absence and presence of Zn(II). Characterization of the PNA in solution showed that Zn(II) interacts with the bipyridine ligands, but the stability of the duplexes was not affected significantly by the binding of Zn(II). The charge transfer properties of these molecules were examined by electrochemistry for self-assembled monolayers of ferrocene-terminated PNAs and by conductive probe atomic force microscopy for cysteine-terminated PNAs. Both electrochemical and single molecular studies showed that the bipyridine modification and Zn(II) binding do not affect significantly the charge transfer of the PNA duplexes.