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The major mechanism responsible for plasmonic enhancement of titanium dioxide photocatalysis using gold nanoparticles is still under contention. This work introduces an experimental strategy to disentangle the significance of the charge transfer and near-field mechanisms in plasmonic photocatalysis. By controlling the thickness and conductive nature of a nanoparticle shell that acts as a spacer layer separating the plasmonic metal core from the TiO2 surface, field enhancement or charge transfer effects can be selectively repressed or evoked. Layer-by-layer and in situ polymerization methods are used to synthesize gold core-polymer shell nanoparticles with shell thickness control up to the sub-nanometer level. Detailed optical and electrical characterization supported by near-field simulation models corroborate the trends in photocatalytic activity of the different systems. This approach mainly points at an important contribution of the enhanced near field. © 2019 American Chemical Society.

Department of Chemical Engineering

World University root node

ACS Applied Nano Materials

Electron Transfer and Near-Field Mechanisms in Plasmonic Gold-Nanoparticle-Modified TiO2 Photocatalytic Systems

Silver-polymer core-shell nanoparticles show interesting optical properties, making them widely applicable in the field of plasmonics. The uniformity, thickness and homogeneity of the polymer shell will affect the properties of the system which makes a thorough structural characterization of these core-shell silver-polymer nanoparticles of great importance. However, visualizing the shell and the particle simultaneously is far from straightforward due to the sensitivity of the polymer shell towards the electron beam. In this study, we use different 2D and 3D electron microscopy techniques to investigate different structural aspects of the polymer coating. © 2018 The Royal Society of Chemistry.

Fulltext

Nanoscale

Characterization of silver-polymer core-shell nanoparticles using electron microscopy

Photocatalytic reactors for the degradation of gaseous organic pollutants often suffer from major limitations such as small reaction area, sub-optimal irradiation conditions and thus limited reaction rate. In this work, an alternative solution is presented that involves a glass tube coated on the inside with (silver-modified) TiO2and spiraled around a UVA lamp. First, the spiral reactor is coated from the inside with TiO2using an experimentally verified procedure that is optimized toward UV light transmission. This procedure is kept as simple as possible and involves a single casting step of a 1 wt% suspension of TiO2in ethanol through the spiral. This results in a coated tube that absorbs nearly all incident UV light under the experimental conditions used. The optimized coated spiral reactor is then benchmarked to a conventional annular photoreactor of the same outer dimensions and total catalyst loading over a broad range of experimental conditions. Although residence time distribution experiments indicate slightly longer dwelling of molecules in the spiral reactor, no significant difference in by-passing of gas between the spiral reactor and the annular reactor can be claimed. Acetaldehyde degradation efficiency of 100% is obtained with the spiral reactor for a residence time as low as 60 s, whereas the annular reactor could not achieve full degradation even at 1000 s residence time. In a final case study, addition of long-term stable silver nanoparticles, protected by an ultra-thin polymer shell applied via the layer-by-layer (LbL) method, to the spiral reactor coating is shown to double the degradation efficiency and provides an interesting strategy to cope with higher pollutant concentrations without changing the overall dimensions. © 2017 Elsevier B.V.

Chemical Engineering Journal

Gas phase photocatalytic spiral reactor for fast and efficient pollutant degradation

Affordable silver-polymer core-shell nanoparticles are prepared using the layer-by-layer (LbL) technique. The metallic silver core is encapsulated with an ultra-thin protective shell that prevents oxidation and clustering without compromising the plasmonic properties. The core-shell nanoparticles retain their plasmonic near field enhancement effect, as studied from finite element numerical simulations. Control over the shell thickness up to the sub-nanometer level is there for key. The particles are used to prepare a plasmonic Ag-TiO2 photocatalyst of which the gas phase photocatalytic activity is monitored over a period of four months. The described system outperforms pristine TiO2 and retains its plasmonic enhancement in contrast to TiO2 modified with bare silver nanoparticles. With this an important step is made toward the development of long-term stable plasmonic (photocatalytic) applications. © 2016 Elsevier B.V.

Applied Catalysis B: Environmental

Silver-polymer core-shell nanoparticles for ultrastable plasmon-enhanced photocatalysis

A plasma-enhanced atomic layer deposition (ALD) process using the Ag(fod)(PEt3) precursor [(triethylphosphine)(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate)silver(I)] in combination with NH3-plasma is reported. The steady growth rate of the reported process (0.24 ± 0.03 nm/cycle) was found to be 6 times larger than that of the previously reported Ag ALD process based on the same precursor in combination with H2-plasma (0.04 ± 0.02 nm/cycle). The ALD characteristics of the H2-plasma and NH3-plasma processes were verified. The deposited Ag films were polycrystalline face-centered cubic Ag for both processes. The film morphology was investigated by ex situ scanning electron microscopy and grazing-incidence small-angle X-ray scattering, and it was found that films grown with the NH3-plasma process exhibit a much higher particle areal density and smaller particle sizes on oxide substrates compared to those deposited using the H2-plasma process. This control over morphology of the deposited Ag is important for applications in catalysis and plasmonics. While films grown with the H2-plasma process had oxygen impurities (â9 atom %) in the bulk, the main impurity for the NH3-plasma process was nitrogen (â7 atom %). In situ Fourier transform infrared spectroscopy experiments suggest that these nitrogen impurities are derived from NHx surface groups generated during the NH3-plasma, which interact with the precursor molecules during the precursor pulse. We propose that the reaction of these surface groups with the precursor leads to additional deposition of Ag atoms during the precursor pulse compared to the H2-plasma process, which explains the enhanced growth rate of the NH3-plasma process. © 2017 American Chemical Society.

Chemistry of Materials

Plasma-Enhanced Atomic Layer Deposition of Silver Using Ag(fod)(PEt3) and NH3-Plasma

Silver nanoparticles are widely used in the field of plasmonics because of their unique optical properties. The wavelength-dependent surface plasmon resonance gives rise to a strongly enhanced electromagnetic field, especially at so-called hot spots located in the nanogap in-between metal nanoparticle assemblies. Therefore, the interparticle distance is a decisive factor in plasmonic applications, such as surface-enhanced Raman spectroscopy (SERS). In this study, the aim is to engineer this interparticle distance for silver nanospheres using a convenient wet-chemical approach and to predict and quantify the corresponding enhancement factor using both theoretical and experimental tools. This was done by building a tunable ultrathin polymer shell around the nanoparticles using the layer-by-layer method, in which the polymer shell acts as the separating interparticle spacer layer. Comparison of different theoretical approaches and corroborating the results with SERS analytical experiments using silver and silver-polymer core-shell nanoparticle clusters as SERS substrates was also done. Herewith, an approach is provided to estimate the extent of plasmonic near-field enhancement both theoretically as well as experimentally. © 2017 American Chemical Society.

ACS Applied Materials and Interfaces

Plasmonic Near-Field Localization of Silver Core-Shell Nanoparticle Assemblies via Wet Chemistry Nanogap Engineering

Air-cooled fin and tube heat exchangers are used as a condenser in the conventional automotive Heating Ventilation & Air-Conditioning (HVAC) systems. In this study, the use of liquid cooled plate heat exchanger as a condenser in the automotive HVAC systems has been investigated. In the proposed configuration, the cabin heat absorbed by the refrigerant in HVAC system is rejected to the coolant through a liquid cooled condenser and then to the ambient air through a low temperature radiator. Hence, the proposed configuration combines heat rejection from HVAC system with a low temperature radiator circuit of power train cooling. Mixture of Ethylene glycol & Water (coolant), which is used in power train cooling system, is used as secondary fluid in the condenser. Primarily, work done involves design of a liquid cooled condenser, determining boundary conditions for the coolant circuit and evaluation of overall performance of the refrigeration cycle in the HVAC system at various operating conditions. The modified configuration has been evaluated through dynamic simulation of the system in Dymola. Use of a liquid cooled plate heat exchanger as a condenser provides packaging benefits for the system. From the results, conclusions are drawn about the viability of the concept for its integration into a passenger vehicle. Copyright © 2014 SAE International.

SAE Technical Papers

Performance evaluation of automotive HVAC system with the use of liquid cooled condenser

Polypyrrole(PPy)titania(TiO2) nanocomposites were prepared by an in situ oxidative polymerization method with two different oxidants, namely ammonium persulfate (APS) and ferric chloride. The effects of oxidant type and TiO2 particle loading level on the physiochemical properties of the PPyTiO2 nanocomposites were investigated in details. The intermolecular interactions within the polymer nanocomposites were explored by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). While scanning electron microscopy (SEM) was used to characterize surface morphology, transmission electron microscopy (TEM) revealed the well-dispersed TiO2 nanoparticles in the PPy matrix. The thermogravimetric analysis (TGA) revealed improved thermal stability of PPy with addition of the nanofillers. The nanocomposites prepared by APS oxidation exhibited lower electrical conductivity at room temperature than that of the PPy nanocomposites from FeCl3 oxidation polymerization. Both nanocomposites and pure PPy follow the three-dimensional variable range hopping (VRH) electron conduction mechanism. The frequency dependent dielectric constants of PPyTiO2 nanocomposites were measured in the range of 20 Hz-2 MHz. © 2011 The Electrochemical Society.

Journal of the Electrochemical Society

Polypyrrole-titania nanocomposites derived from different oxidants

Titania nanostructures have gained much attention lately due to their high specific surface area, ion-exchange ability, and better electrical properties. In this study, pure titania nanotubes (TNTs) were synthesized using hydrothermal method. Phosphorus-doped titania nanotubes (P-TNTs) were fabricated following a wet chemical procedure with dimethyl phosphite as a precursor. Characterization of the prepared pure/phosphorus-doped titania nanotubes was performed using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), XRD analysis, UV-Vis absorption spectra, and BET specific surface area analysis. Phosphorus-doping slightly reduces the surface area but shifts the band gap towards the visible light region. When compared to pure TNTs, the optimal 0.75 wt.% P-TNTs have a similar surface area (272 m2/g vs. 274 m2/g) but with a band gap shift of 0.27 eV towards the visible light region. The photocatalytic activity of 0.75 wt.% P-TNTs was tested using rhodamine B (RhB) as a model pollutant under a 9 W fluorescent lamp and was significantly better than the benchmark Degussa P25 nanoparticles due to the band gap narrowing and an increased surface area. The decolorization follows first-order kinetics with the apparent rate constant k1 of 0.13 min-1 for 0.75 wt.% P-TNT and 0.07 min-1 for Degussa P25. © 2011 Elsevier B.V. All rights reserved.