Electrokinetic Manipulation of Silver and Platinum Nanoparticles and Their Stochastic Electrochemical Detection.

Electrokinetic phenomena such as dielectrophoresis and electrothermal fluid flow are used to increase the rate of mass transfer of silver and platinum nanoparticles and improve their stochastic electrochemical detection. These phenomena are induced by applying a high frequency alternating current (ac) waveform between a counter electrode and a working disk microelectrode. By recording chronoamperograms at room temperature and various ac powers, it is shown that the ac heating leads to an increase in the collision frequency of studied nanoparticles with working electrode surface by a factor of ∼101-103 as well as the increase in the magnitude of the measured faradaic response. It is suggested that the developed methodology could be used in the future to improve the detection of ultralow concentrations of various important bioanalytes.

Covalent modification of photoanodes for stable dye-sensitized solar cells.

This paper describes the surface modification of TiO2 with 3-aminopropyltriethoxysilane (APTES) followed by covalent attachment of Ru-based N719 dye molecules to TiO2 through an amide linkage for use as photoanodes (PAs) in dye-sensitized solar cells (DSSCs). Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) confirms the surface chemistry between the TiO2 and dye. The photovoltaic efficiency of DSSCs with covalently linked dye is very similar (6-7%) to that of traditionally prepared DSSCs prepared by direct immersion when both have similar dye coverage. Importantly, the efficiency of PAs with covalently linked dye did not change after storage for more than 60 days in air, whereas the traditionally prepared PAs decreased dramatically after 1 day and lost most of their efficiency after a week. FTIR and UV-vis characterization of the dye suggests that covalent linkage improves stability by preventing the loss of the thiocyanato ligands and/or tetrabutylammonium cations on the dye. PAs with covalently linked dye are also more stable toward water, acid, heat, and UV light compared to traditionally prepared PAs and are more stable compared to other modified PAs with dye attached through electrostatic or hydrogen-bonding interactions.

Spectroscopic investigation of photoinduced charge-transfer processes in FTO/TiO2/N719 photoanodes with and without covalent attachment through silane-based linkers.

Understanding electron-transfer (ET) processes in dye-sensitized solar cells (DSSCs) is crucial to improving their device performance. Recently, covalent attachment of dye molecules to mesoporous semiconductor nanoparticle films via molecular linkers has been employed to increase the stability of DSSC photoanodes. The power conversion efficiency (PCE) of these DSSCs, however, is lower than DSSCs with conventional unmodified photoanodes in this study. Ultrafast transient absorption pump-probe spectroscopy (TAPPS) has been used to study the electron injection process from N719 dye molecules to TiO2 nanoparticles (NPs) in DSSC photoanodes with and without the presence of two silane-based linker molecules: 3-aminopropyltriethoxysilane (APTES) and p-aminophenyltrimethoxysilane (APhS). Ultrafast biphasic electron injection kinetics were observed in all three photoanodes using a 530 nm pump wavelength and 860 nm probe wavelength. Both the slow and fast decay components, attributed to electron injection from singlet and triplet excited states, respectively, of the N719 dye to the TiO2 conduction band, are hindered by the molecular linkers. The hindering effect is less significant with the APhS linker than the APTES linker and is more significant for the singlet-state channel than the triplet-state one. Electron injection from the vibrationally excited states is less affected by the linkers. The spectroscopic results are interpreted on the basis of the standard ET theory and can be used to guide selection of molecular linkers for DSSCs with better device performance. Other factors that affect the efficiency and stability of the DSSCs are also discussed. The relatively lower PCE of the covalently attached photoanodes is attributed to the multilayer and aggregation of the dye molecules as well as the linkers.

Nanoparticle Characterization Through Nano-Impact Electrochemistry: Tools and Methodology Development.

The field of nanomaterials has been expanding rapidly into many diverse applications within the last 20 years. With this growth, there is a significant need for new method development for the detection and characterization of nanomaterials. Understanding the physical properties of nanoscale entities and their associated reaction kinetics is crucial for monitoring their effect on environmental and human health, and in their use for practical applications. Nano-impact electrochemistry is a novel development in the field of fundamental electrochemistry that provides an ultrasensitive method for analyzing physical and redox properties of nanomaterials and their derivatives. This protocol focuses on the tools required for characterizing silver nanoparticles (AgNPs) by nano-impact electrochemistry, the preparation of microelectrodes and the methodology needed for measurement of the AgNP redox activity. The fabrication of cylindrical carbon fiber as well as gold and platinum microwire electrodes is described in detail. The analysis of nano-impact electrochemistry for the characterization of redox active entities is also outlined with examples of applications.