Kee Eun Lee

Further Understanding of the Adsorption Mechanism of N719 Sensitizer on Anatase TiO2 Films for DSSC Applications Using Vibrational Spectroscopy and Confocal Raman Imaging

Vibrational spectroscopic studies of N719 dye-adsorbed TiO(2) films have been carried out by using SERRS, ATR-FTIR, and confocal Raman imaging. The high wavenumber region (3000-4000 cm(-1)) of dye adsorbed TiO(2) is analyzed via Raman and IR spectroscopy to investigate the role of surface hydroxyl groups in the anchoring mode. As a complementary technique, confocal Raman imaging is employed to study the distribution features of key dye groups (COO-, bipyridine, and C=O) on the anatase surface. Sensitized TiO(2) films made from two different nanocrystalline anatase powders are investigated: a commercial one (Dyesol) and our synthetic variety produced through aqueous synthesis. It is proposed the binding of the N719 dye to TiO(2) to occur through two neighboring carboxylic acid/carboxylate groups via a combination of bidentate-bridging and H-bonding involving a donating group from the N719 (and/or Ti-OH) units and acceptor from the Ti-OH (and/or N719) groups. The Raman imaging distribution of COO(-)(sym) on TiO(2) was used to show the covalent bonding, while the distribution of C=O mode was applied to observe the electrostatically bonded groups.

Preparation and DSSC Performance of Mesoporous Film Photoanodes Based on Aqueous-Synthesized Anatase Nanocrystallites

In this work, anatase nanocrystallites are synthesized from an aqueous titanium(IV) chloride solution by hydrolysis and are used to fabricate mesoporous TiO 2 film photoanodes. The aqueous-synthesized titania nanocrystallites possess high specific surface area (250-350 m 2 /g), 4-5 nm crystallite size, enlarged bandgap, and enhanced surface hydroxylation. Current-voltage measurements of dye-sensitized solar cells (DSSCs) based on the aqueous-synthesized titania showed higher photocurrent (13.0 mA/cm 2 ) and conversion efficiency (5.0%) when compared to cells built from commercial Dyesol (10.7 mA/cm 2 , 4.8%) or P25 (8.5 mA/cm 2 , 4.1%) benchmark nanotitania materials. The enhanced performance is discussed in terms of improved dye loading and associated electron injection and transport facilitated by the nanocrystallite surface characteristics.

The nature of synthetic basic ferric arsenate sulfate (Fe(AsO4)1−x(SO4)x(OH)x) and basic ferric sulfate (FeOHSO4): their crystallographic, molecular and electronic structure with applications in the environment and energy

In this study we investigate a new family of arsenate-bearing phases belonging to one set of structures (Basic Ferric Sulfate-BFS: monoclinic–orthorhombic FeOHSO4) that are significant as an industrial arsenic control material in the environment or a cathodic material in rechargeable Li-ion battery cells. We determine for the first time (after two decades of its known existence in the processing industry) the average crystallographic structure of Basic Ferric Arsenate Sulfate-BFAS: Fe(AsO4)1−x(SO4)x(OH)x·(1−x)H2O) that is a member of this family of phases and how it relates to its parent BFS structure. Moreover, we demonstrate how the substitution of AsO4 ↔ SO4 affects the crystallographic structure of these phases, the phase(s) that are formed and their material properties as environmentally stable arsenic controls or Li-ion battery cathodes.

Vibrational Spectroscopy of Complex Synthetic and Industrial Products

Arsenic and its adverse effects on the environment and society impose a serious risk as it can be observed in cases such as India, Bangladesh, Vietnam, Nepal, and Cambodia. These problems can arise from geochemical processes but also man-made activities like mining and processing of minerals (Copper, Gold, Cobalt, Nickel and Uranium) that may further contribute to the risk of environmental disasters. In either case, problems and environmental disasters maybe prevented if a detailed chemical identification and understanding of the arsenic species and their chemical properties such as solubility is understood. The processing of these mineral ores (containing various metals) generates arsenic-containing solid wastes which are disposed in tailings management facilities outside in the environment (Riveros et al., 2001; Dymov et al., 2004; Defreyne et al., 2009; Mayhew et al., 2010; Bruce at al., 2011). Most often the phases that are produced after the process is completed is often a multicomponent in nature and contains a variety of elemental and individual phases (often ≥ 3-10 phases are expected to be present at the end of the process) produced produced along the chemical process. To complicate the understanding of these phases even more, depending upon the processing conditions, the produced unwanted materials (from an economic and recyclable aspect) may also be of a poorly crystalline nature (nano-scale order) in addition to being multicomponent in nature and as such, simple tasks such as identification and then inferring understanding of its chemical properties (such as arsenic release into the environment) becomes very difficult if not nearly impossible. In general, as a result of their multicomponent nature, and perhaps due to historical relation, the use of lab based XRD has been the main tool to tackle the identification of these phases via the use of peak matching and Rietveld type of phase fitting analysis. Recently, synchrotron based soft and hard X-ray techniques (XANES and EXAFS) have been used in a similar fashion to overcome the poorly crystalline (lack of long range order) and multicomponent barrier of these industrially produced complex samples using similar types of mathematical types of fitting routines (Principal Component Analysis and Target Transformation) which still have limitations in identifying mixtures (>2-3) of similar phases with various coordination numbers/environments for the same probing atom of interest. The need to develop alternative energy storage devices has become one of the main focuses in North America and around the World as a result of the fact that as the population of the world increases, our oil energy supplies are steadily and quickly decreasing with time.

Raman Spectroscopy in the Hydrometallurgical and Materials Engineering World

Autoclave processing of arsenical sulphide feedstocks from which precious metals (Cu, Co, Zn, Ni, Au) are extracted from employs high temperatures (150-225°C) which produces Fe-AsO4-SO4 crystalline phases [1-2]. In 1994, four phases were reported to form for the high temperature (150-225°C) Fe-AsO4-SO4 system [2] but confusion arose in 2007, as the discovery of two new phases were reported [3]. Therefore it was evident that these phases had not been fully identified in terms of arsenate speciation, in spite of the fact that some of these phases are used and advocated in arsenic disposal [2-3]. In the second case, attempts to increase the throughput (extraction of Zn) of an industrial leach autoclave, a massive scale formation never before observed resulted in halting of production. The final case deals with the binding mechanism between the highly commercialized N719 molecule and nano-crystalline anatase (TiO2) as a semiconductor in the DSSC field which has been highly investigated over the last decades [4-5] as a result of the high efficiencies they produce.