Determining the Orientation and Molecular Packing of Organic Dyes on a TiO 2 Surface Using X-ray Reflectometry (original) (raw)
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In-situ evaluation of dye adsorption on TiO2using QCM
EPJ Photovoltaics, 2017
We measured the adsorption characteristics of two organic dyes; triphenylamine-cyanoacrylic acid (TPA-C) and phenoxazine (MP13), on TiO2, directly in a solution based on quartz crystal microbalance (QCM). Monitoring the adsorbed amount as a function of dye concentration and during rinsing allows determination of the equilibrium constant and distinction between chemisorbed and physisorbed dye. The measured equilibrium constants are 0.8 mM −1 for TPA-C and 2.4 mM −1 for MP13. X-ray photoelectron spectroscopy was used to compare dried chemisorbed layers of TPA-C prepared in solution with TPA-C layers prepared via vacuum sublimation; the two preparation methods render similar spectra except a small contribution of water residues (OH) on the solution prepared samples. Quantitative Nanomechanical Mapping Atomic Force Microscopy (QNM-AFM) shows that physisorbed TPA-C layers are easily removed by scanning the tip across the surface. Although not obvious in height images, adhesion images clearly demonstrate removal of the dye.
The Journal of Physical Chemistry B, 2006
Atomically flat terraced single-crystal anatase and rutile surfaces can be prepared allowing for the reproducible adsorption of covalently attached sensitizing dyes. Once reproducible surfaces and dye coverages are achieved, a photochronocoulometric technique is developed to measure the surface coverage of the dyes, an important parameter in determining the efficiency of sensitization. The surface-bound dyes are irreversibly oxidized by exposure to a light pulse with the n-type oxide semiconductor electrode held in depletion. A double-exponential decay of the subsequent photocurrent is then measured, where the integration of the faster decay is associated with the adsorbed dye coverage and the second much slower decay is attributed to trace regenerators, including water, in the nonaqueous electrolyte. The ruthenium-based N3 dye shows the expected linear dependence of the rate constant on light intensity whereas a dicarboxylated thiacyanine dye shows a square root dependence of its photooxidation rate on light intensity. The sublinear response of the thiacyanine dye is discussed in terms of the more complex surface chemistry that is known for this family of sensitizing dyes. †
Structure of a Model Dye/Titania Interface: Geometry of Benzoate on Rutile-TiO2(110)(1 × 1)
The Journal of Physical Chemistry C
Scanned-energy mode photoelectron diffraction (PhD) and ab initio density functional theory (DFT) calculations have been employed to investigate the adsorption geometry of benzoate ([C 6 H 5 COO]-) on rutile-TiO 2 (110)(1×1). PhD data indicate that the benzoate moiety binds to the surface through both of its oxygen atoms to two adjacent five-fold surface titanium atoms in an essentially upright geometry. Moreover, its phenyl (C 6 H 5-) and carboxylate ([-COO]-) groups are determined to be coplanar, being aligned along the [001] azimuth. This experimental result is consistent with the benzoate geometry emerging from DFT calculations conducted for laterally rather well separated adsorbates. At shorter inter-adsorbate distances, the theoretical modeling predicts a more tilted and twisted adsorption geometry, where the phenyl and carboxylate groups are no longer coplanar, i.e. inter-adsorbate interactions influence the configuration of adsorbed benzoate.
Adsorption of organic dyes on the aminosilane modified TiO2 surface
Dyes and Pigments, 2004
Studies were performed on modification of the rutile titanium dioxide surface using 3-aminopropyltriethoxysilane and N-2-(aminoethyl)-3-aminopropyltrimethoxysilane in various solvents (methanol, toluene, acetone and methanolwater mixture). The modified titanium white was subjected to physicochemical evaluation, aimed at estimating its bulk density, capacity to absorb water, dibutyl phthalate and paraffin oil. Organic dyes were deposited on the surface of the modified titanium white. For the obtained pigments their dispersion, grain morphology, structure of individual particles, particle size distribution, and specific surface area were estimated. In the studies DLS and SEM techniques, and BET method were employed. #
Journal of Colloid and Interface Science, 1998
high voltage insulating materials . In all these applica-Dye molecules are frequently used to determine the specific tions, the interface between organic compound and filler can surface area and the ion exchange capacity of high-surface-area play an important role in the resulting mechanical properties materials such as mica. The organic molecules are often considered and the chemical and environmental stability of the composto be planar and to adsorb in a flat orientation. In the present ite systems. Thus the nature of the bond between polymers study we have investigated the orientation and electronic structure (organic species) and mica is of significant importance, and of crystal violet (CV) and malachite green (MG) on muscovite possibilities for the modification of mica surfaces are of mica, prepared by immersing the substrates for extended periods considerable interest for technological applications. Hence into aqueous solutions of the dyes of various concentrations. The the configuration in the adsorbed state as well as the orienta-K / ions of the mica surface are replaced by the organic cations via ion exchange. X-ray photoelectron spectroscopy reveals that tion of organic molecules on these surfaces play a crucial only one amino group is involved in the interaction of CV and role in both fundamental and applied sciences.
Scanning probe microscopy studies on the adsorption of selected molecular dyes on titania
Beilstein Journal of Nanotechnology, 2016
Titanium dioxide, or titania, sensitized with organic dyes is a very attractive platform for photovoltaic applications. In this context, the knowledge of properties of the titania–sensitizer junction is essential for designing efficient devices. Consequently, studies on the adsorption of organic dyes on titania surfaces and on the influence of the adsorption geometry on the energy level alignment between the substrate and an organic adsorbate are necessary. The method of choice for investigating the local environment of a single dye molecule is high-resolution scanning probe microscopy. Microscopic results combined with the outcome of common spectroscopic methods provide a better understanding of the mechanism taking place at the titania–sensitizer interface. In the following paper, we review the recent scanning probe microscopic research of a certain group of molecular assemblies on rutile titania surfaces as it pertains to dye-sensitized solar cell applications. We focus on experi...
Carboxylic Anchoring Dye p-Ethyl Red Does Not Adsorb Directly onto TiO2 Particles in Protic Solvents
The Journal of Physical Chemistry C
Adsorption of the carboxylic anchoring dye, pethyl red (p-ER), onto TiO 2 nanoparticles in protic vs aprotic solvents was studied in situ using the surface-specific technique, second harmonic light scattering (SHS). Two different adsorption schemes were proposed to account for pER interactions with TiO 2 under different solvent environments. In aprotic solvents, pER adsorbs directly onto TiO 2. Conversely, in protic solvents, in which solvent molecules bind stronger than pER with TiO 2 , the dye molecules adsorb onto the solvent shell around the particle but not directly to the TiO 2 surface. In addition, a portion of the pER molecules form hydrogen bonds with the protic solvent molecules. The two different adsorption models reproduce the measured adsorption isotherms detected by SHS. Specifically, the pER molecules adsorb with a smaller free energy change and a larger density in protic solvents than in aprotic solvents. Our results indicate that protic solvents are undesirable for administering adsorption of carboxylic dyes in dye-sensitized solar cell applications as the dye molecules do not directly adsorb onto the TiO 2 particle.
Journal of the Korean Physical Society, 2018
Thin films of titanium oxide (TiO2) deposited on glass substrates were fabricated by using the sol-gel route. The realization of these thin layers was made using the dip-coating technique with a solution of titanium isopropoxyde as a precursor. The samples prepared with different numbers of deposited layers were annealed at 400 • C for 2 hours. The main purposes of this work were investigations of both the effect of the number of thin TiO2 layers on the crystal structure of the anatase form first and, their ability to adsorb the solution of methylene blue in order to make colored filters from a photocatalytic process. The deposited titanium-oxide layers were characterized by using various techniques: namely, X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM) and UV-Visible spectrometry. The result obtained by using the XRD technique showed the appearance of an anatase phase, as was confirmed by using Raman spectroscopy. The AFM surface analysis allowed the surface topography to be characterized and the surface roughness to be measured, which increased with increasing number of layers. The UV-Visible spectra showed that the TiO2 films had a good transmittance varying from 65% to 95% according to the number of layers. The gap energy varied as a function of the number of deposited layers. The as deposited TiO2 layers were tested as a photocatalyst towards the adsorption of methylene blue dye. The results obtained during this study showed that the adsorption capacity varied according to the number of deposited thin layers and the exposing duration to ultraviolet (UV) light. The maximum absorption rate of the dye was obtained for the two-layer sample. Seventy-two hours of irradiation allowed the adsorption intensity of the dye to be maximized for two-layer films.
Isotherm Study of Methyl Orange Dye Adsorption
IJMRAP, 2024
Water pollution is caused by a number of pollutants, such as natural resource extraction, oil pollution, agricultural practices, nuclear waste spillage, and industrial waste. One such industry is the textile industry that utilises a great deal of water and synthetic dyes that can cause harmful effect to living organism. In order to save human life and aquatic eco system, adsorption is the most efficient technique used for treatment of wastewater containing dyes. The aim of this research is to study the adsorption isotherm of MO dye on the adsorption process using the low rank coal (LRC) as adsorbents. Different amount of adsorbent (60-140 mg) was placed in contact with the dye's solution in the required contact time (5-60 min). After the adsorption process was ended, the shaker was turned off and the remained MO dyes concentration was measured using UV-Vis spectrophotometer. The adsorption isotherm of MO dye solution well fit to Freundlich adsorption isotherm.
Journal of Fluorescence, 2006
The fluorescence polarization method, recently developed for the evaluation of the preferential orientation of fluorescent dyes adsorbed in layered materials [F. López Arbeloa, V. Martínez Martínez, J. Photochem. Photobiol. A: Chem. 181 (2006) 44], is readapted to improve its application. Fluorescence polarization was previously obtained by recording the emission intensity for two orthogonal orientations of the emission polarizer (i.e., the horizontal and vertical polarized light) after excitation with vertical or horizontal polarized light. In the method proposed in this work, samples are excited with unpolarized light, reducing the polarization effect of the excitation light scattering at those emission wavelengths close to the excitation wavelength. Moreover, the present method decreases the effect of the orientation of other non-fluorescent species present in the system, which are active in the excitation process. Consequently, the new method is more simple, precise and sensitive. It is applied to evaluate the orientation of rhodamine 6G dye adsorbed in ordered laponite clay films with low and moderated dye loadings.