Determining the Orientation and Molecular Packing of Organic Dyes on a TiO 2 Surface Using X-ray Reflectometry (original) (raw)
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. #
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.
Data from X-ray crystallographic analysis and DFT calculations on isomeric azo disperse dyes
Data in brief, 2018
X-ray crystallography and DFT calculations were used to characterize the molecular nature and excited state properties of isomeric photostable azo dyes for textile fibers undergoing extensive sunlight exposure. Structural data in CIF files arising from X-ray analysis are reported and the complete files are deposited with the Cambridge Crystallographic Data Centre as CCDC 1548989 (https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=1548989) and CCDC 1548990 (https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=1548990). Data from calculating the vertical electronic excitation of 20 excited states for each dye and from calculating excited state oxidation potential (ESOP) and Frontier HOMO/LUMO isosurfaces are also presented. This data is related to the article "Molecular and excited state properties of isomeric scarlet disperse dyes" (Lim et al., 2018) [1].
Adsorption of merocyanine dye on rutile TiO2(110)
Chemical Physics Letters, 2002
Merocyanine dyes that contain a carboxyl group and alkyl chain, like 3-carboxymethyl-5-[2-(3-alkyl-2-benzothiazolinyldene)ethylidene]-2-thioxo-4-thiazolidinone, enhance the efficiency of TiO 2 solar cells. Knowledge of the bonding of this dye molecule to the rutile TiO 2 surface will increase the understanding of the dye-semiconductor electron transfer responsible for the enhanced efficiency. Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) measurements and an ab initio core-excited state molecular orbital calculation for the merocyanine dye were performed. From these results, it was found that the main molecular plane forms a 47°angle with the surface normal, and the carboxyl group that bonds to the TiO 2 surface is in alignment with the surface normal. STM experiments show that the dye molecules form aggregates on the TiO 2 surface.
Quantitative Structure of an Acetate Dye Molecule Analogue at the TiO2−Acetic Acid Interface
The positions of atoms in and around acetate molecules at the rutile TiO2(110) interface with 0.1 M acetic acid have been determined with a precision of ±0.05 Å. Acetate is used as a surrogate for the carboxylate groups typically employed to anchor monocarboxylate dye molecules to TiO2 in dye-sensitized solar cells (DSSC). Structural analysis reveals small domains of ordered (2 × 1) acetate molecules, with substrate atoms closer to their bulk terminated positions compared to the clean UHV surface. Acetate is found in a bidentate bridge position, binding through both oxygen atoms to two 5-fold titanium atoms such that the molecular plane is along the [001] azimuth. Density functional theory calculations provide adsorption geometries in excellent agreement with experiment. The availability of these structural data will improve the accuracy of charge transport models for DSSC.
Introduction Photoactive dye molecular assemblies have an important role for the development of functional devices such as solid state dye lasers, chemical sensors and optical storage devices[1]- . Among various techniques of producing organized molecular assemblies, Langmuir-Blodgett (LB) method is one of the most versatile techniques of making well ordered ultrathin films, which are preferred for many applications and permits the control of the twodimensional structure of these films at the molecular level along with ease of multilayer deposition . The advantage of LB films over thin films obtained by using other conventional techniques is that the molecular architecture may be controlled precisely by monitoring certain parameters carefully such as pH of the subphase, barrier speed, dipping speed, molar composition, temperature and surface pressure of deposition of LB film. LB film's immobilizing functional groups have great advantages for the practical applications such as optical biosensor [6] and molecular electronic device . Although amphiphilic dye molecules and many polyaromatic hydrocarbon derivatives have been extensively investigated in terms of spectroscopic properties, comparatively little effort has been made to study water soluble dye molecules assembled in LB films. Recently, a great deal of attention has been devoted to the LB films containing dye molecules owing to their usefulness in the field of sensors and optical devices . Aggregation of some dye molecules into the restricted geometry of LB films have been reported by Bauman [9]-[10]. Recently, we have studied the incorporation of two anionic dyes namely, chicago sky blue and erythrosin B [12] within the Langmuir monolayer and LB films of cationic octadecylamine. Xanthene dyes are one of the most important classes of pigments used in dye lasers and in various photosensitized reactions. For their outstanding photophysical properties, xanthene dyes are very efficient laser dyes . Eosin Y, an important xanthene dye is widely used for the light-induced electron injection from molecular dyes into semiconductor nanoparticles which is the base of numerous technical applications, such as silver photography , xerography [15] and molecular photovoltaics . EY is examined as sensitizers for colloidal CdSnano particles and also as an alternative in the field of dye-sensitized solar cells .Despite such interesting properties, anionic EY films have never been studied in the restricted geometry of LB films. This is the first report on the interaction of EY andDTAB mixed with SA and formcomplex in the Langmuir and Langmuir-Blodgett films. This study was undertaken in order to reveal the adsorption behavior and organization of EY on the complex monolayer film at the air-water interface. Here, SA-DTAB-EY interaction was studied at the air-water interface by measuring Abstract: Interaction ofwater soluble cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) with anionic stearic acid (SA) in presence of a highly fluorescent dye eosin Y (EY) at the air-water interface has been studied. Adsorption kinetics of the complex formation on the water surface shows that, the rate of reaction depends upon DTAB concentration. The stable monolayer formation is mainly occurred due to the electrostatic interaction between SA and DTAB followed by the SA-DTAB-EY complex formation. FTIR study supports this interaction. The resulting complex films are transferred onto quartz substrate at a particular surface pressure to form LB films. UV-Vis absorption and fluorescence spectroscopic studies of complex LB films indicated the interaction of EY dye with DTAB and SA complex and closer association of dye molecules resulting to the formation of aggregates in the LB films. Scanning electron micrograph certainly confirms the formation of aggregates of EY in the complex LB films.
Chemical Engineering Journal, 2018
• Synthesis of a novel amphoteric adsorbent coating to study the adsorption of anionic and cationic dyes. • Characterization of the novel adsorbent coating by FE-SEM, EDX, zeta potential and FTIR analysis. • Application of the multilayer model with saturation. A new adsorbent (amphoteric adsorbent coating: AAC) based on composite coating with amphoteric function-ality was employed to study the adsorption mechanism of Brilliant Green (BG) and Acid Red 1 (AR1) dyes. This adsorbent was prepared as a coating and supported on cotton cloth by application of a facile method, based on the combined use of smectite-based clay powder, acrylic polymer emulsion (APE) and cationic polyelectrolyte. The novel adsorbent coating was characterized by FE-SEM, EDX, zeta potential and FTIR analysis. Subsequently, the equilibrium adsorption isotherms of AR1 and BG dyes were performed and analyzed at different temperatures (from 303 to 343 K) in order to achieve a thorough comprehension of dyes adsorption mechanism. To this aim, a multilayer model with saturation was developed using statistical physics theory and was applied as a sophisticated tool for data interpretation. The correlations of experimental and theoretical results allowed to understand two distinct behaviours for the adsorption of AR1 and of BG dyes, which were related to the formation of two different adsorbed layers and a variable number of layers, respectively. Based on the parameter of the adopted model, the adsorption geometry of dyes has been described at different temperatures. Interestingly, the adsorption process was energetically typified by estimation of the adsorption energies, which indicated that the adsorption of AR1 and BG dyes were exothermic and endothermic, respectively.
Thermodynamics and adsorption studies of rhodamine-b dye onto organoclay
2017
Thermodynamics and adsorption studies were conducted with a dye of Rhoda mine-B (RB) on <em><strong>Organoclay</strong></em> (OC). Adsorption of the dye was investigated with an initial dye concentration at pH 7±0.3, 298, 308 and 318 K. The adsorption experiments were carried out isothermally at three different temperatures. The Langmuir and Freundlich isotherm models were used to describe the equilibrium data and the results were discussed in details. The thermodynamic parameters such as standard free energy (∆G°), entropy change (∆S°) and enthalpy (∆H°) were calculated for OC. These values showed that adsorption of RB on OC was a spontaneous and endothermic process. <strong><em>Journal of Biodiversity and Environmental Sciences-JBES</em></strong> is an open-access scholarly research journal, published by <strong><em>International Network for Natural Sciences-INNSPUB</em></strong>. JBES published original scien...
Physical Chemistry Chemical Physics, 2012
First-principles computer simulations can contribute to a deeper understanding of the dye/ semiconductor interface lying at the heart of Dye-sensitized Solar Cells (DSCs). Here, we present the results of simulation of dye adsorption onto TiO 2 surfaces, and of their implications for the functioning of the corresponding solar cells. We propose an integrated strategy which combines FT-IR measurements with DFT calculations to individuate the energetically favorable TiO 2 adsorption mode of acetic acid, as a meaningful model for realistic organic dyes. Although we found a sizable variability in the relative stability of the considered adsorption modes with the model system and the method, a bridged bidentate structure was found to closely match the FT-IR frequency pattern, also being calculated as the most stable adsorption mode by calculations in solution. This adsorption mode was found to be the most stable binding also for realistic organic dyes bearing cyanoacrylic anchoring groups, while for a rhodanine-3-acetic acid anchoring group, an undissociated monodentate adsorption mode was found to be of comparable stability. The structural differences induced by the different anchoring groups were related to the different electron injection/recombination with oxidized dye properties which were experimentally assessed for the two classes of dyes. A stronger coupling and a possibly faster electron injection were also calculated for the bridged bidentate mode. We then investigated the adsorption mode and I 2 binding of prototype organic dyes. Car-Parrinello molecular dynamics and geometry optimizations were performed for two coumarin dyes differing by the length of the p-bridge separating the donor and acceptor moieties. We related the decreasing distance of the carbonylic oxygen from the titania to an increased I 2 concentration in proximity of the oxide surface, which might account for the different observed photovoltaic performances. The interplay between theory/simulation and experiments appears to be the key to further DSCs progress, both concerning the design of new dye sensitizers and their interaction with the semiconductor and with the solution environment and/or an electrolyte upon adsorption onto the semiconductor.
Dependence of cationic dyes’ adsorption upon α-MoO3 structural properties
Applied Surface Science, 2021
Orthorhombic molybdenum oxide (α-MoO 3 ) samples were prepared via calcination. During this process, the ratio of the (0 4 0)/(1 1 0) or (0 4 0)/(0 2 1) crystallographic planes was fine-tuned by applying different calcination temperatures. Textural characterization of the samples was carried out to comprehend their differences in photocatalytic and adsorption applications. Except for methyl orange, all the tested dyes (methylene blue, crystal violet, malachite green, and rhodamine B) presented adsorption affinity towards α-MoO 3 . It was revealed that the presence of α-MoO 3 significantly decreased the photocatalytic performance of TiO 2 under UV light irradiation. With the growth of the (0 4 0) facet of α-MoO 3 , the photocatalytic activity increased while the adsorption affinity decreased for cationic dyes. It was found that the solubility of α-MoO 3 depends on the proportional presence of the (0 4 0) facet, which determines both the adsorption and photocatalytic behaviors of the oxide. The solubility of α-MoO 3 is reflected by the decreasing rate of solution pH, hence the adsorption can be measured accurately, but it varies according to the cationic dye structure. Using cationic dyes to assess the photocatalytic activity of α-MoO 3 requires meticulous investigations since adsorption can be mistaken with photocatalytic activity: the adsorption rate depends on both adsorptive and adsorbent structures.
The adsorption of dyes used in the textile industry on mesoporous materials
Colloid and Polymer Science, 2007
An adsorbent material made with a silica lamellar mesoporous material treated with chitosan has been proved to be useful to adsorb both anionic and cationic dyes used in the textile industry. The two tested dyes Tectilon Blue (anionic) and Rhodamine B (cationic) have different adsorption kinetics reflecting a complex mechanism of the phenomenon. Furthermore, the adsorption capacity and interaction strength of Tectilon Blue is higher than those of Rhodamine B. Tectilon Blue molecules are situated with the molecular plane perpendicular to the adsorbent surface, whilst that of the Rhodamine B molecule is flat and parallel to the surface. The differences may be attributed to the different regions of the adsorbent surface on which the dyes are adsorbed because of their different electric charge.
Journal of Water Resource and Protection, 2013
A simple and rapid analytical method for the simultaneous quantification of three commercial azo dyes-Tartrazine (TAR), Congo Red (CR), and Amido Black (AB) in water is presented. The simultaneous assessment of the individual concentration of an organic dye in mixtures using a spectrophotometric method is a difficult procedure in analytical chemistry, due to spectral overlapping. This drawback can be overcome if a multivariate calibration method such as Partial Least Squares Regression (PLSR) is used. This study presents a calibration model based on absorption spectra in the 300-650 nm range for a set of 20 different mixtures of dyes, followed by the prediction of the concentrations of dyes in 6 validation mixtures, randomly selected, using the PLSR method. Estimated limits of detection (LOD) were 0.106, 0.047 and 0.079 mg/L for TAR, CR, and AB, respectively, and limits of quantification (LOQ) were 0.355, 0.157 and 0.265 mg/L for TAR, CR, and AB, respectively. Quantitative determination of the three azo dyes was performed following optimized adsorption experiments onto chitosan beads of mixtures of TAR, CR and AB. Adsorption isotherm and kinetic studies were carried out, proving that the proposed PLSR method is rapid, accurate and reliable.