UV-visible Reflectance Spectroscopy Research Articles

UV-Vis reflection spectroscopy under variable angle incidence at the air–liquid interface

The UV-Vis reflection spectroscopy (UV-Vis-RS) in situ at the air-liquid interface provides information about tilt and aggregation of chromophores in Langmuir monolayers. This information is particularly important given in most cases the chromophore is located at the polar region of the Langmuir monolayer. This region of the Langmuir monolayers has been hardly accessible by other experimental techniques. In spite of its enormous potential, the application of UV-Vis-RS has been limited mainly to reflection measurements under light normal incidence or at lower incidence angles than the Brewster angle. Remarkably, this technique is quite sensitive to the tilt of the chromophores at values of incidence angles close to or larger than the Brewster angle. Therefore, a novel method to obtain the order parameter of the chromophores at the air-liquid interface by using s- and p-polarized radiation at different incidence angles is proposed. This method allowed for the first time the experimental observation of the two components with different polarization properties of a single UV-Vis band at the air-liquid interface. The method of UV-Vis spectroscopy under variable angle incidence is presented as a new tool for obtaining rich detailed information on Langmuir monolayers.

Photoelectrochemical solar cells based on BI2WO6.

In this study, photoelectrochemical solar cells based on bismuth tungstate electrodes were evaluated. Bi2WO6 was synthesized by a hydrothermal method and characterized by scanning electron microscopy, UV-Vis reflectance spectroscopy, and X-ray powder diffraction. For comparison, solar cells based on TiO2 semiconductor electrodes were evaluated. Photoelectrochemical response of Gratzel-type solar cells based on these semiconductors and their corresponding sensitization with two inexpensive phthalocyanines dyes were determined. Bi2WO6-based solar cells presented higher values of photocurrent and efficiency than those obtained with TiO2 electrodes, even without sensitization. These results portray solar cells based on Bi2WO6 as promising devices for solar energy conversion owing to lower cost of production and ease of acquisition.

Fabrication of one-dimensional heterostructured TiO2@SnO2with enhanced photocatalytic activity

TiO2@SnO2 nanosheets@nanotubes heterostructures were successfully prepared by a facile two-step method: prefabricated SnO2@PNT coaxial nanocables based on the in situ growth of SnO2 in the sulfonated gel matrix of polymeric nanotubes, and then the assembly of TiO2 nanoclusters that consist of ultrathin nanosheets through a solvothermal process. These heterostructures were characterized for the morphological, structural and optical properties by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-visible (UV-vis) and diffuse reflectance spectroscopy (DRS). The photocatalytic investigations showed that the TiO2@SnO2 heterostructures possessed enhanced photocatalytic efficiency in the photodegradation of Rhodamine B (RhB) and photocatalytic H2 evolution from water splitting under ultraviolet (UV) light irradiation, compared with the pristine TiO2 nanosheets, SnO2 nanotubes, the mechanically mixed two samples and P25. The enhanced photocatalytic performance can be ascribed to the beneficial microstructure and synergistic effects of coupled TiO2@SnO2 nanosheets@nanotubes heterostructures.

Preparation of CdWO4-deposited reduced graphene oxide and its enhanced photocatalytic properties

Reduced graphene oxide/CdWO4 (RGO-CdWO4) composite photocatalysts were prepared by a simple one-pot hydrothermal method. Namely, the reduction of graphene oxide and the growth of CdWO4 crystal occurred simultaneously in one single process. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy, nitrogen adsorption, UV-vis reflection spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activities of the as-prepared samples were investigated by degradation of methylene blue under UV light irradiation. An enhancement in photocatalytic activity was observed with RGO-CdWO4 composites compared with pure CdWO4. We also investigated the effect of the amount of graphene on the photocatalytic activity of the as-prepared composite photocatalysts. The results showed that there was an optimal amount of 2%. The mechanism of enhancement of the photocatalytic activity was also discussed.

Photocatalytic hydrogen production with non-stoichiometric pyrochlore bismuth titanate

Pyrochlore bismuth titanate (Bi2−xTi0.75x)Ti2O7 was prepared by an aqueous sol–gel method and annealed at different temperatures. Non-stoichiometry was obtained by adjusting the Ti/Bi ratio during synthesis. Additionally the two bismuth titanate phases Bi4Ti3O12 and Bi2Ti4O11 were synthesized. The materials were characterized by X-ray diffraction and UV–vis reflectance spectroscopy. Photocatalytic hydrogen production was tested in the presence of methanol as sacrificial agent after loading the bismuth titanates with nanoparticles of platinum acting as co-catalysts. It was found that stoichiometric Bi2Ti2O7 being completely inactive could be turned into a good photocatalyst by increasing the Ti/Bi ratio to 1.50 corresponding to (Bi1.55Ti0.33)Ti2O7 still crystallizing in a pure pyrochlore phase. The increase in activity is supposed to derive from an optimization of the TiO6-octahedral geometry due to the generation of bismuth and oxygen vacancies in the lattice. If platinum is applied as co-catalyst on (Bi2−xTi0.75x)Ti2O7 samples, stability issues occur during photocatalysis, which are suppressed by coating the platinum particles with a Cr2O3 shell.

Preparation and characterization of doped titanium dioxide printed layers

Thin layers of doped titanium dioxide on Pyrex glass were prepared by the material printing technique. Titanium dioxide was synthesized by the sol–gel method employing titanium(IV)isopropoxide as the precursor. A dedicated experimental inkjet printer Fujifilm Dimatix 2831 was used for the coating process. The influence of various solvents onto sol jettability was investigated. The mixture of absolute ethanol and 2-butanol was finally adopted because of its optimum viscosity and rate of evaporation. A series of experiments with different printing conditions was carried out, the optimum printing settings were determined. Consequently, iron and silver dopants were incorporated into the sol. The influence of doping on the photocatalytic activity of TiO2 as well as the shift of absorption edge towards high wavelengths was investigated. The quality of all layers was studied by optical microscopy. The surface topology was evaluated by atomic force microscopy. The study of surface structure was performed using scanning electron microscopy. Crystallite phases of prepared TiO2 were investigated by X-ray diffraction analysis. Band gap energy was determined by UV–vis reflection spectroscopy. The photocatalytic activity of printed thin films was examined as a degradation rate of stearic acid and 2,6-dichloroindophenol under UV radiation.

Inhibition Effect and Adsorption Behavior of New Azodye Derivatives on Corrosion of Carbon Steel in Acid Medium

The inhibition effects of synthesized azodye derivatives on carbon steel corrosion in 2.0 M HCl were studied using weight loss, potentiodynamic polarization, and electrochemical frequency modulation (EFM) techniques. Potentiodynamic polarization measurements show that azodye derivatives are mixed-type inhibitors. EFM can be used as a rapid and non destructive technique for corrosion rate measurements without prior knowledge of Tafel constants. The results obtained from weight loss, potentiodynamic polarization and EFM measurements were in good agreement. Adsorption of these inhibitors on the surface on carbon steel follows the Langmuir adsorption isotherm. The surface of carbon steel examined using UV-vis reflectance spectroscopy. Quantum chemical calculations have been performed and several quantum chemical parameters were calculated and correlated with the corresponding inhibition efficiencies.

A highly efficient adsorbent synthesized by reactive depositions of chitosan layers on fish scale collagen—Hydrodynamic swelling and dichlorophenol derivative sorption evaluated by continuous long-term solution microcalorimetry

In this work, a new adsorbent material (ADS) was synthesized by immobilization of chitosan layers on fish scale fibrillar collagen in sequential reactions. Characterization of ADS has performed by FTIR, surface-enhanced Raman spectroscopy, TG/DTG and solid-state UV–vis reflectance spectroscopy. The characterization results have pointed that the chemically immobilized chitosan layers present stable adhesion on the collagenous matrix. The interaction of ADS with a dichlorophenol derivative (DCP) was studied by long-term solution microcalorimetry under isothermal conditions. The exothermic low value of the heat of swelling of ADS has related to the low value of the swelling entropy caused by the chemically immobilized chitosan layers on ADS. The energies of DCP sorption were from −2.41 to −4.31Jg−1 and the DCP sorption enthalpies were slightly exothermic. The maximum sorption capacity observed for DCP on ADS (45.7mmolg−1 or about 12,100mgg−1) is highly superior in relation to literature reports. The calorimetric results have suggested that diffusional transport is the main interaction mechanism at ADS/DCP interfaces. The present work underlines the excellent features of the new chitosan-based adsorbent for use in phenol sorption applications.

Visual monitoring and removal of divalent copper, cadmium, and mercury ions from water by using mesoporous cubic Ia3d aluminosilica sensors

The design of a simple, pH-dependent, micro-object optical sensor based on mesoporous Ia3d aluminosilica pellets functionalized by a porphyrinic chelating ligand for the monitoring and removal of ultra-trace levels of toxic metals, such as Hg(II), Cu(II), and Cd(II), from aqueous media, such as drinking water and biological fluids, is described in this study. This micro-object optical sensor has large surface area-to-volume ratios and uniformly shaped pores in three-dimensional (3D) nanoscale gyroidal structures, and its active sites consist of heteroatoms arranged around uniformly shaped pores in 3D nanoscale gyroidal mesostructures. These mesostructures are densely coated with chelating ligand to permit ultra-fast, specific, pH-dependent visualization and the removal of toxic metals at sub-picomolar concentrations (∼10−11moldm−3) from aqueous media, including drinking water and a suspension of red blood cells, via a colorimetric signal visible to the naked eye, as well as via UV–Vis reflectance spectroscopy. The adsorption of metal ions forms a monolayer on the interior pore surfaces of the pellets in this sensor system. Given that the pellets exhibit long-term stability, reproducibility, and versatility over a number of analysis/regeneration cycles, they can be useful for the fabrication of inexpensive sensor devices for naked-eye detection of toxic pollutants. Furthermore, the usage of the pellets to remove metal ions from a physiological fluid (i.e., blood cells) was evaluated.

From Two-Dimensional to Three-Dimensional at the Air/Water Interface: The Self-Aggregation of the Acridine Dye in Mixed Monolayers

The formation of well-defined supramolecular structures on the nanoscopic scale is a fundamental step in nanotechnology. The fine control of the layer-by-layer growth of the supramolecular assemblies at interfaces is most desirable. The collapse of a mixed monolayer composed of two surfactants in an equimolar ratio (the organic dye N-10-dodecyl acridine (DAO) and stearic acid (SA)) is analyzed herein. The collapse process of the DAO/SA mixed monolayer has been monitored using surface pressure-molecular area (π-A) and surface potential isotherms, UV-visible reflection spectroscopy, polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS), Brewster angle microscopy (BAM), and synchrotron-based in situ X-ray reflectivity (XRR) measurements. The collapse of the DAO/SA mixed monolayer leads to an ordered trilayer. The growth of anisotropic 2D domains of micrometric size is observed during the formation of the trilayer, related to the ordering of the acridine polar headgroups. The trilayer is organized with the first and third monolayers displaying the polar headgroups pointing to the aqueous subphase, whereas the intermediate layer displays the polar headgroups pointing to the air. The trilayer is stabilized by the strong self-aggregation acridine dye group of the DAO molecule. The controlled transition from a monolayer to a trilayer described herein is proposed as a model for further interfacial supramolecular structures of tunable thickness comprising organic dyes.

Fabrication, characterization and photocatalytic activity of TiO2 layers prepared by inkjet printing of stabilized nanocrystalline suspensions

Titanium dioxide (TiO2) colloidal dispersions were synthesized by hydrothermal synthesis in acidic pH under various process conditions. Phase structure of prepared TiO2 was identified as pure rutile by X-ray diffraction analysis and crystallite sizes determined by the Scherrer equation were in the range of 10–25nm. These values correlated with particle sizes observed by transmission electron microscopy (TEM). Afterwards, the prepared TiO2 dispersions were used for the formulation of stable inkjet printable “inks”. Thin layers of nanocrystalline TiO2 were deposited by inkjet printing onto soda-lime glass substrates. After sintering at 500°C, thin patterned films were obtained. Their basic physicochemical properties were characterized by standard methods. Optical microscopy and SEM imaging revealed highly structured topography of samples surface. Layer hardness was equivalent to the B pencil as determined by the “Pencil Hardness Test”. The topology and roughness were examined by atomic force microscopy and RMS roughness was in the range of 40–100nm. Band gap energy of TiO2 determined by UV–vis reflection spectroscopy was consistent with known rutile values. The photocatalytic activity of printed layers was evaluated on the basis of 2,6-dichloroindophenoldiscoloration rate monitored by UV–vis spectroscopy and did not exceed the performanceof Aeroxide P-25. Despite average photocatalytic performace of this particular TiO2 type, inkjet printing proved to be an efficient method for the fabrication of patterned titania films originating from nanocrystalline precursor.

Crystal Growth, Structural Characterization, and Magnetic Properties of New Uranium(IV) Containing Mixed Metal Oxalates: Na2U2M(C2O4)6(H2O)4 (M = Mn2+, Fe2+, Co2+, and Zn2+)

A series of new mixed-metal oxalates containing U(4+) and divalent transition metal cations, Na(2)U(2)M(C(2)O(4))(6)(H(2)O)(4) (M = Mn(2+), Fe(2+), Co(2+), and Zn(2+)), were synthesized via a hydrothermal route and structurally characterized by single crystal X-ray diffraction. All of the materials are triclinic, with space group P1. The three-dimensional structure of these isostructural uranates consists of oxalate bridged UO(10) and MO(6) polyhedra. The U(4+) cation is surrounded by five oxalate ligands, while the M(2+) cations are bonded to two oxalate ligands and four water molecules. The magnetic susceptibility data of these mixed metal oxalates were measured as a function of temperature and result in a value of the effective magnetic moment of 3.50 μ(B) for U(4+) cation in the Zn member, while the total effective moment of the Mn(2+), Fe(2+), and Co(2+) members are 6.01, 5.46, and 5.06 μ(B), respectively. For all materials, negative Weiss constants were observed revealing that the materials exhibited local antiferromagnetic interactions. The U(4+) cation exhibits a singlet ground state at low temperature. The materials were further characterized by infrared, UV-vis reflectance spectroscopy, and thermal analysis.

Effects of TiO2 nanoparticles on the NO2 − levels in cell culture media analysed by Griess colorimetric methods

The Griess assay has been used to determine the possible changes in the measured NO2− concentrations induced by TiO2 nanoparticles in three types of nitrite-containing samples: aqueous NaNO2 solutions with known concentrations, and two types of cell culture media—Roswell Park Memorial Institute medium (RPMI-1640) and Dulbecco’s Modified Eagle Medium (DMEM-F12) used either as delivered or enriched in NO2− by NaNO2 addition. We have used three types of titania with average particle sizes between 10 and 30 nm: Degussa P25 and two other samples (undoped and Fe3+-doped anatase TiO2) synthesised by a hydrothermal route in our laboratory. The structural, morphological, optical and physicochemical characteristics of the used materials have been studied by X-ray diffraction, transmission electron microscopy (EDX), Mossbauer spectroscopy, Brunauer–Emmett–Teller nitrogen adsorption, UV–Vis reflectance spectroscopy, dynamic light scattering and diffuse reflectance infrared Fourier transform spectroscopy. The opacity and sedimentation behaviour of the studied TiO2 suspensions have been investigated by photometric attenuance measurements at 540 nm. To account for the photocatalytic properties of titania in a biologically relevant context, multiple Griess tests have been performed under controlled exposure to laboratory natural daylight illumination. The results show significant variations of light attenuance (associated with NO2− concentrations in the Griess test) depending on the opacity, sedimentation behaviour, NO2− adsorption and photocatalytic properties of the tested TiO2 nanomaterials. These findings identify material characteristics recommended to be considered when analysing the results of Griess tests performed in biological studies involving TiO2 nanoparticles.

Artificial Aging of Tin Amalgam Mirrors: A Preliminary Study of Alteration Compounds and Kinetics

This preliminary study aims to investigate for the first time the kinetics of degradation of tin amalgam mirrors reflective layer. For this purpose some specimens of tin amalgam mirrors have been created, characterized and then subjected to artificial aging. The monitoring of the degradation was done by different techniques such as XRD, SEM and UV-VIS Reflectance Spectroscopy. They allowed to evaluate the progressive color and morphology changes of the amalgam layer, but no expected degradation compounds of amalgam, such as cassiterite and romarkite, were detected. The possible mechanisms underlying the experimental results and further experimental procedures and tools are discussed.

Synthesis and characterization of Fe3+ doped cerium–praseodymium oxide pigments

Abstract Inorganic pigments based on (0.95− x )CeO 2 .(0.05)Pr 6 O 11 .( x )α-Fe 2 O 3 ( x = 0.00; 0.01; 0.02; 0.03 and 0.04) were synthesized by the solid state reaction method at 1300 °C for 3 h, and the modified sol–gel method at 900 °C for 3 h. The pigments obtained were characterized by X-ray diffraction, 57 Fe Mossbauer spectroscopy and UV–Vis reflectance spectroscopy, with determination of colorimetric parameters and band gap. In the X-ray diffraction analysis, diffraction peaks related to the PrFeO 3 secondary phase were observed, in the 1–4 mol% α -Fe 2 O 3 doping systems prepared through the solid state reaction. While in the systems synthesized by the modified sol–gel method, only peaks related to the main phase, cerianite, were observed, in 0–3 mol% α -Fe 2 O 3 doping; and the sample with 4 mol% α -Fe 2 O 3 presented the secondary phase PrFeO 3 . The 57 Fe Mossbauer spectroscopy analysis revealed that the sample with 3 mol% α -Fe 2 O 3 , synthesized by the modified sol–gel method presented almost all iron ions incorporated within the lattice, while the samples with 4 mol% α -Fe 2 O 3 , synthesized by the modified sol–gel method and 3 and 4 mol% α -Fe 2 O 3 , synthesized by the solid state reaction method presented hematite signals, together with Fe 3+ signals within the cerium or praseodymium oxide lattice. The addition of dopants (Fe 3+ and Pr 3+/4+ ) to the CeO 2 lattice, even in small proportion, caused distortions in the lattice, decreasing the band gap value, thus allowing energetic absorptions within the visible region. The pigments presented shades ranging from light to dark-brown.

Optical and electrical characteristics of poly(3-alkylthiophene) and polydiphenylamine copolymers: Applications in light-emitting devices

In this work, poly (3-methylthiophene) (P3MT) or poly (3-octylthiophene) (P3OT) films were synthesized electrochemically with polydiphenylamine (PDFA), in layers and blended copolymers, in non-aqueous media through the oxidation of the monomers, using a standard three-electrode cell in acetonitrile with 0.100molL−1 LiClO4. The polymeric thin films were deposited on platinum plates for optimal quality control of the process. The electrochemical behaviors of as-prepared and partial dedoped films obtained by these methods was verified by cyclic voltammetry (CV) and have been characterized by UV–vis reflectance, resonance Raman, electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. Based on data obtained by UV–vis reflectance spectroscopy, it was possible to characterize the chemical species in the polymer matrix using the resonant Raman method. Both Raman and PL spectra results led to the characterization of three structures (aromatic, semi-quinone and quinone forms of thiophene rings) which formed the homopolymers and copolymers chain. The EPR measurements were taken to quantify the semi-quinone species stabilization at 298 and 77K temperatures. The ionization potential (IP), electron affinity (E.A.) and gap energy (Eg) parameters were determined based on the technical analyses carried out.

CdB10O14(OH)4·H2O with an unprecedented decaborate fundamental building block

CdB10O14(OH)4·H2O has been synthesized under boric acid flux condition and characterized by single-crystal X-ray diffraction, infrared spectra, and UV–vis reflectance spectroscopy. It crystallizes in the monoclinic space group P21/n with a=7.7277(8), b=18.95(2), c=9.8616(10)Å, β=91.454(1)°, V=1443.7(3)Å. The structure consists of [B10O16(OH)4] layers of 9-membered borate rings enclosing Cd2+ cations. Adjacent borate layers are interconnected via hydrogen bonding to form a 3D network. It possesses an unprecedented decaborate fundamental building block B10O20. The structure details are discussed together with Sr[B6O9(OH)2]·3H2O, Pb[B8O11(OH)4], Pr[B8O11(OH)5], and Nd[B9O13(OH)4]·H2O, which have correlated FBBs. The band structure calculations show its direct energy band gap of ∼4.68eV, in consistent with the estimated value (4.77eV) from UV–vis. In addition, dielectric constants and refractive indexes are also calculated.

Monitoring the in-situ oxide growth on uranium by ultraviolet-visible reflectance spectroscopy

We demonstrate the in-situ monitoring of oxide growth on U-0.1 wt. % Cr by means of UV-visible reflectance spectroscopy in the thickness range of ∼20-150 nm. Two different approaches are presented: In the “modeling approach,” we employ a model for a metallic substrate covered by a dielectric layer, while taking into account the buildup of oxygen gradient and surface roughness. Then, we fit the simulated spectra to the experimental one. In the “extrema analysis,” we derive an approximated analytical expression, which relates the oxide thickness to the position of the extrema in the reflectance spectra based on the condition for optical interference of the reflected light. Good agreement is found between the values extracted by the two procedures. Activation energy of ∼21 kcal/mole was obtained by monitoring the oxide growth in the temperature range of 22-90 °C. The upper bound for the thickness determination is argued to be mostly dictated by cracking and detachment processes in the formed oxide.

Role of Ligand Acidity in Chelating Adsorption and Desorption of Metal Salts

A method is proposed to establish useful operation conditions for solid separation of materials having different acidities. The effect of ligand acidity on competitive adsorption and desorption of metal salts was studied by using copper sulfate and sulfuric acid as model electrolytes. Adsorption equilibria with four commercial N-donor chelating adsorbents, WP-1 (functional group branched poly(ethyleneimine)), CuWRAM (functional group 2-(aminomethyl)pyridine), Reillex HP (functional group poly(4-vinylpyridine)), and Dowex M 4195 (functional group bis-2-(pyridylmethyl)amine) were measured using potentiometric and batch uptake methods. Moreover, formation of the complexes in the solid phase was studied with reflection UV–vis spectroscopy. Experimental data were correlated with a nonideal competitive adsorption (NICA) model, and the obtained parameters were used in mapping the operation conditions for the studied adsorbents. Acidity of the adsorbents was proved to increase in the order WP-1 < Reillex HP < CuW...

Molecular Interaction of Rifabutin on Model Lung Surfactant Monolayers

Tuberculosis is one of the most relevant problems for global health care. The design of new drugs against tuberculosis is aimed at maximizing impact against the disease, as well as minimizing the toxicological effect on the lung surfactant. In this work, the antituberculosis drug Rifabutin is studied in combination with phospholipid Langmuir monolayers as models of the lung surfactant monolayer. The zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and the anionic 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG) were used as model phospholipids. A combination of in situ experimental techniques of Brewster angle microscopy, polarization-modulated infrared reflection-absorption spectroscopy, and UV-vis reflection spectroscopy with computer simulations has been used. The interactions between Rifabutin and the DPPC and DPPG Langmuir monolayers were described as the formation of an inclusion complex. The phospholipid-Rifabutin inclusion complex prevents the penetration of the Rifabutin into the alkyl chain region of the phospholipids, leading to a disruption of the monolayer structure and a possible toxicological effect.