Search results for "diffuse reflectance"
showing 10 items of 63 documents
Influence of calcination on the structural properties of earth abundant Cu2ZnSnS4
2021
Abstract In the present work, we report on the synthesis of nano-crystalline kesterite copper zinc tin sulfide (CZTS) in powder form and the post-annealing process at high temperatures (calcination), and study their physical properties. We have successfully synthesized CZTS by direct fusion, and the resulting material was crushed to obtain a fine powder. Then, the resulting powder was calcined at high temperatures: 800–1000 ∘C. The calcined samples have been characterized with a number of different structural: X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and optical techniques: photoluminescence (PL), Raman and diffuse reflectance spectr…
Comparison of two vibrational procedures for the direct determination of mancozeb in agrochemicals.
2007
The direct determination of mancozeb in agrochemicals has been made by diamond attenuated total reflectance (ATR) Fourier transform infrared spectroscopy in the middle range (DATR-MIR) and diffuse reflectance infrared Fourier transform spectroscopy in the near range (DR-NIR) methods using in both cases a previous identification of the samples using a dendrographic classification and an appropriate partial least squares (PLS) calibration established from a set of nine external standards and optimized for each type of sample. It was analyzed a heterogeneous population of 11 samples obtained from the Spanish market, containing different co-formulated products, such as fosetyl-Al, copper oxychl…
Testing of the region of Murcia soils by near infrared diffuse reflectance spectroscopy and chemometrics.
2008
A partial least squares near infrared (PLS-NIR) method has been developed for the determination of several physicochemical parameters in soils from different locations of the Region of Murcia. The method was based on the proper chemometric treatment of diffuse reflectance spectra of soil samples. Reflectance spectra were scanned from samples stored in glass vials in the NIR region between 800 and 2600 nm, averaging 36 scans per spectrum at a resolution of 8 cm(-1). Models were built using reference data of 39 samples selected from a dendrogram obtained after hierarchical cluster analysis of NIR spectra of soils and prediction parameters were established from a validation set of 109 addition…
Preliminary results on direct quantitative determination of cocaine in impregnated materials by infrared spectroscopy
2018
Abstract Partial least squares models were built for the direct determination of cocaine in seized impregnated smuggled materials. Measurements are based on the attenuated total reflectance middle infrared spectra (ATR-MIR) and diffuse reflectance spectra in the near range (DR-NIR) obtained directly from the surface of the impregnated materials. The aforementioned procedures offer fast, cheap and environmentally friendly green alternatives to the reference method based on the extraction of the drug and its quantification by gas chromatography. Additionally it has been verified that results found are statistically comparable with those obtained by the reference method with root mean square e…
Influence of platinum on catalytic activity of polycrystalline WO3 employed for phenol photodegradation in aqueous suspension
1998
Abstract A series of polycrystalline WO3 solids loaded with platinum (0.5; 1.0; 2.0 and 3.0 wt%) were prepared and characterised by X-ray diffraction, diffuse reflectance spectroscopy, scanning electron microscopy, specific surface areas determination, X-ray photoelectron spectroscopy. XPS and X-ray results indicate that the samples loaded with Pt up to 1 wt% contained on the surface mainly Pt(2+) species, while those loaded with higher amounts contained Pt(0). Moreover, the samples were employed for a probe reaction, i.e. phenol photooxidation in aqueous suspension, and their photoactivity was compared with that of two TiO2 commercial samples, mainly in the anatase phase. All the Pt–WO3 sa…
Increased conformational rigidity of humic substances by oxidative biomimetic catalysis
2005
A synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride, Fe(TDCPPS)Cl, was employed as a biomimetic catalyst in the oxidative coupling of terrestrial humic materials. High-performance size-exclusion chromatography (HPSEC), solid-state nuclear magnetic resonance (CPMAS-(13)C NMR), electron paramagnetic resonance (EPR), and diffuse reflectance infrared spectroscopy (DRIFT) were used to follow conformational and structural changes brought about in different humic materials by the oxidative coupling. Increase in apparent weight-average molecular weight (Mw(a)) occurred invariably for all humic substances with the oxidative polymerization catalyzed …
Diffuse reflectance and fluorescence multispectral imaging system for assessment of skin
2014
The diffuse reflectance multispectral imaging technique has been used for distant mapping of in vivo skin chromophores (hemoglobin and melanin). The fluorescence multispectral imaging is not so common for skin applications due to complicity of data acquisition and processing, but could provide additional information about skin fluorophores. Both techniques are compatible, and could be combined into a multimodal solution. The multispectral imaging system Nuance based on liquid crystal tunable filters was adapted for diffuse reflectance and fluorescence spectral imaging of in vivo skin. Uniform illumination was achieved by LED ring light. Combination of four LEDs (warm white, 770 nm, 830 nm a…
CO2 to Liquid Fuels: Photocatalytic Conversion in a Continuous Membrane Reactor
2018
The photocatalytic reduction of CO, into value-added chemicals using sunlight is a promising approach to promote energy-bearing products, mitigating the adverse effects of anthropogenic CO2 emissions. In this work, exfoliated C3N4 was incorporated into Nafion matrix and used in a continuous photocatalytic reactor for converting CO2 into liquid fuels. Comprehensive structural and morphological diffuse reflectance spectroscopy (DRS), FT-IR, ATR-IR, and SEM measurements were performed for C3N4-loaded Nafion membrane and then compared with those of a Nafion membrane without any catalyst. The synergic effect of C3N4 organic catalyst embedded in a Nafion dense matrix and a continuous operating mo…
Photoactivity of Nanostructured TiO2 Catalysts in Aqueous System and their Surface Acid-Base, Bulk and Textural Properties
2007
This work reports on the characterisation and determintion of the photocatalytic activity of some TiO2 catalysts prepared using TiCl4 as precursor. The samples, consisting of suspensions, dispersions or powders of nanonstructured anatase or rutile phases, were obtained in very mild conditions, i.e., by boiling the solution obtained after hydrolysis of TiCl4 at atmospheric pressure: it is worth noting that no calcination was necessary to obtain photoactive phases. The samples were characterised by X-ray diffraction (XRD), determination of the BET specific surface area (SSA), scanning electron microscopy (SEM) observations and diffuse reflectance spectroscopy (DRS). FT-IR spectroscopy was use…
Preparation, Characterization, and Photoactivity of Polycrystalline Nanostructured TiO2 Catalysts.
2004
Various preparations of nanostructured TiO2 starting from Ti(iso-OC3H7)4 or TiCl4 are reported. The samples were characterized by X-ray diffractometry, specific surface area and porosity determinations, scanning and transmission electron microscopy, and diffuse reflectance spectroscopy. 4-Nitrophenol photodegradation in aqueous medium was employed as a probe reaction to test the photoactivity of the catalysts. The photoactivity of some samples derived from Ti(iso-OC3H7)4 was found comparable with that of commercial powders. Calcination after the hydrolysis process was necessary to achieve crystallization of the particles before using them as photocatalysts for the reaction studied. The samp…