Ground State Diffuse Reflectance Absorption Research Articles

An Archaeometric Study of the Iron Age Ceramics from Quinta do Almaraz Archaeologic Site (8th to 5th Centuries BC)—Colour and Mineralogical Characterization

The ceramic pastes of ca. 31 samples recovered from the Almaraz archaeological site, located in the south bench of Tagus River, were studied in detail using XRF, micro-Raman and GSDR spectroscopies, as well as the XRD technique. The ceramic sherds could be grouped into six categories, red slip tableware, decorated tableware, yellow slip tableware, grey tableware, common tableware, and handmade pottery. Our studies of the mineralogic composition of the sherds’ body indicate all ceramics were produced locally, using siliceous clays in most cases and calcareous clays in a few ones. Micro-Raman and ground state diffuse reflectance absorption spectroscopy provided useful information regarding the materials used to produce the coloured ceramics: hematite and brookite for the red slip and decorated ceramics, jacobsite or carbon black for the black decoration or grey ceramics. For the yellow slip tableware, a simple engobe rich in yellow clay was used. XRF spectroscopic studies provided the elemental composition of all samples, and biplots of the potassium (K) versus calcium (Ca) contents, normalized to the silicon content of each ceramic paste, clearly show Pliocene and Miocene local clays sources were used to produce most ceramics. Only one sherd can be considered a Lisbon production.

An Archaeometric Study of Lead-Glazed Medieval Ceramics (13th–14th Century) from Santarém, Portugal

Ceramic sherds from approximately 20 samples of lead-glazed tableware, recovered from diverse archaeological sites, including three repurposed storage pits transformed into dumpsters within the medieval city of Santarém (13th–14th century), underwent a meticulous examination. This investigation utilised techniques such as micro-Raman, ground-state diffuse reflectance absorption, and X-ray fluorescence spectroscopies, in addition to X-ray diffraction and stereomicroscopy. A parallel study was conducted on contemporaneous European ceramics (glazed sherds) sourced from archaeological sites dating back to the 13th–15th centuries in Saintonge (France), Ardenne, Zomergem, and Bruges (Belgium), as well as Surrey–Hampshire, Kingston, and Cheam (England). The first premise for comparing the Santarem samples with European production locations was their frequent commercial relations with Portugal and the frequency of these productions being found in Portugal. The colour of the ceramic bodies is predominantly white or whitish, with a few exhibiting a vivid red hue. Analyses of the fabric, mineralogical, and elemental composition of the sherds suggest that the majority of Santarém’s glazed ceramics were locally or regionally produced, potentially derived from a Pliocene kaolin-rich sand formation. However, this conclusion is not supported by the absence of discovered lead glaze kilns or workshops in Santarém for the late Middle Ages.

An archaeometric study of the Phoenician ceramics found at the São Jorge Castle's hill in Lisbon

A detailed archaeometric study of Phoenician ceramics found in an excavation inside the medieval walls of São Jorge's Castle in Lisbon is described here.Thirty ceramic sherds were studied, grouped into six categories, namely amphorae, containers for domestic use, red slip wares, grey wares, cooking wares and also some indigenous tradition handmade wares.Micro-Raman, X-Ray Fluorescence Emission, X-Ray Diffraction and ground state diffuse reflectance absorption measurements were correlated and used as our main analytical techniques to perform this study. At least three totally different local clay sources were used to produce the here studied pottery, one of alluvial origin using clays collected along the river banks, and another one using clays probably extracted in the oriental part of the Castle's hill. Cooking-ware was made with the use of raw materials with sandy detrital origin. Evidence was also found showing that part of the amphorae, common containers, and grey wares were made with the same raw materials as used in the Phoenician kilns of Almaraz, located in the left margin of the Tagus River, roughly facing Lisbon's Castle hill. The temperatures of the kilns used to fire the amphorae and common containers was in most cases higher than the one used for firing red slip and grey tableware.A detailed laboratorial study of the alluvial clays fired at different temperatures and collected in the Tagus River banks, allowed us, in most cases, to establish the origin of the sources used to produce the Phoenician pottery found in Lisbon.

Functionalization of cotton fabrics with plasmonic photo-active nanostructured Au-TiO2 layer

A simple approach to functionalize cotton fabrics with Au and TiO2 nanostructured layer is presented. Hybrid fabrics (Cot-Au-TiO2) are prepared through reduction of AuCl4− on cotton, followed by a non-aqueous sol-gel procedure using tetrabutyltitanate and a hydrothermal treatment at 110°C. The generation of crystalline TiO2 is confirmed by Raman spectroscopy. The fibres morphology and their roughness are characterized by AFM and FE-SEM. XPS shows how the concentration of the NPs precursors (Au and TiO2) affects the layer composition. GSDR (Ground State Diffuse Reflectance Absorption Spectroscopy) and LIL (Laser induced luminescence) reveal a strong quenching effect induced by Au NPs. Photocatalytic activity measured through the Remazol Blue (RB) degradation reveals an enhancement under visible light, which increases with Au loading. This strong enhancement is explained through the surface plasmon resonance brought by Au NPs.

Structural, Morphological, Optical and Photocatalytic Properties of Y, N-Doped and Codoped TiO2 Thin Films

Pure TiO2, Y-N single-doped and codoped TiO2 powders and thin films deposited on glass beads were successfully prepared using dip-coating and sol-gel methods. The samples were analyzed using grazing angle X-ray diffraction (GXRD), Raman spectroscopy, time resolved luminescence, ground state diffuse reflectance absorption and scanning electron microscopy (SEM). According to the GXRD patterns and micro-Raman spectra, only the anatase form of TiO2 was made evident. Ground state diffuse reflectance absorption studies showed that doping with N or codoping with N and Y led to an increase of the band gap. Laser induced luminescence analysis revealed a decrease in the recombination rate of the photogenerated holes and electrons. The photocatalytic activity of supported catalysts, toward the degradation of toluidine, revealed a meaningful enhancement upon codoping samples at a level of 2% (atomic ratio). The photocatalytic activity of the material and its reactivity can be attributed to a reduced, but significant, direct photoexcitation of the semiconductor by the halogen lamp, together with a charge-transfer-complex mechanism, or with the formation of surface oxygen vacancies by the N dopant atoms.

Spectroscopy of 16th century Portuguese tin-glazed earthenware produced in the region of Lisbon

The oldest kilns producing tin glaze wares discovered in the region of Lisbon were located in the south shore of Tagus river at Santo António da Charneca (SAC) and Mata da Machada (MM). Firing this type of pottery from the fourth quarter of the 15th century to mid-16th century, they were located about 20km away from central Lisbon. Many other examples of ceramics produced in Lisbon workshops from that period are also known and exist in museums or archaeological collections, in spite of the fact that only one kiln dated from that period was found in Lisbon until now.Therefore, the spectroscopic characterization of ceramics found in Lisbon archaeological contexts (attributed to Lisbon workshops) – and also from SAC or MM – was needed and was performed here. Sherds representative of these faience production centres in the Lisbon region dated from the 16th/17th centuries were studied with the use of non-invasive spectroscopies, namely micro-Raman, Ground State Diffuse Reflectance Absorption (GSDR) and X-ray fluorescence emission (XRF). X-ray diffraction (XRD) experiments were also performed. Also clays were collected both in the North and South shores of the river Tagus, as much as possible from the same clay sources as used in the initial workshops.The obtained results evidence a clear similarity in the pastes of the pottery of the Lisbon region, quartz, gehlenite and diopside (or augite) being the major components. Clays are from Miocene origin, but differences between the ceramic pastes were detected pointing to the use of several clay sources. The spectroscopic trend exhibited at SAC and MM pottery is remarkably different, quartz being the major component of those pastes, and clays are from Pliocene origin.

Portuguese tin-glazed earthenware from the 17th century. Part 2: A spectroscopic characterization of pigments, glazes and pastes of the three main production centers

Sherds representative of the three Portuguese faience production centers of the 17th century – Lisbon, Coimbra and Vila Nova were studied with the use of mostly non-invasive spectroscopies, namely: ground state diffuse reflectance absorption (GSDR), micro-Raman, Fourier-transform infrared (FT-IR) and proton induced X-ray (PIXE) or X-ray fluorescence emission (XRF). X-ray diffraction (XRD) experiments were also performed.The obtained results evidence a clear similarity in the pastes of the pottery produced Vila Nova and some of the ceramic pastes from Lisbon, in accordance with documental sources that described the use of Lisbon clays by Vila Nova potters, at least since mid 17th century. Quartz and Gehlenite are the main components of the Lisbon’s pastes, but differences between the ceramic pastes were detected pointing out to the use of several clay sources. The spectroscopic trend exhibited Coimbra’s pottery is remarkably different, Quartz and Diopside being the major components of these pastes, enabling one to well define a pattern for these ceramic bodies.The blue pigment from the Lisbon samples is a cobalt oxide that exists in the silicate glassy matrix, which enables the formation of detectable cobalt silicate microcrystals in most productions of the second half of the 17th century. No micro-Raman cobalt blue signature could be detected in the Vila Nova and Coimbra blue glazes. This is in accordance with the lower kiln temperatures in these two production centers and with Co2+ ions dispersed in the silicate matrix. In all cases the white glaze is obtained with the use of tin oxide. Hausmannite was detected as the manganese oxide mineral used to produce the purple glaze (wine color “vinoso”) in Lisbon.

Li–N doped and codoped TiO 2 thin films deposited by dip-coating: Characterization and photocatalytic activity under halogen lamp

Abstract Li-, N-doped and codoped TiO 2 powders and thin films, deposited on glass substrate using dip-coating method and Ti(OBu) 4 as precursor, were prepared and their structural properties were investigated using grazing angle X-ray diffraction (GXRD), Raman spectroscopy, time resolved luminescence, X-ray photoelectron spectroscopy (XPS), ground state diffuse reflectance absorption and scanning electron microscopy (SEM). Unlike the powder samples, thin films with the same composition and calcination temperature exhibited lower crystallinity degree along with the prevalence of the anatase phase. Ground state diffuse reflectance absorption studies carried on the nanopowders have shown that both the Li and N dopants led to an increase of the band gap. XPS studies revealed differences in the binding energy of N in the presence and in the absence of Li, which was explained in terms of a modification in the chemical environment of N when Li is introduced. The photocatalytic activity of the ensuing film toward the degradation of aromatic amine pollutant revealed a huge enhancement upon doping with N or codoping with N and Li. This behavior is probably provide by a charge-transfer-complex mechanism in which neither the photocatalyst nor the organic compounds absorbs visible light by itself. The improvement in the photocatalytic properties occurred simultaneously with the increase of the lifetime of the charge carriers whenever N and Li were introduced at a level 2%.

Bi–Y doped and co-doped TiO2 nanoparticles: Characterization and photocatalytic activity under visible light irradiation

TiO2 nanoparticles, doped or co-doped with bismuth and/or yttrium (Bi/Y), were obtained by a sol–gel approach. GXRD and Raman revealed that TiO2 is under the form of anatase and that the introduction of the doping elements decreases its crystallinity. XPS studies confirmed, directly, the presence of dopant-OTi bonds, at least for the Y case. Ground state diffuse reflectance absorption studies revealed that the Bi-doped and co-doped samples exhibit a large shift to the visible. The time resolved laser induced emission revealed that Bi and (Bi, Y) doping induces a decrease in the recombination rate of the photogenerated holes and electrons. The photocatalytic efficiency under visible irradiation of the unsupported and supported catalysts, in the form of thin film deposited on glass beads, was evaluated using benzoic acid, toluidine and alachlor as pollutant compounds. A meaningful enhancement in the photocatalytic activity was observed upon the co-doping with Y–Bi and is here assigned to the effect of the dopants on the recombination rate of the photogenerated holes and electrons.

Portuguese tin-glazed earthenware from the 16th century: A spectroscopic characterization of pigments, glazes and pastes

Sherds representative of the Portuguese faience production of the early-16th century from the “Mata da Machada” kiln and from an archaeological excavation on a small urban site in the city of Aveiro (from late 15th to early 16th century) were studied with the use of non-invasive spectroscopies, namely: ground state diffuse reflectance absorption (GSDR), micro-Raman, Fourier-transform infrared (FT-IR) and proton induced X-ray (PIXE). These results were compared with the ones obtained for two Spanish productions, from Valencia and Seville, both from same period (late 15th century and 16th century), since it is well know that Portugal imported significant quantities of those goods from Spain at that time.The obtained results evidence a clear similarity in the micro-Raman spectrum in the glaze and clays of Portuguese pottery produced at “Mata da Machada” and sherds found at the mediaeval house of Homem Cristo Filho (HCF) street at Aveiro.The blue pigment in the sample from the household of Aveiro is a cobalt oxide that exists in the silicate glassy matrix in small amounts, which did not allow the formation of detectable cobalt silicate microcrystals. White glaze from Mata da Machada and Aveiro evidence tin oxide micro-Raman signatures superimposed on the bending and stretching bands of SiO2.All these are quite different from the Spanish products under study (Seville and Valencia), pointing to an earlier production of tin glaze earthenware in Portugal than the mid 16th century, as commonly assumed.

Portuguese tin-glazed earthenware from the 17th century. Part 1: Pigments and glazes characterization

Two sherds representative of the Portuguese faience production of the first and second halves of the 17th century were studied carefully with the use of non-invasive spectroscopies, namely: Ground State Diffuse Reflectance Absorption (GSDR), micro-Raman, Fourier-Transform Infrared (FT-IR), Laser Induced Luminescence (LIL) and Proton Induced X-ray (PIXE). These results were compared with the ones obtained for a Chinese Ming porcelain, Wanli period (16th/beginning of the 17th centuries), which served as an influence for the initial Lisbon’s faience production. By combining information of the different non-destructive spectroscopic techniques used in this work, it was possible to conclude that: Co3O4 (Co II and Co III) can be found in the silicate matrix and is the blue pigment in the “Especieiro” sample (1st half of the 17th C.). Cobalt olivine silicate (Co2SiO4, Co II only) was clearly identified as the blue pigment in “Aranhões” sample (2nd half of the17th C.) – 824cm−1 band in the micro-Raman-spectrum. Cobalt aluminate (CoAl2O4, Co II only) is the blue pigment in the Wanli plate – 203 and 512cm−1 bands in the micro-Raman spectrum.The blue pigment in the 1st half 17th century of Lisbon’s production was obtained by addition of a cobalt ore in low concentrations, which gives no specific Raman signature, because of complete dissolution in the glass. However, in most cases of the 2nd half 17th century, the Raman signature was quite evident, from a cobalt silicate. These findings point to the use of higher temperature kilns in the second case.

Li‐doped nanosized TiO2 powder with enhanced photocalatylic acivity under sunlight irradiation

AbstractThis work reports on the synthesis of Li‐doped TiO2 nanoparticles using the sol–gel process and solid‐state sintering, and investigates their potential use as a photocatalyst for degradation under sunlight excitation of different organic model compounds in aqueous solution. The structure of the nanocrystals was examined by X‐ray diffraction, UV‐vis ground state diffuse reflectance absorption spectra and X‐ray photoelectron emission spectroscopy. Results showed that samples prepared by sol–gel process and calcined at 400 °C are composed of a mixture of anatase and rutile phases, in contrast to the one prepared by solid‐state sintering, which exhibits an anatase phase with Li being involved in a spinel phase. The photocatalytic degradation of aqueous solutions of different aromatic compounds was successfully achieved under sunlight excitation in presence of Li‐doped TiO2 prepared via sol–gel process. It was shown that the calcination temperature and the preparation mode greatly affect the photocatalytic efficiency. Copyright © 2010 John Wiley & Sons, Ltd.

Photocatalytic activity of Li +–Rb +–Y 3+ doped or codoped TiO 2 under sunlight irradiation

Doped TiO 2 particles were synthesized by solid grinding and sol–gel methods. The ensuing powders were analysed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ground state diffuse reflectance absorption spectroscopy (GSDR). The doped samples prepared by solid grinding at 400 °C were in the anatase form, while those synthesised via sol–gel method and calcinated at the same temperature were dominated by the rutile phase. The X-ray photoelectron spectroscopy (XPS) revealed a surface segregation of the doping elements namely for Y, Rb and Rb–Y. The photocatalytic activity of the prepared catalysts, under sunlight irradiation, was evaluated using 2-naphthol as a pollutant model. Results showed a great enhancement in the photocatalytic efficiency with incorporation of Y in samples prepared by solid grinding, while in samples prepared via sol–gel process both Rb and Y dopants greatly improve the photocatalytic activity. The Langmuir–Hinshelwood model was used to describe the photocatalytic reactions from which a pseudo-first-order kinetics was established. The repeatability of photocatalytic activity was also tested for several degradation cycles.

Photophysics of Cyanine Dyes on Surfaces: Laser-Induced Photoisomer Emission of 3,3'-Dialkylthiacarbocyanines Adsorbed on Microcrystalline Cellulose

The photophysics of three thiacarbocyanine dyes, 3,3'-dimethylthiacarbocyanine iodide (DMTCC), 3,3'-diethylthiacarbocyanine iodide (DETCC), and 3,3′-dipropylthiacarbocyanine iodide (DPTCC) was studied when adsorbed on microcrystalline cellulose in the concentration range from 5.0 · 10-4 to 10.0 μmol g-1. Using ground-state diffuse reflectance absorption technique, only H aggregate formation was detected for all the probes. The amount of aggregate formed depends on the hydration degree of the sample, always decreasing with sample dryness. The fluorescence quantum yields for all the adsorbed dyes are one order of magnitude higher than those observed in nonviscous solvents, being 0.98 for DMTCC, 0.96 for DETCC, and 0.63 for DPTCC. Laser-induced fluorescence emissions were recorded (using an intensified-charge-coupled-device detection system) as a function of the laser power, showing that for dry concentrated samples irradiated with high laser intensity, a second fluorescence emission band (bathochromically shifted relative to the monomer emission) was detected. This emission shows a supralinear dependence on laser power. The new emissions here detected arise from fluorescent photoisomers formed via singlet monomers, by a two-photon absorption process.

X-ray Photoelectron, UV−vis Absorption, and Luminescence Spectroscopic Studies of 2,2‘-Cyanines Adsorbed onto Microcrystalline Cellulose

1,1‘-Diethyl-2,2‘-cyanine iodide and 1,1‘-diethyl-2,2‘-carbocyanine iodide were adsorbed onto microcrystalline cellulose by two different methods: by deposition from ethanolic solutions, followed by solvent evaporation, and also from ethanolic solutions in equilibrium with the powdered solid. Within experimental error, both methods provided the same fluorescence quantum yield of the adsorbed dyes in the concentration range 0.01−5.0 μmol of dye per gram of cellulose. Ethanol swells cellulose and some dye molecules become entrapped within the natural polymer chains and in close contact with the substrate. The use of dichloromethane, a solvent which does not swell microcrystalline cellulose, provides samples which exhibit a smaller fluorescence quantum yield. This is consistent with a larger degree of mobility (and also the formation of nonplanar and less emissive conformers) of the cyanines adsorbed on the surface of the solid substrate, while entrapment provides more rigid, planar, and emissive fluorophers. At the same time, the adsorption isotherms of 2,2‘-cyanine on cellulose from alcoholic and dichloromethane solutions show that the specific cellulose surface area accessible for dye adsorption is larger when adsorption is from ethanol rather than from dichloromethane. For 2,2‘-cyanine the fluorescence quantum yields (ΦF) determined were about 0.08 when dichloromethane (a solvent which does not swell cellulose) was used for sample preparation, while with ethanol ΦF was approximately 0.30. These values are about 3 orders of magnitude higher than those in solution, showing the importance of the rigid dry matrix in reducing the nonradiative pathways of deactivation of the (π, π*) first excited singlet state of this cyanine. X-ray photoelectron spectroscopic studies present evidence for hydrogen bonding of 2,2‘-cyanine to cellulose at low loadings and for the formation of aggregates at higher loadings adsorbing from both ethanol and dichloromethane. This hydrogen bonding is assigned as involving dye molecules entrapped within the cellulose chains. On the other hand, for 2,2‘-carbocyanine, evidence exists for an increase of hydrogen bonding with dye loading. This result together with evidence from ground-state diffuse reflectance absorption and luminescence is compatible with dye molecules being firmly bonded to the substrate by one of the nitrogen atoms, with the other unbound.

Magnetic structures in the Ca 2Fe 2−ϰAl ϰO 5 system

Two sherds representative of the Portuguese faience production of the first and second halves of the 17th century were studied carefully with the use of non-invasive spectroscopies, namely: Ground State Diffuse Reflectance Absorption (GSDR), micro-Raman, Fourier-Transform Infrared (FT-IR), Laser Induced Luminescence (LIL) and Proton Induced X-ray (PIXE). These results were compared with the ones obtained for a Chinese Ming porcelain, Wanli period (16th/beginning of the 17th centuries), which served as an influence for the initial Lisbon’s faience production. By combining information of the different non-destructive spectroscopic techniques used in this work, it was possible to conclude that: Co3O4 (Co II and Co III) can be found in the silicate matrix and is the blue pigment in the “Especieiro” sample (1st half of the 17th C.). Cobalt olivine silicate (Co2SiO4, Co II only) was clearly identified as the blue pigment in “Aranhões” sample (2nd half of the17th C.) – 824 cm−1 band in the micro-Raman-spectrum. Cobalt aluminate (CoAl2O4, Co II only) is the blue pigment in the Wanli plate – 203 and 512 cm−1 bands in the micro-Raman spectrum.The blue pigment in the 1st half 17th century of Lisbon’s production was obtained by addition of a cobalt ore in low concentrations, which gives no specific Raman signature, because of complete dissolution in the glass. However, in most cases of the 2nd half 17th century, the Raman signature was quite evident, from a cobalt silicate. These findings point to the use of higher temperature kilns in the second case.