Diffuse Reflectance Spectroscopy Measurements Research Articles

Influence of Gd3+ substitution and preparation technique on the optical and dielectric properties of Y3Fe5O12 garnet synthesized by standard ceramic and coprecipitation methods

Micro-size and nano-size samples of (GdxY3−xFe5O12; x = 0, 0.25, 0.5, 0.75, and 1) garnet ferrites were prepared by the standard ceramic method (CER) and the coprecipitation (COP) method. The influences of Gd3+ doping and preparation methods on the optical and dielectric properties were compared for these micro-size and nano-size compositions for the first time. X-ray diffraction data confirmed the formation of a single phase of the garnet cubic structure for all samples. It was found that there is a good agreement between the theoretical and experimental lattice parameter estimated values. The Fourier transform infrared spectroscopy was used to study the cation distributions among the different crystallographic sites. Moreover, values of energy gap (Eg) for the investigated samples were determined from the diffused reflectance spectroscopy measurements. These values were found to be higher for (COP) samples than for (CER) ones and slightly increased by increasing Gd3+ content in both series prepared via the two techniques. Furthermore, resistivity (ρac), dielectric constant (e′), and dielectric loss (e″) showed a decrease with increasing frequency (f) for all samples. For the samples prepared by (CER) method, ρac increases with increasing Gd3+ content while for the samples prepared by (COP) method, ρac increases for 0 ≤ x ≤ 1 except for the sample x = 0.5. Values of ρac for samples prepared by (COP) method are higher than those prepared by (CER) method. Both e′ and e″ had the reverse behavior of ρac. Obtained results were explained according to different models.

Color in subtropical brazilian soils as determined with a Munsell chart and by diffuse reflectance spectroscopy

The color of soils provides useful information about their origin and allows their classification. Soil color has traditionally been determined with a Munsell chart; lately, however, alternative techniques such as diffuse reflectance spectroscopy (DRS) have enabled more accurate quantification. In this work, we determined the color parameters hue, value, chroma and reddening index using a Munsell chart and a DRS instrument for comparison. The data obtained from the DRS measurements were used to develop an accurate soil color map for the Rio Grande do Sul state in Brazil (RS). DRS data were also used for removable continuum calculations to determine the [hematite/(hematite + goethite)] ratio [Hm/(Hm + Gt)] of Brazilian soils. Based on suchratio, the soils were classified as goethitic [Hm/(Hm + Gt) ≤ 25%], goethitic–hematitic [25 < Hm/(Hm + Gt) ≤ 50%], hematitic–goethitic [50 < Hm/(Hm + Gt) ≤ 75%] or hematitic [Hm/(Hm + Gt) ≥ 25%]. Color parameters differed between the two measurement methods, with the Munsell chart often overestimating or underestimating the DRS results. Based on the [Hm/(Hm + Gt)] ratio, the target soils were mainly goethitic.

Optimized in situ crystal growth and disordered quasi-one-dimensional magnetism in Li2Mn2(MoO4)3

The quasi-one-dimensional structure of ${\mathrm{Li}}_{2}{\mathrm{Mn}}_{2}{({\mathrm{MoO}}_{4})}_{3}$ consists of three mutually distinct chains of ${\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}$-centered polyhedra in which Mn ostensibly adopts a $J=5/2\phantom{\rule{4pt}{0ex}}{\mathrm{Mn}}^{2+}$ configuration. In situ x-ray scattering experiments carried out as crystallites emerge from a molten oxide solution facilitate the synthesis of large single crystals. Ex situ x-ray diffraction finds no evidence of long-range Li/Mn occupancy ordering, suggesting that the structure is effectively composed of finite chains of Mn moments of statistically varying lengths. UV/visible diffuse reflectance spectroscopy measurements establish a wide 3.43(12)-eV direct charge gap consistent with the local polyhedral coordination of the nominally ${\mathrm{Mn}}^{2+}$ species. The temperature $T$ dependence of the DC magnetic susceptibility $\ensuremath{\chi}$ reveals a fluctuating moment of only $2.74{\ensuremath{\mu}}_{B}\ifmmode\pm\else\textpm\fi{}0.01{\ensuremath{\mu}}_{B}$/Mn, dramatically reduced from the $5.9{\ensuremath{\mu}}_{B}$/Mn expected for ${\mathrm{Mn}}^{2+}$. Meanwhile, the Weiss temperature ${\mathrm{\ensuremath{\Theta}}}_{W}=\ensuremath{-}89\ifmmode\pm\else\textpm\fi{}1$ K reveals antiferromagnetic fluctuations that are stymied from reaching an ordered state apparently by the chemical disorder intrinsic to the polyhedral chains. Measurements of magnetization vs field $H$ at $T\ensuremath{\le}10$ K are far from saturation even at $H=5$ T and are strongly non-Brillouin-like, instead scaling as $H/{T}^{0.24(3)}$ and suggesting the presence of quantum fluctuations associated with an eventual quasi-one-dimensional, disordered magnetic phase.

Mixed-valent selenium compounds: Noncentrosymmetric Cd3(SeO3)2(SeO4) and Hg3(SeO3)2(SeO4) and centrosymmetric Pb2(SeO3) (SeO4)

Three mixed-valent selenium compounds: Cd3(SeO3)2(SeO4), Hg3(SeO3)2(SeO4) and Pb2(SeO3) (SeO4) were successfully synthesized by hydrothermal methods. Among these three compounds, Cd3(SeO3)2(SeO4) and Hg3(SeO3)2(SeO4) are isostructural and crystalize in the noncentrosymmetric (NCS) polar space group P21. Powder second-harmonic generation (SHG) measurements using 1064 ​nm radiation indicate that Cd3(SeO3)2(SeO4) and Hg3(SeO3)2(SeO4) exhibit SHG intensities of approximately 0.6 and 0.8 times of KH2PO4 (KDP), respectively. Pb2(SeO3) (SeO4) is centrosymmetric (CS) and crystalizes in the space group Pnma. Pb2(SeO3) (SeO4) exhibits a 3D framework composed of chains of edge-sharing [PbO6] octahedra linked to [SeO3] and [SeO4] groups. M3(SeO3)2(SeO4) (M ​= ​Cd, Hg) also exhibits a 3D structure consisting of layers of [MO8], [MO6] and [SeO3] polyhedra connected by [SeO4] groups. For all of the reported compounds, infrared spectroscopy, UV–vis diffuse reflectance spectroscopy and thermogravimetric measurements were performed.

Preparation of TiO2/Bi2S3 Composite Photo-Anode Through Ultrasound-Assisted Successive Ionic Layer Adsorption and Reaction Method for Improving the Photoelectric Performance

One important component of modern thin film solar cell designs is the photo-anode. TiO2 is the most common photo-anode material. However, TiO2 has no response over its wide band-gap to most of the visible light spectrum. Semiconductor coupling can improve the photoelectric conversion efficiency of TiO2 thin film photo-anodes. In our study, TiO2 arrays were coupled with the narrow band gap material Bi2S3 to form a TiO2/Bi2S3 composite. The Bi2S3 was deposited by successive ionic layer adsorption and reaction method (SILAR), then the effect of the number of deposition cycles on the composite film performance was studied. The as-obtained samples were characterized by x-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectroscopy and photo-electrochemical measurements. When the number of deposition cycles reached 10, the composite film showed the best optical and electrical properties. To improve the film performance, the SILAR method was modified with an ultrasound-assist. Under the same deposition cycle number (3 and 5), the current density of TiO2/Bi2S3 by ultrasound-assisted SILAR method was larger than that with the SILAR method alone. During the ultrasound-assisted SILAR process, the high temperature and high pressure provide by ultrasound accelerated the formation of new nuclei and increased the ion diffusion rate in the reaction solution, thus forming more Bi2S3 materials.

Methylene Blue Photodegradation under Visible Irradiation on Ag-Doped ZnO Thin Films

This study synthesized and characterized Ag-doped ZnO thin films. Doped ZnO powders were synthesized using the sol-gel method, and thin films were fabricated using the doctor blade technique. The Ag content was determined by optical emission spectrometers with inductively coupled plasma (ICP plasma). Additionally, X-ray diffraction, Raman spectroscopy, Atomic Force Microscopy (AFM), diffuse reflectance, and X-ray photoelectron spectroscopy (XPS) measurements were used for physicochemical characterization. Finally, the photocatalytic degradation of methylene blue (MB) was studied under visible irradiation in aqueous solution. The Langmuir-Hinshelwood model was used to determine the reaction rate constant of the photocatalytic degradation. The physicochemical characterization showed that the samples were polycrystalline, and the diffraction signals corresponded to the ZnO wurtzite crystalline phase. Raman spectroscopy verified the ZnO doping process. The AFM analysis showed that roughness and grain size were reduced after the doping process. Furthermore, the optical results indicated that the presence of Ag improved the ZnO optical properties in the visible range, and the Ag-doped ZnO thin films had the lowest band gap value (2.95 eV). Finally, the photocatalytic degradation results indicated that the doping process enhanced the photocatalytic activity under visible irradiation, and the Ag-doped ZnO thin films had the highest MB photodegradation value (45.1%), as compared to that of the ZnO thin films (2.7%).

Design of ternary CaTiO3/g-C3N4/AgBr Z-scheme heterostructured photocatalysts and their application for dye photodegradation

Herein we have developed a new type of ternary CaTiO3/g-C3N4/AgBr Z-scheme heterostructured photocatalysts by assembling g-C3N4 nanosheets and AgBr nanoparticles on the surface of CaTiO3 nanocuboids. The structures, micro-morphologies, chemical composition, element valence states, optical properties, surface functional groups and band-edge potentials of the derived CaTiO3/g-C3N4/AgBr photocatalysts were investigated by XRD, SEM, TEM, XPS, FTIR, UV–vis diffuse reflectance spectroscopy and electrochemical measurement. RhB was used as the model pollutant to assess the photodegradation performances of the CaTiO3/g-C3N4/AgBr photocatalysts under simulated sunlight illumination. The optimal sample is observed for CTO/10%CN/50%AgBr, which photocatalyzes 99.6% degradation of RhB after 30 min photoreaction (CRhB = 5 mg L−1, Cphotocatalyst = 0.5 g L−1). The reaction rate constants suggest that the photodegradation activity of the CTO/10%CN/50%AgBr composite is about 28.3, 19.9 and 2.0 times larger than that of bare CaTiO3, g-C3N4 and AgBr, respectively. The enhanced photodegradation performances of the ternary CaTiO3/g-C3N4/AgBr composites can be explained due to the Z-scheme electron transfer mechanism and efficient separation of photoexcited electron/hole pairs.

Mixed lone-pair and mixed anion compounds: Pb3(SeO3)(HSeO3)Br3, Pb3(SeO3)(OH)Br3, CdPb8(SeO3)4Cl4Br6 and RbBi(SeO3)F2

Four new mixed lone-pair mixed anion materials, Pb3(SeO3)(HSeO3)Br3, Pb3(SeO3)(OH)Br3, CdPb8(SeO3)4Cl4Br6 and RbBi(SeO3)F2, were successfully synthesized by hydrothermal and solid-state techniques. All four compounds exhibit three-dimensional crystal structures, however the frameworks are vastly different. Pb3(SeO3)(HSeO3)Br3 exhibits a three-dimensional (3D) structure consisting of sheets of [PbO5Br3], [PbO4Br3] and [PbO4Br2] polyhedra linked to [SeO3] and [SeO2(OH)] groups. Pb3(SeO3)(OH)Br3 also exhibits a 3D framework composed of chains of edge-sharing [PbO3(OH)Br2] and [PbO2(OH)Br3] octahedra connected by [SeO3] groups. The 3D network of CdPb8(SeO3)4Cl4Br6 is composed of 1D [Pb4Br3Cl4] chains attached to [CdSe4O12] units through shared oxygens. Finally, RbBi(SeO3)F2 exhibits a 3D network made up of sheets of corner-sharing [BiO3F4] and [SeO3] polyhedra. For all of the reported compounds, infrared spectroscopy, UV–vis diffuse reflectance spectroscopy and thermogravimetric measurements were performed.

Comparing in vivo and ex vivo fiberoptic diffuse reflectance spectroscopy in colorectal cancer

AbstractIn vivo data acquisition using fiberoptic diffuse reflectance spectroscopy (DRS) is more complicated and less controlled compared to ex vivo data acquisition. It would be of great benefit if classifiers for in vivo tissue discrimination based on DRS could be trained on data obtained ex vivo. In this study, in vivo and ex vivo DRS measurements are obtained during colorectal cancer surgery. A mixed model statistical analysis is used to examine the differences between the two datasets. Furthermore, classifiers are trained and tested using in vivo and ex vivo data. It is found that with a classifier trained on ex vivo data and tested on in vivo data, similar results are obtained compared to a classifier trained and tested on in vivo data. In conclusion, under the conditions used in this study, classifiers intended for in vivo tissue discrimination can be trained on ex vivo data.

Influence of neoadjuvant chemotherapy on diffuse reflectance spectra of tissue in breast surgery specimens

.Diffuse reflectance spectroscopy (DRS) can discriminate different tissue types based on optical characteristics. Since this technology has the ability to detect tumor tissue, several groups have proposed to use DRS for margin assessment during breast-conserving surgery for breast cancer. Nowadays, an increasing number of patients with breast cancer are being treated by neoadjuvant chemotherapy. Limited research has been published on the influence of neoadjuvant chemotherapy on the optical characteristics of the tissue. Hence, it is unclear whether margin assessment based on DRS is feasible in this specific group of patients. We investigate whether there is an effect of neoadjuvant chemotherapy on optical measurements of breast tissue. To this end, DRS measurements were performed on 92 ex-vivo breast specimens from 92 patients, treated with neoadjuvant chemotherapy and without neoadjuvant chemotherapy. Generalized estimating equation (GEE) models were generated, comparing the measurements of patients with and without neoadjuvant chemotherapy in datasets of different tissue types using a significance level of 5%. As input for the GEE models, either the intensity at a specific wavelength or a fit parameter, derived from the spectrum, was used. In the evaluation of the intensity, no influence of neoadjuvant chemotherapy was found, since none of the wavelengths were significantly different between the measurements with and the measurements without neoadjuvant chemotherapy in any of the datasets. These results were confirmed by the analysis of the fit parameters, which showed a significant difference for the amount of collagen in only one dataset. All other fit parameters were not significant for any of the datasets. These findings may indicate that assessment of the resection margin with DRS is also feasible in the growing population of breast cancer patients who receive neoadjuvant chemotherapy. However, it is possible that we did not detect neoadjuvant chemotherapy effect in the some of the datasets due to the small number of measurements in those datasets.

Photophysical and photocatalytic properties of structurally modified UiO-66

UiO-66 metal-organic-frameworks (MOFs) are well known for their stability and photoactivity, especially for CO2 reduction. This work reports different incorporation methods of titanium metal into UiO-66-NH2 based frameworks via post-synthetic as well as in situ metal exchange. Each method successfully produced crystalline material with enhancement in photophysical and photocatalytic properties. The origin of the enhanced photophysical was investigated with electron paramagnetic resonance and ultraviolet-visible diffuse reflectance spectroscopy measurements. The observed decrease in the electronic band gaps of the modified UiO-66-based MOFs is supported by density functional theory (DFT)-electronic structure calculations. The DFT-simulations also confirmed the synergistic effect between –NH2 functionalization and titanium metal incorporation that boosts the reactivity of the respective resulting MOFs. A detailed investigation of CO2 reduction was then carried out with the different MOFs models. A remarkable enhancement of the photocatalytic activity was observed by using the UiO-66-NH2 based frameworks compared to the pristine UiO-66. A nearly doubled photocatalytic activity was obtained by the Ti-Zr mixed MOF materials regardless of the method or the ratio of incorporated titanium metal loading.

Thermal, structural and corrosion inhibition performances of a new phosphate glasses on mild steel in HCl medium

Abstract In this study, new phosphate glasses, having as chemical composition, xBiPO4-(90-x)P2O5-10NbOPO4 (10 ≤ x ≤ 35 mol%), labeled BNPx, were prepared by quenching method and examined by: X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FT-IR) and Raman spectroscopy. Structural analysis showed that adding Bi2O3 lead to the appearance of pyrophosphate (P2O72−) units and to the formation of POBo bonds. The goal of the current study is to investigate the corrosion inhibition of mild steel by BNPx in HCl, using electrochemical analysis. The results exhibit that the studied phosphate glasses, in HCl medium, has a great scope of corrosion inhibitor which depend on the amount of Bi2O3. Diffuse Reflectance Spectroscopy (DRS) measurements confirmed the adsorption of inhibitor glasses on the surface of mild steel. Besides, an analysis of steel surface morphology was elicited using optical microscopy in the presence of BNP35 at 250 ppm.

Synthesis and characterization of (RPh3P)3[Bi3I12] (R = Me, Ph) iodobismuthate complexes for photocatalytic degradation of organic pollutants

Phosphonium iodobismuthates(III) (MePh3P)3[Bi3I12] (1) and (Ph4P)3[Bi3I12] (2) were prepared, and X-ray crystal structures were determined for both complexes. Photophysical behavior of both complexes was determined via diffuse reflectance spectroscopy and photoluminescence measurements. Photoluminescence results for complex 2 revealed room temperature emission, which has been rarely reported by bismuth compounds. Low-temperature luminescence scans further indicated a dramatic change in emission properties between the MePh3P+ and Ph4P+ complexes. Photodegradation studies using both ultraviolet and visible light were carried out to determine the light-absorbing capabilities of both complexes. Visible light-promoted degradation studies in the presence of catalytic amounts of 1 and 2 showed significant degradation of aqueous methylene blue and carbaryl solutions over a period of 1 h. The reported photoirradiation studies indicated the phosphonium iodobismuthate salts promote visible light harvesting and facilitate catalytic dye photosensitization. This sensitization allows for the degradation of organic pollutants in the presence of visible light and suggests coupling with fluorescence dyes is viable in photovoltaic applications.

Diffuse reflectance spectroscopy for identification of carcinogen transformation stages in skin tissue

Abstract Today, to establish a diagnosis, the patient must undergo a biopsy followed by histopathological diagnosis, which causes unnecessary cost, patient trauma, and time delay to obtain a diagnosis. However, the metastases can be discovered by diffuse reflectance spectroscopy, which is a simple method that investigates the light distribution within tissue. The theme of this paper is the use of diffuse reflectance spectroscopy (DRS) to determine the optical spectrum of hamster specimen’s tissue and to differentiate biological changes due to laser irradiation (scattering, and cell changes) under the skin. DRS measurements were made on healthy and malignant tissue to diagnose the stages of cancer formation using a fiber-optic probe. The results show that malignant tissue is characterized by a significant decrease in diffuse reflectance spectrum compared to normal tissue.

Construction of AgIn5S8/gC3N4 composite and its enhanced photocatalytic hydrogen production and degradation of organic pollutants under visible light irradiation

Photocatalysis has received tremendous attention among researchers due to its practical usage of solar energy in the field of degradation of toxic pollutants and energy harvesting. In this work, we reported an AgIn5S8/gC3N4 composite as visible light active photocatalyst for hydrogen production and toxic pollutants degradation. Furthermore, the synthesized composites were properly investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–visible diffuse reflectance spectroscopy (UV–vis DRS) and electrochemical impedance spectroscopy (EIS) measurement. The visible light photocatalytic performance was investigated through the degradation of a cationic dye Rhodamine B (RhB) dye from aqueous solution. The photocatalytic hydrogen production results show that AgIn5S8 loaded with 25% of g-C3N4 exhibited higher hydrogen production rate than pure AgIn5S8 and g-C3N4. All the obtained outputs showed that the combination of AgIn5S8 and gC3N4 could exhibit excellent visible light response and better charge separation behaviour, which leads to better photocatalytic performance in AgIn5S8/gC3N4 composite system. Furthermore, AgIn5S8/gC3N4 composite photocatalyst retains good stability in the performance of consecutive cycle usage. The plausible mechanism of the photocatalytic reactions was also studied and explained.

A facile low-temperature synthesis of nanosheets assembled PbS microflowers and their structural, morphological, optical, photoluminescence, dielectric and electrical studies

In current article we report a simple one pot synthesis of lead sulfide (PbS) microflowers (MFs) assembled with nanosheets at low temperature by chemical co-precipitation route. SEM study confirm the low dimension NFs morphology of final product. Furthermore, MFs were subjected to structural, vibrational, diffused reflectance, photoluminescence and impedance spectroscopy measurements. Structural and vibrational studies proved the development of single phase highly crystalline PbS MFs. The respective average crystallite size, lattice strain and dislocation density was ∼9.950 nm, 0.011 (1/nm2) and 0.003. Direct and indirect energy gaps were determined through Kubelka-Munk method ∼0.71 eV and 0.56 eV, respectively, which are superior than bulk (i.e. 0.41 eV). There is clear enrichment in energy gap of MFs which signify the existence of confinement effect. PL emission shows an intense violet emission bands at ∼386 nm and 407 nm. Dielectric constant, loss and ac electrical conductivity were studied at higher frequencies at different bias voltages and discussed. Obtained results presents a new insight on PbS for optoelectronic device applications.

Fabrication and characterization of high efficient Z-scheme photocatalyst Bi2MoO6/reduced graphene oxide/BiOBr for the degradation of organic dye and antibiotic under visible-light irradiation

A novel Bi2MoO6/reduced graphene oxide/BiOBr (Bi2MoO6/RGO/BiOBr) composite was successfully synthesized via a facile solvothermal synthesis and precipitation method. The Bi2MoO6/RGO/BiOBr composite was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and photoelectrochemical measurements. The photocatalytic properties were explored for removal of methylene blue (MB) and norfloxacin (NFX) under visible-light irradiation. The Bi2MoO6/RGO/BiOBr composite exhibits the highest degradation rate compared with Bi2MoO6, BiOBr and Bi2MoO6/BiOBr composite, and that removal ratios of MB and NFX were 96.93% and 78.12%, respectively. A Z-scheme catalytic mechanism suitable for the system was proposed based on the results of UV–vis DRS, free radical trapping experiments and M–S carve analysis, in which RGO as an electronic medium can accelerate electron transfer. It is noteworthy that the close contact interface structure promotes the separation of electrons and holes and improves the photocatalytic performance.

Bismuth and cerium doped cryptomelane-type manganese dioxide nanorods as bifunctional catalysts for rechargeable alkaline metal-air batteries

Metal-air batteries are energy storage devices (ESD) used in many technological applications ranging from portable, wearable to stationary, owing to its simplicity and low cost. Manganese oxides are suitable materials to be used as electrodes in such devices presenting an electrocatalytic performance for oxygen reactions close to Pt and, most importantly, being a low cost, abundant and environmentally friend material. However, as a drawback, manganese dioxide has low electrical conductivity thus requiring the combination with some highly conductive carbon support to be efficiently used as catalyst for the oxygen reactions in ESD. The low stability of carbon for water splitting reaction, however, limits the MnO2 to act as bifunctional catalyst. In this work, to overcome this problem, three and tetravalent cation doped (Bi3+, Ce4+) manganese dioxide nanorods exhibiting higher electrical conductivity were prepared and used as carbon free electrocatalysts for the oxygen reduction and evolution reactions in alkaline medium. X-ray power diffraction (XRD), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS) and Diffuse Reflectance Spectroscopy (DRS) measurements were performed to determine the structure, morphology, surface chemical composition and band gap values of the catalysts confirming the formation of nanorod structures with lower band gap values (EBG). The electrochemical results of Bi3+ and Ce4+ doped MnO2 confirmed that these materials have higher conductivity than K+1 doped MnO2 in agreement with the lower EBG inferred from DRS measurements. The electrocatalytic performance of doped electrocatalysts for the OER was close to that reported for conventional MnO2/C catalysts. On the other hand, they presented a remarkable performance for the ORR, higher than that presented by a commercial state of art Pt/C catalyst. The excellent catalytic performance was confirmed by Zn-air mini battery tests which presented a peak power density of 45 mW cm−2, higher than that presented by a conventional MnO2/C 50 wt.% catalyst (40 mW cm−2).

Evaluation of carbon-based nanostructures suitable for the development of black pigments and glazes

Five different carbon-based samples were chosen for the fabrication of black pigments and glazes: historical ‘unknown’ wood charcoal, graphite, tailored graphitized soot, as-prepared multi-walled carbon nanotubes (MWCNTs) and purified MWCNTs. Ceramic glazes with carbon pigments were prepared with Pb3O4 and SiO2 in molar ratio of 2.85:1.9 and using 5 wt. % of pigment at 900 °C. The black pigments and glazes were characterized by scanning electron microscopy (SEM), optical microscopy, diffuse reflectance spectroscopy and contact angle measurements. International Commission on Illumination (CIE) parameters L*, a* and b* (CIELab-parameters) of the samples were also determined. It was demonstrated that nanostructured carbon pigments showed better black colour and higher quality of black ceramic glaze. Our investigation let us to conclude that these results possibly were affected by initial microstructure of applied carbon derivatives. The obtained nanostructured carbon black pigments could be successfully used for artefact restoration.

Structure and optical properties of a new AgBiW2O8 polymorph

In this work, we report a novel polymorph of AgBiW2O8, which was synthesized by a simple arc melting method. The structural details of this compound were determined by X-ray powder diffraction, and elemental composition was confirmed with ICP-AES. β-AgBiW2O8 adopts the scheelite structure type with tetragonal space group I41/a and lattice parameters a = b = 5.3019(3) and c = 11.678(2) Å. Structural details and optical properties are discussed in detail. Diffuse reflectance spectroscopy (DRS) measurements of β-AgBiW2O8 showed light absorption profile extended to the visible region, which suggests the material has a smaller band gap energy than Bi2WO6, as expected due to contribution of Ag d-orbitals to the electronic structure.