Coal analysis by diffuse reflectance near-infrared spectroscopy: Hierarchical cluster and linear discriminant analysis

An extensive study was carried out in coal samples coming from several origins trying to establish a relationship between nine coal properties (moisture (%), ash (%), volatile matter (%), fixed carbon (%), heating value (kcal/kg), carbon (%), hydrogen (%), nitrogen (%) and sulphur (%)) and the corresponding near-infrared spectral data. This research was developed by applying both quantitative (partial least squares regression, PLS) and qualitative multivariate analysis techniques (hierarchical cluster analysis, HCA; linear discriminant analysis, LDA), to determine a methodology able to estimate property values for a new coal sample. For that, it was necessary to define homogeneous clusters, whose calibration equations could be obtained with accuracy and precision levels comparable to those provided by commercial online analysers and, study the discrimination level between these groups of samples attending only to the instrumental variables. These two steps were performed in three different situations depending on the variables used for the pattern recognition: property values, spectral data (principal component analysis, PCA) or a combination of both. The results indicated that it was the last situation what offered the best results in both two steps previously described, with the added benefit of outlier detection and removal.     

Multivariate analysis of reflectance spectra from propolis: Geographical variation in Romanian samples

The present study described reflectance spectroscopy as a suitable analytical tool to discriminate the floral origin of 39 Romanian propolis samples. Relevant differences between the UV-vis reflectance spectra of the investigated propolis samples within the 220-850 nm spectral range were found. The results obtained applying cluster analysis, principal component analysis and linear discriminant analysis to the digitized data of zero order, zero order normalized and first order derivative spectra support the reliability of this technique. In addition, the application of the linear discriminant analysis to the score matrices corresponding to the first principal components appeared to be an illuminating solution. Generally, the samples have been assigned to two large groups in a good agreement with their vegetal sampling location, samples originating from predominant forest area and samples originating from meadows. Within the first group, two subgroups were identified according to the dominant type of the forest, deciduous or resinous, while within the last group three subgroups were found according to the extend and variety of the meadow.     

IR specular reflectance spectra of KHSO4 single crystal—Dispersion analysis

Polarized specular reflectance IR spectroscopy was used to provide answers regarding dielectric, vibrational and optical properties of the KHSO₄ single crystal. Applying this technique, spectra with polarization along the principal dielectric axes were recorded. It is shown that reflectance IR spectra at arbitrary direction of polarization recorded from one of the principal planes can be easily calculated if the reflectance spectra along the corresponding two principal axes are known. Using dispersion analysis of the reflectance spectra recorded along the principal dielectric axes and employing downhill simplex iteration method, energy loss function together with the real and imaginary parts of the complex index of refraction and the permittivity tensor were obtained. Employing this data, LO-TO splitting of the modes was further calculated. Discussion concerning the assignment of the bands and its relation to the structure is also given.     

ASTM clustering for improving coal analysis by near-infrared spectroscopy

Multivariate analysis techniques have been applied to near-infrared (NIR) spectra coals to investigate the relationship between nine coal properties (moisture (%), ash (%), volatile matter (%), fixed carbon (%), heating value (kcal/kg), carbon (%), hydrogen (%), nitrogen (%) and sulphur (%)) and the corresponding predictor variables. In this work, a whole set of coal samples was grouped into six more homogeneous clusters following the ASTM reference method for classification prior to the application of calibration methods to each coal set. The results obtained showed a considerable improvement of the error determination compared with the calibration for the whole sample set. For some groups, the established calibrations approached the quality required by the ASTM/ISO norms for laboratory analysis. To predict property values for a new coal sample it is necessary the assignation of that sample to its respective group. Thus, the discrimination and classification ability of coal samples by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) in the NIR range was also studied by applying Soft Independent Modelling of Class Analogy (SIMCA) and Linear Discriminant Analysis (LDA) techniques. Modelling of the groups by SIMCA led to overlapping models that cannot discriminate for unique classification. On the other hand, the application of Linear Discriminant Analysis improved the classification of the samples but not enough to be satisfactory for every group considered.     

Study on difference between epidermis, phloem and xylem of Radix Ginseng with near-infrared and infrared spectroscopy coupled with principal component analysis

Ginseng is a precious traditional Chinese herbal medicine. Different parts of ginseng are deemed to have different medicinal values and properties. Rapid and non-destructive methods, such as diffuse reflectance near-infrared spectroscopy (DR-NIR), Fourier transform infrared spectroscopy with attenuated total reflectance (ATR-FTIR), were used to evaluate the differences of epidermis, phloem and xylem in ginseng, respectively. Samples were grounded into 200-mesh fine powder or cut into slices with about 2 mm thickness for DR-NIR and ATR-FTIR spectra measurement, respectively. To explore the classifications between different parts of ginseng, the spectra of DR-NIR and ATR-FTIR were pretreated to calculate first derivative and then was analyzed with principal component analysis (PCA). The PCA results of DR-NIR spectra indicate that epidermis and xylem part of ginseng have distinct difference, and even different positions of epidermis or xylem part show regular and gradual differences. ATR-FTIR spectra directly show that three parts of ginseng are different at 2920, 2852, 1736 and 925.7 cm⁻¹ peaks, especially for epidermis of ginseng. The PCA results of ATR-FTIR spectra yield clear classifications of the three parts of ginseng.     

Bleachability and characterization by fourier transform infrared principal component analysis of acetosolv pulps obtained from sugarcane bagasse

Sugarcane bagasse Acetosolv pulps were bleached by xylanase and the pulps classified by using Fourier transform infrared (FTIR) spectroscopy and principal component analysis (PCA). Pulp was treated with xylanase for 4–8 h with stirring at 30°C. Some samples were further extracted with NaOH for 1 h at 65°C. FTIR spectra were recorded directly from the dried pulp samples by using the diffuse reflectance technique. Reduction in kappa number of 69% was obtained after sequence xylanase (4 h)-alkaline extraction. During bleaching the viscosity decreased only 12%. FTIR-PCA showed that the first three principal components (PCs) explained more than 90% of the total variance of the pulp spectra. PC2×PC1 plot showed that the points related to pulps from sequence xylanase (4 h)-alkaline extraction are different from the other. This group isenlarged by plotting PC3×PC1 or PC3×PC2 containing all pulps submitted to alkaline extraction. PC2 and PC3 are the principal factor for differentiation of the pulps. These PCs suffer influence of the ester bands (1740 and 1244 cm⁻¹). On the other hand, the pulps bleached only with xylanase could not be differentiated from the nonbleached pulps.     

ZnO/BiOI微球的合成及其光催化性能

通过一步溶剂热法合成ZnO/BiOI纳米复合材料,在Bi（NO₃）₃·6H₂O、KI、ZnO和乙二醇（EG）溶剂中,制备出的样品尺寸和形貌采用X射线粉末衍射（XRD）、场发射扫描电镜（FESEM）、高分辨透射电镜（HRTEM）、紫外-可见漫反射光谱（DRS）、X射线光电子能谱（XPS）、N₂吸附-脱附等,对实验所得产物的组成、结构及光学性质等进行表征。以染料罗丹明B（RhB）水溶液和气态乙醛作为降解对象,采用BiOI、ZnO/BiOI和ZnO微纳材料作为光催化剂,通过对BiOI、ZnO/BiOI和ZnO微纳材料在可见光下光催化降解染料罗丹明B（RhB）水溶液和气态乙醛,结果表明多孔微纳材料的ZnO/BiOI具有更高的降解效率,实验表明多孔微纳材料的ZnO/BiOI具有更高的氧空位浓度,因此使其催化活性增强,讨论了其可能的催化活性机理。     

ZnO/BiOI微球的合成及其光催化性能

通过一步溶剂热法合成ZnO/BiOI纳米复合材料,在Bi（NO₃）₃·6H₂O、KI、ZnO和乙二醇（EG）溶剂中,制备出的样品尺寸和形貌采用X射线粉末衍射（XRD）、场发射扫描电镜（FESEM）、高分辨透射电镜（HRTEM）、紫外-可见漫反射光谱（DRS）、X射线光电子能谱（XPS）、N₂吸附-脱附等,对实验所得产物的组成、结构及光学性质等进行表征。以染料罗丹明B（RhB）水溶液和气态乙醛作为降解对象,采用BiOI、ZnO/BiOI和ZnO微纳材料作为光催化剂,通过对BiOI、ZnO/BiOI和ZnO微纳材料在可见光下光催化降解染料罗丹明B（RhB）水溶液和气态乙醛,结果表明多孔微纳材料的ZnO/BiOI具有更高的降解效率,实验表明多孔微纳材料的ZnO/BiOI具有更高的氧空位浓度,因此使其催化活性增强,讨论了其可能的催化活性机理。     

Er3+/Yb3+共掺纳米In2O3的制备及上转换发光

用低温溶剂热法以乙二醇为溶剂合成了Er3+和Yb3+共掺的In2O3纳米晶。用X射线衍射(XRD)、透射电镜(TEM)、漫反射光谱和上转换发光光谱对样品进行了分析。XRD和TEM结果表明,产物为纯的立方相In2O3结构,粒径约为30 nm;漫反射光谱显示了In2O3∶Er3+,Yb3+纳米晶在522、653和975 nm附近有3个吸收带;在980 nm近红外光激发下,样品发射出中心波长为525及555 nm的绿光和662 nm的红光,分别对应于Er3+的2H11/2→4I15/2、4S3/2→4I15/2和4F9/2→4I15/2跃迁;研究了Er3+和Yb3+离子的不同掺杂浓度对发光强度的影响,确定了Yb3+和Er3+离子的最佳掺杂浓度均为3%;双对数曲线显示绿光和红光的发射过程均为双光子吸收过程,对样品的上转换发光机制进行了初步讨论。     

Photocatalytic oxidation of organic dyes with nanostructured zinc dioxide modified with silver metals

Silver-doped nano-ZnO samples with different Ag loadings were prepared by a one-spot solvothermal method. The structure, physico-chemical and optical properties of the products are characterized by using X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive X-ray analysis (EDS), diffuse reflectance spectroscopy (DRS) and photoluminescence spectra (PL). The photocatalytic activity of the as-prepared samples was examined by using photocatalytic oxidation of methyl orange (MO) as a model reaction, and the effects of the noble metal content on the photocatalytic activity were investigated. The results indicated that the photocatalytic activity of ZnO nanoparticles can be greatly improved by depositing appropriate amount of noble metal on their surface as electron scavengers. In addition, a key mechanism was proposed in order to account for the enhanced activity. The enhancement for the photocatalytic activities can be attributed to the interaction between Ag particles and ZnO, which made Ag particles act as electron traps to effectively separate the excited electron-hole pairs.     

Identification of origin of coal from the Ostrava-Karvina Mining District by infrared spectroscopy and discriminant analysis

Infrared (IR) spectra of coal from five mines of the Ostrava-Karvina Mining District were collected using diffuse reflectance techniques. The spectral data were classified by the application of discriminant analysis. The aim of this paper is to test out identification of coal origin by IR spectroscopy and discriminant analysis. The results of this study confirm that infrared spectroscopy together with multivariate statistical methods could provide a powerful discriminating tool for the identification of origin of the most of coal from the Ostrava-Karvina Mining District.     

Influence of synthesis methods on zirconium doped titania photocatalysts

Synthesis of various zirconium doped titania based photocatalysts were carried out by adapting different synthetic strategies. Doping is done on commercially available anatase titania, sol-gel titania and template mediated sol gel titania. A comparative study of the various prepared photocataysts was done using physico-chemical characterization techniques such as X-ray diffraction (XRD), surface area- pore volume measurements, UV-VIS Diffuse reflectance spectra (DRS), elemental analysis (XRF) and transmission electron microscopic (TEM) studies. The effect of zirconium and preparation methods on the photocatalytic degradation of methylorange is studied extensively. Both the surface properties and photo activity of zirconium doped titania were found to have a great dependence on the preparation methods. Among the different photocatalytic systems, the catalyst prepared by doping in the presence of urea template was found to produce a maximum photodegradation of 97.5%.     

A program for calculating Mahalanobis distances using principal component analysis

A technique for pattern recognition analysis of near-infrared reflectance spectra is described. Classification of samples is achieved by using the Mahalanobis distances of spectra in a principal component subspace. Probability levels for class membership are determined from the Chi-squared distribution.     

Natural history specimen analysis using micro FT-IR attenuated total reflectance spectroscopy and transmission electron microscopy

A combination of micro Fourier transform infrared (FT-IR) attenuated total reflectance (ATR) spectroscopy and transmission electron microscopy (TEM) provided a complete analysis of the interaction between nematode cuticle structure and preservation fluids. Spectroscopic results were successfully correlated with TEM results. While fresh nematode cuticle yielded uniform spectra, damaged cuticles were characterised by large spectrum to spectrum variations in the 1000-1100 cm-1 region. An important outcome of this investigation was the demonstrated potential of micro FT-IR ATR as a technique for the analysis of challenging natural history samples.     

The potential of field spectroscopy for the assessment of sediment properties in river floodplains

Investigations have shown that visible-near-infrared (VNIR) spectroscopy can accurately determine soil properties under laboratory conditions. In situ assessment of soil properties is of great benefit for several applications, as spectra can be acquired fast and almost continuously. The present study used partial least squares (PLS) regression to establish a relationship between soil reflectance spectra measured under field conditions and the organic matter and clay content of the soil. Spectra were acquired with a fieldspectrometer in a recently reconstructed floodplain along the river Rhine in The Netherlands. Several spectral pre-processing methods were employed to improve the performance and robustness of the models. Results indicate that, under varying surface conditions, field spectroscopy in combination with multivariate calibration does result in a qualitative relation for organic matter (R²=0.45) and clay content (R²=0.43) while under laboratory conditions more accurate results are obtained (R²=0.69 and 0.92, respectively). Soil moisture and vegetation cover had a negative influence on the prediction capabilities for both soil properties. Although the performance of the spectra measured in situ is not as accurate as physical analysis, the accuracy obtained is useful for rapid soil characterisation and remote sensing applications.     

Influence of composition and roughness on the pigment mapping of paintings using mid-infrared fiberoptics reflectance spectroscopy (mid-IR FORS) and multivariate calibration

Mid-infrared fiberoptics reflectance spectroscopy (mid-IR FORS) is a very interesting technique for artwork characterization purposes. However, the fact that the spectra obtained are a mixture of surface (specular) and volume (diffuse) reflection is a significant drawback. The physical and chemical features of the artwork surface may produce distortions in the spectra that hinder comparison with reference databases acquired in transmission mode. Several studies attempted to understand the influence of the different variables and propose procedures to improve the interpretation of the spectra. This article is focused on the application of mid-IR FORS and multivariate calibration to the analysis of easel paintings. The objectives are the evaluation of the influence of the surface roughness on the spectra, the influence of the matrix composition for the classification of unknown spectra, and the capability of obtaining pigment composition mappings. A first evaluation of a fast procedure for spectra management and pigment discrimination is discussed. The results demonstrate the capability of multivariate methods, principal component analysis (PCA), and partial least squares discrimination analysis (PLS-DA), to model the distortions of the reflectance spectra and to delimitate and discriminate areas of uniform composition. The roughness of the painting surface is found to be an important factor affecting the shape and relative intensity of the spectra. A mapping of the major pigments of a painting is possible using mid-IR FORS and PLS-DA when the calibration set is a palette that includes the potential pigments present in the artwork mixed with the appropriate binder and that shows the different paint textures. Graphical Abstract

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Coal analysis by application of the partial least squares method to infrared spectra

Summary A method for the rapid characterization of brown coals based on the application of a powerful method of principal component analysis, the Partial Least Squares method (PLS), is described. A data catalogue of 44 brown coals from different deposits of East European and Asian countries was used, which lists analyses of several coal parameters. Infrared spectra of brown coals were recorded and different coal properties were predicted with the help of PLS. The results show that, with the PLS-method used, several coal properties can be predicted and it is possible to describe the classification of a coal for several technological processes. The developed method is useful because of the multiplicity of information obtained within a short time and because it is possible to replace lengthy classical methods.     

Testing of the Region of Murcia soils by near infrared diffuse reflectance spectroscopy and chemometrics

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 additional samples of the same area not considered to build the model. Organic matter, CaCO₃, pH, electrical conductivity (EC), together with several trace metals as Cr, Co, Ni, Cu, Zn, As, Se, Cd and Tl, were employed as characteristic parameters of the soils under study, and found results evidenced that PLS-NIR provides a valuable tool for screening purposes providing residual predictive deviations which ranged from 0.9 to 1.5 as a function of the considered parameter.     

Micro spectroscopy FTIR reflectance examination of paint binders on ground chalk

Summary A restorer's questions on chemical analysis of paint binders to support his complicated work has always had an exceptional appeal for chemists. Non-destructive surface analysis of rather complex materials such as paint binders is possible. The advantages of vibrational spectroscopy related to the details about chemical structure of organic compounds have been combined with sophisticated methods of multivariate data analysis. Reflectance spectra of several paint binders on ground chalk were measured using a fast, sensitive FTIR spectrometer equipped with an infrared microscope. The initial reflectance spectra include sufficient structural information to allow successful classification by hierarchical cluster analysis (HCA). Similarities between the several binders are plotted as dendrograms which are well structured. Their explanation will be discussed in detail. Finally the postulated feature sets will be checked up by principal component analysis (PCA) as to their relevance and information content.     

Photophysics on surfaces: determination of absolute fluorescence quantum yields from reflectance spectra

A method for the calculation of absolute fluorescence quantum yields for dyes attached to solid particles based on reflectance measurements is reported. The same procedure allows calculation of true reflectance spectra (free of fluorescence) for highly fluorescent materials as well. Samples ofcresyl violet were immobilized by adsorption on microgranular cellulose in the concentration range 4.5 x 10(-9) to 3.8 x 10(-6) mol g(-1). Diffuse and total reflectance spectra were recorded with and without insertion of an optical absorption filter between the output of the integrating sphere of a reflectance spectrometer and the photodetector in order to block fluorescence partially. From these data, the relative emission spectrum of the dye, the filter transmission spectrum, and the detector sensitivity, true reflectances and absolute fluorescence quantum yields were recovered. Observed fluorescence quantum yields, affected by dye aggregation and inner filter effects, were concentration and wavelength dependent, ranging approximately between 0.1 and 0.6. The analysis of remission function spectra showed that dye aggregation is negligible up to a concentration of 1.41 x 10(-7) mol g(-1). Fluorescence data were corrected for reemission and reabsorption using a suitable model [Lagorio, M. G.; Dicelio, L. E.; Litter, M. I.; San Roman, E. J. Chem. Soc., Faraday Trans. 1998, 94, 419]. Application of this model to samples showing no aggregation yielded a wavelength-independent true fluorescence quantum yield of 0.60 +/- 0.05, similar to values found in solution. The usage of cresyl violet as a reference for the evaluation of fluorescence quantum yields for weakly fluorescing samples in the solid phase is discussed.