Diffuse Reflectance Spectroscopy Measurements Research Articles

Hyperspectral remote sensing of evaporate minerals and associated sediments in Lake Magadi area, Kenya

Pleistocene to present evaporitic lacustrine sediments in Lake Magadi, East African Rift Valley, Kenya were studied and mapped using spectral remote sensing methods. This approach incorporated surface mineral mapping using space-borne hyperspectral Hyperion imagery together with laboratory analysis, including visible, near-infrared diffuse reflectance spectroscopy (VNIR) measurements and X-ray diffraction for selected rock and soil samples of the study area. The spectral signatures of Magadiite and Kenyaite, which have not been previously reported, were established and the spectral signatures of trona, chert series, volcanic tuff and the High Magadi bed were also analyzed.Image processing techniques, MNF (Minimum Noise Fraction) and MTMF (Mixture Tuned Matched Filtering) using a stratified approach (image analysis with and without the lake area), were used to enhance the mapping of evaporates. High Magadi beds, chert series and volcanic tuff were identified from the Hyperion image with an overall mapping accuracy of 84.3%. Even though, the spatial distribution of evaporites and sediments in Lake Magadi area change in response to climate variations, the mineralogy of this area has not been mapped recently. The results of this study shows the usefulness of the hypersspectral remote sensing to map the surface geology of this kind of environment and to locate promising sites for industrial open-pit trona mining in a qualitative and quantitative manner.

Critical comparison of diffuse reflectance spectroscopy and colorimetry as dermatological diagnostic tools for acanthosis nigricans: a chemometric approach.

Quantification of skin changes due to acanthosis nigricans (AN), a disorder common among insulin-resistant diabetic and obese individuals, was investigated using two optical techniques: diffuse reflectance spectroscopy (DRS) and colorimetry. Measurements were obtained from AN lesions on the neck and two control sites of eight AN patients. A principal component/discriminant function analysis successfully differentiated between AN lesion and normal skin with 87.7% sensitivity and 94.8% specificity in DRS measurements and 97.2% sensitivity and 96.4% specificity in colorimetry measurements.

SiO2 Aerogel Templated, Porous TiO2 Photoanodes for Enhanced Performance in Dye-Sensitized Solar Cells Containing a Ni(III)/(IV) Bis(dicarbollide) Shuttle

High-area photoanodes consisting of silica aerogels, overcoated by atomic-layer-deposited TiO2, were fabricated on transparent conducting oxide platforms for their use in dye-sensitized solar cells (DSCs) in a similar fashion as previously described. These films were characterized by scanning electron microscopy, X-ray diffraction, diffuse reflectance spectroscopy, gas adsorption, and light and dark electrochemical impedance measurements. The use of aerogel-templated photoanodes in DSCs with a Ni(III/IV) bis(dicarbollide) redox shuttle results in a greater than 2-fold enhancement in photocurrent densities, in comparison to similar cells containing photoanodes constructed from TiO2 nanoparticles. This improvement in photocurrent is attributed to a combination of improved electron transport, increased recombination resistance across the TiO2/electrolyte interface, and increased light scattering within the aerogel films. As a result, DSC charge collection efficiencies with this comparatively fast exchanging outer-sphere redox couple are improved in the TiO2 aerogel templated photoanode.

Improved model for myocardial diffuse reflectance spectra by including mitochondrial cytochrome aa3, methemoglobin, and inhomogenously distributed RBC

The aim of this study was to compare a previously used light transport model (I) comprising the chromophores hemo- and myoglobin, fat, and water, with two extended models, where the chromophores of cytochrome aa3, methemo- and metmyoglobin are added (model II), and in addition, accounting for an inhomogenous hemoglobin distribution (model III). The models were evaluated using calibrated diffuse reflectance spectroscopy measurements on the human myocardium. Model II proved a significantly better spectral fitting, especially in the wavelength ranges corresponding to prominent absorption characteristics for the added chromophores. Model III was significantly better than model II and displayed a markedly higher tissue fraction and saturation of hemo- and myoglobin. The estimated tissue chromophore fractions, saturation and oxidation levels, were in agreement with other studies, demonstrating the potential of diffuse reflectance spectroscopy measurements for evaluating open heart surgery. However, the choice of chromophores and vessel packaging effects in the light transport model has a major effect on the results.

Performance of Three Identical Spectrometers in Retrieving Soil Reflectance under Laboratory Conditions

A wide range of electronic and mechanical noise factors can affect soil spectra when using different instruments or even when repeating a specific sample's measurements with the same spectrometer. In soil samples where very weak spectral features are monitored for chemometric purposes, alterations in wavelength location, peak absorption shape, or albedo intensity can limit the use of previously developed spectral models. To quantify this alteration and propose a standardization method, 12 soil samples and three different materials for internal standards (sand, glass and polyethylene) were analyzed. This population was concurrently measured with three identical spectrometers using a strict measurement protocol, and then by different operators with different protocols. Significant changes in the soil spectra were found when different operators performed the measurements, being reduced >50% when the strict protocol was applied. Sand was found to be the ideal internal standard for correcting the spectra to a reference spectrometer, even when different measuring protocols were used. This standardization also showed an improvement in the prediction of soil properties when applying chemometric spectral models even with different instruments, concluding that the use of an internal standard and a strict protocol must be applied for soil spectral measurements. As the measuring factors described in this research also affect any infrared diffuse reflectance spectroscopy measurements, the proposed method should be applicable to any instrumentation and configuration being used. This is crucial to enabling spectral comparisons between different spectrometers or, more importantly, to establishing robust chemometric models and to exchange soil spectral information.

The field emission of vacuum filtered graphene films reduced by microwave

A green, convenient, and inexpensive approach to producing graphene field emitters has been developed. Graphite oxide (GO) produced by hummer method was reduced to graphene in a microwave synthesis system. The vacuum filtration method made it possible to form pure and uniform graphene thin films without any additives and it's easy to transfer to other substrates. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV–vis diffuse reflectance spectroscopy (UV–vis) measurements proved that the graphene prepared by microwave has nearly the same reduction level as that prepared by hydrazine. The results of field emission testing demonstrated that graphene films reduced by microwave are more suitable as field emitters than those reduced by hydrazine, which pave a way to mass-produce low-cost graphene emitter for field emission applications.

Probe pressure effects on human skin diffuse reflectance and fluorescence spectroscopy measurements

Diffuse reflectance and fluorescence spectroscopy are popular research techniques for noninvasive disease diagnostics. Most systems include an optical fiber probe that transmits and collects optical spectra in contact with the suspected lesion. The purpose of this study is to investigate probe pressure effects on human skin spectroscopic measurements. We conduct an in-vivo experiment on human skin tissue to study the short-term (<2 s) and long-term (>30 s) effects of probe pressure on diffuse reflectance and fluorescence measurements. Short-term light probe pressure (P0<9 mN∕mm2) effects are within 0 ± 10% on all physiological properties extracted from diffuse reflectance and fluorescence measurements, and less than 0±5% for diagnostically significant physiological properties. Absorption decreases with site-specific variations due to blood being compressed out of the sampled volume. Reduced scattering coefficient variation is site specific. Intrinsic fluorescence shows a large standard error, although no specific pressure-related trend is observed. Differences in tissue structure and morphology contribute to site-specific probe pressure effects. Therefore, the effects of pressure can be minimized when the pressure is small and applied for a short amount of time; however, long-term and large pressures induce significant distortions in measured spectra.

Effect of Co+ implantation on structural and optical properties in single-crystal TiO2

Ion implantation technique is used for doping Co+ to single crystal TiO2(001). The implanted energies and the fluences of Co+ are 40keV and 11016cm-2; 80 keV and 51015, 11016, 51016, 11017cm-2; 120 keV and 11016cm-2, respectively. And then, the structural and the optical properties of all samples are characterized by using X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), UV - Vis diffuse reflectance spectroscopy (UV-Vis DRS), and these impurities in implanted samples are also analyzed. From the XRD spectra of implanted samples we observe that the greater damage is caused with the increase of the kinetic energy of incident ions. UV - Vis diffuse reflectance spectroscopy measurement shows that the absorbance of visible band is enhanced in all the implanted samples, and the optical band gap decreases with implanted ion fluence increasing from 51015cm-2 to 51016cm-2.

Preparation of Sm-loaded brookite TiO 2 photocatalysts

Pure and Sm-loaded brookite nanoparticles and thin films were prepared using TiCl 4 as precursor of TiO 2. The samples were characterized by X-ray diffraction (XRD), specific surface area (SSA) determination, diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) measurements. The photocatalytic activity of the powders was investigated by employing the photodegradation of 4-nitrophenol in a liquid–solid system whilst the photoreactivity of the films was tested by evaluating the rate of degradation of 2-propanol in a gas–solid system. Loading with Sm resulted in a significant improvement of the photoreactivity of brookite and the beneficial effect was attributed to an increased separation efficiency of the photogenerated electron–hole pairs. The content of samarium was an important factor affecting the photocatalytic activity. The optimum amount of samarium was 1% for the powders and 0.1% for the films. There is a relationship between PL spectra and photoactivity, namely, the lower the PL intensity, the higher the photocatalytic activity.

Visible-light-induced photocatalytic degradation of methylene blue with polyaniline-sensitized [formula omitted] composite photocatalysts

A series of polyaniline (PANI)-sensitized TiO 2 composite photocatalysts (PANI/TiO 2) with different mass ratio of polyaniline to nano- TiO 2 (P25) (1:200–1:700) were facilely prepared by mixing a tetrahydrofuran (THF) solution of camphorsulfonic acid (CSA)-doped polyaniline (PANI-CSA) and TiO 2 nanoparticle suspension in ethanol. Transmission electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible diffuse reflectance spectroscopy (DRS) measurements were used to characterize the resulting composite photocatalysts, and their photocatalytic activities were investigated by degrading methylene blue (MB) under visible-light irradiation ( λ > 400 nm ). The results showed that the surface polyaniline sensitization had no effect on the crystalline structure but aggravated the agglomeration of TiO 2 nanoparticles by forming multi-particles. After being sensitized by PANI, the light response of TiO 2 was extended to visible-light regions and the photocatalytic activity of the composite photocatalysts was enhanced. MB could be degraded more efficiently on PANI/TiO 2 than on the bare TiO 2 when the mass ratio of polyaniline to TiO 2 was in the range 1:400–1:700, and the optimum sensitized effect was found at a mass ratio of 1:500. The determined rate constant of MB degradation over PANI/TiO 2 (1:500) was 0.01515 min −1, which is 1.57 times higher than that of bare TiO 2 (0.00963 min −1). Furthermore, PANI/TiO 2 composite photocatalysts showed good photocatalytic stability after five runs under visible light. The enhancement of photocatalytic activity of the composite photocatalysts could be attributed to the sensitizing effect of PANI. A possible mechanism for the photocatalytic degradation of methylene blue is also proposed.

Integrated autofluorescence endoscopic imaging and point-wise spectroscopy for real-time in vivo tissue measurements

We report on the development of an integrated point-wise spectroscopy and autofluorescence (AF) endoscopic imaging technique for real-time in vivo tissue measurements at endoscopy. We implement a unique point spectrum optical design to realize real-time AF imaging and AF or diffuse reflectance (DR) spectroscopy measurements from a small area of tissue of interest on the AF image. We demonstrate that both the AF image and the point-wise AF/DR spectra can be simultaneously acquired from the oral cavity in vivo within 0.1 s, suggesting the potential of the integrated spectroscopy and endoscopic imaging technique developed to facilitate in vivo tissue diagnosis and characterization at endoscopy.

Poster — Thur Eve — 09: Effects of Small Sample Size on Diffuse Reflectance Spectroscopy for the Identification of Brain Tumours

An optical system using diffuse reflectance spectroscopy (DRS) and time‐resolved laser induced fluorescence spectroscopy (TR‐LIFS) is being developed to identify surgical margins during brain tumour resection. Since initial trials will be performed ex vivo on small samples, we investigated our ability to perform DRS for these small sample volumes. We examined both the effects of decreasing sample volume on the DRS signal and decreasing probe size on our ability to recover optical properties. Sample volume effects were studied by performing DRS measurements on bovine brain tissue samples of various sizes and comparing the signals to those for very large samples. A decrease in DRS signal strength was observed at sample volumes of less than 500 mm3. Probe size effects were studied using Monte Carlo simulations to obtain the spatially‐resolved reflectance using the optical properties of human brain tissue. Varying amounts of noise were added to the reflectance, and optical properties were recovered by fitting to Monte Carlo generated reflectance curves. The recovered properties were compared to their actual values as the maximum radius used for fitting was reduced. Our ability to recover the absorption coefficient was improved when fitting to absolute reflectance data.

Speciation of Copper in Spherical Mesoporous Silicates: From the Microscale to Angstrom

MCM-41 type mesoporous silicate particles with spherical morphology containing copper nanospecies were synthesized by conventional hydrothermal synthesis. A narrow distribution of silicate particle sizes between 2 and 3 μm and a well-defined mesoporosity were evidenced by electronic microscopy, even for loadings of copper of about 10 wt %. Moreover, CuO nanoparticles ∼30 nm in diameter occluded in the amorphous silica, possibly filling some secondary mesoporosity, were also detected. By Fourier transform infrared spectroscopy with pyridine adsorption and UV−vis diffuse reflectance spectroscopy measurements together with reduction experiments under H2 flow, a detailed study about the relationship between copper loading degree and the acid properties with the local isolated Cuδ+ species surroundings was performed. The incorporation of copper into the silica framework generated surface Lewis acid sites which increase with copper content. The origin of these acid sites could be attributed to the presence of isolated Cuδ+ species possibly coordinated with the framework oxygen atoms. It is noteworthy that Brønsted acid sites were not detected in our materials. By X-ray absorption near edge structure spectroscopy, we determine the coexistence of copper +1 and +2 states. The average coordination numbers calculated from extended X-ray absorption fine structure experiments are consistent with a mixture of nanosized species of copper: CuO nanoparticles, besides isolated Cuδ+ cations located in framework positions with oligonuclear clusters like [Cuδ+···Oδ−···Cuδ+]n in its surroundings, confined within the pores.

Guanidinium-Enhanced Production of Hydrogen on Nafion-Coated Dye/TiO2 under Visible Light

Guanidinium cations (abbreviated as G) enhanced the visible light-induced hydrogen production by three times in the dye(Ru(bpy)32+)-sensitized system using TiO2 nanoparticles coated with nafion polymer. The enhanced photoactivity in the presence of G adsorbed on the nafion coating was related to the retardation of the charge recombination between the electrons injected into the TiO2 conduction band (CB) and the oxidized dye molecules, which was confirmed by time-resolved diffuse reflectance spectroscopic measurements. It is proposed that G cations located near the TiO2 surface repel the oxidized dyes to retard the recombination with CB electrons. In addition, the dye luminescence in nafion was enhanced in the presence of G, which was ascribed to the retardation of self-quenching of the excited dyes. The dual roles of G in the nafion layer increase the photoelectron density in TiO2 CB and subsequently enhance the production of hydrogen.

Preparation, Characterization, and Photophysical Study of Thiazine Dyes within the Nanotubes and Nanocavities of Silicate Host: Influence of Titanium Dioxide Nanoparticle on the Protonation and Aggregation of Dyes

The photophysical properties of thionine and methylene blue have been investigated in the absence and presence of titanium dioxide nanoparticles encapsulated into the different nanoporous silicate materials: zeolite-Y, ZSM-5, and MCM-41. The titanium dioxide loaded zeolite samples were prepared by the ion-exchange method and the formation of TiO2 nanoparticles into the zeolite host materials was ascertained by UV−visible diffuse reflectance spectroscopy and ICP-OES measurement. The crystallinity of the silicate host was found to be intact as characterized by powder X-ray diffraction, nitrogen adsorption and desorption isotherm studies and TEM. The encapsulation of TiO2 into the zeolite host leads to the protonation of the dyes, indicating that the acidity of channels increased significantly in the presence of titanium dioxide in the zeolite host. In the case of zeolite-Y, with increasing loading of titanium dioxide nanoparticles, the aggregation of dyes is found to decrease. The absorption and emission spectra of the dyes, thionine and methylene blue, encapsulated into the nanochannel of ZSM-5 show a shift as compared to the spectra of the dyes in aqueous solution indicating that the planarity of the dye was perturbed due to the confinement effect of the nanochannels. ZSM-5 host with encapsulated titanium dioxide nanoparticles shows an increase in the fluorescence intensity of thionine present in the channels that is attributed to the presence of the dye in hydrophobic channels of the ZSM-5 host. The influence of the hydrophobic environment of the host on dye in the excited state was investigated by the pico- and femtosecond time-resolved spectral studies. The N-methyl-substituted analogue of thionine, methylene blue shows a different behavior due to the bulky nature of the dye. The aggregation of methylene blue in the cavities of zeolite-Y is less prevalent and the isomeric forms of the dye are not observed in this case in the excited state of the dye in the host channel.

Synthesis of floriated ZnFe2O4 with porous nanorod structures and its photocatalytic hydrogen production under visible light

Floriated ZnFe2O4 with porous nanorod structures were successfully synthesized via mild hydrothermal and calcination processes by using cetyltrimethylammonium bromide (CTABr) as a template-directing reagent. The resulting ZnFe2O4 was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS) and nitrogen adsorption measurement. It was found that the floriated ZnFe2O4 nanostructures were composed of porous nanorods with an average length of 122 nm and diameter of 29 nm. The obtained ZnFe2O4 with a bandgap of ∼1.94 eV was firstly used as a visible-light-driven photocatalyst for hydrogen production, and exhibits remarkable photostability in an aqueous suspension by using CH3OH as a sacrificial reagent. Moreover, the possible photo-reaction mechanism for the hydrogen production from CH3OH aqueous solution was proposed for better understanding the photocatalytic behavior of ZnFe2O4 without Pt-loading.

Magnetization improvement of Fe-pillared clay with application of polyetheramine

Polyetheramine D2000 (O,O′-Bis(2-aminopropyl)polypropyleneglycol) was used as structural regulator to modify Fe-pillared clay mineral, and treated with acetic acid vapor prior to calcination for improving the magnetization of magnetically modified clay mineral. The magnetization of the magnetically modified clay mineral was improved to 26.78 emu g − 1 with introduction of polyetheramine D2000 to Fe-pillared clay mineral at 70 °C. The molecular spectroscopy including FT-IR and FT-Raman, thermogravimetric analysis (TG) were used to characterize the magnetically modified clay mineral. XRD, SEM and TEM, UV–Vis Diffuse Reflectance spectroscopy (UVDRS) and magnetization measurement were applied to explore the structural information of the magnetically modified clay mineral. The results suggested that the magnetic species of γ-Fe 2O 3 nanophase particles were embedded on the surface of the modified clay mineral and the magnetization was improved significantly due to the increase of iron content by addition of polyetheramine D2000. A possible mechanism was suggested that the polyetheramine D2000 rodlike micelles were formed at 70 °C and interacted with polyhydrated iron to form adducts, which were treated in acetic acid vapor before calcination at 400 °C to produce magnetic species embedded on the surface of Fe-pillared clay mineral. The performance of the magnetically modified clay mineral was evaluated by adsorption of methyl orange and intensified separation by external magnetic field. The results indicate that its excellent performance on adsorption and magnetic separation makes a comprehensive application potential in chemical engineering and environmental pollution control.

The relationship between diffuse spectral reflectance of the soil and its cation exchange capacity is scale-dependent

Diffuse reflectance spectroscopy (DRS) is increasingly being used to predict numerous soil physical, chemical and biochemical properties. However, soil properties and processes vary at different scales and, as a result, relationships between soil properties often depend on scale. In this paper we report on how the relationship between one such property, cation exchange capacity (CEC), and the DRS of the soil depends on spatial scale. We show this by means of a nested analysis of covariance of soils sampled on a balanced nested design in a 16 km × 16 km area in eastern England. We used principal components analysis on the DRS to obtain a reduced number of variables while retaining key variation. The first principal component accounted for 99.8% of the total variance, the second for 0.14%. Nested analysis of the variation in the CEC and the two principal components showed that the substantial variance components are at the > 2000-m scale. This is probably the result of differences in soil composition due to parent material. We then developed a model to predict CEC from the DRS and used partial least squares (PLS) regression do to so. Leave-one-out cross-validation results suggested a reasonable predictive capability (R2 = 0.71 and RMSE = 0.048 molc kg− 1). However, the results from the independent validation were not as good, with R2 = 0.27, RMSE = 0.056 molc kg− 1 and an overall correlation of 0.52. This would indicate that DRS may not be useful for predictions of CEC. When we applied the analysis of covariance between predicted and observed we found significant scale-dependent correlations at scales of 50 and 500 m (0.82 and 0.73 respectively). DRS measurements can therefore be useful to predict CEC if predictions are required, for example, at the field scale (50 m). This study illustrates that the relationship between DRS and soil properties is scale-dependent and that this scale dependency has important consequences for prediction of soil properties from DRS data.

Study on highly visible light active Bi2O3 loaded ordered mesoporous titania

The well-defined two-dimensional (2D) hexagonal mesoporous nanocrystalline anatase TiO2 was synthesized by the nonhydrolytic evaporation-induced co-assembly (EISA) of non-ionic amphiphilic triblock-copolymer template, titanium tetrachloride and tetrabutyl titanate. The ordered mesoporous TiO2 (M-TiO2) was loaded with different % of Bi2O3 using the wet impregnation method. For comparison Degussa P25 impregnated with Bi2O3 was also prepared. The samples were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy, photoluminescence spectra (PLS), Fourier transform infrared spectra (FT-IR), N2 adsorption–desorption (BET) and X-ray photoelectron spectroscopy (XPS) techniques. XRD and Raman spectra showed the pore wall was composed of anatase. 1.0% Bi2O3 loaded M-TiO2 revealed the well-ordered mesostructure. UV–vis diffuse reflectance spectroscopy measurements showed an extension of light absorption into the visible region. PLS analysis indicated that the electron–hole recombination rate have been effectively inhibited when Bi2O3 was loaded with ordered M-TiO2. The photo oxidation efficiency was evaluated by methyl orange (MO) and 2,4-dichlorophenol (2,4-DCP) degradation under visible illumination. The samples loaded with different % of Bi2O3 showed higher photocatalytic activity than M-TiO2 and Bi2O3 loaded P25. The catalyst exhibited high activity due to the Bi2O3-photosensitization and well-ordered 2D pore structure. The ordered mesoporous channels facilitate mass transport of the organic pollutants. TiO2 could extend the spectral response from UV to visible region because of Bi2O3-photosensitization which make the Bi2O3 loaded M-TiO2 photocatalyst visible light responsive.

The record of changing hematite and goethite accumulation over the past 22 Myr on the Chinese Loess Plateau from magnetic measurements and diffuse reflectance spectroscopy

High‐field isothermal remanence (HIRM) and diffuse reflectance spectroscopy (DRS) were used to characterize hematite and goethite in a suite of bulk and particle‐sized fractioned samples from the Chinese Loess Plateau, representing the main changes in magnetic mineralogy over the past 22 Myr. The record of DRS‐defined hematite largely reflects variations in the pedogenic fraction (&lt;2 μm). By contrast, the detrital fraction (&gt;8 μm) makes the main contribution to goethite concentrations in the bulk samples. Pedogenic goethite concentrations generally vary inversely with those of hematite. The lack of consistent correlations between HIRM‐inferred mineral content and DRS measurements casts doubt on the validity of using HIRM to characterize the concentrations and relative proportions of hematite and goethite in sediments representing a long time span or a wide grain size distribution. The progressive decline in the coercivity of the antiferromagnetic minerals in bulk samples throughout the whole period is mainly an expression of changes in the detrital fraction, reflecting changes in the source region, possibly involving increased aluminum substitution. The good correlation between DRS‐defined hematite and frequency‐dependent magnetic susceptibility in several chronologically defined subgroups of samples is consistent with the hypothesis that maghemite forms a transitional phase in a weathering sequence from ferrihydrite to hematite. The results shed new light on using HIRM to characterize hematite and goethite in sediments and on the history of weathering and climate change over the past 22 Myr in the dust source regions and on the Loess Plateau.