Diffuse Reflectance Spectroscopy Techniques Research Articles

Sunlight active photocatalytic studies of Fe2O3 based nanocomposites developed via two-pot synthesis technique

The Fe2O3@MgO, Fe2O3@Mn2O3, and Fe2O3@Co3O4 nanocomposites were developed using a two-pot wet chemical procedure. The structure and the phase were confirmed using the Powder X-Ray diffraction tool (PXRD). The optical properties of the prepared materials were analyzed using Photoluminescence (PL) and Diffuse Reflectance Spectroscopy (DRS) technique. Surface morphology and elemental composition of the prepared samples were studied by Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray Spectroscopy (EDAX). The porosity and the surface area of the materials were studied by Brunauer–Emmett–Teller (BET) analysis. The functional group present in the prepared material is analyzed by Fourier transforms IR analysis (FT-IR). The photocatalytic analysis was done using Methylene Blue (MB), Rhodamine B (RhB) and Phenol. Further the mineralizations of the pollutants are studied by COD experiment and also the radical scavenger experiments are carried out.

Solution combustion synthesized TiO2/Bi2O3/CuO nano-composites and their photocatalytic activity using visible LEDs assisted photoreactor

In this work we have synthesized a series of binary TiO2/Bi2O3 and ternary TiO2/Bi2O3/CuO composites having different amount of Bi2O3 and CuO using the facile solution combustion approach. The characteristics of samples were identified using the X-ray diffraction (XRD), X- ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), photoluminescence (PL) spectroscopy and UV–vis diffuse reflectance spectroscopy (UVDRS) techniques. The Rhodamine B was taken as the organic pollutant to determine the photocatalytic efficiency of the materials under ultra-low power consumption visible LEDs as the source of light. The results demonstrate that the synthesized compounds possess good crystallinity and improved optical characteristics after introduction of Bi2O3 and CuO. The ternary sample having 10% of Bi2O3 and 10% of CuO showed the highest photoremoval of RhB which might be due of the formation of heterojunctions and improved optical characteristics towards the visible region. The beauty of the synthesized samples is their fast rate of removal of pollutant under visible LEDs which is beneficial for development of cost-effective water purification technique.

Characterization of TiO2-activated carbon onto adsorption and photocatalytic properties and its application

This study investigates the characterization of TiO2 in conjunction with activated carbon (AC) on its adsorption and photocatalytic properties. TiO2 in the absence and presence of AC were prepared by the sol-gel method. TiCl4 was used as a precursor to reduce using acidic solution during preparation process. The effects of the amount of AC on the characteristics of composites were investigated. TGA technique was used to evaluate the amount of TiO2 and AC in TiO2/AC composite. The adsorption properties of TiO2/AC were characterized using XRD, TEM, N2 adsorption/desorption, FTIR and UV–Vis diffuse reflectance spectroscopy techniques. The photocatalytic activities of the composites were investigated by measuring the removal of acid dye. Results showed that the specific surface area of TiO2/AC increased with increasing mass fraction of AC, while the energy band gap was reduced. It was clearly shown that TiO2 in the presence of AC produced a synergistic effect of the composite and led to an increase in photocatalytic performance. Also, the reuse of TiO2 with 20% AC nanocomposites for dye removal showed a high reuse efficiency above 90% in photocatalytic dye degradation.

A novel method for the nondestructive classification of different-age Citri Reticulatae Pericarpium based on data combination technique.

The quality of Citri Reticulatae Pericarpium (CRP) is closely correlated with the aging time. However, CRPs in different storage ages are similar in appearance, and the young CRP may be labeled as the aged one to obtain the excess profit by some unscrupulous traders. Most traditional analysis methods are laborious and time‐consuming, and they can hardly realize the nondestructive classification. In this paper, a novel method based on near‐infrared diffuse reflectance spectroscopy (NIRDRS) and data combination technique for the nondestructive classification of different‐age CRPs was proposed. The CRPs in different storage ages (5, 10, 15, 20, and 25 years) were measured. The near‐infrared spectra of outer skin and inner capsule were obtained. Principal component analysis (PCA), soft independent modeling of class analogy (SIMCA), and Fisher's linear discriminant analysis (FLD), with different data pretreatment methods, were used for the classification analysis. Data combination of the outer skin and inner capsule spectra was discussed for further improving the classification results. The results show that multiple sensors provide more useful and complementary information than a single sensor does for improving the prediction accuracy. With the help of data combination strategy, 100% prediction accuracy can be obtained with both second‐order derivative–FLD and continuous wavelet transform–multiplicative scatter correction–FLD methods.

Effect of the cerium modification on acid–base properties of Mg–Al hydrotalcite-derived oxide system and catalytic performance in ethanol conversion

The prospects of using cerium as a modifying additive of Mg–Al hydrotalcite-derived oxide system have been estimated by low-temperature nitrogen ad(de)sorption, X-ray diffraction, scanning electron microscopy, 1H and 27Al solid-state nuclear magnetic resonance (NMR), X-ray photoelectron and UV–Vis diffuse reflectance spectroscopy techniques. The effect of such tuning of structural-textural characteristics and acid–base properties of the surface on its catalytic performance in ethanol conversion has been studied. Solid-state NMR spectroscopic study of the probe molecule adsorption and temperature-programmed desorption of NH3 and CO2 with mass-spectrometry control are used to determine the nature and strength distribution of acidic and basic sites of Mg–Al(–Ce) oxide systems. It has been found that the selectivity towards 1-butanol up to 68.1% (548 K) is achieved in ethanol conversion over Mg–Al–Ce sample at time-on-stream ≤ 2 h. At higher time-on-stream, the specific rates of the target product (1-butanol) formation are comparable for both modified and un-modified catalysts, but the products distribution differs. Cerium modification of Mg–Al oxide catalyst leads to increase in specific rate of acetaldehyde formation due to increase in the number of basic sites and their surface density. Wherein, the rate of ethanol dehydration products (ethylene and diethyl ether) is reduced, apparently, due to decrease in a number of Lewis acidic sites formed by Al3+ cations octahedrally coordinated to oxygen.

Promoting the photocatalytic removal rate of ciprofloxacin antibiotic over carbon fiber decorated tungsten trioxide/titanium dioxide catalysts

This work aimed to enhance the photocatalytic degradation efficiency of WO3/TiO2 catalyst by decorating with carbon fibers (CF) which have excellent conductivity and uniform micropore size distribution. The carbon fiber based catalysts were prepared through a facile solvothermal technique and the as-synthesized samples were characterized by X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) and UV–Vis diffuse reflectance spectroscopy (UV-DRS), Raman and X-ray powder diffraction (XRD) techniques. The photocatalytic activities of carbocatalysts were investigated by degrading the selected antibiotic (ciprofloxacin) under day light illumination. When the amount of carbon fiber was increased from 2.5 wt.% to 9 wt.%, the photocatalytic degradation rate was almost doubled. The effects of different parameters such as carbon fiber amount, solution pH and water matrix on the catalytic performance were explored; and the effect of radical ions was investigated by adding trapping agents. The promoted activity for the carbocatalysts was assigned to the synergetic effect of adsorption/photocatalysis, electrical features of carbon fibers and reduced band gap energy.

Improvement of dielectric properties of ZnO nanoparticles by Cu doping for tunable microwave devices

We report a facile chemical polyol method to synthesize Cu-doped ZnO nanoparticles with various levels of Cu. X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–Visible diffuse reflectance spectroscopy techniques were used to analyze the structural and optical properties of Zn1−xCuxO nanoparticles. The crystallite size varies between 9.8 and 18.9 nm and decreased with the increase of Cu doping. The band energy gaps of pure and Cu-doped ZnO samples are in the range 2.5–3.1 eV. The dielectric properties, ac conductivity and impedance analysis of Zn1−xCuxO nanoparticles were systematically investigated. It was revealed that the doping of ZnO by Cu (with low Cu molar content) leads to obtain high dielectric constant and low tangent loss, which are very encouraging for microwave semiconductor devices.

Effect of sulfate group-containing fuels on the morphology of ZnO powders prepared by solution combustion synthesis

Zinc oxide (ZnO) powders were synthesized via solution combustion route using sodium octyl sulfate (SOS) as a sulfate group containing-anionic surfactant and sodium lauroyl sarcosinate (SLS) surfactant. Combustion behavior, phase evolution, microstructure, textural and optical properties of ZnO powders were investigated by thermal analysis, X-ray diffractometry, scanning electron microscopy, N2 adsorption–desorption isotherms, and diffuse reflectance and photoluminescence spectroscopy techniques as a function of both fuel type and fuel amount. A specific correlation between the fuel type and the morphology of ZnO powder was established on the base of the presence/absence of sulfate group in the fuel. The ZnO powders obtained by the sulfate group-containing fuel (SOS) were composed of sheet-like particles, whereas the SLS fuel led to quasi-spherical and cuboid-like particles. The sheet-like morphology was more appeared at the stoichiometric fuel amount.

Structural, optical, and dielectric investigations in bulk PrCrO3

The polycrystalline powder samples of PrCrO3 have been prepared using conventional solid-state synthesis method. Structural investigations are carried out using Raman spectroscopy and synchrotron X-ray diffraction (SXRD) followed by Rietveld refinement of diffraction data. Investigations of diffraction data suggest that these samples possess centrosymmetric orthorhombic structure with space group $$Pnma$$ $$(or\;Pbnm)$$ . The valence (charge) state of Cr in PrCrO3 has been determined from X-ray absorption near edge spectroscopy (XANES). Optical properties are studied using diffuse reflectance spectroscopy technique. Optical absorption study reveals that absorption in PrCrO3 ceramic is dominated by d–d electrons of chromium cation (Cr3+). The synthesized compound found to have energy bandgap of 3.20 eV. Based on the results observed, energy level diagram for PrCrO3 has been presented. High dielectric permittivity $$(\varepsilon {^{\prime}})$$ of the order $$3\times {10}^{3}$$ is observed for the studied sample. Impedance spectroscopy measurement at room temperature on sintered pellet indicates electronic inhomogeneity in the samples as demonstrated by the presence of dielectric relaxation processes associated with highly conducting grain and low conducting grain boundaries. The relaxation mechanism has been explained on the basis of Cole–Cole model. Observed high dielectric permittivity $$(\varepsilon {^{\prime}})$$ and optical energy bandgap $$({E}_{g})$$ indicates that PrCrO3 may find promising application in optoelectronic devices.

Fabrication and efficient photocatalytic dye degradation over Z-scheme-based BiVO4/CdS heterojunction under visible-light irradiation

Novel Z-scheme-based BiVO4/CdS photocatalysts with efficient charge separation were prepared by simple in situ hydrothermal method. The compact structure of the CdS nanorod and BiVO4 nanosheet has formed a Z-scheme heterojunction. The as-prepared BiVO4/CdS composites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, diffuse reflection spectroscopy, photoluminescence and photocurrent techniques. It was found that the BiVO4/CdS composites had the light-absorbing range and could efficiently degrade malachite green dye under visible-light irradiation. In this report, the result of the best degrading sample could achieve 92% in 30 min under visible light, respectively. BiVO4/CdS composites perform photocatalytic efficiently due to the Z-scheme. Furthermore, the Z-scheme-based BiVO4/CdS composites leaded to a major oxidation site at BiVO4, which successfully avoided photoetching of CdS during photocatalysis. Especially, the BiVO4/CdS system exhibits great photogenerated electron–hole pairs separation capabilities and high redox capabilities. This unique method of synthesizing Z-scheme-based BiVO4/CdS heterojunction has ability to reduce the cost and promote photocatalytic in visible-light range simultaneously.

Landscape-scale spatial variability of kaolinite-gibbsite ratio in tropical soils detected by diffuse reflectance spectroscopy

The use of diffuse reflectance spectroscopy (DRS) has gained prominence in the quantification of soil attributes due to its ease and practicality of obtaining data. This study aimed to evaluate the potential of different methodologies applied to spectral curves given by DRS to estimate kaolinite (Kt) and gibbsite (Gb), and their spatial variability characterization for the Western Plateau of São Paulo. The Western Plateau of São Paulo has 13 million hectares, 2 million of them covered by basalt and 11 million by sandstones. A total of 600 samples were collected at a depth of 0.0–0.20 m. Calibration curves were constructed with pure minerals for x-ray diffraction (XRD) and DRS techniques. The Kt/(Kt + Gb) ratio and the percentages of Kt and Gb were determined by XRD and using the following three methodologies applied to spectral curves: continuum removal technique (CR), direct ratio of the valley (DRV), and multivariate analysis by partial least squares regression (PLSR). The CR procedure had means similar to those observed by XRD, i.e., 0.90 and 0.92, respectively, while DRV overestimated the ratio, with a mean of 1.32. DRS allowed the estimation of the Kt/(Kt + Gb) ratio for the different geological and landscape compartments of the Western Plateau of São Paulo for the CR and DRV procedures. CR procedure allowed constructing models to be more efficient compared to those obtained by DRV and PLSR. The use of geostatistics to interpolate the data of the ratio Kt/(Kt + Gb) by DRS provided important information to define specific management zones accurately and more economically.

Cuprous oxide film sputtered on monolayer graphene for visible light sensitive heterogeneous photocatalysis

A two dimensional thin film catalyst system was produced in this study as Cu2O/2D graphene on the copper foil having catalytic activity in the visible region of solar spectrum. Catalyst structure was characterized by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, atomic force microscopy, UV–visible diffuse reflectance spectroscopy and confocal Raman spectroscopy techniques. Existence of photocatalytic activity was demonstrated by hydrogen peroxide degradation under 14 W LED light. Using monolayer graphene in the design of the catalyst increased the activity almost 16 times compared to the neat catalyst without graphene. Activity in the light was 8.6 times higher than the dark. Graphene used in the catalyst system was perfect monolayer having no defect and its 2D/G ratio was 2.72. Surface roughness of the catalyst according to the atomic force microscopy results was found to be 1.1 µm. Surface morphology of thin film catalyst was channeled like, mostly dimpled but had no apparent micro cracks with a thickness value of 290.9 nm ± 10 nm.

Structural Characterization and Photocatalytic Activity of Synthesized Carbon Modified TiO2 for Phenol Degradation

To promote the photocatalytic performance TiO2 and enlarge its application in visible region, carbon doped TiO2 (C/TiO2) composites were synthesized by wet impregnation method using sucrose as a precursor and used for phenol photocatalytic reaction. The synthesized products were characterized by Nitrogen adsorption-desorption isotherms (BET), X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-visible diffuse reflectance spectroscopy (UV-vis) techniques. The results showed that the obtained TiO2 was anatase phase in the C/TiO2 products, and its crystallite size was 11.7 nm, respectively. Carbon amount and calcined temperature of C/TiO2 can promote phenol removal. In this experiment, 5% carbon and 500 °C are the best choice for photocatalyst preparation. Under the UV light irradiation, 5%C/TiO2 (500 °C, 2 h) exhibited the efficiency of 70.0% for phenol degradation within 150 min whereas TiO2 (500 °C, 2 h) had 53.0% in the same duration of time. Also 5%C/TiO2 (500 °C, 2 h) has higher photocatalytic performance under sunlight than pure TiO2. A combination of factors that include the smallest crystalline size, higher anatase percent, less band gap energy value and more oxygen vacant resulted in higher photocatalytic activities of 5%C/TiO2 (500 °C, 2 h).

Utilisation of lignin as a model biomass component for preparing a highly active photocatalyst under UV and visible light

Lignin-based carbonaceous material (LBC) with graphitic/semi-graphitic skeleton and oxygenated surface functionalities was prepared by hydrothermal carbonization (HTC) method. Thanks to these properties, LBC becomes a strong candidate as a semiconductor support in photocatalytic applications. In this study, LBC was used as a support material for widely known photocatalyst TiO2 and results showed that a chemical interaction occurred between carboxyl groups of LBC and metallic center of TiO2. TiO2 nanoparticles were also synthesized by the hydrothermal method without LBC support (s-TiO2). Effects of LBC- TiO2, s-TiO2 and commercial TiO2 (c-TiO2) on the removal of methylene blue (MB) as a cationic dye and phenol were compared under different irradiations (UVA and visible light). X-ray photoelectron (XPS), Brunauer–Emmett–Teller (BET), UV–Vis diffuse reflectance (UV-DRS) and raman spectroscopy techniques, as well as x-ray diffraction (XRD), scanning electron microscopy energy dispersive spectrometry (SEM-EDX) mapping and scanning and high resulation transmission electron microscopy (HRTEM) analyses, were performed in order to collect valuable information about the material. LBC-TiO2 presented superior apparent first-order rate constants for MB and phenol removal than those obtained on c-TiO2 and s-TiO2 under visible light. It can be concluded that the photocatalytic performance of LBC-TiO2 was definitely higher than that of bare and commercial TiO2 thanks to sensitization and activation effect of LBC. This study reports an economical and environmentally friendly alternative for preparing catalyst supports from lignin.

Optimal fabrication of 0D/1D Cu2O quantum dots sensitized CdS nanorods heterojunction: Efficient photoredox catalyst for H2 generation under visible light irradiation

Abstract The heterogeneous structure of Cu2O quantum dots (QDs) sensitized CdS nanorods (NRs) was synthesized by an easy and cost-effective technique. The morphology, structure and optical properties of as-prepared photocatalysts are thoroughly investigated by field emission gun scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (UVDRS) and photoluminescence (PL) spectroscopic techniques. The different weight percentages (10, 20, and 30) of Cu2O QDs deposited on the CdS NRs structures and their photocatalytic hydrogen (H2) evolution (PCHE) performance are systematically investigated. The Cu2O QDs deposition on CdS NRs shows an increase in the rate of hydrogen (H2) evolution due to the formation of type II heterojunction in between Cu2O QDs and CdS NRs. The 20% loading of Cu2O QDs on CdS exhibits the highest photocatalytic H2 generation than other ratios as well as pure Cu2O QDs and CdS NRs. The photocatalytic rate of H2 evolution of 26060 μmolg-1h-1 was obtained for 20 % Cu2O-CdS, which is18 times more than pure Cu2O QDs and 5.1 times than CdS NRs. Photoelectrochemical (PEC) measurements, electrochemical impedance spectroscopy, and photoluminescence measurements suggest that the Cu2O QDs deposition on CdS NRs reduces interfacial recombination of photogenerated charge carrier owing to the formation of the p-n junction between the components. The apparent quantum yield (AQY) obtained for 20 % Cu2O QDs modified CdS NRs photocatalysts is exceptionally high i.e. 20.67%. This convenient and cost-effective strategy will pave the way for large-scale synthesis of type II heterogeneous photocatalyst for efficient H2 evolution.

High photoelectrochemical performance of reduced graphene oxide wrapped, CdS functionalized, TiO2 multi-leg nanotubes

Absorption of visible light and separation of photogenerated charges are two primary pathways to improve the photocurrent performance of semiconductor photoelectrodes. Here, we present a unique design of tricomponent photocatalyst comprising of TiO2 multileg nanotubes (MLNTs), reduced graphene oxide (rGO) and CdS nanoparticles. The tricomponent photocatalyst shows a significant red-shift in the optical absorption (∼2.2 eV) compared to that of bare TiO2 MLNTs (∼3.2 eV). The availability of both inner and outer surfaces areas of MLNTs, the visible light absorption of CdS, and charge separating behavior of reduced graphene oxide layers contribute coherently to yield a photocurrent density of ∼11 mA cm−2 @ 1 V vs. Ag/AgCl (100 mW cm−2, AM 1.5 G). Such a high PEC performance from TiO2/rGO/CdS photoelectrode system has been analyzed using diffused reflectance (DRS) and electrochemical impedance (EIS) spectroscopy techniques. The efficient generation of charge carriers under light irradiation and easy separation because of favourable band alignment, are attributed to the high photoelectrochemical current density in these tricomponent photocatalyst systems.

Synthesis of yttrium and cerium doped ZnO nanoparticles as highly inexpensive and stable photocatalysts for hydrogen evolution

Yttrium and cerium co-doped ZnO nanoparticles were synthesized by combustion route and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) techniques. The introduction of yttrium ions has efficiently increased the relative percentage of Ce3+ ions in ZnO. Yttrium and cerium co-doped ZnO shows efficient photo activity for hydrogen evolution (10.61 mmol/((g·h)) higher than previously reported optimal value for rare earth co-doped ZnO photocatalysts. This remarkably increased hydrogen evolution can be ascribed to the synergy between electronic anchoring effect of Y3+/Y2+ and Ce4+/Ce3+ redox couples. This report presents new idea for the synthesis of efficient photocatalyst using economical route and ion anchoring effect. The hydrogen evolution was also tested using Na2S and Na2SO3 as electron donors under visible light illumination. The synthesized photocatalysts also exhibit high stability.

Electrospinning–calcination combination process on perovskite Ba1-xSrxMnO3 (x=0.03, 0.07, and 0.10) fibers: Characterization study

In the present work, Ba1-xSrxMnO3 (x = 0.03, 0.07, and 0.10) fibers are synthesized by using the electrospinning–calcinations combinations process. The fabricated fibers were characterized by a combination of analytical technique such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy dispersive analysis of X-rays (EDAX), Fourier Transform Infrared (FT-IR), and Diffuse reflectance spectroscopy (DRS). XRD confirms hexagonal structure of Ba1-xSrxMnO3 fibers. A classical size-strain plot (SSP) method has been applied to estimate the microstructure parameters of the produced fibers from the XRD peak broadening analysis. SEM images show the randomly oriented fibers along with diameter growth upon increasing the Sr content. DRS technique was used to estimate the optical band gap of the synthesized samples. The gas sensing study shows the sensing ability of Ba1-xSrxMnO3 fibers, pressed into pellets, toward ethanol vapors.

Inspecting historical vaulted ceilings by means of physical and chemical analyses: an integrated approach combining active infrared thermography and reflectance spectroscopy

The present study discusses the experimental physicochemical results obtained from the historical vaulted ceilings of an ancient church located in central Italy. Infrared thermography (IRT) in the active configuration was used to map subsurface defects caused by a seismic event and to discover buried structures, while the visible and near-infrared (VIS-NIR) fibre-optics diffuse reflectance spectroscopy (FORS) technique was applied to identify the pigments of wall paintings decorating the vault. Historical photographs are useful to readers in order to clarify the state of conservation before and after the earthquake that took place in 2009. The combination of the experimental results can be useful in restoration processes.

Enhanced photocatalytic activity of reduced graphene oxide/SrSnO3 nanocomposite for aqueous organic pollutant degradation

In this present work, a novel heterostructure rGO - SrSnO3 nanocomposites with different weight percentage of reduced graphene oxide were successfully synthesised by hydrothermal method. The formation of crystalline structure, morphology, elemental composition and optical properties were characterized using Powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Energy dispersive X-ray analysis (EDX), and UV–vis diffuse reflectance spectroscopy (UV DRS) and photoluminescence (PL) spectroscopy techniques. The photocatalytic activity of pure and composite materials was assessed by degradation of aqueous methylene blue dye under UV light irradiation. The highest degradation efficiency of 97 % was obtained for 10 wt.% rGO - SrSnO3 composite. Enhancement in the photocatalytic activity is mainly due to the suppressed photoexcited charge carrier’s recombination rate. Moreover, the reusable and stability of the photocatalyst demonstrated after four consecutive runs of photocatalytic test.