Diffuse Reflectance Absorption Spectroscopy Research Articles

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

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

The evaluation of microbubble concentration using the techniques of optical spectroscopy

We present an accurate and low-cost method for the evaluation of concentration of ultrasound contrast agents, microbubbles (MBs) by utilizing light-scattering properties of MBs. Illuminated by near-infrared light, MBs act as Mie scattering particles. We used absorption spectroscopy to detect the optical density immediately after the preparation of Sonovue MBs, and after MB insonification for total of 187 MB samples. Strong linear correlation (r = 0.97) was determined between optical density of MB suspension, evaluated at 790 nm, and MB concentration in vitro (measured by hematocytometer, up to 3.3 × 107 MBs/ml).Optical density of MB suspension was assessed by simultaneously performing diffuse reflectance spectroscopy and absorption spectroscopy measurements in vitro. Further we aimed to assess MB optical density in tibialis cranialis muscles of C57Bl/CBA mice. The results of diagnostic B-scan imaging and diffuse reflectance spectroscopy shows that optical techniques are excellent for monitoring the changes in MB concentration both in vitro and in vivo.

Pushing the heterometal doping limit while preserving long-lived charge separation in a Ti-based MOF photocatalyst

This study explores the nature, dynamics, and reactivity of the photo-induced charge separated excited state in a Fe3+-doped titanium-based metal organic framework (MOF), xFeMIL125-NH2, as a function of iron concentration. The MOF is synthesized with doping levels x = 0.5, 1 and 2 Fe node sites per octameric Ti-oxo cluster and characterized by powder x-ray diffraction, UV-vis diffuse reflectance, atomic absorption, and steady state Fe K-edge X-ray absorption spectroscopy. For each doping level, time-resolved X-ray transient absorption spectroscopy studies confirm the electron trap site role of the Fe sites in the excited state. Time scan data reveal multiexponential decay kinetics for the charge recombination processes which extend into the microsecond range for all three concentrations. A series of dye photodegradation studies, based on the oxidative decomposition of Rhodamine B, demonstrates the reactivity of the charge separated excited state and the photocatalytic capacity of these MOF materials compared to traditional heterometal-doped semiconductor photocatalysts.

Application of Linear Additive Conditions for Near-Infrared Diffuse Reflectance Absorption Spectroscopy

Determining the homogeneity of material mixing in real time during product processing is critical for quality control. According to the Kubelka–Munk (K-M) function of diffuse reflectance absorption spectrum, absorbance (A) is approximately linear with the content of the components when the sample scattering coefficient (S) is in a certain range. The S is determined by the particle size of powder samples. Therefore, this study determined particle size ranges that satisfy linear additivity in near-infrared diffuse reflectance spectroscopy (NIRDRS). Thus, the proposed NIRDRS analysis technique can be used to determine the homogeneity of material mixes or analyze the percentages of the components in the mixture. In this study, vitamin B3 and vitamin C were used for preparing mixed samples with varying percentages. The experimental results revealed that linear additivity is satisfied when the powder particle size is in the range of less than 280, 280–450, and 450–900 μm. When the confidence level is 0.01, the actual mixed spectra are not significantly different from the “simulated mixed spectra” constructed by linear addition, with their relative deviations less than 1.08%. The absolute errors of the actual and analytic percentages were within 2.98% for each component in the mixtures. The above conclusions also hold for sorghum, which has a complex material composition. Statistical models cannot analyze the percentages of components in the mixture. In contrast, linear addition and direct calibration approach avoids the use of a large number of samples for statistical modeling and analyze the percentages of mixed samples. Meanwhile, it can be used to discriminate and analyze the material mixing uniformity by building a mechanistic model.

Enhanced photocatalytic performance and stability of multi-layer core-shell nanocomposite C@Pt/MoS2@CdS with full-spectrum response

The nanocomposite material C@Pt/MoS 2 @CdS was prepared by a simple microwave-assisted hydrothermal method combined with photoreduction method. The crystal structure, microstructure, and surface physical chemistry properties of the material were analyzed by X-ray diffraction (XRD), ultraviolet–visible diffuse reflectance absorption spectroscopy (UV–vis/DRS), X-ray photoelectron energy spectroscopy (XPS), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), nitrogen adsorption–desorption measurement, photoluminescence spectroscopy (PL), and electrochemical tests. As a result, this material has full-spectrum light absorption property and the composited CdS presents a good hexagonal phase. Moreover, the composite material presents a nanorod-like multi-layer core-shell structure, wherein the rod-like MoS 2 @CdS surface is covered with Pt and C. The formation of the multi-layer core-shell structure increases the specific surface area of as-composite material and strengthens its light absorption performance. The electrochemical impedance and transient photocurrent test results show that C@Pt/MoS 2 @CdS has the highest charge separation efficiency and enhanced photocurrent density compared with other systems. Photogenerated charge carriers have higher separation efficiency, and photogenerated electrons and holes exhibit longer life. During the photocatalysis experiments, the nanocomposite C@Pt/MoS 2 @CdS shows enhanced photodegradation activity under multi-modal photocatalytic experiments and excellent stability under visible light irradiation. In addition, C@Pt/MoS 2 @CdS has a strong photocatalytic water splitting ability. Under the same experimental conditions, its hydrogen production is 60 times that of commercially available P25. Through capture experiments, the reactive species in the photocatalytic reaction process were determined, and the possible photocatalytic reaction mechanism of this multi-layer core-shell C@Pt/MoS 2 @CdS nanocomposite was inferred. • Constructed a multi-layer core-shell structure photocatalytic composite material. • Improved the photocatalytic activity and stability of CdS-based photocatalyst. • The hydrogen production of C@Pt/MoS 2 @CdS was approximately 60 times that of commercially available P25. • Recombination rate of photogenerated charge carriers was effectively restrained.

Synthesis of Rare-Earth Nanomaterials Ag-Doped NaYF4:Yb3+/Er3+@NaYF4:Nd3+@NaGdF4 for In Vivo Imaging.

In this study. a novel near-infrared fluorescent-driven contrast agent (Ag-doped NaYF4:Yb3+/Er3+@NaYF4:Nd3+@NaGdF4) was synthesized using a coprecipitation-hydrothermal-solvothermal-solvothermal (CHSS) method. The results shows that hexagonal NaYF4:Yb3+/Er3+ with a diameter of 300 nm was successfully synthesized by the CHSS method. The new contrast agent was characterized using scanning electron microscopy, fluorescence spectrometry, transmission electron microscopy, energy-dispersive spectrometry and ultraviolet-visible light diffuse reflectance absorption spectroscopy. Even at low concentrations (0.2 M), this proposed contrast agent can be excited by near-infrared light with a wavelength of 980 nm and emits a dazzling green light with a wavelength of 540 nm, and the comparison of the luminescence intensity proves that doping with silver increases the luminescence intensity of the upconverted nanomaterial by nearly 13 times based on the calculated quantum yield. TEM images show the successful preparation of silver nanoparticles with a diameter of 30 nm, and the energy spectrum shows the successful doping of silver nanoparticles and the successful preparation of the core-shell structure of NaYF4:Yb3+/Er3+@NaYF4:Nd3+@NaGdF4. Furthermore, the mechanism of the increased luminous intensity has been studied using simulation calculations. Finally, cytotoxicity tests were used to test material which was modified by 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPE-PEG2K), and the biocompatibility was significantly improved, meeting the standard for biological applications.

Nanoarchitectonics on Bi2MoO6 by alkali etching for enhanced photocatalytic performance

As a layered photocatalyst, the photogenerated carriers separation efficiency of bismuth molybdate (Bi2MoO6) can be improved by introduction of oxygen vacancy. The alkali etching method provides a facile structural tuning way for modifying the bismuth-based semiconductors. Defect state bismuth molybdate (Bi2MoO6) photocatalyst was synthesized by alkali etching. The structure of Bi2MoO6 was tuned by adjusting the concentration of alkali solution. The phase structure, morphology, surface chemistry, and optical property of Bi2MoO6 were characterized by kinds of characterization methods such as X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance absorption spectroscopy. The phase of Bi2MoO6 can be transformed to Bi2O3 accompanied with the change of morphology due to the etching of molybdenum atom and oxygen atom from the Bi2MoO6 body structure by sodium hydroxide solution. Meanwhile, the concentration of oxygen vacancy increased obviously as indicated by the XPS results. Therefore, the separation efficiency of photogenerated carriers was enhanced because of the promotion of oxygen vacancy. Alkali etching Bi2MoO6 by 0.075 M sodium hydroxide solution exhibited an excellent photocatalytic performance owing to the suitable vacancy concentration. Superoxide free radicals instead of hydroxyl radicals took the important role in the photodegradation process.

Spectroscopic Analysis of Parathyroid and Thyroid Tissues by Ground-State diffuse Reflectance and Laser Induced Luminescence: a Preliminary Report.

Intraoperative discrimination of thyroid and parathyroid tissues is fundamental in thyroid surgery. Recent fluorescence studies have shown stronger NIR emission in parathyroid tissue than in thyroid tissue, presenting a potential avenue for the development of a tool for surgical assistance. However, the fluorophore responsible for this emission has not yet been identified. In this work, spectroscopic analysis was performed to ascertain the origin of the emission peaks in parathyroid tissue. Ground-state diffuse reflectance (GSDR) absorption spectroscopy and laser-induced luminescence (LIL) emission spectroscopy were performed in parathyroid, thyroid, and fatty tissue samples and the resulting spectra were compared with the peaks of known fluorophores to identify the origin of each peak. The spectra of the different tissue types were also compared in order to evaluate the wavelength which presents the highest parathyroid emission relative to the emission of the surrounding tissues, representing the ideal wavelength for parathyroid detection. An emission peak in these conditions was observed for both thyroid and parathyroid tissue at 711nm, with a higher intensity in parathyroid sample, making it suitable for detection applications. These results show a potential avenue for the development of a system allowing parathyroid detection in a surgical setting.

Biosynthesis of SnO2 nanoparticles by aqueous leaves extract of Aquilaria malaccensis (agarwood)

Biosynthesis of tin oxide nanoparticles (SnO2 NPs) was cost-effectively carried out in non-toxic aqueous mixture of Aquilaria malaccensis (agarwood) leaves extract and tin (IV) chloride pentahydrate solution at room temperature. The synthesized SnO2 NPs were characterized by using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX) and UV-visible diffuse reflectance spectroscopy (DRS). The results from FT-IR spectra of A. malaccensis leaves shows the presence of functional groups of polyphenolic from bioactive compounds which act as the template for reducing and capping agents during the synthesis activity. The structural properties of the obtained nanoparticles are studied using X-ray diffraction, which indicates that the crystallite size are 6.3 and 3.4 nm for sample synthesized from extract of fresh and old leaves respectively. The morphology of the nanoparticles shows uniform distribution of agglomerated spherical nanoparticles. DRS absorption spectrum indicates the band-gap for both samples 3.23 and 3.35 eV respectively. The green synthesized SnO2 NPs is suggested may play forthcoming significant roles in catalysis and optoelectronic devices.

CoSe as non-noble-metal cocatalyst integrated with heterojunction photosensitizer for inexpensive H2 production under visible light

The development of inexpensive cocatalysts based on earth-abundant-elements, is highly demanding strategy to produce large-scale photocatalytic H2 for real-life applications. Herein, we report the utilization of CoSe as a highly efficient cocatalyst to significantly improve the photocatalytic H2 production on ZnSe/CdS under visible irradiation. The maximum H2 production rate of 785 μmol h−1 was attained under optimized conditions. Furthermore, the current system showed robust stability up to 30 h of irradiation and more than 23 mmol of H2 was produced. The highest apparent quantum yield of the system was 55.3% at monochromatic 420 nm light. Photocurrent responses, UV–vis diffuse reflectance absorption spectroscopy, electrochemical impedance spectroscopy and photoluminescence (PL) spectroscopy were used to explain the mechanistic roles of CoSe and ZnSe in current photocatalytic system. This work showcased the successful usage of CoSe as cocatalyst and ZnSe as visible light active semiconductor for inexpensive conversion of solar energy to H2.

UVC-assisted photocatalytic degradation of carbamazepine by Nd-doped Sb2O3/TiO2 photocatalyst

The photocatalytic degradation of carbamazepine (CBZ) in ultra-pure water was investigated by using neodymium (Nd)-doped antimony trioxide (Sb2O3)/titanium dioxide (TiO2) photocatalyst under the UVC irradiations of 254 nm wavelength. The hydrothermal method was used for the fabrication catalyst samples with different ratios of Nd (0%–2%) dopant, and characterised by X-ray diffraction pattern (XRD) to investigate the crystallinity. Scanning electron microscopy (SEM) provided the surface morphologies, Bruanuer-Emmer-Teller (BET) analysis gave the textural properties, and UV–Vis diffuse reflectance absorption spectroscopy (DRS) was used for the investigation of the optical properties of synthesized catalysts. TEM images of Sb2O3 showed a nanorod-like structure while, in the Nd-doped Sb2O3/TiO2, a small dot-like structure was observed along with the nanorods. The surface area and band gap of 1% Nd-doped Sb2O3/TiO2 were found to be 9.56 m2 g−1 and 3.0 eV respectively. It was observed that the CBZ cannot be degraded in the absence of catalyst under UV light, while photocatalyst 1% Nd-doped Sb2O3/TiO2 at 0.5 g/L of catalyst dose showed the best photocatalytic activity towards CBZ degradation. The main degradation products were identified with high-resolution mass spectrometry. Moreover, the degradation of CBZ followed pseudo first-order kinetics and the rate constant was 0.017 min−1. Quenching tests by the addition of methanol from 100 to 500 mM were carried out to determine the major reactive oxygen species, which showed that OH radicals was involved in the CBZ degradation. Active species-trapping experiments revealed that ∙O2− is also responsible for the degradation of CBZ.

Surface photochemical studies of nano-hybrids of A3B porphyrins and Fe3O4 silica-coated nanoparticles

This study reports a surface photochemistry behaviour of two tetrapyrrolic structures: 5,10,15,20-tetra-(4-carboxymethylphenyl) porphyrin (P1.1) and 5-(4-hydroxy-3-methoxyphenyl)-10,15,20-tris-(4-carboxymethylphenyl) porphyrin (P1.2), covalently bound to silica-coated magnetite nanoparticles (Fe3O4@SiO2) imbibed into a polyethylene glycol (PEG) matrix and in the form of a fine powder. The initial compounds and the nano-hybrids imbibed in the PEG matrix were characterized using Fourier transformed infrared spectroscopy (FT-IR), diffuse reflectance absorption spectroscopy for ground state molecules (GSDR), X-ray diffaction (XRD), transmission electron electron microscopy (TEM) as well as several luminescence emission spectroscopies. The combined use of these methodologies enabled us to obtain a surface photochemistry characterization of these new nano-hybrid materials.For the powdered samples of P1.1 or P1.2 and Fe3O4@SiO2 imbibed into the powdered PEG a detailed absorption study and a correlation of fluorescence emission intensity with the magnetite concentration were performed. New covalent bonds porphyrin-Fe3O4@SiO2 were detected using FT-IR transmission spectra. A donor-acceptor interaction with change of the oxidation level of the porphyrins was also observed. Fluorescence emission quantum yields and lifetimes of the two porphyrins were determined for all samples and two populations of the porphyrin molecules exist, free porphyrin (unquenched) and porphyrin with Fe3O4@SiO2 NPs attached, the quenched porphyrin. In this way, the amount of the available excited porphyrin for singlet oxygen formation is reduced, therefore the presence of the Fe3O4@SiO2 NPs may not favor this specific PDT action by the Type II mechanism, but it prevents aggregation of the porphyrins, even when a PEG matrix is used, and Type I mechanisms remain active.

Rose spherical structure Ag2S/ZnIn2S4/ZnS composites with visible light response: Enhanced photodegradation and hydrogen production performance

Ag2S/ZnIn2S4/ZnS composites were synthesized by a microwave-assisted hydrothermal two-step method. The samples were characterized by X-ray diffraction (XRD), UV–visible diffuse reflectance absorption spectroscopy (UV–vis/DRS), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), and nitrogen adsorption–desorption tests. The results show that the semiconductor ZnS and ZnIn2S4 in the Ag2S/ZnIn2S4/ZnS composite are cubic phases, and the composite exhibits a rose-spherical structure. In the composite, after ZnS is combined with the narrow band gap semiconductor Ag2S and ZnIn2S4, whose light absorption edge is red-shifted, and the absorption in the visible region is obvious. At the same time, compared to the monomer ZnS and the monomer ZnIn2S4, the specific surface area (SBET) of the composite is significantly increased. In order to investigate photocatalytic properties, methyl orange was used as the model molecule. Meanwhile, multi-mode photocatalytic properties of Ag2S/ZnIn2S4/ZnS composites were studied, and its optimal composition ratio was determined. At the same time, the excellent photocatalytic hydrogen production capacity and cycle stability of the composites with 1% Ag2S loading were analyzed. According to the capture experiment results, the possible photocatalytic mechanism of Ag2S/ZnIn2S4/ZnS composites was speculated.

Bismuth Oxide Faceted Structures as a Photocatalyst Produced Using an Atmospheric Pressure Plasma Jet

The photocatalyst bismuth oxide, which is active under visual light, was deposited using an atmospheric pressure plasma jet (APPJ). Sixteen different samples were generated under different parameters of the APPJ to investigate their catalytic activity. The prepared samples were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), laser scanning microscopy (LSM), and UV–vis diffuse reflectance absorption spectroscopy. The measured data, such as average sample thickness, coverage ratio, phase fraction, chemical composition, band gap, and photocatalytic performance were used for comparing the samples. The XRD analysis showed that the deposition process produced a mixed phase of monocline Bi2O3 and tetragonal Bi2O2.33. Using the Rietveld refinement method, phase fractions could be determined and compared with the XPS data. The non-stoichiometric phases were influenced by the introduction of nitrogen to the surface as a result of the deposition process. The band gap calculated from the diffuse absorption spectroscopy shows that Bi2O2.33 with 2.78 eV had a higher band gap compared to the phases with a high proportion of Bi2O3 (2.64 eV). Furthermore, it was shown that the band gap was dependent on the thickness of the sample and oxygen vacancies or loss of oxygen in the surface. All coatings had degraded methyl orange (MO) under irradiation by xenon lamps.

Preparation of Co3O4@ZnO core-shell nanocomposites with intrinsic p-n junction as high-performance photoelectrodes for photoelectrochemical cathodic protection under visible light

In this work, Co3O4@ZnO nanocomposite photoelectrodes with a core-shell structure were prepared, enabling enhanced photoelectrochemical activity under visible light illumination. This was demonstrated by the photoinduced cathodic polarization of 304 stainless steel in 3.5 wt% NaCl solution. The morphology, composition, crystalline structure and optical absorption properties of the photoelectrodes were characterized by various analysis techniques and UV–vis diffuse reflectance absorption spectroscopy. Results show that, compared to the ZnO nanorods, the Co3O4@ZnO nanocomposite photoelectrodes have a red shift of optical absorption and enhanced photoelectrochemical cathodic polarization on stainless steel under visible light. The enhanced photoelectrochemical performance is attributed to the narrow band gap of Co3O4 and the p-n junction formed at the Co3O4/ZnO interface. The Co3O4@ZnO nanocomposite photoelectrodes fabricated in this work achieve a photocurrent density of 10.5 μA/cm2 and a cathodic polarization potential of −720 mV (saturated calomel electrode) for 304 stainless steel in 3.5 wt% NaCl solution under visible light.

Increasing the optical response of TiO2 and extending it into the visible region through surface activation with highly stable Cu5 clusters.

The decoration of semiconductors with subnanometer-sized clusters of metal atoms can have a strong impact on the optical properties of the support. The changes induced differ greatly from effects known for their well-studied, metallic counterparts in the nanometer range. In this work, we study the deposition of Cu5 clusters on a TiO2 surface and investigate their influence on the photon-absorption properties of TiO2 nanoparticles via the computational modeling of a decorated rutile TiO2 (110) surface. Our findings are further supported by selected experiments using diffuse reflectance and X-ray absorption spectroscopy. The Cu5 cluster donates an electron to TiO2, leading to the formation of a small polaron Ti3+ 3d1 state and depopulation of Cu(3d) orbitals, successfully explaining the absorption spectroscopy measurements at the K-edge of copper. A monolayer of highly stable and well fixated Cu5 clusters is formed, which not only enhances the overall absorption, but also extends the absorption profile into the visible region of the solar spectrum via direct photo-induced electron transfer and formation of a charge-separated state.

Investigation of Charge-Transfer Interaction in Mixed Stack Donor–Acceptor Cocrystals Toward Tunable Solid-State Emission Characteristics

The formation of three mixed binary charge transfer (CT) cocrystals with tunable photoluminescence behavior featuring both CT interaction and directional hydrogen bonding is presented. Our strategy consists of the CT induced cocrystallization of three polycyclic (naphthalene, anthracene, and pyrene) carrying α-cyanostilbene (CS) derivatives, namely, 3-(naphthalene-2-yl)-2-(p-tolyl) acrylonitrile (NPA), 3-(anthracene-9-yl)-2-phenylacrylonitrile (APA), and 2-(4-methoxyphenyl)-3-(pyrene-1-yl) acrylonitrile (MPA) as donors (D) with 1,2,4,5-tetracyanobenzene (TCNB) as an acceptor (A). The as-prepared cocrystals were probed in detail by various analytical techniques, namely, X-ray diffraction data, vibrational spectroscopy, diffuse reflectance absorption spectroscopy, fluorescence properties, and fluorescence quantum yields and lifetimes, affirming the formation of CT complexes. Complex IA features a mixed stack arrangement (D–A–D–A–D), while IIA and IIIA revealed (DAD---DAD) stack arrangement. The CT products ...

Synthesis of a nitrogen-doped titanium dioxide–reduced graphene oxide nanocomposite for photocatalysis under visible light irradiation

A nitrogen-doped titanium dioxide–reduced graphene oxide (N-TiO2–RGO) nanocomposite has been synthesized by the combination of a hydrothermal method and a thermal treatment under a NH3/N2 atmosphere. The resulting composites are characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, diffuse reflectance absorption spectroscopy, energy-dispersive X-ray spectroscopy, and Raman characterization techniques. The sequence of the thermal treatment and hydrothermal treatment processes is shown to influence the photocatalytic activity of nitrogen-doped composites. The composites synthesized by using this method show better photocatalytic activities toward the degradation of acetaldehyde under visible light irradiation compared with P25, N-TiO2, and TiO2–RGO. By applying the thermal treatment process after the hydrothermal process, nitrogen atoms can be simultaneously doped in the lattice of TiO2 nanoparticles and on the surface of reduced graphene oxide sheets. The conversion of acetaldehyde, as the model molecule of volatile organic compounds, is measured in a continuous stirred-tank reactor until the steady state condition is reached. The conversion of 50ppm acetaldehyde, in an air flow under illumination from an 80W Hg lamp with a UV cut-off filter, reaches 62% after a 1-h reaction using a 0.07g N-TiO2–RGO sample with an optimum loading of 2wt% graphene oxide. In comparison, the photocatalytic activity of P25 for the degradation of acetaldehyde under visible light irradiation is only 8% under the same reaction conditions. The reaction rates for acetaldehyde degradation are calculated and predicted with pseudo-first-order reaction kinetics, and the activity result of the best N-TiO2–RGO sample is 12.3 times higher than for P25.

Partial nitridation of Li4SiO4 and ionic conductivity of Li4.1SiO3.9N0.1

The Li content and anion lattice of Li4SiO4 were modified to improve ionic conductivity. Li2CO3 and Si3N4 were mixed in a ratio of Li/Si = 4.5 and heated in NH3 at 820 °C, which resulted in the formation of the oxynitride, Li4.1SiO3.9N0.1. Powder X-ray diffraction analyses revealed Li4.1SiO3.9N0.1 and Li4SiO4 to be isostructural with a subtle variation in the lattice constants. Diffuse-reflectance absorption spectroscopy, however, showed a significant decrease in the band gap, from 5.6 eV in Li4SiO4 to 4.8 eV in Li4.1SiO3.9N0.1. X-ray photoelectron spectra of the Li 1s and Si 2p levels revealed enhanced lattice covalency in Li4.1SiO3.9N0.1 compared to the oxide phase. The ionic conductivity of Li4SiO4 and Li4.1SiO3.9N0.1 were measured by ac impedance spectroscopy over the temperature range 100–400 °C. Non-linear fitting analysis of the equivalent circuit revealed that the ionic conductivity of Li4.1SiO3.9N0.1 was approximately one order of magnitude higher than that of Li4SiO4.

Novel kaolin/polysiloxane based organic-inorganic hybrid materials: Sol-gel synthesis, characterization and photocatalytic properties

New hybrid materials using kaolin and the organosilicas methyl-polysiloxane (MK), methyl-phenyl-polysiloxane (H44), tetraethyl-ortho-silicate (TEOS) and 3-amino-propyl-triethoxysilane (APTES) were obtained by sol-gel process. These materials presented specific surfaces areas (SBET) in the range of 20–530 m2 g−1. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed remarkable differences between the kaolin and hybrid structures. Thermogravimetric analysis (TGA) revealed that the hybrid materials presented higher thermal stability when compared with their precursors. The electronic properties of the materials were also studied by Ultraviolet-Visible Diffuse Reflectance Absorption (DRUV) and Diffuse Reflectance spectroscopy (DR), where a new absorption band was observed located around 400–660 nm. In addition, these materials exhibit a decrease in DR from 30% to 70% in the blue-cyan green region and are significantly more transparent in the UV region than the kaolin, which could be useful for photocatalysis applications. These results show that the electronic structure of the final material was changed, indicating a significant interaction between the kaolin and the respective silica derivative. These findings support the main idea of the hybridization afforded by pyrolysis between kaolin and organosilica precursors. In addition, as a proof of concept, these hybrid materials were successfully employed as photocatalyst in the photoreduction of Cr(VI) to Cr(III).