Adsorption of methylene blue onto silylated silica surfaces, studied using visible attenuated total reflection spectroscopy with a slab optical waveguide

The behavior of methylene blue (MB) molecules at silica/water and silylated silica/water interfaces was examined using visible attenuated total reflection spectroscopy with a slab optical waveguide (SOWG). An alkyl silane coating changed the adsorbed form of MB on the surface from a dimer (lambda max = 600 nm, bare silica surface) to a monomer (lambda max = 670 nm), and the carbon number of the silylation reagent influenced the amount of adsorption and the orientation of the molecule. Moreover, the addition of an anionic surfactant, dodecylbenzenesulfonate (DBS), caused the deposition of MB/DBS ion pairs, which gave an identical attenuated total reflection (ATR) spectrum to that of the dimer. Linear dichroism measurements revealed that the ion pairs were adsorbed onto the silylated silica surface randomly in terms of the orientation angle of MB, while the MB monomer was strongly oriented, i.e., the direction of the transition moment of MB roughly parallels the surface plane. This difference in the orientation angles of the adsorbed species can be utilized for their selective detection using polarization SOWG measurements.     

Slab optical waveguide high-acidity sensor based on an absorbance change of protoporphyrin IX

A sensitive and fast-responsive evanescent wave absorption sensor has been constructed for pH measurements in highly acidic ranges. This sensor is based on a pH-dependent color change of protoporphyrin IX (PPIX). For the sensitive detection, a visible attenuated total reflection spectrometer with a slab optical waveguide (SOWG) was laboratory-made, and the guiding layer surface was modified with a PPIX-immobilized acrylamide-based thin membrane. The sensing membrane with a thickness of approximately 1 mum was directly fabricated on the SOWG glass surface by copolymerization of acrylamide, N,N'-methylene bisacrylamide, and PPIX in the narrow space confined by a cover plate. PPIX possesses two double bonds in its structure, and so it can be covalently incorporated into the membrane. The response characteristics of the PPIX-immobilized optode membrane were explored using aqueous solutions with different concentrations of HNO(3) or HCl. The optode membrane provided characteristic Soret band absorption spectra depending on the hydrogen ion concentration; the absorbance at 410 nm increased with increasing the concentrations in the range of 0.15-2 M, corresponding to the range of pH -0.3 to 0.8. The absorption signal reached 90% of its final value within 10 s, while the absorption signal was quite readily returned to background level simply by passing 2 mL of distilled water through a flow cell with a volume of 16.5 muL placed on the SOWG. Due to the rapid response and reversibility, this sensor could be operated in a flow-through mode as well as in a conventional static mode, where deionized water was conveniently used as a carrier and conditioning solution. In terms of the stability and precision, this sensor showed no significant change in response even after 100 assays and after being stored in a dry condition for over 6 months. Relative standard deviations for 10 replicate measurements were less than 1.8% in the linear range, and the detection limit calculated from 3 times of the standard deviation was 0.02 pH unit.     

Characterization of the electrochemical reactions in the Li(1+x)V3O8/Li cell by soft X-ray absorption spectroscopy and two-dimensional correlation analysis

We applied soft X-ray absorption spectroscopy (XAS) and two-dimensional (2D) correlation analysis to the first lithium insertion-extraction cycle in a Li(1+x)V3O8/Li cell in order to investigate the electrochemical reactions of lithium with the Li(1+x)V3O8 electrode. The V L(II,III)-edge and O K-edge spectra of the Li(1+x)V3O8 electrode were obtained for varying electrode lithium content. The insertion of lithium leads to the reduction of the V5+ species present in the pristine Li(1+x)V3O8 electrode, and to the red shift and the broadening of the spectral features of the V L(II,III) edge compared to those of the pristine electrode. In the extraction process, the main spectral features at the highest value of the extraction of lithium show some differences compared to the features of the pristine electrode spectrum due to the residual lithium ions in the Li(1+x)V3O8 structure. The O K-edge spectra revealed that the insertion of lithium mainly affects the V 4sp-O 2p bonds and consequently induces a change in bonding geometry. The 2D correlation analysis of these spectra clearly shows that V-O bonds are significantly perturbed by the insertion-extraction of lithium into the Li(1+x)V3O8 electrode.     

Practically modified attenuated total reflection surface-enhanced IR absorption spectroscopy for high-quality frequency-extended detection of surface species at electrodes

A practically modified ATR configuration has been proposed for in situ electrochemical surface-enhanced IR absorption spectroscopy (SEIRAS) by sandwiching an ultrathin water interlayer between a hemicylindrical ZnSe prism and a Si wafer as an integrated window. This new ATR optics significantly enhances the throughput of an effective IR beam across the ZnSe/gap/Si/metal film, enabling high-quality spectral fingerprints down to 700 cm(-1) to be readily detected at larger incidence angles without compromising the electrochemical feasibility and stability of metallic films deposited on Si. The advantages of this modified ATR-SEIRAS have been initially applied to explore two selected systems: wide-ranged in situ ATR-SEIRA spectra provided strong evidence in support of the formate intermediate pathway for methanol electrooxidation at the Pt electrode in an acid solution; in addition, new spectral fingerprints revealed comprehensive orientational information about of the p-nitrobenzoate species at Pt electrode as a result of the dissociative adsorption of p-nitrobenzoic acid molecules from an acid solution.     

Synthesis and characterization of the N-doped TiO2 photocatalyst for the photodegradation of methylene blue and phenol

To extend the light absorption of TiO2-based photocatalysts towards the visible-light range and to eliminate the rapid recombination of excited electrons/holes during photoreaction, a new type of photocatalyst (N-doped TiO2) powder was prepared through a simple sol-gel process. The crystal phase composition, structure, and light absorption of the new photocatalyst were comprehensively examined via X-ray diffraction, ultraviolet-visible (UV-Vis) absorption spectroscopy, and atomic-absorption spectroscopy. The photo-oxidation efficiency of the photocatalyst was also evaluated in the photodegradation of methylene blue (MB) and of phenol in aqueous solutions under visible-light irradiation from a neon lamp (lambda > 400 nm). The results of the analyses that were performed in this study indicated that the N-doped TiO2 could eliminate the electron/holes recombination and could increase the light absorption in the visible range. The results of the analysis of the UV-Vis diffuse reflection and optical-absorption spectra indicated that a new energy level below 3.2 eV generated in the N-doped TiO2 promoted the optical absorption in the visible-light region and made visible-light excitation possible (E < 3.2 eV). The experiment demonstrated that the photo-oxidation efficiency of MB when N-doped TiO2 powder was used was significantly higher than that when the conventional TiO2 powders were used. The development of such photocatalyst may be considered a breakthrough in the large-scale utilization of solar energy to address the current and future environmental needs.     

Preparation, characterization, and application of electrochemically functional graphene nanocomposites by one-step liquid-phase exfoliation of natural flake graphite with methylene blue

Electrochemically functional graphene nanocomposites have been directly prepared by one-step liquid-phase exfoliation of natural flake graphite with methylene blue (MB). UV-visible spectra of the obtained aqueous dispersions of graphene-methylene blue (G-MB) nanocomposite at different exfoliation time indicate that the concentration of graphene dispersion increased markedly with increasing exfoliation time. Atomic force microscopy (AFM) and Raman spectroscopy verified that the graphene was exfoliated into single-layer or bilayer states. FT-IR spectroscopy of G-MB suggests that a ??-?? stacking interaction is involved in the structure-associated interactions between graphene and adsorbed MB molecules. A G-MB nanocomposite modified glassy carbon (GC) electrode exhibits excellent electrochemical properties and good electrochemical stability. Additionally, the G-MB/GC modified electrode shows more favorable electron transfer kinetics for potassium ferricyanide and potassium ferrocyanide probe molecules, which are important electroactive compounds, compared with reduced graphene oxide (RGO)-MB/GC, RGO/GC, bare GC and graphite/GC electrodes. Furthermore, the G-MB/GC modified electrode exhibits good electrocatalytic activity toward hydrogen peroxide (H₂O₂) and ??-nicotinamide adenine dinucleotide (NADH). The excellent electroactivity, electrochemical stability and electrocatalytic activity of the G-MB nanocomposites prepared in this work are potentially very useful for basic electrochemical studies and for the practical development of electronic devices such as biosensors and photovoltaic cells.      

水热法制备Cu掺杂可见光催化剂BiVO4及其光催化性能研究

以Bi(NO3)3.5H2O、NH4VO3、Cu(NO3)2.3H2O为原料,采用水热法合成了Cu-BiVO4光催化剂,并利用X射线衍射(XRD)、扫描电镜(SEM)、X射线光电子能谱(XPS)、紫外漫反射(UV-Vis)等测试手段对催化剂进行了表征.结果表明,提高前驱液pH值,可得到单斜晶系白钨矿型Cu-BiVO4光催化剂,BiVO4的晶型结构并未随着Cu掺入量的增加而改变.光催化剂中的Cu元素以CuO和Cu2O的形式存在.Cu的引入使可见光吸收带发生红移,吸收强度明显提高.可见光催化降解亚甲基蓝溶液的结果表明,Cu掺杂有利于提高BiVO4的活性.其中pH值为5.0、Cu掺入量为1.0wt%的BiVO4具有最好的光催化效果,可见光照射60 min后,对初始浓度为10 mg/L的亚甲基蓝溶液的最高降解率由纯BiVO4的57.4%提高到97.8%.并对Cu掺入后光催化活性提高的机理进行了分析.     

The Detection of Chemical Vapors in Air Using Optical Emission Spectroscopy of Pulsed Microdischarges From Two- and Three- Electrode Microstructures

Emission spectroscopy of plasma-excited chemical species is widely used for generalized chemical analyses in bench-top systems. This paper explores the use of pulsed microdischarges between two and three electrode microstructures, which operate in air at atmospheric pressure, for use in handheld chemical analyzers. Pulsed microdischarges are fired between two-electrodes spaced apart by 0.2-2 mm. Synchronized optical sampling and time resolved spectroscopy are performed to capture the emission spectra from the microdischarge and its afterglow. The discharge spectra in air consist mainly of wide-band background spectra and line spectra from the nitrogen, and water vapor in air. The detection of vapors in air is limited by the relative strengths of representative lines compared to background spectra rather than by their absolute strength. The separate temporal characteristics of the line and background spectra present opportunities to improve detection. This concept is evaluated using isopropyl alcohol vapors (100 ppm) for which lines corresponding to CH fragments are detected with a handheld spectrometer despite the presence of air spectra. This paper also introduces a three-electrode (flashFET) configuration, which further reduces power consumption and electrode wear. Occupying an active area < 1 mm², it employs a strategically located high-impedance gate electrode that permits the use of pulses < 100 V between the source and drain. The device consumes only 2.5 muJ/pulse at 140 Torr and 22.5 muJ/pulse at atmosphere, as compared to 470 muJ/pulse for two-electrode discharges. The operation of the flashFET as a gas sensor is evaluated using acetone vapors in air ambient. A response curve is obtained by measuring the 388.1 nm emission from acetone fragments for acetone concentrations ranging from 50 to 1000 ppm.     

Surface reaction of LiCoO2/Li system under high-voltage conditions by X-ray spectroscopy and two-dimensional correlation spectroscopy (2D-COS)

We studied the surface reactions of a LiCoO(2)/Li cell under high-voltage conditions using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and two-dimensional correlation spectroscopy (2D-COS). 2D XPS correlation spectra show that Li(2)CO(3) is formed first by decomposition of the organic solvents, and then polycarbonate, which is formed by polymerization of the electrolytes, is produced on the cathode surface of the LiCoO(2)/Li system under high-voltage conditions. XAS measurements also confirm that the solid electrolyte interface (SEI) layer is formed on the LiCoO(2) electrode by decomposition of the organic solvents. The thickness of the SEI layer is less than 100 ?.     

离子液体中Co掺杂介孔TiO2可见光催化剂的制备及性能研究

以离子液体([C₄MIM]BF₄)为模板剂, 采用溶胶-凝胶法制备了介孔TiO₂和Co掺杂的介孔TiO₂光催化剂。研究了Co掺杂对样品的比表面积、晶相、元素价态、吸光特性及可见光活性的影响。结果表明: 所制备的Co/TiO₂光催化剂为介孔结构的具有较大比表面积的锐钛矿相纳米颗粒; XPS分析表明: Co以Co²⁺取代Ti⁴⁺进入TiO₂晶格形成杂质能级, 降低了TiO₂带隙能, 有效拓展了TiO₂的光响应范围。以亚甲基蓝水溶液为降解对象, 在可见光 (λ>420 nm)下考察制备样品的光催化活性, 结果表明: Co掺杂的TiO₂具有可见光活性, 且0.3%Co/TiO₂的活性最高。     

Application of graphene–pyrenebutyric acid nanocomposite as probe oligonucleotide immobilization platform in a DNA biosensor

A stable and uniform organic–inorganic nanocomposite that consists of graphene (GR) and pyrenebutyric acid (PBA) was obtained by ultrasonication, which was characterized by scanning electron microscopy (SEM) and UV–vis absorption spectra. The dispersion was dropped onto a gold electrode surface to obtain GR–PBA modified electrode (GR–PBA/Au). Electrochemical behaviors of the modified electrode were characterized by cyclic voltammetry and electrochemical impedance spectroscopy using [Fe(CN)₆]^3 ?/4 ? as the electroactive probe. A novel DNA biosensor was constructed based on the covalent coupling of amino modified oligonucleotides with the carboxylic group on PBA. By using methylene blue (MB) as a redox-active hybridization indicator, the biosensor was applied to electrochemically detect the complementary sequence, and the results suggested that the peak currents of MB showed a good linear relationship with the logarithm values of target DNA concentrations in the range from 1.0 × 10^? 15 to 5.0 × 10^? 12 M with a detection limit of 3.8 × 10^? 16 M. The selectivity experiment also showed that the biosensor can well distinguish the target DNA from the non-complementary sequences.     

Effects of samarium dopant on photocatalytic activity of TiO<Subscript>2</Subscript> nanocrystallite for methylene blue degradation

Sm³⁺-doped TiO₂ nanocrystalline was synthesized by a sol–gel auto-combustion method and characterized by X-ray diffraction, Brunauer-Emmett-Teller method (BET), UV–vis diffuse reflectance spectroscopy (DRS), and also photoluminescence (PL) emission spectroscopy. The photocatalytic activity of Sm³⁺–TiO₂ catalyst was evaluated by measuring degradation rates of methylene blue (MB) under either UV or visible light. The results showed that doping with the samarium ions significantly enhanced the photocatalytic activity for MB degradation under UV or visible light irradiation. This was ascribed to the fact that a small amount of samarium dopant simultaneously increased MB adsorption capacity and separation efficiency of electron-hole pairs. The results of DRS showed that Sm³⁺-doped TiO₂ had significant absorption between 400 nm and 500 nm, which increased with the increase of samarium ion content. The adsorption experimental demonstrated that Sm³⁺–TiO₂ had a higher MB adsorption capacity than undoped TiO₂ and adsorption capacity of MB increased with the increase of samarium ion content. It is found that the stronger the PL intensity, the higher the photocatalytic activity. This could be explained by the points that PL spectra mainly resulted from surface oxygen vacancies and defects during the process of PL, while surface oxygen vacancies and defects could be favorable in capturing the photoinduced electrons during the process of photocatalytic reactions, so that the recombination of photoinduced electrons and holes could be effectively inhibited.     

Fabrication of TiO2/Ti electrode by laser-assisted anodic oxidation and its application on photoelectrocatalytic degradation of methylene blue

A TiO2/Ti mesh electrode by laser calcination was prepared in this article. The resulting TiO2 film was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS), and it illuminated that the prepared electrode mainly consisted of anatase TiO2 nanoparticles on its surface and exhibited a superior photocatalytic activity. The photodegradation of methylene blue (MB) using the proposed electrode under different experimental conditions was investigated in terms of both UV absorbance at 664 nm and chemical oxygen demand (COD) removal. The electrical bias applied in photoelectrocatalytic (PEC) oxidation was also studied. The experimental results showed that under the optimal potential of +0.50 V (versus SCE), UV absorbance and COD removal during the photodegradation of MB by the proposed TiO2/Ti mesh electrode were 97.3% and 87.0%, respectively. Through the comparison between photocatalytic (PC) oxidation and photoelectrocatalytic (PEC) oxidation, it was found that PEC oxidation was a convenient and effective way to mineralize the organic matters and that laser-treated photoelectrode exceeded the oven-treated one.     

Immobilization of methylene blue on self-assembled iodine monolayers on gold

The immobilization of methylene blue (MB) on iodine-covered Au(111) is studied by electrochemical techniques, scanning tunneling microscopy (STM), Auger Electron Spectroscopy (AES), and Raman spectroscopy. Results show that MB species are efficiently adsorbed on the square root of 3 x square root of 3 R30 degrees I lattice on Au(111). The electrochemical behavior of the adsorbed MB molecules is reversible, indicating a relatively fast electron transfer from the Au(111) surface to the immobilized MB species through the iodine layer. STM images with molecular resolution are consistent with adsorption of MB dimers on a square root of 3 x square root of 3 R30 degrees I lattice placed atop of the Au(111) substrate. Results are compared to those obtained for MB immobilized on Au(111) covered by S(n) (n = 3-8) surface structures.     

Electrophoretic deposition of Sn-doped TiO<Subscript>2</Subscript> nanoparticles and its optical and photocatalytic properties

In this research, Sn-doped TiO₂ (Sn–TiO₂) nanoparticles were synthesized by a simple sol–gel method. The structure and composition of the as-prepared sample were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible absorption spectroscopy. Electrophoretic deposition (EPD) technique was used to deposit thin films of Sn–TiO₂ on 316L stainless steel (316L SS) substrate. In order to achieve a fine and high-quality layer on the electrode surface, N-phenyl-p-phenylenediamine (NPPDA) was used as a new dispersant and charging agent in ethanolic suspensions. Based on zeta potential and conductivity measurements of the suspensions, an optimum concentration of the NPPDA dispersant was found to be 3.0 g l^?1. The in-situ EPD kinetics was also studied. The prepared Sn–TiO₂ film was used for the photodegradation of methylene blue (MB) under UV, visible and sun lights. The results revealed that the Sn–TiO₂ film could be able to degrade the MB under sunlight. The calculated degradations were 44, 65, and 73% after 2, 4 and 5 h, respectively. The relation between \(\ln \left( {\frac{{{{\text{A}}_0}}}{{\text{A}}}} \right)\) and time was linear, so it was proved that the photocatalytic degradation of MB can be characterized by pseudo-first order reaction kinetics.     

Extremely sensitive detection of NO₂ employing off-axis integrated cavity output spectroscopy coupled with multiple-line integrated absorption spectroscopy

We report on the development of a new sensor for NO? with ultrahigh sensitivity of detection. This has been accomplished by combining off-axis integrated cavity output spectroscopy (OA-ICOS) (which can provide large path lengths of the order of several kilometers in a small volume cell) with multiple-line integrated absorption spectroscopy (MLIAS) (where we integrate the absorption spectra over a large number of rotational-vibrational transitions of the molecular species to further improve the sensitivity). Employing an external cavity quantum cascade laser operating in the 1601-1670 cm?1 range and a high-finesse optical cavity, the absorption spectra of NO? over 100 transitions in the R band have been recorded. From the observed linear relationship between the integrated absorption versus concentration of NO? and the standard deviation of the integrated absorption signal, we report an effective sensitivity of detection of approximately 28 ppt (parts in 1012) for NO? To the best of our knowledge, this is among the most sensitive levels of detection of NO? to date.     

Preparation N-F-codoped TiO2 nanorod array by liquid phase deposition as visible light photocatalyst

An efficient method for the preparation of N-F-codoped visible light active TiO₂ nanorod arrays is reported. In the process, simultaneous nitrogen and fluorine doped TiO₂ nanorod arrays on the glass substrates were achieved by liquid phase deposition method using ZnO nanorod arrays as templates with different calcination temperature. The as-prepared samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectra measurements. It was found that calcination temperature is an important factor influencing the microstructure and the amount of N and F in TiO₂ nanorod arrays samples. The visible light photocatalytic properties were investigated using methylene blue (MB) dye as a model system. The results showed that N-F-codoped TiO₂ nanorod arrays sample calcined at 450 °C demonstrated the best visible light activity in all samples, much higher than that of TiO₂ nanoparticles and P25 particles films.     

Quantitative determination of absolute organohalogen concentrations in environmental samples by X-ray absorption spectroscopy

An in situ procedure for quantifying total organic and inorganic Cl concentrations in environmental samples based on X-ray absorption near-edge structure (XANES) spectroscopy has been developed. Cl 1s XANES spectra reflect contributions from all Cl species present in a sample, providing a definitive measure of total Cl concentration in chemically heterogeneous samples. Spectral features near the Cl K-absorption edge provide detailed information about the bonding state of Cl, whereas the absolute fluorescence intensity of the spectra is directly proportional to total Cl concentration, allowing for simultaneous determination of Cl speciation and concentration in plant, soil, and natural water samples. Absolute Cl concentrations are obtained from Cl 1s XANES spectra using a series of Cl standards in a matrix of uniform bulk density. With the high sensitivity of synchrotron-based X-ray absorption spectroscopy, Cl concentration can be reliably measured down to the 5-10 ppm range in solid and liquid samples. Referencing the characteristic near-edge features of Cl in various model compounds, we can distinguish between inorganic chloride (Cl(inorg)) and organochlorine (Cl(org)), as well as between aliphatic Cl(org) and aromatic Cl(org), with uncertainties in the range of approximately 6%. In addition, total organic and inorganic Br concentrations in sediment samples are quantified using a combination of Br 1s XANES and X-ray fluorescence (XRF) spectroscopy. Br concentration is detected down to approximately 1 ppm by XRF, and Br 1s XANES spectra allow quantification of the Br(inorg) and Br(org) fractions. These procedures provide nondestructive, element-specific techniques for quantification of Cl and Br concentrations that preclude extensive sample preparation.     

Structural determination of individual chemical species in a mixed system by iterative transformation factor analysis-based X-ray absorption spectroscopy combined with UV-visible absorption and quantum chemical calculation

A multitechnique approach using extended X-ray absorption fine structure (EXAFS) spectroscopy based on iterative transformation factor analysis (ITFA), UV-visible absorption spectroscopy, and density functional theory (DFT) calculations has been performed in order to investigate the speciation of uranium(VI) nitrate species in acetonitrile and to identify the complex structure of individual species in the system. UV-visible spectral titration suggests that there are four different species in the system, that is, pure solvated species, mono-, di-, and trinitrate species. The pure EXAFS spectra of these individual species are extracted by ITFA from the measured spectral mixtures on the basis of the speciation distribution profile calculated from the UV-visible data. Data analysis of the extracted EXAFS spectra, with the help of DFT calculations, reveals the most probable complex structures of the individual species. The pure solvated species corresponds to a uranyl hydrate complex with an equatorial coordination number (CNeq) of 5, [UO2(H2O)5]2+. Nitrate ions tend to coordinate to the uranyl(VI) ion in a bidentate fashion rather than a unidentate one in acetonitrile for all the nitrate species. The mononitrate species forms the complex of [UO2(H2O)3NO3]+ with a CNeq value of 5, while the di- and trinitrate species have a CNeq value of 6, corresponding to [UO2(H2O)2(NO3)2]0 (D2h) and [UO2(NO3)3]- (D3h), respectively.     

嵌段聚合物模板合成ZnS纳米粒子及其表征

以嵌段聚合物羟基化SBS（SBS-OH）为模板,乙酸锌和硫化钠为前驱物,制备了ZnS纳米粒子。采用紫外-可见吸收光谱（UV-Vis）、荧光光谱（PL）、广角X射线衍射（WAXD）及透射电子显微镜（TEM）对ZnS纳米粒子进行了表征。结果表明,SBS-OH可以在ZnS纳米粒子的生长过程中,起到较好的模板作用,随SBS-O...