Graphene nanosheets: Ultrasound assisted synthesis and characterization

A facile sonochemical route for the synthesis of graphene nanosheets via reduction of graphene oxide (GO) has been reported. The synthesized graphene sheets are characterized using UV–vis spectra, Fourier transform infra-red (FT-IR) spectra, transmission electron microscope, X-ray photoelectron spectra (XPS) and Raman spectroscopic techniques. The UV–vis spectroscopy results showed that the absorption peak was red shifted due to the reduction of GO into graphene. FT-IR and XPS spectra revealed the removal of oxygenated functional groups in graphene after the reduction process. Raman spectra confirmed the restoration of new sp² carbon domains in graphene sheets after the reduction. The sonochemical approach for the synthesis of graphene nanosheets is relatively fast, cost-effective and efficient as compared to other methods.     

Computational study of new azo dyes with different anchoring groups for dye-sensitised solar cells

Some of new azo dyes with different anchoring groups, such as biscarbodithiolic acid, hydroxamic acid, phosphonic acid, carboxcylic acid and sulfonic acid have been investigated theoretically to evaluate the effects of various anchoring groups on the optical and electronic properties of the dyes in dye-sensitised solar cells. Optical and electronic properties, UV–Vis absorption spectra, light-harvesting efficiency, lifetime of the excited state, chemical hardness and lowest unoccupied molecular orbital (LUMO) orbital weight of the dyes on the anchoring groups, have been studied to shed light on how the various anchoring groups influence the properties of the dyes. The biscarbodithiolic acid-based dye shows the longest maximum absorption wavelength and the widest absorption spectra together with the highest light-harvesting efficiency, the longest lifetime of the excited state and the highest the LUMO orbital weight of the dye on the atoms of the anchoring group, suggesting the good ability in electron injection. Theoretical calculations have been also performed on the adsorption of these dyes on the TiO₂ anatase (101) surface. These results show that the biscarbodithiolic acid-based dye has the highest adsorption energy and the largest negative shift of the conduction band of TiO₂ due to the adsorption of the dye onto the TiO₂.     

Effect of doping and annealing on the physical properties of ZnO:Mg nanoparticles

Well-dispersed undoped and Mg-doped ZnO nanoparticles with different doping concentrations at various annealing temperatures are synthesized using basic chemical solution method without any capping agent. To understand the effect of Mg doping and heat treatment on the structure and optical response of the prepared nanoparticles, the samples are characterized using X-ray diffraction (XRD), energy-dispersive X-ray (EDX), UV–Vis optical absorption, photoluminescence (PL), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. The UV–Vis absorbance and PL emission show a blue shift with increasing Mg doping concentration with respect to bulk value. UV–Vis spectroscopy is also used to calculate the band-gap energy of nanoparticles. X-ray diffraction results clearly show that the Mg-doped nanoparticles have hexagonal phase similar to ZnO nanoparticles. TEM image as well as XRD study confirm the estimated average size of the samples to be between 6 and 12 nm. Furthermore, it is seen that there was an increase in the grain size of the particles when the annealing temperature is increased.     

Different strategies for the synthesis of graphene/ZnO composite and its photocatalytic properties

Owing to its unique physical and chemical properties, graphene has attracted tremendous attention in the preparation of graphene-based composites for various applications. In this study, two different strategies have been developed to load zinc oxide (ZnO) nanorods onto reduced graphene oxide (RGO) sheets, i.e., in situ growth and a self-assembly approach. The microstructure and morphology of the synthesized RGO/ZnO nanocomposites was investigated by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM) and Brunauer–Emmett–Teller (BET) measurements. Fluorescence emission spectra (PL) of RGO/ZnO composites were performed to attribute quality of combination between RGO and ZnO. Significantly enhanced photocatalytic activity of RGO/ZnO nanocomposites in comparison to bare ZnO nanoparticles was revealed by the degradation of methylene blue under irradiation, which can be attributed to the inhibition of electron–hole pair recombination and enhanced adsorption due to the presence of RGO sheets.     

Modified g-C3N4/TiO2 nanosheets/ZnO ternary facet coupled heterojunction for photocatalytic degradation of p-toluenesulfonic acid (p-TSA) under visible light

Novel ternary nanocomposites with facet coupled structure were synthesized by using modified g-C₃N₄, TiO₂ nanosheets and nano-ZnO. Nanosheet/nanosheet heterojunction structure was investigated by TEM, XPS and XRD. FT–IR and Nitrogen adsorption were illustrated for chemical/physical structure analyses. Solution of p-Toluenesulfonic acid (p-TSA) was chosen as target pollutant for visible light photodegradation and the excellent removal efficiency was achieved by this structurally modified g-C₃N₄/TiO₂/ZnO hybrid. The visible light absorption improvement and quantum efficiency enhancement, which were testified by UV–vis DRS, PL and p-TSA photodegradation measurements, due to the facet coupled structure and appropriate quantity of modified g-C₃N₄ in the nanocomposites.     

Structural,morphological, optical and antibacterial activity of rod-shaped zinc oxide and manganese-doped zinc oxide nanoparticles

Pure ZnO and Mn-doped ZnO nanoparticles were synthesized by Co-precipitate method. The structural characterizations of the nanoparticles were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. UV–Vis, FTIR and photoluminescence (PL) spectroscopy were used for analysing the optical properties of the nanoparticles. XRD results revealed the formation of ZnO and Mn-doped ZnO nanoparticles with wurtzite crystal structure having average crystalline size of 39 and 20 nm. From UV–Vis studies, the optical band-gap energy of 3.20 and 3.25 eV was obtained for ZnO and Mn-doped ZnO nanoparticles, respectively. FTIR spectra confirm the presence of ZnO and Mn-doped ZnO nanoparticles. Photoluminescence analysis of all samples showed four main emission bands: a strong UV emission band, a weak blue band, a weak blue–green band and a weak green band indicating their high structural and optical qualities. The antibacterial efficiency of ZnO and Mn-doped ZnO nanoparticles were studied using disc diffusion method. The Mn-doped ZnO nanoparticles show better antibacterial activity when higher doping level is 10 at% and has longer duration of time.     

Effect of gamma irradiation on synthesis and characterization of bio-nanocomposite SF/Ag nanoparticles

This study describes the synthesis of silver nanoparticles (AgNPs) using aqueous silk fibroin (SF) solution obtained from Bombyx mori silk under gamma radiation environment. The obtained AgNPs were characterized using UV–visible (UV–Vis) spectroscopy, X-ray diffraction (XRD) measurements, dynamic light scattering experiment (DLS) and transmission electron microscope (TEM) images. The UV–Vis absorption spectra of the samples confirmed the formation of AgNPs by showing surface plasmon resonance (SPR) band in the range of (= 428–435?nm. The XRD study revealed metal silver with the face-centered cubic (FCC) crystal structure. DLS measurements showed the dose-dependent average size of the AgNPs. TEM images showed formed AgNPs are nearly spherical in shape with smooth edges. From this study, it was found that the increasing radiation dose increases the rate of reduction and decreases the particle size. The size of the AgNPs can be tuned by controlling the radiation dose.     

8—羟基喹啉铝的荧光老化机制

报导了８－羟基喹啉铝（Ａｌｑ３）在紫外光照射下发生荧光猝灭的机制,测量了Ａｌｑ３在光照射前后的紫外－可见吸收光谱、荧光光谱、红外吸收光电子能谱（ＸＰＳ）,分析了紫外光照射后Ａｌｑ３分子结构变化,证明了产生结构变化的根源是中水与Ａｌｑ３发生了化学反应,对Ａｌｑ３的我老化机制提出了可能的解释。     

CVD合成的掺杂BNx-石墨烯纳米复合材料:结构和发光性能

用B₄C为硼源,利用CVD系统在N₂-H₂等离子体中合成了掺杂BN_x纳米棒,接着在掺杂BN_x纳米棒表面用CH₄生长了石墨烯纳米片,制备出掺杂BN_x-石墨烯三维纳米复合材料。一系列表征结果说明合成的纳米复合材料由C和O共掺杂的BN_x纳米棒和石墨烯纳米片组成,其形成与碳氢基团的转换和掺杂BN_x纳米棒的形变在石墨烯纳米片中产生的应力有关。室温发光性能表明石墨烯纳米片对掺杂BN_x纳米棒的紫外光和绿光有明显的猝灭作用,起源于掺杂BN_x-石墨烯界面上的电荷转移和电子散射。     

Low-temperature time-resolved vacuum UV spectroscopy of potassium pentaborate crystals

For the first time, subnanosecond time resolution is attained in the low-temperature (at 7 K) measurements of the photoluminescence (PL) spectra (2–6 eV), the PL excitation spectra (4–32 eV), the PL kinetics, and the reflection spectra (4–21 eV) of undoped potassium pentaborate KB₅O₈·4H₂O (KB5) crystals under selective photoexcitation by synchrotron radiation. The PL peaks associated with the intrinsic defects of the KB5 lattice are detected. The PL bands resulting from radiative annihilation of the localized and self-localized electron excitations are singled out; these excitations are most efficiently photogenerated at the fundamental absorption edge in the region where the free exciton formation is expected. The difference between the PL spectra of the fast and slow components is revealed. An effective low-temperature energy transport over the KB5 hydrogen sublattice is deduced from a drop in efficiency of PL excitation in the interband-transition region as a result of nonradiative energy loss. Long-term vacuum UV irradiation of a KB5 crystal at 7 K gives rise to defects in the hydrogen sublattice, which facilitate localization of the electron excitations and reduce the effective length of their diffusion. This leads to a decrease in the nonradiative energy loss, thus enhancing the efficiency of the PL photoexcitation in the band-to-band transition region.     

Induced Quasi-Dynamic Disorder in a Structure of Rhenium Ion-Implanted Quartz Glass

Physics of the Solid State - The ultraviolet (UV) absorption spectra were studied in UV–Vis–IR quartz glasses exposed to the rhenium ion irradiation at the energy of 30 keV. An increase...     

Surface modifications of PADC polymeric material by ion beam bombardment for high technology applications

Surface modification of Poly (allyl diglycol carbonate) (PADC) is induced by 150 keV Ag ions of different fluences. The pristine as well as bombarded samples were investigated by UV–Vis spectroscopy, Fourier transform-infrared analysis (FTIR) and micro-hardness tester. The variations of wettability and surface free energy were determined by the contact angle measurements. The obtained results showed that ion beam bombardment induced increase in the absorption spectra of the UV–Vis with increase of ion fluence as well. The direct and indirect optical band gap decreased from 4.2 to 3.6 eV for pristine sample to 3.2 and 2.5 eV for those bombarded with Ag ion beam at the highest fluence, respectively. Changes in chemical properties were observed by Fourier transform infrared spectroscopy. Increase in the wettability, surface free energy and work of adhesion with increase the ion fluence were observed. Ion bombardment inducing increasing in a micro-hardness surface due to the high carbon surface concentration and cross-linking effects in the polymeric chains. The bombarded PADC surfaces may find special applications to the field of the micro-electronic devices and printing process.     

Synthesis,growth and third order nonlinear optical studies of a rhombohedral crystal: Sodium tetraborate pentahydrate

An apt and a futuristic nonlinear optical material sodium tetraborate pentahydrate (STBPH) was synthesized and grown by the technique of slow evaporation. The structural parameters of the crystal was confirmed by single crystal XRD revealed rhombohedral crystal system. Crystal's broad optical transparency was revealed by UV–Vis absorption spectrum. From the absorption spectrum, theoretical calculations were made to determine absorption coefficient, band gap, Urbach energy and reflectance. The functional groups were identified by FT-IR and FT-Raman spectra. Vicker's microhardness measurement disclosed that the grown crystal belongs to soft material category. Photoluminescence (PL) spectral study of STBPH indicated violet and blue emission peaks respectively at 343.06 nm and at 453.11 nm, 490.19 nm. Dielectric studies reveal the dielectric nature of the grown crystal. TGA-DTA studies showed that the crystal holds good thermal stability. The third order nonlinearities of STBPH was investigated by Z-scan technique manifest its suitability in nonlinear optical applications.     

Enhanced photocatalytic activity of graphene–TiO2 composite under visible light irradiation

Novel graphene–TiO₂ (GR–TiO₂) composite photocatalysts were synthesized by hydrothermal method. During the hydrothermal process, both the reduction of graphene oxide and loading of TiO₂ nanoparticles on graphene were achieved. The structure, surface morphology, chemical composition and optical properties of composites were studied using XRD, TEM, XPS, DRS and PL spectroscopy. The absorption edge of TiO₂ shifted to visible-light region with increasing amount of graphene in the composite samples. The photocatalytic degradation of methyl orange (MO) was carried out using graphene–TiO₂ composite catalysts in order to study the photocatalytic efficiency. The results showed that GR–TiO₂ composites can efficiently photodegrade MO, showing an enhanced photocatalytic activity over pure TiO₂ under visible-light irradiation. The enhanced photocatalytic activity of the composite catalysts might be attributed to great adsorptivity of dyes, extended light absorption range and efficient charge separation due to giant π-conjugation system and two-dimensional planar structure of graphene.     

Temperature-dependent photoluminescence of polyazomethine films

We report absorption and first reliable photoluminescence (PL) studies at various temperatures on relatively thick films of the basic polyazomethine — PPI, i.e., poly(1,4-phenylene-methylidynenitrilo-1,4-phenylenenitrilomethylidine), prepared by chemical vapor deposition (CVD). Both absorption and PL spectra exhibit the vibronic progression due to the C–C stretching mode, characteristic for conjugated polymers. The absorption spectra appear to be practically temperature independent, in contrast to PL spectra, the intensity of which strongly decreases with increasing temperature. The origin of generally weak photoluminescence of PPI is suggested to be the result of a non-radiative electronic state occupied by the lone electron pair on the nitrogen orbital.     

采用紫外光照法在磷酸盐玻璃中合成CdS/Ag复合微粒

掺杂有Ⅱ-Ⅵ族半导体纳米颗粒(如CdS)或者过渡金属(如Ag)的玻璃由于其较大的非线性光学效应而引起人们的极大兴趣,而同时掺杂有半导体/金属的复合微粒则可以进一步增强玻璃的三阶非线性效应,因此成为目前的研究热点。我们利用玻璃沉淀技术及随后的热处理和紫外光还原技术制备了含高浓度(1%)Ag微粒的玻璃,并采用X射线衍射分析了其物相,用高分辨扫描电镜分析了其形貌,以及测试了其吸收和发光性能。从CdS/Ag复合微粒的扫描照片可以发现晶粒均匀分布在玻璃中,尺寸约为1μm。X射线衍射发现经过热处理和紫外光照的样品衍射峰中含有CdS和Ag,而只进行热处理的样品则只含有CdS,未处理的样品则显非晶态。CdS/Ag复合微粒的吸收峰呈现典型的表面等离子共振峰(420nm)以及CdS的峰(600nm),只含有CdS微粒的样品的吸收峰则在480nm附近,未处理的样品在320nm附近有一个吸收峰,这可能是由于样品在快速冷却过程中的微小晶化造成的。只含有CdS微粒的样品有三个明显的发光峰,然而CdS/Ag复合微粒的发过峰则消失。我们提出了共振能量转移机制来解释该现象。讨论了紫外光照还原Ag微粒的机制。可以认为通过紫外光照,CdS表面的电子被激发出来还原Ag+,从而形成银颗粒,伴随着空穴则被表面缺陷所捕获。     

Analysis of the optical properties of poly(3‐octylthiophene) partially dedoped

In this work, poly(3‐octylthiophene) (P3OT) films were synthesized electrochemically in non‐aqueous media through the oxidation of the monomer, (3‐octylthiophene), using a standard three‐electrode cell in acetonitrile with 0.05 mol L^?1 LiClO₄ or 0.05 mol L^?1 Et₄NBF₄. The polymeric films were deposited on fluorine tin oxide (FTO). The partial dedoping was obtained in NH₄OH solution, providing a good chemical stability of the formed material. The films obtained through this method have been characterized by Fourier‐transform infrared spectroscopy (FT‐IR), electron paramagnetic resonance (EPR), UV–Vis absorption, and photoluminescence (PL) spectroscopy. The FT‐IR and EPR spectra together gave the results that led to characterization of two structures (pristine and non‐pristine forms of thiophene rings) while forming the P3OT polymer chain. These results were associated with the stabilization of pristine chains and mixed chains (non‐pristine structures) in the polymeric film. Their bands in the PL spectra are wide and asymmetric and their adjustments by Gaussian functions was necessary; this was the main indication that there are two distinct contributions to the emission spectra. These two contributions are attributed to the emission by mixed chains (Gaussian centered at higher energy) and by pristine chains (Gaussian of lower energy) present in the formed polymeric material. Copyright © 2010 John Wiley & Sons, Ltd.     

硫堇与DNA分子作用机理的光谱研究

用紫外-可见吸收光谱、荧光光谱、圆二色谱和光电子能谱等光谱方法研究了硫堇(TH)与小牛胸腺DNA(CT-DNA)的作用机理。实验结果表明,在pH 7.2的磷酸盐缓冲溶液中, TH与CT-DNA之间的作用方式以嵌入作用为主,嵌入作用使TH的紫外最大吸收峰强度减小,且峰位发生红移。由紫外光谱实验结果线性拟合求得TH与CT-DNA的表观结合常数K＝1.45×104 L·mol-1。荧光光谱实验结果表明：TH与CT-DNA的嵌入作用使TH的荧光发生强烈猝灭,猝灭常数K_SV为1.01×104 L·mol-1。嵌入作用位点主要发生在CT-DNA的鸟嘌呤(G)-胞嘧啶(C)碱基序列富集区。通过对TH的光电子能谱中N,S原子的结合能变化分析,TH分子以杂环上S原子端与CT-DNA的G-C碱基对结合,两者的相互作用对CT-DNA的二级结构构象产生影响。     

氧化石墨烯/硒化锌纳米光电材料的制备及其蓝光发射特性

采用一种简单有效的原位水热合成方法,使用石墨烯氧化物（GO）作为反应物和晶体生长基底成功制备出了还原氧化石墨烯/硒化锌（r-GO/ZnSe）纳米复合材料。采用X射线粉末衍射（XRD）、透射电子显微镜（TEM）、高分辨透射电镜（HRTEM）以及红外-可见光谱（FT-IR）等方法对r-GO/ZnSe纳米复合材料进行了检测。结果表明,平均粒径在30 nm的立方闪锌矿晶体结构的ZnSe粒子均匀分散在氧化石墨烯片层上,构成纳米复合结构。 UV-Vis光谱显示,纳米复合材料的光学吸收的起始波长在445 nm附近。PL光谱显示,纳米复合材料在470 nm附近存在一个很强的发射峰。这种石墨烯基纳米复合材料在白光二极管领域中有重要的应用价值。     

High UV absorption efficiency of nanocrystalline ZnO synthesized by ultrasound assisted wet chemical method

Ultrasound assisted wet-chemical method has been carried out to incorporate different metal and non-metal ions such as; Li, S and Ag into ZnO. Characteristic studies on the structural and optical properties of the samples especially; the ultra-violet (UV) light absorption have been carried out. X-ray diffraction (XRD) analysis shows the formation of hexagonal crystal structure of ZnO along with changes in crystallinity and micro-strain with impurity doping. The morphology of the doped samples changes from particle like structure to flower and rod like structures showing the influence of dopant ions on nano ZnO growth. Infra-red (IR) transmittance spectra give information about the presence of metal–oxygen bond along with other stretching and bending modes. UV–visible absorption studies show the narrowing and sharpening of UV absorption band along with a blue shift for the doped samples. This shows the intensification in the excitonic absorption in ZnO after doping specific elements which will find application in UV blocking agents. Photoluminescence (PL) measurement shows the presence of excitonic emission and emissions due to intrinsic defects and external impurities in UV and visible regions respectively. These emission bands show a change in their position and intensity which has been explained on the basis of the existence of impurity levels in the band gap of ZnO.