Study of Photoinduced Electron Transfer Process in Ruthenium Complex Modified Zinc Oxide Nanoparticles by Ultrafast Time-Resolved Transient Absorption Spectroscopy

We report the preparation of ruthenium complex functionalized zinc oxide nanoparticles and the studies of the photophysical properties by ultrafast time-resolved transient absorption spectroscopy. Diazonium group was used as the anchoring unit on ZnO surface and covalent linkage was formed between the ruthenium complex and ZnO upon UV irradiation. The morphological and electron transfer properties of the ruthenium complex modified ZnO were studied. XPS and EDX results confirmed the presence of covalent linkage. The charge generation and the transport dynamics of this light harvesting system were probed by ultrafast transient absorption (TA) spectroscopy. No positive TA absorption band was observed, which suggested an ultrafast direct electron injection from the singlet ¹MLCT excited state of the ruthenium complex to the conduction band of ZnO without going via the triplet ³MLCT excited state. The time constants for the ground states bleaching of the complex modified ZnO are 8.1 and 167 ps, both of which are shorter than those of the pure ruthenium complex (21.7 and 360 ps). This further suggests a strong electronic coupling between the ruthenium complex and ZnO.     

Dissolution mechanism of cellulose in SO2–amine–dimethylsulfoxide

The dissolution mechanism of cellulose in SO₂–amine–dimethylsulfoxide systems was studied by using ¹H- and ¹³C-NMR spectroscopy. SO₂ and amine (diethylamine or triethylamine) were found to form a complex in DMSO, and the SO₂–amine complex, in turn, reacts with an alcoholic hydroxyl group of methanol to produce a new complex. In the case of cellulose, it was proved that all hydroxyl groups in cellulose react with the SO₂–amine complexes and form the same complexes in the solution state as those formed in methanol.     

Electrical and optical properties of polymer‐Au nanocomposite films synthesized by magnetron cosputtering

Polymer‐Au nanocomposite films were prepared by co‐sputtering from two independent magnetron sources. By sputtering from gold and polytetrafluoroethylene (PTFE) magnetrons, we prepared homogenous composite films using a rotatable sample holder. The microstructure of the nanocomposites was studied by transmission electron microscopy (TEM). The resistivity drops from 10⁷ to 10^?3 Ohm cm over a narrow range of metal content. The thin composite films show a strong optical absorption in the visible region due to surface plasmon resonances. The optical absorption has a strong dependence on the metal content, showing a red shift of the absorption peak from 550 nm to more than 700 nm with increasing gold content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of carbon quantum dots/TiO2 nanocomposite for photo-degradation of Rhodamine B and cefradine

Pure TiO₂ and carbon quantum dots (CQDs)-doped TiO₂ nanocomposite (CQDs/TiO₂ nanocomposite) were prepared by a sol-gel approach for photocatalytic removal of Rhodamine B and cefradine. Analyses by Transmission electronmicroscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), UV–visible spectroscopy and X-ray powder diffraction (XRD) confirmed the successful formation of CQDs/TiO₂ heterostructure. The as-prepared TiO₂ and CQDs/TiO₂ composite possessed small particles, spherical-like shape, and anatase crystal form. Meanwhile, Rhodamine B and cefradine were chosen to evaluate the photocatalytic activity of TiO₂ and CQDs/TiO₂ composite. Results revealed that with the facile decoration of CQDs, the absorption of photocatalyst was extended into visible light region and photocatalytic activity was improved in comparison with pure TiO₂. Furthermore, the mechanism for the improvement of the photocatalytic performance of the composites was discussed on the basis of the results. CQDs play an important role in the photocatalytic process, due to their superior ability to extend the visible absorption and produce more electrons and electron–hole pairs for the degradation of pollutants. In all, the paper offers further insights into the development of CQDs/TiO₂ nanocomposite as photocatalyst for the degradation of antibiotics.     

Ultrasonic assisted synthesis of TiO2–reduced graphene oxide nanocomposites with superior photovoltaic and photocatalytic activities

In this work, TiO₂–reduced graphene oxide (RGO) nanocomposites were successfully produced by an ultrasonication-assisted reduction process. The reduction of graphene oxide (GO) and the formation TiO₂ crystals occurred simultaneously. The synthesized nanocomposite was characterized by SEM, EDX, Raman spectroscopy, FTIR, XRD, XPS, UV–vis spectroscopy, photoluminescence spectrometer and electrochemical impedance spectroscopy. As a result of the introduction of RGO, the light absorption of octahedral TiO₂ was markedly improved. The photocatalytic results revealed that weight percent of RGO has substantial influence on degradation of Rhodamine B under visible light irradiation. The enhancement of the photocatalytic activity can be attributed to the enhancement of the visible-light irradiation harvesting and efficiently separation of the photogenerated charge carriers. Meanwhile, upon the RGO loading, the photoelectric conversion efficiency of TiO₂–RGO nanocomposite modified electrode was also highly improved.     

A comparative study of the preparation and physical properties of polystyrene–silica mesocomposite and nanocomposite materials

In this paper, a comparative study with regard to the preparation and physical properties of as‐prepared polystyrene–silica mesocomposite (PSM) and polystyrene‐silica nanocomposite (PSN) materials is presented. Vinyl‐modified mesoporous silica particles with a wormhole structure were first prepared by doping a sol‐gel metal oxide with an optically active non‐surfactant (dibenzoyl‐L ‐tartaric acid) as a template, followed by template removal through Soxhlet extraction. The as‐prepared silica particles with/without mesopores were subsequently characterized using the Brunauer–Emmett–Teller method and transmission electron microscopy (TEM) and Fourier transform infrared, ¹³C NMR and ²⁹Si NMR solid‐state spectroscopy. A specific feed amount of silica particles was subsequently reacted with styrene monomer by free radical polymerization to yield a series of PSM and corresponding PSN materials. Both as‐prepared composite systems were further characterized using TEM and scanning electron microscopy/energy‐dispersive X‐ray mapping studies. A systematic comparative study of the physical properties of both as‐prepared composite materials clearly illustrated that PSM had effectively enhanced thermal stability, optical clarity and dielectric properties compared to the corresponding PSN counterpart. Evaluation was carried out using thermogravimetric analysis, differential scanning calorimetry, UV‐visible transmission spectroscopy and dielectric constant measurements. Copyright © 2011 Society of Chemical Industry     

Facile hydrothermal synthesis and optical limiting properties of TiO2-reduced graphene oxide nanocomposites

TiO₂/reduced graphene oxide (RGO) nanocomposites Gx (RGO titania nanocomposite, x grams tetrabutyl titanate per 0.03 g RGO, x = 0.25, 0.50, 1.00) were prepared by a hydrothermal method: graphene oxide was reduced to RGO in a 2:1 water:ethanol mixture in the presence of varying quantities of tetrabutyl titanate, which deposited as TiO₂ on the RGO sheets. The nanocomposites were characterized by a combination of Fourier transform infrared spectroscopy, diffuse reflectance ultraviolet–visible spectroscopy, photoluminescence spectroscopy, Raman spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy studies. The nanocomposite G0.25 exhibits enhanced nonlinear optical properties compared to its individual components, which is ascribed to a combination of mechanisms. The role of defects and electron/energy transfer in the optical limiting performance of G0.25 was clarified with the help of Raman and photoluminescence spectroscopies. Intensity-dependent switching between reverse saturable absorption and saturable absorption behavior was observed with the G0.50 nanocomposite.     

Achieving ultra-high electromagnetic wave absorption by anchoring Co0.33Ni0.33Mn0.33Fe2O4 nanoparticles on graphene sheets using microwave-assisted polyol method

The Co_0.33Ni_0.33Mn_0.33Fe₂O₄/graphene nanocomposite for electromagnetic wave absorption was successfully synthesized from metal chlorides solutions and graphite powder by a simple and rapid microwave-assisted polyol method via anchoring the Co_0.33Ni_0.33Mn_0.33Fe₂O₄ nanoparticles on the layered graphene sheets. The Fe³⁺, Co²⁺, Ni²⁺ and Mn²⁺ ions in the solutions were attracted by graphene oxide obtained from graphite and converted to the precursors Fe(OH)₃, Co(OH)₂, Ni(OH)₂, and Mn(OH)₂ under slightly alkaline conditions. After the transformations of the precursors to Co-Ni-Mn ferrites and conversion of graphene oxide to graphene under microwave irradiation at 170?°C in just 25?min, the Co_0.33Ni_0.33Mn_0.33Fe₂O₄/graphene nanocomposite was prepared. The composition and structure of the nanocomposite were characterized by X-ray diffraction (XRD), inductive coupled plasma emission spectroscopy (ICP), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), transmission electron microscopy (TEM), etc. It was found that with the filling ratio of only 20?wt% and the thickness of 2.3?mm, the nanocomposite showed an ultra-wide effective absorption bandwidth (less than ?10?dB) of 8.48?GHz (from 9.52 to 18.00?GHz) with the minimum reflection loss of ??24.29?dB. Compared to pure graphene sheets, Co_0.33Ni_0.33Mn_0.33Fe₂O₄ nanoparticles and the counterparts reported in literature, the nanocomposite exhibited much better electromagnetic wave absorption, mainly attributed to strong wave attenuation, as a result of synergistic effects of dielectric loss, conductive loss and magnetic loss, and to good impedance matching. In view of its thin thickness, light weight and outstanding electromagnetic wave absorption property, the nanocomposite could be used as a very promising electromagnetic wave absorber.     

The interaction of poly(N-methacryloyl-L-alanine) with copper (II)

Summary The poly(N-methacryloyl-L-alanine) (PNMA):Cu system was investigated by visible and U.V. absorption spectroscopy and by circular dichroism.After formation of complex I involving only carboxylate groups, at low pH,the deprotonation of one amide nitrogen at pH c.a.5 leads to the formation of an optically active chelate ring(complex II).At higher pH,an other proton is neutralized with formation of an optically inactive complex III The structure of these complexes is discussed.     

Nanolayer CrAlN/TiSiN coating designed for tribological applications

With the goal to produce a hard and tough coating intended for tribological applications, CrAlN/TiSiN nanolayer coating was prepared by alternative deposition of CrAlN and TiSiN layers. In the first part of the article, a detailed study of phase composition, microstructure, and layer structure of CrAlN/TiSiN coating is presented. In the second part, its mechanical properties, fracture and tribological behavior are compared to the nanocomposite TiSiN coating. An industrial magnetron sputtering unit was used for coating deposition. X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used for compositional and microstructural analysis. Mechanical properties and fracture behavior were studied by instrumented indentation and focused ion beam techniques. Tribological properties were evaluated by ball-on-disk test in a linear reciprocal mode. A complex layer structure was found in the nanolayer coating. The TiSiN layers were epitaxially stabilized inside the coating which led to formation of dislocations at interfaces, to introduction of disturbances in the coating growth, and as a result, to development of fine-grained columnar microstructure. Indentation load required for the onset of fracture was twice lower for the nanolayer CrAlN/TiSiN, compared to the nanocomposite TiSiN coating. This agrees very well with their mechanical properties, with H³/E² being twice higher for the TiSiN coating. However, the nanolayer coating experienced less severe damage, which had a strong impact on tribological behavior. A magnitude of order lower wear rate and four times lower steady state friction coefficient were found for the nanolayer coating.     

Synthesis of MIL-101@g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanocomposite for enhanced adsorption capacity towards CO<Subscript>2</Subscript>

MIL-101@g-C₃N₄ nanocomposite was prepared by solvothermal synthesis and used for CO₂ adsorption. The parent materials (MIL-101 and g-C₃N₄) and the MIL-101@g-C₃N₄ were characterized by X-ray diffraction, argon adsorption/desorption, Fourier transform infrared spectroscopy, thermal analysis (TG/DTA), transmission electronic microscopy, and Energy-dispersive X-ray spectroscopy. The results confirmed the formation of well-defined MIL-101@g-C₃N₄ with interesting surface area and pore volume. Furthermore, both MIL-101 and MIL-101@g-C₃N₄ were accomplished in carbon dioxide capture at different temperatures (280, 288, 273 and 298 K) at lower pressure. The adsorption isotherms show that the nanocomposite has a good CO₂ adsorption affinity compared to MIL-101. The best adsorption capacity is about 1.6 mmol g^?1 obtained for the nanocomposite material which is two times higher than that of MIL-101, indicating strong interactions between CO₂ and MIL-101@g-C₃N₄. This difference in efficacy is mainly due to the presence of the amine groups dispersed in the nanocomposite. Finally, we have developed a simple route for the preparation of an effective and new adsorbent for the removal of CO₂, which can be used as an excellent candidate for gas storage, catalysis, and adsorption.     

Photocatalytic synthesis of aniline from nitrobenzene using Ag-reduced graphene oxide nanocomposite

We used a UV-irradiation reduction method to prepare Ag-reduced graphene oxide (RGO) composite by reducing graphite oxide and silver ion in ethanol. Transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), UV–vis absorption spectrophotometry (UV–vis), and X-ray photoelectron spectroscopy (XPS) characterized the prepared samples. Ag–RGO nanocomposite was tested for reduction of nitrobenzene to aniline under visible light. The Ag–RGO nanocomposites have a high efficiency to convert nitrobenzene to aniline under visible-light irradiation. Therefore, Ag-reduced graphene oxide nanocomposite can be used as a photocatalyst for organic synthesis.     

Facile fabrication of novel Eu‐containing copolymer and luminescent properties

A new Eu‐containing copolymer was successfully fabricated through two steps. First, the Eu‐containing monomer was synthesized from 4‐Vinylbenzoic acid and europium ion (Eu³⁺) complex, which rare‐earth ions connect with the ligand by covalent bands. Next, the copolymer was obtained by free‐radical copolymerization of Eu‐containing monomer with methyl methacrylate using 2, 2′‐azobis(isobutyronitrile) (AIBN) as initiator at low temperature. Infrared spectroscopy, gel permeation chromatography and scanning electron microscopy were applied to characterize the structure of the polymer. UV‐visible absorption/photoluminescence spectra and fluorescence spectra were taken to valuate the photophysical properties of the obtained Eu‐containing copolymer. The experimental result shows that the strong luminescence of europium ions substantiates optimum energy match and effective intramolecular energy transfer between the triplet state energy of coordination complex and the emissive energy level of the rare‐earth ions. A study of the dependence of emission intensities of the Eu‐containing nanoparticles on the Eu content showed that the emission intensities increased nearly linearly with increasing Eu content. In addition, no significant emission concentration quenching phenomenon was observed at the Eu content of 0–4.61 mol%. The hybrid material systems can be expected to have potential applications in light conversion materials. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Radiation synthesis and characterization of poly(vinyl alcohol)/poly(N-vinyl-2-pyrrolidone) based hydrogels containing silver nanoparticles

A series of PVA/PVP based hydrogels at different compositions were prepared by gamma irradiation. The gel fraction degree of swelling were investigated. Highly stable and uniformly distributed silver nanoparticles have been obtained onto hydrogel networks. The morphology and structure of (PVA/PVP) hydrogel and dispersion of the silver nanoparticles in the polymeric matrix were examined by scanning electron microscopy (SEM) and infrared spectroscopy (FT-IR), respectively. The formation of silver nanoparticles has been confirmed by ultraviolet visible (UV–vis) spectroscopy. A strong characteristic absorption peak was found to be around 420 nm for the silver nanoparticles in the hydrogel nanocomposite. The X-ray diffraction pattern confirmed the formation of silver nanoparticles with average particle size of 12 nm. The diameter distribution of silver nanoparticles was determined by dynamic light scattering DLS. Transmission electron microscope (TEM) showed almost spherical and uniform distribution of silver nanoparticles through the hydrogel network and the mean size of silver nanoparticles ranging is 23 nm. The good swelling properties and antibacterial of PVA/PVP-Ag hydrogel suggest that it can be a good candidate as wound dressing.     

Preparation and characterization of PS‐PMMA/ZnO nanocomposite films with novel properties of high transparency and UV‐shielding capacity

High transparent and UV‐shielding poly (styrene)‐co‐poly(methyl methacrylate) (PS‐PMMA)/zinc oxide (ZnO) optical nanocomposite films were prepared by solution mixing using methyl ethyl ketone (MEK) as a cosolvent. The films were characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible (UV–vis) spectra, high‐resolution transmission electron microscopy (HR‐TEM), and atomic force microscope (AFM). Cross‐section HR‐TEM and AFM images showed that the ZnO nanoparticles were uniformly dispersed in the polymer matrix at the nanoscale level. The XRD and FTIR studies indicate that there is no chemical bond or interaction between PS‐PMMA and ZnO nanoparticles in the nanocomposite films. The UV–vis spectra in the wavelength range of 200–800 nm showed that nanocomposite films with ZnO particle contents from 1 to 20 wt % had strong absorption in UV spectrum region and the same transparency as pure PMMA‐PS film in the visible region. The optical properties of polymer are greatly improved by the incorporation of ZnO nanoparticles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and visible light photocatalytic activity of Ag/TiO₂/graphene nanocomposite

Great efforts have been made to develop efficient visible light-activated photocatalysts in recent years. In this work, a new nanocomposite consisting of anatase TiO(2), Ag, and graphene was prepared for use as a visible light-activated photocatalyst, which exhibited significantly increased visible light absorption and improved photocatalytic activity, compared with Ag/TiO(2) and TiO(2)/graphene nanocomposites. The increased absorption in visible light region is originated from the strong interaction between TiO(2) nanoparticles and graphene, as well as the surface plasmon resonance effect of Ag nanoparticles that are mainly adsorbed on the surface of TiO(2) nanoparticles. The highly efficient photocatalytic activity is associated with the strong adsorption ability of graphene for aromatic dye molecules, fast photogenerated charge separation due to the formation of Schottky junction between TiO(2) and Ag nanoparticles and the high electron mobility of graphene sheets, as well as the broad absorption in the visible light region. This work suggests that the combination of the excellent electrical properties of graphene and the surface plasmon resonance effect of noble metallic nanoparticles provides a versatile strategy for the synthesis of novel and efficient visible light-activated photocatalysts.     

酞菁镍-SnO_2纳米复合材料的制备及其光催化性能

采用化学修饰法制备不同摩尔配比的酞菁镍、SnO2(NiPc-SnO2)纳米复合材料。对制备的复合粒子进行XRD和IR表征,测定其在可见光条件下对罗丹明B的光催化降解能力。结果表明,酞菁镍-SnO2纳米复合材料红外光谱图中出现了M-O的振动吸收峰,表明NiPc与SnO2之间形成了部分化学键。在室温和可见光条件下,摩尔配比为1∶50的NiPc-SnO2纳米复合材料对罗丹明B的光催化降解率是64.3%。SnO2经NiPc敏化之后,在可见光范围内具有显著的光催化性能。     

Bismuth oxide cocatalyst and copper oxide sensitizer in Cu2O/TiO2/Bi2O3 ternary photocatalyst for efficient hydrogen production under solar light irradiation

A novel Cu₂O/TiO₂/Bi₂O₃ ternary nanocomposite was prepared, in which copper oxide improves the visible light absorption of TiO₂ and bismuth oxide improves electron–hole separation. The ternary composite exhibited extended absorption in the visible region, as determined by UV–Vis diffuse reflectance spectroscopy. High-resolution transmission electron microscopy images showed close contact among the individual semiconductor oxides in the ternary Cu₂O/TiO₂/Bi₂O₃ nanocomposite. Improved charge carrier separation and transport were observed in the Cu₂O/TiO₂/Bi₂O₃ ternary composite using electrochemical impedance spectroscopy and photocurrent analysis. TiO₂ modified with bismuth and copper oxides showed exceptional photocatalytic activity for hydrogen production under natural solar light. With optimum bismuth and copper oxide loadings, the Cu₂O/TiO₂/Bi₂O₃ ternary nanocomposite exhibited an H₂ production (3678 μmol/h) 35 times higher than that of bare TiO₂ (105?μmol/h). The synergistic effect of improved visible absorption and minimal recombination was responsible for the enhanced performance of the as-synthesized ternary nanocomposite.     

Synthesis and characterization of novel copper/polyaniline nanocomposite and application as a catalyst in the Wacker oxidation reaction

Copper nanoclusters were synthesized by a chemical reduction of an aqueous copper salt solution by sodium borohydride. A polyaniline nanocomposite containing copper nanoclusters was prepared by polymerizing a monomer aniline hydrochloride solution containing the copper nanoclusters using ammonium persulfate as an oxidizing agent. The synthesized nanocomposite was characterized using various techniques such as UV‐visible spectroscopy, FTIR spectroscopy, X‐ray diffraction (XRD), and transmission electron microscopy (TEM). The presence of copper was confirmed by XRD and the size of the copper clusters was found to be ～53 nm, which is in good agreement with that obtained from the TEM. The synthesized nanocomposite was used to serve as a catalyst in a Wacker oxidation reaction for the conversion of 1‐decene to 2‐decanone in the presence of molecular oxygen. The formation of 2‐decanone was confirmed using GC‐MS. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2412–2417, 2003     

A novel ferrocenium salt as visible light photoinitiator for cationic and radical photopolymerization

A novel hybrid photoinitiator for visible light photopolymerization, (η⁶-3-benzoyl-4-chlorodiphenylamine) (η⁵-cyclopentadienyl) iron hexafluorophosphate (Fc-NBP), was synthesized and studied. Its absorption in the UV and visible light regions showed much stronger activity than those of either the commercialized cationic photoinitiator I-261 or the conventional free radical photoinitiator benzophenone, especially above wavelengths of 350 nm. When exposed to visible light, the photoinitiator under study initiates both cationic polymerization and radical polymerization. The photoinitiator's abilities in the photopolymerization of acrylates and epoxides were evaluated by near infrared (NIR) spectroscopy. The results from NIR clearly indicate that Fc-NBP exhibited high efficiency in photopolymerizing acrylate monomers. In the same lamp, however, benzophenone showed no photoinitiating ability. The photopolymerization rate of the diglycidyl ether of the bisphenol-A epoxy (DGEBA) oligomer was found to be slower than that of acrylates when using Fc-NBP as the photoinitiator. This study shows that the polymerization of epoxide DGEBA can be speeded up by adding a photosensitizer benzoyl peroxide (BPO), but BPO and tertiary amines do not affect the free radical photopolymerization of tripropylene glycol diacrylate (TPGDA). We conclude by providing a possible photoinitiation mechanism.