Adsorption of heavy metal ions from aqueous solution by fly ash

The removal characteristics of lead and copper ions from aqueous solution by fly ash were investigated under various conditions of contact time, pH and temperature. The influence of pH of the metal ion solutions on the uptake levels of the metal ions by fly ash were carried out between pH 4 and 12. The level of uptake of Pb²⁺ and Cu²⁺ ions by the fly ash generally increased, but not in a progressive manner, at higher pH values. The effect of temperature on the uptake of Pb²⁺ and Cu²⁺ ions was investigated between 30 °C and 60 °C, the adsorption of being enhanced at the lowest temperature. Rate constants were evaluated in terms of a first-order kinetics. The rate constant, k for uptake of Pb²⁺ and Cu²⁺ ions were 1.77 × 10⁻² s⁻¹ and 2.11 × 10⁻² s⁻¹, respectively. The experimental results underline the potential of coal fly ash for the recovery of metal ions from waste water. The main mechanisms involved in the removal of heavy metal ions from solution were adsorption at the surface of the fly ash and precipitation.     

Preparation and self-assembly of a dual-functional copolymer for cancer therapy

The pH-responsive amphiphilic copolymer poly(SDMA-co-OEGMA) (PSO) was prepared from the pH-sensitive hydrophobic monomer 2-styryl-1,3-dioxan-5-yl methacrylate (SDMA) and the hydrophilic monomer oligo(ethylene glycol) methyl ether methacrylate (OEGMA) by radical polymerization. Polymeric aggregates with about 130 nm diameter were obtained by the self-assembly of PSO in neutral aqueous solution. The critical aggregation concentration of the copolymer was determined to be 6.5 mg/L (1.2 × 10^?7 M). Cinnamic aldehyde (CA) small molecules are broken away from PSO side chains after the hydrolysis of acid-labile cyclic acetal in cultured A375 human melanoma cells and further suppress the proliferation of this kind of tumor cells. Furthermore, the PSO aggregate was demonstrated to be a drug carrier for encapsulating Nile Red as model drug in in vitro testing. Based on the pH-responsive characteristic, the Nile Red molecules loaded in self-assembly process could be released from the aggregate inside cultured B16 mouse melanoma cells.     

Spectral studies of zinc octacarboxyphthalocyanine aggregation

The association of zinc octacarboxyphthalocyanine, was studied using UV–vis absorption and fluorescence emission spectroscopy; the effects of dye concentration, pH and solvents on spectra were discussed. Calculations showed that the dye dimerized in aqueous solutions ranging from 5.0 × 10^?7 to 5.0 × 10^?5 mol/dm³, at 25 °C. The dimerization constant of 10⁶ dm³/mol and the spectral Q band shift of 1185 cm^?1 imparted by dimerization indicated strong π–π interactions between phthalocyanine molecules. Red S₁ fluorescence of the dye monomer was observed in various solutions which was quenched owing to molecular association and other factors. The strong influence of pH on both aggregation and fluorescence was discussed. At pH < 5.0, only dye aggregates were present in solution; monomers appeared at pH ≥ 5.0 and, in alkaline solution, only the monomeric anions of phthalocyanine existed. The spectral absorption and emission data for the dye in binary solvents revealed that at concentrations ranging from 0.5 × 10^?5 to 1.0 × 10^?5 mol/dm³, the dye can be used in photosensitised oxidation reactions.     

Recognition of harmful fused aromatic hydrocarbons via a metal-organic framework with hydrophobic pores

A novel metal-organic framework (MOF) with a π-conjugated porous condition is reported to sensor fused aromatic hydrocarbons molecules. This MOF assembled by N-heterocyclic multi-carboxyl ligands and Cd ions shows hexagonal hydrophobic channels along [100] and [010] directions with size 18.4 × 15.5 Å². Under the excitation of 338 nm, this MOF emits blue light peaking at 397 nm. Under immersing this MOF in the solutions containing aromatic hydrocarbon, including naphthalene, anthracene and phenanthrene within different time, the luminescent intensity of MOF enhanced different degree upon encapsulating aromatic hydrocarbons guest molecules. Therefore, this material shows favourable property of recognition for aromatic hydrocarbons molecules via solid-state photoluminescence.     

Fabrication of highly efficient TiO2/Ag/TiO2 multilayer transparent conducting electrode with N ion implantation for optoelectronic applications

Fabrication of highly conductive and transparent TiO₂/Ag/TiO₂ (referred hereafter as TAT) multilayer films with nitrogen implantation is reported. In the present work, TAT films were fabricated with a total thickness of 100 nm by sputtering on glass substrates at room temperature. The as-deposited films were implanted with 40 keV N ions for different fluences (1×10¹⁴, 5×10¹⁴, 1×10¹⁵, 5×10¹⁵ and 1×10¹⁶ ions/cm²). The objective of this study was to investigate the effect of N⁺ implantation on the optical and electrical properties of TAT multilayer films. X-ray diffraction of TAT films shows an amorphous TiO₂ film with a crystalline peak assigned to Ag (111) diffraction plane. The surface morphology studied by atomic force microscopy (AFM) and field emission scanning electron microscope (FESEM) revealed smooth and uniform top layer of the sandwich structure. The surface roughness of pristine film was 1.7 nm which increases to 2.34 nm on implantation for 1×10¹⁴ ions/cm² fluence. Beyond this fluence, the roughness decreases. The oxide/metal/oxide structure exhibits an average transmittance ~80% for pristine and ~70% for the implanted film at fluence of 1×10¹⁶ ions/cm² in the visible region. The electrical resistivity of the pristine sample was obtained as 2.04×10⁻⁴ Ω cm which is minimized to 9.62×10⁻⁵ Ω cm at highest fluence. Sheet resistance of TAT films decreased from 20.4 to 9.62 Ω/□ with an increase in fluence. Electrical and optical parameters such as carrier concentration, carrier mobility, absorption coefficient, band gap, refractive index and extinction coefficient have been calculated for the pristine and implanted films to assess the performance of films. The TAT multilayer film with fluence of 1×10¹⁶ ions/cm² showed maximum Haacke figure of merit (FOM) of 5.7×10⁻³ Ω⁻¹. X-ray photoelectron spectroscopy (XPS) analysis of N 1s and Ti 2p spectra revealed that substitutional implantation of nitrogen into the TiO₂ lattice added new electronic states just above the valence band which is responsible for the narrowing of band gap resulting in the enhancement in electrical conductivity. This study reports that fabrication of multilayer transparent conducting electrode with nitrogen implantation that exhibits superior electrical and optical properties and hence can be an alternative to indium tin oxide (ITO) for futuristic TCE applications in optoelectronic devices.     

Reforming of methane with carbon dioxide over supported bimetallic catalysts containing Ni and noble metal: I. Characterization and activity of SiO2 supported Ni–Rh catalysts

Cobalt catalysts supported on silica aerogel have been prepared using sol–gel chemistry followed by drying under supercritical ethanol conditions. Three different loadings of cobalt were synthesized: 2, 6, and 10% by weight. Transmission electron micrographs indicate that the metallic cobalt exists as discrete particles 50–70 nm in diameter for the 2 and 6% loadings. The 10% catalyst shows long needles of cobalt. BET and BJH measurements indicate that the catalysts retain the silica aerogel properties of high surface area (∼800 m²/g), large pore volume (∼5 cm³/g), and an average pore diameter in the mesoporous regime (∼25 nm). The catalysts were evaluated for Fischer–Tropsch activity in a laboratory-scale packed bed reactor. All three catalysts were active with the 10% Co catalyst achieving more than 20% CO conversion which corresponds to a rate of 1.53 g CO per g-cat per hour. The catalysts were selective for the C₁₀₊ hydrocarbons with more than 50% of the carbon contained within this fraction. A significant portion of the C₉–C₁₅ hydrocarbon product was observed as 1-olefins which reflects the enhanced mass transport within the very porous aerogel support.     

Diffusion coefficients and electrical conductivities for calcium chloride aqueous solutions at 298.15 K and 310.15 K

Experimental values for mutual diffusion coefficients (interdiffusion coefficients) for CaCl₂ aqueous solutions at 298.15 K and 310.15 K, not available in the literature, were experimentally determined between 0.005 mol dm^?3 and 0.1 mol dm^?3. The measurements were performed by using a conductimetric open-ended capillary cell. Values at infinitesimal concentration, D⁰, were also obtained. These data were analysed using the Onsager–Fuoss and Gordon models. In addition, molar conductance data were measured at 310.15 K for CaCl₂ aqueous solutions at the same concentration range and the value at infinitesimal concentration determined. Afterwards, it was split into the ionic limiting values. By replacing them into the Nernst equation, diffusion coefficients at infinitesimal concentration were derived (1.335 × 10^?9 m² s^?1 and 1.659 × 10^?9 m² s^?1) at both temperatures (298.15 K and 310.15 K, respectively). They agree well with the extrapolated experimental ones (1.312 × 10^?9 m² s^?1 and 1.613 × 10^?9 m² s^?1).     

The characteristics of Li(Ni1/3Co1/3Mn1/3)O2 particles prepared from precursor particles with spherical shape obtained by spray pyrolysis

Spherical and fine-sized Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles were prepared using spray pyrolysis. Precursor particles with mixed Mn₂O₃, Co₃O₄ and NiO compositions were prepared using spray pyrolysis from aqueous and polymeric precursor solutions. The precursor particles prepared from the aqueous solution had hollow and porous morphologies. The precursor particles prepared from the polymeric precursor solution with citric acid and ethylene glycol were spherical in shape and had filled morphologies. The spherical precursor particles with filled morphologies formed spherical, fine-sized Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles with filled morphologies after post-treatment with LiOH. The mean crystallite sizes of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles prepared from spray solutions with and without lithium at the post-treatment temperature of 800 °C were 56 and 31 nm, respectively. The initial discharge capacities of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles prepared using spray pyrolysis from spray solutions with and without lithium were 178 and 181 mAh g⁻¹, respectively, after a post-treatment temperature of 800 °C.     

Copper separation from nitrate/nitric acid media using Acorga M5640 extractant: Part II. Supported liquid membrane study

The facilitated transport of copper(II) from nitrate/nitric acid media through a flat-sheet supported liquid membrane (FSSLM) is investigated, using the commercially available oxime Acorga M5640 as ionophore, as a function of hydrodynamic conditions, concentration of copper (7.9×10⁻⁵ to 1.3×10⁻³ M) and H⁺ (pH 1.0–2.0) and ionic strength in the feed solution, carrier concentration (5–40% v/v) in the membrane and support characteristics. The performance of the system is also compared using various diluents for the organic phase and against other available oxime extractants (MOC-55TD, LIX 860 and LIX 622). A model is presented that describes the transport mechanism, consisting of diffusion through a feed side aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of carrier and its metal complex through the organic membrane. The organic membrane diffusional resistance (Δ_o) and aqueous diffusional resistance (Δ_a) were calculated from the proposed model, and their values were 7.6×10⁶ and 273 s/cm, respectively. It was observed that the copper flux across the membrane tends to reach a plateau at high concentration of copper or a low concentration of H⁺ owing to carrier saturation within the membrane, and leads to a diffusion-controlled process. The values of the apparent diffusion coefficient (D_o^a) and limiting metal flux (J_lim) were calculated from the limiting conditions and found to be 2.0×10⁻⁸ cm²/s and 2.3×10⁻¹¹ mol/cm² s, respectively. The values of the bulk diffusion coefficient (D_o,b) and diffusion coefficient (D_o) calculated from the model were 5.9×10⁻⁹ and 1.6×10⁻⁹ cm²/s, respectively. The polymeric microporous solid support, Durapore GVHP 04700, was selected throughout the study as it gave the best performance.     

Physicochemical approach to nanobubble solutions

Small bubbles of nitrogen, methane, or argon with an average radius of 50 nm, as measured by scanning electron microscopy, were prepared under atmospheric conditions. The lifetime of the nanobubbles extended to more than two weeks. The total amount of gases in the nanobubble solutions reached 600 cm³ per 1 dm³ of water, and the liquid density was about 0.988 g/cm³. The internal pressure of the nanobubbles was estimated to be 6 MPa. The number of nanobubbles was 1.9×10¹⁶ bubbles per 1 dm³ of water. These findings show that almost no gas samples are dissolved homogeneously in the aqueous solution and that the vast majority is present in the form of nanobubbles, that is, nanobubbles should be thermodynamically unstable. Attenuated total reflectance infrared spectroscopy showed that the surfaces of the nanobubbles contain hard hydrogen bonds that may reduce the diffusivity of gases through the interfacial film.     

Azobenzene chemosensor based on nitrogen chelator for the detection of Cu (II) ion in aqueous medium

A bis-pyridine unit containing azobenzene chemosensor for Cu^2 + ion is designed and synthesized with good yield. The structure of the receptor I is determined by FT-IR, ¹H NMR, ¹³C NMR, ESI-MS and single crystal XRD. The receptor I is constructed on the basis of internal charge transfer (ICT) mechanism with bis-pyridine unit acting as the binding part for Cu^2 + ion. In solution, the proposed receptor I produces a cation induced 120 nm blue shift for Cu^2 + ion from 457 nm to 337 nm with remarkable colour change from red to colourless. Whereas no significant colour change is observed upon addition of other metal ions in aqueous HEPES buffer (pH 7.0). Moreover, spectroscopic studies confirm the formation of 1: 1 stoichiometry between the receptor I and Cu^2 + ion with an association constant of ca. 1.45 × 10⁶ M^− 1. The receptor I is highly specific to Cu^2 + ions in aqueous solution attributed to the rational design of the molecular structure.     

Homogeneously distributed magnetite in the polystyrene spherical particles using the miniemulsion polymerization

The polystyrene spherical particles with homogeneously distributed magnetites were prepared using the conventional miniemulsion polymerization. In the first, the magnetite nanoparticles were coated with oleic acid in aqueous Fe³⁺/Fe²⁺ solution using excess ammonium hydroxide via co-precipitation method. In the second, the miniemulsion polymerization of styrene was carried out using various concentrations of potassium persulfate (KPS) as an initiator, H-08E as an emulsifier, hexadecane as a co-emulsifier and acrylic acid as a dispersing agent in the presence of oleic acid coated magnetite at 70 °C for 24 h. The particle size and its distribution of the homogeneously embedded magnetites were influenced by the concentration of the initiator (KPS) and acrylic acid (AAc). In addition, the emulsifier, H-08E, affects the size and the shape of the PS particles. The optimum conditions for the homogeneously distributed magnetite in the spherical PS particles with the narrow distribution were 5 wt.% styrene, 0.2 g KPS, 0.2 g AAc, and 0.12 g H-08E by inducing 364 nm in diameter, 12.04% in the coefficient of variation (C_v) and 22.1% of the maximum magnetite content.     

Formation and stabilization of submicron particles via rapid expansion processes

Submicron particles were produced by rapid expansion of supercritical solution into air (RESS) or an aqueous surfactant solution (RESSAS) to minimize particle growth and to prevent particle agglomeration. Thereby the effect of process conditions on the size of the particles precipitated was investigated. The obtained product was evaluated by measuring particle size by 3-wavelength extinction measurements, dynamic light scattering, specific surface areas by nitrogen gas adsorption, melting behaviour by differential scanning calorimetry, particle morphology by X-ray diffraction, scanning electron micrographs (SEM), and drug loading by high performance liquid chromatography.Prior to the particle formation experiments, the melting temperature of Salicylic acid under CO₂ pressure and the solubility of Salicylic acid in CO₂ were measured. The size of Salicylic acid particles produced via RESS decreased from 230 to 130 nm as the pre-expansion temperature decreased from 388 to 328 K and the specific surface area of the micronized particles was found to be up to 60 times higher than that of the unprocessed material. RESSAS experiments demonstrate that in 1 wt.% Tween 80 solutions Salicylic acid concentrations of 4.6 g/dm³ could be stabilized with particle diameters in the range of 180 nm. Additional experiments show that Ibuprofen nanoparticles with an average size of 80 nm and a drug concentration of 2.4 g/dm³ could be stabilized in 1 wt.% Tween^® 80 solutions. The use of a SDS solution instead of Tween^® 80 results in a stable aqueous suspension of phytosterol nanoparticles, where the average particle size is 50 nm at a drug concentration of 5.6 g/dm³.     

Kinetics of polycyclic aromatic hydrocarbons removal using hyper-cross-linked polymeric sorbents Macronet Hypersol MN200

The search for suitable sorbents for polycyclic aromatic hydrocarbons (PAHs) removal from aqueous solutions prompted the evaluation of polymeric resins incorporating new properties that solve many of the existing problems when using granulated-activated carbon. A new type of non-functionalized macroporous hyper cross-linked resin, Hypersol Macronet (MN200) has been evaluated. Analyses of the respective batch rate data, for a family of six PAHs, with two kinetic models, the homogenous diffusion model (HDM) and the shell progressive model (SPM) were carried out. The process is controlled by the rate of diffusion of the solutes (PAHs) penetrating the reacted layer at PAH concentrations for the range 0.1–10 mg L⁻¹. Effective particle-diffusion coefficients (D_eff) were determined from the rate data proposed by both models. The D_eff values from both HMD and SPM equations varied from 5 × 10⁻¹³–4 × 10⁻¹⁵ m² s⁻¹. Pore diffusion is considered to be the predominant intraparticle transport mechanism inside the cross-linked polymer. The simplest model, the pore diffusion model, was applied first for data analysis. Close fitting of the data using this model requires that the apparent diffusivities are in the same order than the Brownian diffusivity reported in the literature. As a next step, the model of the next level of complexity, the surface diffusion model, was applied for data analysis. This model can explain the data, and the apparent surface diffusivities are the same order of magnitude as the literature values for similar resins.     

Effect of promoter in the oxidative coupling of methane over synthesized Mn/SiO2 nanocatalysts via incipient wetness impregnation

The M–Na–Mn/SiO₂ nanocatalysts (M = W, Mo, Nb, V, Cr) were synthesized with the size of 12–92 nm by incipient wetness impregnation method to study the effect of different promoters on the catalytic performance in the oxidative coupling of methane. The results at 1 atm, 1048 K, 2500 ml h^?1 g^?1, and CH₄/O₂/N₂ = 2/2/1 revealed that C₂ selectivity was significantly increased (31.6%) in the order of W > Mo > Nb > Cr > V whereas moderate enhancement (12.6%) was observed in the CH₄ conversion in the order of W > Cr > Nb > Mo > V. The results of the characterization techniques (Raman, FT-IR, BET, TGA/DTA and XRD) demonstrated that Mn₂O₃ and α-cristobalite were the predominant species and active sites in the nanocatalyst surface and Na₂MoO₄, Na₂WO₄ and Mn₂O₃ crystalline phases contributed to achieving high selectivity of C₂ products. The redox mechanism involving two metal sites such as Mn^3+/2+ and W^6+/5+ or Mn^3+/2+ and Mo^6+/5+ was found to be the most compatible route with the OCM reaction path in which CH₄ and O₂ adsorption was the controlling step.     

D and D/He plasma interactions with diamond: Surface modification and D retention

Chemical vapour deposition (CVD) diamond is of interest as a plasma facing material in magnetically confined nuclear fusion devices. CVD diamond samples were exposed to ion fluences between 1.5 × 10²² ions m^− 2 and 1 × 10²⁴ ions m^− 2 in D, D/He and He plasmas. A significant surface coverage of 10 nm–100 nm sized hemispherical and conical surface features resulted from chemical erosion and subsequent redeposition on samples exposed to ≥ 10²³ ions m^− 2 when exposed to D containing plasmas. Near edge X-ray absorption fine structure (NEXAFS) spectra showed strong diamond features following plasma exposure, indicating that the diamond crystal structure on the surface was largely retained. A small increase in the sp² fraction (from 1.2% to 4–7%), was observed suggesting some amorphous carbon formation. Elastic recoil detection analysis (ERDA) revealed that D retention saturates at ~ 5.4% averaged over the depth resolution of 20 nm from the surface, for an ion fluence of ~ 10²³ ions m^− 2. The addition of He to the plasma resulted in a slower uptake of D, which was attributed to He ion induced desorption of D.     

Nucleation and growth surface conductivity of H-terminated diamond films prepared by DC arc jet CVD

High-quality polycrystalline diamond film has been extremely attractive to many researchers, since the maximum transition frequency (f_T) and the maximum frequency of oscillation (f_max) of polycrystalline diamond electronic devices are comparable to those of single crystalline diamond devices. Besides large deposition area, DC arc jet CVD diamond films with high deposition rate and high quality are one choice for electronic device industrialization. Four inch free-standing diamond films were obtained by DC arc jet CVD using gas recycling mode with deposition rate of 14 μm/h. After treatment in hydrogen plasma under the same conditions for both the nucleation and growth sides, the conductivity difference between them was analyzed and clarified by characterizing the grain size, surface profile, crystalline quality and impurity content. The roughness of growth surface with the grain size about 400 nm increased from 0.869 nm to 8.406 nm after hydrogen plasma etching. As for the nucleation surface, the grain size was about 100 nm and the roughness increased from 0.31 nm to 3.739 nm. The XPS results showed that H-termination had been formed and energy band bent upwards. The nucleation and growth surfaces displayed the same magnitude of square resistance (R_s). The mobility and the sheet carrier concentration of the nucleation surface were 0.898 cm/V s and 10¹³/cm² order of magnitude, respectively; while for growth surface, they were 20.2 cm/V s and 9.97 × 10¹¹/cm², respectively. The small grain size and much non-diamond carbon at grain boundary resulted in lower carrier mobility on the nucleation surface. The high concentration of impurity nitrogen may explain the low sheet carrier concentration on the growth surface. The maximum drain current density and the maximum transconductance (g_m) for MESFET with gate length L_G of 2 μm on H-terminated diamond growth surface was 22.5 mA/mm and 4 mS/mm, respectively. The device performance can be further improved by using diamond films with larger grains and optimizing device fabrication techniques.     

Use of bulk liquid membrane for the removal of Cibacron Red FN-R from aqueous solution using TBAB as a carrier

The transport of Cibacron Red FN-R anionic dye through a methylene chloride bulk liquid membrane (BLM) containing a tetra butyl ammonium bromide (TBAB) as an excellent carrier was studied. The extracted dye simultaneously stripped into aqueous stripping solution. The basic fundamental parameters were determined. These include pH of the feed, nitric acid concentration in the strip solution, TBAB concentration in the membrane phase, initial dye concentration in the feed phase and rate of stirring. The transport efficiency of dye increased with increasing carrier concentration from 6.06 ± 0.1 × 10^?6 to 3.85 ± 0.1 × 10^?4 M. The transport study was highly selective for anionic dye and efficiency of transport was not affected by the presence of electrolytes such as sodium chloride and sodium sulphates in feed solution. The percentage of dye transported across the liquid membrane after 70 min, was 95 ± 0.1%. When the optimum parameters were used for real textile dyeing effluent for recovery of dyes, the results were found to be satisfactory.     

Hydrophobic precipitation of carbonaceous spheres from fructose by a hydrothermal process

We report a new mechanism of hydrophobic ripening for the formation of carbonaceous spheres by the dehydration of saccharides in a hydrothermal aqueous environment using fructose as a model precursor material. We investigated the formation of carbonaceous spheres from fructose in aqueous solutions under hydrothermal conditions. The spheres were found to contain 65.7 wt.% C, 4.3 wt.% H and 30.0 wt.% O, implying incomplete dehydration of the fructose. The spheres, typically ranging between 400 nm and 10 μm in diameter, are found to be constructed entirely of primary particles of ～5 nm. The chemical structure of the carbonaceous spheres and the chemical compositions of residual solutions were analysed using solid state and solution ¹³C nuclear magnetic resonance and Fourier transform infrared spectroscopy. Based on these results, a four-step mechanism for the formation and growth of carbonaceous spheres has been proposed.     

Synthesis and two-photon absorption properties of 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles

Two symmetrical 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles that exhibit strong two-photon absorption and enhanced two-photon excited fluorescence were designed and synthesized based on “push-core-pull-core-push” molecules built from embedding electron-transporting 1,3,4-oxadiazole in aromatic conjugated system through Wittig–Horner reaction. Pumped by nanosecond laser at 800 nm, strong up-conversion emissions with the central wavelength at 507 nm (green) of 2,5-bis[4-(2-N,N-diphenylaminostyryl)phenyl]-1,3,4-oxadiazole and 475 nm (blue) of 2,5-bis[4-{2-(3-N-ethylcarbazolyl)vinyl}phenyl]-1,3,4-oxadiazole in the solution of CHCl₃ have been observed. Their two-photon absorption cross-sections obtained by nonlinear transmission method are 107 × 10⁻⁴⁸ cm⁴ s photon⁻¹ and 66 × 10⁻⁴⁸ cm⁴ s photon⁻¹. A very effective energy transfer from the excited terminal units to the π-conjugated bridging units of the 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles is the dominant contribution to the two-photon absorption.