Quantum dots tailored with poly(para-phenylene vinylene)

In polymernanoparticle composites, uniform dispersion of the nanoparticles carries advantages over cases where nanoparticle aggregation dominates. Such dispersion has been particularly difficult to obtain in the case of composites prepared from nanoparticles and conjugated polymers. Here, we show that cadmium selenide nanocrystals, or quantum dots, can be integrated into thin films of poly(para-phenylene vinylene) (PPV) without aggregation. The two key departures from previous studies of quantum-dot/electronic polymer composites are (1) the synthesis of high-quality quantum dots directly in novel, functional ligands, thus eliminating the need for ligand exchange, and (2) polymerization chemistry that grafts PPV to the quantum dot surface. Solid-state photoluminescence spectra of composite materials prepared by these novel techniques reveal the critical importance of the quantum dot-polymer interface that will enable new investigations in nanoparticle-based light-emitting devices.     

Catalytic decomposition of organic peroxides by 4,4′-diamino-trans-stilbene (DTS)/montmorillonite complex: II.p-nitro andp-methyl dibenzoyl peroxide

The kinetics of the induced decomposition ofp-NO₂- andp-CH₃-dibenzoyl peroxide in the presence of 4,4-diamino-trans-stilbene (DTS) were studied in ethanol under both homogenous and heterogeneous conditions. The heterogeneous reaction was carried out in the presence of the DTS/montmorillonite complex. The decomposition reaction was found to be second order and three-halves order for the peroxide concentration in homogeneous and heterogeneous systems, respectively. The reaction was first order for the amine concentration in the homogeneous system. The activation energies for the decomposition reaction were obtained as 54.7±2 and 59.5±3 kJ mol^–1 forp-NO₂- andp-CH₃-dibenzoyl peroxides, respectively, in the homogeneous systems and are higher than the corresponding values of 41±1.5 and 47.6±1 kJ mol^–1 for thep-NO₂ andp-CH₃ derivatives in heterogeneous media.     

Variable pi-bonding in iron(II) porphyrinates with nitrite, CO, and tert-butyl isocyanide: characterization of [Fe(TpivPP)(NO2)(CO)]-

The addition of the strongly pi-bonding ligands CO or tert-butyl isocyanide to the low-spin five-coordinate iron(II) nitrite species [Fe(TpivPP)(NO2)]- (TpivPP = picket fence porphyrin) gives two new six-coordinate species [Fe(TpivPP)(NO2)(CO)]- and [Fe(TpivPP)(NO2)(t-BuNC)]-. These species have been characterized by single-crystal structure determinations and by UV-vis, IR, and M?ssbauer spectroscopies. All evidence shows that in the mixed-ligand iron(II) porphyrin species, [Fe(TpivPP)(NO2)(CO)]-, the two trans, pi-accepting ligands CO and nitrite compete for pi density. The CO ligand however dominates the bonding. The Fe-N(NO2) bond lengths for the two independent anions in the unit cell at 2.006(4) and 2.009(4) A are lengthened compared to other nitrite species with either no trans ligands or non-pi-accepting trans ligands to nitrite. The Fe-C(CO) bond lengths are 1.782(4) A and 1.789(5) A for the two anions. The two Fe-C-O angles at 175.5(4) and 177.5(4) degrees are essentially linear in both anions. The quadrupole splitting for [Fe(TpivPP)(NO2)(CO)]- was determined to be 0.32 mm/s, and the isomer shift was 0.18 mm/s at room temperature in zero applied field. Both of the M?ssbauer parameters are much smaller than those found for six-coordinate low-spin iron(II) porphyrinates with neutral nitrogen-donating ligands as well as iron(II) nitro complexes. However, the M?ssbauer parameters are typical of other six-coordinate CO porphyrinates signifying that CO is the more dominant ligand. The CO stretching frequency of 1974 cm(-1) is shifted only slightly to higher energy compared to six-coordinate CO complexes with neutral nitrogen-donor ligands trans to CO. Crystal data for [K(222)][Fe(TpivPP)(NO2)(CO)].1/2C6H5Cl: monoclinic, space group P2(1)/c, Z = 8, a = 33.548(6) A, b = 18.8172(15) A, c = 27.187(2) A, beta = 95.240(7) degrees, V = 17091(4) A3.     

Preparation of thiocyanates and isothiocyanates from alcohols, thiols, trimethylsilyl-, and tetrahydropyranyl ethers using triphenylphosphine/2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)/n-Bu4NSCN system

A combination of triphenylphosphine (PPh₃) and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) provides a safe and easily available mixed reagent system for the conversion of 1° and 2° alcohols, thiols, trimethylsilyl-, and tetrahydropyranyl ethers to their corresponding thiocyanates and the 3° ones to isothiocyanates in good to high yields.     

PPh3/DDQ as a neutral system for the facile preparation of diethyl α-bromo, α-iodo and α-azidophosphonates from diethyl α-hydroxyphosphonates

The mixture of triphenylphosphine (PPh₃) and 2,3-dichloro-5,6-dicyanobenzquinone (DDQ) as a neutral system has been used for the preparation of various types of diethyl α-bromo, α-iodo and α-azidophosphonates from their corresponding diethyl α-hydroxyphosphonates in the presence of n-Bu₄NBr, n-Bu₄NI and NaN₃ in good to high yields.     

Environmentally Friendly Recovery and Characterization of Oil from Used Engine Lubricants

The present paper demonstrates the review of some acid processes as well as development of some new solvent processes for reclamation of used lubricating oils. The conventional processes are found to be of low yield (? 50%), laborious, time consuming and environmentally hazardous, because of residual acidic sludge. Based on the findings, a new modified Aluminium sulphate‐sodium silicate‐acid‐base method employing a small quantity of acid and giving a high yield (? 60%) is proposed. Further, to avoid use of acid, new regeneration processes based on solvent extraction were investigated. They are termed CCl₄‐alcohol method, Dodecane‐alcohol method and Toluene‐alcohol method. These processes are not only cost effective in terms of complete solvent recovery, but are rapid, less time consuming, more environmentally friendly and gave a high yield (70–75%). The virgin lubricants (Castrol GTX and Rimula‐C) as well as oils recovered by different methods were also characterized physicochemically to determine kinematic viscosity, density, refractive index, carbon distribution, wear scar diameter, % Conradson carbon residue, % ash, % chloride, pour point, etc. Results obtained show that many of the physico‐chemical properties of the recovered oils are in good agreement with those of virgin oils. The n.d.M analysis was also performed which shows that virgin oils have 73 ± 3% paraffinic carbon, 26 ± 3% naphthenic carbon and about 1% aromatic carbon. The recovered oils also showed nearly the same chemical composition. The UV‐Visible spectra of the recovered oils are all similar to those of virgin lubricants. The results suggest that the oils recovered by solvent treatments, particularly Dodecan‐alcohol and Toluene‐alcohol methods, may serve for lubrication purposes and can be rendered as excellent as virgin lubricants with the addition of certain additives. The proposed methods may be considered as alternative cost effective green techniques for acid reclamation processes and being the motivation of the present investigation.     

Synthesis starting from 3-methyl-2-phenyl-5-(3-methyl-2-phenyl-3,4-dehydropiperidyl-6)pyridine. 2-phenyldinicotinic and 4-azafluorenone-2-carboxylic acids

N-Methyl (ethyl, benzoyl, trifluoroacetyl)-substituted 3-methyl-2-phenyl-5-(3-methyl-2-phenyl-3,4-dehydropiperidyl-6) pyridines and di(N-oxide) of the correspondingly substituted ,ß-dipyridyl were prepared. A method for synthesizing 2-phenyldinicotinic acid was developed. Cyclodehydration of this acid gave 4-azafluorenone-2-carboxylic acid. Transformations of this acid were carried out with respect to two functional groups.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 813–817, June, 1986.     

Pyrrole-based conductive polymer as the solid-phase extraction medium for the preconcentration of environmental pollutants in water samples followed by gas chromatography with flame ionization and mass spectrometry detection

A pyrrole-based polymer was synthesized and applied as a new sorbent for solid-phase extraction (SPE) of some environmental pollutants from water samples. Polypyrrole (PPy) was synthesized by chemical oxidation of the monomer in nonaqueous solution. SPE of selected phenols, pesticides, and polyaromatic hydrocarbons (PAHs) from aqueous samples were performed using 200 mg PPy. The determination was subsequently carried out by gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). The polymer showed much higher recoveries for aromatic compounds than aliphatics. Preconcentration of sample volumes up 11 led to acceptable recoveries for aromatic and other tested polar compounds. The R.S.D. for a river water sample spiked with phenols, pesticides and PAHs at sub-ppb level was lower than 10% (n = 3) and limits of detection for these compounds were between 15 and 120 ng l(-1).     

Average Nusselt number correlation in the thermal entrance region of steady and pulsating turbulent pipe flows

Empirical correlation has been developed for local and average Nusselt numbers in the thermal entrance region of steady and pulsating turbulent air-flows in a pipe. The correlation was based on experimental data obtained from experiment carried out on a pipe heated under uniform heat flux conditions. The rate of flow was periodically varied at frequencies ranging from 1 Hz to 13 Hz while the average Reynolds number varied from 6400 to 42000. Received on 20 October 1998     

Ultrafiltration polyanionic poly (3-sulfopropyl methacrylate) membranes with enhanced antifouling and water flux

Polyethersulfone (PES) membranes are prevalent in the field of water treatment owing to their exceptional separation efficiency, robust mechanical properties, and resistance to chemical degradation. Nevertheless, these membranes are prone to fouling, resulting in a decrease in both flux and ultrafiltration efficiency. In the present study, PES membranes are blended with poly (3-Sulfopropyl Methacrylate) (PSPMA) in various weight percentages (0%–3%) to improve their antifouling and ultrafiltration properties. The physicochemical properties of the blended membranes, including surface morphology, contact angle, hydrophilicity and surface energy are evaluated. The findings indicate that incorporation PSPMA results in an enhancement of the hydrophilic properties and surface charge of the PES membranes, assessed by employing Bovine Serum Albumin (BSA) as a representative protein. Modified blended membranes display greater Flux Recovery Ratio (FRR%) and exhibit superior fouling resistance. Under the same experimental conditions (0.2 MPa applied pressure), a pure water flux of 154.18 L·m⁻²·h⁻¹ for PES/PSPMA membrane found substantially greater than pure PES membrane (103.52 L·m⁻²·h⁻¹) along with Total Fouling Ratio (TFR) of 36% and 64.9% respectively. Exceptional antimicrobial efficacy for modified membranes is revealed against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) using disc diffusion technique rendering them well-suited for water treatment applications.