FTIR study of gamma-irradiated cis-1,4-polyisoprene

The effect of γ-irradiation on the structure and oxidation of cis-1,4-polyisoprene is investigated by ATR-FTIR technique. This method provides the valuable insight into the type of oxidation products produced and the extent and nature of intramolecular cyclization and chain scission reactions. The formation of ketones, alcohols and/or ethers, and hydroperoxides is apparent already at small doses of γ-radiation and it increases with the exposure time significantly. At the highest dose of 309 kGy a decrease in the intensity of C=O stretching mode of ketones (1717 cm⁻¹) was observed while the overall area of the band remained the same as in the case of 188 kGy dose. The shoulders observed at 1740 cm⁻¹ and 1772 cm⁻¹ could be assigned to C=O stretching frequency of esters and five-membered-ring lactones, respectively. Higher doses of γ-radiation also cause the formation of two relatively strong bands in the region of conjugated double bonds. These could origin from the aromatic products or cycloenes with one double bond formed by cyclization and chain scission processes.     

NMR and DSC investigations of the miscibility of blends of cis-1,4-polyisoprene with polybutadienes of different microstructures

Differential scanning calorimetry and torsional braid analysis investigations of the phase diagram of cis-1,4-polyisoprene/polybutadiene blends as a function of the polybutadiene microstructure were reported by several authors. Polybutadienes containing a high vinyl content were shown to be miscible with cis-1,4-polyisoprene on the DSC spatial scale, whereas polybutadienes containing a low vinyl content were immiscible. In this article, we used variable-temperature determinations of ¹H NMR free induction decays and low-temperature, high-resolution solid-state ¹³C NMR measurements of proton spin-lattice relaxation times in the rotating frame to probe the phase behavior of the cis-1,4-polyisoprene/polybutadiene blends at the smaller spatial scale of the NMR technique. Blends of cis-1,4-polyisoprene with a polybutadiene having a large number of vinyl 1,2 linkages appeared to be miscible on the molecular scale, in spite of small regions in which the polybutadiene component is not uniformily dispersed in the other polymer. On the contrary, blends in which the polybutadiene has a low content of vinyl 1,2 sequences were phase separated over the whole temperature range considered and no intermixed regions could be detected. The limiting case was observed with the polybutadiene containing 33 wt % vinyl 1,2 units, for which miscibility on a molecular scale is highly dependent on the blend composition. © 1995 John Wiley & Sons, Inc.     

Sorption of some azo-dyes on wool fiber from aqueous solutions

Sorption of some azo-dyes (acid violet 17, acid blue 90, acid red 1 and direct red 80) on locally available wool fiber from aqueous solution has been investigated as a function of shaking time, pH and dyes concentration as a function of temperature. Sorption isotherms for dyes on wool fiber were obtained. It was found that the increasing temperature induces positive effect on the sorption process. Isosteric heat of adsorption (q_st) have also been calculated at different surface coverage indicating that wool fiber used possessed heterogeneous surface with site of different activity. The results also indicate that initial sorption whether chemical or physical means, occurs first on the most active sites and then, as the concentration of dyes is increased, on sites of lesser activity.     

Fabrication of <Emphasis Type="Italic">trans</Emphasis>-1,4-polyisoprene nanofibers by electrospinning and its crystallization behavior and mechanism

Trans-1,4-polyisoprene (TPI) nanofibers have been fabricated successfully through electrospinning technology. Through the control of electrospinning parameters, highly crystallized TPI fresh fibers composed mainly by β phase were produced. Morphology and diameter of TPI nanofibers can be controlled by adjusting the electrospinning conditions. The in situ observations of FTIR spectra revealed that the crystallinity of the TPI fibers decreased with aging. While for TPI nanofibers aging at 45 °C for 24 h, a decrease in crystallinity as well as β to α transformation was observed with aging and these changings happened in the first 50 h during aging. The mechanism for β-TPI formation during electrospinning process and the reduced crystallinity with aging were proposed.     

Phase structure and crystallization behavior of polyethylene in its blends with cis-1,4-butadiene rubber

Phase structure and crystallization behavior of polyethylene(PE) in its blends with cis-1,4-butadiene rubber(BR) at different blend ratios and sample preparation conditions were studied. The PE is finely dispersed in the BR matrix. For samples hot pressed at 145 °C, circular PE microdomains with randomly oriented PE lamellar aggregates were produced. The domain size and number increase with increasing PE content. When the PE content is over 10 wt%, most of the PE domains impinged each other. The separated PE domains are connected by PE stripes with parallel arranged lamellar aggregates. For samples hot pressed at 140 °C, elongated PE microdomains with oriented PE lamellar aggregates were obtained due to the shear flow. The crystallization of PE in the blends depends on the phase structure. Confined crystallization of PE occurs in small microdomains at relatively low temperature. With the increase of domain size, the crystallization ability of PE increases while the confined crystallization decreases.     

Sorption characteristics and separation of tellurium ions from aqueous solutions using nano-TiO2

Titanium dioxide nanoparticles (nano-TiO₂) were employed for the sorption of Te(IV) ions from aqueous solution. A detailed study of the process was performed by varying the sorption time, pH, and temperature. The sorption was found to be fast, equilibrium was reached within 8 min. When the concentration of Te(IV) was below 40 mg L⁻¹, at least 97% of tellurium was adsorbed by nano-TiO₂ in the pH range of 1-2 and 8-9. The sorbed Te(IV) ions were desorbed with 2.0 mL of 0.5 mol L⁻¹ NaOH. The sorption data could be well interpreted by the Langmuir model with the maximum adsorption capacity of 32.75 mg g⁻¹ (20 ± 0.1 °C) of Te(IV) on nano-TiO₂. The kinetics and thermodynamics of the sorption of Te(IV) onto nano-TiO₂ were also studied. The kinetic experimental data properly correlated with the second-order kinetic model (k₂ = 0.0368 g mg⁻¹ min⁻¹, 293 K). The overall rate process appeared to be influenced by both boundary layer diffusion and intra-particle diffusion. The mean energy of adsorption was calculated to be 17.41 kJ mol⁻¹ from the Dubinin-Radushkevich (D-R) adsorption isotherm at room temperature. Moreover, the thermodynamic parameters for the sorption were estimated, and the ΔH⁰ and ΔG⁰ values indicated the exothermic and spontaneous nature of the sorption process, respectively. Finally, Nano-TiO₂ as sorbent was successfully applied to the separation of Te(IV) from the environmental samples with satisfactory results (recoveries >95%, relative standard deviations was 2.0%).     

DSC and FTIR study of the gamma radiation effect on cis-1,4-polyisoprene

The effect of γ-radiation on the cis-1,4-polyisoprene in the presence of oxygen is investigated by ATR-FTIR technique and non-isothermal DSC measurements. FTIR measurements have shown that the formation of hydroperoxides, ketones, alcohols and/or ethers is apparent already at lower, 20–50 kGy, doses of γ-radiation and it increases significantly with the exposure time. Besides, lactones, anhydrides, peresters, carboxylic acids, and esters are formed, too. Spectral changes in the region of C=C conjugated double bonds indicate a formation of shorter polyene structures and aromatic rings. Kinetic parameters describing the temperature dependence of the induction period have been obtained from DSC measurements using the isoconversional method. Residual stabilities have been calculated in order to characterize the gamma radiation effect on polyisoprene thermooxidative stability. Both methods proved that doses lower than 50 kGy do not cause severe changes in polymer properties.     

精氨酸与2,3-二氯-5,6-二氰-1,4-苯醌的荷移反应研究

用分光光度法研究了精氨酸与2,3-二氯-5,6-二氰-1,4-苯醌(DDQ)的荷移反应.实验表明,在硼砂溶液中,精氢酸与DDQ在室温下反应30 min可获得稳定的络合物,其组成比为2∶1,λmax=342 nm,表观摩尔吸光系数ε=1.65×104 L· mol-1·cm-1,线性范围为2～30μg/mL.应用拟定的方法测定了盐酸精氨酸注射液的含量,结果与文献方法一致,回收率在97.2％～98.1％之间,相对标准偏差小于3.1％.     

左旋多巴与2,3-二氯-5,6-二氰-1,4-苯醌的荷移反应研究

研究了左旋多巴和2,3-二氯-5,6-二氰-1,4-苯醌(DDBQ)的反应条件,确定在硼砂溶液中,在60℃反应70 min可获得稳定的络合物,其λmax=346 nm,组成比为1∶1,表观摩尔吸收系数ε=1.1×104L.mol-1.cm-1,应用拟定的方法测定药物制剂测定结果与文献方法一致,回收率在97.25%~102.7%之间,相对标准偏差在0.7%以内。     

The crystal structure of 1,4-benzenedithiol by rietveld analysis and studies on the mechanism of solid-state addition polymerization of 1,4-benzenedithiol to 1,4-diethynylbenzene

The crystal structure of 1,4-benzenedithiol (BDT) was determined by the Rietveld method based on the calculation of the atomic coordinates of the BDT molecule using the Molecular Mechanics Program (MMP2). The refined crystal structure of BDT was monoclinic P₂₁/c with dimensions, a = 7.795, b = 7.290, c = 5.955 Å, β = 92.16°, z = 2. The R factor of the refined structure was 0.038. Using above results, the mechanism of solid-state addition polymerization of BDT to 1,4-diethynylbenzene (DEB) was studied. Sublimed BDT piles up onto glass plate substrate and forms the layer structure along with the a axis. An inclination angle of the piled BDT column was 60° toward the substrate surface. DEB crystal structure was also monoclinic P₂₁/c with a = 4.007, b = 6.018; c = 15.340 Å, β = 91.42°, z = 2. Sublimation of equimolar mixture of BDT and DEB gave a crystal having 1 : 1 composition, in which DEB column is situated between the columns of BDT. Relative arrangement of both monomers was suitable for the addition of  SH and  CCH groups, since the distance between the two groups is 3.3 Å by CERIUS II calculation. Therefore, the addition polymerization of BDT to DEB easily proceeded by UV irradiation and the resulting polymer had a highly layer structure along with the a axis of BDT crystal. Tentatively estimated crystal structure of polymer obtained is monoclinic with a = 7.73, b = 7.30, c = 5.95 Å, β = 92.16°. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1621–1625, 1997     

Sorption of petrochemicals from aqueous solutions on thermally activated schungite rock

Thermal oxidative treatment enhances the activity of a schungite rock in the sorption of petrochemicals from aqueous solutions. The effect of the thermal oxidative activation on the content and distribution of carbon in the rock and the dependence of the sorption activity on the texture of sorbents were studied. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2233–2238, October, 2005.     

Sorption of carbaryl and naphthols by polymers based on N-vinylamides from aqueous solutions

New cross-linked copolymers based on N-vinylpyrrolidone and N-vinylcaprolactam were proposed for preconcentration of carbaryl and naphthols from aqueous media. The influence of pH, nature of salting-out agent, surfactant, and temperature on the recovery of the analytes was examined. The most efficient sorption systems for recovery of carbaryl and naphthols from aqueous solutions were developed.     

Effects of pH and Concentration on Cs Ions Sorption and Diffusion in Crushed Granite by Using Batch and Modified Capillary Method

A comprehensive evaluation of Cs ions sorption to and diffusion in crushed granite was conducted in this study. The sorption capacity of crushed granite suggested by the Langmuir model was 5.48 × 10^?6 mol‐Cs/g‐granite. The distribution coefficient (Kd) was around 7.5 mL/g and pH independent. By using an in‐diffusion method with a modified capillary column, some diffusion relevant parameters of Cs ions in crushed granite were derived. The apparent diffusion coefficient (Da) seemed unaffected by Cs concentration (1.15 × 10^?10 to 2.82 × 10^?10 m²/s, at 10^?7 and 10^?3 M, respectively). The determined effective diffusion coefficients (De) were located in the window from 8.59 × 10^?10 (10^?7 M) to 1.69 × 10^?9 (10^?3 M) m²/s. Under various pH environments, pH independent Da (9.0 × 10^?9 m²/s) and De (1.0 × 10^?9 m²/s) values were observed. Under current systems, consistently higher De than Da implied the diffusion of Cs ions was governed by surface diffusion phenomenon. Whereas the pH insensitive feature indicated the Cs sorption to crushed granite was mainly through ion‐exchange reaction. Moreover, further SEM/EDS mapping clearly showed the adsorbed Cs ions were highly concentrated on the fracture surface of biotite.     

Efficiency of succinylated-olive stone biosorbent on the removal of cadmium ions from aqueous solutions

Chemical functionalization of olive stone wastes with succinate linkers can potentially improve the performance of wastewater treatment technologies via enhanced adsorption and high affinity of the covalently attached succinate groups for heavy metals. In this study, a novel reusable adsorbent material based on agricultural waste has been synthesized by esterifying the lignocellulosic matrix of olive stones with succinic anhydride in toluene under basic conditions. Characterization of the as-prepared material by FTIR and solid-state MAS ¹³C NMR spectroscopies and TGA confirmed that the heterogeneous esterification has proceeded very efficiently to yield the succinylated-olive stone (S–OS). Subsequent alkaline treatment of S–OS with saturated NaHCO₃ aqueous solution led to the resulting sodic material (NaS–OS), which was subjected to batch experiments in order to evaluate its cadmium-removing efficiency from aqueous solutions at realistic concentrations of cadmium found in industrial effluents. The results obtained from the sorption characteristics have revealed that NaS–OS material is highly effective in removing cadmium from aqueous solutions, with a maximum uptake capacity of 200 mg g⁻¹ (1.78 mmol g⁻¹). The Langmuir isotherm model was found to fit adequately the equilibrium isotherm data. Cadmium adsorption occurs rapidly and the adsorption mechanism is a chemical sorption via ionic exchange between the adsorbate and adsorbent. Thermodynamic parameters were also evaluated from the effect of temperature studies. Regenerability of NaS–OS material was ascertained by quantitative desorption of cadmium with 1 M aqueous NaCl and the reusability of the matrix after five repeated cycles led to nearly no attenuation in its performance (less than 2% in the sorption capacity), indicating that repeated use of NaS–OS is quite feasible. Compared to other low-cost adsorbents utilized for the removal of Cd(II) from water/wastewater, NaS–OS shows higher sorption capacity. These results have important implications for the design of low-cost adsorbents based on agricultural wastes.     

Control of the CT interaction between electron-donor and -acceptor moieties of a 1,4-dicyanonaphthalene-arene dyad for intermolecular exciplex or excimer formation in crystals

Colorless crystals of 1,4-dicyano-2-(4′-methoxybenzyloxy)methylnaphthalene (2), which is a 1,4-dicyano-2-methylnaphthalene (DCMN)-4-methylanisole (MA) dyad linked by an ether unit, selectively form a fluorescent intermolecular DCMN-MA exciplex (greenish blue, ). In contrast, 1,4-dicyano-2-(4′-methylbenzyloxy)methylnaphthalene (3), which is a DCMN-p-xylene dyad, forms a fluorescent intermolecular DCMN-DCMN excimer in the crystalline state (blue, ). These findings demonstrate that a moderate charge transfer interaction takes place between the DCMN moiety of 2 and MA moieties of the adjacent molecules of 2, which successfully facilitates the preparation of light-emissive organic crystals.     

Ion exchange recovery of chromium (VI) and manganese (II) from aqueous solutions

Sorption recovery of toxic ions – chromium (VI) and manganese (II) – from aqueous solutions with different acidity (0.001–0.5 M HCl) was investigated on cation and anion exchangers synthesized with long-chained cross-linking agents (LCA). The initial concentrations of Cr(VI) and Mn(II) were 1 g/L and 5 g/L, respectively. It was shown that the resins with LCA possess high ionic permeability due to the elasticity of polymeric skeleton. High selectivity and good kinetic properties of these sorbents allowed to achieve quantitative (∼100%) recovery and separation of manganese (II) and chromium (VI) in counter-current columns, which results in the complete purification of solutions from toxicants (below the maximum permissible limits), whereas the valuable components (chromium and manganese) can be returned back to industrial process.     

Sorption of Ponceau 4R anionic dye from aqueous solutions on aluminum oxide and polyurethane foam

The sorption of Ponceau 4R (E-124) anionic dye on polyurethane foam based on ethers and γ-Al₂O₃ from aqueous solutions is studied. It is established that sorption is highest in the range of 0.5 M HCl, pH 2 on polyurethane foam and 0.2 M HCl, pH 6.5 on γ-Al₂O₃. Under optimum conditions, the degrees of recovery on polyurethane foam and γ-Al₂O₃ are 20–30 and 70–85%, respectively. A possible scheme of interactions between the dye and the surfaces of sorbents is proposed.     

Sorption of alkaline and alkaline-earth radionuclides on zirconium phosphate sorbent Termoxid-3A from aqueous solutions

Sorption kinetic behavior of¹³⁷Cs,⁸⁵Sr,¹³³Ba and²²³Ra has been studied in the system: inorganic sorbent on the base of zirconium phosphate, Temoxid-3A, and diluted aqeous solutions. Chemosorption mechanism with the limiting step of external diffusion of the reaction between radiostrontium and the sorbent was established (n=1.304±0.0). For barium, radium and cesium radionuclides this mechanism was found to have an ion-exchange character (n<1), with limiting step of external diffusion for barium and radium radionuclides and internal diffusion for radiocesium. Termoxid-3A possesses good sorption kinetic properties. Values of the equilibrium distribution coefficients of the radionuclides studied in the suggested conditions were n·10³. Time for attaining equilibrium does not exeed 40 minutes. Purification coefficient of Moscow potable water from radiostrontium was equal to 100 when 1000 column volumes passed through. Immobilized with strontium sorbent (1.5 mg equiv. of Sr/g sorbent) keeps all its good sorption kinetic characteristics towards radionuclides studied but the mechanism of radiostrontium interaction with the sorbent changes its character from chemosorption to ion exchange (n=0.75).     

Sorptive potential of sunflower stem for Cr(III) ions from aqueous solutions and its kinetic and thermodynamic profile

The sorptive potential of sunflower stem (180-300 μm) for Cr(III) ions has been investigated in detail. The maximum sorption (≥85%) of Cr(III) ions (70.2 μM) has been accomplished using 30 mg of high density sunflower stem in 10 min from 0.001 M nitric and 0.0001 M hydrochloric acid solutions. The accumulation of Cr(III) ions on the sorbent follows Dubinin-Radushkevich (D-R), Freundlich and Langmuir isotherms. The isotherm yields D-R saturation capacity X_m = 1.60 ± 0.23 mmol g⁻¹, β = −0.00654 ± 0.00017 kJ² mol⁻², mean free energy E = 8.74 ± 0.12 kJ mol⁻¹, Freundlich sorption capacity K_F = 0.24 ± 0.11 mol g⁻¹, 1/n = 0.90 ± 0.04 and of Langmuir constant K_L = 6800 ± 600 dm³ mol⁻¹ and C_m = 120 ± 18 μmol g⁻¹. The variation of sorption with temperature (283-323 K) gives ΔH = −23.3 ± 0.8 kJ mol⁻¹, ΔS = −64.0 ± 2.7 J mol⁻¹ K⁻¹ and ΔG_298k = −4.04 ± 0.09 kJ mol⁻¹. The negative enthalpy and free energy envisage exothermic and spontaneous nature of sorption, respectively. Bisulphate, Fe(III), molybdate, citrate, Fe(II), Y(III) suppress the sorption significantly. The selectivity studies indicate that Cr(III), Eu(III) and Tb(III) ions can be separated from Tc(VII) and I(I). Sunflower stem can be used for the preconcentration and removal of Cr(III) ions from aqueous medium. This cheaper and novel sorbent has potential applications in analytical and environmental chemistry, in water decontamination, industrial waste treatment and in pollution abatement. A possible mechanism of biosorption of Cr(III) ions onto the sunflower stem has been proposed.     

A study of the removal of selenite and selenate from aqueous solutions using a magnetic iron/manganese oxide nanomaterial and ICP-MS

Selenium (Se) is naturally occurring in the environment and is an essential nutrient in mammals. However, environmental Se can be increased to toxic levels through different industrial practices. The potential adsorption of the Se oxoanions, selenite and selenate, from aqueous solutions onto nanosynthesized MnFe₂O₄ was investigated using batch techniques and DRC-ICP-MS spectroscopy. The nanomaterial (NM) was laboratory synthesized through slow titration of a mixture of Fe²⁺ and Mn²⁺ ions. X-ray diffraction and Scherrer's equation were used to determine the phase of the material and crystallite size, respectively. The effects of pH, reaction time, competitive anions, and the adsorption capacity of the synthesized NM to bind selenite and selenate were investigated. The Langmuir isotherm was used to determine the binding capacity of the NM. Results showed that the phase of the nanomaterial was similar to Jacobsite with a size of 27.5 nm. Results also showed that the sorption of either 100 ppb of selenite or selenate was pH independent in the pH range 2 to 6 and occurred within 5 min of contact time. The introduction of Cl⁻ and NO₃⁻ anions individually added to solution had no significant effect on the sorption of either selenite or selenate. However, it was found that the addition of SO₄²⁻ had a competitive effect only on the sorption of selenate, first seen at 10 ppm and more pronounced at 100 ppm of SO₄²⁻. In the presence of 100 ppm of PO₄³⁻, the adsorption of selenate decreased to 87% while selenite sorption decreased to 20%. From the Langmuir isotherm equation it was determined that the nano-Jacobsite had a selenite and selenate binding capacity of 6573.76 and 769.23 mg Se/kg of NM, respectively.