Functionalization of Graphene Oxide with 3‐Mercaptopropyltrimethoxysilane and Its Electrocatalytic Activity in Aqueous Medium

In this work, a highly dispersed graphene oxide (GO) was successfully functionalized with 3‐mercaptopropyltrimethoxysilane (MPTS) molecule by silanization method. The chemically generated GO and MPTS functionalized GO (MPTS‐GO) were structurally characterized by thermogravimetric analysis (TGA), X‐ray diffraction analysis (XRD), scanning electron microscope (SEM), energy dispersive X‐ray (EDAX), fourier transform infrared spectroscopy (FT‐IR) and ultraviolet visible spectroscopy (UV‐Vis) techniques. The MPTS‐GO is highly suspensable in water. The thermal and conductivity results for MPTS‐GO are significantly increased compared to GO. Moreover, glassy carbon electrode modified with MPTS‐GO hybrid (MPTS‐GO/GCE) was prepared by casting of the MPTS‐GO solution on GCE. The MPTS‐GO/GCE showed an excellent electrocatalytic activity towards methionine (Met). This was understood from the observed less positive oxidation potential and higher oxidation current when compared to bare GC electrode. The MPTS‐GO has excellent electrocatalytic activity, making it an ideal candidate for sensor applications.     

Polymerization of a Photocleavable Monomer Using Visible Light

The polymerization of the photocleavable monomer, o‐nitrobenzyl methacrylate (NBMA), is investigated using photoinduced electron/energy transfer reversible addition‐fragmentation chain transfer polymerization. The polymerizations under visible red (λ _max = 635 nm, 0.7 mW cm⁻²) and yellow (λ _max = 560 nm, 9.7 mW cm⁻²) light are performed and demonstrate rational evidence of a controlled/living radical polymerization process. Well‐defined poly(o‐nitrobenzyl methacrylate) (PNBMA) homopolymers with good control over the molecular weight and polymer dispersity are successfully synthesized by varying the irradiation time and/or targeted degree of polymerization. Chain extension of a poly(oligo(ethylene glycol) methyl ether methacrylate) macro‐chain transfer agent with NBMA is carried out to fabricate photocleavable amphiphilic block copolymers (BCP). Finally, these self‐assembled BCP rapidly dissemble under UV light suggesting the photoresponsive character of NBMA is not altered during the polymerization under yellow or red light. Such photoresponsive polymers can be potentially used for the remote‐controlled delivery of therapeutic compounds.

     

A chitosan–polypyrrole magnetic nanocomposite as μ-sorbent for isolation of naproxen

An extracting medium based on chitosan–polypyrrole (CS–PPy) magnetic nanocomposite was synthesized by chemical polymerization of pyrrole at the presence of chitosan magnetic nanoparticles (CS-MNPs) for micro-solid phase extraction. In this work, magnetic nanoparticles, the modified CS-MNPs and different types of CS–PPy magnetic nanocomposites were synthesized. Extraction efficiency of the CS–PPy magnetic nanocomposite was compared with the CS-MNPs and Fe₃O₄ nanoparticles for the determination of naproxen in aqueous samples, via quantification by spectrofluorimetry. The scanning electron microscopy images obtained from all the prepared nanocomposites revealed that the CS–PPy magnetic nanocomposite possess more porous structure. Among different synthesized magnetic nanocomposites, CS–PPy magnetic nanocomposite showed a prominent efficiency. Influencing parameters on the morphology of CS–PPy magnetic nanocomposite such as weight ratio of components was also assayed. In addition, effects of different parameters influencing the extraction efficiency of naproxen including desorption solvent, desorption time, amount of sorbent, ionic strength, sample pH and extraction time were investigated and optimized. Under the optimum condition, a linear calibration curve in the range of 0.04–10 μg mL⁻¹ (R² = 0.9996) was obtained. The limits of detection (3S_b) and limits of quantification (10S_b) of the method were 0.015 and 0.04 μg mL⁻¹ (n = 3), respectively. The relative standard deviation for water sample spiked with 0.1 μg mL⁻¹ of naproxen was 3% (n = 5) and the absolute recovery was 92%. The applicability of method was extended to the determination of naproxen in tap water, human urine and plasma samples. The relative recovery percentages for these samples were in the range of 56–99%.     

Preparation,characterization, and applications of a novel solid-phase microextraction fiber by sol-gel technology on the surface of stainless steel wire for determination of poly cyclic aromatic hydrocarbons in aquatic environmental samples

A novel solid-phase microextraction(SPME) fiber was prepared using sol–gel technology with ethoxylated nonylphenol as a fiber coating material. The fiber was employed to develop a headspace SPME–GC–MS method suitable for quantification of 13 polycyclic aromatic hydrocarbons (PAHs) in water samples. Surface characteristics of the fibers were inspected by energy dispersive X-ray (EDX) spectroscopy as well as by scanning electron microscopy (SEM). The SEM measurements showed the presence of highly porous nano-sized particles in the coating. Important parameters affecting the extraction efficiency such as extraction temperature and time, desorption conditions as well as ionic strength have been evaluated and optimized. In the next step, the validation of the new method have been performed, finding it to be specific in the trace analysis of PAHs, with the limit of detection (LOD) ranging from 0.01 to 0.5 μg L⁻¹ and the linear range from the respective LOD to 200 μg L⁻¹with RSD amounting to less than 8%. The thermal stability of the fibers was investigated as well and they were found to be durable at 280 °C for 345 min. Furthermore, the proposed method was successfully applied for quantification of PAHs in real water samples.     

Synthesis and application of a thermosensitive tri-block copolymer as an efficient sample treatment technique for preconcentration and ultra-trace detection of lead ions

We have designed and synthesized a thermosensitive tri-block copolymer for selective trace extraction of Pb(II) ions from biological and food samples. The polymer was characterized by Fourier transform IR and NMR spectroscopy, and by gel permeation chromatography. The critical aggregation concentration and lower critical solution temperature were determined via fluorescence and UV spectrophotometry, respectively. The effects of solution pH value, amount of copolymer, of the temperature on extraction and on phase separation, and of the matrix on the extraction of Pb(II) were optimized. Pb(II) ions were then quantified by FAAS. The use of this copolymer resulted in excellent figures of merit including a calibration plot extending from 0.5 to 160 μg L^?1 (with an R² of >0.99), a limit of detection (LOD) as low as 90 pg L^?1, an extraction efficiency of >98 %, and relative standard deviations of <4 % for eight separate extraction experiments.

Binary and ternary blends of high‐density polyethylene with poly(ethylene terephthalate) and polystyrene based on recycled materials

Binary blends of recycled high‐density polyethylene (R‐HDPE) with poly(ethylene terephthalate) (R‐PET) and recycled polystyrene (R‐PS), as well as the ternary blends, i.e. R‐HDPE/R‐PET/R‐PS, with varying amounts of the constituents were prepared by twin screw extruder. The mechanical, rheological, thermal, and scanning electron microscopy (SEM) analyses were utilized to characterize the samples. The results revealed that both R‐HDPE/R‐PET and R‐HDPE/R‐PS blends show phase inversion but at different compositions. The R‐PET was found to have much higher influence on the properties enhancement of the R‐HDPE compared to R‐PS, but at the phase inverted situation, a significant loss in the tensile strength of R‐HDPE/R‐PET blend was observed due to the weak interaction at this morphological state. However, the ternary blends with higher loading of second phase, namely greater than 50 wt% of R‐PET+R‐PS, demonstrated better mechanical properties than the binary blends with the same content of either R‐PET or R‐PS. Copyright © 2009 John Wiley & Sons, Ltd.     

Application of the UNIFAC model for prediction of surface tension and thickness of the surface layer in the binary mixtures

The specific sorption of Eu(III) and Y(III) on γ-alumina was investigated with solid-state (1)H NMR. Solution pH was shown to influence the recorded (1)H NMR spectra of γ-alumina, and thus, metal ion-containing samples were prepared under constant pH conditions, 8.00±0.05. The metal ion concentration in the samples was varied between 6.58×10(-7) M - 3.95×10(-4) M in case of Y(3+) and 6.58×10(-8) M - 1.32×10(-4) M in case of Eu(3+). The mineral concentration was kept constant at 4 g/l. After separation of the liquid phase, the samples were dried under vacuum to remove physisorbed water from the mineral surface. However, even after 48 h of drying at 150°C and 20 mTorr, water was still detected in the proton spectra as two distinct peaks with chemical shifts at 1.3 and 0.9 ppm. The europium addition to the γ-alumina samples induced significant spectral changes in comparison with yttrium-containing samples. These changes were attributed to the paramagnetism of europium rather than to complexation reactions occurring on the mineral surface. Proton spectra obtained for yttrium samples were therefore used to detect the spectral changes induced by the sorption reaction itself. The results revealed a large distribution of protons being removed from the mineral surface upon yttrium complexation. Removed protons were assigned to both bridging surface hydroxyls such as (Al(VI))(2)-OH as well as to terminal hydroxyls, e.g., of type Al(VI)-OH. Acidic protons belonging to (Al(VI))(3)-OH groups were not observed to participate in the surface reaction.     

An unbreakable on-line approach towards sol-gel capillary microextraction

In this work a novel unbreakable sol-gel-based in-tube device for on-line solid phase microextraction (SPME) was developed. The inner surface of a copper tube, intended to be used as a high performance liquid chromatography (HPLC) loop, was electrodeposited by metallic Cu followed by the self assembled monolayers (SAM) of 3-(mercaptopropyl) trimethoxysilane (3MPTMOS). Then, poly (ethyleneglycol) (PEG) was chemically bonded to the -OH sites of the SAM already covering the inner surface of the copper loop using sol-gel technology. The homogeneity and the porous surface structure of the SAM and sol-gel coatings were examined using the scanning electron microscopy (SEM) and adsorption/desorption porosimetry (BET). The prepared loop was used for online in-tube SPME (capillary microextraction) of some selected polycyclic aromatic hydrocarbons (PAHs), as model compounds, from the aquatic media. After extraction, the HPLC mobile phase was used for on-line desorption and elution of the extracted analytes from the loop to the HPLC column. Major parameters affecting the extraction efficiency including the sample flow rate through the copper tube, loading time, desorption time and sample volume were optimized. For investigating the sorbent efficiency, four loops based on the copper tube itself, the copper tube after electrodeposition with Cu and the tubes with the SAMs and SAMs-sol-gel coating were made and compared. The SAMs-sol-gel coated loop clearly shows a prominently lead of at least 20-100 times of higher efficiency. The linearity for the analytes was in the range of 0.01-500 μg L(-1). Limit of detection (LOD) was in the range of 0.005-0.5 μg L(-1) and the RSD% values (n=5) were all below 8.3% at the 5 μg L(-1) level. The developed method was successfully applied to real water samples while the relative recovery percentages obtained for the spiked water samples were from 90 to 104%. The prepared loop exhibited long life time due to its remarkable solvent and mechanical stability. Different solvents such as methanol, acetonitrile and acetone were passed through the loop for many days and it was also used for more than 100 extractions/desorption of the selected analytes and no decrease in the peak areas was observed.     

Influence of substitution on the strength and nature of CH···N hydrogen bond in XCCH···NH3 complexes

The effect of substitution on the strength and nature of CH···N hydrogen bond in XCCH···NH₃ (X = F, Cl, Br, OH, H, Me) and NCH···NH₃ complexes were investigated by quantum chemical calculations. Ab initio calculations were performed using MP2 method with a wide range of basis sets. With tacking into account the BSSE and ZPVE, the values of BEs decrease. Replacement of the nonparticipatory hydrogen atom of HCCH by the electronegative atoms (F, Cl, and Br), lead to the BEs increases. The BE corresponding to the replacement of the nonparticipatory hydrogen atom of HCCH by the OH and CH₃ groups decreases. A far greater enhancement of the interaction energy arises from replacement of HCCH by the more acidic HCN. The natural bond orbital analysis and the Bader's quantum theory of atoms in molecules were also used to elucidate the interaction characteristics of these complexes. The electrostatic nature of H‐bond interactions is predicted from QTAIM analysis. In addition, the relationship between the isotropic and anisotropic chemical shifts of the bridging hydrogen and binding energy of complexes as well as electron density at N···H BCPs were investigated. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Buckling analysis of stringer-stiffened laminated cylindrical shells with nonuniform eccentricity

In this study, the influence of nonuniformity of eccentricity of stringers on the general axial buckling load of stiffened laminated cylindrical shells with simply supported end conditions is investigated. The critical loads are calculated using Love’s First-order Shear Deformation Theory and solved using the Rayleigh-Ritz procedure. The effects of the shell length-to-radius ratio, shell thickness-to-radius ratio, number of stringers, and stringers depth-to-width ratio on the buckling load of nonuniformly eccentric shells, are examined. The research demonstrates that an appropriate nonuniform distribution of eccentricity of stringers leads the buckling load to increase significantly.