Copper(II) Oxide Nanoparticles Impregnated on Melamine‐Modified UiO‐66‐NH2 Metal–Organic Framework for C–N Cross‐Coupling Reaction and Synthesis of 2‐Substituted Benzimidazoles

A zirconium‐based metal–organic framework, UiO‐66‐NH₂, modified by melamine (Mlm) was used as a support for CuO nanoparticles (NPs). Melamine offered a platform for uniform and homogeneous distribution of NPs on the surface of the frameworks and made a strong bonding to the NPs to avoid undesirable leaching. UiO‐66‐NH₂‐Mlm/CuO NPs were used for the Buchwald–Hartwig C–N cross‐coupling reaction to synthesize arylated anilines from phenyl iodide, bromide, and chloride and primary and secondary amines in DMF at 110°C. The catalyst was also employed for the synthesis of 2‐substituted benzimidazole derivatives from various aromatic aldehydes and o‐phenylenediamine in the absence of an oxidant in EtOH at room temperature. The catalyst was recyclable and reusable for several times and exhibited good stability (examined by BET, XRD, and SEM–EDX) in reaction conditions.     

Electrochemical preconcentration of ultra-trace Cd2+ from environmental and biological samples prior to its determination using carbon paste electrode impregnated with ion imprinted polymer nanoparticles

Cadmium (Cd) is known as one of the most toxic elements among the heavy metals. This study proposes an electrochemical preconcentration method using the ion imprinted polymer nanoparticles modified carbon paste electrode (IIP-CPE) for the stripping voltammetry determination of Cd²⁺ in the environmental and biological samples. These IIP NPs were synthesised using ethylene glycol dimethacrylate as the cross-linker, 2,2?-azobisisobutyronitrile as the free radical initiator and 4?-(4-vinylphenyl)-2,2?:6?,2?-terpyridine as the Cd-binding ligand. The calibration plot was linear in the concentration range of 4–500 nM (R² = 0.9936) with a sensitivity of 918 µA µM^?1 cm^?2. The LOD based on 3S_b/m (where m is the slope of the calibration curve and S_b is the standard deviation for five blank measurements) was found to be 1.94 nM. The relative standard deviations (RSDs) for single-electrode repeatability and electrode-to-electrode reproducibility were 3.0% and 5.6% (n = 5), respectively. The accuracy of the current method was confirmed by the analysis of urine quality control material (QCM, Seronorm^TM Trace Elements Urine, REF NO 201205, Norway) and spiked blood, rice and water samples. Recoveries were found to be above 95.0% for all samples, which confirms the good performance of the proposed voltammetry method.     

Environmentally friendly surface modification of silk fiber: Chitosan grafting and dyeing

In this paper, the surface modification of silk fiber using anhydrides to graft the polysaccharide chitosan and dyeing ability of the grafted silk were studied. Silk fiber was degummed and acylated with two anhydrides, succinic anhydride (SA) and phthalic anhydride (PA), in different solvents (dimethyl sulfoxide (DMSO) and N,N-dimethyl formamide (DMF)). The effects of anhydrides, solvents, anhydride concentration, liquor ratio (L:R) and reaction time on acylation of silk were studied. The polysaccharide chitosan was grafted to the acylated silk fiber and dyed by acid dye (Acid Black NB.B). The effects of pH, chitosan concentration, and reaction time on chitosan grafting of acylated silk were investigated. The physical properties show sensible changes regardless of weight gain. Scanning electron microscopy (SEM) analysis showed the presence of foreign materials firmly attached to the surface of silk. FTIR spectroscopy provided evidence that chitosan was grafted onto the acylated silk through the formation of new covalent bonds. The dyeing of the chitosan grafted-acylated silk fiber indicated the higher dye ability in comparison to the acylated and degummed silk samples. The mechanism of chitosan grafting over degummed silk through anhydride linkage was proposed. The findings of this research support the potential production of new environmentally friendly textile fibers. It is worthwhile to mention that the grafted samples have antibacterial potential due to the antibacterial property of chitosan molecules.     

Determination of BTEX in urine samples using cooling/heating-assisted headspace solid-phase microextraction

Excessive and uncontrolled exposures of the workers to benzene, toluene, ethylbenzene and xylene (BTEX) have currently raised great concerns among industrial hygienist all over the world. Therefore, the effective monitoring of such exposures is assumed to be of prime importance. A cold fiber solid-phase microextraction device based on a cooling capsule as a cooling unit and CO₂ as a coolant was applied to quantitatively analyze BTEX in aqueous samples. A gas chromatography with flame ionization detection was recruited to analyze the target analytes, which had been identified according to their retention times. Several factors such as coating temperature, extraction time and temperature, sample volume and sodium content were optimized. Two modes of extraction, i.e., headspace (HS) and headspace cold fiber (HS-CF) in SPME, were investigated and compared under optimized conditions. The results revealed that HS-CF-SPME has the most appropriate outcome for the extraction of BTEX from aqueous samples. Under the optimized conditions, the calibration curves were linear within the range of 0.2–500 ng ml^?1 and the detection limits were between 0.02 and 0.07 ng ml^?1.The intraday relative standard deviations was lower than about 10%. The method was successfully applied to the determination of BTEX in urine samples with good recovery.     

The role of organic acids on <Superscript>226</Superscript>Ra transfer factor in corn (<Emphasis Type="Italic">Zea mays</Emphasis> L.)

Enrichment of lithium isotopes by displacement chromatography on strong acid cation exchanger was investigated. Narrow particle fraction of Dowex 50 WX 2 cation exchanger having diameter of 150–200 µm and total exchange capacity of 1.31 meq mL^?1 was used as stationary phase. As a mobile phase, 1 mol L^?1 solution of ammonium nitrate solution was used. Shape and position of Li chromatographic peak, was determined by atomic emission spectroscopy (AES). Isotope ratio was estimated by ICP–MS after 1, 8 and 10 enrichment steps. Value of separation factor for ⁶Li in one step was determined to be 1.027.     

Inflation and eversion of functionally graded non-linear elastic incompressible circular cylinders

We study axisymmetric radial deformations of a circular cylinder composed of an inhomogeneous Mooney-Rivlin material with the two material parameters varying continuously through the cylinder thickness either by a power law or an affine relation. It is found that for the exponent of the power law function equal to 1, the hoop stress for an internally pressurized cylinder is uniform in the cylinder. One can tailor the gradation of these two material parameters to make the maximum tensile hoop stress occur either on the inner surface or on the outer surface. Also, the stress concentration in a pressurized thick cylinder strongly depends upon the value of the exponent of the power law variation of the two material parameters. For an affine through-the-thickness variation of the two elastic moduli the hoop stress at the point is nearly the same as that in a cylinder composed of a homogeneous material. Here R_in and R_ou equal, respectively, the inner and the outer radii of the cylinder in the unstressed reference configuration, and R is the radial coordinate of a point in the reference configuration. The stress distribution in an everted cylinder strongly depends upon its thickness in the reference configuration.     

Integer quantum Hall effect in Kekulé-patterned graphene

Y-shaped Kekulébond textures in a honeycomb lattice on a graphene-copper superlattice have recently been experimentally revealed.In this paper,the effects of such a bond modulation on the transport coefficients of Kekulé-patterned graphene are investigated in the presence of a perpendicular magnetic field.Analytical expressions are derived for the Hall and longitudinal conductivities using the Kubo formula.It is found that the Y-shaped Kekulébond texture lifts the valley degeneracy of all Landau levels except that of the zero mode,leading to additional plateaus in the Hall conductivity accompanied by a split of the corresponding peaks in the longitudinal conductivity.Consequently,the Hall conductivity is quantized as±ne²/h for n=2,4,6,8,10,...,excluding some plateaus that disappear due to the complete overlap of the Landau levels of different cones.These results also suggest that DC Hall conductivity measurements will allow us to determine the Kekulébond texture amplitude.     

Investigation of energy performance in a U-shaped evacuated solar tube collector using oxide added nanoparticles through the emitter,absorber and transmittal environments via discrete ordinates radiation method

Journal of Thermal Analysis and Calorimetry - This work is a three-dimensional numerical study of a U-shaped evacuated tube solar collector employing different types of oxide nanofluids including...     

Diminishing vortex intensity and improving heat transfer by applying magnetic field on an injectable slip microchannel containing FMWNT/water nanofluid

In this study, heat transfer and entropy generation were investigated in a microchannel containing FMWNT/water nanofluids given the slip condition. The main focus was on utilizing injection technique in the presence of the magnetic field. The injection from the upper high-temperature wall was incorporated into the flow field. Injection at high Reynolds number causes vortex formation, which ultimately reduces local heat transfer in the adjacent injection zone. By applying the magnetic field, the vortex intensity as well as boundary layer thickness was diminished which in turn improved the heat transfer. Based on numerical results, at higher nanoparticle volume fraction, the effect of the magnetic field on heat transfer enhancement was amplified. Moreover, at higher Reynolds numbers, the magnetic field efficacy is more obvious. The highest heat transfer occurred at the highest values of the Hartmann and Reynolds numbers and eventually the nanoparticle volume fraction. Owing to applying the magnetic field on the injectable microchannel containing nanofluid, heat transfer improvement can reach up to 79%. From the second law prospective, the entropy generation intensified by 82.8%.

     

The structural and magnetic properties of one-step mechanochemical route synthesized La0.8Pb0.2MnO3 manganites

Mechanochemical route has been used to produce La_0.8Pb_0.2MnO₃ (LPMO) nanocrystalline samples from oxide precursors. The samples were characterized using X-ray diffraction, scanning electron microscope and AC susceptibility measurements. The results showed that it is possible to produce LPMO perovskite powders after 10 h of ball milling. The crystallite size and microstrain were estimated using Williamson-Hall equation. The results showed that the crystallite size and microstrain increase initially and then decrease by the increase of milling time. By decreasing particle size the dislocation density (strain) increases and reaches to a saturation point at a particular particle size, further particle size reduction takes place through gliding motion along grain boundaries, which leads to a reduction of the strain. The dynamic properties of 15 h ball-milled sample were investigated by AC susceptibility using the Neel-Brown and Vogel-Fulcher law for superparamagnetism. The frequency dependence of blocking temperature is well described by the Vogel-Fulcher law, and fitting the experimental data with Neel-Brown law gives unphysical value for relaxation time.