Nitrogen doped nano porous graphene as a sorbent for separation and preconcentration trace amounts of Pb,Cd and Cr by Ultrasonic assisted in‐syringe dispersive micro solid phase extraction

Nitrogen doped nano porous graphene was used as an efficient sorbent in solid‐phase extraction process for simultaneous separation and pre‐concentration of metal ions lead (II), cadmium(II), and chromium(III)) in biological samples. Ultrasonic assisted in‐syringe dispersive micro solid phase extraction coupled with micro sampling atomic absorption spectrometry was utilized for the determination of metal ions. Nitrogen doped nano porous graphene was synthesized as a nano sorbent by chemical vapour deposition method. Methane and aniline were used as carbon and nitrogen sources. The characterization of sorbent was performed by field emission scanning electron microscope, transmission electron microscopy, atomic force microscope, fourier transform infrared, chemical element analysis and raman analysis. Effective parameters on the extraction efficiency such as pH, sorbent dosage, eluent volume and eluent concentration were optimized by central composite design and desirability function. Experimental results indicate that the optimal conditions for this extraction were pH = 6.4, 1.42 mg of sorbent, 100 μL of eluent, and 0.84 mol L^‐1 of eluent concentration. The detection limits are as low as 1.5, 0.3 and 0.9 μg L^‐1 for lead, cadmium, and chromium, respectively. The intra‐day precisions were 3.6, 4.38 and 2.94 and Inter‐day precision were 4.83, 5.26 and 4.52 for lead, cadmium, and chromium, respectively. Method performance was investigated by determination of mentioned heavy metals in complicated biological matrixes such as human plasma, urine and saliva samples with good recoveries.     

Two-Fluid Dark Energy Models in Bianchi Type-III Universe with Variable Deceleration Parameter

Some new exact solutions of Einstein’s field equations have come forth within the scope of a spatially homogeneous and anisotropic Bianchi type-III space-time filled with barotropic fluid and dark energy by considering a variable deceleration parameter. We consider the case when the dark energy is minimally coupled to the perfect fluid as well as direct interaction with it. Under the suitable condition, the anisotropic models approach to isotropic scenario. We also find that during the evolution of the universe, the equation of state (EoS) for dark energy ω ^(de), in both cases, tends to ?1 (cosmological constant, ω ^(de)=?1), by displaying various patterns as time increases, which is consistent with recent observations. The cosmic jerk parameter in our derived models are in good agreement with the recent data of astrophysical observations under appropriate condition. It is observed that the universe starts from an asymptotic Einstein static era and reaches to the ΛCDM model. So from recently developed Statefinder parameters, the behaviour of different stages of the universe has been studied. The physical and geometric properties of cosmological models are also discussed.     

A Review on Effects of Lubricant Formulations on Tribological Performance and Boundary Lubrication Mechanisms of Non-Doped DLC/DLC Contacts

Tribological efficiency of industrial applications involving boundary lubrication regime can be improved to an appreciable extent by the deposition of hard coatings on interacting surfaces. Among such coatings, diamond-like carbon (DLC) coatings are considered to be one of the most suitable ones for the said role. DLC coatings possess a unique combination of physical, chemical, and material properties due to which they can help in minimizing friction-induced energy and material losses even under starved lubrication conditions. Since commercial lubricants are optimized for steel surfaces, therefore, a lot of experimental investigations were carried out to analyze the tribological compatibility of these lubricants with various DLC coatings. However, there is still a lack of understanding about how DLC coatings interact with conventional lubricant additives. Some researchers reported tribologically beneficial interactions between DLC coatings and formulated lubricants while others observed no such behavior. To address these inconsistencies, there is a need to rearrange the published data in a more apprehensible and organized manner with a special emphasis on the mechanisms responsible for a particular tribological behavior. In this way, it can be determined whether synergistic or antagonistic correlation exists between a particular DLC-lubricant combination and research on DLC coatings can be continued in a logical way. In this article, most widely investigated non-doped DLC coatings (ta-C, a-C:H, a-C, and ta-C:H) are tribologically analyzed. Average values of friction and wear coefficients are calculated for various DLC-lubricant combinations using already published data and compared to quantify the effectiveness of a particular lubricant additive in enhancing tribological characteristics of symmetrical non-doped DLC contacts. Moreover, tribological performance parameters of non-doped DLC coatings are compared with those of doped-DLC coatings to understand differences in their tribological behavior in combination with additives.     

A hyperbranched polyamidoamine dendrimer grafted onto magnetized graphene oxide as a sorbent for the extraction of synthetic dyes from foodstuff

Microchimica Acta - Graphene oxide nanosheets were modified with magnetite nanoparticles, and a hyperbranched polyamidoamine dendrimer was then covalently attached to their surface. The resulting...     

Electrical Conductance of Fast Extrusion Furnace Carbon Black-Loaded Styrene-Butadiene Rubber during Swelling in Kerosene

The effect of swelling in kerosene on the electrical conductance of 60, 80, and 100 part per hundred parts of rubber by weight of Fast Extrusion Furnace (FEF) carbon black-loaded styrene-butadiene rubber (SBR, 1502) was studied. It was found that there is a characteristic time of swelling after which a sudden decrease in conductivity appears. An ideal and simple model is suggested to calculate the carbon-carbon interspacing distance, D, in the carbon/rubber matrix. The dependence of D on the swelling time is also discussed.     

A Facile One-Pot Synthesis of Highly-Functionalized Stable Heterocyclic Phosphorus Ylides in Aqueous Media

Phthalimide or succinimide undergo a reaction with dialkyl acetylenedicarboxylates and triphenylphosphine to produce highly-functionalized stable heterocyclic phosphorus ylides in good yields in water-tetrahydrofuran (6:1). This methodology is of interest because of the use of water as solvent, thus minimizing the cost, operational hazards, and environmental pollution.     

Solvent Free Synthesis of Coumarins

An efficient synthesis of 3-substituted coumarins under solventless system is described.     

Thermogravimetric studies on catalytic effect of metal oxide nanoparticles on asphaltene pyrolysis under inert conditions

This study investigated the catalytic effect of NiO, Co₃O₄ and Fe₃O₄ nanoparticles toward asphaltene thermal decomposition (pyrolysis) under inert conditions. Asphaltene adsorbed onto the selected nanoparticles were subjected to thermal decomposition up to 800?°C in a thermogravimetric analyzer. The presence of nanoparticles caused a significant decrease in the asphaltene decomposition temperature and activation energy. Activation energies for the process were calculated using the Ozawa?CFlynn?CWall method. All the selected metal oxide nanoparticles showed high catalytic activity toward asphaltene decomposition in the following order NiO?>?Co₃O₄?>?Fe₃O₄. This study confirms that metal oxide nanoparticles can significantly enhance the thermal decomposition of heavy hydrocarbons, like asphaltenes.     

The effect of starvation periods on the performance of a two-liquid-phase mixed tank bioreactor for removal of n-hexane from air streams

In this research the effect of silicone oil as a heavy organic solvent on the performance of a mixed tank bioreactor was investigated. In the first stage of the experiments, the response of a two-liquid-phase mixed tank bioreactor to periods of n-hexane starvation was compared with that of a control bioreactor. In the control bioreactor, after 3?days of starvation, approximately six days were needed to reach the removal efficiency it had before starvation. This figure was only 10?h for the silicone oil-containing bioreactor. The results confirmed that inclusion of a heavy organic solvent can increase the elimination capacity of a bioreactor and to help sustain high elimination capacity after starvation periods. In the second stage of the experiments, the effect of the amount of silicone oil on the performance of the bioreactor was investigated. Increasing the amount of oil from 5 to 10% (v/v) increased the maximum elimination capacity from 106 to 117?g/m³?h.