Facile Non‐enzymatic Lactic Acid Sensor Based on Cobalt Oxide Nanostructures

In this study, we have investigated the effect of counter anions on the morphology of cobalt oxide nanostructures. The nanostructures of cobalt oxide are prepared by a low temperature aqueous chemical growth method. The morphology of cobalt oxide nanostructure material was investigated by scanning electron microscopy and the crystalline structure was studied by powder X‐ray diffraction technique. The cobalt oxide nanostructures exhibit the nanowire, lump, bundle of the nanowire and flower‐like morphologies. The XRD study has revealed a cubic phase of cobalt oxide nanostructures. The electro‐catalytic properties of cobalt oxide nanostructures were explored through cyclic voltammetry and amperometric techniques by sensing of lactic acid in the alkaline media. The cobalt oxide nanostructures prepared from cobalt nitrate have shown a well‐resolved redox peak. The proposed mechanism for the non‐enzymatic lactic acid sensor is elucidated by considering the morphology and cyclic voltammetry response. The limit of detection for the sensor was found to be 0.006 mM and it exhibits a linear range from 0.05–3 mM of lactic acid as shown by cyclic voltammetry. The amperometric response has shown the excellent current‐concentration response and the linear range of sensor was found to be 0.1 mM to 5.5 mM. The lactic acid sensor is stable, selective and can be used for practical applications. This study provides an excellent alternative analytical tool for the determination of lactic acid.     

Thermodynamic and kinetic studies of the retro-Diels-Alder reaction of 1,4-cyclohexadiene, 4H-pyran 4H-thiopyran, 1,4-dioxine,and 1,4-dithiine: a theoretical investigation

Theoretical studies of the retro-Diels-Alder reaction of 1,4-cyclohexadiene, 4H-pyran 4H-thiopyran, 1,4-dioxine, and 1,4-dithiine in the gas phase were carried out using DFT methods at the B3LYP/6–311?+?G(d,p) levels of theory. The barrier height (ΔE^?) and thermodynamic parameters (ΔG^? and ΔH^?) were estimated. The progress of the reactions was followed by means of the Wiberg bond indices. The synchronicity values of the reactions were calculated. The kinetic parameters were calculated for both reactions in 300–1200-K temperature range. Also, fitted equations to the gas phase Arrhenius equation were determined. Effect of the character and number of heteroatoms were illustrated on the thermodynamic and kinetic parameters.

     

Adsorption modeling and mechanistic insight of hazardous chromium on para toluene sulfonic acid immobilized-polyaniline@CNTs nanocomposites

The development of highly efficient adsorbents materials for the purification of wastewater has caught a considerable deal of attention these days. Conducting polymers functionalized adsorbents has become a favorable route for enhancing their adsorption capability due to their ease of synthesis at laboratory scale. In this study, functionalized multiwalled carbon nanotube (CNT)-polyaniline (Pani) composites were fabricated using an oxidation polymerization methodology and later doped with para toluene sulfonic acid (pTSA). The CNTs provided an adequate substrate for the adhesion of Pani as well as a large surface area due to its nano size, and pTSA provided additional functionality for the adsorption of differently charged moieties through strong or weak interactions. The as-synthesized pTSA-Pani@CNT nanocomposite was analyzed by the scanning electron microscopy, transmission electron microscopy for the morphological studies and the structural analysis were done by the X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). The characterization results confirmed that the Pani was adhered to the CNTs as well as its successful functionalization with pTSA. The pTSA-Pani@CNT composite was then applied to the adsorptive removal of hexavalent chromium (Cr(VI)) and the composite showed higher adsorption for Cr(VI) than pTSA-CNT and pTSA-Pani, and the maximum removal level was detected at acidic pH. The analyses of the equilibrium isotherms and adsorption kinetics were performed to elucidate the adsorption mechanism. The XPS analysis indicated that Cr(VI) was strongly bounded to the adsorbent and it further indicated that the amine, imine, and hydroxyl functional groups were involved in the adsorption process. This study presents a new insight for the fabrication of highly functional polymer-carbonaceous nanocomposites for the scavenging of heavy metals from water bodies.     

Analytical solution approach for nonlinear buckling and postbuckling analysis of cylindrical nanoshells based on surface elasticity theory

The size-dependent nonlinear buckling and postbuckling characteristics of circular cylindrical nanoshells subjected to the axial compressive load are investigated with an analytical approach. The surface energy effects are taken into account according to the surface elasticity theory of Gurtin and Murdoch. The developed geometrically nonlinear shell model is based on the classical Donnell shell theory and the von K′arm′an's hypothesis. With the numerical results, the effect of the surface stress on the nonlinear buckling and postbuckling behaviors of nanoshells made of Si and Al is studied. Moreover, the influence of the surface residual tension and the radius-to-thickness ratio is illustrated.The results indicate that the surface stress has an important effect on prebuckling and postbuckling characteristics of nanoshells with small sizes.     

Effect of Temperature on Dynamic Physical Behavior of Poly(vinyl chloride) Gel Structure with Ester Plasticizers

Dynamic viscoelastic properties of poly(vinyl chloride) (PVC)/bis(2-ethylhexyl) phthalate (DOP) and PVC/di-n-butyl sebacate (DBS) gels with molecular weight distribution (M_w/M_n), of 2.16 and various polymer concentrations c, have been studied as a function of temperature. These PVC gels exhibited an elastic solid at room temperature T, and gradually became liquid (sol) with increasing temperature. The sol-gel transition took place at a critical gel temperature at which the scaling law of G′(ω) ∼ G″(ω) ∝ ωⁿ held, allowing an accurate determination of the critical gel temperature by means of the frequency ω independence of the loss tangent. In this study the scaling exponent n, was 0.75–0.77. This is in good agreement with the previous results observed at different temperatures and suggests the formation of a similar fractal structure of the PVC gels. The gel strength S_g, at the gel point increased with increasing PVC concentration. These results suggest a unique character and structure for the gel points of PVC-plasticizers.     

Studying linear and nonlinear vibrations of fractional viscoelastic Timoshenko micro-/nano-beams using the strain gradient theory

Nonlinear Dynamics - In this paper, the vibrational behavior of micro- and nano-scale viscoelastic beams under different types of end conditions in the linear and nonlinear regimes is investigated...     

Single-shot measurement of revival structures in femtosecond laser-induced alignment of molecules

We present a single-shot detection technique for field-free molecular alignment. The method is based on probing the time-varying birefringence of an aligned sample by use of a chirped probe pulse, thus encoding the dependence of the alignment on time onto the spectral domain. The technique is applied to alignment of O2. The recorded signals are well described by an analytical formula.