Preparation and characterization of Mg-Al hydrotalcite-like compounds containing cerium

Hydrotalcite-like compounds (HTlcs) containing Mg(2+), Al(3+), and Ce(3+) in the hydroxide layer and with carbonate as charge-balancing anion have been prepared by a co-precipitation (at constant pH) method. The Al/Ce ratio in the final product depends on the concentration in the initial solution. The crystallinity of the layered materials decreases with the increase in cerium content, probably, due to the distortions introduced by the large difference in the ionic radii of the cations. All the synthesized materials were characterized by XRD, FT-IR spectroscopy and TG/DTA. The textural properties were determined from low-temperature nitrogen adsorption-desorption measurements.     

Adsorption of organic molecules on silica surface

The adsorption behaviour of various organic adsorbates on silica surface is reviewed. Most of the structural information on silica is obtained from IR spectral data and from the characteristics of water present at the silica surface. Silica surface is generally embedded with hydroxy groups and ethereal linkages, and hence considered to have a negative charged surface prone to adsorption of electron deficient species. Adsorption isotherms of the adsorbates delineate the nature of binding of the adsorbate with silica. Aromatic compounds are found to involve the pi-cloud in hydrogen bonding with silanol OH group during adsorption. Cationic and nonionic surfactants adsorb on silica surface involving hydrogen bonding. Sometimes, a polar part of the surfactants also contributes to the adsorption process. Styryl pyridinium dyes are found to anchor on silica surface in flat-on position. On modification of the silica by treating with alkali, the adsorption behaviour of cationic surfactant or polyethylene glycol changes due to change in the characteristics of silica or modified silica surface. In case of PEG-modified silica, adsolubilization of the adsorbate is observed. By using a modified adsorption equation, hemimicellization is proposed for these dyes. Adsorptions of some natural macromolecules like proteins and nucleic acids are investigated to study the hydrophobic and hydrophilic binding sites of silica. Artificial macromolecules like synthetic polymers are found to be adsorbed on silica surface due to the interaction of the multifunctional groups of the polymers with silanols. Preferential adsorption of polar adsorbates is observed in case of adsorbate mixtures. When surfactant mixtures are considered to study competitive adsorption on silica surface, critical micelle concentration of individual surfactant also contributes to the adsorption isotherm. The structural study of adsorbed surface and the thermodynamics of adsorption are given some importance in this review.     

Effect of radiation and chemical reaction on natural convective MHD flow through a porous medium with double diffusion

The influence of radiation and chemical reaction on a natural convective MHD flow through a porous medium bounded by a vertical infinite surface in the presence of transverse magnetic field is studied. The basic equations governing the flow, heat and mass transfer are reduced to a set of ordinary differential equations by appropriate transformations. Governing equations are solved by perturbation technique for velocity, temperature and concentration, and that has been presented graphically for different values of involved parameters. It is observed that effects of magnetic parameter and radiation parameter in the flow field affect the flow significantly.     

Structural and electrical characterization of BiFeO3–NaTaO3 multiferroic

Using a standard high-temperature solid-state reaction technique, polycrystalline samples of (Bi_1?x , Na _x ) (Fe_1?x , Ta _x ) O₃ (x = 0.0, 0.5) were prepared. The formation of the desired materials was confirmed by X-ray diffraction. The surface texture of the prepared materials recorded by scanning electron microscope exhibits a uniform grain distribution with small voids suggesting the formation of high-density pellet samples. The impedance and dielectric properties of the materials were investigated as a function of temperature and frequency. The relative dielectric constant and loss tangent of BiFeO₃ decrease on addition of NaTaO₃ (x = 0.5). The effect of addition of NaTaO₃ on grain and grain boundary contributions in the resistive and capacitive components of BiFeO₃ was studied using complex impedance spectroscopy. The value of activation energy due to both grain and grain boundary of both the samples is nearly same. The nature of variation of dc conductivity confirms the Arrhenius behavior of the materials. Study of frequency dependence of ac conductivity suggests that the materials obey Jonscher’s universal power law and the presence of ionic conductivity.     

Photocatalytic activity of Au/TiO<Subscript>2</Subscript> nanocomposite for azo-dyes degradation

The structural properties of Au/TiO₂ catalyst were studied by X-ray diffraction, UV-visible diffuse reflectance, photoluminescene, scanning transmission and electron microscope, and temperature programmed reduction. The photocatalytic activity of the catalysts was evaluated for the degradation of various azo-dyes such as methylene blue, methyl orange, reactive blue-4, and eosin-B under solar irradiation. It was found that TiO₂ catalyst modified with gold exhibits higher percentage of degradation compared to starting TiO₂. For example, TiO₂ showed 35% of methyl orange degradation whereas gold modified TiO₂ possessed 82%. Effect of different parameters such as pH and dye concentration has been evaluated and the photocatalytic activity was correlated with physico-chemical properties. The dye degradation rate followed first order kinetics.     

Analytical solution to transient inverse heat conduction problem using Green’s function

Journal of Thermal Analysis and Calorimetry - A transient inverse heat conduction problem concerning jet impingement heat transfer has been solved analytically in this paper. Experimentally...     

Recent Progress in LDH@Graphene and Analogous Heterostructures for Highly Active and Stable Photocatalytic and Photoelectrochemical Water Splitting

Photocatalytic (PC) and photoelectrochemical (PEC) water splitting is a plethora of green technological process, which transforms copiously available photon energy into valuable chemical energy. With the augmentation of modern civilization, developmental process of novel semiconductor photocatalysts proceeded at a sweltering rate, but the overall energy conversion efficiency of semiconductor photocatalysts in PC/PEC is moderately poor owing to the instability ariseing from the photocorrosion and messy charge configuration. Particularly, layered double hydroxides (LDHs) as reassuring multifunctional photocatalysts, turned out to be intensively investigated owing to the lamellar structure and exceptional physico-chemical properties. However, major drawbacks of LDHs material are its low conductivity, sluggish mass transfer and structural instability in acidic media, which hinder their applicability and stability. To surmount these obstacles, the formation of LDH@graphene and analogus heterostructures could proficiently amalgamate multi-functionalities, compensate distinct shortcomings, and endow novel properties, which ensure effective charge separation to result in stability and superior catalytic activities. Herein, we aim to summarize the currently updated synthetic strategies used to design heterostructures of 2D LDHs with 2D/3D graphene and graphene analogus material as graphitic carbon nitride (g-C₃N₄), and MoS₂ as mediator, or interlayer support, or co-catalyst or vice versa for superior PC/PEC water splitting activities along with long-term stabilities. Furthermore, latest characterization technique measuring the stability along with variant interface mode for imparting charge separation in LDH@graphene and graphene analogus heterostructure has been identified in this field of research with understanding the intrinsic structural features and activities.     

Radiative stability of neutrino-mass textures

Neutrino-mass textures proposed at high scales are known to be unstable against radiative corrections especially for nearly degenerate mass eigenvalues. We find a mechanism in a class of gauge models including 2HDM where the RG constraints can be evaded. Consequently, a high-scale texture can match the low-energy data or be reproduced at low energies.