Enhanced functionalization of Mn2O3@SiO2 core-shell nanostructures

Core-shell nanostructures of Mn2O3@SiO2, Mn2O3@amino-functionalized silica, Mn2O3@vinyl-functionalized silica, and Mn2O3@allyl-functionalized silica were synthesized using the hydrolysis of the respective organosilane precursor over Mn2O3 nanoparticles dispersed using colloidal solutions of Tergitol and cyclohexane. The synthetic methodology used is an improvement over the commonly used post-grafting or co-condensation method as it ensures a high density of functional groups over the core-shell nanostructures. The high density of functional groups can be useful in immobilization of biomolecules and drugs and thus can be used in targeted drug delivery. The high density of functional groups can be used for extraction of elements present in trace amounts. These functionalized core-shell nanostructures were characterized using TEM, IR, and zeta potential studies. The zeta potential study shows that the hydrolysis of organosilane to form the shell results in more number of functional groups on it as compared to the shell formed using post-grafting method. The amino-functionalized core-shell nanostructures were used for the immobilization of glucose and L-methionine and were characterized by zeta potential studies

Pr2FeCrO6: A Type I Multiferroic

We synthesized double perovskite Pr2FeCrO6 by solid-state method. Analysis of its X-ray powder diffraction shows that the compound crystallizes in a centrosymmetric structure with space group Pbnm. Our X-ray photoelectron spectroscopy (XPS) studies show that all the cations are present in +3 oxidation state. Magnetization studies of Pr2FeCrO6 show that the material is paramagnetic at room temperature and undergoes a magnetic transition below T-CM = 250 K. We observe clear magnetic hysteresis loop, for example, below 150 K. A low remnant magnetization M-r, similar to 0.05 mu(B)/f. u., is inferred from the observed magnetic hysteresis loop. Fe-57 Mossbauer study at 25 K shows a high hyperfine magnetic field of similar to 53 T at the Fe nucleus, which corresponds to a magnetic moment of similar to 6-7 mu(B)/Fe. These two results together suggest a ferrimagnetic (nearly compensated or canted) ordering of the Fe moments. Mossbauer studies dose to the ferrimagnetic ordering temperature suggest interesting magnetic relaxation effects. A dielectric anomaly observed at T-CE = 453 K signals a ferroelectric paraelectric phase transition. We observe at room temperature a clear and well-defined ferroelectric hysteresis loop, P-S = 1.04 mu C/cm(2), establishing ferroelectricity in the material. From these results, we conclude that Pr2FeCrO6 is a type I multiferroic (T-CE > T-CM)

Electrochemical and magnetic properties of nanostructured CoMn2O4 and Co2MnO4

In this study, we have focused on the synthesis of cobalt manganite nanostructures using a simplistic hydrothermal route. We have explored these spinels as alternative low-cost bifunctional electrocatalysts for oxygen reduction/evolution reactions (ORR/OER). Herein, we have developed energy-saving, facile and rapid synthetic methodologies for highly active spinel electrocatalysts. Two spinel phases, cubic Co2MnO4 and tetragonal CoMn2O4 have been successfully obtained by tuning the stoichiometric ratio of Co and Mn salts respectively. These CoMn2O4 and Co2MnO4 nanocubes have been used as bifunctional catalysts towards OER and ORR. Electrocatalytic experiments show that cubic Co2MnO4 nanocubes show five times higher activity towards ORR than tetragonal CoMn2O4 nanocubes while the tetragonal phase is a better electrocatalyst towards OER than the cubic Co2MnO4 phase. XPS studies revealed two types of oxygen (lattice O and surface adsorbed O species like OH-) and the efficiency of the catalyst could be related to the binding affinity of oxygen. This explains the better catalytic activity of cubic Co2MnO4 which has a large percentage of adsorbed oxygen species. The stability of the catalyst was confirmed by carrying out TEM studies on a sample after carrying out 25 cycles. Magnetization experiments reveal that both the tetragonal CoMn2O4 as well as cubic Co2MnO4 show hysteresis at 10 K and 100 K without reaching saturation, which confirms an existing ferrimagnetic order in the samples. Both the tetragonal and cubic phases show T-c similar to 110 K and 150 K respectively

CdS@TiO<SUB>2</SUB> and ZnS@TiO<SUB>2</SUB> core-shell nanocomposites: synthesis and optical properties

Reverse micellar route was used to synthesize CdS@TiO2 and ZnS@TiO2 core-shell nanocomposites. Titanium hydroxyacylate has been used for the first time as the shell-forming agent for the formation of TiO2 shell over CdS and ZnS which ensures the formation of shell over the core nanoparticle due to its slow rate of hydrolysis and thus forms core-shell nanocomposites. HRTEM studies show 3-5 nm sulphide nanoparticles forming the core. A strong quantum confinement for bare nanoparticles and core-shell nanocomposites was observed from the blue shift of the absorption band of these nanocomposites. The size of CdS and ZnS, calculated from spectroscopic studies, corroborated with that observed from HRTEM studies. 2-Mercaptoethanol (used as a capping agent) was found to restrict the size of the CdS core in these nanostructures which resulted in further shift of the absorption and emission bands towards lower wavelength. No quenching in the emission band of CdS was observed for the core-shell nanostructures. In contrast to CdS@TiO2, the optical properties of ZnS@TiO2 core-shell nanostructures do not show any shift in the absorption band when compared to bare ZnS nanoparticles

Enhancement of photocatalytic efficiency using heterostructured SiO₂–Ta₂O₅ thin films

Fabrication of controlled layered structured thin films with tunable physical properties is an important area of research as thin film technology holds potential for a variety of industrial applications. In the present work, we have demonstrated the process for fabrication of multilayer films of silica and tantalum oxide by Langmuir–Blodgett film fabrication technique and investigated their photocatalytic degradation efficiency for organic dye (Rhodamine B) under UV radiation. The photocatalytic degradation of RhB in presence of SiO₂–Ta₂O₅ exhibited remarkably enhanced photocatalytic activity than pure Ta₂O₅. This is because of the high separation efficiency of photo-generated electron–hole pair due to the Lewis acidity of silica and the greater contact area between these two layers. The SiO₂–Ta₂O₅ system was optimized for the number of self-assembled layers of silica and tantalum oxide, and it has been found that 10S–15T–10S–15T–10S–15T (where S and T represents SiO₂ and Ta₂O₅ respectively) pattern has been found to have maximum photocatalytic degradation efficiency of 71% (with 18% degradation per unit area of the film) which is 3.5 fold higher than pure Ta₂O₅ under identical experimental condition. Also, the photocatalytic activity of these films was also proved to be sensitive to the sequence of silica and tantalum oxide layers when the film area of all the samples was kept constant (3.75 cm₂). Further analysis confirms that the degradation of dye molecules has been largely promoted by the photo generated holes, rather than the super oxide radical anions

Nickel cobaltite nanostructures with enhanced supercapacitance activity

Herein, we report a strategy for controlled synthesis of functional nanomaterials desired for energy conversion and power storage applications. NiCo2O4 nanostructures with square sheets, hexagonal sheets, and spherical form have been synthesized using a solvothermal route by tuning of reaction conditions as well as selection of hydrolyzing agents. The synthesized nanostructures exhibited significant shape dependent electrochemical behavior with improved supercapacitance as well as good electrocatalytic properties toward oxygen evolution reaction. Among all the three morphologies, the square sheets, assembled from nanoparticles ∼5 nm diameter, exhibited higher specific capacitance with good stability. Due to high surface area (∼100 m2/g) and the mesoporous nature of the square sheets, NiCo2O4 reveals better pseudocapacitance

Cu-based nanocomposites as multifunctional catalysts

Herein, we report the synthesis of Cu/Cu₂O nanocomposites by a one-step hydrothermal process at 180 °C, for which the resulting morphology is dependent on the hydrothermal reaction time (24, 72, and 120 h). With a longer reaction time of 120 h, a rod-shape morphology is obtained, whereas at 72 and 24 h assemblies of nanoparticles are obtained. The rod-shaped (120 h) particles of the Cu/Cu₂O nanocomposites show a much higher efficiency (6.3 times) than the agglomerates and 2.5 times more than the assemblies of nanoparticles for the hydrogen-evolution reaction. During the oxygen-evolution reaction, the nanorods produce a current that is 5.2 and 3.7 times higher than that produced by the agglomerated and assembled nanoparticles, respectively. The electrocatalysts are shown to be highly stable for over 50 cycles. As catalysts for organic synthesis, a 100 % yield is achieved in the Sonogashira cross-coupling reaction with the nanorods, which is higher than with the other nanocomposite particles. This result demonstrates the significant enhancement of yield obtained with the nanorods for cross-coupling reactions

Efficient entrapment of dye in hollow silica nanoparticles: direct evidence using fluorescence spectroscopy

Using hollow silica nanoparticles we demonstrate a simple and highly efficient way of removing hydrophilic dye (Rhodamine B) from water by encapsulation within these hollow spheres. The hollow silica spheres were obtained by using a surfactant templated procedure. Using fluorescence spectroscopy, we also show the evidence of the dye being absorbed within the hollow core of the silica shell (which is crucial for many applications) and differentiate from the adsorption of dye on the surface of the silica shell. It was found that that up to 94 % of the hydrophilic dye could be entrapped using these hollow shells within 72 h of exposure. Fluorescence spectroscopy shows a red shift in the dye encapsulated in the hollow silica which is due to aggregation of the dye and enables us to follow quantitatively the uptake of the dye molecules by the silica shells with time. The evidence for the encapsulation of the dye in these hollow spheres was reinforced by carrying out a comparative study, using solid silica particles

A facile one step synthesis of Cu/Cu₂O nanocomposites: enhanced hydrogen/oxygen evolution

The exploration of metal/metal oxide nanocomposites as catalysts for hydrogen and oxygen evolution is highly desirable for renewable and clean energy applications. Cu/Cu₂O nanocomposites have obtained one step process by thermal decomposition of aligned copper oxalate nanorods and CuO in 2:1 molar ratio in argon atmosphere at 350 °C. Hydrogen and oxygen evolution reaction (HER and OER) were carried out using these catalyst on glassy carbon as working electrodes in KOH electrolyte solution. Cu/Cu₂O nanocomposites produce 8 times higher current density than Cu and 4.5 times higher than Cu₂O during HER whereas in case of OER study, it is 36 times higher than Cu and 2.9 times higher than Cu₂O. The electrocatalyst is highly stable over 50 cycles. Our studies show an improvement in electrocatalytic activity by properly choosing the composite, and thus, it may be expanded to other electrocatalysts for obtaining increased activity