Electrocatalytic OER behavior of the Bi-Fe-O system: an understanding from the perspective of the presence of oxygen vacancies.

This study aims to understand and correlate the role of the nature and relative concentration of oxygen vacancies with the trend observed in the OER with the Bi-Fe-O system. To understand this, we first investigated the system of oxides using X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR), which revealed the presence of oxygen vacancies in the system. Density functional theory (DFT) was employed to investigate the relative concentration of these vacancies by calculating their formation energies. Positron annihilation lifetime spectroscopy (PALS) was carried out to understand the nature of these oxygen vacancies. We observed that the presence of a higher concentration of monovacancies created due to the absence of oxygen from the structure of Bi2Fe4O9 was mainly responsible for the high performance of the oxide towards the OER compared to that of the other oxides viz-BiFeO3 and Bi25FeO40 of the Bi-Fe-O system.

Understanding the role of ionic flux on the polarity of the exposed surfaces of ZnO.

The role of ionic flux in controlling the polarity of the surfaces of ZnO was evaluated, both experimentally and theoretically. Zinc oxide was synthesized by controlled decomposition of zinc oxalate nanorods in the presence of ionic flux. The degree of preferred orientation for a specific plane, for the ZnO structures, was observed by calculating the texture coefficient. The presence of flux (NaCl, KCl, a mixture of NaCl-KCl and Na2SO4) during decomposition of the oxalate precursor led to the preferential growth of (112[combining macron]0) planes. The value of texture coefficient was found to be high for the (112[combining macron]0) plane when the decomposition was carried out in the presence of a mixture of NaCl and KCl when compared to their counterparts. A decrease in the value of texture coefficient for the (112[combining macron]0) plane was observed when Na2SO4 was used as a flux, which was similar to the value obtained for ZnO synthesized in the absence of flux. The observations from the analysis of texture coefficient were correlated with the photocatalytic degradation of rhodamine B dye, by making use of the fact that the nature of exposed surfaces influences the catalytic activity of a material. On-site Coulomb correlation corrected density functional theory (DFT + U)-based computational studies were performed to get theoretical insight into the role of the ionic flux in surface reconstructions. The surface energies for different ZnO surfaces were computed in the presence and absence of the ionic flux. It was revealed that the pristine (101[combining macron]0) surface is more stable compared to pristine (112[combining macron]0) by 0.04 J m-2 (surface energy), however the scenario changes in the presence of the ionic flux and (112[combining macron]0) becomes more stable by 0.03 J m-2. This indeed corroborated with our experimental observations and explained the fundamental role of ionic flux on the polarity of exposed surfaces of ZnO.

Correction: Understanding the role of co-surfactants in microemulsions on the growth of copper oxalate using SAXS.

Correction for 'Understanding the role of co-surfactants in microemulsions on the growth of copper oxalate using SAXS' by Sunaina et al., Phys. Chem. Chem. Phys., 2019, 21, 336-348.

Understanding the role of co-surfactants in microemulsions on the growth of copper oxalate using SAXS.

This study is an effort to understand the mechanism of the effect of the chain length of co-surfactants on the growth of copper oxalate inside the core of reverse micelles using small angle X-ray scattering (SAXS). In this study, we have used two different kinds of co-surfactants viz. 1-butanol (C4) and 1-octanol (C8) for the formation of the microemulsions. Time-dependent SAXS studies were carried out for these two systems. The data were analyzed using both the model-independent approach and model-dependent approach. For microemulsions containing only water inside the core of reverse micelles (no ions), the shape of the reverse micelles was observed to be ellipsoid and spherical in nature for 1-butanol and 1-octanol respectively. For a system containing copper oxalate nanostructures, the fitting was carried out using the ellipsoidal core-shell model for reverse micelles and spheres, ellipsoids and cylinders for copper oxalate nanostructures with 1-butanol as the co-surfactant. With 1-octanol as the co-surfactant, the two contributions that were used were the spherical core-shell model for reverse micelles and spheres for copper oxalate nanostructures. Based on the analysis of SAXS data, a growth mechanism has been proposed. The study discussed here could open the field of understanding the growth mechanism of complex nanostructures formed using the microemulsion route.

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.

Synthesis of core-shell nanostructures of Co3O4@SiO2 with controlled shell thickness (5-20 nm) and hollow shells of silica.

Synthesis of uniform silica shell over Co3O4 nanoparticles was carried out using the colloidal solutions of Tergitol and cyclohexane. The shell could be controlled to a thickness of up to 20 nm by varying different parameters such as the amount of tetraethylorthosilicate, concentration of Co3O4 nanoparticles, reaction time and the presence of water and 1-octanol. Control of the amount of water (required for hydrolysis) appears to be the key factor for controlling the shell thickness. The methodology used is suitable to form shell over nanoparticles (present in powder form; synthesized at high temperature) which have high degree of agglomeration. Hollow shells of silica were obtained by the dissolution of the oxide core of Co3O4@SiO2 core-shell nanostructures. The composition of these core-shell nanostructures was confirmed by high-resolution transmission electron microscopy and elemental mapping by energy dispersive X-ray analysis. The hollow shells were characterized by using TEM, EDX and IR. Electron paramagnetic resonance studies of the core-shell nanostructures indicate the presence of free radicals on silica shell due to the presence of dangling bonds in the silica. Increase in the magnetic susceptibility was observed for these core-shell nanostructures.

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.

New catanionic surfactants, phase stability and synthesis of ultrafine CdS nanoparticles.

A systematic study on the water-intake capacity of the microemulsion formed using a catanionic surfactant (synthesized by taking equimolar mixture of acid and amine) with varying hydrocarbon chain length of the acid has been carried out. A decrease in the water-intake capacity with increase in the chain length was observed. Shorter chain length of co-surfactant (1-butanol compared to 1-octanol) led to higher water-intake capacity of microemulsions which may also be attributed to the high hydrophilic-lipophilic balance (HLB) of 1-butanol. Three new microemulsions based on catanionic surfactants have been used to synthesize quantum dots of CdS. The size of CdS quantum dots decreased with increase in chain length of the acid component of the catanionic surfactant.

Microemulsion-based synthesis of nanocrystalline materials.

Microemulsion-based synthesis is found to be a versatile route to synthesize a variety of nanomaterials. The manipulation of various components involved in the formation of a microemulsion enables one to synthesize nanomaterials with varied size and shape. In this tutorial review several aspects of microemulsion based synthesis of nanocrystalline materials have been discussed which would be of interest to a cross-section of researchers working on colloids, physical chemistry, nanoscience and materials chemistry. The review focuses on the recent developments in the above area with current understanding on the various factors that control the structure and dynamics of microemulsions which can be effectively used to manipulate the size and shape of nanocrystalline materials.

Controlling the size, morphology, and aspect ratio of nanostructures using reverse micelles: a case study of copper oxalate monohydrate.

This study focuses on understanding the growth and control of nanostructures using reverse micelles. It has been earlier realized that parameters like surfactant, cosurfactant, and aqueous content influence the size and shape of the nanostructures obtained using reverse micelles. However, a concerted effort to understand the role of these factors on the growth of a specific nanomaterial is missing. In this study we have focused on one nanomaterial (copper oxalate monohydrate) and determined how the above-mentioned factors control the size, shape, aspect ratio, and growth of these nanostructures. Our results show that cationic surfactants (CTAB, TTAB, and CPB) favor the formation of nanorods of copper oxalate. The aspect ratio of these rods could be controlled to obtain nanocubes (approximately 80-100 nm) and nanoparticles (approximately 8-10 nm) in the CTAB system using longer chain cosurfactants like 1-octanol and 1-decanol, respectively. Nanocubes of approximately 50-60 and approximately 60-80 nm were obtained using nonionic surfactants Triton X-100 and Tergitol, respectively. The size of the nanostructures could also be controlled by varying the molar ratio of water to surfactant (W0) by using a nonionic (Triton X-100)-based reverse micellar system. The study espouses the versatility of the microemulsion method to realize a variety of nanostructures of copper oxalate monohydrate. Our results will be of use in extending these ideas to other nanomaterials.

Mimicking the biomineralization of aragonite (calcium carbonate) using reverse-micelles under ambient conditions.

Reverse micelles have been used, for the first time, to mimic the conditions suitable for the low-temperature (40 degrees C) synthesis of the high temperature and high pressure orthorhombic phase of calcium carbonate (aragonite) normally crystallizing in the sea as abalone shells and as natural pearls. The aragonite phase undergoes morphological changes under higher temperatures with long Y-junctions (at 40 degrees C) to shorter rod-like structures (at 85 degrees C). Pure calcite is obtained at higher reaction temperature. At a lower temperature (5 degrees C) homogeneous and monodisperse spheres of vaterite is obtained. The spherical particles after longer aging (168 h) aggregate to form nanorods and the self assembly is clearly seen at various stages by electron microscopic images.