Aparna Ganguly

Structural characterization and antimicrobial properties of silver nanoparticles prepared by inverse microemulsion method

Silver nanoparticles have been synthesized in the inverse microemulsions formed using three different surfactants viz., cetyl-trimethyl ammonium bromide (CTAB), Tergitol and Triton X-100. We have done a systematic study of the effect of the surfactants on the particle size and properties of the silver nanoparticles. Microscopic studies show the formation of spheres, cubes and discs shaped silver nanostructures with the size in the range from 8 to 40 nm. Surface plasmon resonance (SPR) peak was observed around 400 nm and 500 nm. In addition to SPR some extra peaks have also been observed due to the formation of silver metal clusters. The surface area increases from 3.45 to 15.06 m(2)/g with decreasing the size of silver nanoparticles (40-8 nm). To investigate the antimicrobial activity of silver nanoparticles, the nanoparticles were tested against the yeast, Candida albicans and the bacterium, E. coli. The results suggest very good antimicrobial activity of the silver nanoparticles against the test microbes. The mode of action of the antimicrobial activity was also proposed.

Reverse micellar based synthesis of ultrafine MgO nanoparticles (8–10 nm): Characterization and catalytic properties

Anisotropic nanostructures of magnesium oxalate dihydrate were synthesized using cationic surfactant based microemulsion method. The cationic surfactant plays an important role in forming the anisotropic structures. The oxalate nanostructures acts as an excellent precursor for the synthesis of fine magnesium oxide nanoparticles (~10 nm). Both the precursor and the oxide were characterized by using PXRD, IR, surface area and HRTEM. The surface area of these surfactant free oxide nanoparticles was found to be 108 m(2)/g. The catalytic activity of this basic oxide was examined for the Claisen-Schmidt condensation reaction and was found to be comparable to the best reported for the conventionally prepared MgO. Chalcone formation was found to increase with time as observed using gas chromatography-mass spectrometry (GC-MS). The reusability of the catalyst was checked by using the same catalyst twice which showed a reduced percentage (50% compared to first cycle) conversion.

Silica mesostructures: control of pore size and surface area using a surfactant-templated hydrothermal process.

The cooperative self-assembly of the silica precursor, tetraethyl ortho silicate (TEOS), with the surfactant molecule followed by the basic hydrolysis led to the formation of mesoporous silica with varying pore sizes. The pores are formed by the removal of the intermediate assemblies of the charged surfactant molecules. In the absence of formation of such assemblies of surfactants (example in the case of nonionic surfactants), the resulting mesostructures have very small pores, giving low surface area mesostructures. This study outlines the precise control of pore size in a wide size distribution (3.4-22 nm) by the systematic variation of the surfactant. The addition of polyethylene glycol (in situ) while carrying out the hydrolysis of TEOS results in the formation of large-sized cavities (∼40 nm). Uniform spherical particles with pores (different from the cavities) as large as 22 nm and surface areas of ∼1100 m(2)/g have been obtained by the combined effect of the hydrothermal conditions on the cetyl trimethyl ammonium bromide-templated synthesis.

A facile low temperature (350 °C) synthesis of Cu2O nanoparticles and their electrocatalytic and photocatalytic properties

We have synthesized Cu2O nanoparticles (∼25 nm) starting from CuO (∼107 nm) and copper oxalate nanorods in an inert atmosphere (Ar) at a very low temperature of 350 °C. The process in the absence of the oxalate nanorods yields Cu2O at a much higher temperature of 850 °C. The Cu2O synthesized at lower temperature (350 °C) has smaller particles than Cu2O synthesized at 850 °C. We explored these nanomaterials as electrocatalysts for hydrogen and oxygen evolution which are highly desirable for renewable and clean energy applications. Electrochemical studies such as the hydrogen evolution reaction and oxygen evolution reaction (HER & OER) were carried out on glassy carbon as well as on platinum as the working electrode in KOH solution. Cu2O synthesized at lower temperature (350 °C) has 14 times higher current density during HER and 2 times higher current density during OER. These electrocatalysts were stable for 50 cycles. However, the Cu2O synthesized at higher temperature (850 °C) showed very efficient (∼98%) degradation of methylene blue (MB) in 120 min and the catalyst is stable up to the 4th cycle whereas Cu2O (350 °C) shows only 40% degradation.

Oxide-based nanostructures for photocatalytic and electrocatalytic applications

Diminishing fossil fuels and global warming issues have forced the scientists to look for alternative sources of energy to cater to the ever increasing demand. Artificial systems are being developed in order to mimic natural photosynthesis and directly harvest and convert solar energy into renewable energy and environmental remediation. Despite significant efforts, it has not been possible to design a single material which has sufficient efficiency, stability and low cost. To integrate the desired characteristics into a single component, heterogeneous photocatalysts are designed with multiple functional components which could combine the advantages of different components to overcome the drawbacks of single component photocatalysts. The present highlight gives a concise overview of heterogeneous catalysts that have been developed and studied in our group and some excellent works of others in recent years. The review focuses on the principles of photocatalytic and electrocatalytic activities followed by some key examples of oxide-based materials. This includes a wide range of structural modification and crystal growth processes leading to composites, heterostructures, including insulator/semiconductor, semiconductor/semiconductor, and multi-heteronanostructures, and core–shell nanostructures which have been modified in order to improve the performance by increasing the light absorption, promoting the charge separation and transportation, and enhancing the redox catalytic activity and intrinsic electrocatalytic properties. The electrochemical processes like hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) have been discussed closely on the effects of size, shape, exposed facets and surface area of electrocatalysts (metal oxides).

Ag3PO4 nanoparticle decorated on SiO2 spheres for efficient visible light photocatalysis

A visible light active photocatalyst, Ag3PO4 (20 nm), in combination with mesoporous SiO2 spheres (200 nm) leads to enhanced photocatalytic activity (∼52 times) in the photocatalytic degradation of Rhodamine B dye compared to bare silver phosphate. The lifetime of the charge carriers is increased by nearly four times (from 0.05 to 0.20 ns) in the composite. The silver phosphate–silica composite has almost no loss of activity after 5 cycles under light irradiation, indicating that the composite has good photocatalytic stability. The addition of SiO2 also reduces the cost of the composite catalyst.

Chemistry of reverse micelles: a versatile route to the synthesis of nanorods and nanoparticles

Nanostructured wires and rods are expected to have interesting optical, electrical, magnetic and mechanical properties as compared to micron sized whiskers and fibers. We have explored a versatile route for the synthesis of nanorods of transition metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates, succinates of few metals (Co and Fe) and SnO2 nanoparticles using reverse micelles. The aspect ratio of the nanorods copper oxalate could be modified by changing the solvent. The aspect ratio of the cobalt oxalate nanorods could be modified by controlling the temperature. The nanorods of metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates were found to be suitable precursors to obtain a variety of transition metal oxide nanoparticles. Our studies show that the grain size of CuO nanoparticles is highly dependent on the nature of non-polar solvent used to initially synthesize the oxalate rods. All the commonly known manganese oxides could be obtained as single phases from the manganese oxalate precursor by decomposing in different atmosphere (air, vaccum or nitrogen). In order to see the templating effect of the ligand we have changed the dicarboxylate ligand by using succinate (4 carbon chain) instead of oxalate (2 carbon chain).We found spherical nanoparticles for iron succinate where the oxidation state of Fe is in +3. Shorter rods of cobalt succinate were observed. Monophasic tin dioxide (SnO2) nanoparticles with an average size of 6-8 nm was obtained at 500°C by the reverse micellar route using liquor NH3 as precipitating agent.

Chapter 6:Nanoscience research in India: Recent contributions (2012–2013)

There has been remarkable progress in the field of nanoscience and technology during the last couple of years across the world. Indian scientists have made significant impact, which is being reflected, in the number of publications in high impact factor journals from the country (Fig. 1: histogram). Nanoscience and nanotechnology has been in the forefront of research in India due to the initiatives of the Department of Science and Technology (DST), Government of India (especially the NanoMission Council of the DST), Department of Biotechnology (DBT), Council of Scientific and Industrial Research (CSIR), Department of electronics and information Technology(DeiTy) and Defence Research and Development organization (DRDO) and several other institutions of the Govt. of India which have also played a major role in encouraging research in nanoscience and nanotechnology. In this direction, several centres of nanoscience and technology have been started in the institutes of technology (IIT’s) and Central Universities and national laboratories. Recently, a new institute “Institute of Nanoscience and Technology” supported by DST has started functioning at Mohali, Punjab. Many of the earlier contributions from India were focussed on synthesis and properties of nanomaterials. In the last few years, the emphasis has shifted to deliver processes/devices in the area of sensors, nanomedicine, environmental and energy – based applications. There has been enormous progress in the field of photocatalysis and electrocatalysis, photovoltaics, nanophotonics, drug delivery, sensors and water purification. (Fig. 2: pie chart). The future is to design nanoscience based solutions for problems specific to India. It is hoped to couple available resources, especially skilled manpower with nanoscience and nanotechnology to apply to challenges being faced by India. One such example would be in the area of medical diagnostics which requires human intervention (skilled) and nanotechnology (imaging or drug delivery). In this article, we have highlighted the major contributions by scientists working in India towards the progress in nanoscience in the recent past (2012–2013). In addition, some high quality work in engineering and technology of nanostructured materials have also been published which has not been covered here.