A. Sreekumaran Nair

Thermal conductivities of naked and monolayer protected metal nanoparticle based nanofluids: Manifestation of anomalous enhancement and chemical effects

Thermal conductivities of two kinds of Au nanoparticles were measured in water and toluene media. The water soluble particles, 10–20 nm in mean diameter, made with citrate stabilization showed thermal conductivity enhancement of 5%–21% in the temperature range of 30–60 °C at a loading of 0.000 26 (by volume). The effect was 7%–14% for Au particles stabilized with a monolayer of octadecanethiol even for a loading of 0.011%. Comparatively lower thermal conductivity enhancement was observed for larger diameter Ag particles for significantly higher loading. Effective enhancement of 9%, even at vanishing concentrations, points to additional factors in the thermal conductivity mechanism in nanofluids. Results also point to important chemical factors such as the need for direct contact of the metal surface with the solvent medium to improve enhancement.

A review on nanomaterials for environmental remediation

This article gives an overview of the application of nanomaterials in environmental remediation. In the area of environmental remediation, nanomaterials offer the potential for the efficient removal of pollutants and biological contaminants. Nanomaterials in various shapes/morphologies, such as nanoparticles, tubes, wires, fibres etc., function as adsorbents and catalysts and their composites with polymers are used for the detection and removal of gases (SO2, CO, NOx, etc.), contaminated chemicals (arsenic, iron, manganese, nitrate, heavy metals, etc.), organic pollutants (aliphatic and aromatic hydrocarbons) and biological substances, such as viruses, bacteria, parasites and antibiotics. Nanomaterials show a better performance in environmental remediation than other conventional techniques because of their high surface area (surface-to-volume ratio) and their associated high reactivity. Recent advances in the fabrication of novel nanoscale materials and processes for the treatment of drinking water and industrial waste water contaminated by toxic metal ions, radionuclides, organic and inorganic solutes, bacteria and viruses and the treatment of air are highlighted. In addition, recent advances in the application of polymer nanocomposite materials for the treatment of contaminants and the monitoring of pollutants are also discussed. Furthermore, the research trends and future prospects are briefly discussed.

Anti-reflective coatings: A critical, in-depth review

Anti-reflective coatings (ARCs) have evolved into highly effective reflectance and glare reducing components for various optical and opto-electrical equipments. Extensive research in optical and biological reflectance minimization as well as the emergence of nanotechnology over the years has contributed to the enhancement of ARCs in a major way. In this study the prime objective is to give a comprehensive idea of the ARCs right from their inception, as they were originally conceptualized by the pioneers and lay down the basic concepts and strategies adopted to minimize reflectance. The different types of ARCs are also described in greater detail and the state-of-the-art fabrication techniques have been fully illustrated. The inspiration that ARCs derive from nature (‘biomimetics’) has been an area of major research and is discussed at length. The various materials that have been reportedly used in fabricating the ARCs have also been brought into sharp focus. An account of application of ARCs on solar cells and modules, contemporary research and associated challenges are presented in the end to facilitate a universal understanding of the ARCs and encourage future research.

A review on self-cleaning coatings

This review article summarizes the key areas of self-cleaning coatings, primarily focusing on various materials that are widely used in recent research and also in commercial applications. The scope of this article orbits around hydrophobic and hydrophilic coatings, their working mechanism, fabrication techniques that enable the development of such coatings, various functions like Anti-icing, Electro-wetting, Surface switchability and the areas where selfcleaning technology can be implemented. Moreover, different characterization techniques and material testing feasibilities are also analyzed and discussed. Though several companies have commercialized a few products based on self-cleaning coating technology, much potential still remains in this field.

A review on counter electrode materials in dye-sensitized solar cells

Dye-sensitized solar cells (DSCs) present promising low-cost alternatives to the conventional silicon (Si)-based solar cells. A DSC consists of several components, the most prominent being a titanium dioxide/metal oxide-based photoanode, a dye, an electrolyte and a counter electrode. The photoexcited electrons from the dye diffuse through the TiO2 network in the photoanode and go to the counter electrode which generally consists of platinum (Pt) sputtered onto a fluorine-doped tin oxide (FTO) plate. The Pt in the counter electrode helps in the regeneration of dyes by catalysing the I− regeneration from the I3− species in the redox couple. The morphology of Pt, its surface roughness, nature of the exposed facet, etc. play a crucial role in determining the overall efficiency of a DSC device. With Pt being a costly noble metal, reasonable efforts have been made to find cheaper alternatives. The review presented below gives a succinct summary of the materials in use as counter electrodes in DSCs, with a conclusion and future prospects section.

Facile Fabrication of TiO2–Graphene Composite with Enhanced Photovoltaic and Photocatalytic Properties by Electrospinning

We report the fabrication of one-dimensional TiO(2)-graphene nanocomposite by a facile and one-step method of electrospinning. The unique nanostructured composite showed a significant enhancement in the photovoltaic and photocatalytic properties in comparison to TiO(2) as demonstrated in dye-sensitized solar cells and photodegradation of methyl orange.

A review on ‘self-cleaning and multifunctional materials’

This review article exemplifies the importance of self-cleaning materials and coatings. Self-cleaning coatings are becoming an integral part of our daily life because of their utility in various applications such as windows, solar panels, cements, and paints. In this review, various categories of materials for the fabrication of hydrophilic, hydrophobic, oleophobic, amphiphobic and multifunctional coatings and their synthesis routes have been discussed. Furthermore, different natural organisms exhibiting superhydrophobic behaviour have been analysed. This review also covers the fundamentals of self-cleaning attributes such as water contact angle, surface energy, and contact angle hysteresis.

A simple recipe for an efficient TiO2 nanofiber-based dye-sensitized solar cell.

Development of highly efficient dye-sensitized solar cells (DSSCs) with good photovoltaic parameters is an active research area of current global interest. In this article, we provide a simple recipe for the fabrication of electrospun TiO(2) nanorod-based efficient dye-sensitized solar cell using a Pechini-type sol. The Pechini-type sol of TiO(2) nanofibers produces a highly porous and compact layer of TiO(2) upon doctor-blading and sintering without the need for an adhesion and scattering layers or TiCl(4) treatment. The best nanofiber DSSCs with an area of ~0.28 cm(2) shows an efficiency of ~4.2% under standard test conditions (100 mW/cm(2), 25°C and AM1.5 G) and an incident photon-to-electron conversion efficiency (IPCE) of ~50%. Impedance measurements show lower charge transfer resistance that improved the fill factor. We believe that simple approaches such as the present one to develop nanofiber DSSCs would open up enormous possibilities in effective harvesting of solar energy for commercial applications, considering the fact that electrospinning is a cost-effective method for the mass scale production of nanofibers and nanorods.

Long term cycling studies of electrospun TiO2 nanostructures and their composites with MWCNTs for rechargeable Li-ion batteries

Nanofiber- and rice grain-shaped TiO2 nanostructures and their composites with functionalized multiwalled carbon nanotubes were fabricated by electrospinning and subsequent sintering process for applications in Lithium ion batteries. The fabricated nanostructures were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning-and transmission electron microscopy and surface area measurements. All nanostructured materials showed average discharge-charge plateaux of 1.75 to 1.95V. The nanofibrous- and rice grain-shaped TiO2 nanomaterials showed stable performances of 136 (± 3) mAh g−1 and 140 (± 3) mAh g−1, respectively, at the end of 800 cycles in the cycling range of 1.0–2.8 V vs.Li at a current rate of 150 mA g−1. TiO2–CNT (4 wt.%) composites showed a slightly lower capacity value but better capacity retention (8% capacity loss between 10–800 cycles). We believe that the present long term cycling materials would have wide interests in lithium ion batteries research.

Electrospun α-Fe2O3 nanostructures for supercapacitor applications

Herein, we report the facile synthesis of two α-Fe2O3 nanostructures with different morphologies via an electrospinning technique using ferric acetyl acetonate as a precursor and polyvinyl acetate and polyvinyl pyrrolidone as the respective polymers. The as-electrospun metal oxide–polymer composite fibers were sintered at 500 °C to obtain two distinct nanostructures, denoted as nanograins and porous fibers throughout this manuscript. These crystalline nanostructures were characterized using powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX) and transmission electron microscopy (TEM). The characterization results elucidated the predominance of hematite (α-Fe2O3) with particle sizes of 21 and 53 nm, for the respective nanostructures. Electrophoretic deposition was carried out in order to fabricate thin film electrodes, which were then subjected to electrochemical analysis. Electrochemical characterization revealed that both of the fabricated electrodes exhibited excellent performance in 1 M LiOH electrolyte with specific capacitance values of 256 and 102 F g−1 for the porous fiber and nanograin structures, respectively, at a scan rate of 1 mV s−1 and excellent capacitance retention, even after 3000 cycles, thus making them promising electrode materials for energy storage devices.