The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

A rapid and ecofriendly fabrication of metal oxide nanoparticles using biogenic sources is the current trend being used to replace the toxic chemical method. The present study was carried out to synthesize magnesium oxide nanoparticles (MgONPs) using the marine brown algae Sargassum wighitii as the reducing and capping agent. The as-prepared MgONPs were characterized by spectroscopic and microscopic analyses. UV–visible spectrum of the MgONPs showed a sharp absorption peak at 322 nm. X- ray diffraction analysis illustrated that the MgONPs were crystalline in nature with a face-centered cubic structure. Presence of magnesium and oxygen were further confirmed by EDX profile. FTIR analysis showed the presence of functional groups specific for sulfated polysaccharides, which might be responsible for the synthesis of MgONPs. Zeta potential and dynamic light scattering analysis illustrated that the MgONPs were highly stable at 19.8 mV with an average size of 68.06 nm. MgONPs showed potent antibacterial activity and antifungal activities against human pathogens. Photocatalytic activity of MgONPs was witnessed by the quick degradation of the organic dye methylene blue on exposure to both sunlight and UV irradiation. MgONPs showed significant cytotoxicity against the lung cancer cell lines A549 in a dose dependent manner with the IC50 value of 37.5 ± 0.34 μg/ml. Safety evaluation using peripheral blood mononuclear cells (PBMCs) illustrated the MgONPs to be non-toxic in nature. Overall, the results concluded that the MgONPs generated using marine algae have exhibited scope for multifaceted biological applications.

Anticancer, antimicrobial and photocatalytic activities of green synthesized magnesium oxide nanoparticles (MgONPs) using aqueous extract of Sargassum wightii.

High temperature processing is essential for the preparation of apatites for biomaterials, lighting, waste removal and other applications. This requires a good understanding of the thermal stability and transitions upon heating. The most widely used is hydroxyapatite (HAp), but increasing interest is being directed to fluorapatite (FAp) and chlorapatite (ClAp). The structural modifications for substitutions are discussed to understand the temperature processing range for the different apatites. This is based on a review of the literature from the past few decades, together with recent research results. Apatite thermal stability is mainly determined by the stoichiometry (Ca/P ratio and structural substitutions) and the gas composition during heating. Thermal stability is lowered the most by a substitution of calcium and phosphate, leading to loss in phase stability at temperatures less than 900 °C. The anions in the hexagonal axis, OH in HAp, F in FAp and Cl in ClAp are the last to leave upon heating, and prevention of the loss of these groups ensures high temperature stability. The information discussed here will assist in understanding the changes of apatites during heating in calcination, sintering, hydrothermal processing, plasma spraying, flame pyrolysis, and other high-temperature processes.

A Review on the Thermal Stability of Calcium Apatite

Zinc sulfide (ZnS) is one of the first semiconductors discovered. It has traditionally shown remarkable versatility and promise for novel fundamental properties and diverse applications. The nanoscale morphologies of ZnS have been proven to be one of the richest among all inorganic semiconductors. In this article, we provide a comprehensive review of the state-of-the-art research activities related to ZnS nanostructures. We begin with a historical background of ZnS, description of its structure, chemical and electronic properties, and its unique advantages in specific potential applications. This is followed by in-detail discussions on the recent progress in the synthesis, analysis of novel properties and potential applications, with the focus on the critical experiments determining the electrical, chemical and physical parameters of the nanostructures, and the interplay between synthetic conditions and nanoscale morphologies. Finally, we highlight the recent achievements regarding the improvement of ZnS novel properties and finding prospective applications, such as field emitters, field effect transistors (FETs), p-type conductors, catalyzators, UV-light sensors, chemical sensors (including gas sensors), biosensors, and nanogenerators. Overall this review presents a systematic investigation of the ‘synthesis-property-application’ triangle for the diverse ZnS nanostructures.

ZnS nanostructures: From synthesis to applications

Biomass utilization and production of biofuels from carbon neutral materials.

Bacterial invasion on biomedical implants is a challenging task for long-term and permanent implant fixations. Prevention of initial bacterial adherence on metallic implants is an important concern to avoid extracellular matrix (biofilm) secretion from bacteria that is resistant to antibacterial agents. In order to overcome this defect, recently, surface coatings such as zirconia (ZrO2) with higher smoothness have been shown to improve implants durability. In the present study, pulsed laser deposition (PLD) was used to deposit ZrO2 and silver (Ag)-ZrO2 composite coatings onto 316L stainless steel (316L SS). Phase purity, surface roughness and surface morphology, thickness of the coatings and elemental compositions of the coatings were analyzed using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). Total viable count (TVC) and epifluorescence microscopy analysis were studied to evaluate antimicrobial efficiency of ZrO2 and Ag–ZrO2 composite coatings using gram negative (gram −ve) Escherichia coli (E.coli) and gram positive (gram +ve) Staphylococcus aureus (S.aureus). On the basis of the present study, it could be speculated that ZrO2 coatings exhibited antibacterial activity against only E.coli, whereas Ag–ZrO2 composite coatings showed superior activity against E.coli and S.aureus strains.

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Antibacterial effects of silver-zirconia composite coatings using pulsed laser deposition onto 316L SS for bio implants

Bionanocomposites are promising green sustainable materials useful for diagnostic and biomedical applications. In the present study, cellulose/copper nanoparticles (CuNP) bionanocomposites were prepared using a bioflocculant as a reductant of the precursor copper ions for the in situ generation of CuNP in the cellulose matrix.. The novel bionanocomposite material was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), antibacterial and corrosion tests. TEM, SEM, EDS, and XRD studies indicated the in situ generation of CuNP in the cellulose matrix. FTIR analysis proved no new bond formation between CuNP and cellulose films. Thermogravimetric analysis indicated single step degradation for neat cellulose whereas the bionanocomposites exhibit multi-step thermal degradation. The new bionanocomposite prepared with a copper precursor concentration of 250 mM was found to exhibit remarkable biocidal activity against E. coli with a zone of clearance of 12 mm and also good corrosion resistance.

Preparation of cellulose/copper nanoparticles bionanocomposite films using a bioflocculant polymer as reducing agent for antibacterial and anticorrosion applications

Protecting from wear and corrosion of many medical devices in the biomedical field is an existing scientific challenge. Surface modification with multilayer ZrN/Cu coating was deposited on medical grade stainless steel (SS) and titanium substrates to enhance their surface properties. Structural results revealed that the ZrN/Cu coatings are highly crystalline and uniform microstructure on both the substrates. Dry and wet tribological measurements of the coated titanium substrate exhibit enhanced wear resistance and low friction coefficient due to the improved microstructure. Similarly, the corrosion resistance was exceptionally improved on titanium substrates, resulting from the high inertness of coating to the SBF electrolyte solution. Antibacterial activity and epifluorescence results signify the effective killing of pathogens by means of ion release killing as well as contact killing mechanisms.

Multifunctional zirconium nitride/copper multilayer coatings on medical grade 316L SS and titanium substrates for biomedical applications.

Yttria stabilized zirconia (YSZ) was deposited onto titanium (Ti) substrates using electron beam physical vapor deposition (EB-PVD) method. The crystalline nature of as-deposited YSZ coating was evaluated using X-ray diffraction (XRD) technique and cubic phase was noticed. Smooth and uniform surface topography was observed by atomic force microscopy (AFM) analysis. The hardness and scratch resistance of the coating was determined by nanoindentation and scratch test analysis respectively. Wettability studies exhibited more hydrophilic nature on YSZ coating and least hydrophilic on uncoated Ti substrate. Anti-adhesion and antibacterial efficiency were performed against gram (-)ve ( E.coli ) and gram (+)ve ( S. aureus ) bacterial strains and revealed that YSZ coating effectively protected bacterial invasion. Hemocompatibility was evaluated by platelets adhesion and their activation behavior was studied onto uncoated and YSZ coated Ti substrates. YSZ coating exhibited less activated platelets; whereas, platelets activation (large number of pseudopods) were seen on uncoated Ti substrates. Furthermore, superior in vitro biomineralization behavior with increased weight gain, higher protein adsorption and superior biocompatible nature with NIH 3T3 fibroblast cells were observed on YSZ coating. Overall results indicated that surface modification by YSZ coating could become a promising material for biomedical applications.

Gobi Saravanan Kaliaraj

Papers

Antibacterial effects of silver-zirconia composite coatings using pulsed laser deposition onto 316L SS for bio implants

Preparation of cellulose/copper nanoparticles bionanocomposite films using a bioflocculant polymer as reducing agent for antibacterial and anticorrosion applications

Multifunctional zirconium nitride/copper multilayer coatings on medical grade 316L SS and titanium substrates for biomedical applications.

Bio-inspired YSZ coated titanium by EB-PVD for biomedical applications

Biological and corrosion behavior of m-ZrO2 and t-ZrO2 coated 316L SS for potential biomedical applications