Green chemical approach towards the synthesis of CeO2 doped with seashell and its bacterial applications intermediated with fruit extracts

Nanomaterials of CeO₂ with A. vera were synthesized by using simple chemical method. Grapes drops are used as an oxidizing agent. Structural and morphological studies of nanomaterials of cerium oxide (CeO₂), were studied for combustion method of preparation. The precursor solution was initialized by a hydrothermal reaction. Cerium hydroxyl carbonate precursors which involves cerium (III) nitrate Ce(NO₃)₃. 6 H₂O with (1.0M) of seashell powder, 3% A. vera, extracts, grapes and pomegranate drops and this complex solution was used to produce the CeO₂ powder particles. We have prepared another sample with 5% of Aloe vera extract and found that 3% Aloe vera extract has lesser grain size and enhanced band gap values, so the article explained the sample analysis of combination with 3% extract of Aloe vera. The product has the rod pattern which was the unusual features appear to originate from the unique crystal chemistry aspects. From the optical absorption spectrum, it has been shown that the CeO₂ rods have 3.847eV of direct band gap energy. The minimum inhibitory concentration (MIC) values of the synthesized compounds exhibited activity towards various microbial pathogens such as B. subtilis (15μg/mL), S. aureus (50μg/mL), S. epidermidis (20μg/mL), E. faecalis (25μg/mL) and towards E. coli (100μg/mL), K. pneumoniae (50μg/mL) and P. aeruginosa (75μg/mL) respectively. The tests on bacterial activities confirmed that the CeO₂ rods are suitable hand for the biological applications. The seashell structure and the phytochemical contents of A. vera might enhance its bacterial activities.

Oxidative Stress in Obese Postmenopausal Women: An Additive Burden for Atherosclerosis

INTRODUCTION

Coronary Artery Disease are on the rise in the general population and is the leading cause of death in both men and women. The impact of CAD is underappreciated in younger women when compared to men. Women have unique risk factors for CAD and postmenopausal women are at higher risk of developing CAD when compared to normal menstruating women.

AIM

The aim of our study was to find out the difference in oxidative stress levels between obese postmenopausal women and normal menstruating women, also to compare the same in normal weight postmenopausal women.

MATERIALS AND METHODS

Thirty one normal and 29 obese postmenopausal women with age more than 45 years who visited obstetrics and gynaecology outpatient department for general clinical evaluation at a tertiary care centre were recruited in this cross-sectional study. Thirty normal menstruating women were compared. Anthropometric measurements were recorded and the body mass index was calculated. Serum Malondialdehyde and superoxide dismutase was measured using a spectrophotometer.

RESULTS

There was a significant difference in mean MDA levels in postmenopausal women (1.477 ± 0.359) when compared to normal menstruating women (0.666 ± 0.302) (p < 0.01). There was no significant difference in mean SOD levels in postmenopausal women (2.836 ± 0.899) when compared to normal menstruating women (2.986 ± 0.686) (p > 0.05). Also, there was a significant increase between mean MDA levels in obese postmenopausal women (2.48 ± 0.52) when compared to normal weight postmenopausal women (1.65 ± 0.36) (p < 0.01). There was a significant difference between mean SOD levels in obese postmenopausal women (1.36 ± 0.96) and normal weight postmenopausal women (2.56 ± 1.03) (p < 0.01).

CONCLUSION

The oxidative stress was higher in obese postmenopausal women when compared to normal weight postmenopausal women and normal menstruating women.

Hierarchically built gold nanoparticle supercluster arrays as charge storage centers for enhancing the performance of flash memory devices

Flash memory devices with high-performance levels exhibiting high charge storage capacity, good charge retention, and high write/erase speeds with lower operating voltages are widely in demand. In this direction, we demonstrate hierarchical self-assembly of gold nanoparticles based on block copolymer templates as a promising route to engineer nanoparticle assemblies with high nanoparticle densities for application in nanocrystal flash memories. The hierarchical self-assembly process allows systematic multiplication of nanoparticle densities with minimal increase in footprint, thereby increasing the charge storage density without an increase in operating voltage. The protocol involves creation of a parent template composed of gold nanoclusters that guides the self-assembly of diblock copolymer reverse micelles which in turn directs electrostatic assembly of gold nanoparticles resulting in a three-level hierarchical system. Capacitance-voltage (C-V) measurements of the hierarchical nanopatterns with a metal-insulator-semiconductor capacitor configuration reveal promising enhancement in memory window as compared to nonhierarchical nanoparticle controls. Capacitance-time (C-t) measurements show that over half the stored charges were retained when extrapolated to 10 years. The fabrication route can be readily extended to programmed density multiplication of features made of other potential charge storage materials such as platinum, palladium, or hybrid metal/metal oxides for next generation, solution-processable flash memory devices.

In situ synthesis and immobilization of metallic nanoparticles on a calixarene monolayer

A covalently immobilized calix[7]hydroquinone monolayer was used as the host matrix to synthesize metallic NPs using an in situ redox process. The characteristics of different metallic ions that affect the synthesis process were studied. Metallic ions with less charges, lower oxidation state in the reaction, and higher standard redox potential provided better yield. Bimetallic NPs with a core-shell structure were synthesized by a sequential deposition of different metals on the same monolayer. The process was applied to form a layer of immobilized NPs on flat and curved surfaces. The ability to synthesize and immobilize well-controlled NPs on different surfaces has promising applications in decoration of irregular surfaces of miniaturized, three-dimensional objects.

In situ synthesis of high density sub-50 nm ZnO nanopatterned arrays using diblock copolymer templates

Fabrication of high density (~155 Gbit in(-2)) ZnO nanopatterns through in situ decomposition of Zn precursors inside diblock copolymer templates and their application as charge storage centers in nonvolatile memory devices is described. The fabrication is performed in a highly controlled fashion with the resulting ZnO nanopatterned arrays exhibiting diameters of 38 nm and heights of 14 nm offering sub-50 nm feature resolutions. The ZnO nanopatterns are naturally n-type due to the presence of zinc interstitials and oxygen vacancies that act as defect levels in trapping charge carriers. Test capacitors (metal-oxide-semiconductor, MOS) constructed using nanopatterns formed on p-Si exhibited a large flatband voltage shift of about ~2.2 V for a low operating voltage of 10 V. A high charge trap density of 3.47 × 10(18) cm(-3) combined with a good retention capacity is observed with low tunneling oxide (thermally grown) thickness of 3 nm. This demonstrates the significant promise of the ZnO nanopatterned arrays to act as charge storage centers for potential application in nonvolatile flash memory devices. The charge trapping characteristics, the capacitance-voltage measurements, and the potential of ZnO nanopatterns as charge storage centers in fabricating nonvolatile memory devices are discussed.

Stable Organic Monolayers on Oxide-Free Silicon/Germanium in a Supercritical Medium: A New Route to Molecular Electronics

Oxide-free Si and Ge surfaces have been passivated and modified with organic molecules by forming covalent bonds between the surfaces and reactive end groups of linear alkanes and aromatic species using single-step deposition in supercritical carbon dioxide (SCCO2). The process is suitable for large-scale manufacturing due to short processing times, simplicity, and high resistance to oxidation. It also allows the formation of monolayers with varying reactive terminal groups, thus enabling formation of nanostructures engineered at the molecular level. Ballistic electron emission microscopy (BEEM) spectra performed on the organic monolayer on oxide-free silicon capped by a thin gold layer reveals for the first time an increase in transmission of the ballistic current through the interface of up to three times compared to a control device, in contrast to similar studies reported in the literature suggestive of oxide-free passivation in SCCO2. The SCCO2 process combined with the preliminary BEEM results opens up new avenues for interface engineering, leading to molecular electronic devices.

Polythiophene-gold nanoparticle hybrid systems: Langmuir-Blodgett assembly of nanostructured films

In this work, we demonstrate a simple method of synthesizing nanoscale polythiophene-gold nanoparticle (AuNP) hybrid systems assembled by the Langmuir-Blodgett (LB) method. Regio-regular poly(3-(2-methoxyethoxy)ethoxymethyl)thiophene-2,5-diyl (PMEEMT) and poly(3-dodecylthiophene) (PDDT) were employed as the polymeric constituents. The presence of PDDT improved the amphiphilicity of PMEEMT by addressing the phase separation that occurred due to convective hydrodynamic instability on the substrate. 4 layer stacks of 90% and 99% PMEEMT films exhibited uniform film structure with a significant reduction in phase separation. A detailed mechanism for minimization of the surface effect has been proposed based on the interaction of polythiophenes with the substrate. For the first time, an ex situ approach has been adopted to incorporate AuNPs into LB films without affecting the film morphology and uniformity. The incorporation of AuNPs into the polythiophene matrix, aided by the affinity of sulphur for gold, was strongly dependent on the molecular arrangement of the matrix, which in turn depended on the composition of the matrix. The hybrid polythiophene films exhibited enhanced conductivity and can be applied in sensors, photovoltaics and memory devices.

In situ application of polyelectrolytes in zinc oxide nanorod synthesis: understanding the effects on the structural and optical characteristics

We report a facile and simple means of synthesizing a macroscopic array of ZnO nanorods with high feature densities using a modified hydrothermal approach that involves the in situ introduction of polyelectrolyte. The ZnO nanorod arrays with heights of 1.5 μm and diameters of 350 nm were consistently reproducible and were bestowed with the advantage of in situ process tunability offered by employing polyethylenimine (PEI) as a surface modifying agent. The fabrication combines benefits from the hydrothermal approach in terms of process simplicity and flexibility and from the use polyelectrolyte that offers a better nanorod surface, quenched defect levels and enhancement of the UV band edge emission. Structural and elemental analysis of the PEI-modified and unmodified nanorods emphasize the fact that the intentional introduction of PEI results in a nanorod with better surface quality as evidenced by photoluminescence (PL) spectra. The tunability of the feature dimensions of the nanorods and an analysis of the bulk and surface (surface defect) responses to the PL point to significant promise of high density orthogonal nanorods in a number of optoelectronic applications. While the defects in the ZnO nanorods can point towards the application of ZnO nanorods in charge trap flash memory devices, highly crystalline, size tunable, high aspect ratio nanorods find applications as building components in solid state lighting.

Thermogravimetric investigation of hydrochar-lignite co-combustion

Co-combustion of hydrochar with lignite was investigated by means of thermogravimetric analysis. Hydrochars were produced from coconut fibers and eucalyptus leaves under hydrothermal conditions at 250°C. The hydrochar was added in varying amounts to lignite for combustion. The results indicated that hydrothermal treatment decreased the volatile matter content and increased the fixed carbon content of the biomaterials. The elevated energy density and decreased ash content of the hydrochar improved its combustion behavior when co-fired with lignite for energy production. The hydrochars derived from coconut fiber and eucalyptus leaves had similar chemical compositions and showed similar influences on lignite combustion. Hydrochar addition increased the burnout and shortened the combustion range of the hydrochar-lignite blends. High combustion efficiency was observed due to the synergistic interactions between hydrochar and lignite during the co-combustion process. A kinetic study showed that the combustion process of hydrochar-lignite blends followed first-order reaction rates.

Enhancing charge-storage capacity of non-volatile memory devices using template-directed assembly of gold nanoparticles

We demonstrate the controlled fabrication of aggregates of gold nanoparticles as a means of enhancing the charge-storage capacity of metal-insulator-semiconductor (MIS) devices by up to 300% at a low biasing voltage of ±4 V. Aggregates of citrate stabilized gold nanoparticles were obtained by directed electrostatic self-assembly onto an underlying nanopattern of positively charged centers. The underlying nanopatterns consist of amine functionalized gold nanoparticle arrays formed using amphiphilic diblock copolymer reverse micelles as templates. The hierarchical self-organization leads to a twelve-fold increase in the number density of the gold nanoparticles and therefore significantly increases the charge storage centers for the MIS device. The MIS structure showed counterclockwise C-V hysteresis curves indicating a good memory effect. A memory window of 1 V was obtained at a low biasing voltage of ±4 V. Furthermore, C-t measurements conducted after applying a charging bias of 4 V showed that the charge was retained beyond 20,000 s. The proposed strategy can be readily adapted for fabricating next generation solution processible non-volatile memory devices.

Covalent assembly of gold nanoparticles for nonvolatile memory applications

This work reports a versatile approach for enhancing the stability of nonvolatile memory devices through covalent assembly of functionalized gold nanoparticles. 11-mercapto-1-undecanol functionalized gold nanoparticles (AuNPs) with a narrow size distribution and particle size of about 5 nm were synthesized. Then, the AuNPs were immobilized on a SiO(2) substrate using a functionalized polymer as a surface modifier. Microscopic and spectroscopic techniques were used to characterize the AuNPs and their morphology before and after immobilization. Finally, a metal-insulator-semiconductor (MIS) type memory device with such covalently anchored AuNPs as a charge trapping layer was fabricated. The MIS structure showed well-defined counterclockwise C-V hysteresis curves indicating a good memory effect. The flat band voltage shift was 1.64 V at a swapping voltage between ±7 V. Furthermore, the MIS structure showed a good retention characteristic up to 20,000 s. The present synthetic route to covalently immobilize gold nanoparticles system will be a step towards realization for the nanoparticle-based electronic devices and related applications.

Multilayered gold-nanoparticle/polyimide composite thin film through layer-by-layer assembly

A novel type of composite thin film consisting of gold nanoparticles (AuNPs) and polymide (PI) was fabricated through layer-by-layer (LBL) assembly. To fabricate such films, bare AuNPs and a poly (amic acid) bearing pendant amine groups, namely, amino poly (amic acid) or APAA, were synthesized and assembled in an LBL fashion. Without any organic encapsulation layer on their surface, AuNPs were bound directly to APAA chains at the amine sites; X-ray photoelectron spectroscopy study suggested that the binding was based on a combined effect of metal-ligand coordination and electrostatic interaction, with the former dominating over the latter. An approximately linear growth of the film started from the second layer of AuNP as revealed by the UV-vis spectroscopy, and the degree of particle aggregation was higher in the first AuNP layer than in the subsequent layers due to the differences in the density of binding sites. The resultant assembly was heated to imidize the APAA, thereby creating a robust composite structure.

Tribological properties of nanoparticle-laden ultrathin films formed by covalent molecular assembly

The tribological properties of ultrathin films containing nanoparticles encapsulated in immobilized dendrimers are investigated. The films were formed by covalent molecular assembly in supercritical carbon dioxide, and the Au nanoparticles were formed in aqueous solution. End-capping of the terminal amine groups of the dendrimer by fluorinated species resulted in a reduction in the size of the nanoparticles formed. The resulting film structure displayed a lower coefficient of friction when the nanoparticles were formed after fluorination. The observed improvement in the tribological properties is attributed to the reduction in agglomeration of the nanoparticles due to the presence of the fluorine moieties.

Covalent molecular assembly of multilayer dendrimer ultrathin films in supercritical medium

Ultrathin films containing dendrimers are fabricated on amine- and anhydride-derivatized silicon dioxide surface through alternate layer-by-layer (LbL) assembly of pyromellitic dianhydride (PMDA) and poly(amidoamine) (PAMAM) dendrimer in supercritical carbon dioxide (SCCO2) with interlayer linkage established by covalent bonds. X-ray photoelectron and UV-visible absorption spectroscopies, atomic force microscopy (AFM), and ellipsometry were employed to study the interfacial chemistry, growth, morphology, and thickness of the assembled film. XPS analysis suggests that the PMDA/PAMAM interlayer covalent bond is established to completion, and functional surfaces for immobilization of the next layer are available after deposition of each layer. UV-visible absorption and ellipsometry revealed layer-by-layer growth of the film. The functional property film as a porous matrix was manifested in the reduction of the refractive index upon introduction of the dendrimer.

Covalent molecular assembly in supercritical carbon dioxide: a comparative study between amine- and anhydride-derivatized surfaces

Layer-by-layer covalent assembly of an oligoimide on an anhydride- derivatized silicon dioxide surface is investigated using supercritical carbon dioxide (SCCO2) as the depositing medium. The deposited films were characterized by X-ray photoelectron spectroscopy (XPS), ellipsometry (VASE), UV-visible spectroscopy, electrochemical impedance spectroscopy, nano indentation, and atomic force microscopy (AFM) and the properties of the films compared with those of an oligoimide deposited on amine-derivatized surfaces. Films formed on the anhydride surface are more uniform and stable possibly because the silane precursor for the anhydride is anchored to the surface through two (-Si-O-Si-) tripods. XPS results indicate that the interfacial reaction resulting in amide formation is almost complete in the case of the anhydride, but not in the case of the amine. We infer that the twin tripods linking the anhydride group to the surface may have improved the accessibility of the functional groups for immobilization of the next layer, thereby contributing to the better quality.

Covalent molecular assembly of oligoimide ultrathin films in supercritical and liquid solvent media

An ultrathin film of oligoimide has been fabricated on amine-modified substrates of silicon and quartz through alternate layer-by-layer (LBL) assembly of pyromellitic dianhydride (PMDA) and diaminodiphenyl ether (DDE), with interlayer links established by covalent bonds. The assembly was formed in supercritical carbon dioxide (SCCO2) and in solution (dimethyl acetamide, DMAc), and the imidization reaction was performed by thermal and chemical methods, in benzene and in the supercritical medium. X-ray photoelectron and UV-visible absorption spectroscopies, atomic force microscopy (AFM), and ellipsometry were employed to study the interfacial chemistry, growth, morphology, and thickness of the assembled film. XPS analysis confirmed the sequential deposition of PMDA and DDE through formation of amic acids. At each deposition step, surface functionalities for the assembly of the next layer were generated. The interfacial chemical reaction was almost complete in the SCF (supercritical fluid) medium, as compared to the conversions observed in conventional assembly. Both the PMDA and DDE molecules were assembled in an organized manner, resulting in uniform surface morphology. Uniform film growth was revealed from the increase of UV absorption intensity and film thickness. The overall growth and quality of the films in SCF medium were greater than that for films formed in DMAc. The results of this novel study show that an environmentally friendly solvent can be used to obtain mechanically robust and thermally stable ultrathin films with little loss of material during the imidization step. In contrast to conventional deposition of the molecular layers that utilizes liquid solvents, use of SCCO(2) avoids solvent effects and posttreatment for solvent removal, while ensuring facile transport during contact.

Modeling gas adsorption and transport in small-pore titanium silicates

Engelhard titanium silicate, ETS-4, is a promising new adsorbent for size-selective separation of mixtures of small gases, a leading industrially important example of which is methane-nitrogen separation. Single component equilibrium and kinetics of oxygen, nitrogen, and methane adsorption in Na-ETS-4 and cation-exchanged Sr-ETS-4, measured in an earlier study over a wide range of temperatures and pressures, are analyzed in this study. The adsorbent crystals were synthesized and pelletized under pressure (without any binder), thus giving rise to a bidispersed pore structure with controlling resistance in the micropores. Change in equilibrium and kinetics of adsorption of the aforementioned gases in Sr-ETS-4 due to pore shrinkage with progressively increasing dehydration temperature has also been investigated. Differential uptakes have been measured at various levels of adsorbate loading, which has allowed the elucidation of the nature of concentration dependence of micropore diffusivity. Both homogeneous and heterogeneous models are examined on the equilibrium data, while a bidispersed pore diffusion model is able to capture the differential uptakes very well. On the basis of chemical potential gradient as the driving force for diffusion, the impact of isotherm models on the concentration dependence of micropore diffusivity is also analyzed. It is shown that pore tailoring at the molecular scale by dehydration can improve the kinetic selectivity of nitrogen over methane in Sr-ETS-4 to a promising level. The models investigated are evaluated to identify essential details necessary to reliably simulate a methane-nitrogen separation process using the promising new Sr-ETS-4 adsorbent.

Application of direct covalent molecular assembly in the fabrication of polyimide ultrathin films

Ultrathin films were fabricated using synthesized hydroxyl polyimide (HPI) in a layer-by-layer fashion on amine-terminated substrates of silicon, quartz, and gold. The interlayer linkages were established by using terephthaloyl chloride as a bridging agent to form ester groups between HPI layers. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV-vis absorption spectroscopy, atomic force microscopy, ellipsometry, and electrochemical impedance spectroscopy were employed to study the interfacial chemistry, stepwise growth, morphology, thickness, optical property, and insulation behavior of the assembled film. The films show excellent stability and strength, which can be attributed to the covalent interlayer linkage.

Effects of Site Occupancy, Cation Relocation, and Pore Geometry on Adsorption Kinetics in ETS-4

Strontium-exchanged titanium silicate, Sr-ETS-4, is a new molecular sieve with promises for exciting applications in gas separation. The literature mentions poor thermal stability and low adsorption capacity as the drawbacks of the as-synthesized Na-ETS-4 and therefore the need for cation exchange. Upon ion exchange, Sr-ETS-4 shows appreciable kinetic selectivity between methane and nitrogen, which can be improved further by controlled dehydration. In this study, we trace the changes at the molecular level behind this improvement. By combining distributed information in the literature, it is shown that the governing factors are changes in pore geometry with progressive dehydration, changes in ion occupancy, and relocation of cations due to Sr exchange.

Self-assembled molecular films of aminosilanes and their immobilization capacities

The assembly of two aminosilanes on silicon dioxide surfaces is investigated in this work. It is found that for 3-aminopropyltrimethoxysilane (APS), a smaller concentration of the silane and trace amounts of water in the deposition medium, an optimum time, and a postdeposition thermal curing are necessary to obtain a high primary-amine content. By optimization of deposition conditions, uniform APS films with a primary-amine content of 88.6% were obtained. The dependence of the primary-amine content on the experimental parameters is related to the extent to which amines are lost to hydrogen bonding with each other or with the substrate surface. Whenp-aminophenyltrimethoxysilane (APhS) was used, the primary-amine content in the film reached 100% and the surface morphology was more uniform than that of APS films under the same conditions. This is attributed to the rigid phenyl component in APhS that reduces opportunities for hydrogen bonding. In a comparison of the immobilization capacities of the different aminosilane substrates for pyromellitic dianhydride (PMDA), it is observed that higher primary-amine content favors higher uptake, and the APhS film yields 100% PMDA coverage. We infer that primary-amine content could be a measure of the film morphology and accessibility of the substrate amine groups.