Metal Oxide Nanostructures and Their Applications

Mesoporous TiO 2 nanoparticle films are used as photoanodes for high-efficiency dye-sensitized solar cells (DSCs). In spite of excellent photovoltaic power conversion efficiencies (PCEs) displayed by titanium dioxide nanoparticle structures, the transport rate of electrons is known to be low due to low electron mobility. So the alternate oxides, including ZnO, that possesses high electron mobility are being investigated as potential candidates for photoanodes. However, the PCE with ZnO is still lower than with TiO 2 , and this is typically attributed to the low internal surface area. In this work, we attempt to make a one-to-one comparison of the photovoltaic performance and the electron transfer dynamics involved in DSCs, with ZnO and TiO 2 as photoanodes. Previously such comparative investigations were hampered due to the morphological differences (internal surface area, pore diameter, porosity) that exist between zinc oxide and titanium dioxide films. We circumvent this issue by depositing different thicknesses of these oxides, by atomic layer deposition (ALD), on an arbitrary mesoporous insulating template and subsequently using them as photoanodes. Our results reveal that at an optimal thickness ZnO exhibits photovoltaic performances similar to TiO 2 , but the internal electron transfer properties differ. The higher photogenerated electron transport rate contributed to the performances of ZnO, but in the case of TiO 2 , it is the low recombination rate, higher dye loading, and fast electron injection.

Thermal plasma processing Structure Mechanical behaviour a b s t r a c t Bulk quantity of the MgAl 2 O 4 spinels with specific composition has been synthesized by thermal plasma method. The process time and compositions of the feed are optimized for a desired stoichiometry. A structural co-relation has been derived from several set of experiments by major variation in the a-Al 2 O 3 content in the feed material. Formation of desired phase with particular feed stoichiometry has been studied by X-ray diffraction pattern (XRD) analysis which is corroborated by Raman scattering analysis. A good structural co-relation between the XRD, Raman and Fourier transform infrared spectroscopy (FTIR) analysis was derived. Additionally, the electron probe microanalysis (EPMA) of the specific sample has been carried out to study the exact compositional distribution and the presence of additional impurity phases in the as-synthesized spinels. Finally, the micro mechanical behaviour of the as-synthesized spinels has been studied and well co-related with the structural data.

Cerium oxide nanoparticles (CeO2 NPs) were
synthesized using Aspergillus niger culture filtrate. The
mycosynthesized CeO2 NPs were characterized by UV–
Visible (UV–Vis), Fourier Transform Infrared (FT-IR),
X-ray diffraction (XRD), Micro Raman, Thermogravi-
metric/Differential Thermal Analysis (TG/DTA), Photo-
luminescence, and Transmission Electron Microscopy
(TEM) analyses. UV–Vis spectrum exhibited a corre-
sponding absorption peak for CeO2 NPs at 296 nm, and
the functional groups present in the fungal filtrate
responsible for the synthesis of NPs were analyzed by
FT-IR. The further characterization of the mycosynthe-
sized CeO2 NPs revealed particles of the cubic structure
and spherical shape, with the particle sizes ranging from
5 to 20 nm. The antibacterial activity of CeO2 NPs was
examined in respect of two Gram-positive (G?) bacteria
(Streptococcus pneumoniae, Bacillus subtilis) and two
Gram-negative (G-) bacteria (Proteus vulgaris, Escher-
ichia coli) by disk diffusion method. The test results for
CeO2 NPs at a concentration of 10 mg/mL showed
higher activities on the zone of inhibition of up to
10.67 ± 0.33 and 10.33 ± 0.33 mm against Streptococ-
cus pneumonia and Bacillus subtilis, respectively, The
CeO2 NPs caused 100 % mortality on first instar of
Aedes aegypti at 0.250 mg/L concentration after 24-h exposure. The mycosynthesis of CeO2 NPs is a simple,
cost-effective and eco-friendly approach and it will also
potentially helpful to control pathogenic bacteria and
dengue vector.

This study aims to observe the changes in the structural characterization and physical properties of calcium-praseodymium-cobalt oxide thermoelectric materials with graphene doping. Structural characterizations were examined via X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), and Fourier Transformed Infrared Spectroscopy (FTIR) measurements. Temperature-dependent thermal conductivity and Seebeck coefficient were measured by Physical Properties Measurement System (PPMS). In the SEM images, the samples were observed to be crystalline and showed enhanced fusion with graphene doping. There were no impurities in the samples according to the EDX results and all sample components were observed in these results. The properties and structures of the bonds in the XRD results were also visible in the FTIR results. According to the PPMS results, it was determined by measurements and graphs that graphene doping provided a significant and changeable effect to the thermoelectric materials. Published by the AVS.

Journal of Vacuum Science & Technology A 37, 061201 (2019); https://avs.scitation.org/doi/pdf/10.1116/1.5121253?class=pdf

<<< Final published version for free until October 27th:  https://authors.elsevier.com/a/1XhJP3IQMPAqsP  >>>
Monitoring of hazardous gases is nowadays very important, since the urbanized environment is more subject to this kind of pollutants. Therefore, a capillary network of small gas sensors capable to check the quality of the environment is necessary. Metal oxide gas nanosensors are small economic devices that can be easily integrated in any context, however they unfortunately lack of selectivity. We present an approach using hydrothermally grown nickel oxide nanowires working at different temperatures and creating a virtual sensors array, thus exploiting the thermal fingerprints (sensor response as a function of temperature) of the gases. Using only one nanostructured material (nickel oxide) and different machine learning techniques, the system can easily discriminate any of 7 harmful gases (C 2 H 5 OH, H 2 , CO, LPG, CO 2 , NH 3 and H 2 S, all of them reducing gases) with an accuracy of 100%. Furthermore, the nanosensor also evaluates the gas concentration with an average error lower than 15%. Our results show that, exploiting thermal fingerprints from a temperature gradient, single metal oxide resistive nanosensors can efficiently discriminate specific hazardous gases.

Present study reports the use of a glassy carbon electrode modified with manganese oxide decorated with platinum nanoparticles (Pt-MnO x /GCE) for electrocatalytic reduction of oxygen dissolved in buffer solution. The electrode exhibits better electrocatalytic activity toward oxygen reduction than bulk platinum due to larger surface area of manganese oxide which also prevents agglomeration of platinum nanoparticles. Best results were obtained with the electrode modified by cycling the potential in a range of −0.25-1.05 V for five times in a cell containing 1.0 mM K 2 PtCl 6 and 0.1 M MnSO 4 in 0.01 M H 2 SO 4 solution. Then, the electrode developed was utilized as a biosensing platform for the monitoring of oxygen consumption due to the bio-catalytic activity of pyranose oxidase. In the pursuit of a stable and rapid response the biocomponent was bridged with an ionic liquid namely 1-butyl-3-methyl imidazolium hexaflourophosphate. Chronoamperometric measurement of oxygen at 0.2 V gave 0.010-0.100 mM linear range with a detection limit of 2.0 M and sensitivity of 6.1 nA M −1 under optimized conditions. In addition, ionic liquid provides a conductive environment which shortens the response time to 3 s for low concentrations. Overall results indicated that fabricated biosensor is a good candidate for automated systems.

For efficient energy storage, Co 3 O 4 @nickel foam exhibiting a plate-like (p-Co 3 O 4) and grass-like (g-Co 3 O 4) nanostructure were prepared as binder-free supercapacitor electrode materials. The electrochemical performance of the electrodes was tested using a redox-additive electrolyte (RAE). The homogeneously grown grass-like nanostructure (g-Co 3 O 4) exhibited superior electrochemical performance to those with the plates-like structure (p-Co 3 O 4) in a KOH electrolyte. In addition, the electrochemical performance of g-Co 3 O 4 was improved using an RAE in a 3 M KOH solution. Remarkably, the specific capacitance of g-Co 3 O 4 (1560 F g À1) was increased to 6580 F g À1 , approximately 4-fold just by varying the RAE concentration in KOH. Carbon nano-onion (CNO) in the form of multi-layer fullerene was introduced as a negative electrode material. Owing to the more favorable morphology and properties of CNO such as exohedral structure, small diameter, high electrical conductivity, and relatively easy aqueous media dispersion than activated carbon and graphene, the as-fabricated asymmetric Co 3 O 4 //CNO supercapacitor delivered a high energy density of 42.5 Wh kg À1 and a high power density of 12.8 kW kg À1 .

Metal–graphene nanostructures (NSs) as photocatalysts, prepared using simple and scalable synthesis methods, are gaining heightened attention as novel materials for water treatment and environmental
remediation applications. Graphene, the unique few layers sheet-like arrangement of sp2 hybridized carbon atoms, has an inimitable two-dimensional (2D) structure. The material is highly conductive, has high electron mobility and an extremely high surface area, and can be produced on a large scale at low cost. Accordingly, it has been considered as an essential base component for producing various metal based NSs. In particular, metal-graphene NSs as photocatalysts have attracted considerable attention because of their special surface plasmon resonance (SPR) effect that can improve their performance for
the removal of toxic dyes and other pollutants. This review summarizes the recent and advanced progress for the easy fabrication and design of graphene-based NSs as photocatalysts, as a novel tool, using a range of approaches, including green and biogenic approaches.

Metal-graphene nanostructures (NSs) as photocatalysts, prepared using simple and scalable synthesis methods, are gaining heightened attention as novel materials for water treatment and environmental remediation applications. Graphene, the unique few layers sheet-like arrangement of sp2 hybridized carbon atoms, has an inimitable two-dimensional (2D) structure. The material is highly conductive, has high electron mobility and an extremely high surface area, and can be produced on a large scale at low cost. Accordingly, it has been considered as an essential base component for producing various metal-based NSs. In particular, metal-graphene NSs as photocatalysts have attracted considerable attention because of their special surface plasmon resonance (SPR) effect that can improve their performance for the removal of toxic dyes and other pollutants. This review summarizes the recent and advanced progress for the easy fabrication and design of graphene-based NSs as photocatalysts, as a no...

We present herein a facile two-step chemical vapor deposition (CVD) approach to synthesize carbon nanotube (CNT) supported vanadium oxide nanosphere nano-composite hetero-structures as electrochemical supercapacitors. The high electronic conductivity of CNTs has been exploited to provide a 3-D electron transport medium on which vanadium oxide nano-droplets interact with electrolyte to exhibit excellent supercapacitor behavior in aqueous media. Thin nano-scale droplets of vanadium oxide deposited on the CNTs exhibit excellent capacitance values as high as 1400 Fg −1 with good rate capability and excellent charge retention up to 200 cycles. The electrochemical mechanisms and materials properties responsible for the supercapacitor properties of CNT supported vanadium oxide have been discussed at length.

A novel investigation on a relationship between temperature-influential self-assembly (70–300 • C) of 4-pentynoic acid functionalized Fe3O4-Fe 2O3 nanoparticles (NPs) on SiO2/n-Si with electrical properties was reported with the interests for metal-oxide-semiconductor applications. X-ray diffractometer (XRD) analysis conveyed that 8 ± 1 nm of the NPs were assembled. Increasing heating temperature induced growth of native oxide (SiO2). Raman analysis confirmed the coexistence of Fe3O4-Fe2O3. Attenuated Total Reflectance Infrared (ATR-IR) spectra showed that self-assembly occurred via Si-O-C linkages. While Si-O-C linkages were broken down at elevated temperatures, formations of Si-OH defects were amplified; a consequence of physisorbed surfactants disintegration. Atomic force microscopy (AFM) showed that sample with more physisorbed surfactants exhibited the highest root-mean-square (RMS) roughness (18.12 ± 7.13 nm) whereas sample with lesser physisorbed surfactants displayed otherwise (12.99 ± 4.39 nm RMS roughness). Field Emission Scanning Electron Microscope (FE-SEM) analysis showed non-uniform aggregation of the NPs, deposited as film (12.6 m thickness). The increased saturation magnetization (71.527 A m 2 /kg) and coercivity (929.942 A/m) acquired by vibrating sample magnetometer (VSM) of the sample heated at 300 • C verified the surfactants' disintegration. Leakage current density-electric field (J-E) characteristics showed that sample heated at 150 • C with the most aggregated NPs as well as the most developed Si O C linkages demonstrated the highest breakdown field and barrier height at 2.58 × 10 −3 MV/cm and 0.38 eV respectively. Whereas sample heated at 300 • C with the least Si O C linkages as well as lesser aggregated NPs showed the lowest breakdown field and barrier height at 1.08 × 10 −3 MV/cm and 0.19 eV respectively. This study opens up better under-standings on how formation and breaking down of covalent linkages as well as accumulation of defects, particularly prior temperature influential self-assembly at the interfaces, affected electrical breakdown field and barrier height. Hence, possible future development of self-assembly silicon-based metal-oxide-semiconductor (MOS) structure particularly in the presence of SiO2 can be deliberated.

Metal-graphene nanostructures (NSs) as photocatalysts, prepared using simple and scalable synthesis methods, are gaining heightened attention as novel materials for water treatment and environmental remediation applications. Graphene, the unique few layers sheet-like arrangement of sp2 hybridized carbon atoms, has an inimitable two-dimensional (2D) structure. The material is highly conductive, has high electron mobility and an extremely high surface area, and can be produced on a large scale at low cost. Accordingly, it has been considered as an essential base component for producing various metal-based NSs. In particular, metal-graphene NSs as photocatalysts have attracted considerable attention because of their special surface plasmon resonance (SPR) effect that can improve their performance for the removal of toxic dyes and other pollutants. This review summarizes the recent and advanced progress for the easy fabrication and design of graphene-based NSs as photocatalysts, as a no...