Porous Nanocrystalline Research Articles

Molecular and Dissociative Adsorbed Water Concentration and Surface Protonic Conduction in Nanocrystalline TiO2.

Surface protonic conduction in porous nanocrystalline oxides is commonly involved in catalytic processes. The configuration of surface adsorbed water on oxides plays a crucial role in surface protonic conduction. However, studies on the impact of complex surface adsorbed water configuration on the surface water concentration and diffusivity remain limited, and hinder an in-depth understanding of surface proton transport mechanisms, and the design of better surface proton conductors. Here, in situ Raman spectroscopy is utilized to quantitatively identify the contribution of dissociative and molecular adsorbed water components on porous nanocrystalline TiO2 surfaces between 25 and 200°C. The variations in molecular and dissociative adsorbed water concentration agree with the predominant surface proton conduction mechanisms at three different temperature stages. From 40 to 125°C, the reduced coverage of molecular adsorbed water layer results in the decreasing proton diffusivity. Water dissociation on the nanocrystalline TiO2 surface is easier in wet N2 than in wet O2, resulting in higher proton conductivity in wet N2; while the surface proton diffusivities in these two atmospheres are similar. The in situ spectroscopy technique enables the improvement of surface proton conducting oxides through quantitative evaluation and modulation of the surface proton concentration and diffusivity.

Structural Properties of Cs<sup>1+</sup> Doped H<sub>3</sub>PMo<sub>12</sub>O<sub>40</sub> Nanocrystalline Polyoxometalate Thin Films

The microwave assisted chemical bath deposition (MA-CBD) technique were used to deposite nanocrystalline thin films of polyoxometalates like phosphomolybdic acid (PMA) (H3PMo12O40) and Cesium (Cs+) doped phosphomolybdic acid (Cs-PMA) (Cs3-PMo12O40). Thermo gravimetric and Differential thermal analysis (TGDTA), Fourier transform infrared spectroscopy (FTIR), Energy dispersive X-ray analysis (EDAX), X-ray diffractometry (XRD) and Scanning electron microscopy (SEM) tools are used for the thermal, structural, morphological and compositional analysis of microwave treated H3PMo12O40 and Cs3- PMo12O40 thin films. The completion of decomposition process at 600 oC of Cs3-PMo12O40 compound is confirmed from TGDTA analysis. The polycrystalline spinel cubic crystal structure of H3PMo12O40 and Cs3-PMo12O40 thin films were confirmed from X-ray diffractometer. The crystallite size of H3PMo12O40 and Cs3-PMo12O40 compound found to be in the range of 50 - 53 nm. The formation of H3PMo12O40 and Cs3-PMo12O40 materials were confirmed from the presence of main four absorption peaks observed in the range from 800 cm-1 to 1100 cm-1. The SEM microphotographs analysis identify the microwave assisted H3PMo12O40 and Cs3-PMo12O40 films have spherical shaped porous nanocrystalline morphology. The grain size of H3PMo12O40 and Cs3-PMo12O40 synthesized material found to be in the range of 10 - 12 A˚ The stoichiometric preparation of H3PMo12O40 and Cs3-PMo12O40 thin films with presence of P, Mo, O and Cs peaks of metal ions is observed from EDAX spectra.

Nanocrystalline Porous Materials for Chiral Separation: Synthesis, Mechanisms, and Applications.

Nanocrystalline Porous Materials for Chiral Separation: Synthesis, Mechanisms, and Applications.

Porous carboxymethyl cellulose nanocrystalline imprinted composite aerogels for selective adsorption of gadolinium

Gadolinium is widely applied in medical and high-tech materials because of special magnetic properties. Recovery of gadolinium from waste rare earth products has both economic and environmental value. In this experiment, honeycomb porous composite aerogels were constructed using sericin and sodium alginate mixed with functionally modified carboxymethylated cellulose nanocrystals for the adsorption and separation of gadolinium ions. There were large numbers of carboxyl groups as well as hydroxyl groups on the surface of sodium alginate and filamentous protein, which provided more sites for the adsorption of gadolinium ions. Besides, a stable honeycomb structure appeared on the surface of composite aerogels when the mixture of filamentous protein and sodium alginate was 1:1, which increased the specific surface area of materials to 140.65 m2 g−1. Additionally, the imprinted composite aerogels Ic-CNC/SSA were prepared by virtue of the imprinting technology, enhancing the adsorption selectivity of composite aerogels for gadolinium. The adsorption experiments revealed that the maximum adsorption capacity of Ic-CNC/SSA reached 93.41 mg g−1 at pH 7.0, indicating good selective adsorption of gadolinium ions. In summary, such composite aerogels provide great potential and reference value for the selective adsorption of gadolinium ions in industry.

Effects of porosity and cyclic deformation on phase transformation of porous nanocrystalline NiTi shape memory alloy: An atomistic simulation

Utilizing molecular dynamics simulation, this study aims to explore the phase transformation behavior of porous nanocrystalline (NC) NiTi shape memory alloys (SMAs) when subjected to cyclic deformation. The influences of porosity and cyclic deformation on the phase transformation of NC NiTi SMAs are examined and discussed. The simulation results show that the increase in the porosity and number of cycles leads to a decrease in both the critical phase transformation stress and peak stress whereas an increase in the residual martensite, phase boundary, and interstitial atoms; the related results can be supported by previous experiments. After cyclic deformation, the reduction in the potential energy for the entire system during the tensile phase occurs at an earlier stage, indicating that the martensitic transformation occurs earlier as the number of cycles increases. Notably, the dissipated energy demonstrates a decrease with an increasing number of cycles, and the potential energy during the austenite elastic unloading stage undergoes a transition from a decreasing to an increasing trend due to the presence of residual martensite increasing with the number of cycles.

Constitutive modeling of porosity and grain size effects on superelasticity of porous nanocrystalline NiTi shape memory alloy

Constitutive modeling of porosity and grain size effects on superelasticity of porous nanocrystalline NiTi shape memory alloy

The influences of diameter distribution change of zeolitic imidazolate framework‐67 crystal on electrochemical behavior for lithium‐sulfur cell cathode

To improve the electrochemical performance of Li‐S batteries, sulfur composites are prepared through sulfur's melt‐diffusion into porous materials such as metal organic frameworks (MOFs). MOFs are porous nanocrystalline materials consisting of metal ions and organic ligands. Due to their high porosity, specific surface area, and easily controllable porous structure, MOFs and their derivatives are considered useful materials for holding sulfur. Herein, the effect of the concentration of the reactants on the particle diameter distribution of ZIF‐67 is studied, and the performance of the product as a sulfur host for Li‐S battery cathode is evaluated. ZIF‐67 was prepared by regulating the Co2+ concentration in solution from 10 to 250 mM, with a constant mole ratio between Co2+ and the organic ligand. Cyclovoltammetry, galvanostatic charge–discharge, and rate capability tests were performed to electrochemically characterize each sample as a sulfur host for Li‐S battery cathodes. MeZ‐50 mM, prepared with 50 mM Co2+ ion solution, had the smallest particle diameter (591 nm). The sulfur cathode utilizing MeZ‐50 mM afforded the best electrochemical performance (883.7 mAh gS−1). This study demonstrates that the particle size of ZIF‐67 can be controlled by adjusting the reactant concentration, enabling manipulation of the electrochemical properties as a sulfur host.

Effects of Thermal Cycling and Porosity on Phase Transformation of Porous Nanocrystalline NiTi Shape Memory Alloy: An Atomistic Simulation

Herein, the effects of thermal cycling and porosity on the martensitic phase transformation behavior of porous nanocrystalline (NC) NiTi shape memory alloys (SMAs) at the atomic scale are investigated by molecular dynamics simulation. The simulation results show that thermal cycling causes the NC NiTi SMAs to repeatedly undergo martensitic phase transformation and inverse phase transformation processes. The martensitic phase transformation capability is suppressed with increasing porosity and number of cycles, but the suppression effect of thermal cycling is weakened with increasing porosity. Moreover, the start temperature of martensitic transformation, residual martensitic phase, and the fraction of interstitial atoms increase with increasing porosity. Thermal cycling causes the disordered structures and shear plastic deformation to accumulate as cycling increases. Recoverable shear deformation is generated within the grain, but shear plastic deformation is mainly concentrated at both grain boundaries and pore surfaces. Residual martensitic phase increases after thermal cycling. These results provide important explanations and references for a deeper understanding of phase transformation behavior and pore effects caused by thermal cycling.

Phase control and induction of visible-light photocatalytic activity in hierarchical porous structure nanocrystalline TiO2 prepared using a MOF-5-derived nanoporous carbon template

BackgroundNanocasting is a powerful method to induce unique structural and morphological characteristics. It is known that the phase, morphology, and nanostructure of TiO2 facilitate its photocatalytic performance and band gap energy. In this context, we simultaneously controlled the TiO2 phase and improved its photocatalytic activity by choosing the appropriate carbon substrate and synthesis process. MethodsIn this study, a high surface area nanoporous carbon with an extremely interconnected mesoporous network and accessible pores in terms of depth and size was derived from MOF-5. This hard template used for the synthesis of titanium oxide (TiO2) nanoparticles by nanocasting. in addition to the anatase phase, the brookite phase was successfully produced using this nanocasting approach by penetrating NaF solution to the template pores under hydrothermal conditions. Significant FindingsThe results showed that, the interconnected mesoporous network of the carbon template led to the formation of brookite and anatase TiO2 with highly developed mesoporous and macroporous structures and very high surface areas of 109 and 126 m2g−1, respectively. Furthermore, the fabricated brookite and anatase showed enhanced photocatalytic efficiency in visible light because of the increase in light harvesting ability and the reduction in band gap energy to 2.84 and 2.60 eV, respectively.

Nanocrystalline Porous Iridium Oxide Coating on Titanium for Bifunctional Electrochemistry Water Splitting in Acidic Media

Nanocrystalline Porous Iridium Oxide Coating on Titanium for Bifunctional Electrochemistry Water Splitting in Acidic Media

The complex structural and chemical nature of monolithic U-10Mo fuel and Zr barrier layer

Nanoscale microstructural characterization by advanced transmission electron microscopy techniques on a U-10Mo/Zr barrier layer monolithic fuel plate was performed to evaluate the microstructural evaluation after high burn-up. Gas bubble superlattice evolution, grain restructuring, and evolution of the Zr interaction layer is investigated through detailed electron microscopy characterization. The use of automated crystallographic orientation mapping to irradiated U-10Mo fuel highlights that the restructured ultra-fine grains are separated by high angle grain boundaries at a burn up of 4.42 × 1021 fissions/cm3. Additionally, advanced chemical analysis and multi-variable statistical analysis shows spatial clustering of solid fission product precipitates. Finally, characterization of a newly observed porous nanocrystalline Zr region in the barrier layer is studied. This work provides insights into the grain subdivision and restructuring process while using advanced microscopy techniques to analyze fission products in neutron-irradiated U-10Mo fuel.

Hierarchical porous TiO2 with a uniform distribution of anchored gold nanoparticles for enhanced photocatalytic efficiency and accelerated charge separation for the degradation of antibiotics.

A novel approach to synthesize porous Au/TiO2 nanocomposites has been achieved through a pyrolytic strategy by employing NH2-MIL-125(Ti) as a TiO2 precursor, and photo-deposition of Au nanoparticles (NPs) onto porous nanocrystalline TiO2 with varying Au contents (0.05-0.5%). TEM images of Au/TiO2 nanocomposites showed that TiO2 particles were spherical structures, highly dispersed, and homogeneous with diameters of 10-15nm, and Au NPs (20-30nm) were anchored onto porous TiO2 matrices with a uniform distribution. The synthesized Au/TiO2 nanocomposites were assessed through the degradation of two antibiotic models, metronidazole (MNZ), and trimethoprim (TMP), under visible light and compared with undoped TiO2 and commercial TiO2 (P-25). The synthesized Au/TiO2 photocatalyst revealed enhanced photocatalytic performance in the mineralization (80%) and degradation (100%) of MNZ and TMP in both water matrices compared to undoped TiO2 (60%, 76%) and commercial P-25 (48%, 65%). The obtained 0.1% Au/TiO2 nanocomposite could complete the mineralization of TMP and MNZ with rate constant values (4.47 × 10-3min-1 and 5.23 × 10-1min-1) owing to the large well-developed porosity and high surface area of TiO2 and the small size of Au NPs with high dispersity, surface plasmon resonance, and stability. The recyclability of the 0.1% Au/TiO2 nanocomposite exhibited high durability without the leaching or loss of photocatalytic performance after four cycles. Complete degradation was achieved within 100min in the water matrix from real wastewater, indicating promising results for the degradation of pharmaceuticals in the different water matrices. The present work opens a new route to synthesize low-cost, effective, and high photocatalytic performance nanocomposites with a small Au content as a cocatalyst onto semiconductor materials.

Nanoporous Titanium (Oxy)nitride Films as Broadband Solar Absorbers.

Broadband absorption of solar light is a key aspect in many applications that involve an efficient conversion of solar energy to heat. Titanium nitride (TiN)-based materials, in the form of periodic arrays of nanostructures or multilayers, can promote significant heat generation upon illumination thanks to their efficient light absorption and refractory character. In this work, pulsed laser deposition was chosen as a synthesis technique to shift metallic bulk-like TiN to nanoparticle-assembled hierarchical oxynitride (TiOxNy) films by increasing the background gas deposition pressure. The nanoporous hierarchical films exhibit a tree-like morphology, a strong broadband solar absorption (∼90% from the UV to the near-infrared range), and could generate temperatures of ∼475 °C under moderate light concentration (17 Suns). The high heat generation achieved by treelike films is ascribed to their porous morphology, nanocrystalline structure, and oxynitride composition, which overall contribute to a superior light trapping and dissipation to heat. These properties pave the way for the implementation of such films as solar absorber structures.

On the Question of the Possibility of Using Nanocrystalline Porous Silicon in Silicon-Based Solar Cells

On the Question of the Possibility of Using Nanocrystalline Porous Silicon in Silicon-Based Solar Cells

Hafnium oxide nanoparticles synthesized via sol-gel route for an efficient detection of volatile organic compounds at room temperature

Porous nanocrystalline hafnium oxide (HfO2) powder was synthesized by a low-cost sol-gel route using ethylene glycol and citric acid as polymerizing and chelating reagents. The prepared sol decomposed and crystallized above 370 °C as obtained from the thermogravimetric analysis. HfO2 powders were prepared at four different calcination temperatures, viz. 500 °C, 600 °C, 700 °C and 800 °C. XRD and FTIR analysis confirmed the formation of monoclinic phase of hafnium oxide. The surface morphology of the prepared samples was examined through the FESEM technique. The optical properties were investigated from UV–Vis diffuse reflectance spectra. The BET surface areas, measured from the N2 adsorption-desorption method, were found to vary from 13.31 m2/g to 20.70 m2/g. The gas sensor characteristics of HfO2 were studied by employing three volatile organic compound gasses– acetone, ethanol and formaldehyde. The XPS analysis of the sample confirms the presence of a significant amount of oxygen vacancies within HfO2 lattice. Hafnium oxide-based gas sensor was found to exhibit an enhanced response at room temperature under ethanol and formaldehyde gas exposure. Furthermore, the linear response, stability, shorter response and recovery time made it a promising candidate for gas sensing applications.

Putative fossils of chemotrophic microbes preserved in seep carbonates from Vestnesa Ridge, off northwest Svalbard, Norway

ABSTRACT The microbial key players at methane seeps are methanotrophic archaea and sulfate-reducing bacteria. They form spherical aggregates and jointly mediate the sulfate-dependent anaerobic oxidation of methane (SD–AOM: CH4 + SO42− → HCO3− + HS− + H2O), thereby inducing the precipitation of authigenic seep carbonates. While seep carbonates constitute valuable archives for molecular fossils of SD–AOM-mediating microbes, no microfossils have been identified as AOM aggregates to date. We report clustered spherical microstructures engulfed in 13C-depleted aragonite cement (δ13C values as low as −33‰) of Pleistocene seep carbonates. The clusters comprise Mg-calcite spheres between ∼5 µm (single spheres) and ∼30 µm (clusters) in diameter. Scanning and transmission electron microscopy revealed a porous nanocrystalline fabric in the core area of the spheres surrounded by one or two concentric layers of Mg-calcite crystals. In situ measured sphere δ13C values as low as −42‰ indicate that methane-derived carbon is the dominant carbon source. The size and concentric layering of the spheres resembles mineralized aggregates of natural anaerobic methanotrophic archaea (ANME) of the ANME-2 group surrounded by one or two layers of sulfate-reducing bacteria. Abundant carbonate-bound 13C-depleted lipid biomarkers of archaea and bacteria indicative of the ANME-2-Desulfosarcina/Desulfococcus consortium agree with SD–AOM-mediating microbes as critical agents of carbonate precipitation. Given the morphological resemblance, in concert with negative in situ δ13C values and abundant SD–AOM-diagnostic biomarkers, the clustered spheres likely represent fossils of SD–AOM-mediating microbes.

Effect of Different Polyethylene Glycol (PEG) and Ethyl Cellulose on Impedance Spectroscopy of CuGaO2 Film

Delafossite materials (CuIMIIIO2) are p-type metal oxides which can be used as hole transport layers in a wide range of heterojunction solar cells. These materials are interesting because of their crystal structure that can facilitate hole diffusion through the valance band. Maximizing the interfacial capacitance within porous nanocrystalline films of CuGaO2 is a primary goal for enhancing their performance in solar cells. The electrochemistry of CuGaO2 can reveal much information about the capacitance of the material and therefore the electronic density of valance band states. Here we have investigated the structural and electrochemical properties of CuGaO2 nanocrystalline thin films in acetonitrile solution with LiClO4 electrolyte. Nanocrystalline films are produced by dispersion of CuGaO2 nanocrystals in a polymer solution designed to control the porosity of the resulting film. We have used different molecular weights of polyethylene glycol and two different chain lengths of ethyl cellulose polymers to understand their impact on film morphology. As the film capacitance is related to surface area, a more porous film is expected to increase the film capacitance. In addition, we have also varied the CuGaO2 : polymer ratio to find the optimum condition for enhanced film capacitance. The films were characterized by powder XRD where peak ratios for (003)/(006) and (012)/(006) planes were calculated to understand the orientation of nanocrystals within the film. Electrochemical Impedance Spectroscopy (EIS) was used to probe the electrochemical behavior and capacitance of the films. We are particularly observing the Creal values at low frequency for comparative study of various films. These studies find that Creal is maximized for the ethyl cellulose polymers and a 2:1 ratio of CuGaO2 : polymer mixture.

Mechanical Strength Enhancement of Porous Nanocrystalline-Silicon (pnc-Si) Membrane via Titanium-oxide (Ti-O) Coating

Porous nanocrystalline silicon (pnc-Si) membrane is mainly studied as a blood filtration membrane, mimicking the glomerulus filtration membrane of a human kidney. However, the pnc-Si material itself is not hemocompatible and enormous membrane area to thickness ratio makes the membrane to be easily fractured. Silicon surface modification via titanium-oxide (Ti-O) thin film layer deposition has been proven to be hemocompatible and the presence of Ti-O layer has been numerically studied to give higher membrane flexural strength. In this work, square pnc-Si membranes of 2 mm × 2 mm × 20 nm size have been fabricated with and without Ti-O layer. Point loading-unloading nanoindentation method has been performed and the membranes’ displacement behaviour subjected to point loads is studied. The pnc-Si membranes with Ti-O layer were found to attain higher fracture strength, membrane bending stiffness and average hardness with the increase of ~20, ~11 and ~24%, respectively, compared to bare pnc-Si membranes. The mechanical strength of a free-standing pnc-Si membrane is improved by depositing a Ti-O thin film layer on the membrane structure.

Multi-layers of TiO2 nanoparticles in the photoelectrode and binary iodides in the gel polymer electrolyte based on poly(ethylene oxide) to improve quasi solid-state dye-sensitized solar cells

A gel electrolyte based on poly(ethylene oxide) is optimized in order to improve dye-sensitized solar cells (DSCs) by varying the contents of a binary mixture of salts, LiI, and Hex4NI (tetrahexylammonium iodide). Two series of electrolytes, one excluding and the other including 1-butyl-3-methylimidazolium iodide (BMII) and 4-tert-butylpyridine (4TBP), are investigated. The added BMII and 4TBP improve the conductivity in electrolytes. The highest conductivities at all the measured temperatures are shown by the electrolyte which includes BMII and 4TBP along with the Hex4NI:LiI molar ratio of 3:2. This composition in gel polymer electrolyte exhibits relatively high ionic conductivities, 4.44 × 10−3 and 6.93 × 10−3 S cm−1 at 25 and 50 °C, respectively. Quadruple-layered and highly porous nanocrystalline photoelectrodes that are prepared by spin coating TiO2 nanoparticles of the size 13 and 21 nm were used for the DSC preparation. DSCs that are assembled with BMII and 4TBP added electrolytes exhibit higher efficiencies. The DSC fabricated using the electrolyte having performance enhancers along with Hex4NI:LiI molar ratio of 2:3 and the photoelectrode having quadruple layers of TiO2 nanoparticles exhibit the highest short-circuit current density (11.1 mA cm−2), open-circuit voltage (770 mV), and efficiency (5.58%). The stability of the DSC performances is monitored by measuring current-voltage as a function of time. The cell optimized in this study exhibits a good short-term stability. The positive effects of TiO2 nanoparticle multilayers in the photoelectrodes, as well as of binary salt and performance enhancers in the electrolyte, are successfully utilized to enhance the performance of DSCs.

Porous nanocrystalline WO3 thin films: fabrication, electrical and optical properties

A well-designed procedure, including ion beam sputtering of aluminium (Al)–tungsten trioxide (WO3) composite films, annealing at an elevated temperature and dealloying of aluminium component, was carried out in sequence to fabricate porous nanocrystalline tungsten trioxide thin films. The texture, morphology and electrical and optical properties of the tungsten trioxide thin films were each characterised. It was found that when the annealing temperature of the aluminium–tungsten trioxide composite film reached 550°C, the obtained tungsten trioxide thin film after dealloying was nanocrystalline with a more pronounced porous structure. Electrical property tests showed that in contrast to that of amorphous tungsten trioxide films, the resistance of the porous nanocrystalline tungsten trioxide film was much greater, with a positive temperature coefficient of resistance (TCR) of +4.1 × 10−2/°C at temperatures of −10 to 5°C and a negative TCR of −2.4 × 10−2/°C at temperatures of 5 to 30°C. It was further demonstrated by ultraviolet–visible spectroscopy that compared with amorphous tungsten trioxide films, the porous crystalline tungsten trioxide film had much higher transmittance at the wavelength of visible light and a larger forbidden band width of 2.75 eV. Therefore, the porous nanocrystalline tungsten trioxide film exhibits unique or excellent electrical and optical properties, which indicate new potential applications in the fields of photoelectric devices and thermistors.