Porous Nanocrystalline Research Articles

Template confined synthetic strategy for three-dimensional free-standing hierarchical porous nanocrystalline tantalum

A template-confined strategy for preparing three-dimensional (3D) porous nanocrystalline tantalum was demonstrated. Free-standing hierarchical porous tantalum monoliths have been obtained for the first time from tantalum oxide xerogels as templates via low temperature magnesiothermic reduction. The similar morphology of tantalum products to that of tantalum oxide xerogels was retained after magnesiothermic reduction and hydrochloric acid etching. Monolithic porous tantalum is composed of cubic Ta nanocrystals, and possessed a high Brunauer-Emmett-Teller (BET) specific surface area (58m2/g). The synthetic mechanism of porous nanocrystlline tantalum was also described. More importantly, combining the template confined route with displacement reaction, the strategy could be used to prepare 3D porous metals from porous metal oxides under relatively mild conditions.

High-performance, low-voltage electroosmotic pumps with molecularly thin silicon nanomembranes

Significance Electroosmotic pumps (EOPs) are a class of pumps in which fluid is driven through a capillary or porous media within an electric field. Current research on EOPs concerns the development of new materials in which high electroosmotic flow rates can be achieved for low voltages. Such pumps could be used for portable microfluidic devices. Porous nanocrystalline silicon (pnc-Si) is a material that is formed into a 15-nm-thick nanomembrane. pnc-Si membranes are shown here to have high electroosmotic flow rates at low applied voltages due to the high electric fields achieved over the ultrathin membrane. A prototype EOP was designed using pnc-Si membranes and shown to pressurize fluid through capillary tubing at voltages as low as 250 mV.

Light Harvest Properties of Dye-Sensitized Solar Cells with Different Spatial Configurations of Reflecting Layer

Dye-sensitized solar cells (DSSCs) were fabricated using an additional porous nanocrystalline titanium oxide reflecting layer in order to improve light harvesting properties. Because of the high reflectance and scattering characters of the nanocrystalline titanium oxide, photocurrent conversion efficiency and short circuit current density of DSSCs were improved. This study reports the relationship between the spatial configuration of the additional reflecting layer and the performance enhancement of DSSCs in order to investigate the optimal condition and the origin of the improved performance because spatial configuration can effect on properties positively or negatively. As the result, we can determine the best spatial configuration of reflecting layer, which have shown photo conversion efficiency enhancement (17.32%).

Hardness of porous nanocrystalline Co-Ni electrodeposits

The Hall-Petch relationship can fail when the grain size is below a critical value of tens of nanometres. This occurs particularly for coatings having porous surfaces. In this study, electrodeposited nanostructured Co-Ni coatings from four different nickel electroplating baths having grain sizes in the range of 11–23 nm have been investigated. The finest grain size, approximately 11 nm, was obtained from a coating developed from the nickel sulphate bath. The Co-Ni coatings have a mixed face centred cubic and hexagonal close-packed structures with varying surface morphologies and different porosities. A cluster-pore mixture model has been proposed by considering no contribution from pores to the hardness. As the porosity effect was taken into consideration, the calculated pore-free hardness is in agreement with the ordinary Hall-Petch relationship even when the grain size is reduced to 11 nm for the Co-Ni coatings with 77±2 at% cobalt. The present model was applied to other porous nanocrystalline coatings, and the Hall-Petch relationship was maintained.

Adsorption and Desorption of Methylene Blue on Porous Carbon Monoliths and Nanocrystalline Cellulose

The dynamic batch adsorption of methylene blue (MB), a widely used and toxic dye, onto nanocrystalline cellulose (NCC) and crushed powder of carbon monolith (CM) was investigated using the pseudo-first- and -second-order kinetics. CM outperformed NCC with a maximum capacity of 127 mg/g compared to 101 mg/g for NCC. The Langmuir isotherm model was applicable for describing the binding data for MB on CM and NCC, indicating the homogeneous surface of these two materials. The Gibbs free energy of -15.22 kJ/mol estimated for CM unravelled the spontaneous nature of this adsorbent for MB, appreciably faster than the use of NCC (-4.47 kJ/mol). Both pH and temperature exhibited only a modest effect on the adsorption of MB onto CM. The desorption of MB from CM using acetonitrile was very effective with more than 94 % of MB desorbed from CM within 10 min to allow the reusability of this porous carbon material. In contrast, acetonitrile was less effective than ethanol in desorbing MB from NCC. The two solvents were incapable of completely desorbing MB on commercial granular coal-derived activated carbon.

Electrocapillary coupling coefficients for hydrogen electrosorption on palladium

The surface stress f, a capillary force at solid surfaces, has important implications for the behavior of nanomaterials. Surface stress is known to vary considerably when atoms adsorb on the surface, yet the underlying mechanisms are poorly understood. Our in situ dilatometry study of H adsorption on porous nanocrystalline Pd provides quantitative data for the response of f to changes in the adsorbate coverage. The porous body is immersed in aqueous electrolyte and H adsorption is controlled and measured electrochemically. The surface stress response is quantified by means of the electrocapillary coupling parameter, ς, defined as the derivative of f with respect to the superficial charge density. The results support previous, more indirect, findings for ς. We show that ς is precisely predicted by a model based on the continuum mechanics of superficial layers containing misfitting solute.

A novel synthesis of CNTs/TiO2 nanocomposites with enhanced performance as photoanode of solar cell

TiO2 nanoparticles are widely used in dye-sensitized solar cells (DSSCs). The combination of one-dimensional materials such as carbon nanotubes (CNTs) with TiO2 nanocrystals by mechanical mixing has been expected to improve the electron transport of anode. However, these methods cannot ensure the connection between one-dimensional materials and collector, which is the key for exerting the fast electron transport property. In this study, a novel synthesis method named gel chapping for CNTs/TiO2 nanocomposites preparation is presented, in which porous nanocrystalline TiO2 film with through-hole cracks is fabricated. By using the porous films with cracks as templates, CNTs are deposited in pores and well connected with the template and current collector which favors the transportation of electrons. The current–voltage curve test reveals that the conversion efficiency of CNTs/TiO2 nanocrystalline composite structures is 2.6 times superior to TiO2 nanocrystalline film.

In situ monitoring magnetism and resistance of nanophase platinum upon electrochemical oxidation

Controlled tuning of material properties by external stimuli represents one of the major topics of current research in the field of functional materials. Electrochemically induced property tuning has recently emerged as a promising pathway in this direction making use of nanophase materials with a high fraction of electrode-electrolyte interfaces. The present letter reports on electrochemical property tuning of porous nanocrystalline Pt. Deeper insight into the underlying processes could be gained by means of a direct comparison of the charge-induced response of two different properties, namely electrical resistance and magnetic moment. For this purpose, four-point resistance measurements and SQUID magnetometry were performed under identical in situ electrochemical control focussing on the regime of electrooxidation. Fully reversible variations of the electrical resistance and the magnetic moment of 6% and 1% were observed upon the formation or dissolution of a subatomic chemisorbed oxygen surface layer, respectively. The increase of the resistance, which is directly correlated to the amount of deposited oxygen, is considered to be primarily caused by charge-carrier scattering processes at the metal–electrolyte interfaces. In comparison, the decrease of the magnetic moment upon positive charging appears to be governed by the electric field at the nanocrystallite–electrolyte interfaces due to spin–orbit coupling.

Proton Conduction in Dense and Porous Nanocrystalline Ceria Thin Films

AbstractThe electrical conductivity of ceria thin films (epitaxial as well as dense and porous nanocrystalline) is investigated in dry and wet atmosphere at temperatures below 500 °C. For the epitaxial and the fully dense nanocrystalline samples, no significant differences can be observed between dry and wet conditions. In marked contrast, the nanocrystalline porous films obtained via spin coating exhibit a considerable enhancement of the protonic conductivity below 300 °C in wet atmosphere. This outcome reveals that the residual open mesoporosity plays the key role for the enhancement of the proton transport at low temperatures and not the high density of grain boundaries. The quantitative analysis of the various pathways, along which the proton transport can take place, indicates that the observed proton conduction can arise not only from bulk water adsorbed in the open pores but also from the space charge zones on the water side of the water/oxide interface.

Deposition of Highly Porous Nanocrystalline Platinum on Functionalized Substrates Through Fluorine-Induced Decomposition of Pt(PF3 )4 Adsorbates

Nanocrystalline platinum is synthesized at room temperature by co-injecting Pt(PF3)4 and XeF2 vapors onto solid supports in vacuum. The Pt nucleation time scales with chemisorbed fluorine coverage, which is controlled by pre-dosing supports with XeF2, and by optional electron or ion beam irradiation under flowing XeF2. The latter is used to increase the chemisorbed fluorine coverage and localize the Pt growth process.

Correction to Electrochemical Mineralization of Perfluorocarboxylic Acids (PFCAs) by Ce-doped Modified Porous Nanocrystalline PbO2 Film Electrode

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionCorrection to Electrochemical Mineralization of Perfluorocarboxylic Acids (PFCAs) by Ce-doped Modified Porous Nanocrystalline PbO2 Film ElectrodeJunfeng Niu*, Hui Lin, Jiale Xu, Hao Wu, and Yangyang LiView Author Information State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, P.R. China*Phone: +86-10-5880 7612; fax: +86-10-5880 7612; e-mail: [email protected]Cite this: Environ. Sci. Technol. 2013, 47, 9, 4959Publication Date (Web):April 22, 2013Publication History Published online22 April 2013Published inissue 7 May 2013https://doi.org/10.1021/es401587yCopyright © 2013 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views918Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (120 KB) Get e-Alerts Get e-Alerts

Optically transparent and permeable microarrays for cellular assays

A new class of porous membrane, porous nanocrystalline silicon (pnc‐Si), offers a unique combination of nanoscale thickness (< 100 nm) and tunable pore sizes in the range of 5 to 100 nm. Pnc‐Si is ideally suited for small volume cell culture devices because the nanometer thinness and high permeability enable rapid diffusion of low abundance species with minimal loss. Two cell types can be cultured within tens of nanometers of one another, allowing cell‐cell communication and other microenvironment‐dependent co‐culture studies. We have developed an approach to create microwells on these suspended membranes using photopolymerized PEG. Cells grown within these microwells are spatially separated, but can readily communicate through the membrane with a feeder cell layer or with neighboring microwells due to PEG permeability. Additionally, pnc‐Si membranes are extraordinarily transparent to light, permitting their use in image‐based, high‐content screening assays. Sources of Funding: NIH and RIT.

Photocurrent improvement in nanocrystalline Cu2ZnSnS4 photocathodes by introducing porous structures

Cu2ZnSnS4 (CZTS) is a potential low-cost photocathode material for solar water splitting. In this study, we prepare dense and porous nanocrystalline Cu2ZnSnS4 films by a facile metal organic decomposition (MOD) method. The porous structures are adjusted by varying the amount of thiourea in the precursor solution. The porous CZTS photocathode yields 3 times higher photocurrent than that of the dense electrode. Thermogravimetric/differential thermal analysis shows that the porous structure comes from decomposition of excess thiourea. Different characterization methods, such as X-ray diffraction, Raman spectroscopy, energy-dispersive X-ray spectroscopy, SEM and UV-vis-NIR transmission, have been carried out to analyze the mechanism of photocurrent improvement. The results suggest that the dense and the porous CZTS photocathodes have similar crystallinity, composition, thickness and light absorption. The relative electrochemical active area indicates that shortening of the electron transport distance is a possible reason for photocurrent improvement in the porous CZTS photocathode.

Synthesis and Characterization of Porous Nano-Crystalline Barium Hexaferrite

Barium hexaferrite/high density polyethylene composite was prepared from synthesized barium hexaferrite as matrix with 0, 10, 20, 30, 40 wt.% of high density polyethylene via a high energy planetary ball milling for 10 h. The milling products were isostatically pressed and finally sintered at 1250 °C for 1 h. Effect of HDPE content on morphology of the products were investigated using scanning electron microscope (SEM). Vibrating samplemagnetometer (VSM) analysis of single phase BaFe12O19 indicates saturation magnetization and coercivity of 52 emu/g and 4300 Oe, respectively. Visually, as the weight percent of the HDPE increases, more porous structure was observed. Moreover, the density of the sintered sampleslinearly decreased from 4.16 to 1.41 g/cm3 by increasing the amount of HDPE from 0 to 40 wt.%.

Porous nanocrystalline TiO2 with high lithium-ion insertion performance

Porous nanocrystalline anatase TiO2 was prepared by a modified hydrolytic route coupled with an intermediary amorphization/recrystallization process. The phase structure and morphology of the products were analyzed by X-ray diffraction, transmission electron microscopy, and field-emission scanning electron microscopy. The electrochemical properties were investigated by cyclic voltammetry, constant current discharge–charge tests, and electrochemical impedance techniques. Applied as an anode in a lithium-ion battery, the material exhibited excellent specific capacities of 130 mAh g−1 (at the rate of 2000 mA g−1) and 96 mAh g−1 (at the rate of 4000 mA g−1) after 100 cycles; the coulombic efficiency was ~99.5 %, indicating excellent rate capability and reversibility. Furthermore, the electrochemical impedance spectra showed improved electrode kinetics after cycling. These results indicate that the porous nanocrystalline TiO2 synthesized by this improved synthesis route might be a promising anode material for high energy and high power density lithium-ion battery applications.

High Photoconductive Response of Gas-Sensitized Porous Nanocrystalline TiO2 Film in Formaldehyde Ambience and Carrier Transport Kinetics

We propose a gas-sensitized porous nanocrystalline TiO2 film with a potential application in photovoltaic devices and report about the systematic photoconductivity study of it. The quantitative results show that the gas-sensitized TiO2 film in formaldehyde atmosphere exhibits much higher photoconductivity (3–4 orders of magnitude) and longer carrier lifetime than usual. The intriguing performance of the gas-sensitized TiO2 film indicates the distinct charge carrier transport kinetic courses, whose contributions to the photoconductivity are shown in a designed flowchart. From the flowchart, it is clearly found that two electron loss processes, recombination and electron scavenging, are suppressed for the gas-sensitized TiO2 film in formaldehyde gas, leading to large improvements of photoconductivity and carrier lifetime. The results provide the potential of improving efficiency of photovoltaic devices, and measuring photoconductivity under target gas appears to be a useful tool for research on photocatalytic and photoelectrical processes.

Electrochemical Mineralization of Perfluorocarboxylic Acids (PFCAs) by Ce-Doped Modified Porous Nanocrystalline PbO2 Film Electrode

The Ce-doped modified porous nanocrystalline PbO(2) film electrode prepared by electrodeposition technology was used for electrochemical mineralization of environmentally persistent perfluorinated carboxylic acids (PFCAs) (~C(4)-C(8)), i.e., perfluorobutanoic acid (PFBA), perfluopentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoheptanoic acid (PFHpA), and perfluorooctanoic acid (PFOA) in aqueous solution (100 mL of 100 mg L(-1)). The degradation of PFCAs follows pseudo-first-order kinetics, and the values of the relative rate constant (k) depend upon chain length k(PFHpA) (4.1 × 10(-2) min(-1); corresponding half-life 16.8 min) ≈ 1.1k(PFOA) ≈ 2.5k(PFHxA)≈ 6.9k(PFPeA) ≈ 9.7k(PFBA). The carbon mineralization indices [i.e., 1 - (TOC(insolution)/TOC(inPFCA,degraded))] were 0.49, 0.70, 0.84, 0.91, and 0.95 for PFBA, PFPeA, PFHxA, PFHpA, and PFOA, respectively, after 90 min electrolysis. The major mineralization product, F(-), as well as low amount of intermediate PFCAs with shortened chain lengths were detected in aqueous solution. By observing the intermediates and tracking the concentration change, a possible pathway of electrochemical mineralization is proposed as follows: Kolbe decarboxylation reaction occurs first at the anode to form the perfluoroalkyl radical, followed by reaction with hydroxyl radicals to form the perfluoroalkyl alcohol which then undergoes intramolecular rearrangement to form the perfluoroalkyl fluoride. After this, the perfluoroalkyl fluoride reforms perfluorinated carboxylic with shorter chain length than its origin by hydrolysis. This electrochemical technique could be employed to treat PFCAs (~C(4)-C(8)) in contaminated wastewater.

Vertical geometry ultraviolet photodetectors with high photosensitivity based on nanocrystalline TiO2 films

Porous and dense nanocrystalline TiO2 films grown on F:SnO substrates used in vertical geometry ultraviolet photodetectors are investigated. Compared with a detector with a dense nanocrystalline TiO2 film (D-detector), a detector with a porous nanocrystalline TiO2 film (P-detector) exhibits one order of magnitude higher responsivity due to a light scattering effect. In addition, the vertical geometry detectors show a fast response time. The rise time and decay time of the P-detector and D-detector are 19 and 136ns, and 14 and 100ns, respectively, which are six orders of magnitude faster than those of lateral geometry detectors based on dense nanocrystalline TiO2 films. It is a result of a decreased mobility fluctuation.

Characterization of Pure Titanium and Ti6Al4V Alloy Modified by Plasma Electrolytic Carbonitriding Process

Porous nanocrystalline thick Ti (CxN1-x) films which bond firmly to the substrate are obtained on commercially pure titanium and Ti6Al4V alloy by plasma electrolytic carbonitriding (PECN) treatment. The microstructures and compositions of the modified layer on different substrates were compared. The results showed that the modified layer is composed of the outer Ti (CxN1-x) film and the diffusion layer. When discharge-treated for 150 min, the thickness of the Ti (CxN1-x) film is ~15μm, irrespective of the different substrate. The TiH2 riched diffusion layer which is 40-45μm thick is located beneath the Ti (CxN1-x) film for the pure titanium substrate, while for Ti6Al4V alloy it is the β-Ti-riched layer which is ~100 μm thick.

Quantitative Imaging of Ion Transport through Single Nanopores by High-Resolution Scanning Electrochemical Microscopy

Here we report on the unprecedentedly high resolution imaging of ion transport through single nanopores by scanning electrochemical microscopy (SECM). The quantitative SECM image of single nanopores allows for the determination of their structural properties, including their density, shape, and size, which are essential for understanding the permeability of the entire nanoporous membrane. Nanoscale spatial resolution was achieved by scanning a 17 nm radius pipet tip at a distance as low as 1.3 nm from a highly porous nanocrystalline silicon membrane in order to obtain the peak current response controlled by the nanopore-mediated diffusional transport of tetrabutylammonium ions to the nanopipet-supported liquid-liquid interface. A 280 nm × 500 nm image resolved 13 nanopores, which corresponds to a high density of 93 nanopores/μm(2). A finite element simulation of the SECM image was performed to assess quantitatively the spatial resolution limited by the tip diameter in resolving two adjacent pores and to determine the actual size of a nanopore, which was approximated as an elliptical cylinder with a depth of 30 nm and major and minor axes of 53 and 41 nm, respectively. These structural parameters were consistent with those determined by transmission electron microscopy, thereby confirming the reliability of quantitative SECM imaging at the nanoscale level.