Research

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9 pages, 880 KiB

Open AccessArticle

Towards the Development of Electrical Biosensors Based on Nanostructured Porous Silicon

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Gonzalo Recio-Sánchez

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Materials 2010, 3(2), 755-763; https://doi.org/10.3390/ma3020755 - 27 Jan 2010

Cited by 16 | Viewed by 13984

Abstract

The typical large specific surface area and high reactivity of nanostructured porous silicon (nanoPS) make this material very suitable for the development of sensors. Moreover, its biocompatibility and biodegradability opens the way to the development of biosensors. As such, in this work the [...] Read more.

The typical large specific surface area and high reactivity of nanostructured porous silicon (nanoPS) make this material very suitable for the development of sensors. Moreover, its biocompatibility and biodegradability opens the way to the development of biosensors. As such, in this work the use of nanoPS in the field of electrical biosensing is explored. More specifically, nanoPS-based devices with Al/nanoPS/Al and Au-NiCr/nanoPS/Au-NiCr structures were fabricated for the electrical detection of glucose and Escherichia Coli bacteria at different concentrations. The experimental results show that the current-voltage characteristics of these symmetric metal/nanoPS/metal structures strongly depend on the presence/absence and concentration of species immobilized on the surface. Full article

(This article belongs to the Special Issue Porous Materials)

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14 pages, 1576 KiB

Open AccessArticle

Preparation and Hydrogen Absorption/Desorption of Nanoporous Palladium Thin Films

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Wen-Chung Li

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Thomas John Balk

Materials 2009, 2(4), 2496-2509; https://doi.org/10.3390/ma2042496 - 23 Dec 2009

Cited by 17 | Viewed by 16278

Abstract

Nanoporous Pd (np-Pd) was prepared by co-sputtering Pd-Ni alloy films onto Si substrates, followed by chemical dealloying with sulfuric acid. X-ray diffractometry and chemical analysis were used to track the extent of dealloying. The np-Pd structure was changed from particle-like to sponge-like by [...] Read more.

Nanoporous Pd (np-Pd) was prepared by co-sputtering Pd-Ni alloy films onto Si substrates, followed by chemical dealloying with sulfuric acid. X-ray diffractometry and chemical analysis were used to track the extent of dealloying. The np-Pd structure was changed from particle-like to sponge-like by diluting the sulfuric acid etchant. Using suitable precursor alloy composition and dealloying conditions, np-Pd films were prepared with uniform and open sponge-like structures, with interconnected ligaments and no cracks, yielding a large amount of surface area for reactions with hydrogen. Np-Pd films exhibited shorter response time for hydrogen absorption/desorption than dense Pd films, showing promise for hydrogen sensing. Full article

(This article belongs to the Special Issue Porous Materials)

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9 pages, 822 KiB

Open AccessArticle

A Self-Propagating Foaming Process of Porous Al-Ni Intermetallics Assisted by Combustion Reactions

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Makoto Kobashi

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Naoyuki Kanetake

Materials 2009, 2(4), 2360-2368; https://doi.org/10.3390/ma2042360 - 15 Dec 2009

Cited by 9 | Viewed by 13607

Abstract

The self-propagating foaming process of porous Al-Ni intermetallics was investigated. Aluminum and nickel powders were blended, and titanium and boron carbide powders were added as reactive exothermic agents. The blended powder was extruded to make a rod-shape precursor. Only one end of the [...] Read more.

The self-propagating foaming process of porous Al-Ni intermetallics was investigated. Aluminum and nickel powders were blended, and titanium and boron carbide powders were added as reactive exothermic agents. The blended powder was extruded to make a rod-shape precursor. Only one end of the rod precursor was heated to ignite the reaction. The reaction propagated spontaneously throughout the precursor. Pore formation took place at the same time as the reaction occurred. Adding the exothermic agent was effective to increase the porosity. Preheating the precursor before the ignition was also very effective to produce porous Al-Ni intermetallics with high porosity. Full article

(This article belongs to the Special Issue Porous Materials)

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23 pages, 1389 KiB

Open AccessArticle

Highly Loaded Fe-MCM-41 Materials: Synthesis and Reducibility Studies

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Malose P. Mokhonoana

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Neil J. Coville

Materials 2009, 2(4), 2337-2359; https://doi.org/10.3390/ma2042337 - 15 Dec 2009

Cited by 18 | Viewed by 14325

Abstract

Fe-MCM-41 materials were prepared by different methods. The Fe was both incorporated into the structure and formed crystallites attached to the silica. High Fe content MCM-41 (~16 wt%) with retention of mesoporosity and long-range order was achieved by a range of new synthetic [...] Read more.

Fe-MCM-41 materials were prepared by different methods. The Fe was both incorporated into the structure and formed crystallites attached to the silica. High Fe content MCM-41 (~16 wt%) with retention of mesoporosity and long-range order was achieved by a range of new synthetic methodologies: (i) by delaying the addition of Fe³⁺(aq) to the stirred synthesis gel by 2 h, (ii) by addition of Fe³⁺ precursor as a freshlyprecipitated aqueous slurry, (iii) by exploiting a secondary synthesis with Si-MCM-41 as SiO₂ source. For comparative purposes the MCM-41 was also prepared by incipient wetness impregnation (IWI). Although all these synthesis methods preserved mesoporosity and long-range order of the SiO₂ matrix, the hydrothermally-fabricated Fe materials prepared via the secondary synthesis route has the most useful properties for exploitation as a catalyst, in terms of hydrothermal stability of the resulting support. Temperatureprogrammed reduction (TPR) studies revealed a three-peak reduction pattern for this material instead of the commonly observed two-peak reduction pattern. The three peaks showed variable intensity that related to the presence of two components: crystalline Fe₂O₃ and Fe embedded in the SiO₂ matrix (on the basis of ESR studies). The role of secondary synthesis of Si-MCM-41 on the iron reducibility was also demonstrated in IWI of sec-Si-MCM-41. Full article

(This article belongs to the Special Issue Porous Materials)

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6 pages, 512 KiB

Open AccessArticle

Porous Ba Ferrite Prepared from Wood Template

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Materials 2009, 2(4), 1923-1928; https://doi.org/10.3390/ma2041923 - 20 Nov 2009

Cited by 7 | Viewed by 12443

Abstract

Ba ferrite materials with porous microstructures were prepared from a natural cedar wood template in order to investigate new electromagnetic shielding materials. The wood templates were infiltrated with barium nitrate and iron nitrate solutions (molar ratio = 1:12) and dried to form ferrite [...] Read more.

Ba ferrite materials with porous microstructures were prepared from a natural cedar wood template in order to investigate new electromagnetic shielding materials. The wood templates were infiltrated with barium nitrate and iron nitrate solutions (molar ratio = 1:12) and dried to form ferrite gel, then, they were sintered in air at a temperature between 800 °C and 1400 °C. The 1-dimensional porous structures were retained after sintering and the pore size was approximately 10–20 μm. These ferrites show large coercive force and anisotropy field. The largest coercive force was obtained for the specimen sintered at 800 °C. Full article

(This article belongs to the Special Issue Porous Materials)

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8 pages, 1391 KiB

Open AccessArticle

Porous Thermoelectric Materials

by

Hiroshi Julian Goldsmid

Materials 2009, 2(3), 903-910; https://doi.org/10.3390/ma2030903 - 05 Aug 2009

Cited by 35 | Viewed by 16029

Abstract

Thermoelectric materials are sometimes prepared using a sintering process in which the achievement of a high density is often one of the objectives. However, it has recently been shown that the introduction of a highly porous material is desirable in synthetic transverse thermoelements. [...] Read more.

Thermoelectric materials are sometimes prepared using a sintering process in which the achievement of a high density is often one of the objectives. However, it has recently been shown that the introduction of a highly porous material is desirable in synthetic transverse thermoelements. Porosity may also be an advantage in conventional longitudinal thermoelectric modules in which a high thermal flux density creates problems, but heat transfer within the pores can degrade the thermoelectric figure of merit. The amount of this degradation is calculated and it is shown that it can be small enough to be acceptable in practical devices. Full article

(This article belongs to the Special Issue Porous Materials)

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Review

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71 pages, 5734 KiB

Open AccessReview

Macroporous Semiconductors

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Materials 2010, 3(5), 3006-3076; https://doi.org/10.3390/ma3053006 - 07 May 2010

Cited by 54 | Viewed by 12371

Abstract

Pores in single crystalline semiconductors come in many forms (e.g., pore sizes from 2 nm to > 10 µm; morphologies from perfect pore crystal to fractal) and exhibit many unique properties directly or as nanocompounds if the pores are filled. The various kinds [...] Read more.

Pores in single crystalline semiconductors come in many forms (e.g., pore sizes from 2 nm to > 10 µm; morphologies from perfect pore crystal to fractal) and exhibit many unique properties directly or as nanocompounds if the pores are filled. The various kinds of pores obtained in semiconductors like Ge, Si, III-V, and II-VI compound semiconductors are systematically reviewed, emphasizing macropores. Essentials of pore formation mechanisms will be discussed, focusing on differences and some open questions but in particular on common properties. Possible applications of porous semiconductors, including for example high explosives, high efficiency electrodes for Li ion batteries, drug delivery systems, solar cells, thermoelectric elements and many novel electronic, optical or sensor devices, will be introduced and discussed. Full article

(This article belongs to the Special Issue Porous Materials)

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56 pages, 5214 KiB

Open AccessReview

Porous Silicon—A Versatile Host Material

by

Petra Granitzer

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Klemens Rumpf

Materials 2010, 3(2), 943-998; https://doi.org/10.3390/ma3020943 - 03 Feb 2010

Cited by 157 | Viewed by 20286

Abstract

This work reviews the use of porous silicon (PS) as a nanomaterial which is extensively investigated and utilized for various applications, e.g., in the fields of optics, sensor technology and biomedicine. Furthermore the combination of PS with one or more materials which are [...] Read more.

This work reviews the use of porous silicon (PS) as a nanomaterial which is extensively investigated and utilized for various applications, e.g., in the fields of optics, sensor technology and biomedicine. Furthermore the combination of PS with one or more materials which are also nanostructured due to their deposition within the porous matrix is discussed. Such nanocompounds offer a broad avenue of new and interesting properties depending on the kind of involved materials as well as on their morphology. The filling of the pores performed by electroless or electrochemical deposition is described, whereas different morphologies, reaching from micro- to macro pores are utilized as host material which can be self-organized or fabricated by prestructuring. For metal-deposition within the porous structures, both ferromagnetic and non-magnetic metals are used. Emphasis will be put on self-arranged mesoporous silicon, offering a quasi-regular pore arrangement, employed as template for filling with ferromagnetic metals. By varying the deposition parameters the precipitation of the metal structures within the pores can be tuned in geometry and spatial distribution leading to samples with desired magnetic properties. The correlation between morphology and magnetic behaviour of such semiconducting/magnetic systems will be determined. Porous silicon and its combination with a variety of filling materials leads to nanocomposites with specific physical properties caused by the nanometric size and give rise to a multiplicity of potential applications in spintronics, magnetic and magneto-optic devices, nutritional food additives as well as drug delivery. Full article

(This article belongs to the Special Issue Porous Materials)

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37 pages, 932 KiB

Open AccessReview

Influence of Chemical Conditions on the Nanoporous Structure of Silicate Aerogels

by

Katalin Sinkó

Materials 2010, 3(1), 704-740; https://doi.org/10.3390/ma3010704 - 26 Jan 2010

Cited by 132 | Viewed by 20274

Abstract

Silica or various silicate aerogels can be characterized by highly porous, open cell, low density structures. The synthesis parameters influence the three-dimensional porous structures by modifying the kinetics and mechanism of hydrolysis and condensation processes. Numerous investigations have shown that the structure of [...] Read more.

Silica or various silicate aerogels can be characterized by highly porous, open cell, low density structures. The synthesis parameters influence the three-dimensional porous structures by modifying the kinetics and mechanism of hydrolysis and condensation processes. Numerous investigations have shown that the structure of porous materials can be tailored by variations in synthesis conditions (e.g., the type of precursors, catalyst, and surfactants; the ratio of water/precursor; the concentrations; the medium pH; and the solvent). The objectives of this review are to summarize and elucidate the effects of chemical conditions on the nanoporous structure of sol-gel derived silicate aerogels. Full article

(This article belongs to the Special Issue Porous Materials)

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27 pages, 349 KiB

Open AccessReview

Porous Dielectrics in Microelectronic Wiring Applications

by

Vincent McGahay

Materials 2010, 3(1), 536-562; https://doi.org/10.3390/ma3010536 - 18 Jan 2010

Cited by 43 | Viewed by 16324

Abstract

Porous insulators are utilized in the wiring structure of microelectronic devices as a means of reducing, through low dielectric permittivity, power consumption and signal delay in integrated circuits. They are typically based on low density modifications of amorphous SiO₂ known as SiCOH [...] Read more.

Porous insulators are utilized in the wiring structure of microelectronic devices as a means of reducing, through low dielectric permittivity, power consumption and signal delay in integrated circuits. They are typically based on low density modifications of amorphous SiO₂ known as SiCOH or carbon-doped oxides, in which free volume is created through the removal of labile organic phases. Porous dielectrics pose a number of technological challenges related to chemical and mechanical stability, particularly in regard to semiconductor processing methods. This review discusses porous dielectric film preparation techniques, key issues encountered, and mitigation strategies. Full article

(This article belongs to the Special Issue Porous Materials)

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36 pages, 3696 KiB

Open AccessReview

A New Approach to the Computer Modeling of Amorphous Nanoporous Structures of Semiconducting and Metallic Materials: A Review

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Materials 2010, 3(1), 467-502; https://doi.org/10.3390/ma3010467 - 15 Jan 2010

Cited by 15 | Viewed by 17164

Abstract

We review our approach to the generation of nanoporous materials, both semiconducting and metallic, which leads to the existence of nanopores within the bulk structure. This method, which we have named as the expanding lattice method, is a novel transferable approach which consists [...] Read more.

We review our approach to the generation of nanoporous materials, both semiconducting and metallic, which leads to the existence of nanopores within the bulk structure. This method, which we have named as the expanding lattice method, is a novel transferable approach which consists first of constructing crystalline supercells with a large number of atoms and a density close to the real value and then lowering the density by increasing the volume. The resulting supercells are subjected to either ab initio or parameterized—Tersoff-based—molecular dynamics processes at various temperatures, all below the corresponding bulk melting points, followed by geometry relaxations. The resulting samples are essentially amorphous and display pores along some of the “crystallographic” directions without the need of incorporating ad hoc semiconducting atomic structural elements such as graphene-like sheets and/or chain-like patterns (reconstructive simulations) or of reproducing the experimental processes (mimetic simulations). We report radial (pair) distribution functions, nanoporous structures of C and Si, and some computational predictions for their vibrational density of states. We present numerical estimates and discuss possible applications of semiconducting materials for hydrogen storage in potential fuel tanks. Nanopore structures for metallic elements like Al and Au also obtained through the expanding lattice method are reported. Full article

(This article belongs to the Special Issue Porous Materials)

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23 pages, 2881 KiB

Open AccessReview

Recent Developments in Carbon Nanotube Membranes for Water Purification and Gas Separation

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Materials 2010, 3(1), 127-149; https://doi.org/10.3390/ma3010127 - 04 Jan 2010

Cited by 234 | Viewed by 26439

Abstract

Carbon nanotubes (CNTs) are nanoscale cylinders of graphene with exceptional properties such as high mechanical strength, high aspect ratio and large specific surface area. To exploit these properties for membranes, macroscopic structures need to be designed with controlled porosity and pore size. This [...] Read more.

Carbon nanotubes (CNTs) are nanoscale cylinders of graphene with exceptional properties such as high mechanical strength, high aspect ratio and large specific surface area. To exploit these properties for membranes, macroscopic structures need to be designed with controlled porosity and pore size. This manuscript reviews recent progress on two such structures: (i) CNT Bucky-papers, a non-woven, paper like structure of randomly entangled CNTs, and (ii) isoporous CNT membranes, where the hollow CNT interior acts as a membrane pore. The construction of these two types of membranes will be discussed, characterization and permeance results compared, and some promising applications presented. Full article

(This article belongs to the Special Issue Porous Materials)

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38 pages, 635 KiB

Open AccessReview

Macroporous Monolithic Polymers: Preparation and Applications

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Ruben Dario Arrua

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Miriam Cristina Strumia

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Cecilia Inés Alvarez Igarzabal

Materials 2009, 2(4), 2429-2466; https://doi.org/10.3390/ma2042429 - 18 Dec 2009

Cited by 47 | Viewed by 19057

Abstract

In the last years, macroporous monolithic materials have been introduced as a new and useful generation of polymers used in different fields. These polymers may be prepared in a simple way from a homogenous mixture into a mold and contain large interconnected pores [...] Read more.

In the last years, macroporous monolithic materials have been introduced as a new and useful generation of polymers used in different fields. These polymers may be prepared in a simple way from a homogenous mixture into a mold and contain large interconnected pores or channels allowing for high flow rates at moderate pressures. Due to their porous characteristics, they could be used in different processes, such as stationary phases for different types of chromatography, high-throughput bioreactors and in microfluidic chip applications. This review reports the contributions of several groups working in the preparation of different macroporous monoliths and their modification by immobilization of specific ligands on the products for specific purposes. Full article

(This article belongs to the Special Issue Porous Materials)

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25 pages, 1274 KiB

Open AccessReview

Surface Chemistry in Nanoscale Materials

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Materials 2009, 2(4), 2404-2428; https://doi.org/10.3390/ma2042404 - 16 Dec 2009

Cited by 117 | Viewed by 18575

Abstract

Although surfaces or, more precisely, the surface atomic and electronic structure, determine the way materials interact with their environment, the influence of surface chemistry on the bulk of the material is generally considered to be small. However, in the case of high surface [...] Read more.

Although surfaces or, more precisely, the surface atomic and electronic structure, determine the way materials interact with their environment, the influence of surface chemistry on the bulk of the material is generally considered to be small. However, in the case of high surface area materials such as nanoporous solids, surface properties can start to dominate the overall material behavior. This allows one to create new materials with physical and chemical properties that are no longer determined by the bulk material, but by their nanoscale architectures. Here, we discuss several examples, ranging from nanoporous gold to surface engineered carbon aerogels that demonstrate the tuneability of nanoporous solids for sustainable energy applications. Full article

(This article belongs to the Special Issue Porous Materials)

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20 pages, 229 KiB

Open AccessReview

Silk Fibroin Based Porous Materials

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Qiang Zhang

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Shuqin Yan

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Mingzhong Li

Materials 2009, 2(4), 2276-2295; https://doi.org/10.3390/ma2042276 - 09 Dec 2009

Cited by 85 | Viewed by 16382

Abstract

Silk from the Bombyx mori silkworm is a protein-based fiber. Bombyx mori silk fibroin (SF) is one of the most important candidates for biomedical porous material based on its superior machinability, biocompatibility, biodegradation, bioresorbability, and so on. In this paper, we have reviewed [...] Read more.

Silk from the Bombyx mori silkworm is a protein-based fiber. Bombyx mori silk fibroin (SF) is one of the most important candidates for biomedical porous material based on its superior machinability, biocompatibility, biodegradation, bioresorbability, and so on. In this paper, we have reviewed the key features of SF. Moreover we have focused on the morphous, technical processing, and biocompatibility of SF porous materials, followed by the application research. Finally, we provide a perspective the potential and problems of SF porous materials. Full article

(This article belongs to the Special Issue Porous Materials)

28 pages, 2295 KiB

Open AccessReview

Nanoporous Gold: Fabrication, Characterization, and Applications

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Erkin Seker

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Michael L. Reed

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Matthew R. Begley

Materials 2009, 2(4), 2188-2215; https://doi.org/10.3390/ma2042188 - 03 Dec 2009

Cited by 208 | Viewed by 22869

Abstract

Nanoporous gold (np-Au) has intriguing material properties that offer potential benefits for many applications due to its high specific surface area, well-characterized thiol-gold surface chemistry, high electrical conductivity, and reduced stiffness. The research on np-Au has taken place on various fronts, including advanced [...] Read more.

Nanoporous gold (np-Au) has intriguing material properties that offer potential benefits for many applications due to its high specific surface area, well-characterized thiol-gold surface chemistry, high electrical conductivity, and reduced stiffness. The research on np-Au has taken place on various fronts, including advanced microfabrication and characterization techniques to probe unusual nanoscale properties and applications spanning from fuel cells to electrochemical sensors. Here, we provide a review of the recent advances in np-Au research, with special emphasis on microfabrication and characterization techniques. We conclude the paper with a brief outline of challenges to overcome in the study of nanoporous metals. Full article

(This article belongs to the Special Issue Porous Materials)

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36 pages, 501 KiB

Open AccessReview

Modelling of Grain Growth Kinetics in Porous Ceramic Materials under Normal and Irradiation Conditions

by

Mikhail S. Veshchunov

Materials 2009, 2(3), 1252-1287; https://doi.org/10.3390/ma2031252 - 10 Sep 2009

Cited by 19 | Viewed by 14478

Abstract

Effect of porosity on grain growth is both the most frequent and technologically important situation encountered in ceramic materials. Generally this effect occurs during sintering, however, for nuclear fuels it also becomes very important under reactor irradiation conditions. In these cases pores and [...] Read more.

Effect of porosity on grain growth is both the most frequent and technologically important situation encountered in ceramic materials. Generally this effect occurs during sintering, however, for nuclear fuels it also becomes very important under reactor irradiation conditions. In these cases pores and gas bubbles attached to the grain boundaries migrate along with the boundaries, in some circumstances giving a boundary migration controlled by the movement, coalescence and/or sintering of these particles. New mechanisms of intergranular bubble and pore migration which control the mobility of the grain boundary under normal and irradiation conditions are reviewed in this paper. Full article

(This article belongs to the Special Issue Porous Materials)

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