http://www.mdpi.com/journal/materials/special_issues/porous-materials/ Dear Colleagues, Porous materials are found in all classes of materials, from microporous zeolite ceramics, to mesoporous metals, to macroporous polymers. They are fundamental in a diverse range of applications, from structural materials to energy technologies. Recent advances in porous materials include the development of nanoporous metals by selective dissolution and their use in catalysis, and phase separation methods to make porous ceramics. This special issue of Materials will be devoted to exploring the wide range of types and applications of porous materials. Special emphasis will be devoted to new fabrication methods, new properties, and new applications of porous materials, and how these impact many different technologies. Prof. Dr. Jonah Erlebacher Guest Editor Submission All papers should be submitted to materials@mdpi.com. To be published continuously until the deadline and papers will be listed together at the special issue website. Submitted papers should not have been published previously, nor be under consideration for publication elsewhere. All papers are refereed through a peer-review process. A guide for authors is available on the Instructions for Authors page. Materials is an international peer-reviewed quarterly journal published by MDPI. Review manuscripts: Before writing their manuscripts, potential authors of review articles should forward the title and a short abstract to materials@mdpi.com. We will then provide feedback on the suitability of the topic. Open Access publication fees are 300 CHF per paper. English correction fees and/or formatting fees (250 CHF) will be added in certain cases (550 CHF per paper for those papers that require extensive additional formatting and/or English corrections). http://www.mdpi.com/1996-1944/3/5/3006/ 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. http://www.mdpi.com/1996-1944/3/5/3006/ Fri, 07 May 2010 00:00:00 CEST Materials 2010-05-07 3 5 Review 3006 3076 1996-1944 Macroporous Semiconductors 2010-05-07 doi: 10.3390/ma3053006 Föll Leisner Cojocaru Carstensen http://www.mdpi.com/1996-1944/3/2/943/ 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. http://www.mdpi.com/1996-1944/3/2/943/ Wed, 03 Feb 2010 00:00:00 CET Materials 2010-02-03 3 2 Review 943 998 1996-1944 Porous Silicon—A Versatile Host Material 2010-02-03 doi: 10.3390/ma3020943 Petra Granitzer Klemens Rumpf http://www.mdpi.com/1996-1944/3/2/755/ 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. http://www.mdpi.com/1996-1944/3/2/755/ Wed, 27 Jan 2010 00:00:00 CET Materials 2010-01-27 3 2 Article 755 763 1996-1944 Towards the Development of Electrical Biosensors Based on Nanostructured Porous Silicon 2010-01-27 doi: 10.3390/ma3020755 Gonzalo Recio-Sánchez Vicente Torres-Costa Miguel Manso Darío Gallach Juan López-García Raúl J. Martín-Palma http://www.mdpi.com/1996-1944/3/1/704/ 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. http://www.mdpi.com/1996-1944/3/1/704/ Tue, 26 Jan 2010 00:00:00 CET Materials 2010-01-26 3 1 Review 704 740 1996-1944 Influence of Chemical Conditions on the Nanoporous Structure of Silicate Aerogels 2010-01-26 doi: 10.3390/ma3010704 Katalin Sinkó http://www.mdpi.com/1996-1944/3/1/536/ 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. http://www.mdpi.com/1996-1944/3/1/536/ Mon, 18 Jan 2010 00:00:00 CET Materials 2010-01-18 3 1 Review 536 562 1996-1944 Porous Dielectrics in Microelectronic Wiring Applications 2010-01-18 doi: 10.3390/ma3010536 Vincent McGahay http://www.mdpi.com/1996-1944/3/1/467/ 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. http://www.mdpi.com/1996-1944/3/1/467/ Fri, 15 Jan 2010 00:00:00 CET Materials 2010-01-15 3 1 Review 467 502 1996-1944 A New Approach to the Computer Modeling of Amorphous Nanoporous Structures of Semiconducting and Metallic Materials: A Review 2010-01-15 doi: 10.3390/ma3010467 Cristina Romero Juan C. Noyola Ulises Santiago Renela M. Valladares Alexander Valladares Ariel A. Valladares http://www.mdpi.com/1996-1944/3/1/127/ 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. http://www.mdpi.com/1996-1944/3/1/127/ Mon, 04 Jan 2010 00:00:00 CET Materials 2010-01-04 3 1 Review 127 149 1996-1944 Recent Developments in Carbon Nanotube Membranes for Water Purification and Gas Separation 2010-01-04 doi: 10.3390/ma3010127 Kallista Sears Ludovic Dumée Jürg Schütz Mary She Chi Huynh Stephen Hawkins Mikel Duke Stephen Gray http://www.mdpi.com/1996-1944/2/4/2496/ 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. http://www.mdpi.com/1996-1944/2/4/2496/ Wed, 23 Dec 2009 00:00:00 CET Materials 2009-12-23 2 4 Article 2496 2509 1996-1944 Preparation and Hydrogen Absorption/Desorption of Nanoporous Palladium Thin Films 2009-12-23 doi: 10.3390/ma2042496 Wen-Chung Li Thomas John Balk http://www.mdpi.com/1996-1944/2/4/2429/ 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. http://www.mdpi.com/1996-1944/2/4/2429/ Fri, 18 Dec 2009 00:00:00 CET Materials 2009-12-18 2 4 Review 2429 2466 1996-1944 Macroporous Monolithic Polymers: Preparation and Applications 2009-12-18 doi: 10.3390/ma2042429 Ruben Dario Arrua Miriam Cristina Strumia Cecilia Inés Alvarez Igarzabal http://www.mdpi.com/1996-1944/2/4/2404/ 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. http://www.mdpi.com/1996-1944/2/4/2404/ Wed, 16 Dec 2009 00:00:00 CET Materials 2009-12-16 2 4 Review 2404 2428 1996-1944 Surface Chemistry in Nanoscale Materials 2009-12-16 doi: 10.3390/ma2042404 Jürgen Biener Arne Wittstock Theodore F. Baumann Jörg Weissmüller Marcus Bäumer Alex V. Hamza http://www.mdpi.com/1996-1944/2/4/2360/ 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. http://www.mdpi.com/1996-1944/2/4/2360/ Tue, 15 Dec 2009 00:00:00 CET Materials 2009-12-15 2 4 Article 2360 2368 1996-1944 A Self-Propagating Foaming Process of Porous Al-Ni Intermetallics Assisted by Combustion Reactions 2009-12-15 doi: 10.3390/ma2042360 Makoto Kobashi Naoyuki Kanetake http://www.mdpi.com/1996-1944/2/4/2337/ 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. http://www.mdpi.com/1996-1944/2/4/2337/ Tue, 15 Dec 2009 00:00:00 CET Materials 2009-12-15 2 4 Article 2337 2359 1996-1944 Highly Loaded Fe-MCM-41 Materials: Synthesis and Reducibility Studies 2009-12-15 doi: 10.3390/ma2042337 Malose P. Mokhonoana Neil J. Coville http://www.mdpi.com/1996-1944/2/4/2276/ 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. http://www.mdpi.com/1996-1944/2/4/2276/ Wed, 09 Dec 2009 00:00:00 CET Materials 2009-12-09 2 4 Review 2276 2295 1996-1944 Silk Fibroin Based Porous Materials 2009-12-09 doi: 10.3390/ma2042276 Qiang Zhang Shuqin Yan Mingzhong Li http://www.mdpi.com/1996-1944/2/4/2188/ 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. http://www.mdpi.com/1996-1944/2/4/2188/ Thu, 03 Dec 2009 00:00:00 CET Materials 2009-12-03 2 4 Review 2188 2215 1996-1944 Nanoporous Gold: Fabrication, Characterization, and Applications 2009-12-03 doi: 10.3390/ma2042188 Erkin Seker Michael L. Reed Matthew R. Begley http://www.mdpi.com/1996-1944/2/4/1923/ 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. http://www.mdpi.com/1996-1944/2/4/1923/ Fri, 20 Nov 2009 00:00:00 CET Materials 2009-11-20 2 4 Article 1923 1928 1996-1944 Porous Ba Ferrite Prepared from Wood Template 2009-11-20 doi: 10.3390/ma2041923 Nobuyasu Adachi Masayuki Kuwahara Chee Kiong Sia Toshitaka Ota http://www.mdpi.com/1996-1944/2/3/1252/ 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. http://www.mdpi.com/1996-1944/2/3/1252/ Thu, 10 Sep 2009 00:00:00 CEST Materials 2009-09-10 2 3 Review 1252 1287 1996-1944 Modelling of Grain Growth Kinetics in Porous Ceramic Materials under Normal and Irradiation Conditions 2009-09-10 doi: 10.3390/ma2031252 Mikhail S. Veshchunov http://www.mdpi.com/1996-1944/2/3/903/ 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. http://www.mdpi.com/1996-1944/2/3/903/ Wed, 05 Aug 2009 00:00:00 CEST Materials 2009-08-05 2 3 Article 903 910 1996-1944 Porous Thermoelectric Materials 2009-08-05 doi: 10.3390/ma2030903 Hiroshi Julian Goldsmid