Formation Of Porous Materials Research Articles

Electrically conductive CNT networks formed by laser

Materials containing conductive CNT networks were investigated in this work. Binding of CNTs to each other was carried out using laser radiation in scanning mode. As a result of experimental studies, radiation energy density at which the effect of SWCNT binding occured was found – 0.061 J/cm2. Mechanism by which formation of porous materials with SWCNTs in composition takes place has been established. Materials from CNTs and biopolymers with controllable pore sizes that make up more than 60% of nanocomposite volume have been made.

Development of Sorbent Materials based on Polymer Waste and their Compounds with Nanomaterials for Oil Spill Remediation

The purpose of this work was to obtain a hydrophobic sorbent material with potential applications in oil spill remediation. The accidents due to oil spills cause long-term ecological damage, especially in the aquatic environment. The cleaning of oil spills can be carried out by many methods and techniques, being absorbents the most attractive due to the possibility of recovery and complete elimination of the hydrocarbons in situ from the water surface. In recent years, interest in polymeric materials for oil spill remediation has increased due to its low cost, high stability, and recyclability. The objective of this work was the development of sorbent materials based on polymer wastes, such as Polyethylene Terephthalate (PET), obtained from recycled bottles, and recycled Polyurethane (PU), for its application in the recovery of oil spills. Sorbent materials were prepared from polymer wastes, using salt molds for the formation of porous materials with a composition of PU of 5, 10 and 15%, which were subsequently hydrophobized using carbon nanotubes or silica nanoparticles by dip-coating technique. The obtained hydrophobic sorbent materials were characterized by Scanning Electron Microscopy (SEM) and Infrared Spectroscopy (FTIR). The resulting absorbent has shown capacity to separate oil from water; the best result was obtained by the sponge of PET-PU (10% PU) hydrophobized with a suspension with low multi-wall carbon nanotubes (MWCNTs) concentration, obtaining an absorption capacity of 2.01 g/g. Besides the standard sorption capacity, these cheap sorbent materials had interesting properties like low density, high hydrophobicity and buoyancy, which could be applied in other applications related to solving oil spills.

Formation of the open-cell foam structures in tetraethoxysilane-based gelling systems

The phase separation process in silica-based gelling systems in the presence of a polymer (polyethylene oxide, PEO) is shown to result in the formation of porous materials with the open-cell foam structure. The PEO concentration range in the reaction mixture where these foam-like structures are observed is determined. It is shown that phase separation begins with the formation of discrete droplets of solvent in the gel phase similar to the phase separation in some polymerizing organic systems. Further, liquid droplets grow and coalesce that leads to the formation of a system of interconnected macropores with a shape close to the spherical one. The macropore sizes are shown to depend on the PEO content, but no significant difference in the mesoporosity and surface area of the monoliths is observed. Dried and calcined porous silica monoliths are obtained with macropore sizes from 0.8 to 41 μm. The maximal compressive strength is 2.2 MPa, porosity is 85%, permeability coefficient is 3.5·10−12 m2, and the specific surface area is 210 m2 g−1. The materials can be used as supports in flow-through catalytic systems.

Structural and Optical Studies of Undoped Porous GaN Prepared by Pt-Assisted Electroless Etching

Porous GaN structures were formed from crystalline GaN on conducting AL2O3 substrate using Pt-assisted electroless etching in HF: CH3OH: H2O2 = 1:4:4 under illumination of 500 W UV lamp. Scanning electron microscope (SEM) photoluminescence (PL) and Raman spectra measurements evidenced important features of the pore morphology, nanostructures and optical properties. According to the SEM micrographs, the three-dimensional ridge structure appears with the formation of porous material between the ridges. The porous layer exhibited a substantial PL intensity enhancement with red-shifted band-edge PL peaks associated with the relaxation of compressive stress. The shift of E2(high) to the lower frequency in Raman spectra of the porous GaN films further confirms such a stress relaxation.

Fabrication of Hybrid Organic-Inorganic Materials with Tunable Porosity for Catalytic Application.

Novel layered organic-inorganic materials functionalized with amino groups have been synthesized by using a two-dimensional zeolitic precursor, IPC-1P, prepared by a top-down approach from zeolite UTL. The formation of porous materials containing silsesquioxane linkers covalently bonded to zeolite layers in the interlayer space was confirmed by a variety of characterization techniques (N2 sorption, XRD, TEM). The textural properties and catalytic behavior of functionalized hybrid materials synthesized by direct pillaring of IPC-1P or by grafting of (3-aminopropyl)silyl groups to the IPC-1P precursor preliminarily pillared with tetraethoxysilane (TEOS) were compared. The use of a mixture of aminosilsesquioxanes and TEOS for pillaring of IPC-1P led to the formation of functionalized materials, which are characterized by excellent textural properties (SBET =154-435 m2 g-1 , Vtotal =0.336-0.630 cm3 g-1 ) and provide a 100 % yield of target benzylidenemalononitrile in the Knoevenagel condensation of benzaldehyde and malononitrile.

Hydrothermal preparation of porous materials from a rutile–quartz concentrate

Synthesis of porous TiO2 from a Yarega rutile–quartz concentrate by using a simple low cost hydrothermal method is reported. Samples were characterized by the X-ray diffraction (XRD) method, energy-dispersive X-ray spectroscopy (EDX), inductively coupled plasma optical emission spectroscopy (ICP-OES) and Brunauer–Emmett–Teller (BET) analysis to determine the specific surface area. The as-synthesized porous material contains 96.95wt% TiO2 with rutile structure and is characterized by high surface area −5.0–5.5m2/g. Formation of porous materials may result from the dissolution of impurities from the rutile matrix of the starting rutile–quartz concentrate during the hydrothermal process.

Hierarchical Hybrid Organic–Inorganic Materials with Tunable Textural Properties Obtained Using Zeolitic-Layered Precursor

Novel layered zeolitic organic-inorganic materials have been synthesized using a two-dimensional zeolite precursor IPC-1P prepared by a top-down approach from zeolite UTL. The formation of porous materials containing organic linkers or polyhedral oligomeric siloxane covalently bonded to zeolite layers in the interlayer space was confirmed by a variety of characterization techniques (N2/Ar sorption analysis, XRD, (29)Si and (13)C NMR, TEM). The organic-inorganic porous hybrids obtained by intercalation with silsesquioxane posessed layered morphology and contained large crystalline domains. The hybrids exhibited mesoporous or hierarchical micro-/mesoporous systems, stable up to 350 °C. Textural properties of the formed zeolitic organic-inorganic materials can be controlled by varying the linker or synthetic conditions over a broad range. Surface areas and pore volumes of synthesized hybrids significantly exceed those for parent zeolite UTL and corresponding swollen material; the amount of micropores increased with increasing rigidity and size of the organic linker in the order biphenyl > phenylene > ethanediyl.

Preparation of Porous ZrO2‐Based Composite Oxides Containing W, Cr, Mo, or V Through a Wall Ion‐Exchange Method

AbstractMOx–ZrO2 (M = W, Cr, Mo, or V) composite oxides with high surface areas and hexagonal pore structures were prepared through a wall ion‐exchange (WIE)–calcination method. A composite (ZS) of Zr(SO4)2·4H2O and cetyltrimethylammonium bromide with ordered hexagonal structure was cast into solutions of M oxyanions. The efficiency of the WIE treatment was first studied on the solutions of tungsten oxyanion in detail. The surface areas of tungsten‐oxyanion‐introduced ZSs (W‐ZSs) after calcination at 673 K in air for 2 h were 3–248 m2 g–1 depending on the pH values of the exchange solutions. The treatments at pH = 5.6–10.1 resulted in the formation of porous materials with surface areas of 38–248 m2 g–1 and pore sizes of approximately 1.2 nm, whereas treatments at pH = 2.5–4.8 gave surface areas of 3–18 m2 g–1. The predominant oxyanion in the former region was a monomeric ion, WO42–. The WIE–calcination method was thus applied to the preparation of Cr‐, Mo‐, or V‐containing ZrO2 composite oxides in which the respective monomeric oxyanions were employed as the exchange ions by adjusting the pH values of the solutions. The surface areas of calcined Cr‐, Mo‐, and V‐ZS were 348, 251, and 229 m2 g–1, respectively, and pore sizes were 1.00–1.12 nm. The WIE–calcination method was proved to be a general method for the preparation of porous ZrO2‐based oxides.

Preparation of Microporous Hybrid Materials by Thermal Removal of Sterically Hindered Carbosilane Side Groups

The preparation of hybrid porous materials by condensation of poly(dimethyl-co-methyl)siloxanes functionalized with side units: i.e., templating –RC(SiMe3)3 [R = (CH2)5, (CH2)2SiMe2], and reactive –Si(OEt)3, of random distribution along the main chain is described. Tetrabutylammonium salts, tetrabutylammonium hydroxide and tetrabutylammonium fluoride were chosen as the catalytic system. The relationship between the steric hindrance of the carbosilane template, the type of n-Bu4N+ catalyst and the structure of cross-linked materials was investigated. It was found that bulky carbosilane substituents can block formation of the porous structure in the cross-linked material. The type of interaction between Si(OEt)3 and the catalyst seems to be an equally important factor for 3D structure formation. Controlled thermolysis of the cross-linked materials, performed in order to remove carbosilane units by thermal degradation, allowed for the formation of porous materials having high specific surface area.

Synthesis and characterization of transparent silica-based aerogels using methyltrimethoxysilane precursor

Silica-based aerogels with high transparency and high bending strength were prepared using methyltrimethoxysilane and non-ionic surfactant under supercritical drying condition of CO2. Non-ionic surfactant, ethylene oxide/propylene oxide block copolymer, was appropriate to form the three dimensional-connected thinner fibers of silica skeletons, which was extruded by soaking the wet gel in hot water at 50 °C, resulting in the formation of porous materials having small pores with narrow size distribution. The transparency of aerogels increased with decreasing the pore size, reaching to higher than 65 and 88% at 400 and 600 nm wavelength, respectively, for 10 mm thickness of sample. The formation of fiber skeletons were discussed using small angle X-ray scattering experiments.

Some properties of milled vanadium phosphates

Mechanochemical modification of vanadium phosphates doped with Bi, Zr, Mo has been studied. Milled samples have been investigated by means of XRD, DTA-TG, FTIR, nitrogen adsorption, electrokinetic measurements. It was found that phase composition of the phosphates does not change upon the mechanochemical modification process. Milling in water causes formation of porous materials. Modification of surface results in changes of the electrokinetic and adsorption properties of the milled samples.

Green chemistry

Although the applications of ultrasound have long been known in both industry and academy, the “green” value of the non-hazardous acoustic radiation has been recognised by synthetic and environmental chemists only recently. The chemical and physical effects of ultrasound arise from the cavitational collapse which produce extreme conditions locally and thus induce the formation of chemical species not easily attained under conventional conditions, driving a particular radical reactivity. This rationale, accessible in a non-mathematical manner, anticipates the advantages of using this technology in a variety of processes that include milder reactions with improved yields and selectivities, easy generation of reactive species and catalysts or replacement of hazardous reagents. Sonication enables the rapid dispersion of solids, decomposition of organics including biological components, as well as the formation of porous materials and nanostructures. This review summarises how ultrasound can be harnessed to develop an alternative and mild chemistry, which parallels the ability of acoustic waves to induce homolytic bond cleavage.

Structure formation in polymer solutions

The formation of porous materials by thermally induced phase separation is discussed and two basic mechanisms are presented: interference of a liquid–liquid demixing with a glass transition and/or crystallization. The possibility of formation of porous `composite' fibres using a blend of two non-compatible polymers is illustrated. The formation of these fibres during extrusion leads to a fibrillar morphology with the porosity oriented along the fibre axis. The formation of porous syndiotactic polystyrene with different degrees of supramolecular organization is discussed. The transformation on heating of the initially amorphous, glassy material into the γ-phase and then into the β-phase makes it possible to maintain the demixed situation up to temperature far above the Θ-temperature of this polymer–solvent system.