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1.
A series of porous chars has been obtained by heat treatment of unconventional raw materials, including plants belonging to short rotation woody crops (Salix viminalis, Salix fragilis). The pyrolysis conditions (1–3 h, 600–900 °C) were the same for the production of all chars, e.g., mesoporous and microporous chars. Salix viminalis wood exhibited an advantage over the other materials, because the obtained material had microporous structure such as carbon molecular sieves. Similar properties (surface area, total pore volume, pore size distribution) were observed for charcoals produced from pine wood (Pinus silvestri), but the thermal stability of these properties was inferior. Furthermore, we have also discussed economical and environmental issues associated with the exploitation of wood resources.  相似文献   

2.
《Fluid Phase Equilibria》2005,231(2):138-149
Reactive canonical Monte Carlo (RCMC) method was performed to simulate the chemical reaction equilibrium of ammonia synthesis in two important porous materials: MCM-41 pores and pillared clays. First, our results were compared with those in slit pores in the literature. Then, the effect of other factors such as pore size, pressure and temperature on the chemical equilibrium was investigated. A parameter of the absolute increase of ammonia mole fraction in the pores against that in the bulk phase, Δabs, is introduced to describe the effect of confinement on the chemical equilibrium. The yield of ammonia increases with the decrease of pore size, but this increase becomes pronounced at pore sizes of 1.5 nm for MCM-41 pores and 1.02 nm for pillared clays. The yield of ammonia also increases with pressure. In addition, the maximum ammonia mole fraction is attained at 100 bar and 573 K in both MCM-41 pores and pillared clays. When the feed mole ratio of N:H of the bulk phase declines from 4:13 to 4:15, the yield of ammonia in the pore phase also decreases. In addition, the effect of porosity in pillared clays on the chemical equilibrium was simulated.  相似文献   

3.
Two different and novel composite monolithic materials with multimodal hierarchical porosity were prepared. The composites were prepared by immobilizing porous clay hetrostructure (PCH) and aluminum pillared clay (PILC), individually, into highly porous framework of a foam like monolith zeolite (MZ). The MZ was prepared hydrothermally, by following a polyurethane foam (PUF) based induced-template procedure and, consists of ZSM-5 framework. The MZ was fabricated into different composite materials through a simple dip coating method. Characterization of these materials with X-ray, SEM, and low temperature nitrogen adsorption techniques shows that composites materials are the morphological mixture (hybrid) of constituting materials. It also show that PCH based composites are meso and microporous, where as PILC based composites are essentially microporous in nature. The materials were further characterized for their hierarchical porosities by adsorption of two VOCs, which were toluene and n-hexane, under ambient conditions. The difference in adsorption of various sized (small to large) molecules was considered to work out the hierarchy of pores in these materials. With help of adsorption data, the hierarchical porosity was established into three size ranges, based on pore volumes of certain pore size ranges (>0.36 nm–<0.49 nm, >0.49 nm–<0.66 nm, and ≥0.66 nm). Water adsorption studies on these materials confirm that the coating of zeolite monolith with clay based adsorbents can also modify the hydrophobicity of original zeolite structure.  相似文献   

4.
In this work, formation of porous TiOx layers and theirs corrosion behavior were studied. Application of H3PO4 electrolytes results in porous TiOx formation. The process is enhanced by small amount of HF content in the electrolyte. The HF results in higher current density, enhancing dissolution. Small 0.5% HF concentration results in nanopores formation, with pore diameter of about 45 nm. Increase of HF concentration up to 10% results in pores with average diameter of about 5.2 μm. An increase of etching time results in larger pore diameter, but between large 2–5 μm diameter pores smallest ones were observed with diameter below 200 nm. In the initial etching process a remnants of the flat surface are presents with initial cracks in the surface, indicating places for growth of the pores.The TiOx layers can be used as a biomaterial. The corrosion behavior of the layer investigated in Ringer’s solution, revealed an excellent corrosion resistance, with respect to pure Ti.  相似文献   

5.
The hydrophilic PVDF-g-PVP powder was used as additive to prepare a series of PVDF/PVDF-g-PVP blend porous membranes via an immersion precipitation phase inversion process. FTIR-ATR measurements confirmed that the hydrophilic PVP preferentially segregated to the interface between membrane and coagulant. SEM images showed that there was no big change in the membrane cross-section with the amount of PVDF-g-PVP increased. However, the membrane surface roughness increased with the amount of PVDF-g-PVP increased according to AFM data. The mean pore size of membranes reached max when the amount of PVDF-g-PVP was 10 wt%. The water contact angle and filtration experiments revealed that the surface enrichment of PVP endowed the membranes with significantly enhanced surface hydrophilicity and protein-adsorption resistance. The flux recovery of the porous membranes was increased from 37.50% to 77.23% with the amount of PVDF-g-PVP increased from 0 to 50 wt%, also indicating that the antifouling property of the porous membranes was improved.  相似文献   

6.
A review of experimental work on ortho-positronium (o-Ps) lifetime in solids under the pressures up to 1 GPa is presented. Among the effects observed at high pressure one can mention: the disappearance of the energy level for Ps at the reduction of free volume size; pressure induced phase transitions; variation of Ps formation intensity with time; increase of o-Ps lifetime after intercalation of high pressure gas to the paraffin samples.  相似文献   

7.
The effects of pyrolysis temperature and heating rate on the porous structure characteristics of rice straw chars were investigated. The pyrolysis was done at atmospheric pressure and at temperatures ranging from 600 to 1000 °C under low heating rate (LHR) and high heating rates (HHR) conditions. The chars were characterized by ultimate analysis, field emission scanning electron microscope (FESEM), helium density measurement and N2 physisorption method. The results showed that temperature had obvious influence on the char porous characteristics. The char yield decreased by approximately 16% with increasing temperature from 600 to 1000 °C. The carbon structure shrinkage and pore narrowing occurred above 600 °C. The shrinkage of carbon skeleton increased by more than 22% with temperatures rising from 600 to 1000 °C. At HHR condition, progressive increases in porosity development with increasing pyrolysis temperature occurred, whereas a maximum porosity development appeared at 900 °C. The total surface area (Stotal) and micropore surface area (Smicro) reached maximum values of 30.94 and 21.81 m2/g at 900 °C and decreased slightly at higher temperatures. The influence of heating rate on Stotal and Smicro was less significant than that of pyrolysis temperature. The pore surface fractal dimension and average pore diameter showed a good linear relationship.  相似文献   

8.
We produce uniform mesoporous single- and multilayers on 4 in. p-type Ge wafers by means of electrochemical etching in highly concentrated HF-based electrolytes. Pore formation by anodic etching in germanium leads to a constant dissolution of the already formed porous layer plus substrate. Alternating the etching bias from anodic to cathodic bias enhances the passivation of the pore walls and substrate. The formation of porous multilayers is possible, since the starting layer is not dissolved during the formation of the separation layer. We report on the production of mesoporous double layers in Ge with different porosities. The change in the porosity of the porous layers is achieved by varying the anodic etching current and the HF concentration of the electrolyte. Porosities in the range of 25–65% are obtained for etching current densities of 1–15 mA cm?2 with the specific resistivity of the Ge substrates lying in the (0.020–0.032) Ω cm range and electrolyte HF concentrations in the range of 35–50 wt.%.  相似文献   

9.
A polymer electrolyte with interconnected pores based on poly(vinylidene difluoride-co-hexafluoropropylene) [P(VDF-HFP)] copolymer was prepared by a simple phase separation process using water as both non-solvent and pore inducer. The prepared porous membrane was characterized by SEM, XRD and DSC. With a narrow pore size distribution and low crystallinity, the resulting polymer electrolyte shows a high ionic conductivity up to 1.76 × 10−3 S cm−1 at room temperature and exhibits low apparent activation energy of 10.35 kJ mol−1 for the transportation of ions. Its low cost and environmentally friendliness provide great promise for the practical application in polymer lithium-ion batteries.  相似文献   

10.
The pore structure of three-dimensional scaffolds applied in tissue engineering may influence the mechanical properties and cellular activity. As the optimal pore size is dependent on the specifics of the biomaterial or tissue engineering application, the ability to alter the pore size over a wide range is necessary for several scaffolds in order to meets the requirements of the applications. The aim of this study is to develop methodologies to produce calcium phosphate scaffolds with acceptable pore size and defined pore-channel interconnectivity. The pore size of calcium phosphate scaffolds is established during the freeze-drying fabrication process. In this process, material suspension is simply frozen and then dried by freeze-drier, which able to produce material with unique porous architectures, where the porosity is almost a direct replica of the frozen solvent crystals. There are two different method of freeze-casting carried out in order to study the effect of freezing temperature by which in the first method; sample being soaked with liquid nitrogen (-196 °C) for about 10 minutes before been place inside a freezer (-40 °C). In the second method, the sample was directly placed inside a freezer for casting at temperature of -40 ̊C. The results show that the pore size of the scaffolds decreased as the freezing temperature was reduced. Taken together, these results demonstrate that the methodologies applied in this study can be used to produce a range of calcium phosphate scaffolds exhibiting better compressive strength, approximately 665-875 KPa for 54-64.3% of porosity with mean pore size from 102-113 μm. The methods developed in this study provide a basis for the investigation on the effects of different freezing temperature in freeze-casting process on the porosity, morphology, and compressive properties of the calcium phosphate scaffolds.  相似文献   

11.
Solid conducting biodegradable composite membranes have shown to enhance nerve regeneration. However, few efforts have been directed toward porous conducting biodegradable composite membranes for the same purpose. In this study, we have fabricated some porous conducting poly(dl-lactide) composite membranes which can be used for the biodegradable nerve conduits. The porous poly(dl-lactide) membranes were first prepared through a phase separation method, and then they were incorporated with polypyrrole to produce porous conducting composite membranes by polymerizing pyrrole monomer in gas phase using FeCl3 as oxidant. The preparation conditions were optimized to obtain membranes with controlled pore size and porosity. The direct current conductivity of composite membrane was investigated using standard four-point technique. The effects of polymerization time and the concentration of oxidant on the conductivity of the composite membrane were examined. Under optimized polymerization conditions, some composite membranes showed a conductivity close to 10−3 S cm−1 with a lower polypyrrole loading between 2 and 3 wt.%. A consecutive degradation in Ringer's solution at 37 °C indicated that the conductivity of composite membrane did not exhibit significant changes until 9 weeks although a noticeable weight loss of the composite membrane could be seen since the end of the second week.  相似文献   

12.
We evaluated the CO2 adsorption capacity on granular and monolith carbonaceous materials, obtained by chemical activation of African palm stones with H3PO4, ZnCl2 and CaCl2 solutions at different concentrations. Textural properties of the synthesized materials were analyzed using N2 adsorption measurements at 77 K, the isotherms showed obtaining of materials microporous and moderately mesoporous, with surface areas between 161 and 1700 m2/g and pore volume between 0.09 and 0.64 cm3 g−1. Were observed different behaviors for textural parameters in each series, associated with the activating agent used in the preparation. The materials obtained have a CO2 adsorption capacity between ∼114 and 254 mg CO2/g, at atmospheric pressure and 273 K. It was established that the total amount of CO2 adsorbed under these experimental conditions is defined by the narrow micropore volume (Vn) and increased the total basicity of the materials.  相似文献   

13.
Electrode materials for supercapacitors are at present commonly evaluated and selected by their mass specific capacitance (CM, F g−1). However, using only this parameter may be a misleading practice because the electrode capacitance also depends on kinetics, and may not increase simply by increasing material mass. It is therefore important to complement CM by the practically accessible electrode specific capacitance (CE, F cm−2) in material selection. Poly[3,4-ethylene-dioxythiophene] (PEDOT) has a mass specific capacitance lower than other common conducting polymers, e.g. polyaniline. However, as demonstrated in this communication, this polymer can be potentiostatically grown to very thick films (up to 0.5 mm) that were porous at both micro- and nanometer scales. Measured by both cyclic voltammetry and electrochemical impedance spectrometry, these thick PEDOT films exhibited electrode specific capacitance (CE, F cm−2) increasing linearly with the film deposition charge, approaching 5 F cm−2, which is currently the highest amongst all reported materials.  相似文献   

14.
Experimental results on back-side illumination electrochemical etching of patterned (hole square-lattices with pitch p from 2 to 50 μm) n-type silicon substrates in HF-based electrolytes are reported. Experiments reveal the existence of a threshold current density Jpitch, which is strictly correlated to the pattern pitch, above which pore formation can be finely controlled beyond commonly accepted state-of-the-art rules. For instance, using the same silicon substrate, pore array with density D spanning over two orders of magnitude (from 0.0025 μm? 2 up to of 0.25 μm? 2) can be etched above a minimum porosity Pmin, and, in turn, a minimum pore diameter dmin, which depends on the pattern pitch. Etching current densities below such a critical value give rise to uncontrolled pore growth. The occurrence of the threshold current density Jpitch is interpreted in terms of current burst model.  相似文献   

15.
In this work, porous carbon with a high specific surface area as electrode materials for supercapacitors are obtained by a carbonization process at various temperatures from 700 °C to 1000 °C without activation process using poly(vinylidene fluoride) (PVDF) as a carbon precursor. The electrochemical performance is characterized by cyclic voltammetry and galvanostatic charge–discharge cycling performance using two-electrode system in 6.0 M KOH as an aqueous electrolyte. The results indicate that carbonization temperature significantly affected the specific surface area and pore volume of the PVDF-derived carbons and their capacitive behavior. In particular, the electrochemical performance of the prepared PVDF-derived carbon is determined by both the electric double-layer capacitance and the pseudo-capacitance resulting from the residual surface functional groups on PVDF-derived carbons.  相似文献   

16.
This article studies the effect of 47 kHz ultrasonic (US) waves on polymeric membranes immersed in an aqueous bath. The membranes under study are made from three different polymers: polyethersulfone (PES), polyvinylidenefluoride (PVDF) and polyacrylonitrile (PAN) and present various molecular weight cut-off (MWCO). The evolution of the polymeric structure exposed to US was followed by the measurement of the water permeability and the Akx parameter which represents the ratio of surface porosity to thickness. Results showed that important variations occurred on certain membranes after irradiation. In addition, microscopic imaging using field emission electron scanning microscopy (FESEM) was performed on irradiated membranes in order to visualize the nature of the degradation. An image analysis method gives the evolution of the pore density, porosity and pore size distribution of a homogeneous area of this membrane before and after irradiation.It has been shown that, over the three materials tested, only the PES is affected by the ultrasonic treatment over all its surface, whereas the others present no significant change in the measured parameters except the PAN (50 kDa) and PVDF (40 kDa) membranes whose edges are affected. In conclusion, in spite of their great efficiency in enhancing filtration processes, ultrasonic waves have to be used with care as the polymeric material itself is sensitive to the ultrasonic waves at the chosen frequency.  相似文献   

17.
Subnanoporosity was introduced into SiOCH-based thin films by mixing tetraethyl orthosilicate with hexamethyldisiloxane (HMDSO) in the plasma enhanced chemical vapor deposition process, and was evaluated by the variable-energy positron annihilation lifetime technique. It was found that with increasing the HMDSO fraction both porosity and pore size were enhanced, as evidenced by the decreased refractive index and increased ortho-positronium lifetime. The lifetimes from 2.0 to 6.8 ns suggested the tunable pore volumes within a range of 0.1–0.7 nm3.  相似文献   

18.
Two sets of adsorbents were prepared from locally available raw materials, characterized and tested. The first set consists of crushed natural attapulgite and crushed attapulgite mixed with petroleum tank-bottom sludge and carbonized at 650 °C. Another set was prepared using trunk of date palm tree (Phoenix dactylifera) activated at 700 and 800 °C. Both sets were characterized using BET surface area and pore distributions, FTIR, XRD, SEM and TEM. Natural attapulgite and attapulgite/sludge composite exhibited different characteristics and adsorptive capacities for oil removal from oily water. Adsorptive capacities were calculated from the breakthrough curves of a column test. An oily water solution of about 500 mg-oil/L was passed through both the attapulgite and attapulgite/sludge columns until the column effluent concentration exceeded a reference limit of 10 mg-oil/L. Uptake was calculated at this limit at 155 and 405 mg-oil/g-adsorbent, respectively. This was lower than the performance of a commercial activated carbon sample (uptake calculated at 730 mg-oil/g-adsorbent). Relatively, the date palm, carbonaceous-based adsorbent samples showed less significant differences in both bulk and surface properties. Uptake significantly improved to 1330–1425 mg-oil/g-adsorbent. Attempt was made to associate this performance with the difference in the surface areas between the two sets. However, other factors are found to be important as the second set has a range of surface area less than that of the commercial sample. As evidenced by FTIR, XRD and TEM, the activated carbonaceous materials developed porous structures which form defective graphitic sheet ensembles that serve as additional adsorption sites in the sample.  相似文献   

19.
Various ultrafiltration and nanofiltration membranes were characterized by solute transport and also by atomic force microscope (AFM). The molecular weight cut-off (MWCO) of the membranes studied were found to be between 3500 and 98,000 Daltons. The mean pore size (μp) and the geometric standard deviation (σp) around mean ranged from 0.7 to 11.12 nm and 1.68 to 3.31, respectively, when calculated from the solute transport data. Mean pore sizes measured by AFM were about 3.5 times larger than calculated from the solute transport. Pore sizes measured by AFM were remarkably fitted to the log-normal probability distribution curve. Pore sizes of the membranes with low MWCO (20,000 Daltons and lower) could not be measured by AFM because of indistinct pores. In most cases, the pore density ranged from 38 to 1291 pores/μm2. In general, the pore density was higher for the membrane having lower MWCO. Surface porosity was around 0.5–1.0% as measured from the solute transport and was 9.5–12.9% as obtained from AFM images. When membranes were coated with a thin layer of sulfonated polyphenylene oxide, mean pore sizes were reduced for all the membranes. Surface roughness was also reduced on coating.  相似文献   

20.
By tuning the structure of hard template kaolinite, we have achieved a template directed synthesis of holey carbon nanosheet/nanotube material. This carbon nanomaterial with in-plane and out-of-plane pores has shown promising electrochemical energy storage capacity.  相似文献   

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