Partial Pore Blockage Research Articles

Sustainable metal-organic framework based paper sheet as wallpaper for passive indoor moisture control

Passive indoor moisture control is a meaningful way to reduce HVAC operation and improve building energy efficiency. Metal-organic frameworks (MOFs) have been considered one of the most promising sorbent materials for passive indoor moisture control. However, the powder form of MOF is challenging to use in the built environment. Typical shaping methods like pellets, beads, and coating can lead to problems like partial pore blocking, insufficient mechanical stability, amorphization, and low material utilization. Here, we report a new sustainable MOF paper sheet comprising 25% cellulosic fibers and 75% MOF MIL-100(Fe) powder. The porous polymer matrix provides good support and fixation for MOF particles, so it’s more applicable in the built environment. The crystalline and pore structure characteristics of the MOF in the membrane are well preserved. Hydro characteristic test results show that MIL-100(Fe) paper sheet has high water vapor uptake, S-shape isotherm, mild regeneration condition, and high MBV. Then, a numerical model was developed to calculate the relation between a material’s MBV and its thickness. MIL-100(Fe) paper sheet with the most efficient thickness was applied as wallpaper in a building energy simulation model. The simulation result shows that the MIL-100(Fe) paper sheet is promising for passive indoor moisture control. It can remove about 45%-55% of the latent cooling load in most European climate types.

Organic template residues confined in silicalite-1 zeolite membranes for tuning pore structures and boosting H2/CO2 separation

Silicalite-1 zeolite membranes were successfully activated at 300–350 °C in a hydrogen atmosphere. FTIR, TGA, and N2 adsorption-desorption characterizations confirmed that the amount of the organic structure directing agent (OSDA) residue in silicalite-1 zeolite channels was tunable. The H2-calcined membrane showed a lower gas permeance than that of the air-calcined membrane due to the partial pore blockage by the OSDA residue. The permeance of H2 and CO2 increased with increasing temperature, showing an activated diffusion-like mechanism. The activation energies for the permeation of H2 and CO2 were in the range of 1.63–4.15 and 0.76–5.90 kJ mol−1, respectively, which confirmed the reduced average membrane pore size and different pore surface chemistry due to the presence of the OSDA residue in the membrane. Significant interactions between CO2 molecules and OSDA residues confined in the membrane resulted in a notably lower CO2 permeance compared to N2 and CH4, despite CO2 having a smaller kinetic diameter. Enhanced H2/CO2 selectivity in the silicalite-1 zeolite membrane, featuring confined OSDA residue, was attributed to the reduction in membrane pore size and the fine-tuning of pore surface chemistry.

A new class of porous silicon electrochemical transducers built from pyrolyzed polyfurfuryl alcohol

Carbon-based nanomaterials are key to developing high-performing electrochemical sensors with improved sensitivity and selectivity. Nonetheless, limitations in their fabrication and integration into devices often constrain their practical applications. Moreover, carbon nanomaterials-based electrochemical devices still face problems such as large background currents, poor stability, and slow kinetics. To advance towards a new class of carbon nanostructured electrochemical transducers, we propose the in-situ polymerization and carbonization of furfuryl alcohol (FA) on porous silicon (pSi) to produce a tailored and highly stable transducer. The thin layer of polyfurfuryl alcohol (PFA) that conformally coats the pSi scaffold transforms into nanoporous carbon when subjected to pyrolysis above 600 °C. The morphological and chemical properties of PFA-pSi were characterized by scanning electron microscopy, and Raman and X-ray photoelectron spectroscopies. Their stability and electrochemical performance were investigated by cyclic voltammetry and electrochemical impedance spectroscopy in [Fe(CN)6]3-/4-, [Ru(NH3)6]2+/3+, and hydroquinone. PFA-pSi showed superior electrochemical performance compared to screen-printed carbon electrodes while also surpassing glassy carbon electrodes in specific aspects. Besides, PFA-pSi has the additional advantage of easy tuning of the electroactive surface area. To prove its potential for biosensing purposes, a DNA sensor based on quantifying the partial pore blockage of the pSi upon target hybridization was built on PFA-pSi. The sensor showed a limit of detection of 1.4 pM, outperforming other sensors based on the same sensing mechanism.

Excellent gas separation performance of hybrid carbon molecular sieve membrane derived from polyimide/10X zeolite for hydrogen purification

Membrane-based gas separation is attracting more and more attention in hydrogen purification and CO2 separation. One critical challenging remaining for large-scale production is fabricating a high-performance membrane with both inexpensive and excellent separation performance. In this work, a novel hybrid-carbon molecular sieve (CMS) membranes were reported for hydrogen purification by pyrolysis of commercial polyimide precursor (PMDA-ODA) with incorporation of modified 10X zeolite. The addition of modified 10X zeolite provided additional gas transport channels to the CMS mixed matrix membrane (MMM), and contained a significant fraction of micropores within the 0.6–0.8 nm range, which greatly enhance hydrogen adsorption capacity. Interestingly, despite this, the selectivity for H2/N2 and H2/CH4 also increases with higher zeolite content. This unexpected phenomenon may be attributed to the partial blocking of zeolite pores by CMS strand, which narrows the 10X pore size to a dimension smaller than CH4 and N2, enabling differentiation between H2 and CH4 gas pairs. Therefore, the permeability and selectivity of H2 was significantly enhanced. The CMS/10X-7.5 (with 7.5 wt % 10X zeolite) exhibited an advanced H2 permeability (1709 Barrer) and high gas selectivity of 551 for H2/CH4 and 105 for H2/N2, respectively, which is higher than other samples and exceed the 2015 trade-off lines. Furthermore, the CMS/10X-7.5 delivered excellent stability after 20 cycles. Therefore, this hybrid CMS/10X-7.5 obtained by carbonization of zeolite-doped polymer precursors has great potential for larger industrial applications.

Effect of binder on CO2, CH4, and N2 adsorption behavior, structural properties, and diffusion coefficients on extruded zeolite 13X

The effect of inorganic binder-based extrusion (Silica sol, Bentonite, Attapulgite, and SB1) in the selective adsorption of CO2, CH4, and N2 on zeolite 13X in the context of flue gas carbon capture and natural gas purification has been studied to reduce CO2 emissions. The effect of extrusion with binders was examined by adding 20 wt% of the mentioned binders to pristine zeolite and the results were analyzed by four approaches; (i) the effect on structural properties was analyzed by XRD patterns followed by Williamson–Hall (W–H) plot, FESEM images, and BET surface area. In addition, the mechanical strength of the shaped zeolites was measured by crush resistance testing; (ii) the effect on the adsorption capacity for CO2, CH4, and N2 were measured by volumetric apparatus up to 100 kPa; (iii) the impact on binary separation (CO2/CH4 and CO2/N2) were investigated; (iv) the influence on diffusion coefficients were estimated by micropore and macropore kinetic model. The results showed that the presence of a binder can cause reductions in BET surface area and pore volume, indicating partial pore blockage. It was found that the Sips model had the best adaptability to the experimental isotherms data. The trend of CO2 adsorption was 13X > pseudo-boehmite > bentonite > attapulgite > silica, in which the adsorption capacity reached 6.02, 5.60, 5.24, 5.00, and 4.71 mmol/g, respectively. Among all samples, silica was found the most suitable binder for CO2 capture in terms of selectivity, mechanical stability, and diffusion coefficients.

Clarification of red araçá (Psidium cattleianum Sabine) juice by membrane process: Analysis of permeate flux and loss of bioactive compounds

Red araçá (Psidium cattleianum Sabine) juice was processed using porous membranes to obtain a clarified product with a high amount of phenolic compounds prior to its use as a juice or other beverage. The variations in the permeate flux and concentrations of phenolics were determined in a cross-flow system using a polyetherimide microfiltration membrane (0.44 µm) and polyethersulfone ultrafiltration membrane (50 kDa). Both membranes reduced the initial turbidity (445 ± 2) to almost zero, and resulted in a clear and transparent permeate with a yellow colour. The microfiltration membrane showed better performance with the lowest phenolic compound retention (23.6%) and the highest permeate flux (40.6 ± 2 kg/m2h) in batch mode operation. The permeate flux of the microfiltration system showed an initial sharp decrease followed by a gradual decrease, reaching almost 60% lower than the initial permeate flux. The permeate flux resistance was mainly due to the polarised layer (70.2%), and the predominant fouling mechanism was the partial pore blockage, thus indicating that the solids present in the raw juice had size of the same order as the membrane pores.

The influence of zeolite X ion-exchangeable forms and impregnation with copper nitrate on the adsorption of phosphate ions from aqueous solutions

Removal of phosphate ions from aqueous environment has become a global concern. Adsorption is one of the most efficient methods for removal of various pollutants. In this study, zeolite NaX derived from fly ash was modified by simple ion exchange with ammonium nitrate solution to obtain ammonium form (NH4X) and calcinated to proton form (HX) of zeolite X. The obtained materials were investigated as potential adsorbents of phosphate ions from aqueous solutions to find out the effect of zeolite form on adsorption capacity. Furthermore, zeolites NaX and NH4X were impregnated with copper nitrate solution and calcinated at 550 °C to obtain materials with Cu content of 3 wt% to simulate the potential utility of spent catalysts. The obtained results indicated that parent zeolite NaX has rather weak affinity towards phosphate ions — 4.38 mg (PO43−) g−1, only. The ammonium and proton forms of zeolite X showed significantly improved adsorption capacities of 12.09 and 35.33 mg (PO43−) g−1, respectively, implying the positive effect of ion exchange on removal of phosphate ions from aqueous solutions. Impregnated zeolites exhibited sufficient adsorption capacities of 11.86 and 26.53 mg (PO43−) g−1 for 3%Cu@NaX and 3%Cu@HX, respectively. However, no synergic effect of impregnation and zeolite form was observed due to partial pore blockage after preparation of zeolite 3%Cu@HX. To gain a deeper knowledge about the adsorption mechanisms, selected samples were subjected to kinetic adsorption studies and XPS measurements.

Dextran and Its Derivatives: Biopolymer Additives for the Modulation of Vaterite CaCO3 Crystal Morphology and Adhesion to Cells

AbstractNowadays, a great demand for the development of novel drug delivery systems with high potential for bench‐to‐market transition attracts scientific attention toward materials that are already approved for biomedical use. Here, controlled fabrication of hybrid organic inorganic mesoporous crystals is realized in physiologically relevant conditions by co‐synthesis of vaterite CaCO3 in the presence of dextran (DEX) or its functional derivatives. The effects of DEX molecular weight and chemical structure on morphology, porosity, and stability of the hybrids are investigated. Molecular weight of DEX does not affect the crystal growth but leads to the partial blocking of crystal pores. Co‐synthesis of DEX functionalized with either carboxymethyl (CM) or diethylaminoethyl (DEAE) groups drastically increased crystal porosity without influencing crystal size. pH‐dependent vaterite‐to‐calcite recrystallization is significantly suppressed by inclusion of carboxymethyl‐dextran (CM‐DEX), making vaterite crystals stable in acidic medium, whereas the incorporation of diethylaminoethyl‐dextran (DEAE‐DEX) has no effect. The hybrids prepared with charged DEX derivatives possess stronger adhesion to normal human dermal fibroblasts: three times higher crystal adherence compared to pristine crystals. These results provide fundamental physical–chemical insights into the crystallization of DEX/vaterite hybrids and are discussed in view of the potential of these functional delivery carriers for biomedical and other applications.

Sorption properties of activated carbons for the capture of methyl iodide in the context of nuclear industry

In the present study, some commercially available activated carbons were evaluated towards the methyl iodide (CH3I) capture in the context of nuclear industry. A specific methodology was implemented in order to establish structure-activity relationships between adsorbent characteristics and its adsorption behavior towards CH3I. On the one hand, the investigated adsorbents were characterized by a combination of physico-chemical techniques. On the other hand, CH3I retention performance from batch sorption tests under different conditions (temperature and relative humidity) was studied using an original experimental setup. In this work, two conditions were investigated: (i) T = 35°C, R.H. = 26 % ([H2O] ∼15,000 ppmv); (ii) T = 75°C, R.H. = 30 % ([H2O] ∼130,000 ppmv). Different trends were obtained depending on the investigated scenario. At ambient conditions (i), CH3I adsorption performance was affected after KI/TEDA impregnation because of partial pore blockage phenomena induced by the of impregnants presence within the microporosity. However, TEDA impregnation was found to be required to enhance the trapping stability and to capture CH3I with superior efficiency at higher temperature (ii).

Silver nanoparticle impregnated polyethersulfone ultrafiltration membrane: Optimization of degree of grafting of acrylic acid for biofouling prevention and improved water permeability

Membrane biofouling limits its lifetime and application. Our objective is to optimize surface modification and subsequent silver nanoparticle impregnation on polyethersulfone (PES) membrane for biofouling prevention. For this, silver nanoparticles were selectively impregnated on the PES membrane, via carbonyl group attachment on membrane surface by acrylic acid grafting. Based on mechanical property and silver loading, three different membranes (AA-Ag-PES-25, AA-Ag-PES-62 and AA-Ag-PES-185 with acrylic acid grafting of 25, 62 and 185 μg cm−2, respectively, and having resultant silver loading of 4.4, 9.06 and 16.94 wt%, respectively) were screened for further testing. Performance of the AA-Ag-PES-62 membrane was best, with least reduction of permeate flux at steady state (12.69%), signifying biofouling prevention, compared to only PES membrane (62.2% permeate flux reduction); the latter due to attached live E. coli cells, in absence of silver nanoparticles. For AA-Ag-PES-25 with a lower silver loading, bacterial cell killing was slower, with resultant permeate flux-drop at steady state (19.7%) being more than the optimum AA-Ag-PES-62 membrane. In contrast, for the higher silver loaded AA-Ag-PES-185, silver nanoparticles formed a surface layer, which resulted in partial pore-blockage with higher permeate flux reduction (27.28%). Regarding long-term performance, for AA-Ag-PES-62, there was neither flux-drop nor bacterial growth till 48 h, whereas, due to low silver content in AA-Ag-PES-25, bacteria re-grew after 24 h, which reflected into permeate flux-drop. AA-Ag-PES-62 membrane provides optimum performance in terms of E. coli killing and anti-biofouling effect, maintaining silver concentration in permeate (29.8 ppb), well within the permissible 100 ppb limit.

Exploring the Occurrence of Clogging in Highly Permeable Coarse Soils of Dam Foundations

Leakage through the permeable coarse soils of dam foundations in Tibet, China, lessened over time without any additional antiseepage measures. In fact, clogging generated during the infiltration process is recognized as the major factor in reducing leakage. A laboratory study was conducted to understand clogging in highly permeable coarse soil of a dam foundation with the primary aim of determining the clogging patterns and optimum clogging particle size (PS). Seven replicate experiments were constructed using soil media with PS ranges of 32–64 mm, 16–32 mm, 8–16 mm, 4–8 mm, 2–4 mm, 1‐2 mm, and 0.5–1 mm to observe clogging after feeding the soil media with sediments of different PSs. The experimental results showed that four clogging patterns were formed in different PSs of the coarse foundation soil. The ratio of the effective aperture of the soil Dea and the equivalent clogging particle size de(de/Dea) had a dominant effect on the four clogging patterns (surface clogging, (de/Dea) > 1; surface‐internal clogging, 0.5 < (de/Dea) ≤ 1; internal partial pore blockage, 0.25 < (de/Dea) ≤ 0.5; and unclogging, (de/Dea) ≤ 0.25). The assessment criterion of the optimum clogging pattern was determined by 0.5 < (de/Dea) ≤ 1, and from that, the optimum clogging PS do was calculated.

Enhanced CO2/CH4 separation performance of BTDA-TDI/MDI (P84) copolyimide mixed-matrix membranes by incorporating submicrometer-sized [Ni3(HCOO)6] framework crystals

The incorporation of metal-organic frameworks (MOFs) into mixed-matrix membranes (MMMs) is gaining widespread attention because of the combined advantages of easy processability and superior separation performance. In this paper, submicrometer-sized [Ni3(HCOO)6] frameworks were incorporated into BTDA-TDI/MDI (P84) matrix as filler material to separate CO2 from CH4. When the loadings of [Ni3(HCOO)6] frameworks in MMMs were 7 and 15 wt%, obvious enhancements in gas separation properties were obtained. Especially at the loading of 15 wt%, CO2 permeability and the CO2/CH4 selectivity increased 76% (from 0.72 Barrer to 1.26 Barrer) and 52% (from 44 to 67), respectively, compared with the pristine P84 membrane. The partial pore blockage was found by the high-pressure gravimetric adsorption measurements and it was deemed to be profitable to separate CO2/CH4. In order to better understand the gas separation behavior, the characterizations of [Ni3(HCOO)6] frameworks (XRD, SEM, Ar adsorption-desorption, CO2 and CH4 adsorption, ATR-FTIR, TGA) and P84/[Ni3(HCOO)6] MMMs (SEM, ATR-FTIR, XRD, TGA, stress–strain tests) were performed.

Fe/SBA-15: Characterization and its application to a heterogeneous solar photo-Fenton process in order to decolorize and mineralize an azo dye

Fe/SBA-15 catalyst with different iron (Fe) loads (6% and 10% wt.) was synthesized via incipient wetness impregnation. The potential photocatalytic properties were tested using solar radiation, as a novel catalyst in heterogeneous Fenton approach to degrade Methyl Orange azo dye. A partial pore blocking of the substrate by Fe nanoparticles was detected and the main form of Fe present was Fe2O3. When the Fe(10%)/SBA-15 catalyst was used for heterogeneous solar photo-Fenton reaction, total discoloration of the effluent was achieved in 90 min, and 89% of COD was removed in 240 min. Short-chain linear carboxylic acids were followed over time, as well as inorganic ions.

Pretreatment for the reclamation of rendering plant secondary effluent with NF/RO: UF flat sheet versus UF hollow fiber membranes

Rendering plants produce large amounts of wastewater that could be reused at the plant with adequate treatment. Membrane fouling is the main problem during the treatment of this type of wastewater by nanofiltration (NF) and reverse osmosis (RO). In order to reduce membrane fouling, the rendering plant secondary effluent was pretreated with two types of ultrafiltration (UF) membranes: MW as a flat sheet and ZW-1 as a hollow fiber membrane. The fouling on NF/RO flat sheet membranes (NF90, NF270, and XLE) was evaluated with the resistance-in-series model, while the fouling mechanisms were assessed with crossflow models. The UF, NF, and RO permeates were characterized to determine its suitability for reuse in the rendering plant. ZW-1 reduced the flux decline by 67.0% for NF270, 1.6% for NF90, and 38.0% for XLE; while MW reduced the flux decline by 72.4% for NF270, 50.1% for NF90, and 68.1% for XLE. The pretreatment with MW resulted in higher fouling reduction and a permeate that is appropriate for industrial reuse (washing purposes in the rendering plant). In terms of fouling resistance, NF270 and XLE membranes showed less fouling resistance during the treatment compared to NF90. The highest quality of permeate was obtained with XLE membrane, satisfying the water requirements for steam generation. The predominant fouling mechanisms for NF/RO were partial and complete pore blocking. The best combination for rendering plant secondary effluent reclamation was UF with MW membrane and RO with XLE membrane.

Improving the Gas-Separation Properties of PVAc-Zeolite 4A Mixed-Matrix Membranes through Nano-Sizing and Silanation of the Zeolite.

Mixed-matrix membranes containing synthesised nano-sized zeolite 4A and PVAc were fabricated to investigate the effect of zeolite loading on membrane morphology, polymer-filler interaction, thermal stability and gas separation properties. SEM studies revealed that, although the membranes with 40 wt % nano-sized zeolite particles were distributed uniformly through the polymer matrix without voids, the membranes with 15 wt % zeolite loading showed agglomeration. With increasing zeolite content, the thermal stability improved, the permeability decreased and the selectivity increased. The effect of silanation on dispersion of 15 wt % zeolite 4A nanoparticles through PVAc was investigated by post-synthesis modification of the zeolite with 3-Aminopropyl(diethoxy)methylsilane. Modification of the nanoparticles improved their dispersion in PVAc, resulting in higher thermal stability than the corresponding unmodified zeolite membrane. Modification also decreased the rigidity of the membrane. Partial pore blockage of the modified zeolite nanoparticles after silanation caused a further decrease in permeability, compared to the 15 wt % unmodified zeolite membrane.

La-modified ZSM-5 zeolite beads for enhancement in removal and recovery of phosphate

Abstract ZSM-5 zeolite beads (ZB) modified with lanthanum (La) were prepared by impregnating ZB in a lanthanum nitrate solution (denoted as La-ZB). La-ZB was characterized via SEM, BET, ICP-OES and XRD techniques, which confirmed the doping of La on the surface of the ZB. The surface area and pore volume of La-ZB decreased marginally after the La-modification due to a partial pore blockage by the La dopant. La-ZB showed an improved phosphate adsorption compared to ZB, and the maximum phosphate adsorption capacities by ZB and La-ZB (determined by Langmuir isotherm) were 59.8 and 106.2 mg/g, respectively. Moreover, the adsorption kinetics proceeded according to the mechanism of the pseudo-second-order model. The phosphate adsorption by La-ZB exhibited an optimum at pH 6. In regeneration process of phosphate-loaded La-ZB, five times adsorption-desorption cycles were applied and 81.8% phosphate was recovery. In a test using wastewater containing a high phosphate concentration (218.6 mg/L), La-ZB exhibited 96.8% phosphate removal, which is 1.8 times higher than that of ZB (53.5%). The results indicate that La-ZB can be a promising recyclable adsorbent for the removal and recovery of phosphate from wastewater.

Benzimidazole linked polymers (BILPs) in mixed-matrix membranes: Influence of filler porosity on the CO2/N2 separation performance

The performance of mixed-matrix membranes (MMMs) based on Matrimid® and benzimidazole-linked polymers (BILPs) have been investigated for the separation CO2/N2 and the dependency on the filler porosity. BILPs with two different porosities (BILP-101 and RT-BILP-101) were synthesized through controlling the initial polymerization rate and further characterized by several techniques (DRIFTs, 13C CP/MAS NMR, SEM, TEM, N2 and CO2 adsorption). To investigate the influence of porosity, the two types of fillers were incorporated into Matrimid® to prepare MMMs at varied loadings (8, 16 and 24 wt%). SEM confirmed that both BILP-101 and RT-BILP-101 are well dispered, indicating their good compatibility with the polymeric matrix. The partial pore blockage in the membrane was verified by CO2 adsorption isotherms on the prepared membranes. In the separation of CO2 from a 15:85 CO2:N2 mixture at 308 K, the incorporation of both BILPs fillers resulted in an enhancement in gas permeability together with constant selectivity owing to the fast transport pathways introduced by the porous network. It was noteworthy that the initial porosity of the filler had a large impact in separation permeability. The best improvement was achieved by 24 wt% RT-BILP-101 MMMs, for which the CO2 permeability increases up to 2.8-fold (from 9.6 to 27 Barrer) compared to the bare Matrimid®.

Li-Crown ether complex inclusion in MOF materials for enhanced H2 volumetric storage capacity at room temperature

The organometallic Li-Crown ether species, formed by the complexation of lithium cation with the hydrophobic 18Crown6 ether, has been included in three Metal-Organic-Frameworks (MOF) structures with different pore size: Cr-MIL-101, Fe-MIL100 and Ni-MOF-74. X-ray powder diffraction, thermogravimetric analysis, proton nuclear magnetic resonance, infrared spectroscopy and inductively coupled plasma atomic emission spectroscopy measurements have proved the successful incorporation of the organometallic units to the three MOFs without altering their crystalline structure. Hydrogen adsorption properties of the post-synthesis modified materials have been evaluated in a wide temperature (77–298 K) and pressure (1–170 bar) range conditions. The post-synthetic modification method used based on the MOF impregnation with a Li-Crown ether complex solution produced a partial pore blocking effect on the microporous Ni-MOF-74, reducing its hydrogen adsorption capacity. However, the inclusion of the crown-ether and particularly the Li-Crown ether complex resulted in an increase of the volumetric hydrogen adsorption capacity at room temperature for Cr-MIL101 and Fe-MIL-100, due to the pore volume reduction, higher confinement of H2 molecules in the cavities and the formation of new specific binding sites for H2 molecules. The inclusion of Li-Crown ether complex also enhances the H2 interaction with the mesoporous MOF structures, attributed to the additional electrostatic interactions produced by the presence of Li+ ions complexed to the crown ether molecules. Further work following this strategy to improve hydrogen adsorption capacity of mesoporous MOFs at room temperature should be extended to other MOF materials, checking its influence on their capacity for gas separation purposes.

Controlled Porosity of MCM-41 Obtained by Partial Blocking of Pores by Silicon Oil

Controlled Porosity of MCM-41 Obtained by Partial Blocking of Pores by Silicon Oil

Controlled Porosity of MCM-41 Obtained by Partial Blocking of Pores by Silicon Oil

Controlled Porosity of MCM-41 Obtained by Partial Blocking of Pores by Silicon Oil