Formation Mechanism Of Porous Structure Research Articles

Enhanced reduction of ilmenite ore by pre-oxidation in the view of pore formation

The promotion effect of pre-oxidation on reduction of ilmenite was revealed from the view of pore formation. The result shows that the enhancement of pre-oxidation on reduction of ilmenite ore is attributed to the formation of porous structure during the reduction process. Reduction of ilmenite is inhibited by iron-rutile topology structure formed on the particle surface. By contrast, porous structure ilmenite is regenerated during the ferric-to-ferrous reduction stage of the pre-oxidized ilmenite with dominant reduction rate over diffusion rate of produced ferrous ω ≥ 33.2 mol/m4. The newly formed porous structure ilmenite enlarges particle surface area with facilitated gas-solid contact, thus it is responsible for the enhancement of the reduction of pre-oxidized ilmenite. A novel formation mechanism of porous structure is also proposed based on the competition and coordination between the reduction rate and diffusion rate determined by reduction potential and temperature.

Universal low-temperature and template-free synthesis of sponge-like porous micron-sized elemental materials for high-performance lithium/potassium storage

Interconnected porous micron-sized materials can effectively enhance the ion transfer kinetics and structural stability, thus improving their rate capability and long-term lifespan, and maintaining high volumetric performance, but developing a universal and low-temperature method for the large-scale synthesis of porous materials remains a formidable challenge. Herein, we develop a universal low-temperature and template-free strategy to fabricate a series of sponge-like, interconnected porous micron-sized elements (e.g., Se, Te, Sb) through H2O2-assisted water bath. The formation mechanism of porous structure is demonstrated, originating from the non-homogeneous and continuous corrosion due to the preferential intergranular corrosion of polycrystalline particles and the soluble reaction products that do not passivate the corrosion interface. The as-obtained sponge-like porous elements present large reversible gravimetric and volumetric capacities and long stable lifespans. Specifically, the porous Te electrode delivers a high reversible capacity of 392.7 mAh g−1 (volumetric capacity: 1531.5 mAh cm−3) with 93.5% utilization ratio of active materials at 0.1 A g−1 and a long-stable lifespan with 500 cycles at 1.0 A g−1 in Li-Te batteries. Besides, in-situ TEM and ex-situ SEM observations demonstrate a small volume expansion and strong structural robustness of porous Te during cycling, stemming from its inward expansion mechanism and 3D stable interconnected porous structure. This work demonstrates a simple and universal strategy to design sponge-like porous materials for energy storage and catalysis, etc.

Hierarchically porous biochar preparation and simultaneous nutrient recovery from sewage sludge via three steps of alkali-activated pyrolysis, water leaching and acid leaching

In this study, preparation of hierarchically porous biochar (PB) and simultaneous nutrient recovery from sewage sludge were realized through three steps of KHCO3-activated pyrolysis, water leaching and acid leaching. The prepared PB samples were applied as adsorbents for the removal of 4-chlorophenol (4-CP) from aqueous solutions. Effect of pyrolysis temperature on the physicochemical properties of PB samples was investigated. The PB prepared at 900 °C (PB-900) had the highest surface area (1476.0 m2/g) and total pore volume (1.138 cm3/g). The formation mechanism of porous structure of PB-900 was revealed by investigating the phase transformation, element distribution and pore structure evolution during its whole preparation process. PB-900 showed a high 4-CP adsorption rate of 14.4 mg/(g∙min), and its maximum adsorption capacity for 4-CP was up to 192.4 mg/g. The mechanism of 4-CP removal by PB-900 was mainly physical adsorption, and its strong aromaticity strengthened its interaction with 4-CP through π-π bonding. The water leaching solution in the preparation process of PB-900 contained a lot of nutrient elements (K, Si, P), which was recovered for grass seeds germination. Compared with the samples cultured with ultrapure water only, the seed germination rate of samples cultured with ultrapure water added with 20% of pretreated water leaching solution increased from 63% to 80%, and the average shoot length of grass grown for 7 days increased by 51.4%. The findings of this study suggest that KHCO3 is an alternative activator to prepare hierarchically porous biochar adsorbent from sewage sludge and realize simultaneous nutrient recovery.

Nano-porous anodic alumina: fundamentals and applications in tissue engineering.

Recently, nanomaterials have been widely utilized in tissue engineering applications due to their unique properties such as the high surface to volume ratio and diversity of morphology and structure. However, most methods used for the fabrication of nanomaterials are rather complicated and costly. Among different nanomaterials, anodic aluminum oxide (AAO) is a great example of nanoporous structures that can easily be engineered by changing the electrolyte type, anodizing potential, current density, temperature, acid concentration and anodizing time. Nanoporous anodic alumina has often been used for mammalian cell culture, biofunctionalization, drug delivery, and biosensing by coating its surface with biocompatible materials. Despite its wide application in tissue engineering, thorough in vivo and in vitro studies of AAO are still required to enhance its biocompatibility and thereby pave the way for its application in tissue replacements. Recognizing this gap, this review article aims to highlight the biomedical potentials of AAO for applications in tissue replacements along with the mechanism of porous structure formation and pore characteristics in terms of fabrication parameters.

Selective tailoring of covalent bonds on graphitized hollow carbon spheres towards controllable porous structure and wideband electromagnetic absorption

Recently, the exploration of a new strategy to create pores on carbon frameworks has received great interest. Herein, the selectively tailoring of the covalent bonding method has been shown to be one of the effective methods to generate pores based on graphitic hollow carbon frameworks (HGC). The mechanism of porous structure formation is due to directional clipping of sp2 C–C- and CO covalent bonds into C–O bonds. Due to the effectively ability for selective tailoring of covalent bonds, the resulting porous HGC has dielectric transition behavior from conductive loss to dipole polarization dependent type, which is greatly beneficial to electromagnetic absorption. The results show that the porous HGC developed by this method has exceptionally EM absorption capacity, and the maximum qualified absorption bandwidth (fE) is 7.7 GHz at the thickness of 2.2 mm. Therefore, this work opens up a potential method for the design and synthesis of high-performance EM absorbers.

Slow pyrolysis polygeneration of bamboo (Phyllostachys pubescens): Product yield prediction and biochar formation mechanism

Slow pyrolysis of bamboo was conducted at 400–600 °C and pyrolysis products were characterized with FTIR, BET, XRD, SEM, EDS and GC to establish a pyrolysis product yield prediction model and biochar formation mechanism. Pyrolysis biochar yield was predicted based on content of cellulose, hemicellulose and lignin in biomass with their carbonization index of 0.20, 0.35 and 0.45. The formation mechanism of porous structure in pyrolysis biochar was established based on its physicochemical property evolution and emission characteristics of pyrolysis gas. The main components (cellulose, hemicellulose and lignin) had different pyrolysis or chemical reaction pathways to biochar. Lignin had higher aromatic structure, which resulted higher biochar yield. It was the main biochar precursor during biomass pyrolysis. Cellulose was likely to improve porous structure of pyrolysis biochar due to its high mass loss percentage. Higher pyrolysis temperatures (600 °C) promoted inter- and intra-molecular condensation reactions and aromaticity in biochar.

A Phase Separation Route to Synthesize α-Fe2O3 Porous Nanofibers via Electrospinning for Ultrafast Ethanol Sensing

A facile and economic procedure was provided to synthesize α-Fe2O3 nanofibers. In this procedure, porous α-Fe2O3 nanofibers were obtained by a single-polymer/binary-solvent system, while solid α-Fe2O3 nanofibers were prepared by a single-polymer/single-solvent system. The crystal structure and morphology of both samples were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption/desorption isotherms. The formation mechanism of porous structure was based on solvent evaporation-induced phase separation by the use of mixed solvents with different volatility. Furthermore, ethanol-sensing performance of the porous α-Fe2O3 nanofibers was evaluated and compared with solid α-Fe2O3 nanofibers. Results from gas-sensing measurements reveal that porous α-Fe2O3 nanofibers exhibit higher sensitivity and slightly longer recovery time than solid α-Fe2O3 nanofibers. Over all, the gas sensor based on porous α-Fe2O3 nanofibers shows excellent ethanol-sensing capability with high sensitivity and ultrafast response/recovery behaviors, indicating its potential application as a real-time monitoring gas sensor.

Evolution and Performance of Porous Structure on the Surface of Fe<sub>76</sub>Si<sub>7.2</sub>B<sub>9.6</sub>P<sub>7.2</sub> Amorphous Ribbon

Porous structures with enhanced specific surface area exhibit higher catalytic activity than the bulk counterpart. In this work, the porous structures with tunable pore size are synthesized through chemical dealloying of the Fe76Si7.2B9.6P7.2 amorphous alloys in corrosion solution. Meanwhile, under the effect of ultrasound-assistance, the distribution of porous and composition are uniform on the amorphous alloys. X-ray diffraction demonstrated that the amorphous structure has not been corrupted or tampered in the dealloyed samples. It was also found that the porous alloy shows superior catalytic activity in degrading phenol-containing wastewater, the degradation rate significantly increases as compared to the un-dealloyed Fe76Si7.2B9.6P7.2 amorphous alloys. Finally, the formation mechanism of porous structure is discussed.

Hierarchically 3D porous films electrochemically constructed on gas–liquid–solid three-phase interface for energy application

Hierarchically porous films constructed on gas–liquid–solid three-phase interface by electrodeposition are reviewed. The formation mechanism of porous structure is discussed. The electrochemical properties of porous films as electrode materials for energy application are highlighted.

Formation mechanism of porous structure in plastic parts injected by microcellular injection molding technology with variable mold temperature

Microcellular Injection Molding (MIM) process combined with rapid heat cycle molding (RHCM) technique can fabricate microcellular foamed plastic parts with excellent surface appearance. The porous structure influences the foamed parts’ performances significantly and its evolution process is very complex in RHCM/MIM process. The temperature field and flow field play a very crucial role in determining the porous structure of the foamed parts. In this study, we developed a non-isothermal mathematical model based on the two-phase model to calculate the temperature field and flow field in RHCM/MIM process. Particularly, the coupling heat transfer between the injection mold and the polymer melt is considered by using the implicit domain coupled algorithm. By comparing with the experimental results, it is found that the developed model can predict the temperature field very accurately. The thermal response characteristics in RHCM/MIM process were further analyzed. By combining the simulation results with the cellular morphology obtained by experiments, we deeply analyzed the formation mechanisms of the cellular morphology in RHCM/MIM process.

Poly(N‐isopropylacrylamide) gel‐based macroporous monolith for continuous‐flow recovery of palladium(II) ions

ABSTRACTMacroporous monoliths, composed of thermoresponsive, tertiary‐aminated, and crosslinking monomers, were prepared for continuous‐flow separation of palladium(II) ions. N‐Isopropylacrylamide was required to form the porous structure in the monoliths, indicating that the mechanism of porous structure formation involved polymerization‐induced phase separation of the poly(N‐isopropylacrylamide) gel. Tertiary‐aminated monoliths showed adsorption selectivity for palladium(II) ions in hydrochloric media, compared with copper(II) ions. The maximum capacities of the monoliths with tertiary amine contents of 10, 20, 30, and 70 mol % for palladium(II) ions were 0.6, 1.1, 1.3, and 2.3 mmol/g, respectively. Darcy's permeabilities of water through the macroporous monolith were 10−14 to 10−13 m2, and those were comparable to that through a commercially available membrane filter with a pore size of several micrometers. In the continuous‐flow process, the macroporous monolith with tertiary amine selectively adsorbed palladium(II) ions in the coexistence of copper(II) ions with 10 times higher concentration than the palladium(II) ions. The palladium(II) ions were eluted from the macroporous monolith, and the concentration of palladium(II) ions in the eluate was up to 45 times of that in the feed solution. The average enrichment factor and total recovery percentage of palladium(II) ions were 8.7 times and 95%, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44385.

Highly Efficient FRET System Capable of Deep Photodynamic Therapy Established on X-ray Excited Mesoporous LaF3:Tb Scintillating Nanoparticles.

Photodynamic therapy (PDT) for deep-seated tumor is largely impeded by the limited penetration depth of excitation light in tissue. X-ray is considered as an ideal energy source to activate photosensitizers (PSs) located deep within the body with the assistance of scintillating nanoparticles (ScNPs). However, the efficacy under this concept is not satisfying due to the low scintillating luminescence and weak energy transfer from ScNPs to PSs. Here, mesoporous LaF3:Tb ScNPs were successfully synthesized by a facile hydrothermal process to act as PS carriers and X-ray energy transducers, owing to their good ionizing radiation stopping power and high luminescence efficiency. The formation mechanism of porous structure was elucidated in detail with classical crystallization theory. After a systematic investigation, LaF3:Tb ScNPs with optimized scintillating luminescence were obtained for loading Rose Bengal (RB) to establish an efficient FRET system, owing to their excellent spectral match. The FRET efficiency between ScNPs and RB was calculated to be as high as 85%. Under irradiation, enhanced (1)O2 generation induced by LaF3:Tb-RB nanocomposites via FRET process was detected. This LaF3:Tb-RB FRET system shows great potential to be applied in X-ray stimulated PDT for deep-seated tumors in the future.

Effects of organic templates on the structural properties of porous clay heterostructures: a non-micellar template model for porous structure

In this study, a series of surfactants with different chain lengths were used to investigate the effect of organic templates on the structural properties of porous clay heterostructures (PCH). The variation tendencies of structural properties and chemical component were characterized by X-ray diffraction, CHN elemental analysis, major element analysis, and nitrogen adsorption/desorption at −196 °C. Non-local density functional theory was employed to characterize pore size distributions in both micropore and mesopore regions owing to the bi-model pore structures of PCH. The major textural parameters of PCH samples increased with increasing the chain length and the intercalated amount of template agent, while the most probable pore size remained unchanged around 1.3–1.4 nm. Based on the structural and chemical component results of PCH, a non-micellar template model was presented to explain the formation mechanism of porous structure. By the extrusion and occupation of polymerizate of TEOS within interlayer, a fixed number of hydrocarbon chains congregate together to form surfactant aggregates (template). The aggregates with different chain lengths cause the increase of pore volume in depth dimension rather than in diameter. The obtained results also shed some light on the different roles of inorganic base clay and organic template agents in the formation of porous structure. Montmorillonite as the inorganic host supplies the space for pillaring reaction and controls the arrangement of template agent within interlayer. As the template agent and modifying agent, the cationic surfactant is the dominant factor in forming pores relative to amine. The neutral amine mainly serves as catalyst for the polymerization of TEOS besides its co-template effect.

Atomic Force Microscopic Studies of Porous TiO2 Thin Films Prepared by the Sol-Gel Method

Porous titanium dioxide thin films were prepared from alkoxide solutions with and without polyethylene glycol (PEG) by the sol-gel method on soda-lime glass. The effects of PEG addition to the precursor solution on the microstructure and roughness of the resultant thin films were investigated by atomic force microscopy (AFM). It was found that TiO2 films prepared from the precursor solution without PEG had granular microstructure and flat texture, and was composed of about 100 nm spherical particles. With an increase in the times of coating cycles, the roughness of films decreased and the size of TiO2 particles increased. On the other hand, the larger the amount and molecular weight of the added PEG in precursor solutions, the larger the diameter and the depth of pores in the resultant films on the decomposition of PEG during heat-treatment. The surface of the films was also rougher, and fewer pores were produced during heat-treatment. The mechanism of porous structure formation in the TiO2 films was explained using the principle of spinodal phase separation.

Orientation of pores in microporous polyethylene films as determined by polarized absorption spectroscopy

Microporous polyethylene films with good mechanical properties can be produced on the basis of hard-elastic specimens by uniaxial deformation. The so called “guest-host” effect [1, 2] was explored to determine the order parameter of pores in a series of PE membranes so produced by polarized absorption spectroscopy using dichroic dyes dissolved in the nematic liquid crystal ZLI 1840 (LC) as indicator. The parameter of the orientation order SA of the pores along the draw direction was found to increase with increasing spin draw. A qualitative comparison of SA with the thermodynamic behavior of the dye + LC systems confined in the pores was made. The results obtained are related to the mechanism of porous structure formation.

Formation mechanism of porous structure in polytetrafluoroethylene (PTFE) porous membrane through mechanical operations

AbstractPolymeric porous membranes were prepared from polytetrafluoroethylene (PTFE) fine powder by a series of mechanical operations, such as extrusion, rolling, and stretching. The structure of the prepared porous membrane was well characterized by a spatial periodicity of nodes (domain of agglomerated PTFE particles) and fibril domains. The fibrils were highly oriented in the direction of the stretching operation, providing pores in the polymeric membrane as slit‐like voids between adjoining fibrils. The unit size of the periodic structure varied depending on the number averaged molecular weight of PTFE and the stretching conditions, the temperature of stretching, and the stretching rate and stretching ratio. A fibril consisted of several thread‐like structures that were easily formed between PTFE particles due to the rolling operation in parallel with their direction. The dependence of the steady tensile stress in the stretching operation on the PTFE molecular weight was much weaker than that presumed for noncrystalline polymeric systems. The activation energy of 11.3 kJ/mol for the growth of fibrils was only several times as large as the thermal energy at the ambient temperature. These results imply that the thread‐like structures can easily be pulled out of PTFE particles. This view is in accordance with the previously proposed microstructure in PTFE particles.

Mechanism of porous structure formation in intermetallic synthesis

The specific features of diffusional mixing of metals in synthesis of intermetallides, with one component being in the liquid state, are considered, and the nature of stresses in the diffusion zone is discussed. A model of a porous powder body is proposed to predict the behavior of mixtures in intermetallic synthesis in a thermal explosion regime. Analytical equations describing the sign and magnitude of volume changes of powder bodies in synthesis are obtained and experimentally checked. Examples are presented to illustrate the synthesis of highly porous materials.

Porous Phosphates of Trivalent Metals: Problems of Their Synthesis and Application

Abstract Porous phosphates are compounds with a branched system of pores, such as X-ray amorphous xerogels of metalphosphates and crystalline phosphates of zeolite type. Having generalized extensive experimental data about the conditions of Al-, Fe-, Cr-, Ga-, In-, Y-phosphate hydrogels synthesis we found the influence of a number of factors on the rates of their formation, stability of structures and the porosity character of xerogels. The mechanism of porous structure formation of xerogels of metalphosphates has been proposed. The problems connected with the regulation of porous structure of xerogels have been discussed. The formation of porous crystalline aluminophosphates of zeolite type has been accomplished through a number of stages. The nature of alkyl ammonium bases influences the direction of the crystallization process and the type of the structure. It was noted that the stoppind of crystallization on different stages of synthesis gives the possibility to obtain new molecular sieves. Thermal ch...

Porous Phosphates of Trivalent Metals: Problems of their Synthesis and Application

Abstract Porous phosphates are compounds with a branched system of pores, such as X-ray amorphous xerogels of metalphosphates and crystalline phosphates of zeolite type. Having generalized extensive experimental data about the conditions of Al-, Fe-, Cr-, Ga-, In-, Y-phosphate hydrogels synthesis we found the influence of a number of factors on the rates of their formation, stability of structures and the porosity character of xerogels. The mechanism of porous structure formation of xerogels of metalphosphates has been proposed. The problems connected with the regulation of porous structure of xerogels have been discussed. The formation of porous crystalline aluminophosphates of zeolite type has been accomplished through a number of stages. The nature of alkyl ammonium bases influences the direction of the crystallization process and the type of the structure. It was noted that the stoppind of crystallization on different stages of synthesis gives the possibility to obtain new molecular sieves. Thermal changes and sorption properties of aluminopnosphates of zeolite type have been studied. During the process of removing organic cations the formation of secondary porosity was established. The effectiveness of applying porous metalphosphates in catalysis and adsorption processes has been showed.