Concept: Soil mechanics
The aim of this study was to develop polyurethane (PU) based fibro-porous membranes and to investigate the size-effect of hierarchical porous structure on permeability and surface properties of the developed electrospun membranes. Non-woven Selectophore™ PU membranes having tailored fibre diameters, pore sizes, and thickness were spun using electrospinning, and their chemical, physical and glucose permeability properties were characterised. Solvents, solution concentration, applied voltage, flow rate and distance to collector, each were systematically investigated, and electrospinning conditions for tailoring fibre diameters were identified. Membranes having average fibre diameters - 347, 738 and 1102 nm were characterized, revealing average pore sizes of 800, 870 and 1060 nm and pore volumes of 44, 63 and 68% respectively. Hydrophobicity increased with increasing fibre diameter and porosity. Effective diffusion coefficients for glucose transport across the electrospun membranes varied as a function of thickness and porosity, indicating high flux rates for mass transport. Electrospun PU membranes having significantly high pore volumes, extensively interconnected porosity and tailorable properties compared to conventional solvent cast membranes can find applications as coatings for sensors requiring analyte exchange.
The design of passive biological filters has evolved and current design practices are predominantly based on flow (either horizontal or vertical) through porous media. To date, no method has been developed to accurately estimate the effective life expectancy of these types of treatment systems, nor have non-intrusive methods to determine the extent of substratum clogging been perfected. This research presents the results of tracer studies on various stages of two hybrid-passive landfill leachate treatment systems: an aerated pretreatment system followed by two different types of vertical-flow through porous media treatment systems. The tracer studies were used to assess changes in the active volumes of the different stages of the leachate treatment systems over a 9-month period. An analytical method, employing the governing equations for flow through porous media, was used to quantify the changes in saturated hydraulic conductivity in the treatment system cells. The results from the analytical method were combined with the results from the tracer study to further the understanding of the flow and mixing within the treatment system cells.
A major goal of metal-organic framework (MOF) research is the expansion of pore size and volume. Although many approaches have been attempted to increase the pore size of MOF materials, it is still a challenge to construct MOFs with precisely customized pore apertures for specific applications. Herein, we present a new method, namely linker labilization, to increase the MOF porosity and pore size, giving rise to hierarchical-pore architectures. Microporous MOFs with robust metal nodes and pro-labile linkers were initially synthesized. The mesopores were subsequently created as crystal defects through the splitting of a pro-labile-linker and the removal of the linker fragments by acid treatment. We demonstrate that linker labilization method can create controllable hierarchical porous structures in stable MOFs, which facilitates the diffusion and adsorption process of guest molecules to improve the performances of MOFs in adsorption and catalysis.
Self-assembled crystalline porous organic salts (CPOSs) formed by the acid-base combination and with one-dimensional polar channels containing water molecules inside the channels have been synthesized. The water content in the channels of the porous salts plays an important role in the proton conduction performance of the materials. The porous salts described in this study feature high proton conductivity at ambient conditions and can reach as high as 2.2 x10-2 S cm-1 at 333 K and high humid conditions, which is among the best conductivity values reported yet for other porous materials e.g. Metal Organic Frameworks, Hydrogen-bonded Organic Frameworks etc. These materials exhibiting permanent porosity represent a novel group of porous materials and can find interesting applications as proton exchange membrane fuel cells.
Sulphur is an attractive cathode material with a high specific capacity of 1,673 mAh g(-1), but its rapid capacity decay owing to polysulphide dissolution presents a significant technical challenge. Despite much efforts in encapsulating sulphur particles with conducting materials to limit polysulphide dissolution, relatively little emphasis has been placed on dealing with the volumetric expansion of sulphur during lithiation, which will lead to cracking and fracture of the protective shell. Here, we demonstrate the design of a sulphur-TiO(2) yolk-shell nanoarchitecture with internal void space to accommodate the volume expansion of sulphur, resulting in an intact TiO(2) shell to minimize polysulphide dissolution. An initial specific capacity of 1,030 mAh g(-1) at 0.5 C and Coulombic efficiency of 98.4% over 1,000 cycles are achieved. Most importantly, the capacity decay after 1,000 cycles is as small as 0.033% per cycle, which represents the best performance for long-cycle lithium-sulphur batteries so far.
- Journal of biomedical materials research. Part B, Applied biomaterials
- Published almost 2 years ago
Research characterizing transport of nutrients and waste in tissue engineering scaffolds has led to the study of scaffold properties that contribute to permeability and porosity of the scaffold. Both permeability and porosity contribute to the transport properties of the scaffold; however, permeability relates to the degree to which pores are interconnected within the scaffold. This work evaluated permeability for woven polymer fiber scaffolds by modulating the following scaffold parameters: material combination, weave configuration, and fiber geometry. Materials tested were poly-l-lactide and poly-l-lactide-co-ɛ-caprolactone in various combinations. Plain and crowfoot weave configurations were compared, and grooved wicking fibers were compared with round cross-section fibers to study fiber geometry. A modification of the constant head hydraulic conductivity test was used in combination with a vertical wicking test to determine levels of permeability of the woven scaffolds. Results showed a significant effect on permeability for combinations of weave configuration, fiber geometry, and material combination. However, modulating fiber geometry demonstrated the most significant contribution to permeability. This result suggests the grooved wicking geometry may be used in scaffold development to regulate transport by selectively moving fluid away or toward the area of interest by capillary action. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2018.
The air permeability coefficient has a high correlation with the water content of municipal solid waste. In this study, continuous drying methodology using a tension meter was employed to construct the soil water characteristic curve of municipal solid waste (M-SWCC). The municipal solid waste air permeability test was conducted by a newly designed apparatus. The measured M-SWCC was well reproduced by the van Genuchten (V-G) model and was used to predict the parameters of typical points in M-SWCC, including saturated water content, field capacity, residual water content and water content at the inflection point. It was found that the M-SWCC was significantly influenced by void ratio. The final evaporation and test period of M-SWCC increase with the increase in void ratio of municipal solid waste. The evolution of air permeability coefficient with water content of municipal solid waste depicted three distinct characteristic stages. It was observed that the water contents that corresponded to the two cut-off points of the three stages were residual water content and water content at the inflection point, respectively. The air permeability coefficient of municipal solid waste decreased with the increase of the water content from zero to the residual water content. The air permeability coefficient was almost invariable when the water content increased from residual water content to the water content at the inflection point. When the water content of municipal solid waste exceeded the water content at the inflection point, the air permeability coefficient sharply decreased with the increase of water content.
- Environmental science and pollution research international
- Published almost 2 years ago
Municipal sludge, composed of numerous types of organic matter with a gel structure, has high water content, low permeability coefficient, and poor mechanical properties. Fenton oxidation-assisted vacuum preloading method for municipal sludge treatment was proposed. First, the municipal sludge was oxidized and treated with Fenton’s reagent; then, drainage consolidation was performed on the sludge with the vacuum preloading method. The optimal dosage of Fenton’s reagent for municipal sludge was determined. Comparative experiments of the one-dimensional consolidation of municipal sludge treated with Fenton’s reagent and the drainage consolidation by Fenton oxidation-assisted vacuum preloading were conducted. The results reveal that the specific resistance of municipal sludge decreases upon Fenton oxidation by approximately 98.6% at the optimal dosage of 22%, sludge water content decreases from 82.14 to 66.67%, volume reduces by ~ 40%, and unconfined compressive strength increases to 55 kPa.
Groundwater is an important factor of slope stability, and 90% of slope failures are related to the influence of groundwater. In the past, free surface calculations and the prediction of water inflow were based on Darcy’s law. However, Darcy’s law for steady fluid flow is a special case of non-Darcy flow, and many types of non-Darcy flows occur in practical engineering applications. In this paper, based on the experimental results of laboratory water seepage tests, the seepage state of each soil layer in the open-pit slope of the Yanshan Iron Mine, China, were determined, and the seepage parameters were obtained. The seepage behaviour in the silt layer, fine sand layer, silty clay layer and gravelly clay layer followed the traditional Darcy law, while the gravel layers showed clear nonlinear characteristics. The permeability increases exponentially and the non-Darcy coefficient decreases exponentially with an increase in porosity, and the relation among the permeability, the porosity and the non-Darcy coefficient is investigated. A coupled mathematical model is established for two flow fields, on the basis of Darcy flow in the low-permeability layers and Forchheimer flow in the high-permeability layers. In addition, the effect of the seepage in the slope on the transition from Darcy flow to Forchheimer flow was considered. Then, a numerical simulation was conducted by using finite-element software (FELAC 2.2). The results indicate that the free surface calculated by the Darcy-Forchheimer model is in good agreement with thein situmeasurements; however, there is an evident deviation of the simulation results from the measured data when the Darcy model is used. Through a parameter sensitivity analysis of the gravel layers, it can be found that the height of the overflow point and the water inflow calculated by the Darcy-Forchheimer model are consistently less than those of the Darcy model, and the discrepancy between these two models increases as the permeability increases. The necessity of adopting the Darcy-Forchheimer model was explained. The Darcy-Forchheimer model would be applicable in slope engineering applications with highly permeable rock.
TiO₂/g-C₃N₄/PVDF composite membranes were prepared by a phase inversion method. A comparison of the performance and morphology was carried out among pure PVDF, g-C₃N₄/PVDF, TiO₂/PVDF and TiO₂/g-C₃N₄/PVDF composite membranes. The results of permeability and instrumental analysis indicated that TiO₂ and g-C₃N₄ organic-inorganic composites obviously changed the performance and structure of the PVDF membranes. The porosity and water content of 0.75TiO₂/0.25g-C₃N₄/PVDF composite membranes were 97.3 and 188.3 L/(m²·h), respectively. The porosity and water content of the 0.75TiO₂/0.25g-C₃N₄ membranes were increased by 20.8% and 27.4%, respectively, compared with that of pure PVDF membranes. This suggested that the combination of organic-inorganic composite with PVDF could remarkably improve UTS, membrane porosity and water content.