Pore Surface Coverage Research Articles

Plasma‐induced formation of coatings on vegetable ivory microparticles immersed in silicone oil: Enhancing surface coverage using natural products

AbstractAiming to enhance the potential applications of bioproducts, we developed an innovative approach for their hydrophobization using plasma activation of liquids. In this study, microparticles of vegetable ivory, a porous hygroscopic material, were treated by an air plasma jet while immersed in silicone oil. The in‐liquid plasma treatment formed coatings that reduced particle water vapor sorption. Pore surface coverage and sorption reduction were enhanced by mixing silicone oil with copaiba oil‐resin (Copaifera spp.). Mulateiro extract (Calycophyllum spruceanum) was not as effective, owing to a lower affinity with silicone oil. For the first time, we demonstrate the plasma‐induced coating formation on particles immersed in liquid mixtures, a process in which liquid–liquid interfacial properties play a fundamental role.

Enhanced tar removal in syngas cleaning through integrated steam catalytic tar reforming and adsorption using biochar

Steam catalytic tar reforming (SCTR) using biochar is a popular technique for tar removal in syngas cleaning. However, its efficacy drops while treating syngas at low temperatures (<750 °C) typically encountered in fluidized or downdraft gasifiers. This work proposes integrating an adsorption section post reforming, that operates at a relatively lower temperature (220 °C) to additionally remove the light tar components using biochar. The integrated approach was assessed for the removal of mallee-wood generated tar using mallee-wood biochar as catalyst and adsorbent. Tar yield estimates revealed overall removal by ∼80 %, with reforming contributing ∼40 % and adsorption ∼60 % of the residual tar. Elaborate tar analysis based on UV-spectroscopy proved substantial removal of light tar compounds in the two-step process. Biochar structural analysis based on Raman spectroscopy revealed a growing predominance of higher aromatics in adsorbent during biochar-volatile interactions, due to adsorption of both heavy and light tar compounds. The evolution trends were validated by correlating the specific reactivity of utilized biochar samples based on thermogravimetric analysis. Biochar morphological analysis through BET analysis showed a steep drop in surface area from 101.40 to 0.043 m2/g, implying pore surface coverage by tar compounds which were also evident from FESEM images.

Application of machine learning in colloids transport in porous media studies: Lattice Boltzmann simulation results as training data

Colloid transport through a porous medium changes geometrical and hydraulic properties of the pore space. The impact of this effect depends on the colloid types and pore space surface properties which determine the likelihood of pore clogging. Colloid attachment and subsequent detachment are key factors in pore clogging. In this study, the impact of four major fluid and colloids properties on the pore surface and hydraulic conductivity alteration during colloids transport were evaluated using machine learning. These four parameters include solution ionic strength, zeta potential, colloid size and fluid flow velocity.A combined lattice Boltzmann-smoothed profile method was used to simulate accurately coupled mechanisms governing colloid transport to evaluate the impact of the four parameters on the resulting pore space properties after colloid transport. The result of several simulations revealed significant changes of pore surface coverage by the attached colloids, and conductivity, void fraction and coordination number of colloid agglomerates created during transport of individual colloids. Since the simulation of the impact of combination of all possible sets of four parameters is very time consuming, an Artificial Neural Network (ANN) was used as a prognostic method to use the results of several simulations to predict the behavior for a wide range of pore, colloidal and fluid properties. Reported results from a set of 162 simulation case studies for different possible combination of solution ionic strength, zeta potentials, colloid size and flow velocity were selected as input parameters for the machine learning. Four output parameters, namely, pore surface coverage, conductivity, void fraction and coordination number of the colloidal particles were selected.To lower the prediction error value, which is targeted to be lower than 10%, networks were trained 50 times using a MATLAB code, and in each training, after at most 10 epochs, networks were trained. A maximum relative error value of 8.95% was obtained, which is very well within the range of training quality criteria. The results show that the ANN can profoundly predict the simulation outcomes for a wide range of ionic strength (IS) and can be directly used to obtain the value of dependent variables through simple calculations using network weights and transfer functions.

Effect of Surface Chemistry on Confined Phase Behavior in Nanoporous Media: An Experimental and Molecular Modeling Study

It is well accepted that nanopore size is a controlling parameter in determining the phase behavior of confined adsorbate molecules. Despite this knowledge, the quantitative effect of surface chemistry on the confined phase behavior is a factor that remains obfuscated. Obtaining a complete understanding of the variables controlling confined phase behavior is a critical step in developing more complete equations of state for predictive modeling. To this end, a combined experimental and molecular modeling study was conducted to investigate the effects of surface chemistry and wetting on the confined phase behavior of propane and n-butane in modified and unmodified silica MCM-41. Isotherms were measured in four types of silica MCM-41 modified with varying sizes of alkyl groups to determine the effects of increasing surface modification. Results showed that increased pore surface coverage of carbon resulted in a notable change in the capillary condensation pressures, adsorption enthalpy, and confined critical temperature of the adsorbate. Correlations between the surface coverage of carbon and the confined critical temperature were presented and supported by thermodynamic arguments. The primary conclusions were partially supported by hybrid molecular dynamics-Monte Carlo simulations of propane adsorption in models of the four types of experimental adsorbents. Several differences were noted and explained between the experimental and modeling results. Energetic heterogeneity on the surface of the modified MCM-41 adsorbents as well as differences in adsorbate entropy induced by surface features and chemistry were suggested as primary driving factors for the observed trends. The results of this work have direct implications for improving understanding of confined phase behavior in materials of varying surface chemistries.

Nanoparticle-Directed Metal-Organic Framework/Porous Organic Polymer Monolithic Supports for Flow-Based Applications.

A two-step nanoparticle-directed route for the preparation of macroporous polymer monoliths for which the pore surface is covered with a metal-organic framework (MOF) coating has been developed to facilitate the use of MOFs in flow-based applications. The flow-through monolithic matrix was prepared in a column format from a polymerization mixture containing ZnO-nanoparticles. These nanoparticles embedded in the precursor monolith were converted to MOF coatings via the dissolution-precipitation equilibrium after filling the pores of the monolith with a solution of the organic linker. Pore surface coverage with the microporous zeolitic imidazolate framework ZIF-8 resulted in an increase in surface area from 72 to 273 m2 g-1. Monolithic polymer containing ZIF-8 coating was implemented as a microreactor catalyzing the Knoevenagel condensation reaction and also in extraction column format enabling the preconcentration of trace levels of toxic chlorophenols in environmental waters. Our approach can be readily adapted to other polymers and MOFs thus enabling development of systems for flow-based MOF applications.

Porous electrospun polycaprolactone fibers: Effect of process parameters

The effect of electrospinning process parameters (solution flow rate, applied voltage, spinning distance) on the size and surface morphology of porous electrospun poly(e-caprolactone) was investigated in this study. Response surface methodology was implemented for the design and conduction of electrospinning experiments. The feed solution was a 12.5% w/v poly(e-caprolactone) (PCL) solution in a binary solvent mixture of 90%v/v chloroform/ dimethyl sulfoxide. Spinning distance of 10-25 cm, applied voltage of 10-25 kV and feed flow rate of 0.5-5 ml/h were the range of limiting values of the independent variables used for the development of a central composite design. Second order polynomial equations, correlating electrospinning process parameters to relative pore coverage and fibre average diameter were developed and validated. An increase in any of the electrospinning process parameters favoured pore formation and fibre diameter increase. Under the experimental conditions investigated, the relative pore surface coverage was 15.8-31.9% and the average fibre diameter was in the range of 1.6-3.3 μm. Applied voltage was proven to be the parameter with the strongest impact on both, fibre diameter and surface morphology.

Drug release through liposome pores

Electrical, ultrasound and other types of external fields are known to induce the formation of pores in cellular and model membranes. This paper examines drug release through field induced liposome pores using Monte Carlo simulations. We find that drug release rates vary as a function of pore size and spacing, as well as the overall fraction of surface area covered by pores: The rate of release from liposomes is found to increase rapidly with pore surface coverage, approaching that of the fully ruptured liposome at fractional pore areas. For a given pore surface coverage, the pore size affects the release rate in the limit of low coverage, but not when the pores cover a relatively high fraction of the liposome surface area. On the other hand, for a given pore size and surface coverage, the distribution of pores significantly affects the release in the limit of high surface coverage: The rate of release from a liposome covered with a regularly spaced array of pores is, in this limit, higher than the release rate from (most) systems where the pores are distributed randomly on the liposome surface. In contrast, there is little effect of the pore distribution on release when the pore surface coverage is low. The simulation results are in good agreement with the predictions of detailed diffusion models.

Efficient detection and extraction of cobalt(II) from lithium ion batteries and wastewater by novel composite adsorbent

This study developed a novel composite adsorbent for highly selective and sensitive detection and extraction of cobalt (Co(II)) from lithium-ion batteries (LIBs) and wastewater. The composite adsorbent was prepared by indirect immobilization of 6-((2-(2-hydroxy-1-naphthoyl)hydrazono)methyl)benzoic acid (HMBA) onto mesoporous silica monoliths. The composite adsorbent enhanced the color formation by stable complexation as [Co(II)–HMBA]n+ complexes during detection and sorption operations. The data evident the one-step detection of wide range Co(II) concentrations into interior pore surface coverage of the composite adsorbent from solutions without using high tech instruments, which was unique feature of this adsorbent. The influence of different sorption parameters, such as: initial Co(II) concentration, equilibration time, solution pH and the presence of competing ions and reuses were studied and discussed systematically. The effective pH range for Co(II) ions detection and sorption was neutral pH region and the maximum sorption capacity of the adsorbent was as high as 189.37mg/g. The adsorbed Co(II) was eluted with stripping agent (0.3M HCl) and simultaneously regenerated into initial form for the next capturing operations after rinsing with water. The data also clarified that the composite adsorbent was selectively extracted Co(II) from LIBs even in the presence of high concentration diverse ions. Importantly, the composite adsorbent was retaining functionality in spite of many chemical treatments during sorption–elution-recovery/regeneration cycles. Therefore, the present study revealed that such a low-cost material could be used as potential adsorbent for the selective detection and recovery of Co(II) ions from LIBs and wastewater streams.

Optical mesosensor for capturing of Fe(III) and Hg(II) ions from water and physiological fluids

This study developed a pH-dependent mesosensor for the optical and selective removal of Hg2+ ions from drinking water and physiological fluids. The fine-tuned surface patterning of the mesoscopic solid aluminosilica scaffolding architectures, which was achieved using a dispersible active agent such as a cationic surfactant, resulted in the dense immobilization of addressable diphenylcarbazide chelating agent. These mesosensor responses can be triggered by the target species and can transduce measurable optical signals under synergistic pH conditions, thus enabling the binding of Fe3+ and Hg2+ metals into a hydrophobic chelating pocket to be simulated. Results verified the one-step removal and optical adsorption efficiency of ultra-trace, wide-range (0.001mg dm−3 to 2.0mg dm−3) concentrations of Fe3+ and Hg2+ ions into the interior pore surface coverage of the DPC-modified mesosensor from drinking water. Importantly, the mesosensor can be repeatedly recycled without damaging the unique mesostructures. Furthermore, the hemolysis test of Hg2+ ion toxicity in red blood cells (RBCs) and the counteraction effect of the phosphatidylserine (Ptd-L-Ser) receptor exposure of RBCs were also investigated in a physiological system such as human blood. Results indicated that the strong binding site-metal interaction enabled the remarkably selective removal of Hg2+ ions from physiological fluids.

The fabrication and surface functionalization of porous metal frameworks – a review

Porous metal frameworks offer potentially useful applications for the aerospace, automotive and bio-medical industries. They can be used as electrodes, actuators, or as selective membrane films. The versatility of the physical features (pore size, pore depth, overall porosity and pore surface coverage) as well as the large range of surface chemistries for both metal oxides and pure noble metals offers scope to functionalise metal nano-particles and networks of nano-porous metal structures. As well as traditional routes to producing metal structures, such as metal sintering or foaming, novel high-throughput techniques have recently been investigated. Nanoparticle self-assembly, metal ion reduction and deposition as well as metal alloy de-alloying were identified as sustainable routes to produce large surface areas of such nano-porous metal frameworks. The main limitations of the current fabrication techniques include the difficulty to process stable and homogeneous arrays of nano-scale pores and the control of their morphology due to the high reactivity of nano-structured metal structures. This paper aims at critically reviewing the various fabrication techniques and surface functionalization routes used to produce advanced functional porous metal frameworks. The limitations and advantages of the different fabrication techniques will be discussed in light of the final material properties and targeted applications.

Sulfur dioxide as an activating agent for sulfur-impregnated activated carbon produced from dense petroleum coke

To develop novel sorbent materials for capturing vapor mercury from industrial flue gases at high temperatures, high-sulfur oil-sands fluid coke was activated using 50% sulfur dioxide (SO2) at 700°C under various pre-treatment conditions. Pyrolysis in nitrogen prior to activation significantly decreased specific surface area (SSA) of the product, which was attributed to the thermoplastic behavior of coke at high temperatures. Air pre-oxidation suppressed this effect and provided an enhancement over non-pyrolyzed coke, with SSA peaking at 447 m2/g after 5 h activation. Acid washing of air pre-oxidized activated coke in 10% hydrochloric acid increased SSA by removal of inorganic ash which added weight but contributed minimal surface area. Decreasing initial particle size range from 212–300 to 53–106 μm significantly increased SSA, which was attributable to an outer porous layer of constant thickness. Under optimized conditions, an SSA of 531 m2/g was achieved – the highest reported in literature for physically activated fluid coke. Coke activated with SO2 displays a high mesoporous fraction and pore surface coverage by sulfur groups that were thermally stable up to 500°C.

Highly ordered self-assembled mesostructured membranes: Porous structure and pore surface coverage

Highly ordered silica and hybrid organic–inorganic membranes have been obtained through a slow and controlled solvent evaporation in the presence of a triblock copolymer as the structure-directing agent. Crack-free mesostructured membranes of large dimensions have been prepared. The mesophase is self-organized into a periodic cubic structure, Im 3 ¯ m , and consists of macroscopic mesostructured domains that maintain the out-of-plane order throughout the material. After calcination at 350 °C the membranes remain transparent even though they break in fragments of some centimeters. Different techniques have been employed to characterize the mesoporous materials: small angle X-ray scattering (SAXS) using synchrotron radiation and transmission electron microscopy to study the porous structure, Fourier transform infrared spectroscopy (FTIR) in vacuum at different partial pressures to investigate the nature of the pore surface. SAXS analysis has been used to map the whole membrane, revealing some differences in the pore organization that can be attributed to a gradient in the evaporation rate. The infrared measurements at different partial pressures have elucidated the mechanism of water adsorption–desorption on the pore surface. The changes of the FTIR spectra with different partial pressure have demonstrated that the pore surface is covered by a layer of molecular water that is hydrogen bonded to silanol species.