Micropore Size Research Articles

Exploring the Charge Storage Dynamics in Donor-Acceptor Covalent Organic Frameworks Based Supercapacitors by Employing Ionic Liquid Electrolyte.

Two donor-acceptor type tetrathiafulvalene (TTF)-based covalent organic frameworks (COFs) are investigated as electrodes for symmetric supercapacitors in different electrolytes, to understand the charge storage and dynamics in 2D COFs. Till-date, most COFs are investigated as Faradic redox pseudocapacitors in aqueous electrolytes. For the first time, it is tried to enhance the electrochemical performance and stability of pristine COF-based supercapacitors by operating them in the non-Faradaic electrochemically double layer capacitance region. It is found that the charge storage mechanism of ionic liquid (IL) electrolyte based supercapacitors is dependent on the micropore size and surface charge density of the donor-acceptor COFs. The surface charge density alters due to the different electron acceptor building blocks, which in turn influences the dense packing of the IL near its pore. The micropores induce pore confinement of IL in the COFs by partial breaking of coulomb ordering and rearranging it. The combination of these two factors enhance the charge storage in the highly microporous COFs. The density functional theory calculations support the same. At 1 A g-1 , TTF-porphyrin COF provides capacitance of 42, 70, and 130 F g-1 in aqueous, organic, and IL electrolyte respectively. TTF-diamine COF shows a similar trend with 100 F g-1 capacitance in IL.

Digital assessment of phase changes and heat transfer for hydrates in microstructures using X-ray CT imaging

Natural gas-hydrates are plural clean energy resource with rich deposits, and hydrate behavior significantly affects the exploration, production and utilization of these energy resources. However, technical difficulties for effective production and utilization of these energy sources still exist. Hydrate formation using xenon and NaBr brine and X-ray computed tomography (CT) imaging experiments are conducted to investigate microstructural morphology phase behaviors of hydrates, and a novel multi-phase color difference separation method to segment the pore, hydrate, water and grain phases is proposed. Effects of underground temperature gradient on thermal properties during the phase changes of hydrates are analyzed, and their effects on flow properties are studied. Results indicate that the temperature fraction, hydrate phase fraction, latent-heat thermal energy (LTE) and total enthalpy decrease with increasing temperature gradient. Hydrates rapidly form approximately at time = 250s for temperature gradient of 50 K and time = 500s for temperature gradients of 100 K, 150 K, 200 K and 300 K, and the hydrate phase equals to each other approximately at time = 95s. The stable LTE and total enthalpy approaches to a maximum when the temperature gradient is 150 K. Moreover, the temperature fraction and total enthalpy decrease on average by 4.73%, 4.69% and 76.13%, 75.87%, and the hydrate phase fraction increases by 7.89% and 7.88% with increasing microporosity and micropore size from 34.66% to 41.93% and from 37.53 μm to 43.22 μm, respectively. The temperature fraction and total enthalpy increase on average by 5.29% and 76.67% with increasing pore-scale hydrate saturation from 0.73 to 1.00. The LTE remains constant with an increase in hydrate pore-scale variables of microporosity, micropore size and hydrate saturation from 34.66% to 41.93%, from 37.53 μm to 43.22 μm and from 0.73 to 1.00, respectively. In addition, numerical permeability computed by the proposed relation of microporosity and pore-scale hydrate saturation agrees well with experimental results, with the average errors all less than 5%. The temperature and total enthalpy in phase change heat transfer of hydrates improve the permeability. The LTE in phase change heat transfer of hydrates hardly changes the permeability, and hydrate phase decreases the permeability. This work provides the quantitative and qualitative evaluations of phase change and heat transfer behaviors of gas-hydrates, which are helpful and provide excellent tools to develop the techniques for the exploration, production and utilization of these energy resources to decrease the energy crisis.

The effect of surface and porous structure on long-term performance of carbon powder cathodes without binder, during a 300-day trial in microbial fuel cells

The performance of microbial fuel cell (MFC) highly depends on the selection of appropriate electrode materials, in particular – cathodes. Herein, two different activated carbons (CWZ-22 and CWZ-35) without binder, as well as the activated carbon modified with silica nanoparticles (CWZ-22/Si), were used to improve the performance of air cathodes. Nearly one year of operation of materials varying in surface area and microporous structure revealed significant differences in their dynamic behaviour. CWZ-22 with lower surface area and a smaller micropore size, reached an internal resistance (Rint) of 162 Ω, and a maximum power density of 23.3 W m−3. CWZ-22/Si, coated with silane-siloxane-based silicone microemulsion displayed a drop of maximum power generation by 10%. CWZ-35, with higher surface area, but also higher micropore size, displayed 22.8 W m−3 and Rint of 159 Ω. The monitoring of electrochemical and performance parameters indicated an improved long-term behaviour of the cathodes in the following order: CWZ-22 > CWZ-22/Si > CWZ-35. This is the first work in which the pore size distribution and surface area are demonstrated to have a long-term impact on cathodic fouling, and, depending on these properties, this impact may be either positive or negative on MFC performance.

Hierarchical porous carbon with tunable apertures and nitrogen/oxygen heteroatoms for efficient adsorption and separation of VOCs

Porous carbon materials are good adsorbent candidates for removing volatile organic compounds (VOCs) due to their reliability and cost-effectiveness. Especially, the pore size distribution (PSD) of porous carbon materials plays a critical role in VOCs adsorption and separation. In this study, we present benzimidazole-derived porous carbons (BICs) with controllable pore size and oxygen/nitrogen heteroatoms. The pore size is controlled by adjusting the reaction degree of inorganic salt (K2CO3) and nitrogen-containing groups in the system. The tunable pore size distribution makes BICs highly efficient for the adsorption and separation of VOCs. BIC-3-900 exhibits a dominant pore size distribution of 3.0–4.0 nm and an exceptionally high total pore volume of 2.42 cm3/g, leading to ultra-high adsorption capacities for benzene and methanol (22.19 and 52.65 mmol/g, respectively) at 293 K. In addition, BIC-1-700 dominated by the micropore size is more favorable for adsorbing low-concentration small molecule VOCs (with a dynamic adsorption capacity of 4.21 mmol/g for methanol at 3800 ppm). In terms of the adsorptive separation performance, BIC-1-900 has an efficient benzene/methanol selectivity (∼30.13) due to its PSD (1.2–2.0 nm) which was more favorable for capturing low-concentration benzene. Moreover, both experimental and simulation (GCMC and DFT) results demonstrate that the abundant N/O heteroatoms doping in BIC-1-700 results in charge heterogeneity and stronger electrostatic affinity for polar VOCs molecules. Herein, our findings suggest that BICs with controllable pore size and oxygen/nitrogen heteroatoms have significant potential in practical VOCs capture and separation.

About Some Peculiarities of Positron Annihilation and Sorption Methods in Microporosity Studies on Polymers

Data on microporosity (micropore size distribution) in the range from several angstroms to several nanometers, obtained by measuring the positron annihilation lifetime (PALS method) and by measuring CO2 sorption (low-temperature gas sorption, LTGS) are collated for a number of polymers with amorphous (polyetherimides, PEI) and semicrystalline (polyphenylene oxides, PPO) structures. The microporosity estimates based on the positron annihilation and CO2 sorption data are compared with published data obtained bothexperimentally and by the group contribution method for the permeability of these materials. The discrepancies found and their possible causes are discussed.

Optimizing fabrication parameters via Taguchi method for production of high yield hydroxyapatite microsphere scaffolds using Drop-on-Demand inkjet method.

Drop on demand (DOD) inkjet method is a cost-efficient way of producing hydroxyapatite (HAp) microsphere scaffolds with narrow size distribution. However, DOD fabrication parameters may influence the yield and characteristics of the microsphere scaffolds. Testing different permutations and combinations of fabrication parameters is costly and time consuming. Taguchi method could be used as a predictive tool for optimizing the key fabrication parameters to produce HAp microspheres with desired yield and properties, minimizing the number of experimental combinations to be tested. The aim of this study is to investigate the influence of the fabrication parameters on the characteristics of the microspheres formed and determine optimum parameter conditions for producing high yield HAp microsphere scaffolds with the desired properties intended to serve as potential bone substitutes. We aimed to achieve microspheres with high production yield, microsphere size of <230 μm, micropore sizes <1 μm, rough surface morphology and high sphericity. Experiments were conducted using Taguchi method with a L9 orthogonal array at three levels per parameter to determine optimum parameter values for (1) operating pressure, (2) shutter speed duration, (3) nozzle height and (4) CaCl2 concentration. Based on signal-to-noise (S/N) ratio analysis, the identified optimum parameter conditions for operating pressure, shutter speed duration, nozzle height and CaCl2 concentration to be 0.9-1.3 bar, 100 ms, 8 cm and 0.4 M respectively. The microspheres obtained had an average size of 213 μm, 0.45 μm micropore size, high sphericity index of 0.95 and high production yield of 98%. Confirmation tests and ANOVA results affirms the validity of Taguchi method in optimizing HAp microspheres with high yield, desired size, micropore size and shape. HAp microsphere scaffolds produced by optimum conditions were subjected to a 7-day in-vitro study. Cells remained viable and continued to proliferate (increased 1.2-fold) over 7 days with microspheres maintaining high cell density with cells bridging between microspheres. Alkaline phosphatase (ALP) assay increased 1.5-fold from day 1, suggesting good osteogenic potency of HAp microspheres as potential bone substitutes.

Study on microstructure of rare earth Mg-9%Gd-2%Y-3%Nd -0.7%Zr alloy and properties of micro-arc oxidation films

The micro-arc oxidation protective film has been prepared on the surface of Mg-9%Gd -2%Y-3%Nd-0.7%Zr alloy by using the microarc oxidation technique of “step by step depressurization”. The microstructure of magnesium alloy substrate and micro-arc oxidation film were measured by OM, SEM and XRD, and the properties of the film were evaluated by electrochemical test of film thickness and surface morphology. The results show that the discontinuous network multiple eutectic phases are distributed in the grain boundary and there are dispersed-granular precipitates in the alloy matrix. After the micro-arc oxidation treatment, the thickness and corrosion resistance of the micro-arc oxidation film increased with the increase of oxidation time, and the surface micropore size increased first and then decreased, and the surface morphology of the micro-arc oxidation film changed from no micro-crack to micro-crack, and finally the micro-crack disappeared.

Alterations in the textural structural properties of coals exposed to flue gas for long-term carbon sequestration

Significant progress has recently been made in carbon sequestration in unmineable coal seams, including the coal physicochemical properties and environmental parameters that may affect the sequestration process. However, the effect of prolonged exposure to a flue gas on the pore structural changes of coals have not yet been considered. This study presents textural properties of two coals from South African coalfields probed using low-pressure gas adsorption (LPGA) of carbon dioxide (CO2) and nitrogen (N2) after flue gas exposure. The coals were obtained from Somkhele and Ermelo coalfields and were subjected to a flue gas synthesized to resemble that of a coal-fired power plant comprising 82% N2, 12% CO2, 5.5% O2, 0.38% SO2, and 0.12% NO2 on short-term (120 h) and long-term (2 232 h) basis. The coal samples were subjected to a flue gas at a high-pressure of 9.0 MPa and a temperature of 60 °C using a volumetric sorption system. After flue gas exposure, the surface area of the coals reduced by a maximum of 39% mainly owing to the reduced active sites. The micropore size distribution pattern for the coals maintained the original shape after being exposed to the flue gas with the pores distributed within a size range of 0.30 and 0.50 nm, showing the existence of narrow micropores in the coals; however, the highest peak value reduced by up to 17.7% relative to untreated coals. The mesopore size distribution acquired from the flue gas treated coals ranges from 1.6 nm to 2.4 nm, validating the existence of wide mesopores yielding an increase in the differential pore volume capacity relative to untreated coals.

Nitric Oxide‐Releasing Poly(L‐glutamic acid) Hybrid Hydrogels for Accelerating Diabetic Wound Healing†

Comprehensive SummaryDiabetic wound healing is threatening worldwide and challenging in wound dressings. Aiming to inhibit heavy inflammation and bacterial infection in diabetic wounds, herein, we facilely construct a kind of NO‐releasing poly(L‐glutamic acid) (PGA) based graphene oxide (GO) hybrid hydrogel of HDGS at a lower solid percentage, presenting large microporous size of about 20 μm, mild photothermal conversion property, and good biocompatibility. Besides improving hemostasis performance, the less amount of GO endowed the hydrogel with near infrared (NIR) responsivity to control fast and pulsatile NO release for killing bacteria and inhibiting heavy inflammation to proheal diabetic wound, in which a broad spectrum of antibacterial activities toward killing S. aureus, E. coli and MRSA was achieved via a combined effect of photothermia and NO release. In vivo effective hemostasis was attained in a rat liver bleeding model with short hemostatic time of ~20 s and lower blood loss of 1.5%—2.0%. Moreover, the treatment of HDGS plus 4 times of mild NIR irradiation (10 min, 808 nm, 1 W/cm2 per time) performed superior full diabetic wound healing within 11—14 d, in which the regenerated skins were characteristic of thick epidermis/dermis, dense blood vessels, some hair follicles‐embedding, and high level of collagens.

Three-dimensional covalent organic frameworks with pto and mhq-z topologies based on Tri- and tetratopic linkers

Three-dimensional (3D) covalent organic frameworks (COFs) possess higher surface areas, more abundant pore channels, and lower density compared to their two-dimensional counterparts which makes the development of 3D COFs interesting from a fundamental and practical point of view. However, the construction of highly crystalline 3D COF remains challenging. At the same time, the choice of topologies in 3D COFs is limited by the crystallization problem, the lack of availability of suitable building blocks with appropriate reactivity and symmetries, and the difficulties in crystalline structure determination. Herein, we report two highly crystalline 3D COFs with pto and mhq-z topologies designed by rationally selecting rectangular-planar and trigonal-planar building blocks with appropriate conformational strains. The pto 3D COFs show a large pore size of 46 Å with an extremely low calculated density. The mhq-z net topology is solely constructed from totally face-enclosed organic polyhedra displaying a precise uniform micropore size of 1.0 nm. The 3D COFs show a high CO2 adsorption capacity at room temperature and can potentially serve as promising carbon capture adsorbents. This work expands the choice of accessible 3D COF topologies, enriching the structural versatility of COFs.

Removal of NO at low concentrations from polluted air in semi-closed environments by activated biochars from renewables feedstocks

Efficient measures are urgently required in large cities for nitric oxide (NO) elimination from air in urban semi-closed environments (parking lots and tunnels), characterized by low NO concentrations (<10 ppmv) and temperatures. One of the most promising abatement alternatives is the NO oxidation to NO2, which can be further easily captured in an alkali solution or over a porous solid. However, most of the research devoted to this topic is focused on the elimination of NO from fuel exhaust gases, with high NO concentrations (400–2000 ppmv). In this work, sustainable and low-cost activated biochars of different origin and having very different ash contents were employed in NO removal at very low concentrations. Thus, low ash content forestry (oak woodchips, OAK) and high ash content from agriculture (oilseed rape straw, OSR) biochars were subjected to physical activation with CO2 at 900 °C (OAK550-A900CO2 and OSR700-A900CO2, respectively). The NO removal performance tests of such activated carbons were carried out at different experimental conditions: i.e., temperature, relative humidity (0–50 vol% RH), NO-containing gas (N2 or air), amount of activated carbon, and NO concentration, to assess how the activated biochar properties influence their NO removal capacity. The sample OSR700-A900CO2 contained a higher population of oxygen surface functionalities, which might play an important role in the NO removal efficiency in dry conditions since they could assist NO oxidation on carbon active sites when used above room temperature (50–75 °C). However, at room temperature (25 °C), the presence of narrow micropore size distribution at 6 Å became a more relevant property, since it facilitates an intimate contact between NO and O2. Accordingly, the activated biochar from OAK was much more efficient, achieving complete removal of NO from air flow (dry or with 50 vol% RH) at 25 °C during 400 min of testing, making it an ideal candidate as biofilter for purifying air streams of semi-closed spaces contaminated with low concentrations of NO.

Zinc gluconate derived porous carbon electrode assisted high rate and long cycle performance supercapacitor

The low energy density of supercapacitor is the main reason that limits the utilization of multifunction. Based on this, it is particularly necessary to establish porous network structure electrode for understanding the energy storage mechanism of advanced supercapacitors. In this work, the strategy of activated zinc gluconate was proposed to prepare porous carbon with different pore structures. The as-prepared zinc gluconate derived activated porous carbon (ZnPCK-3) has rich porous network structure with high specific surface area of 1973 m2 g−1 and microporous pore sizes of 1.9 nm exposing abundant electrochemical active sites. Benefiting from the microstructure promotes the storage of electrolyte ions, the ZnPCK-3 electrode shows excellent rate performance of 143 F g−1 at a current density of 20 A g−1. The symmetrical supercapacitor with obtained ZnPCK-3 electrode assembly achieves energy density of ∼92.6 Wh kg−1 in Et4NBF4 electrolyte and specific capacitance retention of 94.5 % after 10,000 cycles at the current density of 20 A g−1. The proven zinc gluconate assisted strategy affords emerging chances for rational commercial-level design for high performance supercapacitor.

Experimental study on the change of coal structure and microbial community structure during supercritical-CO2-H2O-microorganisms-coal interaction process

To study the effects on coal structure and microbial community diversity during CO2 storage in deep unminable water-bearing coal seams, the lignite in the mining area of Inner Mongolia was selected as the research object. The simulation experiments of supercritical-CO2 (ScCO2)-H2O-microbial-coal interaction under different pressure conditions performed by using an autoclave. Then the solid–liquid phases before and after the reaction were analysed by XPS, low-temperature liquid nitrogen adsorption, 16S rRNA and other testing methods. The results showed that CO2 injection caused the pH and OD600 values in the system to decrease, and the pH and OD600 values in the system decreased more obviously with the increase of ScCO2 pressure. Compared with raw coal, the relative content of carbon elements on the surface of the coal after the reaction increased, and the organic carbon (CC/CH) relative content decreased slightly. In contract, the specific surface area, total pore volume, and the pore size of micropores of coal increased, but the average pore size of the mesopores and macropores decreased. At the same time, with the ScCO2 injection under different pressure conditions, some bacterial cells in the system ruptured and inactivated, resulting in the decrease their relative abundance. In contract, some genera, such as Paraclostridium and Methanoculleus, may have the adaptability to the extreme environment and gradually evolve into the dominant genus. In conclusion, the results provide a theoretical basis for studying the changes of ScCO2 on coal structure and microbial community structure during CO2 storage in deep unminable water-bearing coal seams.

Model for Predicting CO2 Adsorption in Coal Left in Goaf Based on Backpropagation Neural Network

Injecting power plant flue gas into a goaf stores CO2 in the flue gas and effectively prevents the spontaneous combustion of the coal remaining in the goaf. Here, we investigated the adsorption behavior of three types of coal at normal temperature and pressure using a self-developed adsorption experimental device. We used a specific surface area and porosity analyzer to study the effects of pore structure, mineral content, and moisture content on CO2 adsorption in coal. Based on the experimental data, we designed a multifactor CO2 adsorption prediction model based on a backpropagation (BP) neural network. The results indicated that the pore size of most micropores in coal was in the range of 0.5–0.7 and 0.8–0.9 nm. The specific surface area and pore volume were positively correlated with the CO2-saturated adsorption capacity, whereas the mean pore diameter, mineral content, and moisture content were inversely associated with the CO2-saturated adsorption amount. The accuracy of the multifactor BP neural network prediction model was satisfactory: the determination coefficients (R2) of the training and test sets were both above 0.98, the root mean square error (RMSE) and mean absolute error (MAE) of the test set were both less than 0.1, and the prediction results satisfied the requirements. To optimize the prediction performance of the model, we used the random forest algorithm to calculate the importance of each factor. The sum of the importance weights of the specific surface area, moisture content, and pore volume was 91.6%, which was much higher than that of the other two factors. Therefore, we constructed an optimization model with specific surface area, moisture content, and pore volume as input variables. The R2 values of the training and test sets in the simplified model were improved compared with those of the multifactor model, the RMSE and MAE were reduced, and the fitting effect was ideal. The prediction model of CO2 adsorption in coal based on the BP neural network can predict the CO2 adsorption capacity of coal under different physical and chemical conditions, thereby providing theoretical support for the application of CO2 storage technology in goafs.

From the teapot effect to tap-triggered self-wetting: a 3D self-driving sieve for whole blood filtration

Achieving passive microparticle filtration with micropore membranes is challenging due to the capillary pinning effect of the membranes. Inspired by the teapot effect that occurs when liquid (tea) is poured from a teapot spout, we proposed a tap-triggered self-wetting strategy and utilized the method with a 3D sieve to filter rare cells. First, a 3D-printed polymer tap-trigger microstructure was implemented. As a result, the 3 µm micropore membrane gating threshold (the pressure needed to open the micropores) was lowered from above 3000 to 80 Pa by the tap-trigger microstructure that facilated the liquid leakage and spreading to self-wet more membrane area in a positive feedback loop. Then, we implemented a 3D cone-shaped cell sieve with tap-trigger microstructures. Driven by gravity, the sieve performed at a high throughput above 20 mL/min (DPBS), while the micropore size and porosity were 3 µm and 14.1%, respectively. We further filtered leukocytes from whole blood samples with the proposed new 3D sieve, and the method was compared with the traditional method of leukocyte isolation by chemically removing red blood cells. The device exhibited comparable leukocyte purity but a higher platelet removal rate and lower leukocyte simulation level, facilitating downstream single-cell analysis. The key results indicated that the tap-triggered self-wetting strategy could significantly improve the performance of passive microparticle filtration.

Dynamic adsorption separation of c-C4F8/C3F8 for effective purification of perfluoropropane electronic gas

The separation of c-C4F8/C3F8 mixtures at ambient conditions is challenging in the electronic industry due to their similar physical and chemical properties. The object of this work is to explore effective adsorbents for c-C4F8/C3F8 separation and elucidate its separation mechanism. Through screening a series of absorbents, KOH activated glucose-based carbon (GC-K1) stands out as the most effective adsorbent for the separation of c-C4F8/C3F8 mixtures with the highest dynamic selectivity of 3.7 and adsorption uptake of 1.2 mmol/g for c-C4F8, as well as multiple-cycle regenerability. The effects of textural properties, particularly the micropore size, on c-C4F8/C3F8 separation were further investigated experimentally and computationally. The effective c-C4F8/C3F8 separation over GC-K1 may be attributed to the discrepancy in the constrained adsorption affinity of c-C4F8 over C3F8via the small ultramicropore at ∼5.9 Å. This study provides valuable insights into the adsorptive purification of electronic gases using ultramicroporous carbon via the pore confinement effect.

A triboelectric nanogenerator coupled with internal and external friction for gesture recognition based on EHD printing technology

Surface charge density is a critical factor in determining the output performance of triboelectric nanogenerators (TENGs). However, enhancing the surface charge density is a relatively complex process characterized by high cost, fast charge dissipation, and inferior stability. Herein, a TENG with internal and external friction synergistic coupling enhancement that employed an electrohydrodynamic (EHD) printing technique for gesture recognition was proposed. Under the external force, the electrical performance of the triboelectric material could be improved via internal friction formed by the contact between the lines of silver nanowires (AgNWs) mixing with hydroxy propyl methyl cellulose (HPMC) (AgNWs (HPMC)) inside the tribolayer and the PDMS with microgrooves. The effects of dielectric layer thickness, micropore size, the number of micropore arrays, as well as the AgNWs content and the number of AgNWs (HPMC) lines on TENG output performance were analysed systematically. When the micropore arrays TENG (MA-TENG) size was 15 mm × 15 mm, the thickness of a dielectric layer was 240 µm, the number of micropore arrays was 36, and the number of AgNWs (HPMC) lines was 28, the charge transfer quantum of MA-TENG was 34.9 nC, which is about 5.8 times that of flat TENG. The peak power of the MA-TENG was 580 μW, which was about 10 times than that of the flat TENG. Finally, a self-powered gesture recognition was demonstrated successfully based on the developed MA-TENG and revealed its potential in the field of human-computer interaction. This work not only proposed a new method with the advantages of a simple process, low cost, and high output stability, to significantly increase the surface charge density, but also provided a new scheme for electronic skin and wearable devices.

Micropore sites in ferrihydrite are responsible for its higher affinity towards As(III) relative to As(V)

Poorly-crystalline ferrihydrite is ubiquitous in the environment and contributes to controlling the fate of arsenic in sediments and soils. Although there is evidence that ferrihydrite has a higher affinity towards As(III) relative to As(V), little is known about how and why As(III) is readily immobilized by ferrihydrite. In this study, ferrihydrite was employed to evaluate the As(III) and As(V) adsorption behavior. The properties of ferrihydrite such as morphology, pore size distribution, arsenic adsorption species, and adsorption energies of arsenic at different sites were carefully examined using TEM-EDS mapping, positron annihilation lifetime (PAL) spectroscopy, X-ray absorption spectroscopy (XAS), N2 adsorption isotherms, and theoretical calculations of density function theory (DFT). Batch adsorption experiments revealed that the maximum adsorption of As(III) (839.7 μmol g−1) on ferrihydrite, fitted by Langmuir model, was considerably larger than that of As(V) (372.4 μmol g−1). PAL characterization and pore size distribution analysis demonstrated that ferrihydrite had an abundance of vacancy cluster-like micropores, which consisted of 10–20 atom deficiencies (V10-20). The calculated hydrated ion size of As(III) species (4.22 Å) at pH 6.0 was smaller than the size of As(V) (5.90 Å). The higher As(III) adsorption to ferrihydrite was attributed to its surface adsorption sites as well as its abundant micropore adsorption sites, which are available only to As(III) due to their size matching well with the size of the ferrihydrite micropores, thus significantly contributing to greater As(III) immobilization.

Oil shale kerogen-derived adsorbents and their application to trichloroethylene adsorption from aqueous solutions

This paper examines microporous oil shale kerogen-derived semicokes as potential sorbents for environmental cleanup applications. This carbonaceous residue (“semicoke”) left behind during the processing of oil shale kerogen is the main source of adsorptive potential in the processed oil shale. The surface area and porosity of model microporous semicokes were determined using N2 and CO2 adsorption techniques. The model semicoke material had a BET surface area of 494 m2/g of char (net of the minerals), which could be increased by mild thermal activation in the air at 698 K (425 °C) to 857 m2/g-char. The semicokes were tested as potential sorbents by measuring their efficacy at removing trichloroethylene (TCE) from aqueous solutions at 295 K in the concentration range from about 0.1 to 7 mg/L. TCE adsorption isotherms were determined for seven different sorbents – the model semicoke, the air-activated model semicoke, raw unprocessed oil shale, three commercially prepared semicokes, and, for reference, a commercial granulated activated carbon. The present results show that the kerogen-derived carbons have TCE adsorptive capacity values which are comparable to those of a commercial activated carbon (e.g., 70 mg/g-C). The results pointed to the importance of a particular micropore size range for adsorption. While air activation increased the pore volume and surface area of the materials as measured by nitrogen and carbon dioxide, this did not result in an increase in adsorptive capacity for TCE. The critical pore size appears to be in the range of 0.5–0.8 nm.

Corrosion Behavior of Fe2O3/Alumina Layer Produced by Plasma Electrolytic Oxidation of 6061 Al Alloy

This study looked into the influence of iron nitrate (Fe(NO3)3 on the corrosion behavior of a 6061 Al alloy treated by a plasma electrolytic oxidation coating (PEO). PEO coatings were fabricated on Al alloy samples under AC conditions utilizing an alkaline-aluminate electrolyte containing 0 and 5 gr of Fe(NO3)3. Surface examination demonstrated that some Fe2O3 particles were effectively integrated into the coating layer produced in a solution containing Fe(NO3)3. In addition, the porosity and the size of micropores made due to plasma activity were significantly reduced after the PEOO treatment of the 6061 Al substrate in an electrolyte containing Fe(NO3)3. Accordingly, the coating formed in the electrolyte with Fe(NO3)3 exhibited superior corrosion resistance to that treated in the electrolyte without Fe(NO3)3.