Micropore Size Research Articles

Understanding the rate performance of microporous carbons in aqueous electrolytes

Variation of specific capacitance versus current density is studied for microporous carbons. Although literature states that capacitance retention is higher for macro/mesoporous than for microporous carbons, the results reported here show that high capacitance retention can be reached for microporous carbons in combination with aqueous electrolytes (2M H2SO4, 1M KOH and 6M KOH). Six carbon monoliths are studied; three pristine ones and those three heat-treated, so as to reduce their content of surface oxygen groups and develops porosity. The capacitance retention is analyzed based on five parameters: electronic conductivity, surface chemistry and porosity of the monoliths, ionic conductivity and type of electrolyte. The capacitance retention is higher for the monoliths working as negative (H3O+ and K+) electrodes than as positive (HSO4− and OH−) ones, being these results of interest for the use of carbon monoliths in asymmetric and hybrid supercapacitors. The highest capacitance retention is obtained by combining (i) monolith electronic conductivity of 11–14 Scm−1 and micropore size of 0.6–0.8 nm for H3O+, K+ and HSO4−, and of 0.85–0.95 nm for OH−; (ii) electrolyte ionic conductivity above 600 mScm−1 and 6M KOH electrolyte, since this electrolyte performs better than 2M H2SO4 and 1M KOH.

Facile and sustainable synthesis of slit-like microporous N-doped carbon with unexpected electrosorption performance

Carbon materials with high surface area (>1000 m2 g−1) and porosity have been long pursued in capacitive deionization, but most of them normally suffer from relatively low performance, complicated and unsustainable fabrication process. Here, N-doped carbon with slit-like micropores was fabricated by a simple hydrothermal reaction and then pyrolysis with plant fruits as general carbon sources. The whole process did not involve any other chemicals. The carbon possesses a very low surface area of 14.32 m2 g−1 (N2 adsorption-desorption isotherm) and 85.84 m2 g−1 (CO2 adsorption-desorption isotherm), which is less than commercial activated carbon. The carbon is positively charged within a broad range of pH from 1 to 4.46. To our surprise, such a carbon material exhibits a selective adsorption behavior towards Cl− and NO3− with capacity of 31.87 mg g−1 and 72.65 mg g−1, respectively, which are much higher than the activated carbon. Based on characterizations and control experiments, the nitrogen doping, and the shape & size of micropore synergistically interplay together to improve the performance (e.g., selectivity, adsorption capacity) of this carbon material. This research opens a hopeful window in developing electrosorption materials.

Molecular simulation of benzene adsorption on different activated carbon under different temperatures

Abstract Four different structure models of activated carbon were constructed here by molecular simulation method. The four models include three microporous structures with micropore sizes of 9–11 A, 10–12 A, and 13–16 A, respectively, and one microporous-mesoporous structure with pore sizes of 15–17 A and 21–24 A. The microporous-mesoporous structure was easily adjusted by the introduction and deletion of single-wall carbon nanotubes (SWCNTs, 15, 15). The adsorption of benzene on different structure models at temperatures of 273.15, 288.15, 303.15 and 318.15 K were studied by Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods. Adsorption isotherms, average isosteric heats of benzene adsorption, porosity and pore volume change after benzene adsorption at different temperatures were analyzed. The radial distribution function, relative concentration distributions and diffusion coefficients of benzene molecules on different structure models were further studied. Comprehensive analysis results indicate that for low temperature, activated carbon with larger micropores and mesopores is favorable to adsorption of benzene. But for high temperature, activated carbon with smaller micropores is favorable to adsorption of benzene.

Fabrication, microstructure and optical properties of Ce:SrF2 transparent ceramics

Ce:SrF2 powders were synthesized via the co-precipitation method. These synthesized Ce:SrF2 powders were pure SrF2 phase with substitutions of Ce3+ for Sr2+. The average particle size of these powders was estimated to be less than 250 nm, and they also had high dispersibility. The calcination temperature of Ce:SrF2 powders had strong influence on the ceramic sintering properties. The ceramic microstructure became compact when increasing the calcination temperature from 100 °C to 400 °C, because of the gradual decrease in both the number and size of micro-pores. Ce:SrF2 transparent ceramics could be sintered at 910 °C for 2 h under 50 MPa with ceramic powders calcined at 300 °C and 400 °C, because the powders calcined at above 300 °C had nearly no crystal water. The highest in-line transmittance of 71% was obtained at 800 nm. The Ce:SrF2 transparent ceramic was found to have two absorption peaks at 248 nm and 289 nm, and two obvious emission peaks at 308 nm and 327 nm. If the transmittance in the UV range, 200–340 nm, could be effectively improved by reducing scattering centers, Ce:SrF2 transparent ceramic would be a promising direct-pumping solid state UV laser material.

Review on Activated Carbons by Chemical Activation with FeCl3

This study reviews the most relevant results on the synthesis, characterization, and applications of activated carbons obtained by novel chemical activation with FeCl3. The text includes a description of the activation mechanism, which compromises three different stages: (1) intense de-polymerization of the carbon precursor (up to 300 °C), (2) devolatilization and formation of the inner porosity (between 300 and 700 °C), and (3) dehydrogenation of the fixed carbon structure (>700 °C). Among the different synthesis conditions, the activation temperature, and, to a lesser extent, the impregnation ratio (i.e., mass ratio of FeCl3 to carbon precursor), are the most relevant parameters controlling the final properties of the resulting activated carbons. The characteristics of the carbons in terms of porosity, surface chemistry, and magnetic properties are analyzed in detail. These carbons showed a well-developed porous texture mainly in the micropore size range, an acidic surface with an abundance of oxygen surface groups, and a superparamagnetic character due to the presence of well-distributed iron species. These properties convert these carbons into promising candidates for different applications. They are widely analyzed as adsorbents in aqueous phase applications due to their porosity, surface acidity, and ease of separation. The presence of stable and well-distributed iron species on the carbons’ surface makes them promising catalysts for different applications. Finally, the presence of iron compounds has been shown to improve the graphitization degree and conductivity of the carbons; these are consequently being analyzed in energy storage applications.

Hierarchical zeolites: synthesis, structural control, and catalytic applications

Zeolites possess unique ion exchange property, abundant acid sites, and highly hydrothermal stability, which have been widely used in catalysis, separation, and adsorption etc. However, the application of zeolite is greatly restrained in catalytic reactions involved in the large molecules due to their small micropore size (< 2 nm). Zeolites with hierarchically porous structure not only keep the crystalline framework, acidic sites, and highly hydrothermal stability but also improve diffusion of larger molecules. Thus, the catalyst life can be prolonged, which can expand their applications in the catalysis. In this review, the research progresses of hierarchical zeolites in terms of the controllable pore structural and synthetic strategy are summarized. Additionally, the applications of these hierarchical zeolites in catalysis are concluded. Furthermore, the hierarchical zeolites exhibit more excellent catalytic performance than conventional zeolite with sole micropores. Therefore, a perspective for promising application of the hierarchical zeolite in catalysis field is provided.

Highly dispersed Cu supported on mesoporous Al‐KIT‐6 for oxidative carbonylation of methanol to dimethyl carbonate

Microporous NaY zeolite is a common support of Cu catalysts for oxidative carbonylation of methanol, but the dispersion of Cu species on NaY is usually subjected to its micropore size. Here, ordered mesoporous KIT‐6 was employed as the support for Cu catalyst and Al was incorporated into its framework to increase the surface acidity, which eventually improves the surface exchange capacity and Cu dispersion. The evolution of the state of Cu species on KIT‐6 was analyzed combined with control of Cu loading. The physicochemical properties of the supports and corresponding catalysts were characterized by N2 adsorption–desorption, X‐ray diffraction, ammonia temperature programmed desorption, Fourier transform infrared spectra, transmission electron microscopy, hydrogen temperature programmed reduction, and X‐ray photoelectron spectroscopy. It was found that mesoporous KIT‐6 showed better Cu dispersion than microporous NaY zeolite. Agglomerated CuO, dispersed CuO, and Cu2+ are the major Cu species observed on the catalyst surface. The increased surface acidic sites of KIT‐6 by Al incorporation promoted the formation of Cu2+ and dispersion of CuO. With the increase in Cu loading, the Cu2+ content in the catalyst was decreased gradually along with increase in the bulk CuO. It was speculated that some exchanged Cu2+ could be transformed into highly dispersed CuO and even bulk CuO after calcination at a high Cu loading. Combined with the catalyst evaluation results, it was deduced that highly dispersed Cu2+ and CuO particles play significant roles in catalytic activity. The catalyst Cu/Al‐K‐10 achieved the highest space time yield of dimethyl carbonate of 135.4 mg/(g·h), which is 2.7 times the Cu/K‐10 owing to its more dispersed Cu species. This laid the basis for preparing highly dispersed Cu species on mesoporous silica supports.

Catalytic oxidation of NO at ambient temperature over the chars from pyrolysis of sewage sludge

Sludge char (SC) was prepared by pyrolysis of sewage sludge, then nitric acid washing, potassium hydroxide activation, and hydrogen reduction methods were used to seek for the optimum treatment for improving the catalytic oxidation of NO at 30 °C. The optimum NO conversion of 65.6% was achieved when SC was activated and hydrogen-reduced, indicating the promising prospect of NO oxidation catalyst preparation from sewage sludge. The prepared SCs showed an intensive specific pore volume peak at the micropore size of 0.89 nm which is beneficial for NO oxidation. SC characterization like temperature programmed desorption of CO2/NO/NO2, in-situ diffuse reflectance infrared Fourier transform spectroscopy, etc. were conducted to reveal the catalytic oxidation mechanisms of NO. The results indicated that the oxygen-containing functional groups, such as carboxylic acid, carboxylic anhydrites and lactones, were largely removed by hydrogen reduction, leading to marked increases of surface basicity, specific surface area, and catalytic activity of SCs. The NO oxidation over the SCs can be explained quite well by the Eley-Rideal reaction model.

Characterization of Enzymatically Synthesized Titania Thin Films Using Positron Annihilation Spectroscopy Reveals Low‐Cost Approach for Organic/Inorganic Photovoltaic Cells

AbstractA new method is developed to produce mesoporous titania thin films at room temperature using the enzyme papain in a dip‐coating procedure, providing low‐cost titania films in a sustainable manner. Quartz crystal microbalance, positron annihilation Doppler broadening and lifetime spectroscopy, scanning electron microscopy, and X‐ray diffraction are used to determine the deposition and structural properties of the films. As‐deposited films have low densities ρ ≈ 0.6 g cm−3, contain small micropores and proteins, and exhibit corrugated surfaces. Annealing at temperatures of 300 °C or higher leads to the destruction and evaporation of most of the organic material, resulting in a thickness decrease of 50–60%, more pure titania films with increased density, an increase in micropore size and a decrease in the concentration and size of atomic‐scale vacancies. Up to 50 layers could be stacked, allowing easy control over the total layer thickness. Based on these titania films, first test devices consisting of natural dye‐sensitized solar cells are produced, that show photovoltaic activity and indicate possibilities for low‐cost, accessible, organic production of solar cells. Given the wide range of other applications for titania, this new method is a promising candidate for improving the fabrication of those products with respect to cost, sustainability, and production speed.

Synthesis of porous carbon derived from poly(vinylidenefluoride) and its adsorption characteristics for CO2 and CH4

The preparation of carbon adsorbents through carbonization of polymer precursors is drawing attention in that it can form uniform size of micropores. In this study, several carbon adsorbents were prepared by carbonization of poly (vinylidenefluoride) (PVDF) at between 500 and 900 °C under Ar or CO2 carrier flow. The prepared samples exhibited pore size distribution between 0.6 and 1.3 nm, and the pore structure was formed differently according to the carbonization conditions. Especially, the CO2 caused further activation during polymer carbonization, leading to better development of the microporous structure. The formed micropores were found to be uniformly distributed on the adsorbent surface from TEM image, and their structure could be characterized by XPS analysis. The volumetric adsorption measurements revealed that the porous carbon adsorbents had good CO2 and CH4 adsorption performances. Moreover, the measured adsorption capacities were highly dependent on the narrow micropore (<0.8 nm) volume. Based on these results, additional porous carbon adsorbents could be prepared to increase narrow micropore volume by varying the sample amount and temperature increasing/decreasing rates. As a results, one of the prepared porous carbon adsorbents showed remarkable adsorption capacity at 25 °C; 5.02 mmol/g for CO2 and 2.35 mmol/g for CH4.

Cluster circulating tumor cells in surgical cases of lung cancer.

A cancer lesion sheds tumor cells into the circulating blood as circulating tumor cells (CTCs). Since cluster CTCs have been considered as precursor lesions of metastasis, their clinical implication was investigated in this study according to the preoperative status of cluster CTC detection in surgical cases of clinically early-stage lung cancer. Among 104 surgical patients of early-stage lung cancer, CTCs were extracted from the peripheral blood before surgery using a micro-pore size selection method (ScreenCell®) and diagnosed microscopically. Implications of detecting cluster CTC were assessed according to the prognosis and clinicopathological characteristics. The status of CTC detection was not detected in 77 cases (74.0%), single CTC only detection in 7 cases (6.7%), and cluster CTC detected in 20 cases (19.2%). Patients with cluster CTCs exhibited significantly lower recurrence-free survival and overall survival than did patients of other groups. In addition, in hazard ratio analysis, the hazard ratios were independent of other predictors of poor prognosis, and detection of cluster CTCs was associated with predictors of poor prognosis. Cluster CTCs were detected in cases where the original lung cancer lesion had clinical predictors of poor prognosis and were independent negative predictors of survival.

Calcium-Assisted Regulation of the Structures of Porous Carbons at the Micro-Nano Scale

Here a facile and effective method was investigated to regulate the microstructures of porous carbons by adjusting the contents of calcium in precursors. The carbonization characteristics of precursors were characterized by thermogravimetric analysis (TGA) and differential thermogravimetric (DTG), and the results show that the weight loss rates of precursors decrease with the increases of calcium contents. The structures of carbonized samples and their derived porous carbons at the micrometer scale were characterized by Scanning electron microscopy (SEM), and the results show that the structures of carbonized samples change regularly with the increases of calcium contents in precursors, and porous carbons can inherit the structures from their corresponding carbonized samples. The pore characteristics of porous carbons at the nanometer scale were characterized by N2 adsorption and desorption, Barrett Joyner and Halenda (BJH) method and Horvath-Kawazoe (HK) method, and the results show that the existence of calcium in precursors can greatly increase the total pore volumes and specific surface areas of porous carbons derived from precursors, and interestingly it can be noticed that the micropore size distributions of porous carbons in the range of 0.58–10 nm are quite similar.

Synthesis of ZIF-8 at room temperature and reuse filtrate

ZIF-8 has been synthesized with methanol solvent at room temperature (25-30°C), with molar composition of zinc nitrate: 2-methylimidazolate: TEA = 1: 4: 4. Furthermore, ZIF-8 has been synthesized using filtrate from synthesis. Repetition of ZIF-8 synthesis using filtrate from synthesis has been done for six times. The produced samples were investigated using XRD, FT-IR and SEM. XRD pattern showed that ZIF-8 which have been synthesized using reuse filtrate has same peaks with ZIF-8 from first synthesized. FTIR spectra of ZIF-8 showed a peak at 422 cm−1 which indicated the presence of zinc bonded to the nitrogen in ZIF-8. Besides SEM analysis of ZIF-8 particles size whit are synthesized using MeOH and reuse filtrate have yielded that ZIF-8 micropore size. The results showed that the synthesis of ZIF-8 using reuse filtrate was succesfully carried out.

Low-cost and advanced symmetry supercapacitors based on three-dimensional tea waste of porous carbon nanosheets

ABSTRACT With the increasing demand for green energy, the cheap tea waste is recycled to produce three-dimensional framework of porous carbon nanosheets materials with commercial value and excellent electrochemical properties. The TPCN-6 materials were prepared by simultaneous pyrolysis/activation. The density and pore structure of the material depend on the activation concentration. Due to the microporous structure and reasonable pore size distribution of the porous carbon, the TPCN material shows a high specific capacitance of 482.1 F g-1 at 1 A g-1 and perfect cycling stability (retaining 87.6% after 6000 cycles at 10 A g-1) in 6 M KOH aqueous electrolyte. The optimum symmetric supercapacitor device base on TPCN-6//TPCN-6 diaplayed a supreme energy density of 19.1 Wh kg-1 and power density of 325 W kg-1. What's more, it offers a potential way to recycle tea waste into high-valued product in large-scale with disposing of biological waste to relieve environmental concerns.

Dissolution–Recrystallization Formation of Huge Thin 2D Silicalite Lamella for Promoted Sorption

AbstractAn all silica MEL‐type silicalite‐2 nanocrystal is hydrothermally treated in coexistence with cetyltrimethylammonium bromide (CTAB) and tetrapropylammonium hydroxide (TPAOH) at ordinary and elevated temperatures. From monitoring its structural transition process by various physico‐chemical methodologies, it is found that, instead of simple delamination, silicalite‐2 nanocrystal changes with a dissolution and recrystallization mechanism by treatment at an elevated temperature and for a long time, that is, it is first dissolved and then reorganized to huge 2D platelets via an intermediate step forming periodic mesoporous material. The newly formed nanoplatelets (h‐nanoplatelets) from in‐plane growth along a (or b)‐, c‐directions (normal to b (or a)‐axis) are of silicalite (either MEL or MEL/MFI intergrowth)‐type framework topology with a thickness of 3.3 nm (the equivalent of ≈1.6 unit cell) and interspersed with a minor part of small square‐like MFI‐type nanoplatelets (s‐nanoplatelets). The h‐nanoplatelets have expanded lattice parameters and a larger micropore size compared to the parent silicalite‐2 nanocrystal and s‐nanoplatelets, whose micropore structure are modified so as to benefit from both equilibrium adsorption and desorption‐recovering ability of organic contaminants particularly at a low vapor pressure range. This is the first report regarding the dissolution–recrystallization formation of 2D lamella‐type silicalites mediated by popular types of surfactant and base species.

Construction of Microporous Polyimides with Tunable Pore Size and High CO2 Selectivity Based on Cross-Linkable Linear Polyimides

Polyimides with intrinsic microporosity have been well developed and explored in the field of gas adsorption and separation. However, most linear polyimides without rigid and distorted segments do not have porous structure owing to the densely packed polymer chains. Two cross-linked polyimides (PEDA-PI-CL and PEQDA-PI-CL) were synthesized from 3,3′-bis(2,3,5,6-tetrafluoro-4-vinylphenoxy)-4,4′-biphenyldiamine (TFVBPA) with 2,5-bis(3,4-dicarboxyphenoxy)-4′-phenyl dianhydride (PEDA) and 2,5-bis(3,4-dicarboxyphenoxy)-4′-phenylethynyl phenyl dianhydride (PEQDA) through polycondensation and thermal cross-linking reactions. Here, the cross-linked structure is utilized to construct microporous polyimides because it can restrict the movement of polymer segments and prevent the polymer chains from dense packing. The micropore size, microporous structure, and CO2 adsorption performance can be finely tuned by increasing the cross-linking density from PEDA-PI-CL to PEQDA-PI-CL. The micropore size reduces from 1.06 to 0.54 nm and CO2 adsorption increases from 6.32 to 9.88 wt %. Meanwhile, the CO2/N2 and CO2/CH4 selectivity values of PEQDA-PI-CL at 273 K/1 bar are 76.62 and 12.40, respectively, which is better than many other common microporous polyimides. These results reveal that increasing cross-linking density in cross-linked polyimides is favorable for preparing microporous polyimide networks with smaller pores and higher CO2 adsorption selectivity.

Understanding the Loading Dependence of Adsorbate Diffusivities in Hierarchical Metal-Organic Frameworks.

Using atomistic simulations, we studied the diffusion of n-hexane in a series of isoreticular hierarchical metal-organic frameworks (MOFs) NU-100x. Nonmonotonic diffusivity-loading relationships that depend on the pore sizes were observed, which can be explained by the spatial distribution of adsorbates at different loadings. For one of the MOFs in the series, NU-1000-M, the diffusivity-loading relationship is almost identical to the previously reported results of n-hexane diffusion in the hierarchical self-pillared pentasil (SPP) zeolite. Detailed analysis revealed that the similarity results from their similar micropore and window sizes, which was confirmed by free-energy mapping. The effects of temperature and adsorbate chain length on the diffusion were also studied, which supported our conclusion that the diffusivity in hierarchical nanoporous materials is primarily controlled by the sizes of the micropores and the connecting windows, particularly at relatively low loadings.

Strength and microstructure characteristics of cement-soda residue solidified/stabilized zinc contaminated soil subjected to freezing–thawing cycles

The remediation efficiency of the solidification/stabilization (s/s) method on soil contaminated with heavy metals may deteriorate when the treated soil is exposed to freezing–thawing (F–T) cycles. In this study, a series of laboratory tests were conducted to investigate the strength and microstructural characteristics of Zn-contaminated soil treated by cement-soda residue under cyclical F–T conditions. Test results showed that the stress–strain curves were able to be characterized by a strain softening model and the failure mode could be classified as brittle failure before subjecting to F–T cycles. After exposure to the F–T cycles, the stress–strain curves gradually began to resemble the hardening model, and the compressive strength decreased significantly. Unconfined compressive strength (UCS) of the specimens obtained the maximum value at Zn2+ concentration of 2000 mg/kg, regardless of their exposure to the F–T cycles; sample Zn0.2 was the most vulnerable. After being subjected to F–T cycles, micro-cracks formed in the specimens. These cracks would be enlarged by the continuous exposure to F–T cycles, which resulted in the reduction of strength. F–T cycles could significantly damage the crystalline structures of cement hydrates; the damage could also contribute to the deterioration of soil structure. Microstructural analysis results showed that the size of the samples' micro-pores decreased due to the migration of pore water during freezing, while the size of larger pores increased due to ice lens formation and expansion.

DEMINERALIZATION OF PHENOL DERIVATIVES USING SEQUENTIAL ADSORPTION AND BIOLOGICAL DEGRADATION PROCESS

The present investigation was undertaken to assess the degradation of phenol derivatives by sequential adsorption and biological process. Phenols and their derivatives are recognized toxic compounds and known for their carcinogenic and other toxic properties even in trace quantity. Biological treatment is considered more environmentally friendly and cost-effective in comparison with physicochemical treatment. However, the process is less effective for high concentration pollutants. Activated carbons, prepared from Jatropha having micropore size under 125 microns, have been used to carry out the adsorption of Phenol and Chlorophenol in aqueous solution. Observations revealed that the rate of phenol biodegradation was increased because of pretreatment, i.e., adsorption, temperature and glucose concentration. The optimal conditions for Phenol and CP removal were found to be temperature 350C (58-65% removal) and two gpl glucose levels (70-78% removal). The importance of the study is the pretreatment of recalcitrant chemicals with adsorption followed by biodegradation and thus provided with an alternative bioremediation approach.

Comparison of porous carbons derived from sodium alginate and calcium alginate and their electrochemical properties.

Here, sodium alginate and calcium alginate which have the same carbon-forming component (alginic acid) and different regulation component (sodium/calcium) were used to prepare porous carbons, and comparisons were made of the microstructures and electrochemical properties of the obtained charcoals. The morphology was characterized by Scanning electron microscopy (SEM), and the results show that porous carbons can inherit plane or concave structures from their corresponding carbonized samples. The Horvath–Kawazoe (HK) method was used to analyze micropore size distributions, and the results show that, under the same mass ratio of potassium hydroxide to carbonized sample (KOH/C), the positions of extreme points on the two curves are similar, but the extreme values are different, and new extreme points appear at larger pore sizes with increases in the KOH/C ratio. The results of cyclic voltammetry (CV) and galvanostatic charge and discharge (GCD) tests show that the capacitance of sodium alginate-derived porous carbon is greater than that of porous carbon derived from calcium alginate when the KOH/C ratios are 2 and 4, and the size relationship is reversed when the KOH/C ratio is 3. The results of cycling performance tests show that the cycle numbers corresponding to the three stages on the two curves are similar under the same KOH/C ratio, but the cycle numbers at the same stage are significantly different under different KOH/C ratios.