Mesopore Content Research Articles

Effect of rate of pyrolysis on the textural properties of naturally-templated porous carbons from alginic acid

The effect of pyrolysis rate on the properties of alginic acid-derived carbonaceous materials, termed Starbon®, was investigated. Thermal Gravimetry-IR was used to prepare porous carbons up to 800°C at several rates and highlighted increased CO2 production at higher pyrolysis rates. N2 porosimetry of the resultant carbons shows how pyrolysis rate affects both the mesopore structure and thus surface area and surface energy. Surface capacity of these carbons was analysed by methylene blue dye adsorption. In general, as the rate of pyrolysis increased, the mesopore content and adsorbent capacity decreased. It is considered here that the rapid production of volatiles at these higher rates causes structural collapse of the non-templated pore network. The work here demonstrates that pyrolysis rate is a key variable which needs to be controlled to maximise the textural properties of Starbon® required for adsorption applications.

The role of mesopores in achieving high efficiency airborne nanoparticle filtration using aerogel monoliths

Abstract This study evaluates the role of small mesopore volume fraction in aerogel monoliths in achieving high efficiency airborne nanoparticle filtration. The diffusional flow in mesopores (diameter 2–50 nm) is more effective in nanoparticle capture than the viscous flow regime encountered in macropores (diameter > 50 nm). Substantial macropore fraction, however, is essential for achieving high air permeability. This idea is tested by evaluating the filtration efficiency of 25–150 nm diameter airborne sodium chloride nanoparticles and the permeability of air through hybrid aerogel monoliths with about 2–4% by volume mesopore content. The hybrid aerogels are prepared by growing discontinuous silica aerogel particles in the macropores of δ-form syndiotactic polystyrene (sPS). The results show that air permeability is not much affected by the silica content although the particle capture efficiency is increased to >99.95% due to the contribution of diffusional deposition aided by the mesopores. The aerogels develop cracks and reduce filtration efficiency at high silica content due to brittle nature of silica particle networks.

Production of isobutylene from acetone over micro–mesoporous catalysts

The production of isobutylene from acetone over micro–mesoporous catalysts with different mesopore contents, which have been prepared using hydrothermal recrystallization of mordenite (MOR) zeolite modified with cesium acetate by incipient wetness impregnation, has been studied. It has been shown that cesium is inserted into the cation positions during the modification, at the same time the number of Bronsted acid sites in the samples decreased. It has been found that an increase in the content of mesopores in the catalyst leads to an increase in the initial rates of acetone conversion and isobutylene formation as a result of removing diffusion limitations. Bronsted acid sites have been shown to be preferable for the selective production of isobutylene from acetone. Micro–mesoporous materials operate more stably as compared to microporous materials.

Synthesis of Hierarchically Porous SiCN Materials and Pd Catalysts based on it for the Oxidation of Methane

AbstractPolymer derived silicon carbon nitride (SiCN) ceramics are versatile materials with broad potential applications in industry and technology. Their high stability towards thermomechanical and chemical stress makes them a promising support material in heterogeneous catalysis. Due to the challenging process of synthesizing high‐surface‐area porous SiCN only a few examples of porous SiCN based catalysts are reported. Herein, we present a simple and efficient route to obtain mesoporous SiCN containing materials by impregnation of activated carbon with a polymeric silazane precursor. Oxidative removal of the template yields high‐surface‐area SiCN materials with a BET surface area from 200–470 m2·g–1 and high content of mesopores from 70–99 %. By incipient wetness impregnation with palladium, efficient catalysts for the total oxidation of methane were obtained.

Tailoring the textural properties of hierarchical porous carbons for supercapacitors

Hierarchical porous carbons (HPCs) are prepared from humic acid by a simple KOH activation. HPCs show unique pore size distribution: abundant micropores with the size of 1–2nm, mesopores with the size of 3–5nm. Of special interest is the fact that the mesopore content with the size of 3–5nm can be fine-tuned easily. HPCs show high performance for supercapacitors possessing of the optimized capacitance of 189Fg−1 in 3M KOH with high capacitive retention. Furthermore, HPCs also exhibit a superior cycling stability, which can be attributed to the unique pore size distribution.

Modulation of microporous/mesoporous structures in self-templated cobalt-silica.

Finite control of pore size distributions is a highly desired attribute when producing porous materials. While many methodologies strive to produce such materials through one-pot strategies, oftentimes the pore structure requires post-treatment modification. In this study, modulation of pore size in cobalt-silica systems was investigated by a novel, non-destructive, self-templated method. These systems were produced from two cobalt-containing silica starting materials which differed by extent of condensation. These starting materials, sol (SG′) and xerogel (XG′), were mixed with pure silica sol to produce materials containing 5–40 mol% Co. The resultant SG-series materials exhibited typical attributes for cobalt-silica systems: mesoporous characteristics developed at high cobalt concentrations, coinciding with Co3O4 formation; whereas, in the XG-series materials, these mesoporous characteristics were extensively suppressed. Based on an examination of the resultant materials a mechanism describing the pore size formation and modulation of the two systems was proposed. Pore size modulation in the XG-series was caused, in part, by the cobalt source acting as an autogenous template for the condensation of the silica network. These domains could be modified when wetted, allowing for the infiltration and subsequent condensation of silica oligomers into the pre-formed, mesoporous cages, leading to a reduction in the mesoporous content of the final product.

Titanium Carbide Nanocrystals Synthesized from a Metatitanic Acid‐Sucrose Precursor via a Carbothermal Reduction

A TiC powder is synthesized from a micron‐sized mesoporous metatitanic acid‐sucrose precursor (precursor M) by a carbothermal reduction process. Control specimens are also prepared using a nanosized TiO2‐sucrose precursor (precursor T) with a higher cost. When synthesized at 1500°C for 2 h in flowing Ar, the characteristics of the synthesized TiC from precursor M are similar to those of the counterpart from precursor T in terms of the crystal size (58.5 versus 57.4 nm), oxygen content (0.22 wt% versus 0.25 wt%), and representative sizes of mesopores: approximately 2.5 and 19.7–25.0 nm in both specimens. The most salient differences of the two specimens are found in the TiC from precursor M demonstrating (i) a higher crystallinity based on the distinctive doublet peaks in the high‐two‐theta XRD regime and (ii) a lower specific surface area (79.4 versus 94.8 m2/g) with a smaller specific pore volume (0.1 versus 0.2 cm3/g) than the counterpart from precursor T.

Effects of activated carbon characteristics on the electrosorption capacity of titanium dioxide/activated carbon composite electrode materials prepared by a microwave-assisted ionothermal synthesis method

Titanium dioxide (TiO2)/ activated carbon (AC) composite materials, as capacitive deionization electrodes, were prepared by a two-step microwave-assisted ionothermal synthesis method. The electrosorption capacity of the composite electrodes was studied and the effects of AC characteristics were explored. These effects were investigated by multiple analytical techniques, including X-ray photoelectron spectroscopy, thermogravimetry analysis and electrochemical impedance spectroscopy, etc. The experimental results indicated that the electrosorption capacity of the TiO2/AC composite electrode is dependent on the characteristics of AC including the pore structure and the surface property. An enhancement in electrosorption capacity was observed for the TiO2/AC composite electrode prepared from the AC with higher mesopore content and less hydrophilic surface. This enhancement is due to the deposition of anatase TiO2 with suitable amount of Ti–OH. On the other hand, a decline in electrosorption capacity was observed for the TiO2/AC composite electrode prepared from the AC with higher micropore content and highly hydrophilic surface. High content of hydrogen bond complex formed between the functional group on hydrophilic surface with H2O, which will slow down the TiO2 precursor-H2O reaction. In such situation, the effect of TiO2 becomes unfavorable as the loading amount of TiO2 is less and the micropore can also be blocked.

Effect of Pore Structure of Activated Carbon on its Electrochemical Performance in Non-Aqueous Electrolyte

The surface area and pore distribution of activated carbons (ACs) were characterized by nitrogen adsorption isotherms at 77 K, and double layer capacitors were assembled to demonstrate the electrochemical performance. With 1 mol·L-1 tetraethylammonium tetrafluoroborate dissolved in acetonitrile (Et4NBF4/AN) as electrolyte, electrochemical methods including cyclic voltammetry (CV) and galvanostatic charge-discharge tests were used to evaluate the capacitors. Results show that the surface area has a limited effect on the specific capacitance of ACs and the increaing of mesoporous content can decrease the capacitance decay rate at large discharge current. When current increases from 0.15A·g-1 to 9.6A·g-1, the minimum specific capacitance decay rate of mesoporous ACs is 10.93%, while that of the microporous ACs is 15.21%;the contributions of mesoporous surface area to the specific capacitance drop from 10.10 to 9.95μF·cm-2, while that of microporous surface area drop from 5.68 to 4.21μF·cm-2.

Preparation and weak acid dark blue adsorption studies of melamine formaldehyde-based nanoporous carbon

A nitrogen-enriched wormhole-like nanoporous carbon has been prepared from melamine formaldehyde resin by a simple one-step nanocasting method. Results indicate that the obtained three-dimensional carbon nanonetwork is wormhole like. The pore size distribution is narrow with a mean value of 4.7 nm, which is calculated from the desorption branch by Barrett–Joyner–Halenda method. The Brunauer–Emmett–Teller surface area and the nitrogen content of the sample are high up to 521 m2/g and 21%, respectively. The as-obtained carbon nanomaterial is very highly mesoporous, in which the mesopore content is up to 70%. Adsorption experiments show that the obtained material has better adsorption performance than commercial activated carbon. The adsorption efficiency was up to 94.7% at the concentration of 0.05 mg/mL, while activated carbon is only 25.4% in the research.

Removal of lead (Pb2+) from aqueous medium by using chars from co-pyrolysis

The effectiveness of chars from the co-pyrolysis of pine, used tires and plastic wastes for the removal of lead (Pb2+) from aqueous medium, was investigated. The chars were predominantly of macroporous nature, but the introduction of tires in the pyrolysis feedstock enhanced their mesoporous content as well as surface area. Pb2+ sorption with the chars was a slow and unstable process in which sorption–desorption seems to be competing. The highest Pb2+ removal (88%) was attained by the char resulting from the pyrolysis of a mixture composed by equal mass ratios of used tires and plastics, at 48h of contact time. This char was also the one with the overall better performance for Pb2+ sorption, achieving almost 100% of Pb2+ removal on the study of the effect of adsorbent dose. Mixing the three raw materials for pyrolysis had no advantage for the resulting char concerning the removal efficiency of Pb2+. The sorption mechanisms varied according to the pyrolysis feedstock: in chars from feedstock with pine, chemisorption involving complexation with oxygenated surface functional groups followed by cation exchange was the presumable mechanism. In tire rubber derived chars, cation exchange with Ca2+, K+, and Zn2+ played the major role on Pb2+ sorption.

Determining mesopore volumes in coke produced at OAO Evraz NTMK

The structure of porous bodies and methods of determining porous structure are considered theoretically. The mesopore volume is determined in samples of dry- and wet-slaked coke. A relation is established between the total mesopore content of the coke and its properties.

High-performance charge storage by N-containing nanostructured carbon derived from polyaniline

Nitrogen-containing nanostructured carbon materials, C-nanoPANI, C-nanoPANI-DNSA and C-nanoPANI-SSA, were prepared by the carbonization of nanostructured polyaniline (PANI) doped with sulfuric acid, 3,5-dinitrosalicylic acid (DNSA), and 5-sulfosalicylic acid (SSA), respectively. The charge storage ability of these materials was investigated in alkaline solution. It was found that the specific capacitance increased in the order: C-nanoPANI-DNSA<C-nanoPANI<C-nanoPANI-SSA. The highest capacitance, amounting to 410Fg−1 at a scan rate of 5mVs−1, was found for C-nanoPANI-SSA. At a large rate of 10Ag−1, its capacitance displayed a stable value close to 200Fg−1. To explain the observed differences in charge storage properties, the materials were characterized by different techniques able to ascertain their morphology, elemental composition, nitrogen surface concentration, chemical state of nitrogen, pore structure and electrical conductivity. All materials were essentially microporous with relatively small fraction of mesopores and displayed conductivities in the range 0.32–0.83Scm−1. The best charge-storage performance of C-nanoPANI-SSA was attributed to its highest surface fraction of nitrogen, the highest surface content of pyridinic nitrogen groups, and the highest electrical conductivity, as well as to its well-balanced micro- and mesoporosity and highest content of mesopores.

Impact of Pore Size Characteristics on the Electrosorption Capacity of Carbon Xerogel Electrodes for Capacitive Deionization

Conductive, monolithic carbon xerogel electrodes have been synthesized using a flexible carbon support and a resorcinol-formaldehyde (RF) polycondensation reaction with RF precursor weight percentages of 37, 40, 45, and 50 to tailor pore size distributions for electrosorption. Increased RF weight percentages produced carbon electrodes with pore volumes greater than 0.4 cm3/g. External pore size examined by SEM was shown to decrease with increasing RF weight percent from >300 nm to <50 nm for 37 wt% RF and 50 wt% RF, respectively. Carbon electrodes were used in a capacitive deionization cell demonstrating electrosorption capacities between 2.8–3.5 mg NaCl/g carbon using an applied potential of 1.2 V. Surface utilization of the carbon for electrosorption was found to decrease with increasing RF wt% corresponding with decreasing of the external pore size from macroporous to mesoporous. A mixture of macroporous and mesoporous content is preferred for fast time scale applications such as capacitive deionization.

Highly Dispersed Pt Nanoparticles Supported on Mesoporous Carbon and Its Electrocatalytic Performance for Ethylene Glycol Oxidation

Mesoporous carbon (MC) with high mesopore content and narrow pore size distribution was prepared using colloidal silica as hard template and Pluronic F127 triblock copolymer as soft template, re- spectively. Then highly dispersed Pt catalyst supported on MC was achieved by ethylene glycol (EG) reduc- tion method. Electrooxidation behavior of EG on the Pt/MC catalyst electrode in sulfuric solution was inves- tigated using cyclic voltammogram (CV), chronoamperometry, linear sweeping voltammogram (LSV) and electrochemical impedance spectra (EIS) analysis. The experimental results indicate that the electrocatalytic performance of the Pt/MC catalyst for EG oxidation is much higher than that of Pt/XC72R catalyst. EIS analysis further reveals that the electrooxidation reaction of EG on the Pt/MC catalyst electrode has a lower charge-transfer resistance. The higher electrocatalytic activity of the Pt/MC catalyst may be due to the pro-

Utilisation of Rubber Wood Shavings for the Removal of Cu(II) and Ni(II) from Aqueous Solution

The potential of heat and chemically treated rubber wood shavings (RWS) to remove Cu(II) and Ni(II) was evaluated at bench-scale by varying parameters such as initial Cu(II) and Ni(II) concentrations, contact time and adsorbent dosage. Maximum Cu(II) and Ni(II) uptake was achieved using NaOH-treated RWS after 5 h of contact time, pH 5.0 (Cu), 5.5 (Ni) and 6.0 (mixed-metal solution), initial Cu(II) and Ni(II) of 100 mg L−1 and RWS dosage of 0.3% (w/v). Point of zero charge (pHPZC) value of 4.35 suggests the appropriateness of pH range used. Higher Cu(II) and Ni(II) adsorption following NaOH treatment was due to smaller average pore diameter (34.63 A), higher mesopore content and higher surface negativity charge. EDAX analysis confirmed the presence of Cu and Ni on the surface of the RWS. The importance of carboxyl and hydroxyl functional groups during Cu(II) and Ni(II) removal is supported by the FTIR analysis and good correlation (R2 of 0.96–0.99) with the pseudo-second-order adsorption kinetic model. The results indicate the potential of using RWS as an alternative adsorbent to remove Cu(II) and Ni(II) from industrial wastewaters.

Adsorption of Pb(II) ion on mesoporous activated carbon prepared by ZnCl2 activation

The chemical activation with ZnCl2 was conducted to prepare mesoporous activated carbons (ACs) from bamboo chips (BC), and the optimization as well as mechanism of ZnCl2 activation was examined. The pore properties of the prepared ACs were evaluated through N2 adsorption/desorption isotherms. The results showed that both surface area and mesopore volume were significantly developed up to as much as 1900 m2/g and 1.6 cm3/g, respectively, by ZnCl2 activation at the impregnation ratio (ZnCl2/BC) of 9 g/g. The mesopore volume of the ACs could be controlled by varying the amount of ZnCl2 in the impregnation process. The development of porosity was observed around a 400–500 °C activation temperature, and was attributed to the expansion of the carbon microstructure by fusion and vaporization of ZnCl2. The increase in activation temperature to above 500 °C, however, caused a significant reduction of porosity for ACs. This was due to the rapid progression of organization of the graphite structure. Adsorption of Pb(II) ions revealed that it strongly depended on the number of total basic sites on the carbon surface rather than the mesopore volume, while the Pb(II) ion adsorption kinetics was much higher for ACs with a larger mesopore content.

Empirical Analysis of the Contributions of Mesopores and Micropores to the Double-Layer Capacitance of Carbons

Activated carbons with large mesopore volumes were prepared from waste coffee grounds by chemical activation with ZnCl2. These carbons exhibited excellent electrochemical double-layer capacitance of up to 368 F g−1 in 1 M H2SO4. The effect of carbonization temperature and ZnCl2 ratio on carbon pore development and consequently electrochemical double-layer capacitance in 1 M H2SO4 is discussed. Cyclic voltammetry, electrochemical impedance spectroscopy, and galvanic charge−discharge cycles were used to study the effects of mesopores on capacitance at fast charge rates. Activated carbons with greater mesopore content retained higher specific capacitance at fast charge−discharge rates as the mesopores acts as channels or reservoirs for electrolyte transport. An improved model for evaluation of contributions to capacitance from micropore surfaces and mesopore surfaces is proposed. Using this model, the contribution of the mesopores to double-layer capacitance was determined to be 17 μF cm−2. The contribution of micropores to capacitance decreased at fast discharge rates and was found to be dependent on the number of mesopores, which influence the transport of ions through the carbon pore network.

Removal of chromium Cr(VI) by low-cost chemically activated carbon materials from water

Low-cost, chemically activated carbon materials, Pellet-600 and PVA-300, were prepared at relatively low temperatures and show more effective removal efficiency of Cr(VI) from water than commercially available activated carbons tested. The Pellet-600 is a pelletized carbon material with high mesoporous volumes and surface area, and the PVA-300 is composed of a high surface area carbon coating on a fiberglass mat substrate. A much faster adsorption kinetics and a much higher adsorption capacity for Cr(VI) are achieved by the Pellet-600. At very low concentrations of Cr(VI), the PVA-300 displays a strong adsorption ability for Cr(VI). XPS data show an increase in the atomic ratio of Cr/C and oxidation of carbon materials after adsorption of Cr(VI). These results suggest that a high content of mesopores with a high surface area and surface functional groups greatly improve the Cr(VI) removal efficiency from water.

The benefit of mesopores in ETS-10 on the vapor-phase Beckmann rearrangement of cyclohexanone oxime

Mesoporosity in ETS-10 titanosilicate was generated by postsynthesis treatment with hydrogen peroxide under microwave irradiation, resulting in an increased external surface area of the materials. The influence of mesopore content, external surface area, proton-exchange conditions, and solvent on the activity of the modified ETS-10 in the Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam under vapor-phase conditions was investigated. Protonated mesoporous ETS-10 was catalytically active and demonstrated improved performance with increasing external surface area.