Influence Of Specific Surface Area Research Articles

Influence of specific surface area and microporosity-mesoporosity of pristine and Pt-nanoclusters modified carbide derived carbon electrodes on the oxygen electroreduction

Oxygen electroreduction reaction (ORR) on pristine porous carbide derived carbons (CDCs) and on CDC supports modified with Pt-nanoclusters has been studied in 0.5M H2SO4 solution using cyclic voltammetry, rotating disk electrode and electrochemical impedance spectroscopy methods. The CDCs were prepared from Mo2C (noted as C(Mo2C)) at different fixed chlorination temperatures from 600°C to 1000°C. The CDCs have tuneable specific surface area, micro- and mesoporosity, good electrical conductivity and corrosion stability at positive electrode potentials. Pt-nanoclusters were deposited onto/into C(Mo2C) powders using sodium borohydride reduction method. The X-ray diffraction and high-resolution transmission electron microscopy were applied for the structural and chemical characterization, and the nitrogen sorption method was used for the porosity analysis of the electrode materials studied. The cathodic current densities depend strongly on the synthesis temperature of C(Mo2C), indicating that, in addition to the specific surface area and porosity, the crystallinity (density of defects in amorphous areas) has noticeable influence on the ORR rate. Impedance data demonstrated nearly capacitive behaviour in the low AC frequency region, explained by quick cathodic ORR followed by slow adsorption step of the intermediates and reaction products at/inside microporous-mesoporous C(Mo2C) and Pt-C(Mo2C) electrodes.

Deoxygenation effect on hydrophilicity changes of Shengli lignite during pressurized pyrolysis at low temperature

The effect of temperature (200–350°C) and pressure (0.25–8.00 MPa) on the elimination of main oxygen-containing functional groups of Shengli lignite was examined during pyrolysis in a fixed-bed reactor. Effects of the reduction of oxygen-containing functional groups on the moisture holding capacity (MHC) of coal samples were also investigated. The results showed that temperature was the key factor on the removal of carboxyl and phenolic hydroxyl from the lignite. The variation of pressure had few effects on the removal of carboxyl in coal; in contrast, phenolic hydroxyl was reduced to a minimum point at the pressure between 3.00 to 4.00 MPa. The carboxyl content in the lignite played a dominant role on the surface polarity and moisture holding capacity. The influence of specific surface area on the MHC became distinct when the carboxyl content in coal samples kept constant.

The Effect of Specific Surface Area on the Solid Grafting Reaction of Maleic Anhydride-Grafted Polypropylene

In this paper, based on the ultrasonic dispersion principle, the grafting reaction of maleic anhydride (MAH) onto solid PP in water was studied with acetone as the phase physiognomy solvent, ammonium persulfate [(NH4)2S2O8] as the initiator. The influence of specific surface area on the graft ratio was also studied. The results showed that the grafting reaction had obvious relationship with the specific surface area of original PP particles.

Influence of structure of activated carbon with superhigh specific surface area on hydrogen storage capacity

Abstract

Influence of surface features of hydroxyapatite on the adsorption of proteins relevant to bone regeneration

Protein-surface interaction may determine the success or failure of an implanted device. Not much attention have been paid to the specific surface parametes of hydroxyapatite (OHAp) that modulates and determines the formation and potential activity of the layer of proteins that is first formed when the material get in contact with the host tissue. the influence of specific surface area (SSA), crystallite size (CS) and particle size (PS) of OHAp on the adsorption of proteins relevant for bone regeneration is evaluated in this article. OHAp have been prepared by a wet chemical reaction of Ca(OH)2 with H3PO4. One set of reactions included poly acrylic acid in the reactant solution to modify the properties of the powder. Fibrinogen (Fg) Fraction I, type I: from Human plasma, (67% Protein), and Fibronectin (Fn) from Human plasma were selected to perform the adsorption experiments. The analysis of protein adsorption was carried out by UV/Vis spectrometry. A lower SSA and a different aspect ratio are obtained when the acrylic acid is included in the reaction badge. The deconvolution of the amide I band on the Raman spectra of free and adsorbed proteins reveals that the interaction apatite-protein happens through the carboxylate groups of the proteins. The combined analysis of CS, SSA and PS should be considered on the design of OHAp materials intended to interact with proteins.

Removal of two ionic dyes from water by MgO-loaded porous carbons prepared through one-step process from poly(ethylene terephthalate)/magnesium carbonate mixtures

Mixtures of poly(ethylene terephthalate) and magnesium carbonate at different weight ratios were heated up to 850 $^{\boldsymbol\circ}$ C in argon atmosphere. During heating, components of the initial mixtures underwent thermal decomposition yielding porous carbon materials loaded with different amounts of magnesium oxide. Structural characteristics of the prepared materials were determined from adsorption/desorption isotherms of nitrogen, measured at 77 K. For reference, portions of the products obtained were acid-washed to obtain MgO-free carbons. Pore structures of the prepared materials were strongly dependent on the quantitative compositions of starting mixtures. As a rule, specific surface areas determined for acid-washed materials were much higher than those for MgO-loaded carbons. The adsorption abilities of obtained materials towards cationic (Basic Red 18) and anionic (Reactive Red 198) dyes as model contaminants were examined. Surprisingly, in spite of relatively low specific surface areas, substantially high adsorption of the dyes on MgO-loaded carbons was observed. An influence of specific surface area and the role of magnesium oxide presence on the adsorption capacity of the acquired sorbents were studied.

Time-resolved in situ XANES study of the redox properties of Ce0.9Zr0.1O2 mixed oxides

The aim of this paper is to gain further insight in the reduction and reoxidation processes taking place when Ce0.9Zr0.1O2 mixed oxides are in reducing or oxidizing atmospheres, respectively. The reduction process of these mixed oxides synthesized by two stoichiometric nitrate-aminoacid gel-combustion routes using glycine and lysine as fuels is studied by conventional H2-Temperature Programmed Reduction experiments. The results are compared with those obtained by time-resolved in situ X-ray absorption near-edge spectroscopy (XANES) in the energy level corresponding to the Ce LIII absorption edge. The reoxidation process by this last technique is also studied. Even though the identical composition and crystal structure of both samples, the redox processes resulted very different for each solid, suggesting the influence of specific surface area, pore volume and particle size on them.

Adsorption of 1,4-Dioxane from Aqueous Solutions onto Various Activated Carbons

The behavior of the adsorption of 1,4-dioxane (DOX) in water onto eight different activated carbons (ACs) was studied. All adsorption isotherms obtained using batch-type adsorption measurements, were found to fit a Freundlich equation. The amount adsorbed at an equilibrium concentration of 50 μg/L (q50) was obtained, and its correlation with microporosity and chemical properties of each AC was examined. The AC prepared from sawdust by direct activation adsorbed the most DOX (410 μg/g), while adsorption in the other ACs were in the range of 4.3 - 71.1 μg/g. No practical influence of specific surface area on the adsorption of DOX was found. We observed that log q50 mostly decreased linearly with an increase in mean pore diameter. The concentrations of acidic surface oxides and nitrogen in the ACs affected the hydrophilicity of the adsorbent and impaired q50. It was assumed that the main factor for the adsorption of DOX at trace concentration in water was surface chemistry rather than the microporosity of AC.

Modelling of nanocrystalline iron nitriding process — influence of specific surface area

AbstractSamples of iron catalysts of various specific surface areas for ammonia synthesis underwent nitriding with ammonia in a tubular reactor where continuous thermogravimetric measurement and measurements of hydrogen concentration in the gaseous phase were simultaneously performed. The nitriding process was performed under atmospheric pressure at 475°C. It was observed that, along with an increase in the mean size of iron nano-crystallites, the minimum nitriding potential (at which the iron nitriding reaction is initiated) of the gaseous phase also increased. The degree of nitriding of the catalyst samples increased with the increase in the mean size of iron crystallites. On the basis of the values of nitriding potential, nano-crystallite size distributions can be determined.

Biodegradation of corn flour-based materials assessed by enzymatic, aerobic, and anaerobic tests: Influence of specific surface area

A material was produced by extrusion of corn flour with 8 wt% glycerol followed by injection-moulding. The corn flour based material biodegradation kinetics were assessed by an anaerobic biodegradation standard test (ISO 14853), an aerobic burial composting test (ISO/DIS 16929) and a test to assess the susceptibility of corn starch to hydrolysis by amylolytic enzymes. Biodegradation and hydrolysis were more rapid for corn flour based material than for native corn flour. This was probably due to corn flour starch amorphisation during thermomechanical processing at the expense of crystalline regions, which are more resistant to hydrolysis by amylolytic enzymes. This was substantiated by observations during burial composting showing that crystalline zones of this material were less degraded. A comparison of the kinetics of starch hydrolysis or biodegradation of corn flour based material samples with specific surface areas ranging from 0.67 to 30 mm −1 by amylolytic enzymes or microorganisms under anaerobic conditions in a liquid medium (ISO 14853) or aerobic conditions during burial composting (ISO/DIS 16929) allowed (i) observation that the biodegradation level by the latter method always exceeded 90% before 84 days, thus meeting this biodegradability criterion, and (ii) to propose that the test of hydrolysis by amylolytic enzymes might constitute a faster method for initial assessment of the biodegradability of starch based materials.

Effect of Tensile Loading on Chloride Penetration of Concrete Mixed with Granulated Blast Furnace Slag

The effect of loading on chloride penetration into concrete is evaluated in this study. It is found that the chloride penetration rates for OPC concrete and blast furnace slag BFS concrete under the tensile stress were increased by 29% and 77%, respectively. The diffusion coefficient of BFS concrete was lower than that of conventional concrete without BFS, no loads and stress states. Under tensile stress, the diffusion coefficient for BFS and plain concrete showed higher values with increasing stress. The influence of specific surface area on the diffusion coefficient was investigated. As a result, the larger the specific surface areas of BFS are the lower diffusion coefficients. This tendency was more pronounced under the high stress conditions. The diffusion coefficient was found to decline with increases in the ratio of substituted BFS. This result was the same even under the tensile stress conditions. The chloride penetration depth was distributed uniformly when no stress was applied. However, in the case of tensile loading, the diffusion depth was not distributed uniformly, and showed prominent characteristics. This result indicates that analysis using average values of chloride penetration depth is not proper under load conditions.

Influence of Surface Properties of Activated Carbon on Photocatalytic Activity of TiO2 in 4-chlorophenol Degradation

This work shows the influence of specific surface area (BET) and surface pH of different activated carbons on the photocatalytic activity of UV-irradiated TiO2 in the 4-chlorophenol (4CP) photodegradation. Carbons were prepared from sawdust of Tabebuia Pentaphyla wood by physical activation with CO2 and by pyrolysis under N2 flow at tempera- tures from 450 up to 1000oC during 1h Chemical activation was also performed by the impregnation of precursor with ZnCl2, H3PO4 and KOH at different concentrations, followed by activation under N2 flow at 450oC by 1h. Comparison of apparent first-order rate constants between TiO2 against TiO2-AC indicate that TiO2 photoactivity is enhanced or inhibited as a function of AC properties and correlations with surface area and pHPZC were found suggesting that surface pH of car- bons is the most important parameter that influences TiO2 activity in the 4CP photodegradation.

Influence of specific surface area of pyrogenic silicas on their heat of immersion in water and on their surface properties assessed using inverse gas chromatography

The heat of immersion and the surface properties of pyrogenic silicas were examined using microcalorimetry and inverse gas chromatography at finite concentration (FC-IGC). The microcalorimetric measurements showed a regular decrease of the heat of immersion, in water, per area unit with an increase in the surface areas. The desorption isotherms were established using FC-IGC. It is observed that BET constant value goes through a minimum, whereas the shapes of distribution function of the adsorption energies of isopropanol are changing. All results could be interpreted using a model of formation of the pyrogenic silica in the flame, which explains the change of surface functionality and geometry occurring around 200 m 2/g.

The importance of heat evolution during the overcharge process and the protection mechanism of electrolyte additives for prismatic lithium ion batteries

In this work, the rate of heat generation in the overcharge period for 103450 prismatic lithium ion batteries (LIBs) of the LiCoO 2–graphite jellyroll type with a basic electrolyte consisting of 1 M LiPF 6–PC/EC/EMC (1/3/5 in weight ratio) has been found to be more important than the gas evolution which was traditionally considered as the main reason in the overcharge protection mechanism. The cell voltage, charge current, and skin temperature were monitored during the charge process. For a single battery or batteries in parallel, LIBs without any additives is an acceptable design if the cell voltage is not charged above 4.55 V under the common charge program. The rate of heat generation from the polymerization of 3 wt% cyclohexyl benzene (CHB) is high enough to cause the explosion or thermal runaway of a battery, which is not found for an LIB containing 2 wt% CHB + 1 wt% tert-amyl benzene (TAB). In the 12 V overcharge test at 1C, the thermal fuse was broken by the high skin temperature (ca. 80 °C) due to the polymerization of 3 wt% CHB, which was also the case for LIBs containing 2 wt% CHB + 1 wt% TAB. The disconnection of the thermal fuse, however, did not interrupt the thermal runaway of LIBs without any additives because the battery voltage was too high (ca. 4.9 V). The influence of specific surface area of active materials in the anode on the polymerization kinetics of additives has to be carefully considered in order to add correct amount of overcharge protection agents.

Physicochemical Properties Related to Long-Term Phosphorus Retention by Drinking-Water Treatment Residuals

Drinking-water treatment residuals (WTRs) are nonhazardous materials that can be obtained free-of-charge from drinking-water treatment plants to reduce soluble phosphorus (P) concentrations in poorly P sorbing soils. Phosphorus sorption capacities of WTRs can vary 1-2 orders of magnitude, on the basis of short-term equilibration times (up to 7 d), but studies dealing with long-term (weeks to months) P retention by WTRs are lacking. Properties that most affect long-term P sorption capacities are pertinent to the efficacy of WTRs as amendments to stabilize P in soils. This research addressed the long-term (up to 80 d) P sorption/desorption characteristics and kinetics for seven WTRs, including the influence of specific surface area (SSA), porosity, and total C content on the overall magnitude of P sorption by seven WTRs. The data confirm a strong but variable affinity for P by WTRs. Aluminum-based WTRs tended to have higher P sorption capacity than Fe-based WTRs. Phosphorus sorption with time was biphasic in nature for most samples and best fit to a second-order rate model. The P sorption rate dependency was strongly correlated with a hysteretic P desorption, consistent with kinetic limitations on P desorption from micropores. Oxalate-extractable Al + Fe concentrations of the WTRs did not effectively explain long-term (80 d) P sorption capacities of the WTRs. Micropore (CO2-based) SSAs were greater than BET-N2 SSAs for most WTRs, except those with the lowest (<80 g kg(-1)) total C content. There was a significant negative linear correlation between the total C content and the CO2/N2 SSA ratio. The data suggest that C in WTRs increases microporosity, but reduces P sorption per unit pore volume or surface area. Hence, variability in C content confounds direct relations among SSA, porosity, and P sorption. Total C, N2-based SSA, and CO2-based SSAs explained 82% of the variability in the long-term P sorption capacities of the WTRs. Prediction of long-term P sorption capacities for different WTRs may be achieved by taking into account the three proposed variables.

Sintering and microstructure of rare earth phosphate ceramics REPO 4 with RE = La, Ce or Y

Sintering of rare earth phosphates REPO 4 ( RE = La, Ce or Y) was studied using dilatometry. The presence of a secondary rare earth metaphosphate phase RE(PO 3) 3 as sintering aid was investigated. It proved to accelerate the densification but it activated fast grain growth, which was very detrimental to the microstructural design of processed ceramics. A temperature of 1400–1450 °C was required to sinter pure LaPO 4 and CePO 4 ceramics with fine grains. Both compounds behave similar while YPO 4 did not densify even at 1500 °C. The influence of specific surface area of starting powders, temperature and holding time on the sintering rate and microstructures of dense REPO 4 materials is also reported.

The Influence of Particle Characterizations of Inner-Constraining Layer upon Constrained Sintering Shrinkage [Translated]&lt;sup&gt;†&lt;/sup&gt;

Constrained sintering of a substrate with a sandwich structure, which was the laminated inner-constraining alumina layer between the glass-alumina mixed layers, has been studied. The influence of specific surface area of the particles and porosity of inner constraining particle layer upon sintering shrinkage was investigated. Specific surface area of the alumina powder for the inner constraining particle layer could be changed by grinding and blending two different particle size powders. As for the debinded sheet used with ground alumina powder, the pore distribution was sharp, and the bending strength was proportional to the specific surface area. In the case of inner constraining particle layer used with ground alumina powder, penetration length of molten glass from glass-alumina mixed layers obeyed Kozeney-Carman’s equation. On the other hand, as for the debinded sheet with particle size blended powder, the effects of specific surface area on the bending strength and the penetration length of molten glass differed from the results of the grounded one. Sintering shrinkage in X-Y direction of the sandwich substrate was basically related to the bending strength of debinded alumina powder sheet for inner constraining particle layer in both cases.† This report was originally printed in J. Soc. Powder Technology, Japan, 41, 730-737 (2004) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

内部拘束層の粉体特性が焼成無収縮化に与える影響

Constrained sintering of a substrate with a sandwich structure, which was the laminated inner-constraining alumina layer between the glass-alumina mixed layers, has been studied. The influence of specific surface area of the particles and porosity of inner constraining particle layer upon sintering shrinkage was investigated. Specific surface area of the alumina powder for the inner constraining particle layer could be changed by grinding and blending two different particle size powders. As for the debinded sheet used with ground alumina powder, the pore distribution was sharp, and the bending strength was proportional to the specific surface area. In the case of inner constraining particle layer used with ground alumina powder, penetration length of molten glass from glass-alumina mixed layers obeyed Kozeney-Carman's equation. On the other hand, as for the debinded sheet with particle size blended powder, the effects of specific surface area on the bending strength and the penetration length of molten glass differed from the results of the grounded one. Sintering shrinkage in X-Y direction of the sandwhich substrate was basically related to the bending strength of debinded alumina powder sheet for inner constraining particle layer in both cases.

Low-cost sorbents for demetalisation of waste oils via pyrolysis

The behaviour of several solid sorbents during the pyrolysis process of industrial waste oils in a bench-scale pyrolysis unit is studied. The concentrations of V, Ni, Pb, Cd, Cu and Cr in the waste oils and in the original sorbents as well as that obtained in the final valuable product liquid fraction are measured. Limestone, commercial active char, Samca char, activated Samca char and sepiolite were the solid sorbents used. 100% of the lead from the waste oils can be retained on limestone. The behaviour of both metals and sorbents and the influence of specific surface area as well as chemical nature of metals and sorbents are discussed. Final liquid fractions resulted in valuable industrial products.

Influence of particle surface area on the toxicity of insoluble manganese dioxide dusts

The objective of this study was to examine the influence of specific surface area on the biological activity of insoluble manganese dioxide (MnO2) particles. The biological responses to various MnO2 dusts with different specific surface area (0.16, 0.5, 17 and 62 m2/g) were compared in vitro and in vivo. A mouse peritoneal macrophage model was used to evaluate the in vitro cytotoxic potential of the particles via lactate dehydrogenase (LDH) release. In vivo, the lung inflammatory response was assessed by analysis of bronchoalveolar lavage after intratracheal instillation in mice (LDH activity, protein concentration and cellular recruitment). In both systems, the results show that the amplitude of the response is dependent on the total surface area which is in contact with the biological system, indicating that surface chemistry phenomena are involved in the biological reactivity. Freshly ground particles with a specific surface area of 5 m2/g were also examined in vitro. These particles exhibited an enhanced cytotoxic activity, which was almost equivalent to that of 62 m2/g particles, indicating that undefined reactive sites produced at the particle surface by mechanical cleavage may also contribute to the toxicity of insoluble particles. We conclude that, when conducting studies to elucidate the effect of particles on the lung, it is important for insoluble particles such as manganese dioxide to consider the administered dose in terms of surface area (e.g. m2/kg) rather than in gravimetric terms (e.g. mg/kg).