Concentration Of Acid Groups Research Articles

Adsorption of nitrate and nitrite ions onto carbonaceous material produced from soybean in a binary solution system

In this study, soybean (SB) was treated with calcium chloride, hydrochloric acid, and calcination (400, 600, 800, and 1000°C) to introduce chloride ions onto the SB surfaces (SB400, SB600, SB800, and SB1000, respectively). The properties of the adsorbents (pH of the solution, acidic functional group, and basic functional group) were investigated. The adsorption of nitrate and nitrite ions onto SB surfaces at different temperatures was evaluated. SB600 had the highest concentration of acidic functional groups (3.34mmol/g). The amount of nitrate and nitrite ions adsorbed onto SB600 in a binary solution system was lower than that in a single solution system. The amount of nitrate and nitrite ions adsorbed was closely related to the chloride ions. The adsorption mechanism of nitrate and nitrite ions onto SB600 mainly involved an ion exchange (correlation coefficient=0.993). Moreover, chloride ions affected the adsorption process. The adsorption isotherm data using SB600 were fitted to both the Langmuir and Freundlich equations. The amount of nitrate and nitrite ions adsorbed increased with increasing temperature. The adsorption equilibriums of nitrate and nitrite ions onto SB600 were obtained after 24 and 16h, respectively. The experimental data fit the pseudo-second-order model better than the pseudo-first-order model. Thus, SB600 is useful for the adsorption of nitrate and nitrite ions in a binary solution system.

이온 이동에 적합한 아크릴고분자 박막의 조성과 수소이온, 수산화이온, 구리이온의 선택적 검출

광경화 아크릴고분자 필름에서 이온이동에 관한 연구를 하였다. 고분자에 결합된 아민기와 카르복실산 작용기의 함량을 조절하여 수소이온과 수산화이온의 이동에 적합한 필름을 제조하였다. 수소이온 이동 검출을 위해 p-methylred(PMR) 유도체를 사용하였고 수산화이온 검출을 위해 페놀프탈레인 유도체를 합성하여 각각 고분자에 도입하였다. 수소이온의 이동은 아민기의 함량이 많을수록 빠르게 진행되었고 수산화이온은 카르복실산의 함량이 높을수록 빠르게 이동하였다. 수소이온 이동은 필름표면과 내부로 빠르게 진행하였고 PMR 포함 필름의 흡수스펙트럼을 통해 관찰되었다. 산 용액에 감응하는 필름을 사용하여 색상변화의 가역성을 관찰하였고 연속 50회를 실시하는 동안 정확히 재현되었다. 구리(II) 이온은 카르복실산 작용기의 함량이 높은 필름에서 빠르게 이동하였다. 로다민이 도입된 필름에서 구리이온의 배위로 로다민의 고리열림 반응이 진행되었고 광흡수 및 발광특성 측정을 통해 구리이온의 이동을 추적하였다. Ion diffusion and chemical binding to acrylic polymer were investigated in a solid film. The composition of acrylic monomers containing amino group and carboxylic acid was adjusted for rapid ion migration in the film. p-Methylred (PMR) and phenolphthalein derivatives were optically sensitive to the concentration of proton and hydroxyl anion, respectively and verified the ion migration through the film layers. A rapid proton migration was observed in the film of a high amino content. On the other hand, <TEX>$OH^-$</TEX> migration occurred rapidly in a high content of carboxylic acid group. The proton migration occurred through the internal layer as well as surface layer of a film and was reversible during 50 repetition examination. Copper(II) ion migration was examined with a Rhodamine-containing polymer film. The light absorption and emission spectra of a Rhodamine-Cu complex showed the key contribution of carboxylic acid group to the Cu(II) migration in a film.

Effects of Novel Dinuclear Cisplatinum(II) Complexes on the Electrical Properties of Human Molt-4 Leukemia Cells.

The aim of this study was to determine the influence of cisplatin and novel dinuclear platinum(II) complexes on the membrane electrical properties and lipid peroxidation levels of the Molt-4 human leukemia cell line. Changes in cell function may affect the basal electrical surface properties of cell membranes. These changes can be detected using electrokinetic measurements. Surface charge densities of Molt-4 cells were measured as a function of pH. A four-component equilibrium model was used to describe the interaction between the ions in solution and on cell membrane surfaces. Agreement was found between the experimental and theoretical charge variation curves of the leukemia cells at pH 2.5–9. Lipid peroxidation was estimated by measuring levels of 8-iso-prostaglandine F2α [isoprostanes]. Acid and base functional group concentrations and average association constants with hydroxyl ions were smaller in cisplatin- or dinuclear platinum(II) complex-treated leukemia cell membranes compared to those in untreated cancer cells, and the average association constants with hydrogen ions were higher. Levels of lipid peroxidation products in cisplatin- or dinuclear platinum(II) complex-treated leukemia cell were higher than those found in untreated cancer cells.

Relationship between processing, surface energy and bulk properties of ultrafine silk particles

Silk particles of different sizes and shapes were produced by milling and interactions with a series of polar and non-polar gaseous probes were investigated using an inverse gas chromatography technique. The surface energy of all silk materials is mostly determined by long range dispersive interactions such as van der Waals forces. The surface energy increases and surface energy heterogeneity widens after milling. All samples have amphoteric surfaces and the concentration of acidic groups increases after milling while the surfaces remain predominantly basic. We also examined powder compression and flow behaviours using a rheometer. Increase in surface energy, surface area, and static charges in sub-micron air jet milled particles contributed to their aggregation and therefore improved flowability. However they collapse under large pressures and form highly cohesive powder. Alkaline hydrolysis resulted in more crystalline fibres which on milling produced particles with higher density, lower surface energy and improved flowability. The compressibility, bulk density and cohesion of the powders depend on the surface energy as well as on particle size, surface area, aggregation state and the testing conditions, notably the consolidated and unconsolidated states. The study has helped in understanding how surface energy and flowability of particles can be changed via different fabrication approaches.

Activity Enhancement of Semicokes by Ammonia Activated at High Temperatures and High Pressures for Carbon Dioxide Re-forming of Methane

In a WHF-08-type reactor, three kinds of semicokes (Hongce lignite semicokes, Shenmu bituminous coal semicokes, and Jincheng anthracite semicokes) were activated with ammonia at high temperatures and high pressures. Results showed that the catalytic activity of the semicokes was significantly enhanced after activation. It was observed that the conversions of methane and carbon dioxide increased with increases in the concentration of ammonia and the activation temperature and increased and then stabilized as the activation time increased. It was also observed that the activation pressure had relatively weaker effects on the re-forming reaction and the optimal conditions were as follows: 8% ammonia, 300 °C, 6 MPa, and 3 h. The surface structures of semicokes before and after activation were characterized. The results showed that the content of -NO2, -NH2, -CN, and other basic groups increased while the content of acidic groups decreased after activation, and the TNB of the three kinds of semicokes improved ...

Invited: Development of Highly Phosphonated Polymers for Fuel Cell Membranes

Phosphonated polymers may show high intrinsic proton conductivities at low water contents provided that the local concentration of phosphonic acid groups is very high [1,2]. Moreover, the lower acidity of aryl- and alkylphosphonic acids in relation to sulfonic acids requires higher acid contents to reach high conductivities also at higher water contents. In this context, poly(vinylphosphonic acid) (PVPA) has emerged as an interesting component for fuel cell membranes because of its extremely high concentration of phosphonic acid, corresponding to 9.25 mmol –PO3H2 per g dry material. However, the high ionic content leads to complete water solubility as well as poor mechanical properties in the solid state. Consequently, it is necessary to develop synthetic strategies to efficiently immobilize the PVPA in the membranes before practical use. We have previously immobilized PVPA by preparing various block and graft copolymers with PVPA segments [3]. These copolymers where found to self-assemble and form robust membranes with nanostructured morphologies and high proton conductivities. Very recently we have pursued a number of novel synthetic strategies towards different highly phosphonated membranes. These approaches include phosphonated norbornene copolymers prepared via ring opening metathesis polymerization (ROMP) [4], multiblock copolymers selectively grafted with PVPA via anionic polymerization [5], as well as block and graft copolymers containing the more acidic poly(tetrafluorostyrenephosphonic acid) via atom transfer radical polymerization (ATRP) [6]. Challenges and selected results on the synthesis and properties of these copolymers and membranes will be presented and discussed along with future prospects. Acknowledgement We gratefully acknowledge the financial support from the Danish Council for Strategic Research through contract no.09-065198, as well as the funding from the European Community’s Seventh Framework Programme (FP7/2010–2013) under the call ENERGY-2010-10.2-1: Future Emerging Technologies for Energy Applications (FET) under contract 256821 QuasiDry.

Chemical and spectroscopic characterization of insoluble and soluble humic acid fractions at different pH values

BackgroundHumic acids (HA) are organic molecules with complex structure and function and variable properties. They are insoluble in strongly acid pH conditions. At present, it is not clear how much is the amount of HA in solution at the pH of natural soils nor are known the characteristics of the different soluble fractions and their possible association with the inorganic phase of soil. The scope of this work was to characterize the soluble and insoluble fractions obtained by acidifying Na humate solution at pH values 3, 5, and 7 and to compare these fractions with the HA obtained at pH 1. At each pH, the precipitate and the soluble fractions were separated and characterized by elemental analysis, total acidity and carboxylic group content, infrared, and 13C NMR and 1H NMR spectroscopy.ResultsThe HA fraction insoluble at pH 1 had a high acid group content and aromaticity but a low content of O- and N-containing groups. At pH 3, a fraction with nearly the same characteristics was obtained. At pH 1 and pH 3, the inorganic phase bound to the insoluble humic material was largely constituted by clay minerals and some Al and Fe hydroxides. The soluble fractions at pH values 1 and 3 were very poor and they were composed of a silica gel-like phase associated with polar organic material rich in carboxylic and metal-carboxylate groups. At pH values 5 and 7, only a small fraction of the Na humates precipitated. The fractions remaining in the solution were mainly composed of organic material particularly rich in aromatic and aliphatic groups, while the inorganic phase contained phyllosilicates. The fractions insoluble at pH values 5 and 7 contained a large amount of inorganic material that consisted mainly of phyllosilicates.ConclusionsThe soluble fractions obtained at pH values 5 and 7 represent the humic component that in environmental situations would be dissolved in the soil solution. Our findings could be very useful for a more detailed investigation into the way HA influence plant metabolism under environmental-like conditions, both as regards pH conditions and interaction with the mineral fraction.

Synthesis and characterization of sulfonated polymers containing triazoles as low-humidity proton exchange membranes

A series of copolymers, sulfonated poly (aryl ether ketone sulfones) containing triazoles (SPAEKST), were synthesized by direct polycondensation reactions. The content of sulfonic acid and triazole groups was controlled by adjusting the molar ratio of feeding. The structures of triazole monomer and SPAEKST copolymers were confirmed by their 1H NMR and FTIR spectral analyses. The performance of membranes such as thermal and oxidative stabilities was clearly improved with increasing content of triazole groups. The morphology of SPAEKST membranes was investigated by TEM analyses, and the results indicate that the sulfonic acid groups were dispersed evenly. No clear phase separation was observed. The contact angle tests showed that the presence of triazoles clearly improved the hydrophilicity of membranes. The water desorption curves showed that the water retention of membranes increased with increasing content of triazole groups. The proton conduction of membranes exhibited a low dependence on relative humidity. At 80 °C, the proton conductivity of SPAEKST-30 % reached to 1.1 mScm−1 under 20 % RH.

Enhancement of proton conductivity of chitosan membrane enabled by sulfonated graphene oxide under both hydrated and anhydrous conditions

In this study, sulfonated graphene oxide (SGO) nanosheets with controllable sulfonic acid group loading are synthesized via the facile distillation–precipitation polymerization, and then incorporated into chitosan (CS) matrix to prepare nanohybrid membranes. The microstructure and physicochemical properties of the resulting membranes are extensively investigated. Compared with CS control and GO-filled membranes, SGO-filled membranes attain enhanced thermal and mechanical stabilities due to the strong electrostatic attractions between –SO3H of SGO and –NH2 of CS, which inhibit the mobility of CS chains. Additionally, the inhibited mobility reduces the area swellings of SGO-filled membranes, reinforcing their structural stabilities. The incorporation of SGO generates acid–base pairs along CS–SGO interface, which work as facile proton-hoping sites and thus construct continuous and wide proton transfer pathways, yielding enhanced proton conductivities under both hydrated and anhydrous conditions. Meanwhile, the conductivity can be elevated by increasing the sulfonic acid group loading and content of SGO. Particularly, incorporating 2.0% S4GO can afford the nanohybrid membrane a 122.5% increase in hydrated conductivity and a 90.7% increase in anhydrous conductivity when compared with CS control membrane. The superior conduction properties then offered a significant enhancement in H2/O2 cell performances to the nanohybrid membranes, guaranteeing them to be promising proton exchange membranes.

Biodiesel wastes: An abundant and promising source for the preparation of acidic catalysts for utilization in etherification reaction

Abstract Environmentally friendly sulfonated black carbon (BC) catalysts were prepared from biodiesel waste, glycerol. These black carbons (BCs) contain a high amount of acidic groups, mainly sulfonated and oxygenated groups. Furthermore, these catalysts show a high catalytic activity in the glycerol etherification reaction with tert-butyl alcohol, the activity being larger for the sample prepared with a higher glycerol:sulfuric acid ratio (1:3). The yield for mono-tert-butyl glycerol (MTBG), di-tert-butyl glycerol (DTBG) and tri-tert-butyl-glycerol (TTBG) were very similar to those obtained using a commercial resin, Amberlyst-15. Furthermore, experimental results show that the carbon with the lowest acidic surface group content, BC prepared in minor glycerol:sulfuric acid ratio (10:1), can be chemically treated after carbonization to achieve an improved catalytic activity. The activity of all BCs is high and very similar, about 50% and 20% for the MTBG and DTBG + TTBG, respectively.

The effect of sulfonic acid group content in pore-filled silica colloidal membranes on their proton conductivity and direct methanol fuel cell performance

We prepared mesoporous silica colloidal membranes pore-filled with polymer brushes with different degrees of sulfonation. In these membranes, the assembly of silica colloidal spheres serves as a rigid matrix containing a continuous network of interconnected mesopores and providing mechanical and thermal stability, non-swelling and water retaining properties, while sulfonic acid group-containing polymer brushes grown on the surface of silica provide proton conductivity. We studied the proton conductivity of these membranes as well as open circuit voltage and linear polarization of the fuel cells prepared using these membranes as a function of sulfonic acid group content in the pore-filling polymer brushes. We found a sigmoidal dependence of the proton conductivity on the amount of sulfonic acid groups. We showed that the proton conductivity of the membrane does not increase significantly after reaching ca. 75% sulfonic acid group content. The fuel cell performance, on the other hand, decreased after reaching ca. 65–70% sulfonic acid group content, which was attributed to the increased methanol permeability of the membranes at higher sulfonic acid group content.

Synthesis of highly phosphonic acid functionalized benzene-bridged periodic mesoporous organosilicas for use as efficient dye adsorbents

Periodic mesoporous organosilicas (PMOs) with benzene bridging groups in the silica wall were functionalized with a tunable content of phosphonic acid groups. These bifunctional materials were synthesized by co-condensation of two different organosilane precursors, that is, 1,4-bis(triethoxysilyl)benzene (BTEB) and sodium 3-(trihydroxysilyl)propyl methyl phosphate (SPMP), under acidic conditions using nonionic surfactant Brij-S10 as template. The materials exhibited well-ordered mesostructures and were characterized by X-ray diffraction, nitrogen sorption, TEM, TGA, FTIR, and solid-state NMR measurements. The materials thus obtained were employed as adsorbents to remove different types of dyes, for example, cationic dyes methylene blue and phenosafranine, anionic orange II, and amphoteric rhodamine B, from aqueous solutions. The materials exhibited a remarkably high adsorption capacity than activated carbon due to their ordered mesostructures, a large number of phosphonic acid groups, and high surface areas. The adsorption was mainly governed by electrostatic interaction, but also involved π–π stacking interaction as well as hydrogen bonding. The adsorption kinetics can be better fitted by the pseudo-second order model. The adsorption process was controlled by the mechanisms of external mass transfer and intraparticle diffusion. The materials retained more than 97% dye removal efficiency after use for five consecutive cycles.

Predicting the pKa and stability of organic acids and bases at an oil-water interface.

We have used density functional theory and the implicit solvent model, COSMO-RS, to investigate how the acidity constant, pKa, of organic acids and bases adsorbed at the organic compound-aqueous solution interface changes, compared to its value in the aqueous phase. The pKa determine the surface charge density of the molecules that accumulate at the fluid-fluid interface. We have estimated the pKa by comparing the stability of the protonated and unprotonated forms of a series of molecules in the bulk aqueous solution and at an interface where parts of each molecule reside in the hydrophobic phase and the rest remains in the hydrophilic phase. We found that the pKa for acids is shifted by ∼1 pH unit to higher values compared to the bulk water pKa, whereas they are shifted to lower values by a similar amount for bases. Because this pKa shift is similar in magnitude for each of the molecules studied, we propose that the pKa for molecules at a water-organic compound interface can easily be predicted by adding a small shift to the aqueous pKa. This shift is general and correlates with the functional group. We also found that the relative composition of molecules at the fluid-fluid interface is not the same as in the bulk. For example, species such as carboxylic acids are enriched at the interface, where they can dominate surface properties, even when they are a modest component in the bulk fluid. For high surface concentrations of carboxylic acid groups at an interface, such as a self-assembled monolayer, we have demonstrated that the pKa depends on the degree of deprotonation through direct hydrogen bonding between protonated and deprotonated acidic headgroups.

English

In order to reveal the formation mechanism of hydrochemical characteristics in Tongchuan City, we collected and detected 39 samples of underground water. Correlation analytical method, hydrochemical method and ion ratio coefficient method were employed to investigate the hydrochemical characteristics, influencing factors and principles of changing. Results demonstrate that the main factors, controlling the shallow water salinization, are the SO42-, NO3-, Cl- and K+. The contents of SO42-, NO3- and Cl- are greatly different and other indexes are relatively stable. The values of &gamma;Na/&gamma;Cl demonstrate that the Na+ is released from the soil aquifer in the runoff process. There is an exchange between the Ca2+ in water and Na+ in soil, which leads to &gamma;Na＞&gamma;Cl. As the exchange time in deep water is longer than that of shallow water, the exchange and adsorption of ions are more sufficient. The value of &gamma;Na/(&gamma;Na+&gamma;Cl) demonstrates that with increasing of ground water depth, the level of cation exchange enhances, which leads to the dominant cation turning to Ca2+ from Na+. The value of &gamma;HCO3+&gamma;SO4/&gamma;Ca+&gamma;Mg demonstrates the shallow water is mainly from atmospheric rainfall and the influence of cation exchange is more obvious on deep water. The types of shallow water in Tongchuan City are mainly HCO3&middot;SO4-Ca. Its classification is relatively complex. Whereas, the deep water is mainly HCO3-Na and the category of underground water is simple. As for shallow water, the content of alkaline earth metal is larger than that of alkali metal. For the deep water, the content of weak acid group is larger than that of strong acid group. In the region of upper reaches, the features of both shallow and deep waters are mainly weak acid and alkaline earth metal. The chemical composition mainly consists of carbonate leaching. With the flowing of underground water, the shallow water turns to be strong acid and alkaline earth metal and the deep water turns to be weak acid and alkali metal. &nbsp; Key words: Tongchuan City, underground water, hydrochemical characteristics, ion ratio coefficient method.

Obtaining and characterizing modified tannins by physical-chemical methods

Abstract After oxidation of tannins (Tannins 1–3) extracted from grape seeds, Tanoxil compounds with increased solubility and enhanced antioxidant activities were synthesized. In this research, ABTS+· assay and a chemiluminescence method were used for antioxidant measurement of hydrophilic compounds (Tanoxils 1–3). It was observed that the antioxidant activity (AA, %) is very similar for the three samples, while at the same time AA is quite high (93.16%–96.48%). The percentage of inhibition by ABTS+· is higher for Tanoxil 2 (96.4%) as compared to Tannin 2 compound (14.34%). Moreover, the total content (TCF) of carboxyl and phenolic groups was investigated. TCF values, determined for Tanoxil products, revealed a double (Tanoxil 1) or triple (Tanoxil 2) increase as compared to the value of the TCF of Tannin 1. Tanoxil products represent an interest for future research as they have a high AA (96.4%) and the content of acidic groups is significant (TCF, 0.191 meq g−1).

Effect of oxidation debris on spectroscopic and macroscopic properties of graphene oxide

Oxidation debris (OD) and graphene oxide (GO) before and after OD removal were characterized by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, mass spectroscopy, X-ray diffraction, transmission electron microscopy and potentiometric titration, respectively. OD removal decreased GO absorption intensity in UV/Vis spectra, caused changes in peak position and absorption intensity in FTIR spectra, and resulted in the decrease of ID/IG in Raman spectra. OD was amorphous and had higher content of acidic groups than purified GO. OD contributed 10–25% of overall surface charge density to unpurified GO in spite of small amount (ca. 1% mass). OD removal decreased significantly GO dispersibility in aqueous solution, but increased obviously the electrical conductivity of reduced graphene oxide (rGO) and the apparent density of compacted rGO. The removal of OD was necessary because of its striking effects on both GO spectroscopic and macroscopic properties. Batch desorption in NaOH solution was recommended for OD removal from as-prepared graphite oxide because of slow OD desorption kinetics.

Nanostructured bacterial cellulose-poly(4-styrene sulfonic acid) composite membranes with high storage modulus and protonic conductivity.

The present study reports the development of a new generation of bio-based nanocomposite proton exchange membranes based on bacterial cellulose (BC) and poly(4-styrene sulfonic acid) (PSSA), produced by in situ free radical polymerization of sodium 4-styrenesulfonate using poly(ethylene glycol) diacrylate (PEGDA) as cross-linker, followed by conversion of the ensuing polymer into the acidic form. The BC nanofibrilar network endows the composite membranes with excellent mechanical properties at least up to 140 °C, a temperature where either pure PSSA or Nafion are soft, as shown by dynamic mechanical analysis. The large concentration of sulfonic acid groups in PSSA is responsible for the high ionic exchange capacity of the composite membranes, reaching 2.25 mmol g(-1) for a composite with 83 wt % PSSA/PEGDA. The through-plane protonic conductivity of the best membrane is in excess of 0.1 S cm(-1) at 94 °C and 98% relative humidity (RH), decreasing to 0.042 S cm(-1) at 60% RH. These values are comparable or even higher than those of ionomers such as Nafion or polyelectrolytes such as PSSA. This combination of electric and viscoelastic properties with low cost underlines the potential of these nanocomposites as a bio-based alternative to other polymer membranes for application in fuel cells, redox flow batteries, or other devices requiring functional proton conducting elements, such as sensors and actuators.

The Chemistry of Membrane Degradation in PEM Fuel Cells

The lifetime of proton exchange membrane (PEM) fuel cells depends largely on the durability of the PEM and is a critical issue in the commercialization of PEM fuel cell technology (1, 2). Perfluorosulfonated acid (PFSA) membranes, such as Nafion®, are the most widely used electrolyte material for PEM fuel cells.Many factors can cause PEM failure, including manufacturing and design issues, material properties, and fuel cell operation conditions. Each factor results in failure through a particular degradation mode. These modes can be classified as thermal, mechanical, and chemical modes (3-7). Because fuel cells typically operate at temperatures below that at which Nafion thermally degrades, chemical and mechanical degradation are generally considered the most important modes of membrane degradation.Although there has been a lot of progress in the area, the exact chemical membrane degradation mechanisms, the most susceptible points, and the impact of test conditions on degradation are not completely understood. The formation of radicals and their reactivity during the fuel cell operation have been confirmed as the main cause of PEM chemical degradation (8-11). These radicals are formed as a result of the reaction of crossover H2 and O2 on the surface of Pt or other metal ion contaminants (4). In addition to the electrodes, Pt particles have been observed to migrate into the membrane, producing another site for radical formation. Radical attack leads to loss of fluorine, sulfur, and organofluorine compounds from the PEM, and PEM thinning, all resulting in loss of mechanical integrity. The radical formation mechanisms and the impact of test conditions on radical formation are also not completely understood.It has been suggested that earlier versions of Nafion membranes chemically degrade through radical attack on carboxylic acid groups end groups (12-14) or at the C−S or O−C bonds in the side chain and main chain (12, 14-18), as shown in Figure 1. Chemically stabilized Nafion, e.g., Nafion 211, has been developed where the concentration of terminal carboxylic acid groups was decreased to negligible levels and, as a result, degradation decreased substantially (13). The use of radical scavengers such as ceria have increased the durability of PFSA membranes by as much as 1000-fold compared to unmitigated membranes (19). Despite the recent durability improvements, there is evidence that PFSA membranes are still susceptible to chemical damage.Typical indicators for chemical degradation of Nafion membranes include increased H2crossover, decreased ion exchange capacity, decreased proton conductivity, and decreased PEM thickness. Localized crossover tests have shown that membrane damage occurs preferably at the perimeter of the active area. The quantitative method of choice used for detecting chemical degradation is typically detection of fluoride in fuel cell outlets, reported as a fluoride emission rate (FER).Figure 1. Proposed locations of radical attack in NafionTo improve PEM chemical durability, a true understanding of the decay mechanisms is required. Models of some of the decay modes have been developed and they show a consistent but incomplete understanding of membrane decay. Through a combination of specific modeling and directed testing, an overall decay model can be developed.

Effect of phosphorus and water contents on physico-chemical properties of SAPO-34 molecular sieve

SAPO-34 molecular sieves with different P and H2O contents were synthesized by adjusting P2O5/Al2O3 and H2O/Al2O3 molar ratios in starting gel. The crystal structure, crystal size, elemental composition, and acid site density of the synthesized samples were characterized with XRD, SEM, ICP, TPD, and FTIR. The morphology, crystallinity, and acidity of SAPO-34 materials varied with P2O5/Al2O3 and H2O/Al2O3 molar ratios in the starting gel and different Si substitution mechanisms were accompanied correspondingly. Samples with P2O5/Al2O3 and H2O/Al2O3 molar ratios of 1 and 60 had the best crystallinity with the largest crystals and maximum surface area. Increasing the concentration of strong acidic hydroxyl groups for samples SP-1 and SW-60 indicated the presence of a higher amount of Bronsted acid sites.

Differences in the adsorption of enzymes onto lignins from diverse types of lignocellulosic biomass and the underlying mechanism

BackgroundNon-productive cellulase adsorption onto lignin has always been deemed to negatively affect the enzymatic hydrolysis of lignocellulosic feedstocks. Therefore, understanding enzyme-lignin interactions is essential for the development of enzyme mixtures, the processes of lignocellulose hydrolysis, and the genetic modification of lignocellulosic biomass and enzymes. In this work, we examined the properties of six lignins from diverse types of lignocellulosic biomass (aspen, pine, corn stover, kenaf, and two Arabidopsis lines, wild-type and SALK mutant of fah1) to determine the mechanism of differences in their adsorption of enzymes.ResultsWe found that lignin sources affected enzyme adsorption using structural features, such as functional groups and lignin composition. Guaiacyl (G) lignin had a higher adsorption capacity on enzymes than syringyl (S) lignin. The low S/G ratio and high uniform lignin fragment size had good correlations with high adsorption capacity. A higher content of phenolic hydroxyl groups and a lower content of carboxylic acid groups resulted in stronger adsorption affinity for corn stover lignin (CL) than for kenaf lignin (KL) and aspen lignin (AL). The lower amount of aliphatic hydroxyls that reduced hydrophobic interactions could explain the higher adsorption capacity of pine lignin (PL) than CL. Enzyme activity assays, as well as the hydrolysis of Avicel, phosphoric acid-swollen cellulose (PASC), and holocellulose, were performed to study the behaviors of mono-component enzymes that resulted in adsorption. We found that cellobiohydrolase (CBH) and xylanase were adsorbed the most by all lignins, endoglucanase (EG) showed less inhibition, and β-glucosidase (BG) was the least affected by lignins, indicating the important role of carbohydrate-binding module (CBM) in protein adsorption.ConclusionLignin sources affect enzyme adsorption using structural features and lignin composition, such as S/G ratio, carboxylic acid, aliphatic hydroxyl, and phenolic hydroxyl. For mono-component enzymes, the adsorption capacity decreased in the order CBH, xylanase > EG > BG. These investigations revealed the difference in lignin properties between diverse biomass and adsorption capacity of enzymes to lignins, and the possible underlying mechanism. The results can also serve as a reference for the genetic modification of lignocellulosic biomass and enzymes.