Amount Of Sulfonic Acid Groups Research Articles

Mixed-acidic cation-exchange material for the separation of underivatized amino acids

Mixed-acidic cation-exchange (MCX) columns with both strongly (SCX) and weakly (WCX) acidic functional groups were developed for the separation of standard amino acids. The resins were prepared by carboxylation of highly crosslinked monodisperse poly(styrene-divinylbenzene) copolymer particles with performic acid and subsequent sulfonation with sulfuric acid. The degree of functionalization was varied independently for each processing step and controlled by measuring pH dependent retention of the obtained resins. A series of mixed-acidic resins with different SCX/WCX-ratios was chromatographically characterized by variation of formic acid and acetonitrile concentration in the aqueous eluent. The overall cation-exchange capacity was varied from 33 to 68 µmol/mL. The comparison with two commercial columns (Metrohm Metrosep C6, WCX and Hamilton PRP X-200, SCX) revealed the additive character of the different functional group properties within MCX columns and a unique selectivity which can be adjusted by both eluent composition and SCX/WCX-ratio of the resin. The retention window between neutral and basic amino acids was altered by varying the amount of sulfonic acid groups attached to the polymer. Orthogonality plots demonstrated constant selectivity for neutral amino acids. Correlating the retention data with log P data demonstrated the influence of non-ionic hydrophobic and π-π-interactions for the separation of amino acids on PS/DVB-based cation-exchangers. An isocratic IC-ESI-MS method was developed to separate and quantitate 20 underivatized standard amino acids within 30 min. Limits of detection were between 4 and 64 nmol L−1 and a high linearity of calibration curves was obtained for all analytes. The method was validated by comparing a certified reference standard with external calibration data.

Acetalization of glycerol with hexanal in the presence of SBA-15 with sulfonic acid groups

Acetalization of glycerol with hexanal was studied over sulfonic acid-functionalized mesoporous silica (SBA-15), at 70 ºC. The product obtained were (2-pentyl-1,3-dioxolan-4-yl)methanol and 2-pentyl-1,3-dioxan-5-ol. Materials with different amounts of sulfonic acid groups were prepared. The support functionalization was achieved by the introduction of 3-(mercaptopropyl)trimethoxysilane onto the surface of these materials by grafting technique. The [SO3H]-SBA-15 catalysts were characterized by nitrogen adsorption at 77 K, X-ray diffraction, SEM and titrations. All the catalysts were active in the studied reaction being the [SO3H]3-SBA-15 the best one. It was observed that the reaction rate increase with the amount of sulfonic acid groups on SBA-15 until a maximum. With high amounts of sulfonic groups, a decrease of activity is observed. Good values of selectivity to (2-pentyl-1,3-dioxolan-4-yl)methanol were obtained with mesoporous silicas anchored sulfonic acid groups. Catalytic stability of the [SO3H]3-SBA-15 was evaluated by performing consecutive batch runs with the same catalyst sample. The material showed a good catalytic stabilization.

Multivariate Sulfonic-Based Titanium Metal-Organic Frameworks as Super-protonic Conductors.

The proton-conducting performances of a microporous Ti-based metal-organic framework (MOF), MIP-207, were successfully tuned using a multicomponent ligand replacement strategy to gradually introduce a controlled amount of sulfonic acid groups as a source of Brönsted acidic sites while keeping the robustness and ecofriendly synthesis conditions of the starting material. Typically, multivariate sulfonic-based solids MIP-207-(SO3H-IPA)x-(BTC)1-x were prepared by combining various ratios of trimesate 1,3,5-benzenetricarboxylate (BTC) moieties and 5-SO3H-isophthalate (SO3H-IPA). The best sulfonic-MOF candidate that combines structural integrity with high proton conductivity values (e.g., σ = 2.6 × 10-2 S cm-1 at 363 K/95% relative humidity) was further investigated using ab initio molecular dynamics simulations. These calculations supported that the -SO3H groups act as proton donors and revealed that the proton transfer mechanism results from the solvation structure of protons through the fast Zundel/hydronium interconversion along the continuous H-bonded network connecting the adsorbed water molecules.

Oxidative upgrade of furfural to succinic acid using SO3H-carbocatalysts with nitrogen functionalities based on polybenzoxazine

SO3H-carbocatalysts with nitrogen functionalities were prepared using the carbonization of polybenzoxazine derived from four different amines (aniline, ethylenediamine, triethylenetetramine, and tetraethylenepentamine) and then sulfonation. The obtained SO3H-carbocatalysts underwent catalytic testing for furfural oxidation with H2O2 to produce succinic acid. The effects of nitrogen functionalities were reported for the first time. The results showed that all carbon samples exhibited a microporous characteristic with comparable textural properties and contained various nitrogen functionalities (N-6, N-5, N-Q, and N-X). After sulfonation, the SO3H-carbocatalyst prepared from tetraethylenepentamine-based polybenzoxazine had the highest amount of sulfonic acid groups (1.45 mmol g−1) and a high nitrogen content (4.23%), providing a maximum succinic acid yield of 93.0% within a rapid reaction time of 60 min under the optimized conditions. This was higher than from Amberlyst-type catalysts and SO3H-carbocatalyst without nitrogen functionalities and was ascribed to the synergistic activity of the sulfonic acid groups and nitrogen functionalities. The XPS spectra and computational study confirmed that such nitrogen functionalities, especially N-5, are capable of forming hydrogen bonding with furfural, facilitating the formation of an intermediate compound and thereby enhancing the catalytic efficiency. However, after four cycles, the succinic acid yield decreased to 40% due to leaching of the sulfonic acid groups.

Coupling Ru nanoparticles and sulfonic acid moieties on single MIL-101 microcrystals for upgrading methyl levulinate into γ-valerolactone

Heterogeneous catalytic conversion of biomass-derived methyl levulinate (ML) to γ-valerolactone (GVL) is highly attractive as a sustainable route to mitigating the dependence on nonrenewable fossil resources. However, this route is limited by its low selectivity toward GVL and severe reaction conditions. Here, we present a synergistic catalytic process that offers exclusive GVL selectivity with complete ML conversion under mild conditions (80 °C, 0.5 MPa of H2 pressure). This is achieved over a dual-functionalized catalyst of Ru nanoparticles (Ru-NPs) and Brønsted acid SO3H groups in a Cr-based metal-organic framework (MIL-101). The Ru-NPs served as metal sites for the hydrogenation of ML to methyl-3-hydroxyvalerate (MHV) and the acidic SO3H moieties promoted the cyclization of MHV to generate GVL via lactonization. In contrast, GVL production was significantly suppressed over the physically mixed congener (2.0 wt% Ru/MIL-101 + MIL-101-SO3H). This result demonstrates an unrivalled advantage of the dual integration of metal/acid sites in a single MOF crystal, and the relative amount of sulfonic acid groups in the catalyst can exert significant influence on the overall catalytic performances. The activation energies for the hydrogenation and lactonization steps with the developed catalyst were 29.5 and 42.1 kJ/mol, respectively, which are much lower than those observed with the traditional 5.0 wt% Ru/AC catalyst.

Preparation and properties of DMFC membranes from polymer-brush nanoparticles

We describe a novel approach for the preparation of proton-conducting membranes using polymer brush nanoparticles (PBNPs). PBNPs can be assembled into the membranes directly, or the membranes can be prepared by first assembling porous scaffolds from unmodified NPs followed by surface modification with polymer brushes. In both cases, proton-conducting channels are formed in the interstitial spaces between the nanoparticles. First, proton-conducting membranes were prepared using silica nanoparticles (SNPs) surface-grafted with 40–400nm sulfonated polymer brushes, poly(3-sulfopropylmethacrylate), pSPM, and poly(4-styrenesulfonic acid), pSSA, grown via surface-initiated atom transfer radical polymerization (SI-ATRP). The membranes prepared from the NPs carrying longer polymer chains possessed polymer-like characteristics, compared to the stiffer membranes made with shorter polymer brushes. All these membranes showed comparable proton conductivities, with a maximum value of ~0.06S/cm at 98°C and 70% R. H. Second, we prepared proton-conducting pore-filled membranes. In this case, nanoporous colloidal crystals were first assembled from unmodified SNPs, followed by filling the pores with pSPM or pSSA brushes covalently attached to the pore surface using SI-ATRP. The membranes could be hydrated almost completely and did not swell. The proton conductivity was similar for both polymer-filled membranes, with a maximum value of ~0.02S/cm achieved at 30°C and 94% R. H. A sigmoidal dependence of the proton conductivity on the amount of sulfonic acid groups was found for pSPM pore-filled membranes. The proton conductivity remained relatively low at low degrees of sulfonation, increased rapidly around 50% sulfonic acid group content, and did not increase significantly after reaching ca. 75% sulfonic acid group content. We found that OCV for DMFC MEAs built using these membranes reached its maximum at 65% sulfonic group and decreased after that. We attribute this effect to the increased methanol cross-over, which was confirmed by methanol uptake measurements for the membranes.

Synthesis of Bio-fuel Additives From Glycerol Over Poly(Vinyl Alcohol) With Sulfonic Acid Groups

Condensation of glycerol with acetone was carried out over poly(vinyl alcohol) with sulfonic acid groups at 70°C. The main product of glycerol acetalization is solketal. Catalysts with different amounts of sulfonic acid groups were prepared. It was observed that the catalytic activity increases with the crosslinking degree, due to the increases of the amount of sulfonic acid groups on poly(vinyl alcohol). Further, the influence of various reaction parameters, such as catalyst loading, molar ratio glycerol to acetone, and temperature, on the acetalization of glycerol over PVA40 was studied. It was found that at 70°C, with 0.2 g of catalyst loading and with a molar ratio of glycerol to acetone 1:6, a glycerol conversion of about 94% after 3 h can be obtained. The PVA40 catalyst was recycled and reused with negligible loss in the activity, after the fifth use.

Thermoresponsive anionic copolymer brushes containing strong acid moieties for effective separation of basic biomolecules and proteins.

A thermoresponsive copolymer brush possessing the sulfonic acid group, poly(N-isopropylacrylamide (IPAAm)-co-2-acrylamido-2-methylpropanesulfonic acid (AMPS)-co-tert-butylacrylamide (tBAAm)), was grafted onto the surface of silica beads through surface-initiated atom transfer radical polymerization. Prepared copolymer and copolymer brushes on silica beads were characterized by observing the phase transition profile, CHNS elemental analysis, X-ray photoelectron spectroscopy, and gel permeation chromatography. The phase transition profile indicated that an appropriate AMPS composition for enabling thermally modulated property changes is 5 mol %, while excessive amounts of sulfonic acid groups prevented copolymer phase transition. Chromatographic elutions of catecholamine derivatives and basic proteins were observed, using the prepared copolymer brush-modified beads as chromatographic matrices, and the results suggest that the beads interact with these analytes through relatively strong electrostatic interactions. Thus, poly(IPAAm-co-AMPS-co-tBAAm) brush-modified beads will be useful for effective thermoresponsive chromatography matrices that separate basic biomolecules through strong electrostatic interactions.

Durable Sulfonated Poly(benzothiazole-co-benzimidazole) Proton Exchange Membranes

Two series of random sulfonated poly(benzothiazole-co-benzimidazole) polymers (sPBT-BI) with 70% and 60% degree of sulfonation were evaluated as proton exchange membranes. sPBT was also prepared for a comparative study. The mechanical properties of sPBT-BI were greatly enhanced by incorporation of benzimidazole (BI); sPBT-BI70-10 showed a tensile strength of 125 MPa and elongation at break of 38.9%, an increase of 56.5% and 145%, respectively, compared with sPBT. The solubility, dimensional stability, thermal properties, and oxidative stability of sPBT-BI were also improved. The ionic clusters of sPBT-BI membranes in both AFM phase images and TEM images became narrower with increasing amounts of BI while containing the same molar amount of sulfonic acid groups. This resulted in lower dimensional swelling and higher mechanical strength, but the proton conductivity decreased. However, high proton conductivity was achieved by incorporating an appropriate content of BI. PEMFC H2/air single cell performances and durabilities were improved by incorporation of 5% of BI units in sPBT.

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.

Esterification of free fatty acids over chitosan with sulfonic acid groups

Chitosan, which is an abundant biopolymer, with sulfonic acid groups was used as an efficient, environmentally friendly heterogeneous catalyst for the esterification of free fatty acids with methanol into their more fatty acid methyl ester. Sulfonic acid catalysts supported on chitosan have been studied in the esterification of palmitic acid with methanol at 60°C. The sulfonic acid groups were introduced onto chitosan (CT) through cross-linking with sulfosuccinic acid (SSA). The catalytic activity increased as the amount of sulfonic acid groups present in chitosan was increased. However, with large amounts of sulfonic acid groups, the catalytic activity decreased. This behaviour can be explained by the factors that limit the diffusion. The catalytic stability of the CT4 (2.08mmol sulfonic acid groups/g) sample was evaluated through consecutive batch runs performed with the same catalyst sample. After the second batch, the catalytic activity stabilised. The CT4 catalyst was also used as a catalyst in the esterification of oleic and stearic acids with methanol. A good catalytic activity of CT4 for the different substrates used in the esterifications was observed.

Sulfonic acid-functionalized aerogels as high resistant to deactivation catalysts for the etherification of glycerol with isobutene

Silica aerogel and lyogel have been successfully sulfonated in one step by a simple post-synthesis method using microwaves as well as conventional heating. The use of microwaves allowed loading higher amounts of sulfonic acid groups in both silicas, according to the higher S/Si atomic ratio determined by XPS, and the higher sulfur content determined by TGA, also exhibiting lower surface area and higher acidity. Sulfonated aerogels showed higher conversion and selectivity to h-GTBE (glycerol di- and tri-ethers) than sulfonated lyogels for the acid-catalyzed etherification of glycerol with isobutene. This was attributed to the higher content of sulfonic acid groups incorporated in aerogel. Microwave-assisted sulfonated aerogel yielded 75% of selectivity to h-GTBE, which can be used as fuel additive, for practically total conversion. Interestingly, larger porosity of aerogel avoided the partial blocking of pores by reaction products observed when other micro- and mesoporous catalysts were tested for this reaction. The combination of high conversion, high selectivity to h-GTBE, practically no formation of undesired di-isobutylenes and very high resistance to catalyst deactivation makes microwave-assisted sulfonic acid functionalized aerogel a promising catalyst for this etherification reaction.

SBA-15 with sulfonic acid groups as a Green Catalyst for the acetoxylation of α-pinene

The acetoxylation of α-pinene was carried out over SBA-15 with sulfonic acid groups. The products of acetoxylation of α-pinene are acetates (α-terpinyl acetate, bornyl acetate and β-fenchyl acetate) and hydrocarbons (camphene, tricyclene, limonene, γ-terpinene, terpinolene and α-terpinene).Catalysts with different amount of sulfonic acid groups were prepared. It was observed that the activity increases with increase of the surface area and porous volume.Catalytic stability of the sample that showed the highest activity (C1) was evaluated by performing consecutive batch runs with the same catalyst sample. After the fifth batch, the catalyst exhibited a good initial activity.

Boosted selectivity toward high glycerol tertiary butyl ethers by microwave-assisted sulfonic acid-functionalization of SBA-15 and beta zeolite

We report for the first time the post-synthesis sulfonic acid-functionalization of commercial beta zeolite in one step, by conventional heating as well as with microwaves, and the introduction of higher amounts of sulfonic acid groups in SBA-15 with microwaves. In beta zeolite, dealumination occurred due to the acidic medium used during sulfonation that favored the generation of new silanols groups, which in turn reacted with the organosulfonating agent resulting in the incorporation of the sulfonic acid groups. Microwave-assisted sulfonated catalysts showed higher selectivity toward di- and triethers of glycerol (83–91%) than those sulfonated by conventional heating and much more than a commercial acid macroporous resin type Amberlyst (35%) after 4h of reaction. It is remarkable the high selectivity to the bulkier triether achieved with functionalized beta samples (32–36%) demonstrating that microporosity is not a barrier for the formation of triether when having appropriate amount and strength of Brønsted acidity.

Nafion-sulfonated dendrimer composite membranes for fuel cell applications

Novel proton conducting composite membranes were synthesized by blending Nafion ® polymer with sulfonated organosilicon dendrimers (G3-S). Blending G3-S with Nafion resulted in stable, flexible membranes with loadings up to 10% by weight. The high amount of sulfonic acid groups on the dendrimer increased the ion exchange capacity and improved the water retention capability of the composite membranes with less swelling. The proton conductivity of the composite membranes was higher at all measured temperatures under both high and low relative humidity conditions, compared to pure Nafion ®. The proton conductivity of Nafion ® increased from 0.086 S/cm (at 80 °C at 100% relative humidity) for the pure polymer to 0.156 S/cm for the 10 wt% loading of dendrimer.

Investigation on the optimal oxidation agent for a maximum yield of sulfonic acid groups in MCM-41

For proton conduction e.g. in PEM fuel cells as well as acid catalysis materials with high and uniformly distributed loading with highly acidic moieties like SO 3H groups are required. Thus, mesoporous Si-MCM-41 was functionalized with bis(3-triethoxysilylpropyl)-disulfide (TESPD) by the co-condensation method. In order to find an optimum oxidation agent for transferring sulfur containing compounds into SO 3H groups with a maximum yield without using certain catalysts or solvents, the TESPD modified MCM-41 materials were oxidized with different oxidation agents, i.e. (i) Br 2, (ii) H 2O 2 and (iii) HNO 3. The amount of sulfonic acid groups which are anchored by organic linkages on the mesoporous surface were determined by ion exchange capacity. A maximum yield of sulfonic acid was found for samples oxidized by Br 2 (98%), followed by H 2O 2 (80%) and HNO 3 (66%). The surpassing yield of SO 3H groups achieved with Br 2 as a new oxidation agent was demonstrated by proton conductivity measurements since it increases with increasing amount of SO 3H groups.

Sulfonated Polystyrene Fiber Network-Induced Hybrid Proton Exchange Membranes

A novel type of hybrid membrane was fabricated by incorporating sulfonated polystyrene (S-PS) electrospun fibers into Nafion for the application in proton exchange membrane fuel cells. With the introduction of S-PS fiber mats, a large amount of sulfonic acid groups in Nafion aggregated onto the interfaces between S-PS fibers and the ionomer matrix, forming continuous pathways for facile proton transport. The resultant hybrid membranes had higher proton conductivities than that of recast Nafion, and the conductivities were controlled by selectively adjusting the fiber diameters. Consequently, hybrid membranes fabricated by ionomers, such as Nafion, incorporated with ionic-conducting nanofibers established a promising strategy for the rational design of high-performance proton exchange membranes.

Proton conductivity and stability of low-IEC sulfonated block copolyimide membrane

The proton conductivity and membrane stability of sulfonated block copolyimide membranes with a low ion exchange capacity (IEC) synthesized by chemical imidization using a two-pot procedure were investigated. The proton conductivity of the low-IEC block copolyimide membrane at 80 °C and 98% relative humidity was 16 times larger than that measured for the low-IEC random copolyimide membrane, while that of the high-IEC block copolyimide membrane at the humidity was 4 times than that of the high-IEC random copolyimide membrane, suggesting that the protons in the low-IEC block copolyimide membrane were effectively transported. In addition, the hydrolytic and oxidative stabilities of the low-IEC sulfonated block copolyimide membranes were estimated in detail from FT-IR and 1H NMR. These stabilities of the low-IEC membranes were significantly enhanced compared to those of the high-IEC membranes. The oxidative stability problem in the low-IEC block copolyimide membranes was found to be primarily caused by a decrease in the sulfonic acid groups rather than by polyimide chain scission. These findings indicate that a sulfonated block copolymer consisted of a small amount of sulfonic acid groups is desirable for the development of proton exchange membranes, when considering the balance between the proton conductivity and membrane stability of the proton exchange membranes.

Preparation o fMagnetic Sulfonated Carbon-Based Solid Acid Catalysts for the Hydrolysis of Cellulose

Magnetic sulfonated carbon. based solid acid catalysts (Fe/C-SO3H) were prepared by the pyrolysis of cellulose and subsequent sulfonation. The catalyst samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X. ray diffraction (XRD), X. ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and vibrating sample magnetometry (VSM). Their catalytic properties for the hydrolysis of cellulose were investigated. Results show that Fe exists in the carbon body in the form of gamma-Fe2O3 and the Fe/C-SO3H catalyst has superparamagnetic properties. In the hydrolysis reaction, cellulose conversion reached 40.6% over Fe/C-SO3H under optimal conditions. Furthermore, the catalyst could be steadily dispersed in the reaction mixture and be separated using an externally applied magnetic field. However, the catalytic performance dropped after the first run. The reason for deactivation is deduced to be a reduction in the amount of sulfonic acid groups on the surface of the catalyst.

MnO 2/SiO 2–SO 3H nanocomposite as hydrogen peroxide scavenger for durability improvement in proton exchange membranes

Membrane durability was a key problem to the development of proton exchange membrane fuel cells (PEMFCs). A novel nanocomposite MnO 2/SiO 2–SO 3H was prepared to mitigate the hydrogen peroxide attack to the membranes at fuel cell condition. The nanocomposites were synthesized by the wet chemical method and three-step functionalization. The crystal structure was characterized by X-ray powder diffraction (XRD), the crystallite size and the distribution of the nanocomposites were investigated by TEM. SEM-EDX was used to analyze the elemental distribution on the surface of the nanocomposite. And the surface functional groups (–SO 3H) were evaluated by FT-IR. The amount of sulfonic acid groups introduced onto the silica surface was determined by titration method. The radical scavenging ability was estimated by UV–VIS spectroscopy using dimethyl sulfoxide (DMSO) as the trapping agent. The membrane durability was investigated via ex situ Fenton test and in situ open circuit voltage (OCV) accelerated test. In these tests, the fluoride emission rate (FER) reduced by nearly one order of magnitude with the dispersion of MnO 2/SiO 2–SO 3H nanocomposites into Nafion membrane, suggesting that MnO 2/SiO 2–SO 3H nanocomposites had a promising application to mitigate the degradation of the proton exchange membrane.