Subsequent Sulfonation Research Articles

Preparation of a Carbon-Silica Mesoporous Composite Functionalized with Sulfonic Acid Groups and Its Application to the Production of Biodiesel

A carbon-mesoporous silica (CS) composite functionalized with sulfonic acid (−SO3H) groups was prepared by controlled arbonization of sucrose impregnated in SBA-15 mesoporous silica and its subsequent sulfonation. The moderate vapor phase sulfonation of the CS composite with fuming sulfuric acid (H2SO4·20%SO3) was the key step in preparing the strong acid solid material (CS-SO3H). Structural analysis and reaction data revealed that sulfonic acid groups were successfully incorporated into the mesoporous CS composite, and the Brønsted acid site density was tunable from 0.09 to 0.70 mmol/g by tuning the carbon loading. The sample with 35 wt% carbon exhibited a remarkable catalytic activity for biodiesel production by the esterification of palmitic acid and the transesterification of soybean oil with methanol. 利用化学浸渍法将蔗糖负载到 SBA-15 介孔材料孔道内部, 高温炭化形成的多聚苯环经发烟硫酸气相磺化处理后, 得到磺酸基团功能化的新型碳-硅介孔复合材料. 发烟硫酸气相磺化处理是该材料合成的关键步骤. X 射线衍射、扫描电镜和氮气吸附结果表明, 碳-硅介孔复合材料经磺酸化处理保持了高度有序的介孔结构. 热重、傅里叶变换的红外光谱及吡啶吸附红外光谱结果证明, 磺酸功能基团成功的嫁接于碳-硅介孔复合材料孔道的内表面, 反应活性中心为 Brønsted 酸, 酸密度在 0.09$ $0.70 mmol/g 可以有效调变. 当碳负载量为 35% 时, 该复合材料在生物柴油的绿色合成中显示出最优的催化性能, 且可重复使用 3 次以上.

Radiolytic preparation of PFA-g-PVBSA membranes as a polymer electrolyte membrane

In this study, a polymer electrolyte membrane, PFA-g-PVBSA was prepared through the radiation-induced graft copolymerization of vinylbenzyl chloride (VBC) monomer onto a poly(tetrafluoroethylene-co-perfluoropropylvinyl ether) (PFA) film and subsequent sulfonation processes. The IEC values and water uptakes of the prepared membranes increased when increasing the contents of the poly(vinylbenzyl sulfonic acid) (PVBSA) graft polymers in the membranes. Compared with Nafion 212, the degree of grafting (DOG) of membranes of 50% and 70% showed higher proton conductivity with significantly lower methanol permeability. The combination of these properties suggests that the prepared membranes are promising for future application in direct methanol fuel cells.

A study on the characterization of FEP-g-PVBSA membranes as polymer electrolytes for direct methanol fuel cells

Poly(vinylbenzyl sulfonic acid)-grafted poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP- g-PVBSA) electrolyte membrane was prepared by radiation-induced grafting of vinylbenzyl chloride onto FEP film with subsequent sulfonation processes. An energy dispersive X-ray analysis was used to observe the cross-sectional distribution behaviors of the hydrophilic sulfonic acid groups and hydrophobic fluorine groups. The characteristics of an ion-exchange capacity (IEC), water and methanol uptake, methanol permeability, and proton conductivity as a function of the degree of grafting were studied. The IECs and water uptakes of membranes with different degrees of grafting (36 to 102%) were measured in the range of 0.8 to 1.62 meq g−1 and 10 to 30%, respectively. The proton conductivity was higher than that of a Nafion 212 membrane (6.1 E−02 S cm−1), when the degree of grafting reached 60%. The methanol permeability and uptake of the FEP- g-PVBSA membrane was significantly lower than that of the Nafion 212 membrane, and even the degree of grafting reached 102%.

Chemical modification of lignin assisted by microwave irradiation

Abstract Soda lignin was converted into sulfonated lignin by oxidation, hydroxymethylation, and sulfonation assisted by microwave irradiation. Oxidation and hydroxymethylation under these circumstances led to lignins with much higher reactivity toward subsequent sulfonation, and the sulfonation degree could be elevated up to 2.75 mmol g-1. A suitable microwave irradiation time is beneficial to obtain oxidized lignin with small molecular size, but the irradiation time must be selected adequately. Under optimal conditions, the sulfonated lignin exhibits a good dispersive effect to TiO2 suspension. Compared to conventional water bath heating, microwave irradiation not only increases the sulfonation degree of lignin, but also sharply shortens the reaction time.

Preparation of poly(ethylene terephthalate)‐based proton‐exchange membranes through the ultraviolet‐induced graft copolymerization of allyl methacrylate for applications in fuel cells

AbstractThe ultraviolet‐induced graft copolymerization of allyl methacrylate into poly(ethylene terephthalate) films and the subsequent sulfonation of the grafted film were performed to prepare a polymer electrolyte membrane (PEM). The sulfonation reaction occurred at the grafted chain under mild conditions; that is, the grafted film was easily transformed into a PEM. The mechanical, chemical, and thermal properties of the prepared PEM (i.e., the ion‐exchange capacity, water uptake, tensile strengths at different water uptakes and temperatures, stability in hydrogen peroxide solutions, and proton conductivity) were measured with titrimetric and gravimetric analyses; most were found to be better than those of Nafion. The maximum ion‐exchange capacity and proton conductivity of the PEM were observed to be 0.072 mmol/g and 0.0458 S/cm, respectively. Because this PEM is inexpensive to prepare with available raw materials and has the properties required for fuel cells, it could be an attractive and suitable device for use in fuel‐cell technology. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Melatonin receptors, melatonin metabolizing enzymes and cyclin D1 in human breast cancer

Background. Melatonin suppresses breast cancer cell proliferation by inhibiting the upregulation of estrogen-induced cyclin D1 via its G-protein-coupled receptor MT1. Additionally, melatonin stimulates the expression of the estrogen sulfotransferase, SULT1E1. However, metabolism of melatonin via 6-hydroxylation by CYP1A1/1A2 and subsequent sulfonation by SULT1A1/1A3 decreases its intracellular concentration. This could have a negative impact on its oncostatic action in breast cancer.Patients and methods. In this pilot study, we performed immunohistochemical (IHC) analysis of MT1 and cyclin D1 in breast cancer specimens from 33 patients. Also, we investigated the expression of CYP1A1/1A2, SULT1A1/1A3/1E1, and cyclin D1 in cancer (CANC) and adjacent non-cancer (NCANC) specimens from 10 representative breast cancer patients using quantitative real-time reverse transcription polymerase chain reaction.Results. CYP1A1-mRNA-expression was found only in three CANC and in one NCANC. CYP1A2 mRNA was below the detection limit in all patients. SULT1A1 was observed only in two of the 10 CANC and one of the 10 NCANC specimens. But, all 10 CANC and NCANC samples showed high SULT1A3 levels. Cyclin D1 mRNA levels were found in all 10 CANC and NCANC specimens. Furthermore, IHC-staining of cyclin D1 was observed in 27 of 33 CANC and correlated positively with estrogen receptor positivity (p = 0.015).Conclusion. The low or even absent expression of CYP1A1 or CYP1A2 in breast cancer specimens suggested that melatonin might be involved in cell cycle arrest.

Synthesis of monodisperse SiO2/P(DVB-SO3H)/SiO2/P(DVB-SO3H) tetra-layer polyelectrolyte microspheres and the corresponding hollow P(DVB-SO3H)polyelectrolyte microspheres with a shell-in-shell structure

The hollow poly(divinylbenzyl sulfonic acid) (P(DVB-SO3H)) polyelectrolyte (PE) microspheres with a shell-in-shell structure were prepared by selective etching of the silica core and third-layer with hydrofluoric acid from the corresponding SiO2/P(DVB-SO3H)/SiO2/P(DVB-SO3H) tetra-layer PE microspheres, which were synthesized by a combination of the controlled sol–gel hydrolysis of tetraethylorthosilicate (TEOS) for the preparation of silica core and third-layer, and the distillation precipitation polymerization of divinylbenzene (DVB) in acetonitrile for the construction of polydivinylbenzene (PDVB) layer with subsequent surface modification of the phenyl group to afford P(DVB-SO3H) PE second and outer shell-layer. The silica/poly(divinylbenzylsulfonate 4-vinylpyridinium) (SiO2/P(DVB-SO3−VPyH+) core-shell PE microspheres were prepared by the neutralization of 4-vinylpyridine (4-VPy) with sulfonic acid groups on the surface of SiO2/P(DVB-SO3H) core-shell microspheres, which were synthesized by the distillation precipitation polymerization of DVB in the presence of 3-(methacryloxy)propyl trimethacrylate (MPS)-modified silica nanoparticles as seeds to afford SiO2/PDVB core-shell microspheres with subsequent sulfonation of the phenyl groups of PDVB shell in concentrated sulfuric acid. SiO2/P(DVB-SO3H)/SiO2/P(DVB-SO3H) tetra-layer PE microspheres were synthesized by sulfonation of SiO2/P(DVB-SO3−VPyH+)/SiO2/PDVB tetra-layer microspheres in concentrated sulfuric acid, which were prepared by distillation precipitation polymerization of DVB with MPS-modified SiO2/P(DVB-SO3−VPyH+)/SiO2 tri-layer microspheres as seeds via coating of silica-layer onto SiO2/P(DVB-SO3−VPyH+) nanoparticles. The morphology and properties of the resultant microspheres, and the corresponding hollow P(DVB-SO3H) microspheres with a shell-in-shell structure were characterized by transmission electron microscopy (TEM), Fourier transform spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS).

Water-Soluble Graphite Nanoplatelets Formed by Oleum Exfoliation of Graphite

A facile route to water-soluble graphite nanoplatelets that uses graphite as the starting material is described. The method relies on the addition of phenyl radicals with subsequent sulfonation of the phenyl groups. Atomic force microscopy, high-resolution transmission electron microscopy, and scanning tunneling microscopy images show that a high degree of exfoliation occurs during the sulfonation step. The sheet resistance of the bulk films of the nanoplatelets prepared by vacuum filtration using an anodisc membrane was found to be 212 Ω/sq.

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.

Synthesis of novel water-soluble sulfonated cellulose

Water-soluble sulfonated cellulose (SC) samples were synthesized by oxidizing hardwood kraft pulp with sodium periodate followed by the sulfonation reaction with sodium bisulfite. Six levels of oxidation/sulfonation were obtained by using different mmols (0.93–4.67) of periodate per gram of pulp. The aldehyde and sulfonic acid contents, surface morphology, and water solubility property of these treated fibers were characterized. It was found that carbonyl group content increased with the periodate charge and so did the sulfonic acid content in subsequent sulfonation step. Scanning electron microscopy images showed a significant change in surface morphology of the sulfonated samples. Solubility of sulfonated cellulose in water was determined from 1H NMR spectra and a solubility of 28.57g/L was found when cellulose was oxidized with 4.67mmol periodate per gram cellulose followed by the sulfonation reaction.▪

TEMPO addition into pre-irradiated fluoropolymers and living-radical graft polymerization of styrene for preparation of polymer electrolyte membranes

We prepared proton exchange membranes (PEMs) by 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO)-mediated living-radical graft polymerization (LRGP) of styrene into fluoropolymer films and subsequent sulfonation. Poly(vinylidene fluoride) (PVDF) and poly(ethylene- co-tetrafluoroethylene) (ETFE) films were first irradiated and then treated with TEMPO solutions in various solvents. TEMPO addition was confirmed by the test of styrene grafting into TEMPO-treated films at 60 °C, at which the LRGP never proceeds. This test enabled us to differentiate the LRGP from the conventional graft polymerization. In order to gain a deep insight about TEMPO-addition reaction, the TEMPO-penetration behavior into the base polymer films was examined by a permeation experiment and computer simulation. Xylene and dioxane were appropriate solvents for the complete introduction of TEMPO into PVDF and ETFE films, respectively. Then, the LRGP of styrene was performed based on the fully TEMPO-capped films at 125 °C with various solvents. By using an alcoholic solvent, the degree of grafting was enhanced and it reached a maximum of 38%. This grafted film was sulfonated to prepare a PEM showing an ion exchange capacity of 2.2 meq/g and proton conductivity of 1.6×10 −1 S/cm.

Electro-electrodialysis of HI–I 2–H 2O mixture using radiation-grafted polymer electrolyte membranes

In the thermochemical water-splitting iodine–sulfur process for hydrogen production, new polymer electrolyte membranes were applied in an electro-membrane process (electro-electrodialysis, EED) to increase the HI molality of HIx solution (HI + I 2 + H 2O mixture) to be over quasi-azeotropic. Radiation grafting of a styrene monomer into a poly(ethylene- co-tetrafluoroethylene) base film and subsequent sulfonation provided electrolyte membranes that had ion exchange capacities (IECs) of 1.1–1.6 mmol/g. With the EED of the HIx solutions using [HI] = [I 2] = 10 mol/kg at 40 °C the transport number of protons, ratio of permeated quantities of water to the protons, and current efficiency all appeared to depend on the IEC of the resulting membranes. When compared to Nafion, the self-made membranes exhibited lower electric cell resistance, and thereby decreasing up to 32% of the overall energy required in the concentration operation.

Radiation-induced graft polymerization of styrene into a poly(ether ether ketone) film for preparation of polymer electrolyte membranes

Radiation-induced graft polymerization of styrene into crystalline poly(ether ether ketone) (PEEK) with 32% crystallinity, an aromatic hydrocarbon polymer and so-called “super-engineering plastics”, which has excellent mechanical properties at elevated temperature as well as excellent gas barrier properties, was investigated with differential scanning calorimetry (DSC), thermogravimetry (TGA), X-rays diffraction analysis (XRD), and electron spin resonance spectroscopy (ESR). The endothermic heats of melting of the original and styrene-grafted PEEK (grafted PEEK) films were similar, indicating that the crystallinity was almost completely maintained during the graft polymerization of styrene up to a grafting degree of 51%. Lower glass transition temperature ( T g) of the grafted PEEK film in the DSC profile, and the absence of an extra halo originating from amorphous polystyrene grafts in the XRD strongly indicate that the grafting of styrene to crystalline PEEK films proceeded in the amorphous region of PEEK. This is probably because polystyrene grafts have hydrocarbon structures similar to a base PEEK polymer, resulting in compatibility to the amorphous phase of the PEEK films. The grafted PEEK films can be converted to PEEK-based electrolyte membranes (PEEK-based PEM) by subsequent sulfonation of the polystyrene grafts. The PEEK-based PEM had conductivity of more than 0.01 S/cm and exhibited higher water content above 100%.

Surface-Initiated Growth of Ionomer Films from Pt-Modified Gold Electrodes

The ability to chemically wire ionomer films to electrode surfaces can promote transport near interfaces and impact a host of energy-related applications. Here, we demonstrate proof-of-concept principles for the surface-initiated ring-opening metathesis polymerization (SI-ROMP) of norbornene (NB), 5-butylnorbornene (NBH4), and 5-perfluorobutylnorbornene (NBF4) from Pt-modified gold substrates and the subsequent sulfonation of olefins along the polymer backbones to produce ultrathin sulfonated polymer films. Prior to sulfonation, the films are hydrophobic and exhibit large barriers against ion transport, but sulfonation dramatically reduces the resistance of the films by providing pathways for proton diffusion. Sulfonated films derived from NBF4 and NBH4 yield more anodic potentials for oxygen reduction than those derived from NB or unfunctionalized electrodes. These improvements are consistent with hydrophobic structuring by the fluorocarbon or hydrocarbon side groups to minimize interfacial flooding and generate pathways for enhanced O(2) permeation near the interface. Importantly, we demonstrate that the sulfonated polymer chains remain anchored to the surface during voltammetry for oxygen reduction whereas short-chain thiolates that do not tether polymer are removed from the substrate. This approach, which we extend to unmodified gold electrodes at neutral pH, presents a method of cleaning the ionomer/electrode interface to remove molecular components that may hamper the performance of the electrode.

Amphoteric ion exchange membrane synthesized by radiation-induced graft copolymerization of styrene and dimethylaminoethyl methacrylate into PVDF film for vanadium redox flow battery applications

Poly(vinylidene difluoride) (PVDF) film was grafted with styrene (St) and dimethylaminoethyl methacrylate (DMAEMA) using γ-irradiation techniques. Through subsequent sulfonation and protonation processes, a new kind of amphoteric ion exchange membrane (AIEM) was synthesized. The grafting yield ( GY) increased with absorbed dose and leveled off at about 60 kGy. The composition of poly(St- co-DMAEMA) grafts was correlated to the ratio of St to DMAEMA monomer in the feed. Micro-FTIR and XPS analyses testified that the grafting and sulfonation of St unit in poly(St- co-DMAEMA) grafts had been carried out as designed. Further characterizations showed that the properties of the AIEM strongly depended on the composition and GY of the film, i.e. higher content of DMAEMA brought lower permeability of vanadium ions and conductivity, while higher GY led to higher water uptake, ion exchange capacity ( IEC) and conductivity. Finally, an AIEM with a GY of 26.1% was assembled and tested in the vanadium redox flow battery (VRFB) system. It was found that the VRFB assembled with the AIEM maintained an open circuit voltage (OCV) higher than 1.2 V after placed for 68 h, which was much longer than that with the Nafion117 membrane. Therefore, this work provides a novel method to develop potential substitute of Nafion membranes to be applied in VRFB system.

A study on the distribution of polystyrene sulfonic acid grafts over the cross-section of a PFA film

In this study, the distribution behaviors of polystyrene sulfonic acid (PSSA) grafts over the cross-section of grafted PFA membranes (PFA- g-PSSA) were investigated by using SEM-EDX analysis. Membranes with various degrees of grafting (DOG) and thicknesses were prepared by a simultaneous radiation grafting of styrene and a subsequent sulfonation with chlorosulfonic acid. A SEM-EDX instrument was utilized to directly observe that the distribution behaviors of the PSSA grafts over the cross-section of grafted PFA membranes and the results showed that the distribution behaviors were largely affected by the grafting conditions such as the degree of grafting, monomer concentration, and film thickness.

Thermal stability of proton exchange fuel-cell membranes based on crosslinked-polytetrafluoroethylene for membrane-electrode assembly preparation

We investigated thermal properties of proton exchange membranes (PEMs) prepared by the radiation-induced grafting of styrene into crosslinked-polytetrafluoroethylene films and the subsequent sulfonation for fuel-cell applications. A conventional thermogravimetric analysis was found to be unreliable because the resulting curve varied greatly with the heating rate. Thus, in order to obtain accurate information, we performed an ex-situ heat-treatment analysis, which involved heating of the PEMs at fixed temperatures of 200–350 °C and measurement of their remaining weight, ion exchange capacity (IEC) and proton conductivity ( σ) after washing in pure water. The IEC and σ did not change at any temperature up to 200 °C, indicating high thermal stability. At 250 °C, however, the PEM properties deteriorated probably via radical cleavage of the C–S bond between a sulfonic acid group and an aromatic ring, and condensation of two sulfonic acid groups. Finally, the PEM was hot-pressed with two electrodes at 200 °C to produce a good membrane-electrode assembly for a fuel cell.

Effect of SiO2 nanoparticle addition on the characteristics of a new organic–inorganic hybrid membrane

Poly(vinylidene fluoride) composite membranes filled with different weight fractions of SiO2 nanoparticles have been prepared by a blending method. Cation-exchange groups were introduced by the copolymerization of glycidyl methacrylate with divinylbenzene and subsequent sulfonation. These hybrid membranes have been characterized by Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and water uptake and ion-exchange capacity measurements. Membrane potential and membrane conductivity measurements have been carried out with different counter ions to investigate the relationship between ionic migration and the SiO2 nanoparticle content. The counter-ion transport number and permselectivity of these membranes are found to be highly dependent on the SiO2 content in the membrane phase and the nature of the counter ion. Membrane conductance was analyzed in terms of phenomenological coefficients using non-equilibrium thermodynamic principles. It can be concluded that these hybrid membranes exhibit high thermal stability, improved selectivity, and moderate membrane conductivity, and may be suitable for use in the electro-driven separation processes.

Synthesis and Characterization of Poly(vinylidene fluoride)-g-sulfonated Polystyrene Graft Copolymers for Proton Exchange Membrane

A series of poly(vinylidene fluoride)-g-sulfonated polystyrene (PVDF-g-SPS) graft copolymers were systematically synthesized and examined with the focus of understanding how the polymer microstructure (backbone molecular weight, graft density, graft length, sulfonic acid concentration, ion exchange capacity, etc.) affects their morphology, water uptake, and proton conductivity under various environmental conditions (temperature and relative humidity). The synthesis of these relatively well-defined graft structures involves three reaction steps, including the preparation of PVDF copolymers containing a few mol% of chlorotrifluoroethylene (CTFE) units, the ATRP graft-from reaction to incorporate several polystyrene side chains, and the subsequent sulfonation reaction on the PS side chains. The PVDF-g-SPS graft copolymer with a combination of a high PVDF backbone molecular weight (Mn >300 000 g/mol), very low SPS graft density (0.3 mol%), and high graft length (SPS content >30 mol%) presents an interesting material for the proton exchange membrane (PEM). This graft copolymer self-assembles into a microphase-separated morphology with randomly oriented long-range lamella/cylinder ionic channels (with small widths) that are imbedded in the hydrophobic semicrystalline PVDF matrix. This graft copolymer morphology offers a high ion exchange capacity (IEC = 2.75 mmol/g) and resistance to excessive water swelling, which yields notably higher proton conductivity than Nafion under 30−120 °C and high humidity conditions.

Positron Annihilation Lifetime Study of Graft-Type Fluorinated Polymer Electrolyte Membranes

Positron annihilation lifetime spectroscopy (PALS) measurements were performed on polymer electrolyte membranes (PEMs) synthesized by radiation-induced graft polymerization of styrene into crosslinked-polytetrafluoroethylene (cPTFE) films and subsequent sulfonation. The base cPTFE and polystyrene grafted films were also measured as references. The cPTFE based PEM was found to have free-volume holes with different radius of 0.28-0.30 nm and 0.44-0.45 nm. The larger holes may be located in PTFE amorphous regions, while the smaller ones are considered to exist in both PTFE crystallites and poly(styrene sulfonic acid) grafts containing no water.