State 13C Nuclear Magnetic Resonance Research Articles

Accumulation of aliphatic compounds in soil with increasing mean annual temperature

Chemical recalcitrance of biomolecules, physical protection by soil minerals and spatial inaccessibility to decomposer organisms are hypothesized to be primary controls on soil organic matter (SOM) turnover. Previous studies have observed increased sequestration of plant derived aliphatic compounds in experimentally warmed soils but did not identify the mechanisms for this enhanced preservation. To further test the role of environmental conditions in the preservation of aliphatic carbon, we analyzed native soils along a bicontinental, longitudinal, mean annual temperature (MAT) gradient to examine relationships between SOM composition, soil physical properties and temperature. Using biomarker analysis by gas chromatography–mass spectrometry and solid state 13C nuclear magnetic resonance to characterize SOM, we observed that the concentration of aliphatic compounds derived from the waxes and cuticles of plant leaves increased with MAT. We did not observe any significant correlations between aliphatic SOM and clay mineral content which suggests that their inherent chemical recalcitrance is responsible for their persistence in soils. Other SOM components were not correlated with MAT, indicating that temperature alone does not control the overall preservation and biodegradation of soil carbon. As such, other environmental factors (e.g., microbial community structure and activity, litter quality and quantity, mineral surfaces, soil moisture content and antioxidant capacity) also play a role in the selective preservation or accumulation of various SOM components. However, our study shows that the accumulation of aliphatic SOM components is highly correlated to MAT.

The Solid State 13C NMR Study of Gamma Radiation of Ethylene-Octene Copolymer

Ethylene-octene copolymer (POE) samples exposed to γ-radiation under a series of absorbed doses have been investigated using thermal analysis, sol–gel analysis and solid state 13C nuclear magnetic Resonance (NMR). The chemical shift of POE was assigned and peak evolution as a function of radiation dose was discussed. An obviously evolution is that the peak area of 33.6 ppm decreases as a function of the increase of radiation dose, and at the same time, the peak shape broadens gradually. This indicates that the chain scission occurred between α-C and branch chain C (methine) or between C1 (the sidegroup hexyl) and branch chain C (methane) after radiation. The chain scission is severer with the increase of absorbed dose.The 13C NMR spectra of the corresponding gels confirmed the result. The variation in linewidth of the resonance at 33.6 ppm in samples of POE irradiated to different doses was attributed to information of chain, scission, new cross linking, and crystalline components.

Preparation, Characterization and Voltammetric Aspects of a Silsesquioxane Organofunctionalized With Imidazole Groups and Subsequent Reaction With Silver and Potassium Hexacyanoferrate (III)

This paper describes the interaction of a octa (3-chloropropyl)octasilsesquioxane (SS) functionalized with imidazole (SSI) groups, and its subsequent reaction with silver (AgSSI) and hexacyanoferrate (III) (AgHSSI). The materials SS, SSI were characterized by infrared (FTIR); solid state 13C and 29Si nuclear magnetic resonance (NMR). The AgSSI and AgHSSI were characterized by electronic (Uv-Vis) and infrared spectroscopy (FTIR). The AgHSSI was incorporated into a graphite paste electrode and the electrochemical studies were conducted with cyclic voltammetry. The AgSSI system was studied first, followed by the AgHSSI. The spectroscopic studies reveals that preparation was conducted with success. The cyclic voltammogram of AgSSI obtained from a graphite paste electrode modified (50% m/m) exhibited a redox couple with average potential (E?’) of 0.01 V (vs Ag/AgCl(s), KNO3, 1.0 mol L-1; v = 20 mV s-1), attributed to the Ag0/Ag+ redox process. The cyclic voltammogram of AgHSSI with AgHSSI (50% m/m) exhibited a single redox couple, much wider with E?’= 0.14 V, (vs Ag/AgCl(s), KNO3, 1.0 mol L-1, v = 20 mV s-1) attributed to the Fe2+(CN)6/ Fe3+(CN)6 process.

Physico-chemical of organo-functionalized magnesium phyllosilicate prepared by microwave heating

In this work, organo-functionalized magnesium phyllosilicates were prepared via hydrothermal synthesis with four sources of silicon: 3-aminopropyltriethoxysilane (AMPTS), N-[3-(trimethoxysilyl)propyl]-ethylenediamine (TMSPEDA), N-[3-(trimethoxysilyl)propyl]-diethylenetriamine (TMSPETA) and tetraethoxyorthosilane (TEOS). Microwave radiation (MW) was employed as heating source and the results were compared with the analogous materials synthesized by conventional heating in an oven (CE). The materials obtained were characterized using X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), solid state 29Si and 13C nuclear magnetic resonance (NMR), thermogravimetry (TG) and elemental analysis of carbon, nitrogen and hydrogen (CHN). The 2:1 type of trioctahedral phyllosilicate was confirmed by the presence of the 060/330 reflection, at 59.5° 2θ. The presence of the organic modifier was proven by the bands at 2930, 2850, and 1490cm−1 and the typical features of the phyllosilicate were found at 3700cm−1 (Mg–OH) and 1014cm−1 (Si–O–Si). 13C-NMR showed that the organic chains were intact in the interlayer space (5–64ppm). Thermogravimetry indicated that these pending groups were stable in this support until 200°C when they begin to decompose. Silicon-29 NMR confirmed that the pending groups were bound directly to the silicon atoms by the resonance of Si–C bond at 48 and 55ppm. The results showed the success of the procedure for all the proportions of the silicon sources used, with a reduction of reaction time in the range from 91% to 96% using microwave radiation in relation to the conventional heating oven.

Structural characterization of ion-vapor deposited hydrogenated amorphous carbon coatings by solid state 13C nuclear magnetic resonance

In the present study, unique structural heterogeneity was observed in ion-vapor deposited a-C:H coatings by performing 13C MAS and 1H-13C CPMAS experiments on solid state nuclear magnetic resonance devices. Two distinct types of sp2 C clusters were discovered: one of them denoted as sp2 C′ in content of 3–12 at. % was non-protonated specifically localized in hydrogen-absent regions, while the other dominant one denoted as sp2 C″ was hydrogenated or at least proximate to proton spins. On basis of the notably analogous variation of sp2 C′ content and Raman parameters as function of substrate bias voltage in the whole range of 0.5 kV–3.5 kV, a model of nano-clustering configuration was proposed that the sp2 C′ clusters were embedded between sp2 C″ clusters and amorphous sp3 C matrix as trapped interfaces or boundaries where the sp2 carbon bonds were highly distorted. Continuous increase of bias voltage would promote the nano-clustering and re-ordering of dominant sp2 C″ clusters, thus results in a marked decrease of interspace and a change of the content of sp2 C′ clusters. Further investigation on the 13C magnetization recovery showed typical stretched-exponential approximation due to the prominent presence of paramagnetic centers, and the stretched power α varied within 0.6–0.9 from distinct types of sp2 C clusters. Differently, the magnetization recovery of 1H showed better bi-exponential approximation with long and short T1(H) fluctuated within 40–60 ms and 0.1–0.3 ms approximately in content of 80% ± 5% and 20% ± 5%, respectively, varying with various bias voltages. Meanwhile, the interrupted 13C saturation recovery with an interval of short T1(H) showed that most of quick-relaxing protons were localized in sp2 C″ clusters. Such a short T1(H) was only possibly resulted from a relaxation mechanism associated with electron-nuclear dipolar interaction or spinning diffusion, and its partial distribution in sp2 C″ clusters may imply more complex configurations of unpaired electrons in studied a-C:H coatings.

Biomimetic nanocomposites of carboxymethyl cellulose–hydroxyapatite: Novel three dimensional load bearing bone grafts

An innovative biomimetic synthesis of novel three dimensional micro/macro porous carboxymethyl cellulose (CMC)–hydroxyapatite (HA) nanocomposites having four systematically different compositions has been established for its possible application as a load bearing synthetic bone graft. Our process, being in situ, involves a simple and cost effective route akin to a matrix mediated biomineralization process. Developed synthesis route not only controls the size of HA particles in the range of 15–50nm, embedded in CMC matrix, but also assists in the formation of a mechanically strong three dimensional nanocomposite structures due to physical cross linking of HA impregnated CMC matrix. The process does not involve any toxic cross linker and works at near ambient conditions. The nanocomposites are systematically structurally and mechanically characterized using various techniques like scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform IR (FTIR), solid state 13C nuclear magnetic resonance (13C NMR), thermo-gravimetric analysis (TGA) and Universal mechanical test. It reveals that the ionic/polar or electrostatic interactions are the main driving force for formation of load bearing three dimensional nanocomposites via a process similar to matrix mediated biomineralization. Compressive strength and compressive modulus of nanocomposites, being in the range of 1.74–12MPa and 157–330MPa, respectively, meet the desired range of compressive strength for the synthetic grafts used in cancellous bone. An increase in the compressive strength with increase in the porosity has been an interesting observation in the present study. In vitro cytotoxicity of the synthesized nanocomposites has been evaluated using bone marrow mesenchymal stem cells (BMSC) isolated from Wistar rat.

Analysis of Carbon Functional Groups in Mobile Humic Acid and Recalcitrant Calcium Humate Extracted from Eight US Soils

Solid state 13C nuclear magnetic resonance (NMR) spectroscopy is a common tool to study the structure of soil humic fractions; however, knowledge regarding carbon structural relationships in humic fractions is limited. In this study, mobile humic acid (MHA) and recalcitrant calcium humate (CaHA) fractions were extracted from eight soils collected from six US states and representing a variety of soils and ecoregions, characterized by this spectroscopic technique and analyzed for statistical significance at P = 0.05. We found that the abundances of COO and N-C=O functional groups in the MHA fractions were negatively correlated to soil sand content, but were positively correlated to silt, total N and soil organic carbon contents. In contrast, the abundances of the COO and N-C=O functional groups were only positively correlated to the content of clay in the CaHA fractions, indicating that the two humic fractions were associated with different soil components. The two 13C NMR peaks representing alkyls and OCH3/NCH were negatively correlated to the peaks representing aromatics, aromatic C-O and N-C=O/COO. Comparison of the sets of data from 13C NMR spectroscopy and ultrahigh resolution mass spectrometry revealed that the aromatic components identified by the two methods were highly consistent. The comparison further revealed that protein in MHA was associated with, or bound to, the nonpolar alkyl groups, but a component competitively against (or complementary to) aromatic groups in the MHA composition. These observations provided insight on the internal correlations of the functional groups of soil humic fractions.

Characterization of soil organic matter using microwave assisted acid and base hydrolysis

Sequential microwave assisted HCl hydrolysis and tetramethylammonium hydroxide (TMAH) hydrolysis (in MeCN at 140 and 190°C) were used to analyze the hydrolysable constituents of soil organic matter (SOM) from a forest soil. At each step, the organic or aqueous extracts were analyzed using gas chromatography–mass spectrometry (GC–MS) and the residues investigated using solid state 13C nuclear magnetic resonance (NMR) spectroscopy, Curie point pyrolysis (CuPy) and thermochemolysis (CuTHM). The composition of the aqueous extract from microwave assisted HCl hydrolysis strongly depended on hydrolysis temperature and was dominated by carbohydrates at 140°C and amino acids and 2-amino sugars at 190°C. The 13C NMR spectrum of the residue from acid hydrolysis at 190°C was consistent with the removal of most of the carbohydrates. The organic extract was dominated by aromatic compounds, 50% of which retained the glyceryl side chain of the arylglycerol-β-aryl ether units of lignin. However, comparison of the thermochemolysates of the residue from acid hydrolysis and of the initial SOM showed no great differences in the composition and relative abundance of aromatic lignin-derived compounds. This suggested that microwave assisted acid hydrolysis might account for only the unprotected or unaltered lignin in SOM. Thus, although more time consuming, microwave assisted acid hydrolysis provided information about hydrophilic constituents and unaltered lignin-derived constituents of SOM, which was not available from pyrolysis. Microwave assisted TMAH hydrolysis released predominantly aliphatic compounds from cutin and suberin. The release of cutin- and suberin-derived constituents from SOM upon microwave assisted base hydrolysis was supported by the 13C NMR spectrum, CuPy pyrolysate and CuTHM thermochemolysate of the residue.

Medium term effects of fire induced soil organic matter alterations on Andosols under Canarian pine (Pinus canariensis)

Andosols are characterized by high organic matter (OM) content defining the specific properties of these soils and representing an efficient carbon (C) sink within the global C cycle. In the present study, the medium-term alterations of the soil organic matter (SOM) pool of the topsoils of burnt and unburnt Andosols taken eleven years after a severe wildfire were evaluated. The soils derived from Monte la Esperanza in Tenerife Island, Spain and were covered predominantly by Pinus canariensis. The double shot pyrolysis Gas Chromatography/Mass Spectrometry (GC/MS) was applied after optimizing the suitable temperatures by thermogravimetry. Analytical pyrolysis was complemented by solid state 13C nuclear magnetic resonance (NMR) spectroscopy. Soil OM content decreased harshly in fire-affected soil, leading to a noteworthy reduction of the water holding capacity. Generally, surface horizons of control and burnt Andosols have a rather similar SOM composition as analyzed by Py-GC/MS. In addition, this technique illustrated (i) the presence of markers of conifers and angiosperms in the burnt soil, which points to the recovery of the vegetation; (ii) the increase in short chain n-alkanes due to thermally induced breakdown processes during fire; (iii) the dominance of furans in contrast with the low contribution of C6-based polysaccharide specially in the BS indicate the alteration of the carbohydrates, and (iv) a relative enrichment of aromatic compounds released at 600°C in the burnt soil when compared to that unaffected by fire. The latter points to the formation of black carbon like material during the fire event, which was also detected by thermogravimetric analyses and evidenced by the increase in the signal in the aromatic region of the 13C NMR spectrum.The high content of polysaccharides derived products and the low alkyl C/O-alkyl C ratio determined by NMR spectroscopy in the fire affected soil clearly indicate the inputs of plant material during the post fire recovery time.The results suggest that the severe wildfire causing the loss of large quantities of organic C which decreased the recalcitrant C pool but also led to a destruction of the A horizon to an extent unexpected for fire-affected soils without andic properties. Although this study cannot exclude that the present A horizon contains still pre-fire remnants, analytical pyrolysis complemented by NMR spectroscopy provided strong evidence that post-fire pedogenesis determined the quality of its SOM. Most tentatively a quick development of a new vegetation cover prevented a complete removal of the mineral soil by erosion and provided enough new organic material for a fast partial recovery of the C stocks in the A horizon.

Laboratory charring conditions affect black carbon properties: A case study from Quebec black spruce forests

Black carbon (BC) is an important residue of wildfires in boreal forests, but its characteristics depend on its formation conditions. The objective of this study was to characterize the chemical and physical properties of BC produced under controlled laboratory conditions, while mimicking a gradient of wildfire severity. We used fuels originating from mosses, ericaceous shrubs and spruce trees, as they constitute the major types available in boreal forests. We varied the maximum temperature (MT) from 75 to 800°C, the duration of charring from 0.5 to 24h and the abundance of O2. BC properties were analyzed using elemental analysis and proximate analysis, solid state 13C nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM) and surface area (SA) analysis. MT was the most significant factor affecting both chemical and physical changes. Results from 13C NMR spectroscopy indicated that 350°C was a threshold temperature, above which spectra became dominated by aromatic structures for all fuels. Charring duration affected BC composition at both low (250°C for 12h vs. 24h) and high (600°C for 0.5h vs. 6h) MT. The presence of O2 influenced BC composition mainly at low MT (250°C) and resulted in accelerated alkyl C degradation, accompanied with a distinct decrease in yield. Results from the SA analysis and the SEM micrographs showed that fuel type influenced BC physical properties, with moss-derived BC presenting higher surface area and microporosity than BC of woody origin.

Predicting C aromaticity of biochars based on their elemental composition

Three models were examined to predict C aromaticity (fa) of biochars based on either their elemental composition (C, H, N and O) or fixed C (FC) content. Values of fa from solid state 13C nuclear magnetic resonance (NMR) analysis with Bloch-decay (BD) or direct polarisation (DP) techniques, concentrations of total C, H, N, and organic O, and contents of FC of 60 biochars were either compiled from the literature (dataset 1, n=52) or generated in this study (dataset 2, n=8). Models were first calibrated with dataset 1 and then validated with dataset 2. All models were able to fit dataset 1 when atomic H to C ratio (H/C)<1 (except two ash rich biochars) and to estimate fa of HF treated biochars (H/C<1). Model 1, which was based on values of H/C only and calibrated with a root mean square of error (RMSE) of 0.04 fa-unit (n=41), could predict the experimental data with a RMSE=0.02 fa-unit (n=6). Model 2, which was based on biochar elemental composition data, showed the most accurate prediction, with a RMSE of 0.03 fa-unit (n=41) for the calibration data, and of 0.02 fa-unit (n=6, H/C<1) for the validation data. Model 3, which was based on contents of FC and C, and modified with a correction factor of 0.96, displayed the highest RMSE (0.06 fa-unit, n=19) among the three models. Models 1 and 2 did not work properly for samples having either an H/C ratio >1, high concentrations of carbonate or high inorganic H. These models need to be further tested with a wider range of biochars before they can be recommended for classification of biochar stability.

Molecular level analysis of long term vegetative shifts and relationships to soil organic matter composition

Soil organic matter (SOM) is one of the earth’s largest reservoirs of actively cycled carbon and plays a critical role in various ecosystem functions. In this study, mineral soils with the same parent material and of similar approximate age were sampled from the same climatic region in Halsey, Nebraska to determine the relationship between overlying vegetation inputs to SOM composition using complementary molecular level methods (biomarker analyses and solid state 13C nuclear magnetic resonance (NMR) spectroscopy). Soil samples were collected from a native prairie and cedar and pine sites planted on the native prairie. Free and bound lipids isolated from the pine soil were more enriched in aliphatic and cutin-derived compounds than the other two soils. Cinnamyl type lignin-derived phenols were more abundant in the grassland soil than in the pine and cedar soils. Acid to aldehyde ratios (Ad/Al) for vanillyl and syringyl type phenols were higher for the pine soil indicating a more advanced stage of lignin oxidation (also observed by 13C NMR) in the soil that has also been reported to have accelerated carbon loss. In agreement with the more abundant aliphatic lipids and cutin-derived compounds, solid state 13C NMR results also indicated that the SOM of the pine soil may have received more aliphatic carbon inputs or may have lost other components during enhanced decomposition. The observed relationship between vegetation and SOM composition may have important implications for global carbon cycling as some structures (e.g. aliphatics) are hypothesized to be more recalcitrant compared to others and their accumulation in soils may enhance below ground carbon storage.

Structure and composition of hard coke deposited on industrial fluid catalytic cracking catalysts by solid state 13C nuclear magnetic resonance

Carbonaceous deposits (hard coke) were studied by various solid state 13C nuclear magnetic resonance (NMR) techniques after demineralization of the spent and regenerated fluid catalytic cracking (FCC) catalysts obtained from Indian refineries. A number of structural parameters such as aromaticity, H/C ratio, fraction of protonated (faP) and non-protonated (faNP) aromatic carbons, number of pericondensed rings per average molecule (Nperi), and aromatic condensation index (γar) are derived from the NMR data. Findings of thirty-two and thirty-nine aromatic rings in coke from regenerated catalysts and five and nineteen rings in coke from spent catalysts are rationalized by various parameters such as feed, temperature and process conditions of FCC reactor on the basis of condensation. The coke are found more condensed in regenerated catalysts compared to spent catalysts revealing that the temperature has a marked effect in the evolution of coke structure whereas feeds and other process conditions govern the nature and composition of coke.

Organic matter composition and stabilization in a polygonal tundra soil of the Lena Delta

Abstract. This study investigated soil organic matter (OM) composition of differently stabilized soil OM fractions in the active layer of a polygonal tundra soil in the Lena Delta, Russia, by applying density and particle size fractionation combined with qualitative OM analysis using solid state 13C nuclear magnetic resonance spectroscopy, and lipid analysis combined with 14C analysis. Bulk soil OM was mainly composed of plant-derived, little-decomposed material with surprisingly high and strongly increasing apparent 14C ages with active layer depth suggesting slow microbial OM transformation in cold climate. Most soil organic carbon was stored in clay and fine-silt fractions (&lt; 6.3 μm), which were composed of little-decomposed plant material, indicated by the dominance of long n-alkane and n-fatty acid compounds and low alkyl/O-alkyl C ratios. Organo-mineral associations, which are suggested to be a key mechanism of OM stabilization in temperate soils, seem to be less important in the active layer as the mainly plant-derived clay- and fine-silt-sized OM was surprisingly "young", with 14C contents similar to the bulk soil values. Furthermore, these fractions contained less organic carbon compared to density fractionated OM occluded in soil aggregates – a further important OM stabilization mechanism in temperate soils restricting accessibility of microorganisms. This process seems to be important at greater active layer depth where particulate OM, occluded in soil aggregates, was "older" than free particulate OM.

Emulsion Copolymerization of Vegetable Oil Macromonomers Possessing both Acrylic and Allylic Functionalities

AbstractSummary: A soybean oil‐based vegetable oil macromonomer (VOMM) was incorporated as a comonomer into an all‐acrylic copolymer via semi‐continuous emulsion polymerization. Structurally, VOMMs are comprised of long hydrocarbon fatty acid moieties with allylic double bonds which enable auto‐oxidative crosslinking at ambient temperature. VOMMs facilitate low temperature film formation and the fatty acid chains tethered to the polymer backbone auto‐oxidize upon film formation to yield crosslinked films. Latexes with varying VOMM levels were synthesized to elucidate the effect of VOMMs on the pre‐cure and post‐cure glass transition temperature (Tg) and minimum film formation temperature (MFT). Thermoplastic control latexes (without VOMM) were also synthesized via copolymerization of butyl acrylate and methyl methacrylate. This paper details the characterization performed to validate and quantify the VOMM allylic unsaturation retention before, during, and after polymerization, and to quantify and confirm the increase in Tg resulting from auto‐oxidative crosslinking via solid state 13C nuclear magnetic resonance spectroscopy and differential scanning calorimetry.

Correlative study of critical reactions in polyacrylonitrile based carbon fiber precursors during thermal-oxidative stabilization

The correlations and differences among the processes of critical reactions in polyacrylonitrile (PAN) copolymer [containing itaconic acid (IA)] [P(AN–IA)] and terpolymer [containing itaconic acid (IA) and methyl acrylate (MA)] [P(AN–IA–MA)] fibers during thermal-oxidative stabilization have been studied by the comparative method. Fourier transform infrared spectroscopy (FTIR) analyzed the chemical kinetics and structural evolution in two types of PAN precursor fibers; the results indicates that P(AN–IA) possesses lower reaction rates and higher activation energies for critical reactions compared with P(AN–IA–MA). Differential scanning calorimetry (DSC) analyses show that the thermal stability of P(AN–IA) is superior to that of P(AN–IA–MA). FTIR and DSC results demonstrate that the stabilization process of P(AN–IA) is easier to control. By solid state 13C nuclear magnetic resonance, the mechanism of critical reactions verifies that the isomerization among quasi-pyridone, hydroxyl pyridine and pyridone structures in oxidized PAN leads to the amount of resultant groups first increasing and then decreasing.

A transdermal diltiazem hydrochloride delivery device using multi-walled carbon nanotube/poly(vinyl alcohol) composites

Membranes with high strength and elasticity are of great demand in patch therapy. Similar membranes have been developed by combining carboxy-functionalized multiwalled carbon nanotube (c-MWCNT) with different poly(vinyl alcohol) (PVA) as potential diltiazem delivery device through aqueous mixing. High molecular weight PVA (PVAH) produced stronger interaction with c-MWCNT than low molecular weight PVA (PVAL) preferably at low concentration. Positive changes in favor of PVAH in infrared and solid state 13C nuclear magnetic resonance spectroscopy, wide angle X-ray scattering, thermal stability, morphology and dry and wet mechanical properties clearly demonstrate that. Fibrillar c-MWCNT array at 1wt.% in PVAH (PVAH/1) has drastically improved PVA crystalline cell dimension, tensile strength (201%) and elongation (196%) than neat PVAH whereas the similar improvement is much less (100% and 185%) in PVAL (PVAL/1) due to globular morphology. Instead, c-MWCNT performed better at 0.5wt.% in PVAL (PVAL/0.5). The kinetic data reflects better encapsulation and slower release by PVAH (5.87%) than PVAL (10.17%) due to greater interfacial interaction.

Influence of oxygen on the stabilization reaction of polyacrylonitrile fibers

AbstractStabilized polyacrylonitrile (PAN) fibers pretreated under N2 and air atmospheres were prepared and their thermal behaviors were compared by differential scanning calorimetry and thermogravimetry methods. The results indicated that the subsequent stabilization reaction of PAN pretreated in air was more obvious than that in N2. In addition, the thermal stability of PAN pretreated in air is better than that in N2. The structural analysis by Fourier transform infrared spectroscopy and solid state 13C nuclear magnetic resonance implied that oxygen promoted dehydrogenation and a compact conjugated structure was formed in PAN. In addition, the CO structures were generated in air and increased gradually with temperature. The contents of oxygen in PAN fibers studied by elemental analysis corresponded with the structural evolution. Further investigation indicated that the CO structures helped dehydration and also promoted formation of the cross‐linked structures. A mechanism for structural evolution in PAN during stabilization in air was proposed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Hydrophobic precipitation of carbonaceous spheres from fructose by a hydrothermal process

We report a new mechanism of hydrophobic ripening for the formation of carbonaceous spheres by the dehydration of saccharides in a hydrothermal aqueous environment using fructose as a model precursor material. We investigated the formation of carbonaceous spheres from fructose in aqueous solutions under hydrothermal conditions. The spheres were found to contain 65.7wt.% C, 4.3wt.% H and 30.0wt.% O, implying incomplete dehydration of the fructose. The spheres, typically ranging between 400nm and 10μm in diameter, are found to be constructed entirely of primary particles of ∼5nm. The chemical structure of the carbonaceous spheres and the chemical compositions of residual solutions were analysed using solid state and solution 13C nuclear magnetic resonance and Fourier transform infrared spectroscopy. Based on these results, a four-step mechanism for the formation and growth of carbonaceous spheres has been proposed.

The development and characterisation of novel hybrid sol–gel-derived films for optical pH sensing

This paper focuses on the development and detailed characterisation of a novel hybrid sol–gel material derived from 3-glycidoxypropyltrimethoxysilane (GPTMS) and ethyltriethoxysilane (ETEOS). The material has been doped with a fluorescent pH-sensitive dye, modified 8-hydroxy-1,3,6-pyrene trisulfonic acid (HPTS) and its application as a high-performance optical ratiometric pH sensor has been demonstrated. The optimum sol–gel-based material composition has been characterised using atomic force microscopy (AFM), scanning electron microscopy in combination with energy dispersive X-ray spectroscopy (SEM-EDX), thermal gravimetric-infrared (TGA-IR) analysis, Fourier transform infrared (FT-IR) and Raman spectroscopy, solid state 29Si and 13C nuclear magnetic resonance (NMR). AFM and SEM images demonstrated a high degree of homogeneity of the pH films. FT-IR, Raman and NMR results have shown that hydrolysis and condensation reactions were almost completed and extensive crosslinking occurred in the final material. They also revealed that an opening of the epoxy ring in GPTMS took place which was key to optimum pH response. The pH sensor produced using the hybrid material compares very well with the current state-of-the-art and exhibits very good reversibility, reproducibility, stability, short response time and no leaching. The dynamic range extends from pH 5.0 to 8.0 which is compatible with bioprocessing, environmental and clinical monitoring applications.