Aqueous Slurry Systems Research Articles

Formation of CeO2 coatings on Si–SiC foams by electrophoretic deposition and sintering in air

Abstract We demonstrate that AC-EPD, using an aqueous slurry system followed by sintering in air, is an effective technique to form thick ceramic coatings on porous Si–SiC cellular ceramic substrates. As an example, CeO2 particles with high surface area dispersed in water have been deposited successfully on Si–SiC foams by optimizing the zeta potential and dispersion conditions. Moreover, the parameters for AC-EPD were determined by controlling voltage, frequency, time, and degree of signal asymmetry to minimize water electrolysis in this aqueous system. The microstructure of CeO2 layer has been controlled by adjusting sintering conditions to obtain porous and dense layers at 1200 and 1400 °C, respectively. The grain growth of the CeO2 deposit upon the heat treatment was explained by the diffusion of SiO2 into the CeO2 coating layer, which resulted in a firm joining with the Si–SiC substrate.

Electron transfer in ZnO–Fe2O3aqueous slurry systems and its effects on visible light photocatalytic activity

The strong interactions between ZnO and Fe2O3modify the nanocomposite's electronic structure producing efficient charge separation and superior photoactivity.

The effect of octenylsuccinylation on morphological, rheological, and in vitro digestibility properties ofCanna edulisKer starch

Canna edulisKer (canna) starch was modified in aqueous slurry systems with octenyl succinic anhydride (OSA) and the effect of four major reaction parameters (concentration of starch slurry (%), reaction time (h), reaction temperature (°C), and pH) on the degree of substitution (DS) were evaluated by both single‐factor and response surface methodology (RSM) methods. Octenylsuccinylation‐induced changes in morphological, rheological, andin vitrodigestibility properties were also examined. The RSM results indicated that the optimal conditions for the preparation of OSAcannastarch (DS = 0.0121) was 35% (w/v) starch concentration at pH 8.0, reacted at 35°C for 3.5 h, and the highest RS content obtained was 52.2%. Light microscopy revealed that octenylsuccinylation did not cause remarkable morphological changes as indicated by clear birefringence under polarized light. In conclusion, though octenylsuccinylation was a surface esterification, OSA‐modification increased the viscosity ofcannastarch dramatically. However, increased DS did not further improve the viscosity of OSAcannastarch, possibly due to high amounts of RS.

Photosensitizing Properties of Thiolated Gold Clusters. Exploring Beyond Plasmonics

Metal nanoparticles possess unusual catalytic and optical properties. Specifically, larger size particles exhibit plasmonic effects as they interact with incident photons. However, the plasmon resonance activity ceases as the size of metal nanoparticles decrease. However, such small size nanoparticles with few atom metal clusters continue to exhibit photoactivity in the visible. The gold clusters containing 10-25 metal atoms exhibit molecular like properties with relatively long lived excited state (lifetime ∼ 800 ns). When a mesoscopic TiO2 film sensitized by Aux-GSH NCs was used as the photoanode in a photoelectrochemical cell, we can generate photocurrent under visible light irradiation with a photoconversion efficiency of 2%. The reversible reduction (E0= -0.63 V vs. RHE) and oxidation (E0= 1.51 V vs. RHE) potentials make them suitable as visible sensitizers for driving the water splitting reaction. Additionally, sensitizing Pt/TiO2 nanoparticles with Aux-GSH NCs has been explored in an aqueous slurry system and irradiating with visible light resulted in hydrogen production. These metal nanoclusters which serve as a new class of visible photosensitizers exhibit significantly higher photoactivity than the larger nanoparticles and thus offer new opportunities as light harvesting assemblies.

Glutathione-Capped Gold Nanoclusters as Photosensitizers. Visible Light-Induced Hydrogen Generation in Neutral Water

Glutathione-capped metal nanoclusters (Aux-GSH NCs) which exhibit molecular-like properties are employed as a photosensitizer for hydrogen generation in a photoelectrochemical cell (PEC) and a photocatalytic slurry reactor. The reversible reduction (E(0) = -0.63 V vs RHE) and oxidation (E(0) = 0.97 and 1.51 V vs RHE) potentials of these metal nanoclusters make them suitable for driving the water-splitting reaction. When a mesoscopic TiO2 film sensitized by Aux-GSH NCs is used as the photoanode with a Pt counter electrode in aqueous buffer solution (pH = 7), we observe significant photocurrent activity under visible light (400-500 nm) excitation. Additionally, sensitizing Pt/TiO2 nanoparticles with Aux-GSH NCs in an aqueous slurry system and irradiating with visible light produce H2 at a rate of 0.3 mmol of hydrogen/h/g of Aux-GSH NCs. The rate of H2 evolution is significantly enhanced (∼5 times) when a sacrificial donor, such as EDTA, is introduced into the system. Using metal nanoclusters as a photosensitizer for hydrogen generation lays the foundation for the future exploration of other metal nanoclusters with well-controlled numbers of metal atoms and capping ligands.

Enhancing the surface properties of the immobilized Degussa P-25 TiO2 for the efficient photocatalytic removal of methylene blue from aqueous solution

A method has been developed for enhancing the surface properties of immobilized Degussa P-25 TiO2 nanoparticles on glass plate supports with excellent photocatalytic activity. The immobilization technique utilized a dip-coating method involving a coating solution containing Degussa P-25 TiO2 particles, epoxidized natural rubber (ENR-50) and poly vinyl chloride (PVC) in a mixture of toluene and dichloromethane. The optimum ratio of ENR/PVC blend was found to be 1:2. Immobilization process of the composite appeared to reduce the specific surface area by at least half of the pristine P-25 TiO2 particles. However, a systematic removal of ENR-50 additive via a 5h photocatalytic process enabled the immobilized photocatalyst (P-25TiO2/ENR/PVC/5h) to regenerate the surface area to within 86% of the pristine P-25 TiO2 particles, produce bigger pore volume and smaller particle size. The enhanced surface properties of the immobilized P-25/ENR/PVC/5h photocatalyst system generated a photocatalytic performance as good as the slurry method of the P-25 TiO2 nanoparticles for the photocatalytic degradation of MB dye in aqueous solution. The immobilized P-25TiO2/ENR/PVC/5h catalyst plate was also found to be highly reusable up to at least 10 runs without losing its photocatalytic efficiency. Above all, the system could avoid tedious filtration step of the treated water as normally observed with the aqueous slurry system.

Characteristics and application of octenyl succinic anhydride modified waxy corn starch in sausage

AbstractNative and acid‐hydrolyzed wx corn starches were modified by octenyl succinic anhydride (OSA) in aqueous slurry systems. The characteristics of the modified wx corn starches and their effects on chicken meat sausages were evaluated by means of FT‐IR, rapid visco analyser, SEM, and texture profile analysis. FT‐IR spectroscopy indicated that the ester carbonyl groups in the OSA modified native and acid‐hydrolyzed starches were characterized at 1725 cm−1. The process of OSA modification could achieve starch derivatives, which had higher viscosities, better paste clarity and freeze–thaw stability than the native counterparts. Texture results showed that the hardness, springiness, cohesiveness, and chewiness of the sausage increased as OSA‐H0 was added (p < 0.05). SEM revealed that the sausages with native wx corn starch had larger and uneven pores, while it was comparatively compact for the sausages with OSA starches. The OSA modified wx corn starch offered a great potential to be used in meat products to enhance textural quality.

Synthesis of Octenyl Succinic Derivative of Mechanically Activated Indica Rice Starch

AbstractIndica rice starch was mechanically activated by ball milling and then esterified by octenyl succinic anhydride (OSA) in aqueous slurry systems. The process of esterification was studied with respect to the time of mechanical activation, OSA/starch ratio, temperature, pH, starch slurry concentration and reaction time. The effects of these reaction conditions were evaluated on the basis of degree of substitution (DS) and reaction efficiency (RE). The results indicated that mechanical activation could enhance the reaction of OSA and starch. The DS and RE of OSA starch increased sharply when the time of mechanical activation increased from 0 h to 10 h, after which it was not significantly affected until 50h. The suitable conditions for the synthesis of OSA starch from Indica rice starch that was mechanically activated for 10 h (MAIS10) were an OSA/starch ratio 3%, temperature 35°C, pH 8.5, starch slurry concentration 12.5% and reaction time 3h. For native Indica rice starch (NIS), all conditions were identical to MAIS10 except for the starch slurry concentration of 40% and reaction time of 4 h. The maximum DS and RE of OSA‐MAIS10 (0.02037, 88.03%) was higher than that of OSA‐NIS (0.01700, 73.46%) at OSA/starch ratio 3%. The esterification of MAIS10 with OSA showed a low sensitivity to pH and a higher stability than OSA‐NIS. Scanning electron microscopy (SEM) revealed that the modified OSA starches did not show any detectable change in the morphological structural characteristics. The esterification between OSA and starch was confirmed by Fourier transform infrared (FT‐IR) spectroscopy.

Preparation and properties of octenyl succinic anhydride modified potato starch

Potato starch was esterified with octenyl succinic anhydride (OSA) in aqueous slurry systems and the major factors affecting the esterification were systematically investigated. The physico-chemical properties of the products were determined by means of Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction and a viscosity analyser (VA). The results indicated that suitable parameters for the preparation of OSA starch from potato in aqueous slurry systems were as follows: concentration of starch slurry, 35% (in proportion to water, w/w), reaction period, 3 h, pH of reaction system, 8.0, reaction temperature, 35 °C, amount of OSA, 3% (in proportion to starch, w/w), OSA dilution-fold, 5. The degree of substitution (DS) was 0.017 and the reaction efficiency (RE) was 72 ± 1.8%. FT-IR spectroscopy showed characteristic absorption of the ester carbonyl groups in the OSA starch at 1724 cm −1. SEM and X-ray diffraction revealed that OSA groups acted by first attacking the surface and some pores formed, but OSA modification caused little change in the crystalline pattern of potato starch (DS 0.045). Apparent pastiness measurement indicated that the starch derivatives gelatinized within a shorter time to achieve higher viscosities over the range of designed concentration of OSA potato starch.

Synthesis and paste properties of octenyl succinic anhydride modified early Indica rice starch.

Octenyl succinic anhydride (OSA) modified early Indica rice starch was prepared in aqueous slurry systems using response surface methodology. The paste properties of the OSA starch were also investigated. Results indicated that the suitable parameters for the preparation of OSA starch from early Indica rice starch were as follows: reaction period 4 h, reaction temperature 33.4 degrees C, pH of reaction system 8.4, concentration of starch slurry 36.8% (in proportion to water, w/w), amount of OSA 3% (in proportion to starch, w/w). The degree of substitution was 0.0188 and the reaction efficiency was 81.0%. The results of paste properties showed that with increased OSA modification, the starch derivatives had higher paste clarity, decreased retrogradation and better freeze-thaw stability.

Preparation and Properties of Octenyl Succinic Anhydride Modified Early Indica Rice Starch

AbstractOctenyl succinic anhydride (OSA) modified early indica rice starch was prepared in aqueous slurry systems and the major factors affecting the esterification were investigated systematically. The physicochemical properties of the products were determined by means of Fourier transform infrared (FT‐IR) spectroscopy, scanning electron microscopy (SEM), X‐ray diffraction and Rapid Visco Analyser (RVA). The results indicated that the suitable parameters for the preparation of OSA starch from early indica rice starch in aqueous slurry systems were as follows: concentration of starch slurry 35% (in proportion to water, w/w), reaction period 4 h, pH of reaction system 8.5, reaction temperature 35°C, amount of OSA 3% (in proportion to starch, w/w). The degree of substitution (DS) was 0 018 and the reaction efficiency (RE) was 78%. FT‐IR spectroscopy showed characteristic absorption of the ester carbonyl groups in the OSA starch at 1724 cm‐1. SEM and X‐ray diffraction revealed that OSA groups acted by first attacking the surface and some pores formed, but OSA modification caused no change in the crystalline pattern of rice starch up to DS 0.046. RVA results indicated that the starch derivatives gelatinized at shorter time to achieve higher viscosities with increased OSA modification.

Studies of Starch Esterification: Reactions with Alkenylsuccinates in Aqueous Slurry Systems

Starch esters prepared by modifications with hydrophobic alkenyl succinic anhydrides provide an opportunity to regulate the hydrophobic characteristics of these products. This is of great interest since many potential applications of modified starch products exploit their amphiphilic character. The objective of this work was to develop a greater understanding of how the reaction parameters in aqueous slurry reactions affect the efficiency of starch modification with dodecenyl succinic anhydride (DDSA). A systematic study was performed to determine how changes in the starch concentration, starch/anhydride ratio, pH, temperature, and reaction time affect the efficiency of esterification. Surprisingly, variations in the starch concentration (25 to 65 % w/w relative to water) at a 10 % anhydride concentration (w/w relative to starch) caused little change in the reaction efficiency. Maintaining the reaction within a pH range of 8.5–9.0 and at a temperature between 22 and 27 °C was preferred. The reaction efficiency decreased as the ratio of anhydride to starch increased. Also, extending the reactions beyond 48 h resulted in products of lower substitution. After a set of preferred reactions conditions were established, a comparison of reaction efficiencies as a function of the n-alkenyl chain length of the anhydrides used was performed. As the alkenyl chain length increased from 8 to 18 carbons a substantial decrease in the reaction efficiency occurred.

Studies of Starch Esterification: Reactions with Alkenylsuccinates in Aqueous Slurry Systems

Starch esters prepared by modifications with hydrophobic alkenyl succinic anhydrides provide an opportunity to regulate the hydrophobic characteristics of these products. This is of great interest since many potential applications of modified starch products exploit their amphiphilic character. The objective of this work was to develop a greater understanding of how the reaction parameters in aqueous slurry reactions affect the efficiency of starch modification with dodecenyl succinic anhydride (DDSA). A systematic study was performed to determine how changes in the starch concentration, starch/anhydride ratio, pH, temperature, and reaction time affect the efficiency of esterification. Surprisingly, variations in the starch concentration (25 to 65 % w/w relative to water) at a 10 % anhydride concentration (w/w relative to starch) caused little change in the reaction efficiency. Maintaining the reaction within a pH range of 8.5–9.0 and at a temperature between 22 and 27 °C was preferred. The reaction efficiency decreased as the ratio of anhydride to starch increased. Also, extending the reactions beyond 48 h resulted in products of lower substitution. After a set of preferred reactions conditions were established, a comparison of reaction efficiencies as a function of the n-alkenyl chain length of the anhydrides used was performed. As the alkenyl chain length increased from 8 to 18 carbons a substantial decrease in the reaction efficiency occurred.

Effect of Aliphatic Nonaqueous Phase Liquids on Naphthalene Biodegradation in Multiphase Systems

AbstractBiodegradation of naphthalene by a Coryneform bacterium was examined in multiphase aqueous slurry systems containing a nonaqueous phase liquid (NAPL). The evolution of 14CO2 provided an index of biodegradation under aerobic conditions. The effect of NAPL hydrophobicity was evaluated by considering a homologous series of n‐alkanes (C6–C16). Experiments were conducted in NAPL‐water and soil‐NAPL‐water systems where the inoculum was pre‐incubated with a sandy aquifer material. Relative to aqueous systems, conversion to CO2 increased in the presence of decane, dodecane, and hexadecane. Biodegradation was apparent, but decreased in the presence of octane, and was negligible in the presence of hexane. Thus biodegradation was sustained in multiphase systems where log Kow of the NAPL was >5, and was inhibited in systems where the log Kow of the NAPL was <4. Naphthalene partitioning between water and each of the NAPLs was similar, indicating that the observed differences in biodegradation among the homologous series were not due to differences in naphthalene distribution. Naphthalene sorption to the sandy aquifer material was minimal and the aquifer material did not significantly modify biodegradation. Mineralization rates were reduced in multiphase systems when compared with aqueous systems; CO2 production curves were described with a first‐order kinetic model. Reduced mineralization rates in soil‐NAPL‐water systems can be explained by the lower aqueous phase concentration. This was not the case in the NAPL‐water system, suggesting a direct effect of the NAPL on the bacteria.

Fission Fragment Impact Trapping by ThO2Slurry Particles

Assuming a uniform distribution of ThO2 slurry particles suspended in an aqueous medium, the probability of a recoil fission fragment escaping the parent slurry particle and then coming to rest within another slurry particle has been estimated. The results indicate that for the slurry particle diameters and volume concentrations that may be expected in certain homogeneous reactor systems only a small percentage of the fission fragments will end their range within slurry particles. The theoretical predictions compare favorably with experimental results from a U-0 aqueous slurry system.