Acidic Suspension Research Articles

Soursop juice stabilized with soy fractions: a rheologial approach

The potential use of soybean soluble polysaccharide (SSPS) as a stabilizer in acidic beverages was evaluated using rheological and stability studies. For this purpose, soy-based beverages were formulated with soy protein isolate (SPI) and soursop juice due to the low stability of this kind of dispersion. The influences of the concentrations of soybean soluble polysaccharide, calcium chloride, and soy protein isolate on the stability and rheology of soursop juice were evaluated using a factorial experimental design. Interactions between the concentrations of soybean soluble polysaccharide and soy protein isolate exerted a positive effect on the maximum Newtonian viscosity. The stability was positively influenced by the soybean soluble polysaccharide and soy protein isolate concentrations, but the interactions between soy protein isolate and CaCl2 also affected the sedimentation index. These results suggest that soybean soluble polysaccharide is effective in stabilizing fibers and proteins in acidic suspensions due to the increase in viscosity and steric effect caused by the formation of complexes between the soybean soluble polysaccharide and soy protein isolate.

In situ synthesis, characterization, and catalytic performance of tungstophosphoric acid encapsulated into the framework of mesoporous silica pillared clay

Mesoporous silica pillared clay (SPC) incorporated with tungstophosphoric acid (HPW) has been synthesized via in situ introducing P and W source in the acidic suspension of the clay interlayer template during the formation of the silica pillared clay. The samples were characterized by XRD, XRF, FT-IR, TG-DTA, N2 adsorption–desorption, and SEM techniques. The results showed that the HPW formed by in situ method has been effectively introduced into the framework of mesoporous silica pillared clay and its Keggin structure remained perfectly after formation of the materials. In addition, samples with similar HPW loadings were also prepared by impregnation method using SPC as the support. HPW in the incorporated samples was better dispersed into the silica pillared clay than in the impregnated samples. The results of catalytic tests indicated that the encapsulated materials demonstrated better catalytic performance than the impregnated samples in oxidative desulfurization (ODS) of dibenzothiophene (DBT).

Aqueous synthesis and transmission electron microscopy observation of seed-grown spherical ferrite nanoparticles

Uniform-sized spherical iron ferrite nanoparticles grew on seed crystals in an aqueous solution containing sucrose. Using the seed crystals which were highly dispersed in acidic or alkaline seed-crystal suspension without relation to pH of the suspension, we widely controlled the particle diameter in the range 20–200 nm by changing the additive amount of the seed crystals. By transmission electron microscopy observation and X-ray diffraction analysis, it indicated that the particles were highly crystalline but not amorphous. Selected area diffraction patterns of the particles by using transmission electron microscope revealed that the particles were composed of one to several crystals. Thus we provided the evidence that the particles grew on clusters composed of one to several seed crystals to which those of several dozen seed crystals were disintegrated.

The stability of halloysite nanotubes in acidic and alkaline aqueous suspensions

The long term stability of natural halloysite nanotubes was studied at room temperature (22 ± 2 °C) in pure water, acidic and basic aqueous suspensions. The structural and morphological transformations of nanotubes were studied by TEM, SEM, nitrogen adsorption, XRD Raman and FTIR spectroscopy accompanied by monitoring the concentration of dissolved Si(IV) and Al(III) in solution. It has been revealed that, in 1 mol dm−3 H2SO4 solution, the dissolution of halloysite is initiated on the inner surface of nanotubes, leading to the formation of amorphous spheroidal nanoparticles of SiO2 whereas, in 1 mol dm−3 NaOH solution, dissolution of the inner surface of nanotubes is accompanied by the formation of Al(OH)3 nanosheets.

Maximum Bleaching of Vegetable Oils by Acid-Activated Bentonite: Influence of Nanopore Radius

The optimum conditions necessary for preparing a bleaching earth (BE) with maximum bleaching power (BP) towards soybean oil (SO) and cottonseed oil (CSO) were investigated. BEs were obtained by H2SO4 activation of a white calcium bentonite (CaB) sample from the Kütahya region of Turkey. After drying for 4 h at 105 °C, the CaB samples were activated by heating their acidic aqueous suspensions for 6 h at 97 °C, the acid content of the dry bentonite/acid mixture being varied in the 0–70% mass range. The respective specific surface area (S) and specific nanopore volume (V) of the BEs were determined from nitrogen adsorption/desorption data obtained at −196 °C. For natural CaB, the values of S and V were 44 m2/g and 0.11 cm3/g, respectively. These values attained a maximum of 135 m2/g and 0.30 cm3/g for the BE sample prepared employing 40% H2SO4 for acid activation. Interestingly, the maximum BP was not associated with the maximum S and V values. The optimum values for the percentage H2SO4, S and V for attaining the maximum BP were 20%, 100 m2/g and 0.17 cm3/g, respectively. The mean nanopore radius (r) of each BE was calculated using the corresponding S and V values. Nanopores with a mean radius in the range 3.5–5.5 nm, which was close to the diameter of the coloured pigment, were found to be mostly responsible for the BP towards SO and CSO. The results obtained in the present study indicate that the value of r was more effective than the S and V values of BEs in the bleaching of vegetable oils. Adsorption of a pigment onto a BE was found to depend not only on the physicochemical interaction between the pigment molecule and the BE surface, but also on the mean nanopore size.

Synthesis of PMMA-co-PMAA Copolymer Brush on Multi-Wall Carbon Nanotubes

Poly(methyl methacrylate)/poly(methacrylamide) copolymer (PMMA-co-PMAA) was synthesized by a free radical copolymerization of MMA and MAA monomers in methylethyl ketone using AIBN as radical initiator. Multi-wall carbon nanotubes (MWCNT) were oxidized in KMnO4 acidic suspension. Carboxyl groups on the surface oxidized MWCNT were reacted with primary amide group of PMMA-co-PMAA copolymer in MEK solution under ultrasound to form polymer brush on the surface of MWCNT. With the help of TG analyses the amount of covalently grafted PMMA-co-PMAA copolymer onto MWCNT surface was determined as ?47 wt%. TEM analyses identified thin co-polymer layer adhered onto MWCNT surface with average thickness ?5 nm.

Unique photocatalytic oxidation reactivity and selectivity of TiO2–graphene nanocomposites

Mesoporous TiO(2)-graphene nanocomposites are fabricated in high yield via two successive steps: (1) hydrothermal hydrolysis of Ti(SO(4))(2) in an acidic suspension of graphene oxide to gain TiO(2)-graphene oxide nanocomposites; (2) UV-assisted photocatalytic reduction of graphene oxide to get the TiO(2)-graphene nanocomposites. The anatase TiO(2) nanocrystals with a crystallite size of 10-20 nm are densely packed and supported on meshy graphene sheets with close interfacial contacts, which is confirmed by transmission electron microscopy (TEM) together with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Although a low graphene loading (0-2 wt%) slightly influences the textural properties (including the crystallite size, specific surface areas, and pore volume etc.), the incorporation of graphene in TiO(2)-graphene nanocomposites greatly increases the adsorption capacity towards azo dyes such as MO and MB, which is possibly associated with their unique surface properties. Significantly, the incorporated graphene exerts combined effects on the adsorption and charge transfer dynamics in TiO(2)-graphene nanocomposites, which together endow them with good photocatalytic reactivity and tunable photocatalytic selectivity in decomposing MO and MB in aqueous solution.

Preparation, characterization and catalytic performance of the silica pillared clay incorporated with phosphotungstic acid using different surfactants as template

The mesoporous silica pillared clay (SPC) incorporated with Keggin-type H 3PW 12O 40 (HPW) heteropoly acid was prepared by introducing HPW into clay interlayer template in an acidic suspension using sol–gel method. The materials are readily separable mesoporous materials with high specific surface areas. The results indicate that the surfactants play a decisive role in the introduction of HPW molecule and the pore formation. Moreover, the surface area and pore size of the materials can be controlled by the molecular length and functional groups of the surfactants. The formation mechanism of the materials was also proposed. The synthesized materials exhibited good catalytic performance in oxidative desulfurization of dibenzothiophene-containing model oil. Under the best conditions, the sulfur removal can reach up to near 100%. The excellent catalytic performance for oxidative desulfurization opens up new opportunities for applications of the synthesized materials in catalysis.

Preparation, characterization and application in deep catalytic ODS of the mesoporous silica pillared clay incorporated with phosphotungstic acid

Mesoporous silica pillared clay (SPC) materials with different contents of H3PW12O40 (HPW) heteropoly acid were synthesized by introducing HPW into clay interlayer template in an acidic suspension using sol–gel method. Samples with similar HPW loadings were also prepared by impregnation method using SPC as the support. The results of the characterizations showed that HPW was dispersed more homogeneously in the encapsulated samples than in the impregnated samples. The encapsulated materials exhibited better catalytic performance than the impregnated samples in oxidative desulfurization of dibenzothiophene-containing model oil. The sulfur removal reached up to 98.6% for the model oil under the experiential conditions.

Photocatalytic reduction of nitrobenzenes to aminobenzenes in aqueous suspensions of titanium(iv) oxide in the presence of hole scavengers under deaerated and aerated conditions

Photocatalytic reduction of nitrobenzenes to corresponding aminobenzenes in aqueous suspensions of titanium(IV) oxide (TiO(2)) containing hole scavengers under various conditions was examined. In photocatalytic reduction of m-nitrobenzenesulfonic acid (m-NBS) in the presence of formic acid (FA) under deaerated conditions, m-aminobenzenesulfonic acid (m-ABS) was produced almost quantitatively in acidic suspensions and high efficiency (>99%) in FA utilization as a hole scavenger was achieved. No re-oxidation of m-ABS occurred in acidic conditions both in the presence and absence of FA. The high yield of m-ABS was explained by strong ability of FA as a hole scavenger and possible repulsion of the reduced functional group (ammonium group, -NH(3)(+)) from the protonated, i.e., positively charged TiO(2) surface in acidic suspensions avoiding re-oxidation of m-ABS. Using TiO(2) samples of various physical properties, which had been synthesized by a solvothermal method and post-calcination at various temperatures, effects of physical properties of the TiO(2) samples on m-ABS yield were also investigated. A linear correlation between the amount of m-NBS adsorbed and the m-ABS yield was observed, suggesting that ability of TiO(2) for m-NBS adsorption is one of the key factors for effective photocatalytic reduction of m-NBS to m-ABS. This photocatalytic system can be applied for reduction of aminonitrobenzenes to corresponding diaminobenzenes (DAB) in the presence of oxalic acid as a hole scavenger. High yields of m-ABS and DAB were achieved even when the reactions were performed in the presence of oxygen.

Photocatalytic degradation of reactive orange 16 dye over Au-doped TiO<SUB align=right>2 in aqueous suspension

The effect of nanosized Au deposits on TiO2 particles for the photocatalytic degradation of reactive orange 16 dye (RO 16) as model compound was investigated. The deposition of Au on TiO2 was carried out by deposition-precipitation (DP). The catalysts were characterised by XRD, TEM, and XPS analyses. The photocatalytic experiments were carried out under a radiation source of low-pressure mercury vapour lamp (6 W) emitting ultraviolet light with maximum intensity at 253.7 nm. The Au deposits significantly enhanced the degradation rate of the dye. The significant enhancement of the Au/TiO2 photocatalyst can be ascribed to the trapping of photogenerated electrons by nano-sized gold particles, which subsequently increase the lifetime of the photogenerated hole for oxidation process and also increased light absorption by crystalline defects. The catalytic activity was found to be dependent on the metal content on TiO2 and showed a maximum at 2 wt% Au. The amount of catalyst was optimised as 2.5 g/L. The photocatalytic activity was strongly dependent on the initial pH of the suspension; pH values in the range 5-10 showed better activity, whereas highly acidic and basic suspensions resulted in a considerable decrease in the activity.

In vitro Evaluation of Acyclovir/Chitosan Floating Systems.

Chitosan (CS) floating lyophilized formulations (L) for gastric drug delivery of acyclovir (ACV) have been developed. The freeze-dried formulations were obtained from acidic aqueous suspensions prepared with different ACV/CS ratios. No changes in ACV crystallinity were observed during X-ray diffraction powder studies as a consequence of the manufacturing process. Considering that fed and fasted states modified the intragastric pH, swelling and in vitro dissolution studies were carried out in different acidic media (0.1 M HCl and progressive pH medium) in order to understand the influence of these physiological states on ACV/CS formulations. Swelling behavior of the floating lyophilized formulations was dependent on CS and ACV proportions within L and on medium nature due to pH dependent CS solubility. Furthermore, no interactions between ACV and CS were detected in solid state according to the X-ray studies. In vitro dissolution of ACV from L was influenced by the swelling behavior. However, it is feasible to optimize the ACV/CS ratios to achieve a desired formulation that releases the total quantity of ACV at a specific time. Moreover, floatability was assessed by buoyancy tests. The results demonstrated that the freeze-drying process achieved effective floating systems capable of remaining within the stomach while the total amount of ACV is released from L.

Photoreductive dissolution of Fe‐containing mineral dust particles in acidic media

In this study, the photoreductive dissolution of Fe‐containing mineral dust particles in acidic media is investigated. Photolysis experiments were performed using a solar simulator to irradiate acidic mineral dust suspensions prepared from source materials of Inland Saudi sand (IS), Saharan sand (SS) and one commercial sample, Arizona test dust (AZTD). The results show that Fe dissolution is a pH‐dependent process, and total Fe solubility decreases with the solution pH increasing. Comparing iron dissolution from different source materials, Fe(II)‐containing AZTD is more soluble than IS and SS samples, irrespective of the presence or absence of light. Experiments performed at three different temperatures of 278, 293, and 308 K show that both total dissolved Fe and dissolved Fe(II) increase with temperature and upon light exposure. Results of dissolution studies with AZTD performed at low pH also illustrate that the nature of the acid strongly influences iron solubilization. Fe solubility decreases in the suspensions of H2SO4 and HNO3 in the presence of light, whereas Fe solubility increases in the HCl solution under the irradiation compared to the dark reaction. Finally, our results confirm earlier work showing that photoreductive dissolution of Fe is very sensitive to dissolved oxygen. Results from this laboratory study show that mineralogy and speciation of iron, as well as environmentally relevant factors including pH, light, O2, and nature of the inorganic anion, NO3−, SO42−, and Cl−, must be considered when modeling the input of iron to the oceans.

Identification of Surface Structures on 3C-SiC Nanocrystals with Hydrogen and Hydroxyl Bonding by Photoluminescence

SiC nanocrystals (NCs) exhibit unique surface chemistry and possess special properties. This provides the opportunity to design suitable surface structures by terminating the surface dangling bonds with different atoms thereby boding well for practical applications. In this article, we report the photoluminescence properties of 3C-SiC NCs in water suspensions with different pH values. Besides a blue band stemming from the quantum confinement effect, the 3C-SiC NCs show an additional photoluminescence band at 510 nm when the excitation wavelengths are longer than 350 nm. Its intensity relative to the blue band increases with the excitation wavelength. The 510 nm band appears only in acidic suspensions but not in alkaline ones. Fourier transform infrared, X-ray photoelectron spectroscopy, and X-ray absorption near-edge structure analyses clearly reveal that the 3C-SiC NCs in the water suspension have Si-H and Si-OH bonds on their surface, implying that water molecules only react with a Si-terminated surface. First-principle calculations suggest that the additional 510 nm band arises from structures induced by H(+) and OH(-) dissociated from water and attached to Si dimers on the modified (001) Si-terminated portion of the NCs. The size requirement is consistent with the observation that the 510 nm band can only be observed when the excitation wavelengths are relatively large, that is, excitation of bigger NCs.

Effect of pH on Carbon Dioxide Hydrate Formation in Mixed Soil Mineral Suspensions

We investigated the effect of pH on CO2 hydrate formation in the presence of phyllosilicate mixtures. Different pH conditions of phyllosilicate suspensions (Na-montmorillonite-rich and phyllosilicate-rich suspensions) with and without NaCl (3.5%) were prepared and controlled by the addition of an acid or base before the dissolution of CO2. The formation of CO2 hydrates was observed in all phyllosilicate suspensions (30 bar and 273.45 K). The temperature-time plot results showed that hydrate formations were suppressed more in acidic mineral suspensions than in basic suspensions. The fastest hydrate induction time can be observed in Na-montmorillonite-rich and phyllosilicate-rich suspensions with and without NaCl at near neutral conditions (pH 6-8), followed by basic (approximately pH 12.0) and acidic (approximately pH 2.0) pHs. Hydrate induction time can be significantly affected by various chemical species forming under different suspension pHs. The distribution of chemical species in each mineral suspension was estimated by a chemical equilibrium model, PHREEOC, and used for the identification of hydrate formation characteristics in the suspension. Particle-particle and particle-water interactions may possibly contribute to the delay of hydrate formation. NaCl was not an efficient inhibitor but a possible promoter for hydrate formation when pH-dependent solid surfaces were present in the system.

Photocatalytic Reduction of Nitrobenzene to Aniline in an Aqueous Suspension of Titanium(IV) Oxide Particles in the Presence of Oxalic Acid as a Hole Scavenger and Promotive Effect of Dioxygen in the System

Abstract Nitrobenzene was effectively and selectively reduced to aniline in an acidic aqueous suspension of titanium(IV) oxide photocatalyst in the presence of oxalic acid as a hole scavenger and the aniline yield was improved in the presence of a small amount of dioxygen.

Octahedral molecular sieves of the type K-OMS-2 with different particle sizes and morphologies: Impact on the catalytic properties in the aerobic partial oxidation of benzyl alcohol

Abstract Manganese-based octahedral molecular sieves of the type K-OMS-2 (cryptomelane structure) with different morphologies and specific surface areas in the range of 20–135 m2 g−1 were prepared via synproportionation of KMnO4 and Mn2+ salts, either in acidic aqueous suspension (reflux method) or by a solid-state reaction, and via oxidation of MnSO4 either by K2Cr2O7 or by molecular oxygen in aqueous solution. For the reflux method, the influence of K+ cations for the formation of the OMS-2 structure was proven. When KMnO4 is replaced by Ba(MnO4)2, the anion in the Mn2+ salt exerts a strong influence on the synthesis product. All materials were characterized by elemental analysis (ICP-OES), XRD, nitrogen sorption, scanning electron microscopy and TGA. For the oxidation of benzyl alcohol with molecular oxygen in liquid toluene at 110 °C, the catalytic activity of the K-OMS-2 materials is directly correlated to their specific surface area ABET. Since ABET increases with decreasing average crystallite diameter, the catalytic conversion presumably occurs at the outer crystallite surface. These relations are independent of morphology or synthesis procedure. The K-OMS-2 materials are more active than crystalline manganese oxides (MnO, Mn2O3, Mn3O4, β-MnO2), but less active than amorphous MnO2. Regeneration of deactivated K-OMS-2 catalysts can be achieved by calcining at 300 °C in air, partly due to the reversible desorption of water.

Iodide mediated electrolysis of acidic coke/coal suspension

Hydrogen is among the emerging energy vectors that are being developed to replace nonrenewable hydrocarbon energy sources. The preferred method to produce hydrogen without generating greenhouse gases is the electrolysis of water using renewable energy. The reduction of energy during the water electrolysis process is a desirable goal regardless of the source of electric power. Similar to ferrous/ferric mediation, iodide can be used as a mediator in the electrolysis of an acidic suspension of coke or coal. The iodide ion is oxidized at a far lower anodic potential than the alternative oxygen evolution reaction. This reduces the cell electrolysis voltage and, consequently, reduces electricity use. The iodide consumed at the anode is continuously regenerated by chemical reaction with the coke/coal in suspension.

Adsorption of itaconic acid from aqueous solutions onto alumina

Itaconic acid, IA (C5H6O4), was investigated as a potential flocculant for the aqueous processing of alumina powders. The adsorption of IA, as a function of its concentration and pH value of the solution, onto the alumina surface was studied by the solution depletion method. The stability of the suspensions in the presence of itaconic acid was evaluated in light of the surface charge of the alumina powder used, the degree of dissociation of IA, as well as the sedimentation behavior and rheology of the suspensions. It was found that the adsorption process is extremely pH dependent; the maximum adsorption of IA onto alumina surface occurring at a pH close to the value of the first IA dissociation constant, pKa1. Also, IA does not influence the value of the point of zero charge of alumina. It was shown that IA represents an efficient flocculant for concentrated acidic alumina suspensions.

Electrochemical capacitance of MWCNT/polyaniline composite coatings grown in acidicMWCNT suspensions by microwave-assisted hydrothermal digestion

Acidic suspensions of multi-walled carbon nanotubes (MWCNTs) in 5 MHNO3 solutions have been readily obtained by microwave-assisted hydrothermal digestion.FT-IR and XPS analyses indicated rapid functionalization of the surface of theMWCNTs could be achieved by a less environmentally hazardous approach. Compositecoatings of MWCNTs and polyaniline (PANI) were grown in situ onto graphiteelectrodes in an acidified suspension of MWCNTs and aniline. The as-grownMWCNT/PANI composites were characterized by SEM, cyclic voltammetry,chronopotentiometry and electrochemical impedance spectroscopy. The results confirmedthat the composite coatings had a lower resistance and much improved mechanical integritythan the pure PANI ones. The capacitance per geometric electrode surface area(F cm−2) of the composites increases linearly relative to the deposition charge, reaching as high as3.6 F cm−2, which can be compared favorably with the capacitance of2.3 F cm−2 of the pure PANI, and comparable to a capacitance of3.5 F cm−2 for the similar composite coating with the traditionally acid-treated carbon nanotubes. Theadvantage of the integrity of the MWCNTs after microwave exposure was used toimprove the conductivity and the mechanical strength of the composite coatings,especially when an utmost thick coating was attempted for a high capacitance.