Higher NaOH Concentrations Research Articles

Controllable synthesis of sodalite submicron crystals and microspheres from palygorskite clay using a two-step approach

Sodalite submicron crystals and microspheres were successfully synthesized from natural palygorskite clay through a two-step approach by varying the synthetic parameters. The effects of initial NaOH concentration, SiO2/Al2O3 molar ratio, and aluminium source on the morphology and particle size of synthetic sodalite were investigated, as well as the formation scheme of synthetic sodalite. Experimental results showed that the alkalinity of the synthesis gel controlled by initial NaOH concentration and SiO2/Al2O3 molar ratio was a critical factor for the formation of sodalite crystals and microspheres. Sodalite crystals could be synthesized at high initial NaOH concentration and SiO2/Al2O3 molar ratio, however, low initial NaOH concentration and SiO2/Al2O3 molar ratio were beneficial for the formation of sodalite microspheres via submicron crystal aggregation.

Effect of Mineralizer on the Hydrothermal Synthesis of Bi<sub>0.5</sub>Na<sub>0.5</sub>TiO<sub>3</sub> Lead-Free Piezoelectric Crystals

The effect of mineralizer upon the fabrication of lead-free, piezoelectric Bi0.5Na0.5TiO3 ( BNT) was investigated using a hydrothermal reaction technique. Results indicated that BNT crystals can be formed in a basic environment controlled by a NaOH mineralizer. The morphologies and sizes of the resultant particles are determined by the concentration of NaOH: a lower alkaline concentration leads to the particles with a spherical shape consisting of a number of small, intergrown BNT crystals while a higher NaOH concentration (e.g. > 12 mol/L) results in large, individual BNT cubes. Possible growth mechanisms of the BNT particles were discussed in conjunction with surface hydration, dehydration and free water content during the hydrothermal reaction.

Degradation of Poly(l-Lactic Acid) and Bio-Composites by Alkaline Medium Under Various Temperatures

Ribbons of poly(lactic acid) (PLA) and PLA containing 10 or 25% Osage Orange (OO) biocomposites of various sized heartwood particles were exposed to non-composting soil conditions either outdoors or in a greenhouse. No appreciable degradation was evident after 208 day treatments. An artificial alkaline degradation test system was developed to reduce the study time required to evaluate PLA compositional properties on degradation. Ribbons of PLA and PLA-OO biocomposites of various sized particles were subjected to hydrolysis in alkaline concentrations (0, 0.05, 0.1, 0.15, and 0.25 M NaOH) under various temperatures (15, 20, 25, 30, 35, 40, and 80 °C) up to 56 days. Higher concentrations of NaOH (e.g., 0.25 M) caused more dramatic and rapid deterioration of PLA and PLA-OO composites than lower NaOH concentrations for all temperatures tested. Incubation in either the low temperatures (15 and 20 °C) or the highest temperature (80 °C) was consistently more effective in PLA-OO degradation than employing 35 or 40 °C. Several alkaline and temperature test combinations are offered to study accelerated PLA degradation. Ribbons immersed in NaOH were examined with the scanning electron microscope to analyze for morphological alterations.

Crystal transition from cellulose I to cellulose II in NaOH treated Agave americana L. fibre

This study investigates the cellulose polymorphic transformation of Agave americana L. fibre during alkali processing at different NaOH concentrations. X-ray diffraction was used. The polymorphic transition from cellulose I to cellulose II begun at NaOH concentrations at the order of 5–10% and the complete transformation was achieved for the alkali concentration of 15%.The crystallinity index of agave fibre increased for alkali treatments not exceeding 2% (w/v), whereas higher NaOH concentrations (>2%) induce a considerable decrease of the crystallinity index. The unit cell parameters of A. americana L. fibre vary with the NaOH concentration which results from the formation of different alkali celluloses during the mercerisation process.As far as mechanical properties are concerned, treatments with low alkali concentrations produce fibres that are stronger than the untreated fibres, whereas treatments with high concentrations (>2% w/v) result in weaker fibres.

Anchorage of steel bars in concrete by geopolymer paste

This paper presents the bonding strength between the embedded rebar and substrate concrete by using geopolymer paste as the bonding agent. The determination of the suitable mix proportions of geopolymer paste as bonding agent was the main interest. Twelve different mix proportions of geopolymer paste by varying the amount of starting binder materials and alkaline concentration were prepared and tested for compressive and bonding strengths. The tested results indicated that both RHBA and SF incorporating with FA could be used in preparation of geopolymer paste. Mixes with SF gave the higher compressive and bonding strengths while the mixes with RHBA required the longer curing time. The bonding strengths of round bar and geopolymer pastes were slightly higher than that of control concrete (1.05–1.12 times) and there were significantly high in case of deformed bars (1.03–1.60 times). The ratios of bonding strength on the compressive strength were also presented. In comparison with commercial repair materials, the bonding strengths of geopolymer paste were higher than those of epoxies about 1.24–1.81 times. These tested results indicated that the bonding strengths using geopolymer paste were high enough and possibly used as bonding material for repair works. The mixtures containing high SF content and high NaOH concentrations were recommended to enhance both compressive and bonding strengths.

Formation of titanate nanostructures under different NaOH concentration and their application in wastewater treatment

The effects of the concentration of NaOH on the formation and transformation of various titanate nanostructures were studied. With increasing NaOH concentration, three different formation mechanisms were proposed. Nanotubes can only be obtained under moderate NaOH conditions, and should transform into nanowires with prolonged hydrothermal treatment, and their formation rate is accelerated by increasing NaOH concentration. Low concentration of NaOH results in the direct formation of nanowires, while extra high concentration of NaOH leads to the formation of amorphous nanoparticles. Adsorption and photocatalysis studies show that titanate nanowires and nanotubes might be potential adsorbents for the removal of both heavy metal ions and dyes and photocatalysts for the removal of dyes from wastewater.

CuO/Cu(OH)2 hierarchical nanostructures as bactericidal photocatalysts

Various morphologies of CuO/Cu(OH)2 nanostructures with different adsorbed –OH contents were synthesized on an acid-treated Cu foil through variation of NaOH concentration from 0 to 50 mM with an in situoxidation method. X-ray diffractometry and X-ray photoelectron spectroscopy (XPS) indicated formation of CuO on the Cu(OH)2 crystalline phase at a growth temperature of 60 °C for 20 h. Antibacterial activity of the nanostructures against Escherichia coli bacteria was studied in the dark and under light irradiation. The nanostructures grown at a NaOH concentration of 30 mM showed the highest surface area and the strongest antibacterial activity among the samples. After elimination of the contribution of the effective surface area of the nanostructures to the antibacterial activity, it was found that the surface morphology and chemical composition of the nanostructures were the other most important parameters in the antibacterial activity of the nanostructures. Using XPS analysis, the better photocatalytic activity per surface area of the nanostructures prepared at higher NaOH concentrations was substantially attributed to the amount of adsorbed OH bonds on the surface of the nanostructures.

The Effect of Coal Fly Ash Crystallinity toward Methyl Violet Adsorption Capacity

Coal fly ash (CFA) generated by coal-based thermal power plants is mainly composed of some oxides having high crystallinity, like quartz and mullite. In this study, the effect of CFA crystallinity toward methyl violet (MV) adsorption capacity was investigated. To decrease crystallinity of CFA, the solution of sodium hydroxide (NaOH) of 1-7 M was used to treat CFA at various temperatures and reflux time. Then, to evaluate the effect of NaOH-treated CFA with respect to adsorption capacity, the original and NaOH-treated CFA were tested its MV adsorption capacity in batch experiments. Original or NaOH-treated CFA was contacted with 50 mL of MV solution at temperature of 26 o C. The effects of contact time, pH of solution, adsorbent dose and initial concentration of dye on the adsorption of MV were investigated. The results show that CFA treated with low NaOH concentration (1-3 M), temperature of 60 o C and 2 hours reflux time, the crystallinity of quartz and mullite decreases, but its capacity on MV adsorption increases from 34% to 97%. At higher NaOH concentration (>3M), in the range of studied reflux temperature and time, it is found that decreasing quartz and mullite crytallinity are followed by a hydroxysodalite formation which causes the decreasing of MV adsorption from 97% to 83%. The highest adsorption capacity of NaOH-treated CFA was found 1.24 x 10-5 mol g -1 . Adsorption kinetics of MV onto NaOH-treated CFA could be approximated with a pseudo second order kinetic model with the rate constant was 3.2 x 10 3 g mol -1 min -1 .

Activation of H2O2 by methyltrioxorhenium(VII) inside β-cyclodextrin

The effect of β-cyclodextrin on the catalytic stability and reactivity of methylrhenium trioxide (MTO), CH3ReO3, which has been used for activation of hydrogen peroxide toward oxidation and epoxidation reactions, was studied using UV–Vis spectrophotometery. The stability and reactivity of the new catalytic system (MTO/β-CD) to activate H2O2 toward oxidation of indigo blue dye were investigated in basic media. Furthermore, effects of inclusion stoichiometry, temperature and concentrations of hydrogen peroxide on the stability and reactivity of the MTO/β-CD system were investigated. The formation of the inclusion complex between MTO and β-CD was confirmed experimentally using the changes in the UV–Vis absorption spectra. The results of this study demonstrate that the complexation process was better guaranteed when the amount of β-CD is higher than that of MTO, using a 1:2 molar ratio of MTO:β-CD enhances both the activity and stability of the catalyst. The results showed that the stability of the catalytic system was enhanced in presence of β-CD with maintaining good reactivity of the MTO even in the presence of high concentration of NaOH. The changes of thermodynamic activation parameters (ΔH≠ and ΔS≠) for the oxidation reaction of indigo with H2O2 catalyzed by MTO/β-CD system were determined on the basis of the experimental data.

Development of a model of benign esophageal stricture in rats: the optimal concentration of sodium hydroxide for stricture formation

To investigate the optimal concentration of sodium hydroxide (NaOH) on esophageal stricture formation in rats to establish an animal model of benign esophageal stricture (BES). Corrosive esophageal burn was produced by internal application of different concentrations of NaOH to the distal esophagus in rats. As much as 66 male rats were randomly divided into eight groups: Group A (control, n = 6), Group B (sham-operated group, n = 6), Group C (5% NaOH, n = 8), Group D (10% NaOH, n = 8), Group E (20% NaOH, n = 8), Group F (30% NaOH, n = 10), Group G (40% NaOH, n = 14), and Group H (50% NaOH, n = 6). Surviving rats were killed at 28 days. The survival rate, body weight gain, symptoms, and histopathological changes were assessed. The mortality rate was high in Groups G and H (73 and 67%). The prevalence of symptoms of BES was 43% in Groups D and E, 50% in Group F, 75% in Group G, and 100% in Group H. Statistically significant stricture formation of the esophagus was observed in Groups F and G. The degree of tissue damage was significantly higher in Groups E, F, and G. A high concentration of NaOH of 30% was required to establish a survivable BES model in rats.

The effects of alkali treatment on the interfacial adhesion of bamboo fibres

In the present work, the potential of using bamboo fibres as reinforcement for polyester composites was evaluated. Two types of bamboo fibres were used: untreated and treated with different NaOH concentrations (1, 3, and 5wt%). Mechanical properties of both treated and untreated fibres were investigated. In addition, single-fibre pull-out tests were performed to study the interfacial shear strength of the fibres with the polyester matrix at different embedment length of fibres. Scanning electron microscopy was used to study the surface morphology of the fibres before and after the tests. Results revealed that an untreated fibre has the best strength and stiffness but lowest strain at break. An increase in alkali concentration reduces the strain at failure and ductility of bamboo fibres. However, the strength and stiffness of the fibres were increased. In addition, the interfacial shear strength was improved with longer embedment length and higher NaOH concentration.

Alkali-aided enzymatic viscosity reduction of sugar beet mash for novel bioethanol production process

Abstract Ethanol fermentation of fresh sugar beet mash (SBM) could give a benefit on reducing energy input for sugar diffusion, juice separation, and water evaporation as used in conventional practices, thus offering promise as a low energy process. Actions of cell-wall degrading enzymes provide a mash with low viscosity, which can be easily fermented to ethanol. However, a several-fold higher enzyme loading was required for viscosity reduction of SBM compared with that of potato mash. In this study, the use of dilute alkali treatment (0.025–0.15 N NaOH, 25 °C, 1 h) in enhancing enzymatic viscosity reduction of SBM was evaluated. The results showed that higher NaOH concentration enhanced demethylation and deacetylation of SBM, resulting in greater performances of the enzymes on reducing viscosity. Efficient enzymatic viscosity reduction of SBM was observed with the 0.1 N NaOH treatment. On the other hand, untreated SBM was highly resistant to viscosity reduction, even though a 20-fold more enzyme loading was used. The resulting mash containing 12–13% (w/v) sucrose yielded 7–8% (v/v) ethanol after 24 h of fermentation (90% efficiency). Accordingly, alkali treatment can be applied for facilitating the use of fresh sugar beet for ethanol production.

Single-step polyol synthesis of alloy Pt7Sn3 versus bi-phase Pt/SnOx nano-catalysts of controlled size for ethanol electro-oxidation

Disordered alloy and bi-phase PtSn nanoparticles of nominal Pt:Sn ratio of 70:30 atomic % with controlled size and narrow size distribution were synthesized using a single-step polyol method. By adjusting the solution pH it was possible to obtain Pt7Sn3 nanoparticles of various sizes from 2.8 to 6.5 nm. We found that the presence of NaOH in the synthesis solution not only influenced the nanoparticle size, but as it was revealed by XRD, it apparently also dictated the degree of Pt and Sn alloying. Three catalysts prepared at lower NaOH concentrations (CNaOH < 0.15 M) showed disordered alloy structure of the nominal composition, while the other three catalysts synthesized at higher NaOH concentrations (CNaOH > 0.15 M) consisted of bi-phase nanoparticles comprising a crystalline phase close to that of pure Pt together with an amorphous Sn phase. These observations are plausibly due to the phase separation and formation of monometallic Pt and amorphous SnOx phases. A proposed reaction mechanism of Pt7Sn3 nanoparticle formation is presented to explain these observations along with the catalytic activities measured for the six synthesized carbon-supported Pt7Sn3 catalysts. The highest catalytic activity towards ethanol electro-oxidation was found for the carbon-supported bi-phase catalyst that formed the largest Pt (6.5 nm) nanoparticles and SnOx phase. The second best catalyst was a disordered alloy Pt7Sn3 catalyst with the second largest nanoparticle size (5 nm), while catalysts of smaller size (4.5–4.6 nm) but different structure (disordered alloy vs. bi-phase) showed similar catalytic performance inferior to that of the 5 nm disordered alloy Pt7Sn3 catalyst. This work demonstrated the importance of producing bi-metallic PtSn catalysts with large Pt surfaces in order to efficiently electro-oxidize ethanol.

Effects of Hydrothermal Conditions of ZrO2 on Catalyst Properties and Catalytic Performances of Ni/ZrO2 in the Partial Oxidation of Methane

ZrO2 was prepared via the hydrothermal method and used as the support of nickel catalysts in the partial oxidation of methane to syngas. The hydrothermal conditions (such as hydrothermal temperature, hydrothermal time, and the concentration of NaOH used) necessary for ZrO2 preparation were investigated and optimized. The physicochemical properties of ZrO2 supports and Ni/ZrO2 catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption, temperature-programmed reduction (TPR), and thermogravimetric analysis (TGA). The results showed that low hydrothermal temperatures, short hydrothermal time, and low concentrations of NaOH benefited the formation of tetragonal ZrO2. Elevating the hydrothermal temperature (from 160 °C to 200 °C), prolonging the hydrothermal time (from 6 h to 48 h), or increasing the concentration of NaOH (from 5 wt % to 40 wt %) would lead to the disappearance of tetragonal ZrO2 and an increase in the degree of monoclinic ZrO2 crystallization. The Ni/ZrO2 catalysts with ZrO2 prepared with high NaOH concentration or with ZrO2 prepared at long hydrothermal times possessed excellent catalytic activities and resistance to carbon formation. Whereas the Ni/ZrO2 catalysts with ZrO2 prepared with low NaOH concentration or with ZrO2 prepared at short hydrothermal time deactivated soon because of carbon deposition.

Viability and surface properties of spores subjected to a cleaning-in-place procedure: Consequences on their ability to contaminate surfaces of equipment

This study was designed to evaluate how conditions encountered by spores during cleaning-in-place (CIP) procedures affected their surface properties, their viability and ability to contaminate materials. Spores from five Bacillus cereus strains were treated with NaOH at high temperature. Results revealed that high temperatures (exceeding 60 °C) and NaOH concentrations (over 0.5%) were required to significantly decrease spore viability (3–5 log decrease). In these conditions, modifications were also clearly observed by microscopy to various surface structures of spores (appendages, exosporium, and especially to the hair-like nap) but also to their coat. Therefore, the ability of culturable spores to adhere decreased for the majority of strains tested. We then demonstrated that spores in suspension in NaOH could adhere to surfaces of a CIP rig and that the contamination level was controlled by flow pattern. Consequently, re-adhesion along the processing line might occur during CIP procedures and this phenomenon must be taken into account when defining cleaning strategies.

Synthesis and characterization of nickel chains assembled by microspheres via a polymer-free hydrothermal method

Ni chains assembled by Ni spheres have been synthesized via a polymer-free hydrothermal approach. The products were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectrometry (XPS). In order to investigate the formation mechanism of the Ni chains, a series of assistant experiments have been performed. These experiments demonstrated that the pre-formation of Ni(C 4H 2O 6) 2− and the presence of high concentration of NaOH were two important factors for the formation of Ni chains. Based on the results of assistant experiments, a growth mechanism for Ni chains was proposed. The magnetic property investigation of the obtained Ni chains illustrated that they have ferromagnetic behavior and significantly enhanced coercivity. Such a simple hydrothermal process can be expanded to fabricate chains of other materials.

Preparation and characterization of Na-LTA zeolite from Tunisian sand and aluminum scrap

Pure Na-A (LTA) zeolite has been prepared from aluminosilicate gel obtained by a mixture of metasilicate and aluminate solutions. Metasilicate sol; used as silica source; was prepared from an alkaline attack of Tunisian sand in an autoclave under agitation at 220 ∘C and pressure of 27 bar. The aluminate solution was obtained by dissolution of aluminium scraps in NaOH solution. The crystallization of Na-LTA zeolite is controlled by the alkalinity of the mixture and the reaction time. At 90 ∘C, well crystallized LTA have been obtained after 3h. The Zeolite LTA converts into the more stable HS after long reaction times according to Ostwald’s law. The alkalinity of the reaction mixture changes the nature of the obtained zeolite. At lower NaOH concentration (0.1 M), Na-X zeolite was obtained; whereas the crystallization of LTA was promoted at higher NaOH concentration (3M).

Synthesis of monodispersed mesoporous silica spheres (MMSSs) with controlled particle size using gemini surfactant

A series of mesoporous silica spheres with tunable particle size were synthesized by the self-assembly of cationic gemini surfactant and silica source under basic condition. By varying the initial synthesis conditions, such as molar composition, temperature and addition of co-solvent, the particle sizes of the MMSSs with radially oriented pore structure were controlled in a range of 120–490nm, and the pore sizes changed from 2.2 to 3.4nm. The MMSSs have been obtained under different conditions when ethanol was used as co-solvent. With increasing the concentration of ethanol, the sphere diameter varied from 70 to 460nm. The increasing of reaction temperature from 0 to 90°C led to the average diameter of the mesoporous silica spheres changing from 90 to 410nm. Higher NaOH concentration and lower surfactant concentration have been found to facilitate the formation of MMSSs with larger particle size. MMSSs with diameter of 180–380nm were also synthesized with the addition of the co-solvents such as isopropanol, acetone, acetonitrile, dimethyl sulfoxide and methanol. The possible mechanism responsible for the shape and structure of MMSSs was discussed.

Reaction progress of alkaline-activated metakaolin-ground granulated blast furnace slag blends

Ground granulated blast furnace slag (ggbf slag) and metakaolin were blended and the combination was activated by sodium hydroxide solution. Two mix series were investigated, one with low NaOH concentration (9–16 wt%) and the other with a high NaOH concentration of 25 wt%. The reaction progress of the alkali-activated pastes was indirectly measured by isothermal calorimetry as well as by ultrasonic measurements. Both methods show an acceleration of the condensation reaction of the alkali-activated blends compared to both single phases. The acceleration effect is more considerable at the higher activator concentration related to a higher reaction degree of the metakaolin.

Solvation of Dimethyl Succinate in a Sodium Hydroxide Aqueous Solution. A Computational Study

Molecular dynamics simulations were carried out to study dimethyl succinate/water/NaOH solutions. The potential of mean force method was used to determine the transport mechanism of a dimethyl succinate (a diester) molecule across the aqueous/vapor interface. The computed number density profiles show a strong propensity for the diester molecules to congregate at the interface, with the solubility of the diester increasing with increasing NaOH concentration. It is observed that the major contribution to the interfacial solvation free-energy minimum is from electrostatic interactions. Even at higher NaOH concentrations, the increasing electrostatic interaction between the diester and ions is not large enough to favor the solvation of diester in bulk solutions. The calculated solvation free energies are found to be -2.6 to -3.5 kcal/mol in variant concentrations of NaOH aqueous solutions. These values are in qualitative agreement with the corresponding experimental measurements. The computed surface potential indicates that the contribution of diester molecules to the total surface potential is about 25%, with the major contribution from interfacial water molecules.