High pH Solutions Research Articles

First-Principles Study of Catalytic Activity of Cu, Ni and Pd Surface for Formaldehyde and Hypophosphite As Reducing Agents in Electroless Deposition

Electroless deposition process has been applied to various industrial fields as a fundamental technique to fabricate metal thin films. To improve the controllability of this process, investigations of the reaction mechanism and the catalytic activity of metal surfaces for each reducing agent reaction are essentially important. For systematic analyses, theoretical calculation can be employed as a powerful tool. Our previous theoretical studies suggested that the dehydrogenation step of the reducing agents could be a rate-determining step in most cases [1]. This study investigates the reaction mechanisms of reducing agents with solvent molecules on Cu, Ni, and Pd, analyzing the electronic states during the reaction to identify the origin of the catalytic activity observed in each metal surface, by using density functional theory (DFT). All calculations were performed by using Vienna Ab initio Simulation Package (VASP). The cutoff energy for the plane wave basis set was set at 400 eV. The core electrons were described by pseudopotentials constructed with the Projector Augmented Wave (PAW). The exchange-correlation energies were evaluated with the Perdew, Burke and Ernzerhof (PBE) functional. The k-point grids were taken as 3 × 3 × 1 for the geometry optimization and 15 × 15 × 1 for the density of states (DOS) calculations. Assuming that the process employs high pH solution, the molecular structures of formaldehyde and hypophosphite ions were modeled as H2CO(OH)- and H2PO2 -, respectively. The solvation structures were prepared by locating several explicit H2O molecules, which were directly interacting with the molecules of the reducing agents. Previous study of each elementary step, such as the adsorption and the dehydrogenation, indicated that H2O played an important role to determine the geometrical structure or electronic state in those steps. To obtain a reasonable result of the solid-liquid interface system, the solvation structures of each reducing agent were investigated. H2O molecules turned out to interact mainly with O atoms of formaldehyde via H atoms in the solvation structure (Fig. 1), which was almost the same as the case of hypophosphite. Due to the sterically bulky structure around O atoms, the two reducing agent molecules adsorbed on each metal surface via H atoms; H and center atoms locate on atop and bridge sites, respectively. The solvation structure prevented unreasonable dissociation of the molecules on metal surfaces, suggesting that the surrounding solvent molecules are necessary to build the practical adsorption model. The reaction energies of the dehydrogenation on each metal surface have good agreement with the catalytic activity shown in the experimental results [2]. DOS profiles demonstrate that the electronic state of the dissociated H atom of formaldehyde is sufficiently stabilized by the effective interaction with Cu surface atom, while that of hypophosphite is not. Such a detailed investigation for the electronic state of the reducing agents at each surface during the reaction is helpful to elucidate their reactivity. [1] M. Kunimoto, T. Shimada, S. Odagiri, H. Nakai, T. Homma, J. Electrochem. Soc., 158, D585-D589 (2011). [2] I. Ohno, O. Wakabayashi, S. Haruyama, J. Electrochem. Soc., 132, 2323-2330, (1985). Figure 1

Preparation of Stable Colloidal Silica with Controlled Size Nano Spheres from Sodium Silicate Solution

The formation process of stable colloidal silica solution was discussed in this article. The affecting parameter including pH, zeta potential, and colloidal concentration was investigated to elucidate the stability of colloid. Sodium silicate was used as the silica source. The colloidal silica prepared via sol-gel method at the base condition. Sodium ion of sodium silicate was removed by ion-exchanging to obtain the active silicic acid which was titrated with potassium hydroxide (KOH) solution to form the colloidal silica. Size distribution and solution zeta potential were measured by Particle Size Distribution (PSA). In this experiment, the results showed that the higher solution pH (affect the decreasing of zeta potential value) and higher colloidal concentration (affect the increasing of zeta potential value) play important role in the stability of colloidal silica and controlling the particle growth to form the larger particle size. The colloidal silica formed at this condition was agglomeration free for a long period that indicated the colloids were stable.

Interaction of micro/nano-metric size of Jordanian aluminosilicate raw materials with high pH solution

This study analyses the influence of particle size on the dissolution behaviour of three Jordanian raw materials. Kaolin, volcanic tuff and silica sand samples were dissolved in sodium hydroxide solution 10 M at 25 °C, and shaken for 168 h. To better understand the dissolution process, the alkaline solution was renewed after the desired time in order to know the degree of Al-Si raw material removed to the dissolution. The concentrations of leached Al and Si was used to evaluate the dissolution behaviour of the studied raw materials. The three raw materials have higher extent of leaching of Si4+ and Al3+ with decreasing the particle size.

Atmospheric CO2 Sequestration in Iron and Steel Slag: Consett, County Durham, United Kingdom.

Carbonate formation in waste from the steel industry could constitute a nontrivial proportion of the global requirements for removing carbon dioxide from the atmosphere at a potentially low cost. To utilize this potential, we examined atmospheric carbon dioxide sequestration in a >20 million ton legacy slag deposit in northern England, United Kingdom. Carbonates formed from the drainage water of the heap had stable carbon and oxygen isotope values between -12 and -25 ‰ and -5 and -18 ‰ for δ13C and δ18O, respectively, suggesting atmospheric carbon dioxide sequestration in high-pH solutions. From the analyses of solution saturation states, we estimate that between 280 and 2900 tons of CO2 have precipitated from the drainage waters. However, by combining a 37 year long data set of the drainage water chemistry with geospatial analysis, we estimate that <1% of the maximum carbon-capture potential of the deposit may have been realized. This implies that uncontrolled deposition of slag is insufficient to maximize carbon sequestration, and there may be considerable quantities of unreacted legacy deposits available for atmospheric carbon sequestration.

Development of diamond composite electrode for anodic oxidation of organic pollutants

Nano-diamond composite electrode was prepared and used as anode for anodic oxidation process for organic chemicals. Electrochemical techniques such as impedance and cyclic voltammetry have been used to characterize the diamond composite electrode properties. The oxidation power of the electrode was 0.8 V vs. Ag/AgCl, the charge transfer rate was 12.1 ohm, and the double layer capacitance was less than 1 μF. The anodic oxidation behavior of p-benzoquinone, 2-chlorophenol, and phenol over diamond composite electrode were investigated by cyclic voltammetry in 0.1 M H2SO4 (pH 3) solution and 0.25 M Na2SO4 (pH 6.8) solution. Results marked that the electro-oxidation of p-benzoquinone was more active than phenol and 2-chlorophenol in the both solutions. The performance of the diamond composite electrode during incineration of 200 mg/L p-benzoquinone, 2-chlorophenol, phenol were investigated in an aqueous solution of pH 3 and pH 6.8 with 0.25 M Na2SO4 as the supporting electrolyte and applied current density of 40 mA/cm2. Results showed that the degradation rate of benzoquinone was faster than 2-chlorophenol and phenol in both different pH solutions. Moreover, the benzoquinone degradation rate was enhanced at high pH solution, on the contrary of that of 2-chlorophenol and phenol were clearly favored in acid medium.

PH-triggered Release of Boron and Thiamethoxam from Boric Acid Crosslinked Carboxymethyl Cellulose Hydrogel Based Formulations

ABSTRACTBoric acid crosslinked carboxymethyl cellulose hydrogels were synthesized to develop pH-triggered release formulations (pH-TRFs) of boron and thiamethoxam. The developed hydrogels showed pH sensitive water absorption capacity (16.75 to 110.80 g/g xerogel). Entrapment of thiamethoxam was done through an ex-situ loading technique. The boron and thiamethoxam release was studied in pH buffer solutions (4.0, 7.0 and 9.2). Release kinetics analysis using mathematical models showed fast release in high pH solution as compared to acidic pH. These pH-TRFs may find usefulness in selective release of nutrients and pesticides in plant rhizospheric zone of problem soils viz. acidic soils and alkaline soils.

Oxidation of Cr(III)-Fe(III) Mixed-Phase Hydroxides by Chlorine: Implications on the Control of Hexavalent Chromium in Drinking Water.

The occurrence of chromium (Cr) as an inorganic contaminant in drinking water is widely reported. One source of Cr is its accumulation in iron-containing corrosion scales of drinking water distribution systems as Cr(III)–Fe(III) hydroxide, that is, FexCr(1–x)(OH)3(s), where x represents the Fe(III) molar content and typically varies between 0.25 and 0.75. This study investigated the kinetics of inadvertent hexavalent chromium Cr(VI) formation via the oxidation of FexCr(1–x)(OH)3(s) by chlorine as a residual disinfectant in drinking water, and examined the impacts of Fe(III) content and drinking water chemical parameters including pH, bromide and bicarbonate on the rate of Cr(VI) formation. Data showed that an increase in Fe(III) molar content resulted in a significant decrease in the stoichiometric Cr(VI) yield and the rate of Cr(VI) formation, mainly due to chlorine decay induced by Fe(III) surface sites. An increase in bicarbonate enhanced the rate of Cr(VI) formation, likely due to the formation of Fe(III)-carbonato surface complexes that slowed down the scavenging reaction with chlorine. The presence of bromide significantly accelerated the oxidation of FexCr(1–x)(OH)3(s) by chlorine, resulting from the catalytic effect of bromide acting as an electron shuttle. A higher solution pH between 6 and 8.5 slowed down the oxidation of Cr(III) by chlorine. These findings suggested that the oxidative conversion of chromium-containing iron corrosion products in drinking water distribution systems can lead to the occurrence of Cr(VI) at the tap, and the abundance of iron, and a careful control of pH, bicarbonate and bromide levels can assist the control of Cr(VI) formation.

Mechanisms of interaction between arsenian pyrite and aqueous arsenite under anoxic and oxic conditions

Pyrite affects the conversion and migration processes of arsenic in soils and waters. Adsorption and redox reactions of arsenite (As(III)) occur on the surface of pyrite, and the interaction processes are influenced by the arsenic incorporated into pyrite. This work examined the effects of arsenic content, pH and oxygen on the interaction between arsenian pyrite and aqueous As(III) and investigated the underlying mechanisms. The results indicated that arsenic incorporation led to a high content of Fe(III) in pyrite, and that As(III) was mainly adsorbed on pyrite surface and part of As(III) was oxidized to As(V) by the newly formed intermediates including hydroxyl radicals and hydrogen peroxide. The oxidation rate increased with increasing arsenic content in the pyrite and the presence of air (oxygen), and first decreased and then increased with increasing pH from 3.0 to 11.0. Hydroxyl radicals and hydrogen peroxide significantly contributed to the oxidation of pyrite and aqueous As(III) in acidic and alkaline solutions, respectively. Although pyrite oxidation increased with increasing arsenic content as indicated by the elevated concentrations of elemental S and SO42−, the percentage of released arsenic in total arsenic of the arsenian pyrite decreased due to the adsorption of arsenic on the surface of newly formed ferric (hydr)oxides, especially the ferric arsenate precipitate formed in high pH solutions. The present study enables a better understanding of the important interaction process of dissolved arsenite and natural pyrites in the study of groundwater contamination, arsenic migration/sequestration, and acid mine drainage formation.

Adsorption of tobacco-specific nitrosamine 4-(methylnitrosamino) -1- (3-pyridyl)-1-butanone from aqueous solution with graphene aerogel

The adsorption behavior of graphene aerogel in the 4-(Methylnitrosamino)-1-(3-pryidyl)-1-butanone (NNK) aqueous solution was studied. The adsorption kinetics fitted pseudo-second-order model with the rate constant (k2) of 0.154 g/mg·h. The adsorption isotherm was investigated and fitted Langmuir and Freundlich models well, and the maximum adsorption capacity (qm) was 59.66 mg/g estimated from Langmuir isotherm. Thermodynamic result indicated that the process of adsorption of NNK onto graphene aerogel was spontaneous and exothermic. Higher pH solution was favorable for NNK adsorption on graphene aerogel. The adsorption for NNK on graphene aerogel arose from the π-π interaction between them, and the high adsorption efficiency was resulted from the -NO2 functional groups. The capability of graphene aerogel was maintained after repeated absorption-desorption cycles, which was benefit for convenient separating and recycling of graphene aerogel.

SCC Initiation for X80 Pipeline Steel Under AC Application in High pH Solution

SCC Initiation for X80 Pipeline Steel Under AC Application in High pH Solution

SCC Initiation for X80 Pipeline Steel Under AC Application in High pH Solution

SCC Initiation for X80 Pipeline Steel Under AC Application in High pH Solution

Choosing mineral flotation collectors from large nanoparticle libraries

Polystyrene nanoparticles can promote froth flotation of mineral particles if the nanoparticles are sufficiently hydrophobic and are colloidally stable in the high ionic strength solutions typical of commercial flotation operations. A library of 80 unique polystyrene nanoparticle types was prepared with click chemistry and used to determine if particles that were sufficiently hydrophilic to be colloidally stable in high ionic strength and high pH solutions, were also capable of promoting flotation. The conflicting requirements of colloidal stability and hydrophobicity can be achieved in 9 mM sodium carbonate, a very challenging environment. Instead of testing all 80 samples with laborious flotation testing, automated assays measuring colloid stability and nanoparticle hydrophobicity were employed. The colloid stability assay measured the critical coagulation concentrations (CCC). Nanoparticle hydrophobicity was characterized by water contact angle, measurements (CA). A smaller cohort of the most promising nanoparticle candidates for detailed flotation testing were identified by mapping nanoparticle properties on the CA versus CCC plain – a “Flotation Domain Diagram”. We believe that this work was the first time that combinatorial synthesis and high throughput screening have been used in the development of flotation chemicals. Finally, based on the accumulated evidence, effective nanoparticle flotation collectors are likely to be ∼50 nm in diameter, with a soft hydrophobic polymer shell and with surface functional group densities in the order of magnitude of 0.1 nm−2.

Does the major aluminium-resistance gene in wheat, TaALMT1, also confer tolerance to alkaline soils?

A major limitation to plant growth in acid soils is the prevalence of toxic Al3+. Most genotypic variation for acid soil-tolerance in wheat is linked with the Al3+-activated efflux of malate anions from roots which is controlled by TaALMT1 on chromosome 4DL. Recent studies have also linked TaALMT1 with tolerance to high pH solutions and alkaline soils. This study tested the hypothesis that an Al3+-resistant allele of TaALMT1 also confers tolerance to alkaline conditions. The near-isogenic wheat lines, ET8 (Al3+-resistant) and ES8 (Al3+-sensitive), have different alleles of the TaALMT1 gene and contrasting resistance to Al3+ toxicity. Growth of these lines was compared in acid and alkaline soils with contrasting mineralogy and in a range of high pH hydroponic solutions of varying composition. No consistent differences in root or shoot growth were detected between the lines in the alkaline soils or in the high pH hydroponic treatments. Malate efflux was detected from ET8 in acidic solution with Al3+ but no substantial malate efflux was detected at pH 9.0 treatment with added Na2SO4. The results are inconsistent with the hypothesis that the TaALMT1 gene confers an advantage to wheat on alkaline soils.

Anion-Exchange Membranes for Alkaline Fuel-Cell Applications: The Effects of Cations.

Alkaline anion-exchange membrane fuel cells (AEMFCs) are attracting much attention because of their potential use of nonprecious electrocatalysts. The anion-exchange membrane (AEM) is one of the key components of AEMFCs. An ideal AEM should possess high hydroxide conductivity and sufficient long-term durability at elevated temperatures in high-pH solutions. Herein, recent progress in research into the alkaline stability behavior of cations (including quaternary ammonium, imidazolium, guanidinium, pyridinium, tertiary sulfonium, phosphonium, benzimidazolium, and pyrrolidinium) and their analogous AEMs, which have been investigated by both experimental studies and theoretical calculations, is reviewed. Effects, including conjugation, steric hindrance e, σ-π hyperconjugation, and electrons, on the alkaline stability of cations and their analogous AEMs have been discussed. The aim of this article is to provide an overview of some key factors for the future design of novel cations and their analogous AEMs with high alkaline stability.

Synthesis and characterization of poly(ether sulfone) block copolymers containing pendent quaternary ammonium- and imidazolium groups as anion exchange membranes

A class of poly(ether sulfone) (FPES) block copolymers containing pendent quaternary ammonium (QA) and imidazolium (IM) groups were prepared as anion exchange membranes by reaction involving nucleophilic substitution, benzylic bromination, quaternization and anion exchange with hydroxide ions. Highly reactive hexafluorobenzene (HFB) was utilized as a linkage group for relatively low temperature (e.g., 105°C) coupling between hydrophobic and precursor hydrophilic oligomer blocks. The phase separated morphology, water uptake, swelling ratio, conductivity, and chemical stability of the resultant copolymer membranes were also investigated. The hydroxide conductivity of the ionomer membranes (IEC~2.0 mequiv./g) was 21–22mS/cm and 56–63mS/cm at 30°C and 80°C respectively. The FPES-IM membrane showed relatively very good dimensional integrity in high pH solution, whereas under the similar condition the FPES-QA membrane broke into pieces. However, the degradation of the imidazolium cations in FPES-IM was relatively faster in comparison to the ammonium cations in FPES-QA.

Impact of an Alkaline Solution on the Chemistry, Mineralogy, and Sorption Properties of a Typic Rhodudult Soil

Abstract The preferred option for disposal of short-lived low and intermediate level radioactive wastes is a near surface disposal facility in which soil is one of the barriers that avoid radionuclide migration outside the controlled area. For construction of that kind of facility, concrete is widely used, and its interaction with water induces its degradation, resulting in a high pH solution. The alkaline solution may affect the near-field environment of radioactive waste repositories, including the soil, promoting mineralogical alterations that [...]

Alteration of Interfacial Properties by Chemicals and Nanomaterials To Improve Heavy Oil Recovery at Elevated Temperatures

Heavy oil containing carbonate and sand reservoirs exhibits reverse wettability characteristics. Dependent upon the temperature, phase of injected steam, and rock type, the wettability may be altered to more water-wet. The addition of chemicals to hot water (or steam) may further change the interfacial properties (more water-wet and less interfacial tension). Surfactants were tested extensively for this process in the past, and their temperature resistance was an obstacle. New-generation chemicals need further investigation from a technically and economically success point of view. The objective was to investigate the alteration of interfacial properties induced by different types of chemical agents under high-temperature conditions. To achieve this, four experimental tools (contact angle measurement, interfacial tension measurement, atomic force microscopy, and spontaneous imbibition tests) were applied. High-pressure and high-temperature contact angle measurements enabled a quick method to identify the suitability of the chemicals for wettability modification. Interfacial tension between oil and different chemical solutions was measured with a variation of the temperature. In the imbibition tests, core samples were exposed to heating for longer time periods, so that the temperature resistance of the chemicals was also tested. Imbibition experiments were conducted at ambient pressure and 90 °C. The combination of the contact angle and interfacial tension provided insight into the recovery enhancement mechanisms. Six different chemicals, including an ionic liquid, three nanofluids (silica, aluminum, and zirconium oxides), a cationic surfactant, and a high-pH solution, were chosen based on our screening study. Heavy oil used was obtained from a field in Alberta (6000 cP). Contact angles were measured on mica, calcite, sandstone, and limestone plates. The experimental temperature ranged from 25 to 200 °C, and the pressure was changed to keep the solution in the aqueous phase. Promising modifiers for different rock types under different temperatures were screened separately. Visual data illustrating the deposition of the chemicals on the surface of mica and well-polished calcite substrates and removal of the existing oil layer after the treatment with different chemicals were obtained by atomic force microscopy. Finally, spontaneous imbibition tests were performed on sandstone and limestone cores with screened promising modifiers. Oil recovery in this phase was continuously monitored to evaluate wettability alteration capability, and the mechanism(s) involved were analyzed for different chemicals. Analysis of wettability alteration mechanisms and interfacial tension reduction capabilities is expected to be useful in the selection of suitable and temperature-resistant chemicals for high-temperature applications in different reservoir rocks.

Probing the Interaction Mechanism between Air Bubbles and Bitumen Surfaces in Aqueous Media Using Bubble Probe Atomic Force Microscopy.

Surface interactions involving deformable air bubbles have attracted tremendous interest in a wide range of engineering applications, such as mineral flotation and bitumen extraction. In this work, for the first time, the interaction forces between air bubbles and bitumen surfaces in complex aqueous media of varying pH, salinity, and salts were directly measured using a bubble probe atomic force microscope (AFM) technique. The AFM topographic imaging reveals that bitumen surface tends to be rougher and form distinct domains at high NaCl concentration or under strongly alkaline environment. The force measurements demonstrate the critical role of ionic strength and solution pH in bubble-bitumen interaction and attachment, which could be well described by a theoretical model based on Reynolds lubrication theory and augmented Young-Laplace equation by including the effect of disjoining pressure. In 1 mM NaCl, the electrical double layer (EDL) repulsion inhibited bubble-bitumen attachment, and such a repulsive effect could be further strengthened with increasing solution pH. In 500 mM NaCl, the hydrophobic attraction could lead to bubble-bitumen attachment, while a high solution pH could weaken the hydrophobic interaction. The addition of calcium ion in 500 mM NaCl could enhance the hydrophobic interaction and facilitate the bubble-bitumen attachment, most likely attributed to the bridging effect between calcium ions and the functional groups (e.g., carboxyl group) of interface-active molecules on bitumen surfaces, thus leading to higher surface roughness and hydrophobic moieties/aggregates on bitumen as confirmed by AFM imaging. Our results provide quantitative information on the interaction mechanism between air bubbles and bitumen surfaces in complex aqueous solutions at the nanoscale, which has useful implications to many related interfacial interactions in industrial processes such as oil production, oil-water separation, and wastewater treatment.

Efficient activation of ozone by zero-valent copper for the degradation of aniline in aqueous solution

Abstract A series batch experiments were performed to explore the catalytic role of zero-valent metals, including Fe(0), Co(0), Al(0) and Cu(0), in ozonation degradation of aniline in aqueous solution. It was found that Cu(0) exhibited the best catalytic activity of ozonation. Approximately 98% of the initial aniline (10 mg/L) was destructed by ozone assisted with Cu(0) within 24 min. The dosage of Cu(0) and solution pH were two critical factors affecting aniline degradation. The increase of Cu(0) dosage promoted aniline degradation. And aniline could be effectively removed in an initial pH range of 4–10, whereas a lower or higher solution pH was not favorable for the degradation of aniline. Free radicals were investigated by electron paramagnetic resonance technique, which confirmed that ·OH was the primary active oxidant responsible for the degradation of aniline. The further mechanism investigation revealed that the generation of ·OH is ascribed to Fenton-like reaction between Cu(I) and H 2 O 2 , both of which are in situ yielded through a series subsequent of reactions starting with oxidation–reduction reaction between ozone and Cu(0). Based on the results obtained in this study, it can be inferred that ozone activated with Cu(0) is a promising approach to degrade organic pollutants.

Electrochemical Induced Calcium Phosphate Precipitation: Importance of Local pH.

Phosphorus (P) is an essential nutrient for living organisms and cannot be replaced or substituted. In this paper, we present a simple yet efficient membrane free electrochemical system for P removal and recovery as calcium phosphate (CaP). This method relies on in situ formation of hydroxide ions by electro mediated water reduction at a titanium cathode surface. The in situ raised pH at the cathode provides a local environment where CaP will become highly supersaturated. Therefore, homogeneous and heterogeneous nucleation of CaP occurs near and at the cathode surface. Because of the local high pH, the P removal behavior is not sensitive to bulk solution pH and therefore, efficient P removal was observed in three studied bulk solutions with pH of 4.0 (56.1%), 8.2 (57.4%), and 10.0 (48.4%) after 24 h of reaction time. While P removal efficiencies are not generally affected by bulk solution pH, the chemical-physical properties of CaP solids collected on the cathode are still related to bulk solution pH, as confirmed by structure characterizations. High initial solution pH promotes the formation of more crystalline products with relatively high Ca/P molar ratio. The Ca/P molar ratio increases from 1.30 (pH 4.0) to 1.38 (pH 8.2) and further increases to 1.55 (pH 10.0). The formation of CaP precipitates was a typical crystallization process, with an amorphous phase formed at the initial stage which then transforms to the most stable crystal phase, hydroxyapatite, which is inferred from the increased Ca/P molar ratio from 1.38 (day 1) to the theoretical 1.76 (day 11) and by the formation of needle-like crystals. Finally, we demonstrated the efficiency of this system for real wastewater. This, together with the fact that the electrochemical method can work at low bulk pH, without dosing chemicals and a need for a separation process, highlights the potential application of the electrochemical method for P removal and recovery.