NaOH H2O Research Articles

Effects of hydrothermal etching and conversion on photocatalytic hydrogen evolution and overall water splitting with nanoparticulate and mesoporous TiO2 and SrTiO3/TiO2 composites

Hydrothermal treatment of mesoporous photocatalysts in diluted NaOH solution or H2O might be a simple and promising strategy to improve photocatalytic activities in general, as we show for TiO2 and SrTiO3/TiO2 composites.

PHASE FORMATION IN ALKALINE TITANOSILICATE SYSTEMS DURING HYDROTHERMAL SYNTHESIS

The investigations in the polycomponent high alkaline systems – TiO2–H2SO4–Na2SiO3–NaOH–H2O and TiO2–H2SO4–(NH4)2SO4–Na2SiO3–NaOH–H2O under hydrothermal synthesis conditions have been carried out to provide new products with the given technical properties. It has been shown that by directed selection of structure-forming components, in particular titanium compounds, together with optimal parameters of hydrothermal treatment of the obtained precursor, it is possible to form compounds with the given phase and chemical composition, morphology and particle size. It was found that the rate of structural transformations during synthesis depends on the phase composition of titanosilicate precursors. During their hydrothermal treatment, alkaline and thermal hydrolysis with subsequent dehydration of hydrolyzed phases of titanium (IV) and silicon take place. The process is accompanied by localization of free bonds providing formation of Ti–O–Si–O-bridges and their subsequent transformation into structured new formations.

Synthesis of 5-methylidene-2-thio- and 2-selenohydantoins from isothiocyanates or isoselenocyanates and l-serine

3-Aryl-5-methylidenethiohydantoins and 3-aryl-5-methylidene-selenohydantoins were obtained by one-pot reaction of aryl isothiocyanates or isoselenocyanates with l-serine in NaOH–H2O–Py mixture followed by room temperature HCl-promoted dehydration.

Production of Iron Alloy by Direct Electrolytic Reduction Using Suspension Electrolysis in an Alkaline Electrolyte

Iron alloys were produced by suspension electrolysis in a 50 wt% NaOH–H2O electrolyte at 383 K, and Fe–Cr and Fe–Ni alloys were obtained using a suspension of Fe2O3+Cr2O3 and Fe2O3+Ni(OH)2 particles, respectively. Highly ordered columnar deposits comprising cubic Fe–Cr particles with approximately 5-micrometer-long sides were obtained on a disk cathode with a current efficiency higher than 90% at 100–300 mA･cm−2. In contrast, disordered columnar deposits of Fe–Ni particles with diameters of approximately 1.0 μm were obtained on a disk cathode with a current efficiency of approximately 50% at 200 mA･cm−2. The proposed method affords iron alloys with compositions in the stainless-steel region that depend on the electrolysis conditions, namely, the current density and Fe2O3/Cr2O3 or Fe2O3/Ni(OH)2 content ratio.

An efficient and mild recycling of waste melamine formaldehyde foams by alkaline hydrolysis

Melamine formaldehyde foam (MFF) generates many poisonous chemicals through the traditional recycling methods for organic resin wastes. Herein, a high MFF degradation ratio of ca. 97 wt.% was achieved under the mild conditions (160 °C) in a NaOH–H2O system with ammelide and ammeline as the main degradation products. The alkaline solvent had an obvious corrosion effect for MFF, as indicated by scanning electron microscopy (SEM). The reaction process and products distribution were studied by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and 13C nuclear magnetic resonance (NMR). Besides, the MFF degradation products that have the similar chemical structures and bonding performances to those of melamine can be directly used as the raw material for synthesis of melamine urea-formaldehyde resins (MUFs). Moreover, the degradation system demonstrated here showed the high degradation efficiency after reusing for 7 times. The degradation process generated few harmful pollutants and no pre- or post-treatments were required, which proves its feasibility in the safe removal or recovery of waste MFF.

Solid–Liquid Phase Boundaries in the System: Glycine–NaOH–NaHCO3–H2O

In this work, the solid–liquid equilibrium (SLE) of the systems glycine (Gly)–H2O, Gly–NaOH–H2O, Gly–NaHCO3–H2O, and Gly–NaOH–NaHCO3–H2O was determined using a freezing point depression (FPD) setup. A total of 131 new data points are listed in the concentration range 0 < b (sodium glycinate (SG)) < 25 mol SG/kg water. The system Gly–NaOH–H2O with five different mole ratios (nNaOH:nGly) 1:1, 1:2, 1:5, 2:1, and 5:1 and the CO2-loaded system Gly–NaOH–NaHCO3–H2O were analyzed in a loading range of 0.1–1 mol CO2 per mol SG. Eutectic points and hydrate formations were identified in the systems Gly–H2O, Gly–NaOH–H2O, and Gly–NaOH–NaHCO3–H2O. The solubility of SG increased linearly with higher concentrations for systems with an excess of NaOH. The solubility of SG decreased significantly with an excess addition of NaOH and glycine. The same trend was observed in the CO2-loaded system. The new data create a better understanding of phase equilibria in this system. This understanding is useful for the thermodynamic modeling of the system, which can potentially be used for CO2 capture. The data give a clear representation of the degree of safe operation in terms of managing a plant without solid formation.

Revealing nitrogen-containing species in commercial catalysts used for ammonia electrosynthesis

Stimulated by the growing demand for sustainable and/or economical distributed ammonia synthesis, the electrochemical nitrogen reduction reaction has attracted considerable interest. The nitrogen-containing impurities in commercial metal-based nitrogen reduction reaction catalysts such as metal oxides and metallic irons have, however, been overlooked. Herein we report the presence of nitrogen-containing species in NOx− or nitrides at substantial levels revealed from many commercial catalysts. We call attention to the necessity to screen the NOx−/nitrides impurities in commercial catalysts, as the nitrogen impurities are not commonly listed in vendors’ assay documents. A simple two-step procedure (alkaline/acidic treatment followed by HPLC/UV–vis analysis) is recommended as a reliable protocol for screening NOx−/nitrides impurities in catalyst materials. A case analysis is also carried out on the previously reported H2O–NaOH–KOH system with both 15N-isotopic labelling and nitrogen elemental tracking, reassigning the true nitrogen source of the electrochemically produced NH3 from gaseous N2 to nitrogen-containing impurities in catalysts. The electrochemical nitrogen reduction reaction has recently attracted significant interest, but the true source of ammonia formation remains sometimes unclear. This Analysis reports a systematic investigation of the presence of nitrogen-containing species in a number of commercial catalysts, revealing substantial levels of NOx− and nitrides impurities for some of them.

Synthesis and characterisation of Co(iii) complexes of N-formyl hydroxylamines and antibacterial activity of a Co(iii) peptide deformylase inhibitor complex.

The X-ray crystal structure and pKa values of GSK322, a well-known and effective peptide deformylase inhibitor and antibacterial drug candidate, are reported. The first examples of Co(iii) complexes of N-formyl hydroxylamines are reported. Reaction of N-hydroxy-N-phenylformamide (HFA) with [Co(tren)Cl2]Cl and [Co(tpa)Cl2]Cl (where tren = tris(2-aminoethyl)amine, tpa = tris(2-pyridylmethyl)amine) with one equivalent of NaOH in H2O afforded [Co(tren)(HFA-1H)](PF6)1.5Cl0.5 (1) and [Co(tpa)(HFA-1H)]Cl2 (2), respectively. X-ray crystal structures of both complexes revealed that the N-formyl hydroxylamine group acts as a bidentate ligand, coordinating the Co(iii) centres via the carbonyl oxygen and deprotonated hydroxy group (O,O'), a coordination mode typically observed for closely related mono-deprotonated hydroxamic acids. Reaction of the N-formyl hydroxylamine-based GSK322 with [Co(tpa)Cl2]Cl afforded the corresponding Co(iii) chaperone complex of the peptide deformylase inhibitor, [Co(tpa)(GSK322-1H)](PF6)2. GSK322 and [Co(tpa)(GSK322-1H)](PF6)2 exhibited better Gram-positive activity than Gram-negative, where low MICs (1.56-6.25 μM) were determined for S. aureus strains, independent of their antibiotic susceptibility.

Ion-ion interactions enhance aluminum solubility in alkaline suspensions of nano-gibbsite (α-Al(OH)3) with sodium nitrite/nitrate.

Despite widespread industrial importance, predicting metal solubilities in highly concentrated, multicomponent aqueous solutions is difficult due to poorly understood ion-ion and ion-solvent interactions. Aluminum hydroxide solid phase solubility in concentrated sodium hydroxide (NaOH) solutions is one such case, with major implications for ore refining, as well as processing of radioactive waste stored at U.S. Department of Energy legacy sites, such as the Hanford Site, Washington State. The solubility of gibbsite (α-Al(OH)3) is often not well predicted because other ions affect the activity of hydroxide (OH-) and aluminate (Al(OH)4-) anions. In the present study, we systematically examined the influence of key anions, nitrite (NO2-) and nitrate (NO3-), as sodium salts on the solubility of α-Al(OH)3 in NaOH solutions taking care to establish equilibrium from both under- and oversaturation. Rapid equilibration was enabled by use of a highly pure and crystalline synthetic nano-gibbsite of well-defined particle size and shape. Measured dissolved aluminum concentrations were compared with those predicted by an α-Al(OH)3 solubility model derived for simple Al(OH)4-/OH- systems. Specific anion effects were expressed as an enhancement factor (Alenhc) conveying the excess of dissolved aluminum. At 45 °C, NaNO2 and NaNO3-containing systems exhibited Alenhc values of 2.70 and 1.88, respectively, indicating significant enhancement. The solutions were examined by Raman and high-field 27Al NMR spectroscopy, indicating specific interactions including Al(OH)4--Na+ contact ion pairing and Al(OH)4--NO2-/NO3- ion-ion interactions. Dynamic evolution of the α-Al(OH)3 particles including growth and agglomeration was observed revealing the importance of dissolution/reprecipitation in establishing equilibrium. These studies indicate that incomplete ion hydration, as a result of the low water activity in these concentrated electrolytes, results in: (i) enhanced reactivity of the hydroxide ion with respect to α-Al(OH)3; (ii) increased concentrations of Al(OH)4- in solution; and (iii) stronger ion-ion interactions that act to stabilize the supersaturated solutions. This information on the mechanisms by which α-Al(OH)3 becomes supersaturated is essential for more energy-efficient aluminum processing technologies, including the treatment of millions of gallons of Al(OH)4--rich high-level radioactive waste.

New Concentration Correlations of NaOH Aqueous Solutions for a Thermodynamic Process

Some processes such as air conditioning absorption systems have been developed as a feasible and economical alternative to help reduce the consumption of fossil fuels and prevent the impact of gas emission produced by electrical air conditioning. However, a main disadvantage of these systems is the absorbent’s crystallization phenomenon in the working mixture, which occurs when the absorbent concentration is higher than the saturation point. Among the aqueous working mixtures, NaOH solution shows several advantages for absorption system applications. The aim of this paper is to propose new mathematical correlations to predict or estimate the NaOH concentrations and refractive index in aqueous solutions (H2O–NaOH) for an air conditioning absorption system application. The experimental measurements of NaOH concentration and refractive index were made in situ from aqueous solutions with concentrations from 20 to 50% (weight/weight %, with increases of 5%) and temperatures between 10 and 60 °C (with increments of 1 °C). Two correlations for predicting the concentration of NaOH and refractive index based on cubic regression models with R2 of 0.99704 and 0.99918, respectively, are presented for the first time. The normalized error for NaOH estimation using experimental data lies between −0.026 and 0.040, and for refractive index, the estimation lies between −0.002 and 0.001. Both correlations present a good fit to predict the NaOH concentration between 25 and 45% of concentration ratio.

Comparative Analysis of Material Fluctuation Response based on Data Set Groups

Multi spectral capacitive sensor (MSCS) is a sensor that is formed based on the concept of white noise impedance spectroscopy. This concept utilizes the spectral noise frequency approach of the frequency domain signal resulting from the field effect on the dielectric. As a sensor, the consistency results obtained is stable, so that it can facilitate analysis. In this study, we tried to compare data groups, starting with 100 data sets and 300 data sets from a total of 600 data sets for H2O and H2O mixed with NaOH materials and H2O mixed with HCl using a new transformation, namely Tamsir statistical transformation (TST). Furthermore, grouping data uses the total amplitude value of each data set obtained. We obtain the results in the form of differences between groups of data with fluctuations in response patterns that are close together which are shown in 2D graphics. Hence, we can implement the data groups as a reference pattern of fluctuations in a material.

Study of Equilibria in the “CuCl2–H2O–NaOH” System by Potentiometric Titration

Equilibrium processes in the “CuCl2–H2O–NaOH” system are studied with the consideration of the formation of low soluble phases of various compositions based on mathematical processing of experimental results from potentiometric titration using EQ-5 software. The values of instability constants of copper complex ions and dynamic equilibrium constants of copper low soluble compounds are calculated along with their stoichiometric compositions and regions of stable existence.

Equilibria in a ZnCl2–H2O–NaOH System, According to Data from Potentiometric Titration, and Selecting Conditions for the Hydrochemical Synthesis of ZnS and ZnSe Films

Equilibrium processes that occur in the ZnCl2–H2O–NaOH system are studied via the potentiometric titration of zinc chloride in the 0.00006–1.01 mol/L range of concentrations. Based on mathematical simulations, a number of polynuclear structures and soluble phases are identified in the system. Values of the instability constants of complex forms and the constants of the dynamic equilibria of weakly soluble zinc compounds are calculated, along with their stoichiometric compositions and areas of sustainable existence. Refined boundary conditions are determined, along with areas of the formation of ZnSe and ZnS when they are precipitated using sodium selenosulfate and thiourea, respectively. ZnSe and ZnS layers around 1000 and 200 nm thick are obtained via hydrochemical deposition on glass-ceramic substrates. Based on electron microscopy data, it is concluded that the layers consist of spherical aggregates with mean sizes of around 350–450 nm for ZnSe and 50–200 nm for ZnS, generated from primary particles with sizes of around 20–60 and 20–30 nm, respectively.

The mechanism of nickel ferrite formation by glow discharge effect

The influence of various factors on the formation of nickel ferrite by the glow discharge effect has been studied. The ferritization process in the system FeSO4–NiSO4–NaOH–H2O has been studied by the methods of potentiometric titration, measurement of electrical conductivity, residual concentrations and apparent sediment volume. It has been established that the process proceeds in a multistage fashion at pH 11–12 with the formation of polyhydroxo complexes, an intermediate compound and the ferrite formation by its oxidation with active radicals.

Calculating Equilibrium Constants in the SnCl2–H2O–NaOH System According to Potentiometric Titration Data

The potentiometric titration of tin chloride SnCl2 is performed in the concentration range of 0.00009–1.1 mol/L with a solution of sodium hydroxide NaOH. According to potentiometric titration data based on modeling equilibria in the SnCl2–H2O–NaOH system, basic equations are generated for the main processes, and instability constants are calculated for the resulting hydroxo complexes and equilibrium constants of low-soluble tin(II) compounds. The data will be of interest for specialists in the field of theory of solutions.

Polythermal diagrams of aqueous boundary ternary systems involving sodium borohydride hydrolysis for hydrogen generation

The comprehension of solid-liquid equilibria involved in the quaternary system NaBH4–NaBO2–NaOH–H2O allows us to follow the evolution of mixtures during the sodium borohydride hydrolysis reaction for hydrogen generation. The addition of sodium hydroxide on saturated solutions of sodium borohydride and metaborate have been studied in a temperature range of −10 °C up to 50 °C which is the operational temperature range of a hydrogen generator for consumer electronics application. The solubility data was monitored at low temperatures by Differential Scanning Calorimetry, DSC analyses. Given the large number of solid phases that may crystallize in a stable or metastable state, the definition of a specific protocol was required in order to evaluate a ternary mixture via DSC analyses presenting a good repeatability. The nature of different solid phases present in this system was confirmed by powder X-ray analyses. Finally, two polythermal diagram outlines of aqueous boundary ternary systems involving water, sodium borohydride, sodium hydroxide and sodium borate were proposed. The results obtained in the water-rich area show that the sodium hydroxide hydrates are relatively soluble and the risk of precipitation is mainly due to the sodium borohydride dihydrate (NaBH4.2H2O) and sodium metaborate tetrahydrate (NaBO2.4H2O). The crystallization areas were defined as function of temperature and composition.

Investigation of an HD Engine Thermal Storage System

This paper presents a theoretical calculation and a preliminary design of a thermal storage system (TSS) for a heavy duty diesel engine, in order to re-utilise the wasted heat from the engine when in operation and reduce the warm-up time, thus reducing the engine emissions and improve the performance. The thermal storage mainly comprises of a heat exchanger filled with phase change material. A group of candidate materials were evaluated and NaOH H2O was selected for the particular application, as its phase change temperature is suitable and latent heat is relatively high. The storage was preliminarily designed considering the size of the engine and the quantity of heat requested, and the improvement of the engine was evaluated. The theoretical calculation suggested that nearly 40% improvement in warm-up time could be achieved with the TSS.

ChemInform Abstract: Synthesis and the Temperature‐Dependent Luminescent Properties of SrWO4:Eu3+ Ultralong Nanowire Phosphors.

AbstractSrWO4:Eu3 + nanowires with high aspect ratio are prepared by solvothermal reaction of Sr(NO3)2, Eu(NO3)3, and Na2WO4 which are subsequently added to a solution of NaOH in H2O, oleic acid, EtOH, and cyclohexane as a poor solvent‐induced self‐assembly process (180 °C, 12 h).

Simulating equilibrium processes in the Ga(NO3)3–H2O–NaOH system

Equilibrium processes in the Ga(NO3)3–H2O–NaOH system are simulated with allowance for the formation of precipitates of various compositions using experimental data from potentiometric titration and theoretical studies. The values of the instability constants are calculated along with the stoichiometric compositions of the resulting compounds. It is found that pH ranges of 1.0 to 4.3 and 12.0 to 14.0 are best for the deposition of gallium chalcogenide films.

Bismuth functionalized PVA film: field, plasmonic and pH effect on PVA originated broad photoluminescence

Bismuth (Bi) NPs have been synthesized by Laser Ablation Synthesis in Solution (LASiS) at different pH in different aqueous solutions [viz. H2O (H), H2O + NaOH (HN), and H2O + HCl (HC)].