Increasing Hydroxide Concentration Research Articles

Hydroxide Concentration Dependence of Magnetic Behavior at Low Temperature in MnFe2O4 Nanoparticles

MnFe2O4 nanoparticles of various particle sizes were prepared by co-precipitation, in which different hydroxide concentrations were employed to control particle growth. X-ray diffraction and scanning electron microscopy were used to investigate the nanoparticle structure and morphology (shape and size). The particle size increased with increasing hydroxide concentration. The magnetization and coercivity field were measured by vibrating sample magnetometry. Changes in magnetic behavior were observed in the magnetic hysteresis loop curves of nanoparticles with increasing hydroxide concentration. In the absence of hydroxide, nanoparticles exhibited paramagnetic behavior. Increasing the hydroxide concentration caused a gradual conversion to ferrimagnetic behavior. An increased Neel temperature was observed with increasing hydroxide concentration, and the saturation magnetization exhibited a sharp decrease. Nonuniform hysteresis was observed in the magnetization curve for the sample prepared from hydroxide and ammonium.

Quantitative Difference in the Rates of the β-O-4 Bond Cleavage between Lignin Model Compounds with and without γ-Hydroxymethyl Groups during the Alkaline Pulping Process

To examine the effect of the presence of γ-hydroxymethyl groups on the rate of the β-O-4 bond cleavage during the alkaline pulping process, the rates of the β-O-4 bond cleavage of non-phenolic lignin model compounds without a γ-hydroxymethyl group, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)ethanol (G’G) and 2-(2,6-dimethoxyphenoxy)-1-(3,4-dimethoxyphenyl)ethanol (G’S), were compared with those of analogous model compounds with a γ-hydroxymethyl group, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol (GG) and 2-(2,6-dimethoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol (GS), under alkaline pulping conditions. The disappearance of G’G or G’S was accompanied by the quantitative liberation of 2-methoxyphenol or 2,6-dimethoxyphenol, respectively, indicating that the disappearance resulted from the β-O-4 bond cleavage. The disappearance rate of G’G or G’S was in between those of the erythro and threo isomers of GG or GS, respectively. This result seems to be reasonably explained when the steric repulsions of the three staggered conformations are taken into consideration. The disappearance rate of G’G or G’S increased, but the increment became moderate with increasing hydroxide concentration.

The effect of strong hydroxide solutions on the stability of aggregates and hydraulic conductivity of soil

SummaryThe effect of two hydroxides (NaOH and KOH) and two chlorides (NaCl and KCl) on aggregate stability and saturated hydraulic conductivity (Ks) was studied in three New Zealand soils using concentrations (0.003, 0.03, and 0.3 m) typical of the range of pH found in strongly alkaline industrial liquid wastes. The different solutions were used as pretreatments prior to aggregate stability measurements and as influent solutions for Ks measurements.The concentration of hydroxide appeared to be the most important factor affecting aggregate stability and KS in all soils. Aggregate stability and Ks decreased with increasing hydroxide concentration, but were generally unaffected by chloride solutions. Relative Ks decreased to <2.5% of initial kS with all hydroxide concentrations, but the time until a decrease ocurred depended on concentration. In contrast, relative kS remained > 100% with chloride solutions, but decreased substantially when distilled water replaced the chloride solutions. Differences in aggregate stability and Ks due to the cation present (either Na+ or K+) appeared to be very small. A surface crust formed in the upper 1 cm of the soils leached with hydroxide solutions. This surface crust had substantially less organic carbon than the upper 1 cm of soil from the cores leached with chloride.A two‐stage process explains the decrease in ks when strongly alkaline solutions are applied to soil. First, organic matter dissolution decreases aggregate stability, with the rate of organic matter dissolution depending on hydroxide concentration; and second, increased repulsion of soil particles (due to increased pH) causes movement of dislodged particles into pore spaces, resulting in decreased Ks.

Photocatalytic hydrogen production from water over SrTiO 3 crystal surfaces, electron spectroscopy studies of adsorbed H 2, O 2 and H 2O

Hydrogen production from metal-free, as well as from platinized, SrTiO 3 crystals has been observed upon illumination in water vapor saturated films of soluble ionic compounds and in aqueous electrolytes. Hydrogen production occurs at the illuminated surface of metal-free crystals, implying a mechanism rather different from that operating in SrTiO 3/Pt photoelectrochemical cells. Hydrogen production rates increase with increasing hydroxide concentration in the electrolyte. This [OH −] dependence of the rate is particularly strong in the 5N–20N concentration range. Photoemission studies have identified a reduced surface species ascribed to Ti 3 and hydroxyl groups on SrTiO 3(111). This surfacc species is involved in, photoactivity related to oxygen adsorption and photodesorption. The concentration of surface hydroxyl groups can be monitored with UPS.

Photocatalytic hydrogen production from water on Pt-free SrTiO3 in alkali hydroxide solutions

Semiconductor surfaces can act as photosensitizers for small molecules which on their own do not absorb solar photons. Such sensitizers can be used for the photoassisted decomposition of water to hydrogen and oxygen. Most previous work on this process has concentrated on photoelectrochemical ceils using oxide semiconductor photoanodes for oxygen evolution and platinum cathodes for the evolution of hydrogen1–3. We report here the sustained photogeneration of hydrogen on SrTiO3 single crystal surfaces by a different mechanism, when no platinum coating or platinum counterelectrode is present. Hydrogen yields far exceed the monolayer amounts (∼1015 molecules cm−2) expected from a surface stoichiometric reaction. The reaction takes place on illumination of the crystal with band gap radiation (hv ≧ 3.2eV) in aqueous alkaline solution. The rate of hydrogen evolution increased with increasing hydroxide concentration in the solution. We also report the use of water vapour as a reactant through saturation of a layer of a basic deliquescent compound, such as NaOH, which coated the crystal. The photocatalytic generation of hydrogen on the illuminated surface of metal-free SrTiO3 crystals shows that strongly reductive as well as oxidative reactions can be carried out and sustained on illuminated oxide semiconductors. A wide range of photocatalytic reactions may possibly be carried out in conditions not amenable to the operation of photoelectrochemical cells by using this new mechanism.

Chalcone dihalides—VII: The course of the cyclization of 2′-hydroxy-6′-methoxyl derivatives

2′-hydroxychalcone dibromides substituted by OMe in the 6′-position are found to yield little or no aurone in dilute aqueous ethanolic potassium hydroxide. The proportion of aurone to flavone in their products parallels increasing hydroxide concentration. It is proposed that the course of aurone formation is chalcone dibromide → α-bromochalcone → chalcone bromohydrin → chalcone epoxide → aurone hydrate → aurone and that the initial function of the nuclear substituent(s) is to sterically prevent deactivation of the carbonyl group by the phenoxide anion.

Untersuchungen zur Ammoniakbildung bei der Hydrazinzersetzung

While examining the formation of ammonia when hydrazine decomposes on electrocatalysts (platinized platinum, Raney nickel and amalgamated sinter-nickel) on open circuit as well as under load, the following facts were established: (1) The amount of NH 3 which has formed decreases with increasing hydroxide concentration. The relation of x = c OH − / c N 2H 4 is the critical quantity for concentration dependency. (2) The ammonia formation rate is independent of the potential within a potential region of ±300 mV. (3) Ammonia is produced only when the electrode has adsorbed sufficient hydrogen. Therefore the NH 3 formation on the amalgamated electrode is largely suppressed under anodic loading. In view of these results, several suggestions for the reaction mechanism are discussed.