pH Value Of Reaction Solution Research Articles

Influence of pH values on (Nd + Y):Al molar ratio of Nd:YAG nanopowders and preparation of transparent ceramics

The Nd:YAG ceramics were fabricated by vacuum sintering at 1750 °C for 20 h, where the raw nanopowders were synthesized by the co-precipitation method, and calcined at 1050 °C for 2 h. The effect of the pH values of reaction solution on the (Nd + Y):Al mole ratio of the powders was discussed here. It was found that the pH value range of 7.9–8.2 was suitable for the preparation of the Nd:YAG nanopowders. Secondary phases and pores appeared in and between the grains of Nd:YAG ceramic with the (Nd + Y):Al mole ratio of 0.576. The specimens with the (Nd + Y):Al mole ratio range of 0.598–0.603 had fine microstructures, and their transmissions were both over 80% at the near infrared wavelength. If the (Nd + Y):Al mole ratio reached 0.648, many secondary phases occurred along the grain boundaries.

Co-Precipitation Synthesis and Optimization Process for LiCo<sub>1/3</sub>Ni<sub>1/3</sub>Mn<sub>1/3</sub>O<sub>2</sub>

With the acetates of nickel, manganese and cobalt as raw materials and lithium hydroxide as precipitation agent, the precursor Ni1 / 3 Co1 / 3 Mn1 / 3 (OH) 2 was first prepared by chemical coprecipitation method, which was then mixed and ballmilled with certain stoichiometric ratios of LiOH∙H2O, and ultimately obtained LiCo1/3Mn1/3Ni1/3O2 after calcination process. Single-factor experiment method, in conjunction with XRD, SEM, and charge-discharge test, was utilized to study the influence of various factors, including the dispersion way of precursor, pH value of reaction solution, and the content of ballmilling lithium on the electrochemical properties of LiCo1/3Mn1/3Ni1/3O2. The results indicated that: (1) the material dispersed by ultrasonic treatment revealed excellent cycling performance, its ratio of capacity fading decreased at least 34.1% compared to those without ultrasonic process; (2) the optimum conditions of fabricating LiCo1/3Mn1/3Ni1/3O2 may be summarized as the treatment of ultrasonic dispersion, suitable pH value (12~13) and stoichiometric ratio (1.0) of ballmilling lithium.

Photocatalytic Reduction of Nitrobenzene by Titanium Dioxide Powder

AbstractThe feasibility of photocatalytic reduction of nitrobenzene using titanium dioxide powder as photocatalyst, under the protection of nitrogen and presence of hole scavenger conditions, was studied. Effects of the illumination time, amount of catalyst and sorts of solvent on the photocatalytic reduction of nitrobenzene were investigated, respectively. The results showed that, for the photocatalytic reduction of nitrobenzene, aniline was the main product. When the illumination time was 6 h, 8.15×10−4 mol/L of nitrobenzene could be photocatalytically reduced completely, with the yield of aniline being 88.5%. The optimum amount of TiO2 used was 4.0 g/L, the optimum initial pH value of reaction solution was 4.0 and the best solvent was methanol. The kinetics and mechanisms of the photocatalytic reduction of nitrobenzene were also discussed.

The oxidative transformation of sodium arsenite at the interface of α-MnO2 and water

Arsenite is acute contaminant to human health in soil and water environment. In this study, Pyrolusite (alpha-MnO(2)) was used to investigate the oxidative transformation of arsenite into arsenate with batch experiments under different reaction conditions. The results showed that arsenite transformation occurred and was accompanied by the adsorption and fixation of both As(III) and As(V) on alpha-MnO(2). About 90% of sodium arsenite (10mg/L) were transformed by alpha-MnO(2) under the conditions of 25 degrees C and pH 6.0, 36.6% of which was adsorbed and 28.9% fixed by alpha-MnO(2). Increased alpha-MnO(2) dosages promoted As (III) transformation rate and adsorption of arsenic species. The transformation rate and adsorption of arsenic species raised with increasing pH values of reaction solution from 4.7 to 8.0. The oxidation rate decreased and adsorbed As(III) and As(V) increased with increasing initial arsenite concentration. The enhancement on oxidative transformation of sodium arsenite may result from abundant active sites of alpha-MnO(2). Along with adsorption and fixation of arsenic species during the reaction, the crystal structure of alpha-MnO(2) did not change, but the surface turned petty and loosen. Our results demonstrated that alpha-MnO(2) has important potential in arsenic transformation and removal as the environmentally friendly natural oxidant in soil and surface water.

In situ assembly of ZSM-5 nanocrystals into micro-sized single-crystal-like aggregates via acid-catalyzed hydrolysis of tetraethylorthosilicate

ZSM-5 aggregates were synthesized with the silica source tetraethylorthosilicate (TEOS) being hydrolyzed at acidic conditions to produce siliceous precursors, followed by the addition of aluminum sulfate and tetrapropyl ammonium bromide (TPABr), and with the resulting gel mixture being hydrothermally crystallized at basic conditions. The obtained products were characterized by XRD, SEM, and N2 adsorption. Well crystallized ZSM-5 can be successfully synthesized through the sulfuric acid-catalyzed hydrolysis of TEOS within a short crystallization time 35 h. The thus produced micro-sized single-crystal-like zeolite ZSM-5 aggregates (10 μm) are made of uniformly distributed nanocrystals with sizes of about 200 nm. Moreover, by adjusting the hydrothermal reaction parameters, such as increasing the crystallization temperature, the TPABr/SiO2 ratio and the pH value of reaction solution, the crystallization is accelerated substantially. Also, the moderate H2O/SiO2 molar ratio of 20–60 in the synthesis mixture can lead to pure ZSM-5, and yet the optimal ratio is 40.

Preparation and Characterization of Cu-Coated Nano SiC Composite Particles

The Cu-coated nano SiC composite particles were prepared by heterogeneous nucleation method. For the heterogeneous nucleation process, the dispered nano SiC particles and the active Cu2O precipitation were both prefabricated. The composite particles were characterized by means of XRD, SEM, EDS, TEM and ED analysis technics. It is found that Cu layers are coated on the nano SiC particles, which are continuous and dense, and partly oxidized to Cu2O, and the oxidation rate can be reduced by improving experimental processes. The investigation on reaction mechanism shows the disproportionating reaction speed of Cu+ can be controlled by adjusting the pH value of reaction solution, which makes the degree of supersaturation of Cu crystallites accord with the conditions of heterogeneous nucleation.

Single Nanocrystals of Anatase-Type TiO2 Prepared from Layered Titanate Nanosheets: Formation Mechanism and Characterization of Surface Properties

Anatase-type TiO2 single nanocrystals with boatlike, comblike, sheetlike, leaflike, quadrate, rhombic, and wirelike particle morphologies were prepared by hydrothermal treatment of a layered titanate nanosheet colloidal solution. The formation reactions and surface properties of the TiO2 nanocrystals were investigated using XRD, TEM, TG-DTA analyses, and measurements of BET specific surface area, photocatalytic activity, and ruthenium dye (N719) adsorption. The crystal morphology can be controlled by reaction temperature, pH value of reaction solution, and exfoliating agent. The titanate nanosheets were transformed to the TiO2 nanocrystals by two types of reactions. One is an in situ topotactic structural transformation reaction, and the other is a dissolution-deposition reaction on the surface. The anatase nanocrystals formed by the in situ topotactic structural transformation reaction retain the sheetlike particle morphology of the precursor, and they preferentially expose the (010) plane of anatase structure. The crystal surface of anatase nanocrystals prepared in this study showed higher photocatalytic activity and higher ruthenium dye adsorption capacity than did the Ishihara ST-01 sample, a standard anatase nanocrystal sample. The results indicated the (010) plane of the anatase structure has high photocatalytic activity and high ruthenium dye adsorption ability.

Sulfur mustard destruction using ozone, UV, hydrogen peroxide and their combination

Numerous methods are used for destruction of sulfur mustard. Oxidation is one of those methods. There have been only limited data concerning application of the advanced oxidation technologies (AOTs) for mustard destruction available before. In this study sulfur mustard oxidation rate depending on kind of the oxidative system and process parameters used was assessed using selected AOT. The following were selected for mustard oxidation: ozone (O 3), UV light (UV), hydrogen peroxide (H 2O 2); double systems: UV/O 3, UV/H 2O 2, and O 3/H 2O 2; a triple system: O 3/H 2O 2/UV and Fenton reaction. Effectiveness of the selected AOT methods has been evaluated and the most suitable one for mustard destruction was chosen. Using ozone in various combinations with hydrogen peroxide and UV radiation mustard can be destroyed much quicker comparing to the classical oxidizers. Fast mustard oxidation (a few minutes) occurred in those systems where ozone alone was used, or in the following combinations: O 3/H 2O 2, O 3/UV and O 3/H 2O 2/UV. When those advanced oxidation technologies are used, mustard becomes destroyed mainly in course of the direct oxidation with ozone, and reactions of mustard with radicals formed due to ozone action play a secondary role. Rate of sulfur mustard oxidation in the above mentioned ozone-containing oxidative systems decreases with pH value increasing from 2 to 12. Only when pH value of reaction solutions is close to pH 5, mustard oxidation rate is minimal, probably due to “disappearance” of radicals participating in oxidation in this pH. Sulfur mustard can be most effectively destroyed using just ozone in pH 7. In that case mustard destruction rate is only slightly lower than the rate achieved in optimal conditions, and the system is the simplest.

Microwave-Assisted Aqueous Synthesis: A Rapid Approach to Prepare Highly Luminescent ZnSe(S) Alloyed Quantum Dots

In this paper, we present a new procedure for the rapid synthesis of luminescent ZnSe nanocrystals in aqueous phase by microwave irradiation with controllable temperature. The effects of microwave irradiation and experimental conditions on the synthesis of nanocrystals were investigated systematically. It was found that there were significant effects of pH value of reaction solutions, molar ratio of precursors, and heating time of microwave irradiation on the optical properties of the ZnSe nanocrystals. A series of nanocrystals with different size was prepared in 1 h, and the photoluminescence quantum yield reached up to 17% at the optimal reaction condition. The results of HRTEM and XRD showed that the as-prepared nanocrystals had high crystallinity. The characterizations of EDS spectra and elemental analysis showed that the sulfur content of nanocrystals increased with the growth of nanocrystals. We speculated that the structure of nanocrystals was an alloy ZnSe(S) shell on the surface of the ZnSe particles core. Furthermore, we found that the oxygen from air in the reaction vessel played an important role in the decomposition of the thiol group under microwave irradiation.

Synthesis and Growth Kinetics of Monodispersive Indium Hydrate Particles

Nano‐ or submicron In(OH)3 and In2O3 particles of different morphologies were synthesized from a nitrate solution by a homogeneous precipitation process. By using X‐ray diffractometer, thermogravimetric analysis, transmission and scanning electron microscopes, and inductively coupled plasma‐optical emission spectrometry, the properties of particle growth were analyzed. The results indicated that the kinetics of the hydrolysis reaction of In3+ was a zero‐order reaction with an activation energy of 128 kJ/mol, which implied that the reaction was controlled by the decomposition kinetic of urea additive. The growth anisotropic of particles, pH value of reaction solutions, residual In3+ concentration relative to aging time with different temperatures and starting concentrations were reported in this study. Calcination of the hydrate to form In2O3 particles between 300° and 900°C did not greatly change the morphologies of the particles.

Effects of oxalate on Fe-catalyzed photooxidation of dissolved sulfur dioxide in atmospheric water

Abstract Fe-catalyzed photochemical oxidation of dissolved sulfur dioxide (SO 2 ), S(IV), in the presence of oxalate has been studied under the conditions typical for acidified atmospheric water. The Fe(III)-catalyzed oxidation of S(IV) is first order with respect to S(IV) concentration in the absence of oxalate. The presence of oxalate strongly inhibits Fe(III)-catalyzed S(IV) oxidation due to the formation of Fe(III)–oxalato complexes both in the dark and under UV–visible light. However, under UV–visible light irradiation, the generation of photooxidants, such as H 2 O 2 and OH radicals, by photochemical/chemical cycling of Fe(III)/Fe(II)–oxalato complexes, leads to the photochemical oxidation of S(IV). The initial oxidation rate increases with oxalate and Fe(III) concentration in the concentration ranges studied. The rate of Fe(III)-catalyzed photochemical oxidation of S(IV) in the presence of oxalate increases with increasing pH value of reaction solution and with decreasing irradiation wavelength. The concentrations of oxalate and other organic ligands are sufficiently large to significantly change the rates of Fe-catalyzed oxidation of dissolved SO 2 in atmospheric water droplets during both day- and night time.

Titania-supported bimetallic catalysts for photocatalytic reduction of nitrate

Photocatalytic reduction of nitrate in the presence of hole scavenger has been studied by using TiO 2-supported bimetallic catalysts for the first time. Compared with monometallic catalysts, bimetallic catalysts, especially Ni–Cu/TiO 2 catalyst, show more excellent photocatalytic reduction activity. Furthermore, the effects of metal weight ratio, total metal content, different hole scavengers and pH value of the solution are also investigated. It is found that pH value of reaction solution plays an important role in the photocatalytic reduction of nitrate ions. A mechanism is proposed to discuss enhancement effect of the bimetallic catalyst in photocatalytic reduction of nitrate ions in this paper.

Kinetics and mechanism on the epoxidation of cis-1-propenylphosphonic acid in H2O catalyzed by tungstate(VI) or molybdate(VI)

Epoxidation of cis-1-propenylphosphonic acid (CPPA) was carried out by using Na2WO4 or Na2MoO4 as catalyst, 30% hydrogen peroxide as an oxidant in H2O. Kinetic study showed that the epoxidation was zero-order both in H2O2 and in CPPA with perfect linearity. The reaction was first-order only in catalysts. IR spectra showed that the active peroxo group in the epoxidation was a metal–dioxygen ring. The characteristic absorption peaks were 856 and 866 cm−1 for Mo– and W–dioxygen rings, respectively. A mechanism of the epoxidation was suggested and discussed. The pH value of reaction solution and the negative charge on the carbon atoms of double bonds play an important role because they could influence the concentration of active complexes and the rate of insertion reaction. The research indicated that not only in non-protic solvents but also in H2O, the active peroxo groups were the metal–dioxygen rings for the epoxidation of olefins catalyzed by W(VI) or Mo(VI) complexes.

Preparation, structure and performance of zinc oxide with high electrochemical discharge capacity

Zinc oxide powders were prepared by a complexation–precipitation method and characterized by XRD, SEM and BET. Their electrochemical capacities were tested by the charge–discharge method. The influences of some key preparative conditions such as the pH value of reaction solution and the content of aqueous ammonia on the performance of the ZnO samples have been studied by theoretical analysis and experimental investigation. The ZnO samples with high tapping density and electrochemical activity have been obtained under the optimum preparative conditions. The relation between the structure and electrochemical performance of zinc oxide was also discussed.