pH Value Of Aqueous Solution Research Articles

Identification of tin species released in solution during the water leaching of solids from the alkaline smelting (NaOH-KOH) of stanniferous ores

Tin species were studied Makundju ores in DRCongo. Identification of tin species released in aqueous solution during leaching of solids from the alkaline smelting (NaOH-KOH) was done to prepare added-value mining products on tin ores mined in the eastern DR Congo. Prior to alkaline fusion to have the smelting products (SP), the initial sample (IS) was processed for tests and characterization of tin species. Alkaline fusion in molten KOH-NaOH system was used and leached solution was considered for further analyses. Various physicochemical techniques including X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and FTIR spectroscopy were used to characterize the initial ore and the molten cake. Water leached cake solution at a solid/liquid ratio of 1:10 was used to identify and characterize tin species. ICP-OES analysis of the pH 11.9 solution revealed a content of 4506.3 ppm, which is equivalent to a 95.87% leaching yield. Such yield attests to the stable Sn(OH)<sup>2-</sup><sub>6(aq)</sub> ion as confirmed by UV-Vis. Crystallizations of M<sub>2</sub>Sn(OH)<sub>6(s)</sub> (M = Na and/or K) was studied using XRD, FTIR and TGA. As pH decreases below 9, Sn(OH)<sup>2-</sup><sub>6(aq)</sub> ion changes to other tin species such as Sn(OH)<sup>-</sup><sub>5(aq)</sub>, Sn(OH)<sub>4(S)</sub>, Sn(OH)<sup>+</sup><sub>3(aq)</sub>, Sn(OH)<sup>2+</sup><sub>2(aq)</sub>, Sn(OH)<sup>3+</sup><sub>(aq)</sub> and Sn(OH)<sup>4+</sup><sub>(aq)</sub>. The stability of each the tin species was determined at different pH values in aqueous solution. Hence, alkaline hexahydroxostannate nanoparticles, used in many electronic applications, can be produced from tin ores.

Synthesis, properties, and applications of all-solid-state reference electrode based on AgTi2(PO4)3

High-density AgTi2(PO4)3 as a solid electrolyte was synthesised by a high-temperature solid-state process. The optimal sintering temperature was determined to obtain the best structural and electrical performance. Based on the as-prepared AgTi2(PO4)3 fast-ion conductor, a new type of all-solid-state reference electrode was prepared, and its electrochemical properties, such as cyclic voltammetry curves and potentials at varying pH, were investigated. A pH sensor was designed by combining an AgTi2(PO4)3 reference electrode with an Ir/IrO2 pH electrode. This pH sensor exhibited a good linear response to pH values in aqueous solutions and simulated seawater samples. In addition, a metal ion sensor, comprising the as-fabricated solid-state reference electrode, a Pt counter electrode, and a glassy carbon working electrode, was employed to quantify Cu2+, Hg2+, and Pb2+ concentrations using differential-pulse anodic stripping voltammetry. The resulting peak currents correlated with the metal ion concentrations and exhibited a low detection limit, good linearity, and wide detection range, which is suitable for performing chemical analysis in harsh marine environments.

Synergistic Effect of the Moisture Content and pH Value of Aqueous Solutions on Oxidation Characteristics of Coal.

In order to study the synergistic effect of the moisture content and pH value of aqueous solutions on coal oxidation, coal samples with different moistures were prepared by using aqueous solutions with different pH values (3, 5, 7, and 8). The CO, C2H4 production, oxygen consumption rate, and crossing point temperature parameters in the process of low-temperature oxidation of the prepared coal and raw coal samples were studied by using a low-temperature oxidation device. Thermogravimetry-derivative thermogravimetry (TG-DTG) curves of coal samples with different moistures were obtained on the basis of thermogravimetric analysis of coal by using a synchronous thermal analyzer. According to the characteristic temperature, the process of coal spontaneous combustion (CSC) can be divided into the water evaporation and desorption stage, oxygen absorption and weight gain stage, thermal decomposition and combustion stage, and burnout stage. The Coats-Redfern integral method was used to select the appropriate reaction mechanism function to calculate the apparent activation energy at different stages of the coal reaction process. The results show that the activation energy of the oxidation reaction of the coal sample with a moisture of 15% is the smallest, and the oxidation reaction is the most easy to occur. When the coal samples with a moisture of 15% were oxidized at low temperature, the CO and C2H4 emissions and oxygen consumption rates were the highest. The pH value of the aqueous solution has dual effects on CSC. When the moisture is 15%, the higher the pH value of the aqueous solution, the weaker the promotion effect on the coal oxidation process is and the lower the pH value of the aqueous solution is, the higher the production of CO and C2H4 and the oxygen consumption rate is and the earlier the crossing point temperature is reached during low-temperature oxidation of the coal sample.

Electrochemical and Biocatalytic Signal-Controlled Payload Release from a Metal-Organic Framework.

A metal-organic framework (MOF), ZIF-8, which is stable at neutral and slightly basic pH values in aqueous solutions and destabilized/dissolved under acidic conditions, is loaded with a pH-insensitive fluorescent dye, rhodamine-B isothiocyanate, as a model payload species. Then, the MOF species are immobilized at an electrode surface. The local (interfacial) pH value is rapidly decreased by means of an electrochemically stimulated ascorbate oxidation at +0.4V (Ag/AgCl/KCl). Oxygen reduction upon switching the applied potential to -0.8V allows to return the local pH to the neutral/basic pH, then stopping rapidly the release process. The developed method allows electrochemical control over stimulated or inhibited payload release processes from the MOF. The pH variation proceeds in a thin film of the solution near the electrode surface. The switchable release process is realized in a buffer solution and undiluted human serum. As the second option, the pH decrease stimulating the release process is achieved upon an enzymatic reaction using esterase and ester substrate. This approach potentially allows the release activation controlled by numerous enzymes assembled in complex biocatalytic cascades. It is expected that related electrochemical or biocatalytic systems can represent novel signal-responding materials with switchable features for delivering (bio)molecules within biomedical applications.

Nanopore based electrokinetic purification of oil-in-water emulsion with thermal and pH modulation

Abstract Efficient purification of oil-in-water emulsion is significant for protecting global water resource. Nevertheless, the traditional passive technologies for handling oil-in-water emulsion suffer from the drawback of low cost-effectiveness for using robust filtration membranes. In our previous research, an active electrokinetic based oil droplet filtration technique is firstly developed relying on a negative dielectrophoretic phenomenon induced by the huge difference between dielectric properties of oil and water. However, the effects of temperature and pH value of wastewater on the electrokinetic filtration efficiency of oil droplet have never been clarified. In the current work, a multi-physical theoretical model of electrokinetic purification of oil-in-water emulsion with thermal and pH modulation is constructed. The dimensionless ratio of dielectrophoretic force over hydrodynamic force on oil droplet is an essential criterion for its dynamic behavior, and it exhibits a positive correlation with purification effectiveness of oil-in-water emulsion. From numerical modelling, the magnitude of dielectrophoretic force to hydrodynamic force ratio on oil droplet is enhanced with a decreasing temperature, increasing ion concentration, and neutralized (pH=7.0) property of oily wastewater. Then, the critical direct current voltage for realizing successful oil droplet filtration through insulated nanopore under electrokinetics is analyzed under different parametric conditions, which indicates that the energy consumption of oil-in-water emulsion purification can be reduced by cooling down temperature and neutralizing pH value of aqueous solution. The current work offers a theoretical understanding of electrokinetic purification of oil-in-water emulsion, contributing to its development towards industrial applications.

Study of magnesium-sodium double phosphates ceramic for bone treatment

Ceramics based on magnesium-sodium double phosphate MgNaPO4 and magnesium-sodium double orthophosphate Mg4Na(PO4)3 were synthesized. The most suitable calcination temperatures were found as 800 °C for MgNaPO4 and 900 °C for Mg4Na(PO4)3. At higher sintering temperatures, crack formation was observed, which can be explained by the presence of polymorphic transformations and thermal decomposition of MgNaPO4. The crystal structures and lattice parameters for magnesium-sodium double phosphates were refined by using powder X-ray diffraction method. Obtained ceramic samples based on MgNaPO4 and Mg4Na(PO4)3 are characterized by pH values in aqueous solutions of 7.1 and 8.2, respectively, which are close values to physiological pH values. They also undergo resorption in a model environment, and may be promising in regenerative surgery.

Immobilization of the Polar Group into an Ultramicroporous Metal-Organic Framework Enabling Benchmark Inverse Selective CO2/C2H2 Separation with Record C2H2 Production.

One-step harvest of high-purity light hydrocarbons without the desorption process represents an advanced and highly efficient strategy for the purification of target substances. The separation and purification of acetylene (C2H2) from carbon dioxide (CO2) by CO2-selective adsorbents are urgently demanded yet are very challenging owing to their similar physicochemical properties. Here, we employ the pore chemistry strategy to adjust the pore environment by immobilizing polar groups into an ultramicroporous metal-organic framework (MOF), achieving one-step manufacture of high-purity C2H2 from CO2/C2H2 mixtures. Embedding methyl groups into prototype stable MOF (Zn-ox-trz) not only changes the pore environment but also improves the discrimination of guest molecules. The methyl-functionalized Zn-ox-mtz thus exhibits the benchmark reverse CO2/C2H2 uptake ratio of 12.6 (123.32/9.79 cm3 cm-3) and an exceptionally high equimolar CO2/C2H2 selectivity of 1064.9 at ambient conditions. Molecular simulations reveal that the synergetic effect of pore confinement and surfaces decorated with methyl groups provides high recognition of CO2 molecules through multiple van der Waals interactions. The column breakthrough experiments suggest that Zn-ox-mtz dramatically achieved the one-step purification capacity of C2H2 from the CO2/C2H2 mixture with a record C2H2 productivity of 2091 mmol kg-1, surpassing all of the CO2-selective adsorbents reported so far. In addition, Zn-ox-mtz exhibits excellent chemical stability under different pH values of aqueous solutions (pH = 1-12). Moreover, the highly stable framework and excellent inverse selective CO2/C2H2 separation performance showcase its promising application as a C2H2 splitter for industrial manufacture. This work paves the way to developing reverse-selective adsorbents for the challenging gas separation process.

Hydrothermal synthesis of zeolitic material from circulating fluidized bed combustion fly ash for the highly efficient removal of lead from aqueous solution

The utilization of coal fly ash derived from circulating fluidized bed combustion (CFBFA) still faces great challenges because of its unique characteristics. In this study, a zeolitic material with Na-P1 zeolite as the main phase was successfully synthesized via a hydrothermal method by using CFBFA as the raw material. The effects of hydrothermal temperature, time, and added CTAB amount on the characterizations of synthesized materials were investigated by XRD, SEM, and XPS. The properties of the optimal zeolitic material and its adsorption performance for Pb2+ in aqueous solution were evaluated. The influences of pH, initial concentration, dosage, and temperature on Pb2+ adsorption were also examined. Results revealed the following optimal parameters for the synthesis of zeolitic material: NaOH concentration of 2 mol·L−1, solid-to-liquid ratio of 1:10 g·ml−1, hydrothermal temperature of 110 °C, hydrothermal time of 9 h, and CTAB amount of 1 g (per 100 ml solution). The adsorption capacities of the zeolitic material reached 329.67, 424.69, and 542.22 mg·g−1 when the pH values of aqueous solution were 5, 6, and 7, respectively. The Pb2+removal efficiency can reach more than 99% in aqueous solution with the initial concentrations of 100–300 mg·L−1 under pH 6 and suitable adsorbent dosage. The adsorption and kinetics of Pb2+ on the zeolitic material can be described by Langmuir isotherm and pseudo-second-order kinetic models, respectively. The ion exchange between Pb2+ and Na+ and chemisorption are the main adsorption mechanism. All these findings imply that the synthesis of low-cost adsorbent for Pb2+ removal from weak acid and neutral aqueous solution provides a highly effective method to utilize CFBFA.

Dual‐mode color‐changing pH sensor based on fluorescent MOF embedded photonic crystal hydrogel

AbstractIn this work, a novel pH‐responsive hybrid hydrogel namely MOF/PC hydrogel was prepared by incorporating metal–organic framework CDs@UiO‐66(OH)2 into the matrix of photonic crystal hydrogel. MOF/PC hydrogel could display colorful structure colors under visible light and emit blue fluorescence under UV light owing to the stop‐bond effect of photonic crystal and fluorescence emission capacity of CDs@UiO‐66(OH)2, respectively. Benefiting from these two optical phenomena, MOF/PC hydrogel could work as a dual‐mode color‐changing sensor, in structure color mode and fluorescence mode, for the sensing of pH. When incubating in aqueous solutions with different pH values, MOF/PC hydrogel could adjust its structure color to the corresponding one ranging from green to pink in 10 s, and this visible color‐changing can be used to determine the approximate pH values of the sample by naked eyes without any assistance of instruments. As for the fluorescence mode, the fluorescence intensity of MOF/PC hydrogel showed a good linear relationship with pH value in the range of 3.0~7.0, and it can be used to determine the pH value of aqueous solutions quantitatively. Moreover, the as‐prepared sensor is reusable and can be applied to the pH sensing of real water samples.

Robust network-like superhydrophobic magnesium hydroxide surface via cathodic electrodeposition with xanthan gum

Economic cost of raw materials has become an important limiting factor for the further application of superhydrophobic surface. Magnesium hydroxide is an innocuous, antibacterial, eco-friendly, and especially cheap material. Superhydrophobic surface fabricated with magnesium hydroxide was safe, environment friendly, and of very low cost. However, magnesium hydroxide superhydrophobic surfaces prepared through traditional electrodeposition method was always fragile and easy to peel off substrate, due to the discontinuous platelet-like structure which led to weak mechanical property. In this work, we electrodeposited a robust network-like magnesium hydroxide layer on iron substrate under the structure direction of xanthan gum which formed network with helical conformation at low temperature and proper pH value in aqueous solution. Electrodeposition factors such as concentrations of xanthan gum and glucose, bath temperature, pH value of electrolyte and current intensity were studied. The magnesium hydroxide layer fabricated at the optimum condition (0.5 mol/L magnesium nitrate, 4 mg/L XG, 4 mg/L glucose, 2.6 pH value and 35 mA at 15°C for 20 min) was with network-like structure, and exhibited excellent superhydrophobicity (water contact angle, 153.56° sliding angle, 2.2°) and self-cleaning property after stearic acid modification. The robust layer kept superhydrophobic until 600 mm abrasion length facing 1000 grit SiC sandpaper under 100 g weight, and with detachment less than 5% after cross hatch tape adhesion test. The layer also demonstrated good long-term immersion stability, and was still superhydrophobic with 48 h immersion in 3.5 wt% NaCl aqueous solution at room temperature. The inhibition efficiency of the layer reached 99.03%, due to its extremely high corrosion resistance (Rct = 2.87 × 105 Ω/cm2, Rf = 2.53 × 106 Ω/cm2). The introduced method of electrodepositing robust network-like MH layer made the further application of low-cost superhydrophobic surface with magnesium hydroxide possible.

Stable pH sensitivity of LaAlO3/SrTiO3 interfacial electronic gas

Probing pH value is essential for many applications. The request of developing stable and highly sensitive pH sensor with small size are increased recently, this is a challenge to the traditional glass pH sensors. This work investigated the pH sensing performance of the novel two-dimensional electronic gas (2DEG) at the LaAlO3/SrTiO3 heterostructure interface discovered recently. The experimental results demonstrated that the devices host excellent sensing ability to the pH value of aqueous solutions. Quite stable output current is realized for a given pH value, and the output current is linearly dependent on pH value as required by sensor applications. This work would prompt the application research of LaAlO3/SrTiO3 heterostructure and design of new generation of advanced pH sensors.

Amphiphilicity-adaptable graphene quantum dots to stabilize pH-responsive pickering emulsions at a very low concentration

Hypothesis: Stimuli-responsive Pickering emulsions have attracted considerable interest due to their widespread potential applications. Especially pH-responsive behavior could be easily implemented. In this work, we reported a pH-responsive Pickering emulsion based on amphiphilic graphene quantum dots at a low concentration which shows a great potential from the environmental and economic perspective. The stimuli responsive properties would make the smart Pickering emulsifiers recyclable and reusable.Experiments: The amphiphilic-adaptable graphene quantum dots functionalized by alkyl groups (C-GQDs) were synthesized by a facile one-step pyrolysis method. The pH-responsive emulsion performances were investigated, and the mechanism of pH-responsive of C-GQDs was studied by dynamic light scattering.Findings: The amphiphilicity of C-GQDs could be acquired controllably and effectively by this facile one-step pyrolysis method, which are able to stabilize Pickering emulsion at a very low concentration (0.001%). The amphiphilicity of C-GQDs are capable of changing in response to environmental stimuli. When the pH value of aqueous solution adjusts to 2, these C-GQDs aggregate in contrast to their stability in neutral condition due to the alternation of surface charges. The pH-responsive aggregation/ dispersion behavior of C-GQDs allows us to tune the interactions between oil-in-water emulsion droplets without introduction of destabilization agents. This will provide huge economic benefits in industrial applications in the future.

Preparation of electroconductive film based on self-assembled aminothiophene/poly(γ-glutamate) nanoparticles and its application in biosensor

An electroconductive nanoparticles (NPs) film consisting of sodium poly(γ-glutamate) (γ-PGANa) and 3,4-diaminothiophene dihydrochloride (DATh) was simply prepared through macromolecular self-assembly and electropolymerization methods. Firstly, the γ-PGANa and the DATh underwent a complexation to form DATh/γ-PGANa composites through the electrostatic interaction; the DATh/γ-PGANa composites were then self-assembled into DATh/γ-PGANa NPs through decreasing the pH value in aqueous solution. Next, an electroconductive NPs film was formed on the surface of a gold electrode by casting the DATh/γ-PGANa NPs and subsequently electropolymerizing the DATh. Last, horseradish peroxidase and Nafion were cast onto the NPs film to obtain an enzymatic biosensor for H2O2 detection. The electroconductive DATh/γ-PGANa NPs film endowed the biosensor with high sensitivity. Under the optimal conditions, the prepared biosensor showed a linear range from 1 × 10−11 to 1 × 10−4 mol·L−1 with a detection limit of 3 × 10−12 mol·L−1 for H2O2 detection. The biosensor can retain its detection performance for 4 weeks. The response currents of the biosensor changed little after adding the interferent into the analyte. The standard deviation of the response between different biosensors did not exceed 2.5%.

A neoteric dual-channel spectral sensor for wide-range pH detection based on variables in UV-vis peak and intensity.

A water-soluble 2',4',6'-trihydroxy phenylazo luminol dye (THPL) with a D-π-A conjugated structure was developed for the first time for the dual-channel spectral sensing of a wide-range of pH values in aqueous solutions, using phloroglucinol as the electron-donating group, heterocycle amide luminol as the electron-accepting one and -NN- as the π-conjugated bridge. Its UV-vis absorption spectrum, especially its spectral response to pH, was investigated in detail. The results confirmed that the proposed THPL exhibited superior UV-vis spectral properties, a strong molar absorption coefficient (εmax = 3.35 × 104 L mol-1 cm-1) and a small half-band width of ca. 126 nm. In particular, either the absorption intensity (Abs) or peak (λmax) changed linearly with pH values from 3.0 to 10.0 under the optimized conditions. Notably, THPL expressed an exclusive dual-channel spectral response to pH, i.e., Abs (a.u.) = 0.1316 + 0.0278 pH (R2 = 0.9921), λmax = 441.5 - 6.64 pH (R2 = 0.9968, pH = 3.0-6.0) and λmax = 359.6 + 7.38 pH (R2 = 0.9879, pH = 6.0-10.0). Under the optimized conditions, THPL was applied to detect pH values in some aqueous and fruit juice samples with satisfactory results. The reversible recognition mechanism was deduced by UV-vis titration, 1H NMR titration and theoretical calculation.

Natural hydroxyapatite from fishbone waste for the rapid adsorption of heavy metals of aqueous effluent

In this paper, metal ions removal using hydroxyapatite (HAp) derived from fishbone waste was reported. Various characterization techniques confirmed the presence of HAp. Optimal adsorption occurred in the first 5 min of contact for both Ni2+ and Cu2+ ions. Larger particle size favor higher adsorption efficiency for Ni2+ case while the reverse was displayed for Cu2+ case. More than 80% ions removal was achieved in all cases for Ni2+, but for the case with Cu2+ ions, only particle size of 53μm achieved optimal ions removal of > 87%. In both cases, heat treatment was unnecessary. The samples after contact with Cu2+ required neutralization but no treatment was required for Ni2+ case. SEM results showed that higher ion removal efficiency was attributed to higher porosity. Further testing with atomic adsorption spectroscopy carried out with Ni2+, Cu2+ and Zn2+ showed the optimal particle size was 53μm and > 95% ion removal efficiency achieved with optimal setting for all cases. Cu2+ adsorption was fitted with Langmuir adsorption isotherm while Ni2+ and Zn2+ adsorption were fitted with Freundlich adsorption equation. Unchanged pH value of aqueous solution for Cu2+ case led to the conclusion that HAp performed best as a bioadsorbent at a more neutral pH. This study is expected to contribute to metal ions removal in water purification and wastewater treatment.

Modification of isolation methods and physico-biochemical properties of preparations of fungal oxidoreductases

The results of the modification of methods for producing enzymatic preparations (EP) of peroxidases and catalases of extra- and intracellular finding from fungal cultures are presented. Strains of Flammulina velutipes F-vv, Lentinula edodes 523 and Pleurotus ostreatus P-01 were used as producers of oxidoreductases. The producers were cultured in glucose-peptone medium, modified for each strain. Protein fractionation was carried out by leaching with ammonium sulfate at a saturation of 40–70% for peroxidases and 80% for catalases. The obtained solutions of protein fractions were additionally subjected to purification by dialysis, gel filtration on Molselect G-50 and G-75 granules, and also freeze drying. The yield of enzymatic preparations per unit mass of mycelium and the volume of culture fluid were calculated. The individual characteristics of EP – enzymatic activity, the mass percentage of protein and associated amino acids, the ratio of the latter in groups depending on the nature of the radicals (amphotericity) of protein molecules are established. It was proved that the amino acid content in the proteins of fungal EP catalases and peroxidases indicates their acidic nature and this is confirmed by the pH values of aqueous solutions. Examination and toxicity testing of enzymatic preparations were carried out in certified laboratories, which confirmed their characteristics and compliance with safety requirements. The therapeutic properties of amino acids that are part of proteins or are in a free state in enzyme preparations are analyzed. In this way, the methods have been developed for producing enzymatic preparations of peroxidases and catalases of extra- and intracellular location, which allow new antioxidant enzymes with individual properties to be obtained, and, as a result, bring prospects for use in various industries and scientific research.

Modification of isolation methods and physico-biochemical properties of preparations of fungal oxidoreductases

The results of the modification of methods for producing enzymatic preparations (EP) of peroxidases and catalases of extra- and intracellular finding from fungal cultures are presented. Strains of Flammulina velutipes F-vv, Lentinula edodes 523 and Pleurotus ostreatus P-01 were used as producers of oxidoreductases. The producers were cultured in glucose-peptone medium, modified for each strain. Protein fractionation was carried out by leaching with ammonium sulfate at a saturation of 40–70% for peroxidases and 80% for catalases. The obtained solutions of protein fractions were additionally subjected to purification by dialysis, gel filtration on Molselect G-50 and G-75 granules, and also freeze drying. The yield of enzymatic preparations per unit mass of mycelium and the volume of culture fluid were calculated. The individual characteristics of EP – enzymatic activity, the mass percentage of protein and associated amino acids, the ratio of the latter in groups depending on the nature of the radicals (amphotericity) of protein molecules are established. It was proved that the amino acid content in the proteins of fungal EP catalases and peroxidases indicates their acidic nature and this is confirmed by the pH values of aqueous solutions. Examination and toxicity testing of enzymatic preparations were carried out in certified laboratories, which confirmed their characteristics and compliance with safety requirements. The therapeutic properties of amino acids that are part of proteins or are in a free state in enzyme preparations are analyzed. In this way, the methods have been developed for producing enzymatic preparations of peroxidases and catalases of extra- and intracellular location, which allow new antioxidant enzymes with individual properties to be obtained, and, as a result, bring prospects for use in various industries and scientific research.

Examination of UV-absorption spectroscopy for analysis of O3, NO2−, and HNO2 compositions and kinetics in plasma-activated water

To examine UV-absorption spectroscopy as a tool for the analysis of reactive oxygen and nitrogen species in plasma-activated water, we attempted to separate the NO2− and HNO2 concentrations depending on the pH value of aqueous solution by identifying their different features of absorption spectra within deep-UV and near-UV ranges. For the measurement of O3, we examined the molar absorption coefficient ε at 260 nm using two methods. In the first method, the absorption of degassed O3 from water was measured, whereas in the second method, using an aqueous reaction of O3 with NO2−, the decrease in O3 was compared to the decrease in NO2− and increase in NO3−. The values of ε derived from both methods were slightly different, but were within ±5% of the value of 3.0 × 103 M−1 cm−1, as commonly found in the literature. The reactive uptake of O3 on aqueous solution of NaNO2 was also estimated.

Effect of chemical reaction mechanism on the formation of ZnS colloid particles with structure disordering

ZnS colloid particles were obtained in wide pH range by using different sulfide-generating precursors, namely, thiourea (NH2)2CS, thioacetamide CH3C(S)NH2, sodium thiosulfate Na2S2O3 and sodium sulfide Na2S. Using different types of chemical precipitation technique made it possible to form ZnS nanoparticles with different crystal structure. The influence of pH value of aqueous solutions was shown to play a crucial role in ZnS structure disordering. The structure characterization of the final products was accomplished through X-ray diffraction and transmission electron microscopy. ZnS was formed in the colloidal/nanocrystalline state regardless of the sulfur agent.

L-proline functionalized pH-responsive copolymers as supported organocatalysts for asymmetric aldol reaction in water

pH-Responsive copolymers with reversible transformation ability have been investigated as new effective carriers for L-proline to catalyze asymmetric aldol reaction in water. A series of block copolymers of mPEG-b-P(DEAx-co-L-ProlAy) (mPEG-PDL) bearing L-proline catalytic sites and pH-responsive poly (diethylaminoethyl methacrylate) (PDEA) segments were synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization in the presence of methyl polyethylene glycol (mPEG) trithiocarbonate macro-RAFT agent. The pH-induced self-assembly behaviors of three copolymer catalysts with different contents of PDEA were investigated via the combination of UV–visible spectrometer (UV–vis), dynamic light scattering (DLS) and transmission electron microscopy (TEM). Catalytic activity and stereoselectivity of these copolymer catalysts were evaluated by direct asymmetric aldol reaction of p-nitrobenzaldehyde and cyclohexanone in water. The results indicated that catalytic activity and stereoselectivity effected by the pH value of aqueous solution and the structures of copolymer catalyst assemblies. mPEG-PDL-2 give the aldol product with high conv., yield, anti/syn, and ee (92%, 91%, 92/8, 96%), respectively at pH 7.0. Furthermore, these pH-responsive copolymers supported L-proline are easily recycled by a reversible phase transition.