Synthesis and characterization of Ti(IV)-substituted calcium hydroxyapatite particles by forced hydrolysis of Ca(OH)2-Na5P3O10-TiCl4 mixed solution

Ti(IV)-substituted calcium hydroxyapatite (TiHap) particles were prepared by aging Ca(OH)₂, TiCl₄, and sodium triphosphate (sodium tripolyphosphate, Natpp: Na₅P₃O₁₀) mixed solution at 100 °C for 18 h. The ellipsoidal secondary TiHap particles with ca. 100～150 nm in length composing by aggregation of small ellipsoidal primary particles with ca. 20 nm in length were produced at atomic ratio of Ti/(Ca+Ti) [X_Ti]≦0.2. The in situ IR spectra of these TiHap particles exhibited very small bulk OH^? band at 3,570 cm^?1. This result indicated that the TiHap particles were formed by aggregation of fine primary particles and OH^? ions along with c-axis in the primary particles were disordered. The TiHap particles with Ca/P atomic ratio larger than theoretical value of 1.67 did not exhibit surface P–OH groups at 3,659 and 3,682 cm^?1. The diffuse reflectance UV spectra of TiHap particles revealed that these particles have a UV absorption property, especially fabricated at X_Ti?=?0.1. The particles prepared at X_Ti?=?0.6 and 0.8 were amorphous and nanoparticles with 5～10 nm in diameter, but those precipitated at X_Ti?=?1.0 were poorly crystallized anataze-type TiO₂ nanoparticles.     

Surface and Structural Properties of Gold Nanoparticles and Their Biofunctionalized Derivatives in Aqueous Electrolytes Solution

Gold nanoparticles reduced by sodium citrate (d ～ 10 nm) and purchased gold colloid particles (d ～ 500 nm) were examined and compared. The properties of both gold particles and their biofunctionalized derivatives with L-cysteine and L-glutathione were studied in the presence of sodium nitrate. The structural investigations indicated an aggregated inner structure.

The isoelectric points of pure gold, citrate reduced gold, and functionalized gold were measured and compared. The low isoelectric point of pure gold/water interface was explained by considering the distribution and accumulation of H⁺ and OH^? ions within the interfacial water layer, being more pronounced for OH^? ions.      

Temperature dependence of DC electrical conductivity of kaolin

The samples from kaolin Sedlec were investigated by the help of DTA, TG, and temperature dependences of DC conductivity using Pt wire electrodes and linear heating up to 1,050 °C. After drying, the samples contained ~1.5 mass% of the physically bound water. DTA and TG reflected generally known facts about a release of the physically bound water, dehydroxylation, and metakaolinite → Si–Al spinel transformation. The results of electrical measurements showed the electric current passed over the maximum at 60 °C. The self-ionization of water results in the process H₂O → H⁺ + OH^? in the water layers on the crystal surfaces; consequently, OH^? and H⁺ are the main charge carriers in the low-temperature region. The water molecules simultaneously evaporate from the sample which decreases the number of the charge carriers. When the physically bound water evaporates, the current is carried mostly by K⁺ and Na⁺ ions. During dehydroxylation, the hydroxyls OH^? split into H⁺ and O^2?. The ions H⁺ jump to the neighboring OH^? groups creating the water molecules. The ions O^2?remain bounded to the newly created metakaolinite lattice. Therefore, mobile protons contribute to the electric current. At the same time, this contribution gradually decreases because of the escape of H₂O from the sample. The sharp current peak and DTA peak at 970 °C imply relatively fast metakaolinite → Si–Al spinel transformation. This DC current peak results from the shift of Al³⁺ and O^2? ions into new positions.     

Kinetic studies on H+- and OH−-catalysed aquation of bis-aspartatochromium(III)

A potential synthetic biochromium source, bis-aspartatochromium(III) ion (where Asp is a tridentate N,O,O′-ligand, bonded via amine nitrogen and carboxylate oxygen atoms) has been obtained and characterized in aqueous solution. Kinetics of partial dechelation of the complex catalysed by H⁺ and OH^? ions has been studied spectrophotometrically within 0.1–1.0 M HClO₄ and 0.1–1.0 M NaOH ranges under first-order conditions. A linear dependence of the k _obs,H on [H⁺] and independence of the k _obs,OH on [OH^?] were established. The derived rate expression and identification of components of the reaction mixture provide evidence for a reaction mechanism, where the key role in the overall process is the formation of an intermediate species with bidentate N,O-bonded Asp via both spontaneous and H⁺(OH^?)-catalysed reaction paths. The intermediate is meta-stable and at pH 5–7 restores the substrate.     

Investigation of the water exchange mechanism of the Plutonyl(VI) and Uranyl(VI) ions with quantum chemical methods

The water exchange reactions of [PuO₂(OH₂)₅]²⁺ and [UO₂(OH₂)₅]²⁺ were investigated with density functional theory (DFT) and wave function theory (WFT). Geometries and vibrational frequencies were calculated with DFT and CPCM hydration. The electronic energies were evaluated with general multiconfiguration quasi-degenerate second-order perturbation theory (GMC-QDPT2). Spin-orbit (SO) effects, computed with SO configuration interaction (SO–CI), are negligible. Both Actinyl(VI) ions react via an associative exchange mechanism, most likely I_a. The Gibbs activation energies (ΔG^?) at 25 °C are 33–34 and 30–37 kJ mol^?1 for [PuO₂(OH₂)₅]²⁺ and [UO₂(OH₂)₅]²⁺, respectively. ΔG^? for dissociative mechanisms (D, I_d) is higher by more than 15 kJ mol^?1.     

Optimizing the preparation conditions of polypyrrole electrodes for enhanced electrochemical capacitive performances

Here, we put forward an optimum proposal to prepare high-performance polypyrrole (PPy) electrodes for supercapacitor applications. A detailed study regarding the effects of different preparation conditions including electropolymerized mode, parameter, and current collector on the electrochemical capacitive performances of PPy electrodes is carried out. Fourier transform infrared spectroscopy and X-ray diffraction tests indicate the above preparation conditions have no effect on the component and crystal structure of PPy prepared. Electrochemical measurements manifest a significant effect of current collector on supercapacitive properties of PPy electrodes. Graphite foil as the current collector with low resistance shows remarkably superior capacitive performances compared with FTO-conducting glass and ITO conductive plastic. SEM characterizations show galvanostatically polymerized PPy particles have obviously smaller aggregation degree than potentiostatically polymerized PPy particles, which results in better electrochemical properties for former. Among different preparation conditions, the PPy deposited on graphite foil under galvanostatic mode with 2 mA cm^?2 shows the best electrochemical capacitive properties. The optimized PPy/graphite electrodes show a high specific capacitance of 173.0 mF cm^?2 at 0.2 mA cm^?2, superior rate capability, and outstanding cycling stability (retaining 90.5% of initial capacitance for 5000 cycles).     

Role of reactive oxygen species and effect of solution matrix in trichloroethylene degradation from aqueous solution by zeolite-supported nano iron as percarbonate activator

The role of reactive oxygen species (ROSs) and effect of solution matrix have been investigated for the degradation of trichloroethylene (TCE). Zeolite-supported nano iron (Z-nZVI) was synthesized as an activator to catalyze sodium percarbonate (SPC) with or without hydroxylamine, i.e. as reducing agent (RA). The probe tests confirmed the generation of OH^· and O ₂ ^?· in the Z-nZVI activated SPC system in absence of the RA, while the presence of RA significantly increased the generation of OH^· and O ₂ ^?· radicals. Scavenger tests demonstrated that OH^· was the main ROS responsible for TCE degradation, whereas O ₂ ^?· also participated in TCE degradation. From the solution matrix perspective, the experimental results confirmed significant scavenging effects of Cl^? (1.0, 10.0, and 100 mmol L^?1) and HCO₃ ^? (1.0 and 10.0 mmol L^?1), whereas the scavenging effects were fairly impeded at 100 mmol L^?1 concentration of HCO₃ ^?. On the other hand, a considerable decline in scavenging effect was observed in the presence of RA in tested Cl^? and HCO₃ ^? concentration ranges. In addition, negligible scavenging effects of NO₃ ^? and SO₄ ^2? anions were found in all tested concentrations. The effect of initial solution pH on catalytic activity indicated a significant increase in the TCE degradation in the presence of RA even at higher pH value of 9. The results indicated that the Z-nZVI activated SPC system in presence of RA can effectively degrade chlorinated organic solvents, but it is important to consider the intensive existence of anions in groundwater.     

Bimolecular Fluorescence Quenching Reactions in Didodecyldimethylammonium Bromide and Chloride Vesicles and Micelles

Fluorescence decays have been measured for pyrenesulfonate (PyS^?) in the presence of anthraquinone-1-sulfonate (AQ1S^?), for pyrene (Py) at various concentrations, and Py in the presence of AQ1S^? in 5 mmol·dm^?3 didodecyldimethylammonium bromide (DDABr) vesicle solutions. Reaction rate constants were found to increase in the order Py*–Py < PyS^?*–AQ1S^? < Py*–AQ1S^?. Fluorescence decays have also been measured in 5 mmol·dm^?3 didodecyldimethylammonium chloride (DDACl) solutions; the results showed micellar solution behavior, and micellar aggregation numbers and quenching rate constants were obtained. The quenching rate constants in vesicles and micelles were converted to the two dimensional rate constants having the same units. Two dimensional diffusion coefficient and reaction distance were obtained for the PyS^?*–AQ1S^? system on the DDABr vesicle surface.     

Mechanism of sorption of pertechnetate onto ordered mesoporous carbon

Ordered mesoporous carbon (OMC) was used as an adsorbent for the removal of pertechnetate (TcO₄ ^?) anion. The maximum uptake (93 %) of TcO₄ ^? was obtained after 60 min of contact. The adsorption of TcO₄ ^? is almost pH-independent in very wide pH region (from 4.0 to 10.0). Maximum K _d of 6.6 × 10³ cm³ g^?1 was found at pH 2.0. TcO₄ ^? interacts with carboxylic functional groups present at the surface of the OMC by displacing the OH^? ions with TcO₄ ^? via ion exchange mechanism.     

The role of counter-anions in photocatalytic reduction of Ni(II) with a trace amount of titania nanoparticles

The reduction of Ni(II) ion, originated from nitrate or sulfate salts, was investigated based on photo-generated electrons in UV-irradiated TiO₂ aqueous suspensions. Design of experiments, modeling, and process optimization were performed using central composite design of response surface methodology. Influence of pH, temperature, and nickel concentration was investigated based on percentage of reduction efficiency (RE). Under operating conditions of pH = 9.3, T = 40 °C, [Ni(II)]_o = 5 mg L^?1, [TiO₂] = 100 mg L^?1 and after 90 min treatments, 64.8 and 76.1 % RE were achieved for nitrate and sulfate counter-anions, respectively. The higher efficiency obtained with sulfate anion was attributed to the more ionic strength and its interaction with titania nanoparticles. Rate of Ni(II) ions reduction, originated from both of the nickel salts, obeys pseudo-first-order kinetic model. As a relevant criterion, the electrical energy consumption and other criteria were evaluated and were compared with other previously reported processes.     

Quantum chemical models of alkali metal hydroxide-water-dimethylsulfoxide superbasic media (MOH-H<Subscript>2</Subscript>O-DMSO,M = Li,Na, K)

Models of alkali metal hydroxide-water-dimethylsulfoxide superbasic media have been constructed using Hartree Fock and DFT (B3LYP) quantum chemical methods; the structure and energies of anion complexes are considered. The hydroxide anion in the models is stabilized as complexes of OH^?·H₂O and OH^?· 2H₂O types.     

Effects of Alkaline Ferrocyanide on Non-faradaic Yields of Anodic Contact Glow Discharge Electrolysis: Determination of the Primary Yield of OH· Radicals

Non faradaic yields of anodic contact glow discharge electrolysis (CGDE) originate through H^· and OH^· radical generated during the process. Scavenging effects of Fe(CN) ₆ ^4? on OH^· radicals, in alkaline media have been investigated. A kinetic analysis of the competing reactions of O^? with different species in the system leads to an yield of 9.8?mol?mol?electron^?1 of OH^· and H^· radicals each in the liquid phase reaction zone of anodic CGDE in good agreement with the yield reported from a study involving H^· radical scavengers.     

Microrheology of polysaccharide nanogel-integrated system

The viscoelastic behavior of a cholesterol-modified pullulan (CHP) nanogel at various concentrations was measured using passive particle-tracking microrheology. Microrheology measures stress–strain relationships in small volumes of material by monitoring the response of probes embedded in the medium. Although microrheology is a useful way to overcome sample volume limitations, the application of the method to CHP nanogel systems has not been reported. The viscoelastic spectra of the CHP nanogels obtained from the microrheological measurements were in good agreement with the bulk rheological measurements for each sample, demonstrating that microrheological measurement is effective in CHP nanogel systems. The gelation behavior of CHP nanogel dispersions containing pullulans of different molecular weights was also investigated by microrheology. CHP nanogels made from 1.0 or 4.0?×?10⁵ molecular weight pullulans formed a macrogel at around 3.0 wt%, whereas the CHP nanogel consisting of 0.55?×?10⁵ molecular weight pullulan did not form a macrogel. This suggests that the mechanical properties of the system can be controlled by the molecular weight of the pullulan used. These insights into gelation behavior should be useful in predicting the most favorable conditions for developing novel materials.     

The Oxidation of Iron(II) with Oxygen in NaCl Brines

The oxidation of nanomolar levels of iron(II) with oxygen has been studied in NaCl solutions as a function of temperature (0 to 50?°C), ionic strength (0.7 to 5.6 mol?kg^?1), pH (6 to 8) and concentration of added NaHCO₃ (0 to 10 mmol?kg^?1). The results have been fitted to the overall rate equation: $$\mathrm{d}\mbox{[Fe(II)]}/\mathrm{d}t=-k_{\mathrm{app}}\mbox{[Fe(II)]}[\mbox{O}_{2}]$$ The values of k _app have been examined in terms of the Fe(II) complexes with OH^? and CO ₃ ^2? . The overall rate constants are given by: $$k_{\mathrm{app}}=\alpha_{\mathrm{Fe}2+}k_{\mathrm{Fe}}+\alpha_{\mathrm{Fe(OH)}+}k_{\mathrm{Fe(OH)}+}+\alpha_{\mathrm{Fe(OH)}2}k_{\mathrm{Fe(OH)}2}+\alpha_{\mathrm{Fe(CO3)}2}k_{\mathrm{Fe(CO3)}2}$$ where α _i is the molar fraction and k _i is the rate constant of species i. The individual rate constants for the species of Fe(II) interacting with OH^? and CO ₃ ^2? have been fitted by equations of the form: $$\begin{array}{l}\ln k_{\mathrm{Fe}2+}=21.0+0.4I^{0.5}-5562/T\\[6pt]\ln k_{\mathrm{FeOH}}=17.1+1.5I^{0.5}-2608/T\\[6pt]\ln k_{\mathrm{Fe(OH)}2}=-6.3-0.6I^{0.5}+6211/T\\[6pt]\ln k_{\mathrm{Fe(CO3)}2}=31.4+5.6I^{0.5}-6698/T\end{array}$$ These individual rate constants can be used to estimate the rates of oxidation of Fe(II) over a large range of temperatures (0 to 50?°C) in NaCl brines (I=0 to 6 mol?kg^?1) with different levels of OH^? and CO ₃ ^2? .     

Synthesis and thermal decomposition of neodymium(III) peroxotitanate to Nd<Subscript>2</Subscript>TiO<Subscript>5</Subscript>

Neodymium(III) peroxotitanate is used as a precursor for obtaining Nd₂TiO₅. The last one possesses numerous valuable electrophysical properties. TiCl₄, Nd(NO₃)₃·6H₂O and H₂O₂ in mol ratio 1:2:10 were used as starting materials. The reaction ambience was alkalized to pH = 9 with a solution of NH₃. The obtained neodymium(III) peroxotitanate and intermediate compounds of the isothermal heating were proved by the help of quantitative analysis and infrared spectroscopy (IRS). It has Nd₄[Ti₂(O₂)₄(OH)₁₂]·7H₂O composition. The absorption band observed in IRS at 831 cm^?1 relates to a triangular bonding of the peroxo group of Ti, at 1062 cm^?1—terminal groups Ti–OH and at 1491 and 1384 cm^?1—the bridging OH^?-groups Ti–O(H)–Ti. Nd₂TiO₅ was obtained by thermal decomposition of neodymium(III) peroxotitanate. The isothermal conditions for decomposition were determined on the base of differential thermal analysis, thermogravimetric and differential scanning calorimetry results in the temperature range of 20–1000 °C. The mechanism of thermal decomposition of Nd₄[Ti₂(O₂)₄(OH)₁₂]·7H₂O to Nd₂TiO₅ was studied. In the temperature range of 20–208 °C, a simultaneous decomposition of the peroxo groups by the separation of oxygen and hydrate water is conducted and Nd₄[Ti₂O₄(OH)₁₂] is obtained. From 208 to 390 °C, the terminal OH^?-groups are separated and Nd₄[Ti₂O₇(OH)₆] is formed. In the range of 390–824 °C, the bridging OH^?-groups are completely decomposed to Nd₂TiO₅. The optimal conditions for obtaining nanocrystalline Nd₂TiO₅ are 900 °C for 6 h and 20–80 nm.     

Effect of silver nanoparticles concentration on the metal enhancement and quenching of ciprofloxacin fluorescence intensity

Concentration effect of silver nanoparticles (AgNPs) on the photophysical properties of ciprofloxacin (Cip) have been investigated using optical absorption and fluorescence techniques. When performed AgNPs solution was added to the Cip solution, metal-enhanced fluorescence intensity and a blue-shift of 20 nm in the maximum emission spectra of Cip has been observed. The enhanced intensity of this system is strongly dependent on the AgNPs concentration and largest at the 6.0 × 10^?6 mol L^?1. With increase of AgNPs concentration, quenching of fluorescence is observed. Stern–Volmer quenching constants have been calculated at four temperatures. The results show the quenching constants are directly correlated with temperature. It indicates the quenching mechanism is the dynamic quenching in nature rather than static quenching. From which we determined the activation energy for the quenching of Cip-AgNPs to be about 31.1 kJ mol^?1. In addition, in the presence of optimum AgNPs concentration, a sensitive fluorimetric method for the determination of ciprofloxacin at the range 5.0 × 10^?7–3.0 × 10^?5 mol L^?1 and the detection limit of 2 × 10^?8 mol L^?1 in solution is proposed.     

Complex formation of cetirizine drug with bivalent transition metal(II) ions in the presence of alanine: synthesis,characterization, equilibrium studies,and biological activity studies

Mononuclear cobalt(II), nickel(II), and copper(II) complexes of cetirizine·2HCl (CTZ = 2-[2-[4-[(4-chlorophenyl)phenyl methyl]piperazine-1-yl]-ethoxy]acetic acid) in the presence of alanine (Ala) as a representative example of amino acids were synthesized and elucidated by different physical techniques. All complexes have been characterized with the help of elemental analyses, molecular weights, molar conductance values, magnetic moments, and spectroscopic data. The measured molar conductance values in DMSO indicate that the complexes are nonelectrolytes. Quantum chemical calculations were performed with semi-empirical method to find the optimum geometry of complexes. The metal–oxygen bond length in the synthesized complexes obeys the order M–OH₂ > M–O_CTZ > M–O_Ala. Formation equilibria of the ternary complexes have been investigated. Ternary complexes are formed by a simultaneous mechanism. Stoichiometry and stability constants for the complexes formed are reported. The concentration distributions of various species formed in solution were also evaluated as a function of pH. CTZ and its metal chelates have been screened for their antimicrobial activities against some selected types of gram-positive (G⁺) and gram-negative (G^?) bacteria. They were more active against (G⁺) than (G^?) bacteria.     

Reactions of mer(exo)‐ and mer(endo)‐[Co(dien)(dapo)X]2+ Isomers (X=OH,Cl, ONO2, N3)

Properties indirectly determined, or alluded to, in previous publications on the titled isomers have been measured, and the results generally support the earlier conclusions. Thus, the common five‐coordinate intermediate generated in the OH^?‐catalyzed hydrolysis of exo‐ and endo‐[Co(dien)(dapo)X]²⁺ (X=Cl, ONO₂) has the same properties as that generated in the rapid spontaneous loss of OH^? from exo‐ and endo‐[Co(dien)(dapo)OH]²⁺ (40±2% endo‐OH, 60±2% exo‐OH) and an unusually large capacity for capturing (R=[CoN₃]/[CoOH][]=1.3; exo‐[CoN₃]/endo‐[CoN₃]=2.1±0.1). Solvent exchange for spontaneous loss of OH^? from exo‐[Co(dien)(dapo)OH]²⁺ has been measured at 0.04 s^?1 (k₁, 0.50M NaClO₄, 25°) from which similar loss from the endo‐OH isomer may be calculated as 0.24 s^?1 (k₂). The OH^?‐catalyzed reactions of exo‐ and endo‐[Co(dien)(dapo)N₃]²⁺ result in both hydrolysis of coordinated via an OH^?‐limiting process =153 M ^?1 s^?1; =295 M ^?1 s^?1; K_H=1.3±0.1 M ^?1; 0.50M NaClO₄, 25.0°) and direct epimerization between the two reactants =33 M ^?1 s^?1; =110 M ^?1 s^?1; 1.0M NaClO₄, 25.0°). Comparisons are made with other rapidly reacting Co^III‐acido systems.     

First‐principles calculation of OH−/OH adsorption on gold nanoparticles

The OH^? and OH adsorption structures on Au₅₅ and Au₁₃ nanoparticles surfaces are analyzed using density functional theory. The most stable OH^? adsorption site of Au₅₅ and Au₁₃ nanoparticles is found to be the vertex top site followed by the (111)‐(100) edge bridge site. On the contrary, the stability order of OH adsorption is opposite to that of OH^?. The adsorption of OH^? is calculated to be weaker than that of OH, which shows different charge transfer and interactions with gold surface. Coadsorption on nanoparticles is studied to find that multiple OH^? species prefer the most stable sites of single OH^? adsorption. The hydrogen bonding between adsorbed OH^? on gold surface is a key factor in stabilizing the adsorbates on the Au surface. © 2015 Wiley Periodicals, Inc.     

Gelation behavior and phase separation of macroporous methylsilsesquioxane monoliths prepared by in situ two-step processing

An in situ two-step processing using an initial acid catalysis step accompanied by an epoxide-mediated condensation step in the presence of ammonium chloride (NH₄Cl) is reported, and macroporous cocontinuous methylsilsesquioxane (MSQ) monoliths have been successfully prepared by this processing. We explain the hydrolysis, gelation behavior and phase separation of MTMS(methyltrimethoxysilane)-MeOH(methanol)-HCl-PO(propylene oxide) system and the in situ effect of NH₄Cl, and examine the macroporous morphology and pore structures of MSQ monoliths obtained under different conditions. Macroporous MSQ monolith under optimized conditions possesses a narrow macropore size distribution between 3 to 10 μm, surface area as high as 366 m²·g^?1 and minimal shrinkage of only 1 %.