Strong Acidic Conditions Research Articles

Electrodeposited WO3 Film on Various Metal Substrates and Its Morphological Effect for Photoelectrochemical Water Splitting

Metal oxides such as TiO2, WO3, ZnO, SnO2 etc. have widely investigated because of low cost, environmental friendliness, and the application to various energy related devices. In particular, WO3 having the energetic band gap of about 2.8 eV has the absorption of more visible light, the suitable position of conduction band to transfer the photogenerated electrons to the substrate, and the stable photoresponse in the strong acidic condition. Herein, we prepared the WO3 film by electrodeposition that provides the clean and reproducible technique. That is, a compact structured WO3 film with a thickness of 780 nm was prepared by facile electrodeposition at a constant potential of -0.47 V versus saturated Ag/AgCl electrode. For a nanoporous structured WO3 film, polystyrene (PS) beads with a size of 320 nm were used as the template, and the electrodeposition was performed under the same experimental conditions by varying the reaction time from 1 to 3 min to adjust the thickness of the depositing layer. The PS beads were completely removed from the template by the calcination at 450 °C for 3 h under air, affording inverse opal WO3 films with a pore size of 300 nm. For the inverse opal WO3 film with a thickness of 790 nm prepared by electrodeposition for 1 min, the highest photocurrent density (1.75 mA/cm2 at 1.5 V versus sat. Ag/AgCl) was achieved, followed by compact WO3, inverse opal WO3 (2 min), and inverse opal WO3 (3 min) films with photocurrent densities of 1.2, 0.74, and 0.35 mA/cm2, respectively. The further discussion on the morphological and crystalline properties of the prepared WO3 film was confirmed by a field emission scanning electron microscope and X-ray diffraction.

Jacket-free stir bar sorptive extraction with bio-inspired polydopamine-functionalized immobilization of cross-linked polymer on stainless steel wire

Stainless steel wire (SSW) is a good substrate for stir bar sorptive extraction (SBSE). However, it is still a challenge to immobilize commonly used cross-linked polymers onto SSW. In this work, we present a new approach for immobilization of the cross-linked organic polymer onto SSW for jacket-free SBSE. A dopamine derivative was firstly synthesized; by introducing a mussel-inspired polydopamine process, a stable coating layer was finally generated on the surface of SSW. Secondly, the cross-linked polymer was synthesized on the polydopamine-modified SSW by using acetonitrile as the porogen, acrylamide (AA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker and 2,2′-azobis (2-methylpropionitrile) as the initiator. A diluted pre-polymerization solution was carefully prepared to generate a thin layer of the polymer. The prepared poly(EGDMA-AA)-modified stir bar showed high stability and good tolerance toward stirring, ultrasonication, organic solvents, and strong acidic and basic conditions. Morphology and structure characterization of coatings were performed by scanning electron microscopy and Fourier transform infrared spectra, respectively. The prepared poly(EGDMA-AA)-modified stir bar showed great extraction efficiency toward protoberberines, with enrichment factors of 19–42. An SBSE-HPLC method was also developed for quantitative analysis of protoberberines. The method showed low limits of detection (0.06–0.15ngmL−1), wide linear range (0.5–400ngmL−1), good linearity (R≥0.9980) and good reproducibility (RSD≤3.60% for intra-day, RSD≤4.73% for inter-day). The developed method has been successfully applied to determine protoberberines in herb and rat plasma samples, with recoveries of 88.53–114.61%.

PH-controlled voltammetric behaviors and detection of phytohormone 6-benzylaminopurine using MWCNT/GCE

The electrochemical detection of phytohormones is extremely difficult owing to their poor electrochemical activities, strong electrode passivation (fouling), and complicated electrochemical behaviors and reaction mechanism. In this paper, an interesting electrochemical phenomenon on voltammetric behaviors for the electrochemical oxidation of 6-benzylaminopurine (6-BAP) which was one of the well-known phytohormones under the different pH conditions was investigated, and the content of 6-BAP in real samples was detected by the adsorptive stripping voltammetry using MWCNT/GCE. The pH-controlled voltammetric behaviors like peak potentials, peak currents, peak shapes and peak number of 6-BAP were discussed by the protonation–dissociation equilibria of 6-BAP in combination with electrocatalytic oxidation mechanism of 6-BAP. The electrochemical sensing performance such as the linear range, limit of detection (LOD), limit of quantification (LOQ), sensitivity, selectivity, precision and applicability for the pH-controlled stripping voltammetric detection of 6-BAP was also evaluated. There was an observable difference in the number of peaks for the electrochemical oxidation of 6-BAP under strong acidic (three peaks), near neutral (two peaks), and strong alkaline (one peak) pH conditions. The electrochemical oxidation reaction of 6-BAP was adsorption-controlled irreversible processes, which were not affected by three different pH values. Oxidation peaks with relatively well-defined peak shapes and high peak currents were selected for the adsorptive stripping voltammetric detection of 6-BAP, and peak currents were proportional to 6-BAP concentrations in linear ranges of 0.3–50μM with LOD of 0.098μM and LOQ of 0.326μM at pH 3.0, 0.5–60μM with LOD of 0.165μM and LOQ of 0.545μM at pH 7.0, and 0.7–60μM with LOD of 0.235μM and LOQ of 0.776μM at pH 10.0. The adsorptive stripping voltammetric determination of 6-BAP content with real samples in acid solution was more feasible and applicable.

Application and degradation mechanism of polyoxadiazole based membrane for vanadium flow batteries

A new type of membrane composed of poly (4,4′-diphenylether-1,3,4-oxadiazole) (POD) was prepared and first investigated in a vanadium flow battery (VFB). In contrast to traditional hydrocarbon ion exchange membranes, the proton transport of POD was driven by the interaction between the acid in the electrolytes and the heterocyclic atoms in the POD backbone. A VFB single cell assembled with a POD membrane exhibits higher columbic efficiency (96.87%) and energy efficiency (83.29%) than does a Nafion 115 membrane (CE 94.6%, EE 82.1%) under the same operating conditions. However, the cell performance of the assembled POD membrane suddenly drops after continuously running for 60 cycles. The degradation mechanism of POD under strongly acidic and oxidized medium was investigated by UV–vis spectrometry, nuclear magnetic resonance (NMR) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The chemical structure of the degradation product was clarified, and the degradation mechanism was proposed, indicating that the oxadiazole ring in POD membrane becomes a strong electrophilic center due to the protonated ethereal oxygen atom and highly electronegative nitrogen atoms under strong acidic conditions. Next, the electrophilic center was attacked by the lone electron pair of the vanadium oxygen species. This work will provide valuable information to further improve the stability of polyoxadiazole under VFB conditions.

ChemInform Abstract: New Cofactor‐Independent Hydration Biocatalysts: Structural, Biochemical, and Biocatalytic Characteristics of Carotenoid and Oleate Hydratases

AbstractReview: [77 refs.

Temperature effect on electrochemical properties of Ti4O7 electrodes prepared by spark plasma sintering

In this paper, Magneli phase Ti4O7 powders were successfully synthesized and used to fabricate high quality Ti4O7 electrodes by the spark plasma sintering (SPS) technique. The micro-structure, conductivity and electrochemical properties of the Ti4O7 electrode were investigated respectively. Furthermore, temperature’s effect on the electrochemical properties of Ti4O7 working electrode was studied by the cyclic voltammetry measurements under strong sulfuric acid and alkaline conditions at different temperature to simulate actual operating temperature in various electrolyte such as in lead–acid or zinc–air batteries. The results showed that Ti4O7 electrodes prepared by SPS without doping of adhesives had high conductivity, favorable electrochemical activities in function of temperature and electrochemical stability under strong sulfuric acid and alkaline conditions. It would be feasible candidate to bipolar lead–acid battery and used as air cathodes in zinc–air batteries.

Responsiveness and Release Characteristic of Semi-IPN Hydrogels Consisting of Nano-Sized Clay Crosslinked Poly(Dimethylaminoethyl Methacrylate) and Linear Carboxymethyl Chitosan.

PH and temperature double responsive semi-IPN hydrogels consisting of poly(dimethylaminoethyl methacrylate) (PDMAEMA) network crosslinked by nano-sized inorganic clay and linear carboxymethyl chitosan (CMCS) were synthesized by in situ, free radical polymerization in aqueous solution. The effect of the mass and carboxymethyl substitution of CMCS on the responsiveness, swelling/deswelling and drug release characteristic of gels were investigated. Comparing to the gels without CMCS, the resulting gels (named as C-NC gels) showed similar LCST and temperature response behavior. However, with the increase of added CMCS, the swelling ratio of gels decreased considerably around the isoelectric point (IEP) of CMCS, while increased in both strong acidic and alkaline condition. The deswelling rate was improved significantly when the content of CMCS is high. In drug load and release test by using theophylline as target, the C-NC gels exhibited an excellent load ability and controlled-release in simulated human intestinal and stomachic condition. Additionally, all properties of gels were affected by the DS of added CMCS due to the different ratio and interaction of negative and positive ions in gels.

Application of lithium-silicate based oxynitrideglass into pH-responsive glass for improvement of responsibility and stability

A pH glass electrode is made of lithium-rich special glass, and the durability is often inferior in comparison with general hard glass. The glass electrode is often used under strong alkalinity or acidic conditions, wherein the electrode has an extremely short life. In recent years, oxynitrideglasses have been reported, in which a part of oxygen in the glass structure was replaced with nitrogen, for superior durability in strong acid and strong alkaline solutions. In this study, Li2O-SiO2-Si3N4 glass was prepared, and the possibility of the application as the pH responsive glass was checked. As a result, the new glass electrodes showed good response time for pH standard as short as ten seconds. Furthermore, its sensitivity between pH 4 and pH 9 was more than 97 % against theoretical value. The glass showed approximately half of silicon and lithium elution in alkaline solution for the chemical durability, compared with traditional pH responsive glass.

Reduced graphene oxide-grafted cylindrical like W doped BiVO4 hybrids with enhanced performances for photocatalytic applications

Reduced graphene oxide (RGO) grafted W doped BiVO4 (WBVO) hybrids have been obtained using two-step wet-chemical approach. At first, WBV was synthesized by hydrothermal method in strong-acid condition. And second, the WBVO/GO mixture was transformed into WBVO/RGO hybrids by hydrothermal treatment under ethanol–water condition. The photocatalytic activity of WBV/RGO can be optimized by controlling the content of RGO at 4wt%. Such a novel composite photocatalyst might find potential application for air purification and waste water treatment.

Origin and geographical characteristics of ponds in a high mountain region of central Japan

This study examines the role of landforms in pond formation in alpine and subalpine regions of central Japan. Mountain ponds larger than ca. 50 m2 were detected by interpretation of stereo-paired aerial photographs, and mapped in areas over 2000 m (above sea level). The mapped ponds totaled 304 in the 1347 km2 study area. Mass movement landforms are the major sites of pond basins, comprising 66.5 % of the total number; 65 ponds occur in depressions in displaced masses downslope of ridges, and 137 occur in linear depressions along main ridges. These ponds occur frequently in the snowiest parts of the study area, although geological setting also affects pond formation. The second and third major types of landforms with ponds are of volcanic and glacial origins, accounting for 16.8 and 15.8 % of all ponds, respectively. Nearly 90 % of these mapped ponds have an area smaller than 1000 m2. The size distribution of ponds varies with origin type. Mass movement landforms have a greater range of pond sizes, including both small (<1000 m2) and medium (1000–6000 m2), than do glacial and periglacial landforms. Volcanic landforms have the largest ponds, which exceed 10,000 m2 in some cases. Ponds on glacial landforms are at higher elevations and may be of uniform age post-glaciation, while other landform types can occur at any elevation and may span a wide range of ages. Landslide ponds may provide better habitats for aquatic species than those originating from other landforms, because they are not subject to the strong acid conditions of volcanic ponds or the longer snow-covered period of ponds on glacial landforms.

Adsorption of Selenite Ions onto Poly(1,8-diaminonaphthalene) Synthesized by Using Ammonium Persulfate

In the present work, poly(1,8-diaminonaphthalene) (poly(1,8-DAN)) was synthesized by chemical oxidation of 1,8-diaminonaphthalene (1,8-DAN) monomer with ammonium persulfate (APS) oxidant and it was used in the adsorption of selenite ions. The polymer samples synthesized at various molar ratios of 1,8-DAN to APS were characterized by FTIR analysis and they were used in the adsorption experiments. The effects of initial acidity, the molar ratio, and initial selenium concentration on the adsorption behavior of poly(1,8-DAN) were examined by using batch adsorption technique. It was found that selenite was adsorbed onto poly(1,8-DAN) in strong acidic conditions (3-8 M HCl). The experimental adsorption data were applied to the Langmuir and Freundlich isotherms. The adsorption capacities of the polymer samples at the molar ratios of 1/0.5 and 1/2 were calculated as 75.19 and 45.05 mg Se/g, respectively. It was estimated that the adsorption mechanisms of selenite ions onto poly(1,8-DAN) were governed by electrostatic interaction (>NH2+SeOCl3−) and piazoselenol type binding (-N=Se=N-).

Effect of in-situ loading of nano titania particles on structural ordering of mesoporous SBA-15 framework

Abstract Highly mesoporous TiO 2 /SBA-15 nanocomposites have been synthesized by direct incorporation of nano titania species in SBA-15 framework via one step in-situ method using TiCl 4 and TEOS as titania and silica source respectively. This in-situ method is a facile one-pot approach where co-condensation of Ti and Si precursors occurs simultaneously under strong acidic conditions and thus the specific surface area and pore diameter of the nanocomposite can be controlled by tuning the concentration of TiCl 4 solution. A combination of X-ray diffraction (XRD), N 2 adsorption–desorption (BET), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray (EDX) spectroscopy has been utilized to characterize the composition and structure of the TiO 2 /SBA-15 nanocomposite. It was found that SBA-15 retained its mesoporous structural ordering even at high wt% loading of TiO 2 . Anatase TiO 2 nanoparticles, without blocking the pore walls of SBA-15 were observed to be homogeneously dispersed inside the mesoporous framework over wide range of loadings (1–20 wt%). The in-situ method of synthesis of nanocomposite leads to co-condensation of titania and silica species whereby maintaining the mesoporosity of the obtained nanocomposite. Physicochemical properties study reveals that a decrease in the surface area and pore size of nanocomposite was observed with consecutive increment of TiO 2 concentration in SBA-15.

Controlled acid hydrolysis and kinetics of flavone C-glycosides from trollflowers

Abstract Acid hydrolysis mechanisms of orientin-2″- O -galactopyranoside (OGA), orientin and other flavone C -glycosides in the trollflowers ( Trollius chinensis Bunge) were studied in this report for the first time. Hydrolysis parameters including temperature, acidity, solvent and reaction time were comprehensively investigated. OGA could be hydrolyzed to orientin, followed by an isomerization to isoorientin via a reversible Wessely–Moser rearrangement reaction under stronger acidic conditions. A first-order kinetic model fitted the hydrolysis process of OGA well. Under the optimal hydrolysis conditions of 80 °C, 1.0 mol/L H + and 7 h reaction time, about 77% OGA was transformed to orientin with no detectable isoorientin. These results could be helpful for better understanding of the acid hydrolysis kinetics of flavone C -glycosides, as well as the preparation of these valuable components under controlled acid hydrolysis conditions.

Theoretical Analysis of Cobalt Hangman Porphyrins: Ligand Dearomatization and Mechanistic Implications for Hydrogen Evolution

The design of molecular electrocatalysts for hydrogen evolution has been targeted as a strategy for the conversion of solar energy to chemical fuels. In cobalt hangman porphyrins, a carboxylic acid group on a xanthene backbone is positioned over a metalloporphyrin to serve as a proton relay. A key proton-coupled electron transfer (PCET) step along the hydrogen evolution pathway occurs via a sequential ET-PT mechanism in which electron transfer (ET) is followed by proton transfer (PT). Herein theoretical calculations are employed to investigate the mechanistic pathways of these hangman metalloporphyrins. The calculations confirm the ET-PT mechanism by illustrating that the calculated reduction potentials for this mechanism are consistent with experimental data. Under strong-acid conditions, the calculations indicate that this catalyst evolves H2 by protonation of a formally Co(II) hydride intermediate, as suggested by previous experiments. Under weak-acid conditions, however, the calculations reveal a mech...

High-Throughput Screening for Acid-Stable Oxygen Evolution Electrocatalysts in the (Mn–Co–Ta–Sb)O x Composition Space

Solar generation of fuel is a promising future energy technology, and strong acidic conditions are highly desirable for integrated solar hydrogen generators. In particular, water splitting near pH 0 is attractive due to the availability of high theoretical efficiency, high performance hydrogen evolution catalysts, and robust ion exchange membranes. The lack of a stable, earth-abundant oxygen evolution catalyst inhibits deployment of this technology, and development of such a material is hampered by the strong anti-correlation between electrochemical stability and catalytic activity of non-precious metal oxides. High-throughput screening of mixed metal oxides offers a promising route to the identification of new stable catalysts and requires careful design of experiments to combine the concepts of rapid experimentation and long-term stability. By combining serial and parallel measurement techniques, we have created a high-throughput platform to assess the catalytic activity of material libraries in the as-prepared state and after 2 h of operation. By screening the entire (Mn–Co–Ta–Sb)O x composition space, we observe that the compositions with highest initial activity comprised cobalt and manganese oxides, but combinations with antimony and tantalum offer improved stability. By combining the desired properties of catalytic activity and stability, the optimal composition regions are readily identified, demonstrating the success and fidelity of this novel high-throughput screening platform.

Effects of pH and Sm3+ doping on the structure, morphology and luminescence properties of BiPO4:Sm3+ phosphors prepared by hydrothermal method

BiPO4 and Bi1−xPO4:xSm3+ phosphors were successfully synthesized by a simple hydrothermal method at different pH. The influences of pH and Sm3+ doping on the structure, morphology and luminescence properties of BiPO4:Sm3+ were investigated systematically. X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) results reveal that a phase transition from low temperature monoclinic phase (LTMP) to hexagonal phase (HP) occurs with increasing pH and Sm3+ doping, accompanied by a morphology transition from octahedron-like to short rod-like. At pH 0.5, the crystal structure and morphology of the Bi1−xPO4:xSm3+ remain the same with Sm3+ doping, indicating that the structural transition induced by Sm3+ doping can be suppressed under strong acid condition. The photoluminescence (PL) spectra suggest that the optimal emission intensity of BiPO4:Sm3+ appears at pH 0.5, which may be attributed to the single LTMP. The concentration quenching occurs when x is beyond 0.11, which is ascribed to dipole-dipole interaction.

Processing of porous spherical Co-doped SiO2/Cu-grafted TiO2 hybrid particles for the decomposition of gaseous acetaldehyde in the dark and under visible light

Spherical Co-doped SiO2/Cu-grafted TiO2 hybrid particles were prepared using organic spherical monolith particles as a template. Rutile was crystallized in the monolith particles impregnated with a TiO2 precursor solution by hydrothermal treatment in a strong acid condition (2M HCl). Subsequent UV illumination assisted efficient decomposition of organic compounds in the particles during firing. The solvent of the solution for Cu grafting affects the pore structure. Ethanol was more suitable than water for the particles prepared in this study. The hybrid particles, after firing at 500°C in air, possessed decomposition activity against gaseous acetaldehyde both in the dark and under visible light.

Preparation of esterified derivatives of α-lactalbumin and investigation of their antibacterial activity

α-lactalbumin (α-La) is one of the major milk proteins that in addition of nutritional value it can get many other useful novel functions such as antiviral and tumoricidal activities via structural modifications by enzyme or chemical methods. Several researches show antiviral activity of esterified milk proteins because of their new functional properties followed by structural modifications. In this research, the hypothesis based on antibacterial activity of esterified α-La was examined. The esterification reaction as an important tool for modifying food proteins was employed in this study by using different alcohols under strong acidic condition at 4 °C for 3 days. α-La was esterified to the extent of 53.8%, 34.95%, 32.2% , 6.07% and 46.8% with methanol, ethanol, 1-butanol, 2-pentanol and 1-hexanol, respectively, showed the influence of molar ratio, type of used alcohol and time of reaction on the reaction yield. Then the effects of esterified derivatives of α-La were tested on the growth of some positive and negative gram bacteria(including Bacillus cereus, methicylin resistant Staphylococcus aureus (MRSA), Escherichia coli, and Klebsiella) by disc assay. After 24-48 h incubation, no inhibition zone surrounding the discs was observed which represents the fail of any antibacterial activity of α-La and its esterified derivatives.

New fluorescent pH probes for acid conditions

New pyrazoline-based pH fluorescent probes have been synthesized and characterized. These probes respond to acidic pH with short response time (less than 1min), high selectivity and sensitivity. They have good reversibility and nearly no interference from common metal ions. These probes are suitable for strong acid conditions and can quantitatively detect pH value based on equilibrium equation, pH=pKa−log(Ia−Ix)/(Ix−Ib), with very good linear relationship. Moreover, using 1H NMR analysis, we verified that the protonation of the nitrogen in thiazole weakened the thiazole ring's ability to donate electrons to pyrazoline moiety and changed the intramolecular charge transfer that was actually the mechanism of the fluorescence quenching phenomenon under strongly acidic conditions. More importantly, these probes can image strong acidity in Saccharomyces cerevisiae.

New Cofactor‐Independent Hydration Biocatalysts: Structural, Biochemical, and Biocatalytic Characteristics of Carotenoid and Oleate Hydratases

AbstractIn industrial biocatalytic processes the class of lyases (EC 4) is underrepresented and only a few enzymes are used in industrial scale reactions. Hydro‐lyases (EC 4.2.1) catalyze the non‐hydrolytic and non‐oxidative addition of water to a CC bond. Without a biocatalyst, this reaction proceeds under strong acidic conditions with no enantioselectivity. From a chemical point of view carotenoid 1,2‐hydratase (CrtC) performs a very challenging addition of water to an isolated CC bond. This hydration reaction proceeds without assistance of electron withdrawing groups or transition metals, which makes it very interesting from both an industrial, as well as enzymatic point of view. Oleate hydratase (OHase) catalyzes the enantioselective conversion of oleic acid into 10‐hydroxystearic acid. The crystal structure of OHase from Lactobacillus acidophilus was published recently, which contributes to the understanding of this enzyme. These enzymes could broaden the organic chemist’s toolbox.