Facile synthesis of nanorods of tetragonal barium titanate using ethylene glycol

Tetragonal barium titanate (BaTiO₃) nanorods were synthesized from hydroxide precursor by a hydrothermal/solvothermal method with 10 vol% ethylene glycol as solvent. The hydroxide precursor slurry was prepared by the addition of 10 M NaOH to a mixed solution of BaCl₂ and TiCl₄. When the above aqueous slurry was heated with water only at 200 °C, cubic BaTiO₃ nanocrystals formed, whereas tetragonal BaTiO₃ nanorods were obtained when heated with 10 vol% ethylene glycol. The crystallization of cubic BaTiO₃ via dissolution–reprecipitation of precursor could be suppressed by the addition of ethylene glycol, resulting in the formation of tetragonal BaTiO₃ under hydrothermal treatment at 200 °C.     

Hydrothermal synthesis and activation of graphene-incorporated nitrogen-rich carbon composite for high-performance supercapacitors

Graphene-incorporated nitrogen-rich carbon composite with nitrogen content of ca. 10 wt.% has been synthesized by an effective yet simple hydrothermal reaction of glucosamine in the presence of graphene oxide (GO). The nitrogen content of carbon composite is nearly twice as high as that of hydrothermal carbon without graphene. GO is favorable for the high nitrogen doping in the carbon composite by the reaction between the glucosamine-released ammonia and GO. The hydrothermal carbon composite is further activated by KOH, and graphene in the activated carbon composite demonstrates a positive effect of increasing specific surface area, pore volume and electrical conductivity, resulting in superior electrochemical performance. The activated carbon composite with higher specific surface area and micropore volume possesses higher specific capacitance with a value of 300 F g⁻¹ at 0.1 A g⁻¹ in 6 M KOH aqueous solution in the two electrode cell. Larger mesopore volume and higher conductivity of the activated carbon composite will provide fast ion and electron transfer, thus leading to higher rate capacity with a capacitance retention of 76% at 8 A g⁻¹ in comparison to the activated hydrothermal carbon without graphene.     

Cadmium ion-selective sorbent preconcentration method using ion imprinted poly(ethylene glycol dimethacrylate-co-vinylimidazole)

The present study focuses on the preparation of an Cd²⁺-imprinted poly(ethylene glycol dimethacrylate-co-vinylimidazole) for selective extraction/preconcentration of Cd²⁺ ions from aqueous solution, with further determination by FAAS using a flow system. Sorbent extraction/preconcentration system was optimized by using chemometric tools (factorial design and Doehlert matrix). Under optimized conditions, the method presented a limit of detection of 0.11 μg L^?1 and linear analytical curve from 1.0 up to 50.0 μg L^?1 (r = 0.993). The preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were found to be 38.4, 0.39 mL and 14.3 min^?1, respectively. The selectivity coefficient of ion imprinted polymer was compared with the selectivity coefficient of NIP (non-imprinted polymer) for the Cd²⁺/Pb²⁺, Cd²⁺/Cu²⁺ and Cd²⁺/Zn²⁺ binary mixtures, where the respective values of relative selectivity coefficient (k′) of 157.5, 4.44 and 1.38 were obtained. The proposed method was successfully applied for cadmium determination in different types of water samples, urine and certified reference material (Lobster Hepatopancreas).     

Metal sorption on macroporous poly(GMA-co-EGDMA) modified with ethylene diamine

Two samples of macroporous crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), poly(GMA-co-EGDMA), with different porosity parameters were synthesized by suspension copolymerization and modified by ring-opening reaction of the pendant epoxy groups with ethylene diamine (EDA). The samples were characterized by mercury porosimetry, FT-IR spectroscopy and elemental analysis. The sorption rate of the modified copolymer, poly(GMA-co-EGDMA)-en for Cu(II) ions determined under non-competitive conditions was relatively rapid, i.e. the maximum capacity was reached within 30 min. Batch sorption capacities for Cu(II), Fe(II), Mn(II), Cd(II), Zn(II), Pb(II), Cr(III) and Pt(IV) ions were determined under non-competitive conditions in the pH range 1.25–5.5 at room temperature. The maximum sorption capacities of poly(GMA-co-EGDMA)-en under non-competitive conditions were 1.30 mmol/g for Pt(IV) at pH 5.5, 1.10 mmol/g for Cu(II) at pH 5.5, 1.06 mmol/g for Pb(II) at pH 1.25 and 0.67 mmol/g for Cd(II) ions at pH 5.5. The selectivity of poly(GMA-co-EGDMA)-en towards Cu(II), Co(II), Ni(II), Pb(II) and Pt(IV) ions was investigated under competitive conditions. Poly(GMA-co-EGDMA)-en showed high selectivity for Pt(IV) over Cu(II), Co(II), Ni(II) and Pb(II) ions at pH 2.1. At pH 5.5, the metal sorption capacities of poly(GMA-co-EGDMA)-en decreased in the order: Cu(II) > Co(II) > Pt(IV) ≈ Ni(II) > Pb(II). Regeneration of the Cu(II), Ni(II) and Pb(II) loaded poly(GMA-co-EGDMA)-en with 2 M H₂SO₄ showed that the polymer can be reused in several sorption/desorption cycles.     

Corrosion inhibition by poly(N-ethylaniline) coatings of mild steel in aqueous acidic solutions

Poly(N-ethylaniline) (PNEA) coatings on mild steel have been electrodeposited from 0.1 to 0.5 M aqueous oxalic acid solutions containing 0.1 M N-ethylaniline (NEA) using potentiodynamic synthesis technique. The effect of oxalic acid concentration on the corrosion behavior of PNEA coated mild steel surfaces were investigated by DC polarization and electrochemical impedance spectroscopy (EIS) techniques in 0.1 M HCl and 0.05 M H₂SO₄ solutions. Corrosion test results showed that corrosion resistance of PNEA coatings decreases with increasing concentrations of oxalic acid in polymerization solution. Decreasing acidity of the polymerization solution causes more effective protection against corrosion in aqueous acidic corrosive medium.     

The influence of sodium and potassium hydroxide on alite hydration: Experiments and simulations

The basic nature of alkali hydroxides (NaOH, KOH) when added to mixing water, increases the pH in proportion to the level of salt addition. For alite (impure tricalcium silicate; MIII-Ca₃SiO₅) hydration, this pH increase accelerates the rate of hydration and reduces the duration of the induction, acceleration and deceleration regimes. This study evaluates alite hydration in solutions of varying compositions and alkalinities (0.1 M, 0.2 M and 0.5 M NaOH and KOH) in context of their heat release behavior and analysis of the solid/liquid phases. The modeling platform, μic, is used to simulate, describe and discriminate the impact of the pore solution chemistry and reaction product formation parameters on alite hydration (Bishnoi and Scrivener, 2009 [1]). Numerical predictions of the solid and liquid phase compositions and the heat release response show good agreement with experimental determinations. The simulations indicate that the effects up to the end of the induction period follow directly from a change in the pore solution composition under a solution controlled dissolution mechanism, which leads to the faster precipitation of portlandite. The changes in the main heat evolution peak appear to be related to an increase in the nucleation density of C–S–H in alkali hydroxide solutions. Examination under the SEM did not indicate significant difference in C–S–H morphology and composition in the presence of NaOH/KOH.     

Supercritical hydrothermal synthesis of titanium dioxide nanostructures with controlled phase and morphology

A novel template- and organic-free synthesis of TiO₂ nanostructures with controlled phase and morphology was realized through batch supercritical hydrothermal treatment (400 °C) of titanate nanotubes (TNTs) with H₂O₂ in NaOH aqueous solution. Well-defined 3D titanate hierarchical spheres (THSs), 2D multilayered titanate nanosheets (TNSs), and 1D monodisperse anatase nanorods (ANRs) exposing (0 1 0) facets were prepared in 15 min by slightly varying the NaOH solution pH. Specifically, the obtained Na/H-THSs (without/with HCl neutralization) exhibited highly porous structures with large specific surface area (109 m² g⁻¹ and 196 m² g⁻¹, respectively). Temperature-dependent phase and morphology evolutions of products under subcritical condition (200 and 300 °C) were investigated. The formation of the TiO₂ nanostructures from TNTs was proposed mainly following a dissolution–nucleation-growth mechanism, suggesting that both supercritical temperature and NaOH solution pH were determinant factors governing the nucleation and growth process and thus the phase and morphology.     

Microphase separated structures in the solid and molten states of double-crystal graft copolymers of polyethylene and poly(ethylene oxide)

Transitions from one microphase separated structure in the solid state to a different one in the molten state in polyethylene-graft-poly(ethylene oxide) copolymers, PE-g-PEO, were investigated by variable temperature X-ray scattering measurements and thermal analyses. Small-angle X-ray scattering patterns from polymers with PEO grafts with 25, 50 and 100 ethylene oxide (EO) units show that the polymer passes through three distinct structures at ～10 nm length scales with increase in temperature (T): lamellar structures of PE and PEO at T < T_m^PEO, PE lamellae surrounded by molten PEO at T_m^PEO < T < T_m^PE, and microphase separated structures at T > T_m^PE when both PE and PEO are molten (T_m refers to the melting temperature). These phase transformations also occur during cooling but with hysteresis. Crystalline phases of PEO side chains and PE main chains could be identified in the wide-angle X-ray diffraction profiles indicating that the PE backbone and PEO grafts crystallize into separate domains, especially with longer grafted chains (50 and 100 units). At EO segment lengths > 50, PEO shows the expected increase in melting and crystallization temperatures with the increase in the grafted chain length. PE does not affect T_m^PEO but does decrease the onset of crystallization upon cooling. PEO grafts result in fractionation of PE, decrease the melting point of PE and increase the undercooling for the onset of crystallization of PE.     

Synthesis of hierarchical carbon sphere@NiMoO4 composite materials for supercapacitor electrodes

In this work, hierarchical Carbon sphere@NiMoO₄ (C@NiMoO₄) composite was successfully synthesized by cost-effective two-step hydrothermal method. The samples were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction analysis and Thermogravimetric analysis. The Electrochemical measurement demonstrated that hierarchical C@NiMoO₄ electrode materials exhibited good specific capacitance (Csp) of 268.8 F g⁻¹ at a current density of 1 A g⁻¹ in 2 M NaOH aqueous electrolyte solution, as well as good cycling stability (88.4% retention after 2000 cycles). Compared to pure NiMoO₄, the excellent capacitive properties and stability suggest that the hierarchical structure C@NiMoO₄ could be promising electroactive material for supercapacitors.     

Thermogelation properties of poly(N-isopropylacrylamide) – block – poly(ethylene glycol) – block – poly(N-isopropylacrylamide) triblock copolymer aqueous solutions

Low polydispersity PNIPAM–PEG–PNIPAM triblock copolymers with PEG blocks of 1–6 kDa and PNIPAM chains of 5–30 kDa were synthesized and their thermogelation behavior in aqueous solution as a function of their composition and block length was investigated for the first time. DSC, dynamic rheometry and the tube inverting method were employed to characterize the gelation process at various polymer concentrations, and their results were compared. The thermogelation process depended mainly on the length of both PNIPAM and PEG blocks. Both association and aggregation temperatures of the PNIPAM chains decreased with the MW of PNIPAM and increased with the length of the PEG block. The amplitude of these effects depended on the molecular weights of the blocks forming the copolymer as a consequence of the partial mixing of PNIPAM and PEG chains during the association/aggregation process, while the overall hydrophilicity of the entire copolymer played only a minor role. The length of the PEG block proved also to be the most important factor for the preparation of a stable gel in 20 wt.% solutions, while the hydrophilic groups/hydrophobic groups ratio had no importance.     

Epoxidation of pendant allyl groups in poly(ester-anhydride)s proposed for application in drug delivery

This paper describes the synthesis and modification of functional poly(ester-anhydride)s that have potential for a variety of applications in drug delivery. Functional poly(ester-anhydride)s with pendant allyl groups were synthesized by two step polycondensation of oligo(3-allyloxy-1,2-propylene succinate) terminated with carboxyl end groups (OSAGE) and one of diacids (DA): sebacic (SBA) or dodecanedicarboxylic acid (DDC). Poly(ester-anhydride)s with molecular weights with range of 3100–7300 Da and with varying degree of functionality were oxidized with m-chloroperbenzoic acid (MCPBA) to yield respective polymers with epoxy pendant groups. The OSAGE to DA ratio in the poly(ester-anhydride)s, polymer concentration in the reaction solution, excess of MCPBA and duration of the reaction, had influenced the conversion of allyl groups into glycidyl ones. For all types of poly(ester-anhydride)s conditions were set up in which 100% of epoxidation could be achieved. Completely oxidized poly(ester-anhydride)s were characterized by means of ¹H NMR spectroscopy and DSC technique. Their thermal and solubility characteristics were compared with characteristics of initial poly(ester-anhydride)s. Initial and oxidized polymers containing 80% of SBA or DDC were formulated into microspheres using O/W emulsion technique. The presence of epoxy groups at the surface of microspheres were confirmed by ATR IR spectroscopy. Microspheres obtained were subjected to hydrolytic degradation at 37 °C, in aqueous phosphate buffer solution of pH = 7.41 (PBS).     

Synthesis and swelling properties of poly[acrylamide-co-(crotonic acid)] superabsorbents

Superabsorbent polymers of acrylamide (AAm)/crotonic acid (CA) were synthesized by foamed polymerization in an aqueous solution of AAm with CA as a comonomer, initiated by an initiator couple of ammonium persulfate and N,N,N′N′-tetramethylethylenediamine. A crosslinking agent N,N′-methylenebisacrylamide, a foaming agent sodium bicarbonate, and a foam stabilizer, a triblock copolymer of polyoxyethylene/polyoxypropylene/polyoxyethylene, were used in the polymerization. The influences of the relative contents of CA, crosslinking agent, and initiator, on the swelling properties of the superabsorbent polymer systems were examined. The superabsorbent polymer synthesized with an AAm/CA ratio of 98:2 by mole, 0.5 wt.% of N,N′-methylenebisacrylamide and 1 wt.% of ammonium persulfate at 250 rpm and 50 °C for 30 min of polymerization time produced the highest water absorption of 211 ± 9 times its dried weight and could absorb water up to 162 ± 4 g g⁻¹ of the dry copolymer within 10 min. The electrochemical reaction for acrylamide–crotonic acid polymerization was investigated by cyclic voltammetry. The anodic current indicated that acrylamide acting as an electron donor whereas crotonic acid performed as an electron receiver, then providing the cathodic current. The diffusion of water into the superabsorbent polymer was non-Fickian (case II and anomalous). Acrylamide–crotonic acid superabsorbents containing various crosslinker concentrations had a water swelling in the range of 79–289 g g⁻¹. The diffusion coefficients varied between 6.9 × 10⁻⁹ and 5.1 × 10⁻⁸ cm² s⁻¹. Adsorption of the basic dye by the superabsorbent was a monolayer evaluated by the Langmuir isotherm. The superabsorbents can thus be used to adsorb cationic dyes in textile industry.     

Preparation of poly (ethylene glycol) acrylate grafted polystyrene resin for solid-phase peptide synthesis

The solid-phase synthesis resin with high loading capacity was prepared through grafting poly (ethylene glycol) acrylate monomer from Merrifield resins via activators generated by electron transfer atom transfer radical polymerization. The grafted resins demonstrate well-swellability in both polar and nonpolar solvent such as dichloromethane, dimethylformamide, ethanol, tetrahydrofuran, acetonitrile, methanol and water. Particularly, the swelling ability of the grafted resin has reached two-fold of Merrifield resin in the polar solvent such as acetonitrile, methanol and water, and it enable high functional loadings up to 0.5–1.2 mmol g⁻¹ compared with the conventional polystyrene-grafting-poly (ethylene glycol) (0.15–0.25 mmol g⁻¹). This resin was derived to be used for synthesis of a difficult sequence-acyl carrier protein fragment 65-74 (ACP 65-74). The quantity and purity of peptide obtained from the grafted resin were higher than when the commercial Wang resin was used. The synthesis efficiency enhanced with the increase of grafting chains’ length within the range of hydroxyl capacity at 0.5–1.0 mmol g⁻¹. It was relative that the longer grafting chains were favor to suppress the hydrophobicity of the Merrifield resin.     

Improved electrochemical performances of reduced graphene oxide based supercapacitor using redox additive electrolyte

Reduced graphene oxide (rGO) is prepared by simple and eco-friendly hydrothermal reduction method. X-ray photoelectron spectroscopy and Ultraviolet–visible analysis corroborated the reduction of graphene oxide into rGO in basic medium. The flexibility of the prepared rGO is inferred from transmission electron micrographs. Further, the identification of suitable electrolyte is carried out using different anions (SO₄²⁻, Cl⁻, OH⁻) and cations (K⁺, Na⁺) for the superior performance of the rGO based supercapacitors. The electrochemical performance revealed that K⁺ and OH⁻ ions are more active species in aqueous solutions. Subsequently, an effort was taken to improve the specific capacitance in the optimized 1 M KOH electrolyte by KI as redox additive at different concentrations (0.025, 0.05, 0.075 and 0.1 M). The calculated specific capacitance and energy density of rGO electrode in the optimized 1 M KOH + 0.05 M KI electrolyte is 500 F g⁻¹ and 44 Wh kg⁻¹, respectively. On the other hand, it exhibited the specific capacitance of 298 F g⁻¹ at 0.83 A g⁻¹ in non-aqueous polymer gel (PVA + KOH + KI) electrolyte. Finally, the charged aqueous device is utilized to glow the light emitting diode.     

Hydrothermal and electrochemical growth of complex oxide thin films for electronic devices

Thin film growth of complex oxides including BaTiO₃, SrTiO₃, BaZrO₃, SrZrO₃, KTaO₃, and KNbO₃ were studied by the hydrothermal and the hydrothermal–electrochemical methods. Hydrothermal–electrochemical growth of ATiO₃ (A = Ba, Sr) thin films was investigated at temperatures from 100 to 200 °C using a three-electrode cell. Current efficiency for the film growth was in the range from ca. 0.6 to 3.0%. Tracer experiments revealed that the ATiO₃ film grows at the film/substrate interface. Thin films of AZrO₃ (A = Ba, Sr) were also prepared on Zr metal substrates by the hydrothermal–electrochemical method. By applying a potential above ca. +2 V versus Ag/AgCl to the Zr substrates, AZrO₃ thin films were formed uniformly. Thin films of KTaO₃ and KNbO₃ were prepared on Ta metal substrates by the hydrothermal method. Perovskite-type KTaO₃ thin films were formed in 2.0 M KOH at 300 °C. Pyrochlore-type K₂Ta₂O₆ thin films were formed at lower temperatures and lower KOH concentrations.     

Facile synthesis of activated carbon/carbon nanotubes compound for supercapacitor application

A large number of carbon nanotubes (CNTs) have been produced commingled in activated mesocarbon microbeads (AMCMBs) activated by potassium hydroxide in a stainless steel container at 900 °C, in which an especial buried-protection method with petroleum coke powders was used to protecting the product during activation. The CNTs were found to be about 50 nm in diameter and characteristic length more than 10 μm. In addition, the AMCMBs/CNTs compound when used for electrode material of electrochemical double-layer capacitors exhibited a specific capacitance of 243 F g^?1 in 6 M KOH aqueous solution.     

Anodic dissolution of titanium in NaCl-containing ethylene glycol

Anodic dissolution behavior of titanium in NaCl-containing ethylene glycol has been examined to obtain electropolished titanium surface. During anodic polarization in 1 mol dm^?3 NaCl ethylene glycol solution at 293 K, the titanium electrode covered with oxide dissolves with gas evolution at potentials higher than 10 V (Ag/AgCl) while it is in passive state at potentials lower than 5 V. However, after removal of the oxide layer by pre-polarization at gas-evolving potentials, no gas evolution is observed, and the titanium electrode shows a limiting dissolution current as tetravalent species at potentials higher than 5 V, producing a smooth surface. The polarization of the rotating disk titanium electrode reveals that the kinetics of the mass transfer reaction for electropolishing of titanium is controlled by titanium species dissolved into the solution, not by chloride ions or water containing in the solution. Repetition of dynamic polarization gives a well-electropolished surface.     

Facile synthesis of functionalized porous carbon with three-dimensional interconnected pore structure for high volumetric performance supercapacitors

Functionalized porous carbon with three-dimensional (3D) interconnected pore structure has been successfully synthesized through direct heat-treatment of KOH-soaked soybeans. Benefiting from heteroatoms (N, O) doping, interconnected porous carbon framework with high surface area as well as high packing density (up to 1.1 g cm⁻³), the as-obtained porous carbon material exhibits high volumetric capacitance of 468 F cm⁻³, good rate capability and excellent cycling stability (91% of capacitance retention after 10,000 cycles) in 6 M KOH electolyte. More importantly, the as-assembled symmetric supercapacitor delivers high volumetric energy density of 28.6 Wh L⁻¹ in 1 M Na₂SO₄ aqueous solution.     

Preparation and one-step activation of microporous carbon nanofibers for use as supercapacitor electrodes

Microporous carbon nanofibers were prepared by electrospinning from resole-type phenolic resin, followed by one-step activation. KOH was utilized to tune the fiber diameter and improve porous texture. By adjusting KOH content in the spinning solution, the fiber diameter could be controlled in the range of 252–666 nm and the microporous volume and specific surface area could be greatly improved. The electrochemical measurements in 6 M KOH aqueous solution showed that the microporous carbon nanofibers possessed high specific capacitance, considerable rate performance, and superior specific surface capacitance to conventional microporous carbons. The maximal specific capacitance of 256 F g⁻¹ and high specific surface capacitance of 0.51 F m⁻² were achieved at 0.2 A g⁻¹. Furthermore, the specific capacitance could still remain 170 F g⁻¹ at 20 A g⁻¹ with the retention of 67%. Analysis showed that the high specific surface capacitance of the resultant carbons was mainly attributed to optimized pore size (0.7–1.2 nm) and the excellent rate performance should be principally due to the reduced ion transportation distance derived from the nanometer-scaled fibers.     

Kinetic studies of the oxidation of quercetin,rutin and taxifolin in the basic medium by (ethylenediaminetetraacetato) cobalt(III) complex

The quercetin in 0.01 M NaOH solution underwent steady oxidation when it was exposed to air with the formation of the quinone product. For the taxifolin and rutin, the oxidation occurred only when the solutions were saturated with O₂, but very slowly. The kinetics of the oxidation of flavonoids in 0.01 M NaOH solution by Co(edta)^? complex was carried out and the rate constants are 3.44 × 10², 1.04 × 10^? 1 and 1.46 × 10^? 2 M^? 1 s^? 1 for quercetin, rutin and taxifolin, respectively, at μ = 0.10 M LiClO₄. The deprotonation of the C₃ hydroxyl group and the conjugation between pyrone and catechol rings account for the reactivity of quercetin.