Chemical Titration Method Research Articles

Study on the dehydrofluorination of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymer

This study evaluates the dehydrofluorination of fluoroelastomer (poly(VDF-co-HFP) copolymer) which was dissolved by organic solvent and reacted with different concentrations of KOH and different amount of phase transfer catalyst (PTC) at 20–60 °C.The structures, sequence types and contents of double bonds of samples were analyzed and investigated by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy(ATR-FTIR), 1H nuclear magnetic resonance (NMR), 19F NMR spectroscopy and chemical titration method. The results revealed that dehydrofluorination of the studied fluoroelastromers could be carried out at room temperature in alkaline environments, wherein the temperature and alkali concentration were the great factors. And the dehydrofluorination of poly(VDF-co-HFP) copolymer conformed mainly to Zaitsev's rule and partially to Hofmann's rule. The double bonds (–C=C–) would generate in five positions of molecular chains and contents could be controlled. With increase of alkali concentration or reaction temperature, there would be dehydrofluorination accompanied with oxidation reaction whereby some –C=C– converted to hydroxyl groups. Finally, the mechanism of reaction was also deduced.

Dehydrofluorination mechanism, structure and thermal stability of pure fluoroelastomer (poly(VDF-ter-HFP-ter-TFE) terpolymer) in alkaline environment

This study evaluates the dehydrofluorination mechanism, structure and thermal stability of pure fluoroelastomer which was dissolved by organic solvent and reacted with different concentrations of KOH at 20∼60°C. The sequence types and contents of double bonds and other oxygen-containing groups of samples were analyzed and investigated by Attenuated total reflectance/Fourier transform infrared (ATR-FTIR), 1H nuclear magnetic resonance (NMR), 19F-NMR spectroscopy and chemical titration method; thermal decomposition temperatures of samples were analyzed by thermogravimetric analysis (TGA). The results revealed that dehydrofluorination of fluoroelastomer would accompain with oxidation reaction whereby some double bonds conforming to Hofmann’s rule had been converted to hydroxyl groups, wherein the temperature and alkali concentration were the important factors. The double bonds generated in seven positions of molecular chains, sequence types were mainly conformed to Hofmann’s rule and Zaitsev’s rule supplemented. With the increase of reaction temperature and concentration of KOH, the thermal stability of fluoroelastomer decreased obviously since hydroxyl groups had a greater effect on it. Finally, the mechanism of reaction was also deduced.

Butanal Condensation Chemistry Catalyzed by Brønsted Acid Sites on Polyoxometalate Clusters

AbstractThe connection of active site structures and their catalytic chemistry during butanal deoxygenation on polyoxometalate clusters with varying H+ site densities and identity of central atoms [HxNa4−xSiW12O40 (x=0–4) and HyNa3−yPW12O40 (y=0–3)] was established with rate assessment, IR spectroscopic, and chemical titration methods. Butanal adsorbs on the H+ or Na+ ions on polyoxometalate clusters and forms RC=O⋅⋅⋅H+ or RC=O⋅⋅⋅Na+ complexes at 348 K. A portion of the adsorbed butanals on the H+ sites converts to surface acetates through their reactions with vicinal framework oxygen atoms, as confirmed from the detection of νas(OCO) band at approximately 1580 cm−1, and remains as the spectator species. Bimolecular reactions of butanals on the remaining H+ sites lead to 2‐ethyl‐2‐hexenal as the predominant products, within which a small fraction undergoes sequential cyclization–dehydration to produce aromatics. A trace amount of butanal converts through minor, competitive pathways that form light olefins and dienes. These findings on the connection between active sites and their catalytic chemistry provide mechanistic insights useful for tuning the rates of the various concomitant paths and thus yields towards the different products during deoxygenation reactions.

Promoting Effect of Inorganic Alkali on Carbon Dioxide Adsorption in Amine-Modified MCM-41

Three kinds of inorganic alkali are introduced into tetraethylenepentamine (TEPA) and polyethyleneimine (PEI)-modified MCM-41 as the CO2 adsorbents. X-ray diffraction, N2 adsorption, fourier-transform infrared and thermo gravimetric analysis are used to characterize the surface structures and the thermal stability of adsorbents. Chemical titration method is used to measure the alkali amounts of adsorbents. Thermo-gravimetric analysis with 10% CO2/90% N2 as the simulated flue gas is used to test the CO2 adsorption performance of adsorbents. The results show that all three kinds of inorganic alkali-containing adsorbents exhibit higher CO2 adsorption capability than traditional TEPA and PEI modified samples. Ca(OH)2 and PEI modified samples exhibit the highest adsorption capacity and recyclable property. The introduction of inorganic alkali changes the chemical adsorption mechanism between CO2 and adsorbent surface due to the increased hydroxyl groups. The CO2 adsorption capacities have a linear dependence relation with the alkali amounts of adsorbents, indicating that alkali amount is a critical factor for the exploration of novel adsorbents.

Preparation of TPI-g-MAH and the application in toughened PA6

Maleic anhydride grafted trans-1,4-polyisoprene (TPI-g-MAH) was successfully prepared, and characterised through FTIR and the chemical titration method. Furthermore, effect of TPI-g-MAH on the mechanical properties of the glass fibre reinforced nylon 6 was investigated. The results show that TPI-g-MAH can improve the toughness of glass fibre reinforced PA6 composite material, and composite material has excellent comprehensive performance when the content of TPI-g-MAH reaches 4%.

ChemInform Abstract: Catalytic Deoxygenation on Transition Metal Carbide Catalysts

AbstractReview: 110 refs.

A new, high electrochemical activity and chromium tolerant cathode for solid oxide fuel cells

The commercialization of solid oxide fuel cell (SOFC) technologies requires the development of cathode materials not only with high electrochemical activity and stability but also with excellent tolerance and resistance towards contaminants such as chromium. Here, a new electrode, Sm0.5(1−x)Sr0.5(1−x)BaxCo1−0.3xFe0.2xNb0.1xO3−δ (SSBCFN with x = 0.4, 0.5, 0.6) is developed based on the combined composition of Sm0.5Sr0.5CoO3−δ (SSC) and Ba(Co0.7Fe0.2Nb0.1)O3−δ (BCFN). SSBCFN with x = 0.5 (SSBCFN5) shows a high electronic conductivity of 128–221 S cm−1 in the temperature range of 500–900 °C, an essential requirement of SOFCs electrode materials and low electrode polarization resistance of 0.53 Ωcm2 at 600 °C, significantly lower than 1.79 Ωcm2 for the reaction on SSC and 0.64 Ωcm2 on BCFN. SSBCFN5 shows cubic perovskite structure with a high oxygen non-stoichiometry, δ = 0.514 ± 0.027, based on chemical titration method. Compared to SSC and BCFN electrodes, SSBCFN5 shows better electrochemical activity for the oxygen reduction reaction and most importantly, it exhibits excellent stability and resistance toward chromium deposition and poisoning under SOFC operation conditions from 700 to 900 °C. The results indicate that SSBCFN5 is a promising potential cathode of SOFCs with high activity, stability and high tolerance towards contamination by Cr.

Photodriven Multi-electron Storage in Disubstituted Ru(II) Dppz Analogues.

Four derivatives of the laminate acceptor ligand dipyrido-[3,2-a:2',3'-c]phenazine (dppz) and their corresponding ruthenium complexes, [Ru(phen)2 (dppzX2 )](2+) , were prepared and characterized by NMR spectroscopy, ESI-MS, and elemental analysis. The new ligands, generically denoted dppzX2 , were symmetrically disubstituted on the distal benzene ring to give 10,13-dibromodppz (dppz-p-Br), 11,12-dibromodppz (dppz-o-Br), 10,13-dicyanodppz (dppz-p-CN), 11,12-dicyanodppz (dppz-o-CN). Solvated ground state MO calculations of the ruthenium complexes reveal that these electron-withdrawing substituents not only lower the LUMO of the dppz ligand (dppz(CN)2 <dppzBr2 <dppz), but that the para disubstitution results in a lower LUMO than the ortho disubstitution (dppz-p-CN<(dppz-o-CN), and dppz-p-Br<dppz-o-Br). The validity of the calculations was confirmed experimentally using cyclic voltammetry. Of the complexes evaluated in this study, only the dicyanodppz complexes showed multiple dppz-based reductions prior to reduction of the phen ligands. The capacity to form singly and doubly reduced dppz-based anions at modest reduction potentials was confirmed using a combination of spectroelectrochemical and chemical titration methods. When subjected to photolysis with visible light in the presence of a sacrificial donor, such as triethylamine, both cyano complexes showed multi-electron reduction. The other complexes only show a single reduction.

Changes of oxygen-containing groups during thermal treatment and their influences on moisture readsorption of lignite

ABSTRACTThe changes in oxygen-containing groups in the thermal treatment process of lignite were analyzed and the moisture readsorption amounts of upgraded coals were related in this study. A chemical titration method was applied to determine the types and contents of oxygen-containing groups in raw lignite and upgraded coals obtained in the temperature range of 353–633 K under atmospheres of argon, air, and carbon dioxide. Experimental results showed that the oxygen-containing groups mainly involved carbonyl, phenolic hydroxyl, and carboxylic groups (including carboxyl and carboxylate), among which phenolic groups were dominant. These different oxygen-containing groups decomposed discriminatingly with temperature according to thermal stability. The removal of oxygen-containing groups proceeded more easily in a CO2 atmosphere compared to in Ar. The oxidation reaction occurring on the surface of lignite exposed to air led to an increase in oxygen-containing groups. The different types of oxygen-containing groups possessed various combining abilities with water, among which carboxyl was considered the most important group for the moisture readsorption. Decomposition of oxygen-containing groups in the thermal treatment process of lignite mainly caused a reduction in monolayer water adsorption and further decreased the multilayer water.

Energy-Resolved Measurement of Electron Traps in Metal-Oxide Particulate Photocatalysts By Newly Developed Reversed Double-Beam Photoacoustic Spectroscopy

Metal-oxide photocatalysts such as titanium(IV) oxide (titania) have long been called "semiconductor photocatalysts" presumably because they show n-type semiconducting properties of dark-current rectification and anodic photocurrent when they are used in the form of electrodes. However, there seems no influence of such semiconducting properties on their photocatalytic activities when used in a particle form. Then, why should metal-oxide photocatalysts be of semiconductor? Based on the results and discussion on the metal-oxide photocatalysis, the authors came across a hypothesis that electron traps liberated by electron detachment from donor impurity levels below the bottom of conduction band (CB) in n-type semiconductors. It is expected that deep traps may enhance recombination of photoexcited electrons and positive holes and shallow traps may enhance electron migration through trap–detrap mechanism. Therefore, energy-resolved measurement of trap density is required to design highly active photocatalysts. It is well known that photoirradiation of metal oxide particles or a single crystal in the presence of electron donors and in the absence of electron acceptors such as oxygen induces electron accumulation. The energy levels in particulate titania samples have been estimated by a chemical titration method to be 100–200 meV below the CB bottom,1 which is consistent with the hypothesis, though the energy resolution is not sufficient and alternative easier measurement technique should be developed. A group of the authors has developed double-beam photoacoustic spectroscopy (DB-PAS) by which the total density of electron traps can be estimated in relatively short time of measurement.2 In DB-PAS system, two beams, modulated probe light and continuous pump light, are used to detect photoabsorption at the wavelength of the probe light induced by photochemical reaction induced by pump light; change in photoabsorption intensity, even for opaque samples such as powder, under photoirradiation can be measured and thus total density of electron accumulation in titania particles have been measured. Recently, we have developed a new PAS system, reversed DB-PAS (RDB-PAS) modifying DB-PAS to make energy-resolved electron trap measurements possible. In RDB-PAS, a titania sample was filled in a PA cell, methanol-saturated argon was flowed and the cell was tightly sealed. The detection-light source was an LED (625 nm) and the output intensity was modulated by a digital function generator at 80 Hz. In addition to the modulated light, continuous scanning monochromatic light was also irradiated for direct excitation from valence band to electron traps of a sample. The acquired spectra were differentiated from long-wavelength side. RDB-PA signal from titania samples was observed at the wavelength longer than the rise of PA spectra corresponding to the band gap (3.2 eV and 3.0 eV for anatase and rutile respectively). It is suggested that RDB-PA signal corresponds to the accumulation of electrons into electron traps by direct excitation from valence band to electron traps. Increase in RDB-PA signal was not observed when platinum (Pt) was loaded on titania due to electron transfer to Pt. Derivative RDB-PA spectra of TIO-2 (anatase) and CR-EL (rutile) were shown in Fig. 1, where broad peaks at ca.0—0.45 eV and 0—0.25 eV, respectively, below the bottom of conduction band were observed. It is presumed that derivative RDB-PA spectra correspond to the energy-resolved distribution of the density of electron traps in titania photocatalyst powders. [1] Phys. Chem. Chem. Phys., 5, 778 (2003). [2] J. Phys. Chem. C, 111, 11927 (2007).

Comparison of Chloride Binding Capacity of Binary and Ternary Binders

Reinforced concrete structures work in the marine environment are easily erroded by the environment, the most dangerous intrusion by chloride ions. Chloride ions from the environment penetrate into concrete layer and cause reinforcement corrosion. The high chloride binding capacity in concrete helps reducing the reinforcement corrosion. The chloride binding capacity in concrete is largely dependent on the cement type. This paper investigated the chloride binding capacity of various binary and ternary binders. Chloride contents in mortars prepared with various binary and tinery binders were determined by chemical titration methods combining with microstructure analysis SEM. The experimental results showed that the chloride binding capacity of tinery binders which contains Ordinary Portland cement (OPC), blast furnace slag mixed with silica fume is highest.

Identification of MnOx species and Mn valence states in MnOx/TiO2 catalysts for low temperature SCR

As the selective catalytic reduction (SCR) catalysts for NOx removal, various Mn-based catalysts have been widely investigated in the academic world. However, few studies focus on the identification of MnOx species and Mn valence states in Mn-based catalysts. In this study, Mn-based catalysts, which were prepared by using different precursors or pure MnOx species, were investigated for their activities for SCR of NO by NH3. Meanwhile, according to XRD, TG and H2-TPR measurement, a mass of crystalline and/or amorphous MnOx species were detected, while a very small amount of amorphous MnOx species could be observed with the TG–DSC-MS by detecting the oxygen coming from manganese oxides because of the decomposition. In addition, the contents and distributions of Mn2+, Mn3+ and Mn4+ as well as the average valences of manganese in catalysts were tested with the chemical titration method, while the XPS results could not identify the MnOx species, showing a semi-quantitative assessment of Mn2+, Mn3+ and Mn4+ contents. Furthermore, based on the SCR performance, Mn2O3 and Mn3O4 species were active for NOx reduction.

A titration model for evaluating calcium hydroxide removal techniques.

Objective Calcium hydroxide (Ca(OH)2) has been used in endodontics as an intracanal medicament due to its antimicrobial effects and its ability to inactivate bacterial endotoxin. The inability to totally remove this intracanal medicament from the root canal system, however, may interfere with the setting of eugenol-based sealers or inhibit bonding of resin to dentin, thus presenting clinical challenges with endodontic treatment. This study used a chemical titration method to measure residual Ca(OH)2 left after different endodontic irrigation methods.Material and Methods Eighty-six human canine roots were prepared for obturation. Thirty teeth were filled with known but different amounts of Ca(OH)2 for 7 days, which were dissolved out and titrated to quantitate the residual Ca(OH)2 recovered from each root to produce a standard curve. Forty-eight of the remaining teeth were filled with equal amounts of Ca(OH)2 followed by gross Ca(OH)2 removal using hand files and randomized treatment of either: 1) Syringe irrigation; 2) Syringe irrigation with use of an apical file; 3) Syringe irrigation with added 30 s of passive ultrasonic irrigation (PUI), or 4) Syringe irrigation with apical file and PUI (n=12/group). Residual Ca(OH)2 was dissolved with glycerin and titrated to measure residual Ca(OH)2 left in the root.Results No method completely removed all residual Ca(OH)2. The addition of 30 s PUI with or without apical file use removed Ca(OH)2 significantly better than irrigation alone.Conclusions This technique allowed quantification of residual Ca(OH)2. The use of PUI (with or without apical file) resulted in significantly lower Ca(OH)2 residue compared to irrigation alone.

Study on the pore structure and oxygen-containing functional groups devoting to the hydrophilic force of dewatered lignite

In order to explore the water-holding capacity of dewatered lignite and the contribution of pore structure and oxygen-containing functional groups to it, a kind of typical Chinese lignite was dried under the atmosphere of nitrogen for different temperatures and times, and then was subjected to a process of moisture re-adsorption at the temperature of 25°C and relative humidity of 75%. Nitrogen adsorption and chemical titration methods were used to examine the pore structure parameters and amounts of oxygen-containing functional groups, respectively. The results indicate that the porous structure and oxygen-containing functional groups in lignite are two main factors influencing the hydrophilicity of dewatered coal, and their contributions are varied with the change of drying conditions. The change of water-holding capacity of pore structure is primarily attributed to the shrinkage or collapse of macro- and mesoporous and it decreases with the increase of drying temperature. The oxygen-containing functional groups mainly include phenolic hydroxyl, carbonyl, carboxyl and methoxyl groups, and the order of their hydrophilicity is: carboxyl group>phenolic hydroxyl group>carbonyl group>methoxyl group. Moreover, the water-holding capacity for the same kind of oxygen-containing functional groups in dewatered coal obtained at different temperature is not a fixed one, their hydrophilic forces decrease with the increase of drying temperature. For the coal samples dried for 60min under different temperature, the contribution of pore structure and oxygen-containing functional groups to the equilibrium moisture content (EMC) of dewatered lignite is: pore structure>phenolic hydroxyl group>carboxyl group>carbonyl group>methoxyl group. The contribution of total oxygen-containing functional groups to the EMC at below 280°C is more obvious, and that of pore structure is the principal factor thereafter.

Producing High Quality CaCO&lt;sub&gt;3&lt;/sub&gt; by Phosphogypsum with New Ammonia-Base Carbonation Method

Phosphogypsum is a by-product of industrial phosphoric acid producing with wet method, a simple and efficient way to produce high quality CaCO3by phosphogysum is presented in this work. Calcium in the phosphogypsum converts into Ca (OH)2with the addition of NaOH, acid insoluble substances and metal ion which was also separated from calcium in phosphogypsum by HCl and NH3·H2O respectively. The purity and whiteness of CaCO3produced by the carbonization of purified CaCl2solution are 98% and 96%. The optimum mass ratio of phosphogypsum, NaOH and HCl was 25:12:35. Chemical characterization of the resultant CaCO3was performed by XRD, SEM, TG and chemical titration method, which indicate that this method is effective in producing spherical CaCO3at room temperature, moreover, the purity, whiteness and thermostability of calcium carbonate can meet most of application requirements for industrial CaCO3.

Determine the Average Particle Size of Silica Sol

At present, the methods of analysising the average particle size of silica sol are the intuitive analysis, such as analysising the size distribution and morphology of the particle by the laser particle size instrument and the transmission electron microscopy. But some of the small particles tend to be ignored. Using the classical chemical titration method and BET to auxiliary analysis can make the date more complete. Through the comprehensive analysis with the four methods, found that longer reaction time have the effect of purification of sol system.

A convenient chemical titration method to measure M(ii)/M(iii) ratios of layered double hydroxides

The M(II)/M(III) ratio is an important structural feature of layered double hydroxides (LDHs). Here, we report a convenient chemical titration method to measure the M(II)/M(III) ratio of LDHs. The measured results have a relative standard deviation of less than 1.0%, and agree with the data measured by inductively coupled plasma (ICP) atomic emission spectroscopy very well.

Effects of Different Solvents on the Surface Acidic Oxygen-containing Functional Groups on Xanthoceras sorbifolia Shell

This study reports the preparation of a novel biomaterial from a forestry residue - Xanthoceras sorbifolia shell (XSS) - by solvent modification. The effects of acid and base (hydrochloric acerbic, acetic acid, sodium hydroxide, ammonia water) and some organic solvents (ethanol, acetone, ethyl acetate, chloroform, petroleum ether, and n-hexane) on the surface acidic functional groups (SAFGs) on XSS were investigated. The amount of SAFGs was quantified using acid and alkali chemical titration methods, and the characteristics of virgin XSS were compared with treated ones by FT-IR spectroscopy. It was found that acid solutions can increase the concentration of SAFGs, while alkaline solutions reduce it. The XSS treated in 0.5 M HCl has the largest number of total acidic functional groups and phenolic hydroxyl groups. The shell extracted with 2 M acetic acid has the highest concentration of carboxyl. The SAFG contents were remarkably increased by treatments with ethanol and acetone, due to the outstanding enhancement of phenolic hydroxyl. These changes in the SAFGs of XSS brought about by treatments with various solutions could be a theoretical foundation for modifying this residue to create a new type of highly efficient absorbent material.

Chemical Characteristics and Antioxidant Content Properties of Cold Pressed Seed Oil of Wild Milk Thistle Plant Grown in Jordan

This study aimed to examine the chemical characteristics and antioxidant content properties of cold-pressed milk thistle seed oil. Acidity and peroxide value were determined by chemical standard titration method and oxidative stability index was determined by Rancimate. Using GLC, fatty acid composition, phytosterols and squalene were measured. While, alpha-tocopherol content was determined by HPLC. The total phenolic content, radical-scavenging capacity and total antioxidant capacity were determined spectrophotometrically. The chemical characteristics of cold-pressed oil were as follows: acidity (0.64%), peroxide value (0.34 meq O2/kg of oil), oxidative stability index (55.7 and 12.9 h at 80 and 100°C, respectively), fatty acid composition (19.5, 22.9 and 57.6% for SAT, MUFA and PUFA, respectively), phytosterol (2520 mg/kg), squalene (9.35 mg/kg), alpha-tocopherol content (237.4 mg/kg), total phenolic content (1.16 mg GAE/g oil), radical-scavenging capacity against stable DPPH radical (IC50 = 3.34 mg/mL) and total antioxidant capacity (2.29 mmol/L). These data suggest that cold-pressed milk thistle seed oil may serve as dietary source of high PUFA and MUFA, phytosterols, phenolic compounds and natural antioxidants and can be a remarkable candidate for use in healthy food preparations mixed with other vegetable oils or alone.

Impacts of Inherent O-Containing Functional Groups on the Surface Properties of Shengli Lignite

Shengli (SL) lignite was thermally treated by heating at 200–350 °C in an effort to reduce the number of O-containing functional groups and water present. The presence of carboxyl groups, phenolic hydroxyl groups, and methoxy groups was characterized using a chemical titration method. The moisture holding capacity (MHC), wettability, and ζ potential of the SL lignite were measured before and after the low-temperature heat treatment. The results revealed that the main reactions that occurred below 350 °C were decarboxylation and dehydration, corresponding to the decomposition of more than 60% of the carboxyl groups and phenolic hydroxyl groups. SL lignite treated at 350 °C displayed an approximately 50% reduction in its MHC. The O-containing functional groups (the carboxyl groups, in particular) played an important role in water adsorption, indicating that the formation of the hydrogen bond between the O-containing functional groups and water contributed most significantly to the water adsorption process. The contact angle decreased as the number of hydrophilic sites decreased as a result of the decomposition of O-containing functional groups. The ζ potential of the SL lignite decreased significantly as the concentration of O-containing functional groups decreased. MHC was successfully correlated with the presence of O-containing functional groups and the quantity of surface area without oxygen groups, as follows: MHC = 2.655[−COOH] + 2.912[−OH] + 0.209[−OCH3] – 3.321Snon-O + 1.341, where Snon-O for the lignite is defined as Snon-O = Si(1 – Ci/C0), where Si is the surface area of the lignite and Ci and C0 are the total contents of O-containing functional groups in the heat-treatment or as-received lignites.