Base Titration Research Articles

Spectroscopic and Modeling Investigation of Eu(III)/U(VI) Sorption on Nanomagnetite from Aqueous Solutions

Nanomagnetite was synthesized by heating natural siderite in nitrogen conditions and was characterized using XRD, XPS, TEM, FT-IR and acid–base titration. Characteristic results illustrated that the reactive site density (17.91 sites/nm2) of nanomagnetite was significantly higher than that of natural siderite (3.63 sites/nm2), whereas average pore size (14.9 nm) of nanomagnetite decreased compared to natural siderite (52.5 nm). Effects of different ambient conditions (i.e., pH, contact time, temperatures and ionic strength) on removal behaviors of Eu(III)/U(VI) on nanomagnetite were conducted by batch experiments. Removal isotherms and kinetics of Eu(III)/U(VI) on nanomagnetite fitted well by models of Langmuir and pseudo-second kinetic, respectively. Additionally, the max sorption capacity of nanomagnetite with Eu(III) (11.95 mg/g) at pH = 2.5 and T = 328 K was significantly higher than sorption capacity of U(VI) (4.93 mg/g). The XPS analysis demonstrated that the surface oxygen groups of nanomagnetite p...

Glucose Isomerization Using Alkali Metal and Alkaline Earth Metal Titanates

AbstractGlucose isomerization was performed using various titanate catalysts, which include SrTiO3, BaTiO3, CaTiO3, Na2Ti6O13, K2Ti6O13, and Sr3Ti2O7, prepared using a conventional solid‐phase method. Among the titanates, SrTiO3, CaTiO3, and Na2Ti6O13 offered a relatively high fructose yield (32 %) with a high selectivity (68–78 %). The yields are comparable to yields reported previously using a Sn‐modified BEA zeolite, which shows a high efficiency for glucose isomerization as a Lewis acid catalyst. A study of the mechanism of glucose isomerization on a SrTiO3 catalyst surface by using 1H NMR spectroscopy suggested that the titanates catalyze the isomerization as base catalysts. Thus, the effect of the basicity of the titanates on glucose isomerization was investigated in terms of the base quantity and strength. The analysis was performed by using an acid–base titration method and FTIR spectroscopy with CHCl3 as a probe molecule. It is proposed that glucose isomerization on the titanates depends not only on the base amount but also on the base strength.

Tautomerism, crystal structure, and copper(ii) complexation of pyridonylazo dyes derived from methyl 4‐aminobenzoate

Four heterocyclic dyes, derived from methyl 4‐aminobenzoate and pyridine‐2,4‐dione components, with different N‐substituents in the latter [CH3, CH2CH3, CH2CH2OH, CH2CH2CH2OCH(CH3)2], were synthesised by the traditional diazotisation‐coupling strategy. Furthermore, a Cu(ii) dye–metal complex was prepared and characterised by X‐ray single‐crystal diffraction for comparison, where the configuration transformation from hydrazone to deprotonated azo forms was found before and after Cu(ii) ion complexation. In addition, the azo–hydrazone transformation could be observed by acid–base titration experiments. To the best of our knowledge, this work is the first structural study of pyridone dyes based on methyl 4‐aminobenzoate and the corresponding dye–metal complex.

Monitoring Acid–Base Titrations on Wax Printed Paper Microzones Using a Smartphone

This study describes the use of a smartphone for monitoring acid–base titrations on wax printed paper microzones. An array of twelve microzones of 5 mm diameter each was wax printed on filter paper. The analytical performance of the proposed devices was explored with acid–base titrations examples, where jaboticaba peel extract was used as a natural pH indicator. The color intensity was captured using a smartphone and analyzed through a free App named Photometrix®. Before titrations, color intensity versus pH was calibrated to be used as a reference in titrations as (i) strong acid versus strong base; (ii) strong base versus strong acid; and (iii) weak acid versus strong base. In all examples, images were obtained after the addition of each aliquot of titrant solutions. The obtained titration curves showed the same behavior as the conventional titration curves. After evaluating the feasibility of the proposed methodology, the concentration level of acetic acid was obtained in three vinegar samples. Although the obtained values ranged from 5% to 8% compared to the concentrations on the conventional method, the proposed methodology presented high analytical reliability. The calculated concentrations of acetic acid in three samples ranged from 3.87% to 3.93%, and the proposed methodology did not significantly differ from classic acid–base titration at a confidence level of 95%. The acid–base titration on paper-based devices is outstanding, since any titration can be completed within 5 min using 20 µL volumes. Besides, the use of a smartphone to capture images followed by analysis in a free app offers simplicity to all users. The proposed methodology arises as a new strand to be exploited in the diffusion of the analytical chemistry education field as well as an alternative for quantitative analysis with extremely simplified instrumentation.

Epoxy resin modified maleic anhydride‐grafted‐liquid polybutadiene on the properties of short aramid fiber reinforced natural rubber composite

A novel compatibilizer with high grafting degree (GD%) of maleic anhydride (MA) onto liquid polybutadiene (LPB) was synthesized via a solution method, in particular, very low gel rate was produced by the synergetic effects of acetanilide and epoxy resin (EP), and the GD% was improved by adding the EP resin and acetanilide. The structure and thermal stability of the MA‐grafted‐liquid polybutadiene (LPB‐g‐MA) were characterized by acid base titrations, FTIR, and TGA techniques. The results showed that both MA and EP resin have been grafted onto the macromolecular chains of LPB with a good thermal stability. Then, it was used as compatibilizer in short aramid fiber (AF) reinforcing natural rubber (NR)/carbon black (CB). The synthetic compatibilizer (LPB‐g‐MA) enhanced the interfacial interaction between the fiber and the rubber matrix with a lower swelling degree and lower peak of loss factor, and the mechanical properties including tensile strength, tensile modulus 100%, tear strength and elongation at break of the final composites increased with the increase of m (E51)/m (LPB). AF and CB had a synergistic effect to reinforce the properties of NR. The dynamic stiffness of the rubber was obviously improved by the short AF, especially in the presence of the compatibilizer. POLYM. COMPOS., 39:E2006–E2015, 2018. © 2017 Society of Plastics Engineers

<i>Hippeastrum hybridum</i> anthocyanins as indicators of endpoint in acid – base titrations

Anthocyanins from Hippeastrum hybridum (Amaryllis) were investigated as indicators of endpoint in acid- base titrations. Extraction of the anthocyanins was done using distilled water, methanol and methanol containing 0.5% acetic acid. The extracts were used in determination of endpoint in titrations between strong acid/strong base, strong acid / weak base, weak acid / strong base and weak acid / weak base at concentration levels of 0.1 M, 0.5 M and 1.0 M. The titres were compared to those obtained using phenolphthalein, methyl orange and mixed indicator. The shelf life of anthocyanin extracts kept in amber bottles at room temperature (16.8 0C – 29.1 0C) was also investigated. The plant extracts gave accurate and precise results in titration of strong acids with strong bases and weak acids against strong bases at all concentrations investigated (0.1, 0.5 and 1.0 M) that were very comparable to the values obtained using phenolphthalein, methyl orange and mixed indicator. In titration of weak acids against weak bases, the plant extracts gave accurate results when concentration was 0.1 M but failed for 0.5 M and 1.0 M. On average the anthocyanins from Hippeastrum hybridum could be used in the titration of strong acid versus strong base, weak acid versus strong base and weak acid versus weak base. The anthocyanins from Hippeastrum hybridum had a good shelf life of 90 days when kept at room temperature. The extracts can thus be used in any place including those that have no access to refrigeration facilities since they can be kept at room temperature for some time before they undergo degradation.© 2016 International Formulae Group. All rights reserved.Keywords: Hippeastrum hybridum, anthocyanins, pH indicators, acid-base titrations, shelf life

Effect of pore structure and oxygen-containing groups on adsorption of dibenzothiophene over activated carbon

Activated carbons chemically treated by steam and concentrated H2SO4, were used as adsorbents for removing organic sulfur compounds from a model diesel. The modified activated carbon was characterized by N2 sorption, base titration and FTIR spectroscopy. As compared with the untreated activated carbon, the treatment by a steam at 900°C increased the mesoporous volumes from 0.248 to 0.856cm3/g and sulfur adsorption capacity for dibenzothiophene from 10.9 to 20.6mg/g and the treatment by a concentrated H2SO4 at 250°C increased the amount of surface acidic-oxygenated groups from 0.05 to 1.95mmol/g, and total adsorption capacity for dibenzothiophene from 10.9 to 33.3mg/g. The total adsorption capacity for dibenzothiophene is found to be proportional to the mesoporous volume and the amount of surface oxygen-containing groups. It is proposed that direct interaction between the sulfur atom and surface oxygen-containing groups plays an important role in the adsorption of organic sulfur compound.

Determining a Solubility Product Constant by Potentiometric Titration To Increase Students’ Conceptual Understanding of Potentiometry and Titrations

Potentiometric titrations are widely taught in first-year undergraduate courses to connect electrochemistry, stoichiometry, and equilibria and to reinforce acid–base titrations. Students perform a potentiometric titration that is then analyzed to determine analyte concentrations and the solubility product constant of the solid species.

The role played by different TiO2 features on the photocatalytic degradation of paracetamol

Abstract Photocatalytic reactions promoted by TiO 2 can be affected by a large number of oxide features ( e.g. surface area, morphology and phase composition). In this context, the role played by the surface characteristics ( e.g. surface acidity, wettability, etc. ) has been often disregarded. In this work, pristine and Ta-doped TiO 2 nanomaterials with different phase composition (pure anatase and anatase/brookite mixture) were synthesized by sol–gel and characterized under the structural and morphological point of view. A careful characterization of the acid properties of the materials has been performed by liquid–solid acid–base titration by means of 2-phenylethylamine (PEA) adsorption to determine the acid site density and average acid strength. Photocatalytic tests were performed in the degradation of paracetamol (acetaminophen) under UV irradiation and results were discussed in the light of the detailed scenarios describing the different oxides. The surface acidity of the samples, was recognized as one of the key parameters controlling the photocatalytic activity. A possible molecule degradation route is proposed on the ground of GC–MS and ESI–MS analyses.

Amine-functionalized silica particles with magnetic core as magnetically removable adsorbents of Ag(I) ions

Adsorption of silver ions over amine-functionalized silica particles with magnetic core has been studied. This adsorbent has been synthesized via sol–gel method, in the presence of Fe3O4 particles as magnetic cores. As a comparison, magnetic silica adsorbent with non-functionalized surface was also synthesized. As-obtained materials have been characterized by elemental analysis, acid–base titration, nitrogen sorption measurements, X-ray photoelectron spectroscopy and scanning electron microscopy. What is more, parameters of electrical double layer at the silica adsorbent/electrolyte solution interface were also examined. Kinetic of adsorption and isotherms of silver ions were determined. The obtained adsorption of Ag(I) ions for the studied materials was in the range of about 0.2–0.3 mmol/g.

The synthesis of polyhydroacridines by covalent 5-sulfobenzoic acid-functionalized graphene oxide as a novel, green, efficient, and heterogeneous catalyst

A novel graphene oxide (GO)-based catalyst with 5-sulfobenzoic acid-functional groups is synthesized. Graphene oxide is covalently functionalized by partly safe chemical compounds through aryl diazonium salts to give 5-sulfobenzoic acid-functionalized graphene oxide (SBGO). Combined characterizations of X-ray powder diffraction, field emission scanning electron microscopy, and also transmission electron microscopy techniques show that SBGO has a nanosheet structure. Energy-dispersive X-ray spectroscopy survey discloses that SBGO catalyst contains only O and S heteroatoms which confirms it is green, sustainable, and environmentally benign heterogeneous catalyst. Fourier transform infrared spectroscopy displays that SBGO has a S=O bond. Acid–base titration demonstrates that the acidic concentration of the catalyst is 2.8 mmol H+ g−1. The Raman spectrum of SBGO shows increased D/G bonds intensity ratio compared to that in graphene oxide which confirms the functionalization of graphene oxide. Thermogravimetric curves show the decomposition temperature (230 °C) of the SBGO (a weight loss of about 10%) that attributed to the sulfonic groups decomposition. This catalyst is applied for the multicomponent synthesis of polyhydroacridine derivatives and high activity of solid acid catalyst was observed even after nine runs, which is referred to the stable functionalized groups on the catalyst.

Room-Temperature Synthesis of UiO-66 and Thermal Modulation of Densities of Defect Sites

UiO-66 is an archetypal zirconium-based metal–organic framework (MOF) that is constructed from hexanuclear zirconium oxide clusters as secondary building units (SBUs) and 1,4-benzenedicarboxylate (bdc) linkers. For the first time, a room-temperature solution-based synthesis is reported for UiO-66 and several of its derivatives, UiO-66-X (X = NH2, OH, or NO2), resulting in materials that are as porous and crystalline as those made at elevated temperatures. In addition, via modulation of the temperature at which UiO-66 is synthesized, the number of defect sites can be varied. It was found through N2 sorption isotherm analysis and potentiometric acid–base titrations that increasing the synthesis temperature from 25 to 130 °C results in a systematic decrease in the number of defect sites in UiO-66. The results suggest that, with respect to this synthetic procedure, a maximal number of defect sites is achieved [∼1.3 missing linkers per Zr6O4(OH)4(bdc)6] at a temperature of 45 °C.

A simple, openable and electroosmotic flow-free PMMA chip for electrophoretic titration of moving reaction boundary

Poor control of electroosmotic flow (EOF) often occurs in chip electrophoretic titration (ET) of moving reaction boundary due to both absence of PMMA channel coating and coexistence of acid-base. Also, chip ET still suffers from low reproducibility, instability, disposability and high cost as well. To address these issues, a reusable ET chip (60mm×60mm×5.0mm) was designed via an upper PMMA sheet, a middle silicon membrane and a lower sheet. In the upper sheet, enlarged channel (500μm×200μm×12mm) was fabricated and linked to the anodic and cathodic wells. The upper sheet, middle membrane and lower sheet could be easily assembled together in 20s as an ET chip of supporting 1.4kg tension force, indicating good mechanical stability. Regeneration and reassembling of chip could be finished in 50s. EOF could be simply suppressed by mass chemical cross-linked polyacrylamide gel or physical agarose gel in the enlarged channel. The EOF-free chip could be well used for: (i) acid-base ET; (ii) EOF monitoring; (iii) pKa determination; (iv) protein content analysis. The EOF-free chip showed the following merits: (i) 98% success rate in contrast to less than 30% in normal channels (80μm×20μm×5.0mm); (ii) more than 30 times reuse, indicating reusability and low cost; (iii) less than 10% of relative standard deviation, suggesting fair stability; and (iv) good recovery and accuracy. The developed chip makes great advancement towards real use of chip in acid- base titration, EOF monitoring, pKa determination and protein content analysis.

Effects of Competitive Active-Site Ligand Binding on Proton- and Electron-Transfer Properties of the [Co4(H2O)2(PW9O34)2]10− Polyoxometalate Water Oxidation Catalyst

The polyoxometalate [Co4(L)2(PW9O34)2]10−, where L is typically H2O, (1) is a much-studied homogeneous water oxidation catalyst that facilitates the conversion of water to dioxygen through a mechanism that remains poorly understood due to difficulty measuring electrochemical and acid–base properties in aqueous media. Studies in a non-aqueous, polar aprotic solvent such as acetonitrile, MeCN, are useful for probing the properties of this catalyst in the absence of reactive substrates or in the presence of competitive substrates. We report that in MeCN, 1 can be electrochemically and chemically oxidized to an unstable species, 1 ox , which reverts to 1 over time. Dioxygen formation is not observed in MeCN under catalytic conditions. In water, the presence of MeCN does not significantly affect kinetics of oxidation but significantly inhibits the yield of dioxygen. X-ray crystal structure determination shows that MeCN coordinates to the two external Co centers in the solid state; changes in the visible spectrum indicate that aqua and MeCN ligands on these Co centers exchange in the solution state. In agreement with these observations, acid–base titration behavior is shifted to reflect competitive binding and density-functional theory calculations show a 2.1 kcal mol−1 stronger interaction for MeCN than H2O. This competitive binding and the effects on water oxidation support the direct involvement of these two Co centers in binding substrate water and/or trapping of reactive intermediates by MeCN.

Microelectrode generator–collector systems for electrolytic titration: theoretical and practical considerations

Electochemical generator-collector systems, where one electrode is used to generate a reagent, have a potentially large field of application in sensing and measurement. We present a new theoretical description for coplanar microelectrode disc-disc systems where the collector is passive (such as a potentiometric sensor) and the generator is operating at constant flux. This solution is then used to develop a leading order solution for such a system where the reagent reacts reversibly in solution, such as in acid-base titration, where a hydrogen ion flux is generated by electrolysis of water. The principal novel result of the theory is that such devices are constrained by a maximum reagent flux. The hydrogen ion concentration at the collector will only reflect the buffer capacity of the bulk solution if this constraint is met. Both mathematical solutions are evaluated with several microfabricated devices and reasonable agreement with theory is demonstrated.

Formation of cellulose-carbene complex via depolymerization in ILs: Dependence of IL types on kinetics, conformation and dispersity

This study focused on the influence of anion type on the depolymerization and its effect on the molecular state, dynamics and dispersity of cellulose. GPC and the van Gurp-Palmen plot showed that molar mass was more significantly decreased by 1-butyl-3-methylimidazolium chloride ([C4C1Im][Cl]) comparing to 1-butyl-3-methylimidazolium acetate ([C4C1Im][OAc]). Acid-catalyzed hydrolysis of cellulose in IL was proved using base titration which was monitored by conductivity and pH value. On the contrary to the depolymerization case, [C4C1Im][OAc] solution needed more base to be neutralized than [C4C1Im][Cl] solution. The generated carbene was combined with reducing ends of cellulose, which was facilitated in low molar mass consisting of a large number of reducing ends. The formation of cellulose-carbene substitution caused steric hindrance of cellulose chain, thus resulting in increased segmental friction with high molecular density. The cellulose particle combined with carbene can be dispersed stably in aqueous media.

Efficient catalytic system for the direct transformation of lignocellulosic biomass to furfural and 5-hydroxymethylfurfural

A feasible approach was developed for the co-production of 5-hydroxymethylfurfural (5-HMF) and furfural from corncob via a new porous polytriphenylamine–SO3H (SPTPA) solid acid catalyst in lactone solvents. XRD, SEM, XPS, N2 adsorption–desorption, elemental analysis, TG–DTA, acid–base titration and FTIR spectroscopy techniques were used to characterize the catalyst. This study demonstrates and optimizes the catalytic performance of SPTPA and solvent selection. SPTPA was found to exhibit superior catalytic ability in γ-valerolactone (GVL). Under the optimum reaction conditions, simultaneously encouraging yields of furfural (73.9%) and 5-HMF (32.3%) were achieved at 448K. The main advantages of this process include reasonable yields of both 5-HMF and furfural in the same reaction system, practical simplicity for the raw biomass utilization, and the use of a safe and environmentally benign solvent.

Adsorption of hexavalent chromium onto Bamboo Charcoal grafted by Cu2+-N-aminopropylsilane complexes: Optimization, kinetic, and isotherm studies

Abstract The adsorption mechanism of Cr(VI) uptake onto Bamboo Charcoal grafted by Cu2+-N-aminopropylsilane complexes (BC/Cu-N) was investigated. The properties of BC/Cu-N were characterized using XRD, FTIR, SEM, EDS, potentiometric acid–base titration and electrochemical analysis. Results indicated that the framework integrity of BC was kept after modification and the quantity of functional groups on BC/Cu-N surface has changed. There existed functional groups on the BC/Cu-N which could consume OH− and the pHpzc was found to be 6.20. Moreover, electrochemical analysis showed that new electron transfer pathway was imported. Parameters such as pH, initial Cr(VI) concentration, adsorbent dosage and temperature were optimized using RSM. Analysis of variance of the quadratic model for Cr(VI) was suitable to predict the adsorption of Cr(VI) (F value = 134.23 and P value

Synthesizing Substituted 2-Amino-2-chromenes Catalyzed by Tertiaryamine-Functionalized Polyacrylonitrile Fiber for Students To Investigate Multicomponent Reactions and Heterogeneous Catalysis

A multistep experiment for a synthesis laboratory course that incorporates topics in organic synthesis, chemical analysis, and instrumental analysis was developed. Students prepared a tertiaryamine-functionalized polyacrylonitrile fiber (PANTF), and it was subsequently utilized as an immobilized catalyst in a three-component condensation reaction among an aromatic aldehyde, malononitrile, and α-naphthol in ethanol to synthesize substituted 2-amino-2-chromenes in one pot. The fiber catalyst exhibits the advantages of high yield, excellent recyclability and reusability, simple post-treatment, and environmental friendliness. Thus, students were able to apply the concept of green chemistry through catalysis. Moreover, this comprehensive experiment involves a number of unit operations, such as vacuum distillation, filtration, recrystallization, and acid–base titration, which can train the fundamental operation capability of students, and improve their experimental skills.

Experimental investigation of the effects of crosslinking processes on the swelling and hygroscopic performances of a poly(vinyl alcohol) membrane

ABSTRACTPoly(vinyl alcohol) (PVA) membranes crosslinked with L‐malic acid were prepared, and the effects of the heat‐treatment temperature and crosslinker concentration on their swelling and hygroscopic performances were investigated. Both the swelling and hygroscopic performances of the PVA membranes decreased with increasing heat‐treatment temperature; while the former decreased, the latter increased with increasing crosslinker concentration. The PVA membranes were characterized with differential scanning calorimetry (DSC), acid–base titration, and Fourier transform infrared spectrometry. The DSC results indicated that there was freezing and nonfreezing water in the swollen membranes, whereas there was only nonfreezing water in the moistened membranes. In addition, acid–base titration analysis revealed that both increased heat‐treatment temperature and increased crosslinker concentration increased the bilateral ester group levels (crosslinking degree) and decreased the content of freezing water. By contrast, the content of hydrophilic groups decreased and increased with increasing heat‐treatment temperature and crosslinker concentration, respectively; this resulted in decreased and increased levels of nonfreezing water, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2017,134, 44481.