Showing papers on "Titration published in 2015"
TL;DR: In this paper, the performance of Mn-based catalysts was investigated for selective catalytic reduction (SCR) for NOx removal by NH3, where a mass of crystalline and/or amorphous MnOx species were detected.
145 citations
TL;DR: In this paper, the effects of variables such as pH, initial dye concentration, cadmium ion concentration, adsorbent mass (g) and contact time on the adsorption of Cd2+ ion and MG were examined by central composite design (CCD).
89 citations
TL;DR: The Triple Layer Model (TLM) successfully described surface complexation of Sb onto soybean stover-derived biochar at pH 4-9, and suggested the formation of monodentate mononuclear and binuclear complexes.
89 citations
TL;DR: In this article, a rapid sample preparation protocol was developed to determine the sulfate half-ester content of CNCs from various cellulosic feedstocks (for H- and Na-CNCs, in both never-dried and redispersed dried forms) by conductometric titration.
Abstract: Charged groups on the surface of cellulose nanocrystals (CNCs) control the colloidal stability and electrostatic and rheological properties of aqueous CNC suspensions, as well as their ability to self-assemble into liquid crystalline structures with unique optical properties. CNCs extracted from wood pulp by sulfuric acid hydrolysis typically contain 200–300 mmol/kg of anionic sulfate half-esters introduced at some of the hydroxyl sites. Two analysis methods to determine CNC surface charge are presented in the published literature: total sulfur content determination by elemental analysis and protonated sulfate half-ester group determination by conductometric titration with sodium hydroxide. The main drawbacks to elemental analysis are the expensive and complicated instrumentation and sample preparation procedures it requires. Conductometric titration is a much simpler method, but requires complete protonation of the CNC samples in order to obtain an accurate value. Unfortunately, significant discrepancies between the sulfate half-ester contents measured with the two techniques are often observed in the literature, particularly with neutralized Na-CNCs. There are specific assumptions and pitfalls inherent to both analysis methods which must be taken into account and reconciled if comparable results are to be achieved by titration and elemental analysis. In particular, sample preparation is crucial to obtaining accurate determinations of sulfate half-ester content by conductometric titration; however, methods differ widely among laboratories and are often not specified in detail, rendering published results meaningless. We have developed a rapid sample preparation protocol which allows quantitative and accurate determination of the sulfate half-ester content of CNCs from various cellulosic feedstocks (for H- and Na-CNCs, in both never-dried and redispersed dried forms) by conductometric titration, yielding results in good agreement with the total sulfur content determined by elemental analysis.
88 citations
TL;DR: The results provide the updated parameters that are applicable to any experiment conducted using inexpensive and commercially available PAR and its complexes accurately with Zn(2-Pyridylazo)resorcinol, as well as several titrations of zinc finger peptides and zinc chelators.
73 citations
TL;DR: The surface chemistry of synthetic calcium aluminosilicate glasses exposed to aqueous solutions of varying pH was described using zeta potential measurements and batch surface titrations.
Abstract: The surface chemistry of synthetic calcium aluminosilicate glasses exposed to aqueous solutions of varying pH was described using zeta potential measurements and batch surface titrations. Element release and proton consumption were measured to characterize the reactions at the surface as a function of pH. It was found that proton-metal exchange or leaching was the dominant proton consumption process at low pH. The exchange reaction was observed to maintain charge balance, indicating that over the limited duration of the experiments no repolymerization of the silica-rich leached layer occurred. At high pH, dissolution and hydrolysis of aqueous ions controlled the proton mass balance, no evidence for the formation of leached layers was found. Silica-rich glasses were found to be more resistant to corrosion by either proton-metal exchange or dissolution than CaO-rich glasses. Glass basicity was found to be reflected in the establishment of a higher pH when immersing the glass in neutral aqueous solutions and in a reduced stability of the glass surface toward aqueous solutions. High pH, high surface charge and reduced glass network polymerization act together in enhancing the reaction of CaO-rich glasses with aqueous solutions.
70 citations
TL;DR: The fitting experimental data with conventional models reveal the applicability of isotherm models Langmuir model for their well presentation and description and Kinetic real rate of adsorption at most conditions efficiently can be represented pseudo-second order, and intra-particle diffusion.
65 citations
TL;DR: The use of silver nanoparticles (AgNPs) for colorimetric ascorbic acid quantification in a paper-based sensor is demonstrated for the first time and results presented limit of detection which was comparable to analytical laboratory-based methodologies.
61 citations
TL;DR: In this paper, the starting pH affects acid-base chemistry of the silica/aqueous interface, and the presence and relative abundance of these sites is very sensitive to starting pH.
Abstract: Second harmonic generation (SHG) is commonly employed to monitor processes at mineral oxide/liquid interfaces. Using SHG, we determine how the starting pH affects the acid–base chemistry of the silica/aqueous interface. We observe three different sites with pKa values of approximately 3.8, 5.2, and ∼9 (pKa-I, pKa-II, pKa-III, respectively), but the presence and relative abundance of these sites is very sensitive to the starting pH. For titrations initiated at pH 12, all three sites are observed, whereas only two sites are observed for titrations initiated at pH 2 or pH 7. Moreover, exposure to pH 2 facilitates the formation of pKa-II and pKa-III sites, while exposure to pH 7 results in pKa-I and pKa-III sites. Based on previous computational work, we assign these sites to three different hydrogen bonding environments at the interface including a hydrophobic site for the most acidic silanol corresponding to pKa-I.
59 citations
TL;DR: In this article, the authors used the ambient temperature adsorption of methanol in the Henry law region as a molecular probe to determine the concentration of surface oxygen functional groups (Ca) on carbon adsorbents.
52 citations
TL;DR: In this paper, a mutual titration of soy proteins and gum arabic was performed using isothermal titration calorimetry (ITC), turbidity, sedimentation and ternary phase boundaries.
TL;DR: In this article, an Activated Carbon produced from pomelo peels (PPAC) was tested for its effectiveness in the removal of malachite green (MG) dye from aqueous solution.
Abstract: Activated carbon produced from pomelo peels (PPAC) was tested for its effectiveness in the removal of malachite green (MG) dye from aqueous solution. The PPAC prepared was characterized using TGA, BET, FTIR, SEM, pHpzc, Elemental analysis and Boehm titration, respectively. The extent of dye adsorption was investigated as a function of pH, contact time, adsorbate concentration and solution temperature. Dye removal was pH dependent, resulting in 95.06% removal at pH 8.0. Quantum chemical studies suggested that the cationic MG dye possessed minimal molecular size at planar geometry coupled with high-electrostatic interaction thereby, enhancing the adsorption at high pH. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) equilibrium isotherms were used to fit the adsorption data. Langmuir isotherm fit the adsorption data most with maximum monolayer adsorption capacity of 178.43 mg/g. The kinetic data fitted the pseudo-second-order model with correlation coefficient greater than 0.99. The mean free en...
TL;DR: In this article, the extinction coefficients of hexaniobate ions were determined from multiple samples in various media and a simple and low-cost method was then developed for the determination of the niobium content of both synthetic and industrial samples.
Abstract: The UV-visible properties of hexaniobate (HxNb6O19x−8) and hexatantalate (HxTa6O19x−8) ions were investigated experimentally and by DFT calculations. Due to the huge discrepancies among the reported values found in prior studies, the extinction coefficients of hexaniobate ions were determined from multiple samples in various media. A simple and low-cost method was then developed for the determination of the niobium content of both synthetic and industrial samples. Taking advantage of the UV spectra of the hexaniobate ions, the first protonation constant of Nb6O198− could be determined experimentally (pKa = 13.4 ± 0.1 at 25 °C, ΔrH = −95 kJ mol−1 in 3 M KOH/KCl) and is in accordance with the reported values previously extrapolated from potentiometric measurements (pKa = 13.3 ± 0.6). UV batch titrations performed at different ionic strengths suggest that the equilibrium between the monoprotonated and the deprotonated forms of the Lindqvist ion is accompanied by an exchange of potassium ions and that the cluster is easier to deprotonate in Na+ media. This study highlights the importance of the ion-pairing on the chemistry of these polyoxometalates. The tremendous difference between the UV spectrum of Nb6O198− and Ta6O198− was investigated by DFT computations. The UV spectra were reproduced and show a good agreement with the experimental data. Moreover this study revealed some insights into the evolution of the spectra together with the pH of the medium by studying the nature of the transitions involved in this spectral domain.
TL;DR: The ratiometric fluorescence pH probe ECBT is facilely developed by ethylene bridging of N-ethyl-3-carbazolecarboxaldehyde and benzothiazole, which is a useful fluorescent probe for strongly acidic pH sensing and exhibits high selectivity and sensitivity, good photostability and excellent reversibility for pH sensing.
Abstract: A ratiometric fluorescence pH probe 2-(N-ethylcarbazole-3-vinyl)-benzothiazole ( ECBT ) is facilely developed by ethylene bridging of N-ethyl-3-carbazolecarboxaldehyde and benzothiazole, which is a useful fluorescent probe for strongly acidic pH sensing. The pH titration indicates remarkable fluorescence enhancement effect and an emission red-shift of 87 nm with pH decreasing from 7.00 to 1.00. Furthermore, the solution color changes from light blue to orange under a UV lamp illumination. A p K a value of 1.62 and a good linearity in the pH range of 1.23–2.10 indicate that the probe can be used in quantitative fluorescence imaging under strongly acidic condition. In addition, ECBT exhibits high selectivity and sensitivity, good photostability and excellent reversibility for pH sensing. The probe is further applied successfully to imaging extreme acidity in Escherichia coli cells without influence of autofluorescence in biological systems.
TL;DR: In this paper, an automated analysis system was developed for laboratory and shipboard measurements of total alkalinity at a rate of 6 samples per hour, based on single-point hydrochloric acid (HCl) titrations of seawater samples of a known volume with bromocresol purple as an indicator.
TL;DR: In this article, five carbon materials were prepared by soaking of fibrous cellulose with different solutions containing inorganic compounds suitable for creation of micropores, after drying, materials were carbonized at 500-800°C, characterized by BET, acidbase titration, HRTEM and SAXRD methods and tested on their adsorption capabilities for pertechnetate.
Abstract: Activated carbon can potentially be used as an adsorbent for removing Tc from aqueous solutions. Five carbon materials were prepared by soaking of fibrous cellulose with different solutions containing inorganic compounds suitable for creation of micropores. After drying, materials were carbonized at 500–800 °C, characterized by BET, acid–base titration, HRTEM and SAXRD methods and tested on their adsorption capabilities for pertechnetate. Adsorption kinetics of the pertechnetate ion on these materials is relatively fast and depends on pH. For some sorbents, a 99 %-adsorption within 1 min was found. One of the variables used to characterize of pertechnetate adsorption is distribution coefficient Kd. Maximum Kd of about 7 × 104 mL g−1 was measured for acidic pH (pH 2–3). In general, Kd was decreasing with increasing pH; however, the sample treated with zinc chloride sorbed TcO4
− very well even at pH 8 (Kd = 5 × 103 mL g−1).
TL;DR: This work studied the ionization dependent behavior of an oleic acid bilayer using a new extension of the stochastic titration constant-pH MD method, and the results strongly supports its usefulness to sample the coupling between configuration and protonation in these types of biophysical systems.
Abstract: Oleic acid is a simple molecule with an aliphatic chain and a carboxylic group whose ionization and, consequently, intermolecular interactions are strongly dependent on the solution pH. The titration curve of these molecules was already obtained using different experimental methods, which have shown the lipid bilayer assemblies to be stable between pH 7.0 and 9.0. In this work, we take advantage of our recent implementations of periodic boundary conditions in Poisson-Boltzmann calculations and ionic strength treatment in simulations of charged lipid bilayers, and we studied the ionization dependent behavior of an oleic acid bilayer using a new extension of the stochastic titration constant-pH MD method. With this new approach, we obtained titration curves that are in good agreement with the experimental data. Also, we were able to estimate the slope of the titration curve from charge fluctuations, which is an important test of thermodynamic consistency for the sampling in a constant-pH MD method. The simulations were performed for ionizations up to 50%, because an experimentally observed macroscopic transition to micelles occurs above this value. As previously seen for a binary mixture of a zwitterionic and an anionic lipid, we were able to reproduce experimental results with simulation boxes usually far from neutrality. This observation further supports the idea that a charged membrane strongly influences the ion distribution in its vicinity and that neutrality is achieved significantly far from the bilayer surface. The good results obtained with this extension of the stochastic titration constant-pH MD method strongly supports its usefulness to sample the coupling between configuration and protonation in these types of biophysical systems. This method stands now as a powerful tool to study more realistic lipid bilayers where pH can influence both the lipids and the solutes interacting with them.
TL;DR: The results of spectroscopic measurements and calorimetric measurements indicate exothermic and spontaneous combination of an antitumor drug, 5-fluorouracil, by both cationic PAMAM G5-NH2 dendrimer and its hydroxyl analog PamAM G 5-OH in aqueous solutions at room temperature.
TL;DR: The real-time bioimaging of the probe was successfully achieved and the MTT assay showed low cytotoxicity of the Gel and the pH titration indicated that it could monitor the pH fluctuations linearly and rapidly within the pH range of 6.0-9.0.
TL;DR: It is found that pH can promote the self-assembly transition of Ace(m)-2-Ace(n) from surfactant monomers to aggregates through protonation between H(+) and the tertiary nitrogen group.
Abstract: A new series of pH-regulated asymmetric amino-acid gemini surfactants N,N′-dialkyl-N,N′-diacetate ethylenediamine (Ace(m)-2-Ace(n)), differing by the asymmetric degree and length of the carbon tails (m = 8 and 10, n = 10, 12, 14, and 16), were synthesized in three steps. On the basis of pKa values obtained by pH titration, surface tension, fluorescence, dynamic light scattering (DLS), and transmission electron microscopy (TEM) measurements were performed to study the surface adsorption and aggregation properties in aqueous Ace(m)-2-Ace(n) solution. The new compounds have higher surface activity and better pH adaptability in comparison with that of symmetric gemini surfactants Ace(n)-2-Ace(n). The molecule behavior of Ace(m)-2-Ace(n) can be adjusted by either the hydrophobic group or the pH. With increasing alkyl chain length, the surface adsorption declines but its ability to form aggregates increases. We find that pH can promote the self-assembly transition of Ace(m)-2-Ace(n) from surfactant monomers to aggregates through protonation between H+ and the tertiary nitrogen group. TEM data further confirm the pH-regulated molecular self-assembly process and the existence of vesicles at neutral or weak acidic pH. pH-recyclability is found to be reversible by pH-light transmittance recycle tests.
TL;DR: This simulation provided an explanation for the precipitation of metallic copper in lens and cornea, and was used to predict, for the first time, metal-ligand equilibria in the biofluids of the human eye.
Abstract: Protonation constants for the biologically-important thioamino acids cysteine (CSH), penicillamine (PSH) and glutathione (GSH), and the formation constants of their complexes with Cu(I), have been measured at 25 °C and an ionic strength of 1.00 mol dm(-3) (Na)Cl using glass electrode potentiometry. The first successful characterisation of binary Cu(I)-CSH and Cu(I)-GSH species over the whole pH range was achieved in this study by the addition of a second thioamino acid, which prevented the precipitation that normally occurs. Appropriate combinations of binary and ternary (mixed ligand) titration data were used to optimise the speciation models and formation constants for the binary species. The results obtained differ significantly from literature data with respect to the detection and quantification of protonated and polynuclear complexes. The present results are thought to be more reliable because of the exceptionally wide pH and concentration ranges employed, the excellent reproducibility of the data, the close agreement between the calculated and observed formation functions, and the low standard deviations and absence of numerical correlation in the constants. The present formation constants were incorporated into a large Cu speciation model which was used to predict, for the first time, metal-ligand equilibria in the biofluids of the human eye. This simulation provided an explanation for the precipitation of metallic copper in lens and cornea, which is known to occur as a consequence of Wilson's disease.
TL;DR: In this paper, sulfur functionalized starch has been successfully prepared via an iso-thiouronium salt intermediate, from the reaction of thiourea with chloroacetylated starch.
Abstract: In this study, sulfur functionalized starch has been successfully prepared, via an iso-thiouronium salt intermediate, from the reaction of thiourea with chloroacetylated starch. The later was synthesized by a chloroacetylation reaction. Thiolation via an iso-thiouronium ion intermediate is an innovative green approach to achieve thiol functionalization of starch with an innocuous low cost thiourea reagent. The thiol products are amenable for further derivatization and were modified to a sulfide and a sulphonium salt. The sulphonium structure was accomplished by exhaustive alkylation with iodoethane as an alkylating agent, which resulted in permanent charge generation on the starch backbone. The above-mentioned reactions were also carried out using microwave heating to achieve maximum yet uniform modification of starch. The extent of the derivatization processes was confirmed by iodine titration and precipitation titration and also by characterization of the synthesized samples by FTIR spectroscopy, 1H-NMR, 13C-NMR, SEM-EDX, XRD, zeta potential measurements and elemental analysis (CHNS) to confirm the reaction output at every synthetic stage. Evidence that the degree of substitution of the thiol groups was ≥ 2 was obtained from titrimetry, SEM-EDX and elemental (CHNS) characterization results. Additionally, the generation of the permanent charge on the sulphonium structure was confirmed using zeta potential measurements.
TL;DR: The complexation of U(vi) at the proteinaceous surface layer (S-layer) of the archaeal strain Sulfolobus acidocaldarius was investigated over a pH range from pH 1.5 to 6 at the molecular scale using time-resolved laser-induced fluorescence spectroscopy and extended X-ray absorption fine structure (EXAFS).
Abstract: The complexation of U(VI) at the proteinaceous surface layer (S-layer) of the archaeal strain Sulfolobus acidocaldarius was investigated over a pH range from pH 1.5 to 6 at the molecular scale using time-resolved laser-induced fluorescence spectroscopy (TRLFS) and U LIII-edge extended X-ray absorption fine structure (EXAFS). The S-layer, which represents the interface between the cell and its environment, is very stable against high temperatures, proteases, and detergents. This allowed the isolation and purification of S-layer ghosts (= empty cells) that maintain the size and shape of the cells. In contrast to many other microbial cell envelope compounds the studied S-layer is not phosphorylated, enabling the investigation of uranyl carboxylate complexes formed at microbial surfaces. The latter are usually masked by preferentially formed uranyl phosphate complexes. We demonstrated that at highly acidic conditions (pH 1.5 to 3) no uranium was bound by the S-layer. In contrast to that, at moderate acidic pH conditions (pH 4.5 and 6) a complexation of U(VI) at the S-layer via deprotonated carboxylic groups was stimulated. Titration studies revealed dissociation constants for the carboxylic groups of glutamic and aspartic acid residues of pKa = 4.78 and 6.31. The uranyl carboxylate complexes formed at the S-layer did not show luminescence properties at room temperature, but only under cryogenic conditions. The obtained luminescence maxima are similar to those of uranyl acetate. EXAFS spectroscopy demonstrated that U(VI) in these complexes is mainly coordinated to carboxylate groups in a bidentate binding mode. The elucidation of the molecular structure of these complexes was facilitated by the absence of phosphate groups in the studied S-layer protein.
TL;DR: The pKa values and intensities of the proton binding sites are the fundamental molecular properties of EPSs that affect the EPS charge, molecular interactions, and metal complexation characteristics and can advance Derjaguin-Landau-Verwey-Overbeek-based concentration polarization modeling, facilitate the estimation of the osmotic pressure of the EPS concentration polarization layers, and lead to a deeper understanding of the role ofMetal complexation in membrane fouling.
TL;DR: In this paper, a fluorogenic signalling probe (E)-3-(4-methoxyphenyl)-4-[(4-nitrobenzylidene)amino]-1H-1,2,4-triazole-5(4H)-thione (6) was developed through microwave assisted Schiff base formation reaction.
Abstract: A novel fluorogenic signalling probe (E)-3-(4-methoxyphenyl)-4-[(4-nitrobenzylidene)amino]-1H-1,2,4-triazole-5(4H)-thione (6) for the carbonate and bicarbonate ions has been developed through microwave assisted Schiff base formation reaction. The anion recognition occurs through hydrogen bonding assessed by 1H NMR titration experiments. The photophysical results of probe 6 corroborates its applicability as an optical sensing platform for carbonate as well as bicarbonate ions in mixed aqueous organic media depending on pH of reaction solution. The fluorescence emission signal enhancement at 424 nm and considerable shift in the signal position as well as molar absorptivity to the probe absorption bands upon CO32− and HCO3− addition suggest the affinity of probe 6 towards these ions in comparison to a variety of competitive ions in aqueous/ethanol (7:3, v/v) at neutral pH and ambient temperature. From the fluorescence titration experiment, the limit of detection was calculated to be 1.91 μM.
TL;DR: In this article, the authors investigated the effect of conditions such as surfactant/metal ions molar ratio on the removal efficiency of trace heavy metal ions and determined the Zeta potential of gas bubbles in the AEC solutions, and isothermal titration calorimeter (ITC) determination was utilized to demonstrate the interaction.
TL;DR: In this paper, the influence of hydrogen peroxide and ozone and singlet oxygen co-agents on the functional groups of the carbon black surface was examined and it was found that the carbon oxidation depends on the sample structure.
TL;DR: A new method, based on slice-selective NMR spectroscopy of inhomogeneous mixtures, is introduced to perform NMR titrations and reaction monitoring in a single experiment.
TL;DR: In this paper, a multivariate curve resolution (MCR) algorithm was used to calculate the concentrations and spectral signatures of the pure components (TEMPO, Cl(+1) and TEMPO + ).
Abstract: A iodometric titration method was introduced to study the conversion of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) to the corresponding N -oxoammonium cation (TEMPO + ) by hypochlorite in the absence and presence of bromide ion. The validity of the titration was verified with UV–vis spectroscopy combined with a multivariate curve resolution (MCR) algorithm to calculate the concentrations and spectral signatures of the pure components (i.e., TEMPO, Cl(+1) and TEMPO + ). The formation of the oxoammonium cation was successfully followed during the activation of TEMPO by HOCl and HOBr. It was found that HOBr is a more effective activator for TEMPO than HOCl is. Moreover, the importance of a separate activation step for TEMPO with bromide-free TEMPO oxidations could be identified with this titration method. The content of TEMPO + was also monitored during the TEMPO-mediated oxidation of a cellulosic pulp by hypochlorite in the absence and presence of bromide. It was found that the oxidation of the alcoholic groups by TEMPO + was generally the rate-determining step and much slower than the regeneration of TEMPO + through oxidation of the hydroxylamine by HOCl and HOBr. However, at high pH the latter reaction became rate-limiting.
TL;DR: In this article, an activated carbon (HHPCAC) was used for the removal of Pb(II) from aqueous solutions by investigating a number of effective factors such as initial pH, contact time, dosage, and initial concentration.
Abstract: Hazelnut husk, an agricultural waste, was used to prepare an activated carbon (HHPCAC) by chemical activation using K2CO3. HHPCAC was characterized by FT-IR spectroscopy, BET surface area determination, SEM, Boehm titration, proximate, and elemental analysis. HHPCAC has a high surface area (980.9 m2 g−1) and contains 2.60 mmol g−1 of total acidic functional groups. HHPCAC was used for the removal of Pb(II) from aqueous solutions by investigating a number of effective factors such as initial pH, contact time, dosage, and initial concentration. Adsorption of Pb(II) ions is highly dependent on pH of the solution, and its optimal value was found to be 5.0. Time to equilibrium was found as 20 h. Kinetics of Pb(II) adsorption on HHPCAC followed pseudo-second-order model. Adsorption equilibrium data were analyzed by Langmuir and Freundlich models. Maximum adsorption capacity of HHPCAC for Pb(II) was calculated as 109.9 mg g−1 using Langmuir equation. From the findings, it could be concluded that HHPCAC i...