Quartz Microgravimetry Research Articles

Pickering emulsion stabilization with colloidal lignin is enhanced by salt-induced networking in the aqueous phase

We study the effect of electrolytes on the stability in aqueous media of spherical lignin particles (LP) and its relevance to Pickering emulsion stabilization. Factors considered included the role of ionic strength on morphology development, LP size distribution, surface charge, interfacial adsorption, colloidal and wetting behaviors. Stable emulsions are formed at salt concentrations as low as 50 mM, with the highest stability observed at a critical concentration (400 mM). We show salt-induced destabilization of LP aqueous dispersions at an ionic strength >400 mM. At this critical concentration LP flocculation takes place and particulate networks are formed. This has a profound consequence on the stability of LP-stabilized Pickering emulsions, affecting rheology and long-term stability. The results along with quartz microgravimetry and confocal microscopy observations suggest a possible mechanism for stabilization that considers the interfacial adsorption of LP at oil/water interfaces. The often-unwanted colloidal LP destabilization in water ensues remarkably stable Pickering emulsions by the effect of network formation.

Anion-Specific Water Interactions with Nanochitin: Donnan and Osmotic Pressure Effects as Revealed by Quartz Microgravimetry.

The development of new materials emphasizes greater use of sustainable and eco-friendly resources, including those that take advantage of the unique properties of nanopolysaccharides. Advances in this area, however, necessarily require a thorough understanding of interactions with water. Our contribution to this important topic pertains to the swelling behavior of partially deacetylated nanochitin (NCh), which has been studied here by quartz crystal microgravimetry. Ultrathin films of NCh supported on gold-coated resonators have been equilibrated in aqueous electrolyte solutions (containing NaF, NaCl, NaBr, NaNO3, Na2SO4, Na2SO3, or Na3PO4) at different ionic strengths. As anticipated, NCh displays contrasting swelling/deswelling responses, depending on the ionic affinities and valences of the counterions. The extent of water uptake induced by halide anions, for instance, follows a modified Hofmeister series with F– producing the highest swelling. In marked contrast, Cl– induces film dehydration. We conclude that larger anions promote deswelling such that water losses increase with increasing anion valence. Results such as the ones reported here are critical to ongoing efforts designed to dry chitin nanomaterials and develop bio-based and sustainable materials, including particles, films, coatings, and other nanostructured assemblies, for various devices and applications.

Microgravimetric study of electrochemical properties of PEDOT/WO3 composite films in diluted sulfuric acid

Poly-3,4-ethylenedioxythiophene composite films with tungsten oxide (PEDOT/WO3) were obtained by potentiodynamic deposition of tungsten oxide from acidic metastable solution of isopolytungstates into poly-3,4-ethylenedioxythiophene film, pre-deposited on an Au-quartz crystal. The electrochemical deposition of tungsten oxide into poly-3,4-ethylenedioxythiophene was investigated by electrochemical quartz microgravimetry (EQCM), the masses of PEDOT and tungsten oxide deposits were estimated. The electrochemical behavior of PEDOT/WO3 composite films with different masses of deposited tungsten oxide was studied by cyclic voltammetry and EQCM in the 0.5 M sulfuric acid electrolyte. The change of the fraction of tungsten oxide in the PEDOT/WO3 composite film results in the change of the slope of the Δf–E dependency in the potential region, corresponding to WVI/WV redox process. It is due to an oppositely directed mass transport (anion and cation) during the redox process in the composite film. The average molar mass of transferred species involved in the redox process in tungsten oxide was estimated to be 26 ± 4 g mol−1. It was shown that the fraction of electrochemically active tungsten oxide deposit is dependent on its mass in the composite, with increase of the mass of tungsten oxide in PEDOT/WO3, the fraction of electroactive tungsten oxide WO3 decreases due to decrease in its active area.

New Nickel(II) Complexes with Tetradentate Schiff Bases Containing Electron-Acceptor Substituents

Complexes [Ni(3-NO2SalEn)] and [Ni(3-NO2SaltmEn)] were synthesized and identified, and polymers based on them were obtained. It was found with the help of voltammetry that the introduction of nitro groups in the complexes shifts their redox activity in the direction of positive potentials; it was shown by in situ quartz microgravimetry and in situ absorption spectroscopy methods that fragments of the polymer complexes under study can undergo reversible two-electron oxidation at the expense of formation of polarons and bipolarons in the ligand surrounding.

Synthesis and study of catalysts of electrochemical oxygen reduction reaction based on polymer complexes of nickel and cobalt with Schiff bases

The article presents the results of studies of new nanosize catalysts of electrochemical oxygen reduction reaction (ORR) obtained using the method of thermal decomposition of polymer complexes of nickel and cobalt with tetradentate (N2O2) Schiff bases. The catalysts are characterized using the methods of thermogravimetry, electrochemical quartz microgravimetry, scanning electron microscopy with X-ray microanalysis, XPS. The ORR process on electrodes modified by the above catalysts was studied using the voltammetry and rotating disk electrode techniques. The obtained catalysts manifested high specific activity per initial polymer mass (more than 600 mA/mg).

Conformal Atomic Layer Deposition of TA-Based Diffusion Barrier Film Using a Novel Mono-Guanidinate Precursor

In this work, we present elaboration of Ta-based thin films by ALD from a novel tantalum precursor, the eta2-N,N'-isopropylethylguanidinato-tetra-diethylamino tantalum ([eta2-(i)PrNC(NEt2)NEt]Ta(NEt2)4, IEGTDEAT). Ammonia was used as reducing agents. The experimental conditions were optimized by quartz microgravimetry, studying the influence of duration of precursors and purge pulses and the substrate temperature. An optimal deposition temperature of 260 degrees C was showed. Ta-based thin films deposited on planar and patterned substrates showed a perfect conformality and continuity, even at low number of cycles.

Kinetics of silver anodic dissolution in thiosulfate electrolytes

The regularities of silver anodic dissolution are studied by using the voltammetry (at the potential scan rates from 5 to 1000 mV/s) on the electrode, which was renewed immediately in the solution by cutting-off a thin surface metal layer, and quartz microgravimetry, for various concentrations of sodium thiosulfate (0.05–0.2 M). It is shown that, in the potential range from 0 to 0.4 V (normal hydrogen electrode), the polarization curves reflect the silver dissolution, whereas the contribution of oxidation of S2O 3 2− ions is insignificant. At low potential scan rates, the process kinetics is of mixed nature. The kinetics and mechanism of anodic process are studied by using the measurements at high potential scan rates (100–200 mV/s) and the calculations of equilibrium composition of near-electrode layer. It is found that the exchange current in the electrolytes studied is 5 × 10−5 A/cm2, the transfer coefficient α is approximately 0.5, and both parameters are virtually independent of the concentration of S2O 3 2− ions. The reaction order of silver dissolution with respect to the ligand \( \left. {\frac{{\partial logi}} {{\partial logc}}} \right|_E \) is close to unity and is independent of potential. With regard for the literature data on the adsorption of thiosulfate ions on silver, this result is interpreted as the evidence for the involvement of one S2O 3 2− ion from bulk solution, along with adsorbed ligands, in the elementary act of metal dissolution.

Peculiarities of anodic behavior of gold electrode in thiosulfate electrolytes

Using the methods of quartz microgravimetry and voltammetry, the anodic behavior of gold electrode in thiosulfate electrolytes is studied in the pH range of 7 to 11. It is found that, in the potential range from 0.15 to 1.0 V (NHE), the anodic current is associated predominantly with the oxidation of thiosulfate ions, and the gold dissolution rate in this electrolyte is negligibly low (< 0.02 mA/cm2). It is shown that the study of anodic processes in the neutral thiosulfate electrolytes requires stabilization of solution acidity, because the near-anode layer can be acidified to the pH values, which are sufficient for the formation of elemental sulfur. It is found that the use of Britten-Robinson buffer solution with pH 7 as the supporting electrolyte changes significantly the polarization curve of thiosulfate ion oxidation, but does not raise the gold dissolution rate. An increase in the solution pH to 11 and an exposure of electrode at various potentials (−0.5 and 0.15 V) prior to the onset of potential scanning also do not accelerate considerably the gold dissolution in the thiosulfate electrolyte. A comparison between the regularities of gold anodic behavior in the thiosulfate solutions and earlier studied gold dissolution in the cyanide and thiocarbamide electrolytes showed that they are similar. It is supposed that the specific features of anodic processes in these cases are of a similar nature: the metal dissolution proceeds with the formation of two-ligand complexes with linear structure, which is typical for all aforementioned ligands.

Effect of solution pH on the electrochemical behavior of thiocarbamide at gold and platinum electrodes

The effect of solution pH on the electrochemical behavior of thiocarbamide at gold and platinum electrodes is studied by using cyclic voltammetry and quartz microgravimetry. It is shown that with the increasing of pH the half-wave potential of thiocarbamide oxidation shifts toward negative values in both cases. In the cathodic branches of the cyclic voltammograms, up to pH ≃ 4 the potential region of reduction of the thiocarbamide oxidation product remains practically unchanged; this allows concluding that the oxidation product is formamidine disulfide (at platinum) or its mixture with gold complex ions (at gold electrode). Further increasing of pH up to 9.5–10 results in the increase of the contribution of the reduction current of these ions to the cathodic signal. An explanation for this phenomenon is given. At the same time, new signals appear at E < −0.4 V; they may be interpreted as the current of elemental sulfur reduction. Increasing of pH over 10 leads to gold passivation by the elemental sulfur; this manifests itself as the electrode mass increase during the microgravimetry measurements. Introducing of sodium silicate (recommended in the literature as a solution stabilizer) to the solution does not eliminate the passivation of gold.

Mechanism of electrochemical reactions of polyaniline films formed under the conditions of cathodic oxygen reduction

Polyaniline films (further, CPANI) were obtained under the conditions of oxygen cathodic reduction in the aniline-containing solution on the electrodes of mixed indium tin oxide (ITO), graphite, and gold. CPANI films are characterized by redox processes in the potential ranges of 0.1–0.2 V and ∼0.4 V (SCE). These processes are caused by the polymer chain fragments of different structure and the ratio between the peaks corresponding to these processes varies significantly as dependent on the synthesis conditions (electrode material, stirring, etc). The mechanism of electrode processes on CPANI is studied using the methods of cyclic voltammetry and quartz microgravimetry. It is found that only hydrogen cations and supporting electrolyte anions participate in the electrode process at the potentials of 0.1–0.2 V. The mechanism of redox processes on the obtained polymer films is discussed.

Mass tranfer of ions and solvent at redox processes in poly-3,4-ethylenedioxythiophene films

The work presents the data on mass transfer at the interface of the poly-3,4-ethylenedioxythiophene film with different propylene carbonate electrolyte solutions (TBAPF6, LiClO4, NaClO4, TBAClO4, TBABF4) obtained using the quartz microgravimetry method in combination with cyclic voltammetry. It is shown that two parts of different nature can be observed in the region of electric activity of poly-3,4-ethylenedioxythiophene films on Δm, ΔQ curves. They evidence the change in mass transfer conditions at achieving different film oxidation degrees.

Effect of the displacement reaction on the composition of the magnetic layer in electrodeposited layered nanostructures Co-Cu/Cu and Ni-Cu/Cu

Methods of stripping voltammetry, quartz microgravimetry, and x-ray-fluorescence analysis are employed to explore the copper displacement process on thin electrodeposited layers of pure cobalt and nickel and on deposits of these metals with inclusions of copper. The displacement reaction proceeds at a considerable rate on cobalt in the sulfate and sulfosalicylate solutions and virtually does not proceed on nickel in both the sulfate or sulfate-chloride solutions. An estimate of the rate of the copper displacement reaction following a change in the concentration of copper ions in the solution and in the pH of the sulfosalicylate solution is given. A decrease in the contact exchange rate is facilitated by a decrease in the concentration of copper ions in solution and their participation in the formation of complexes.

Anodic dissolution of magnetic layers based on cobalt and nickel in conditions of electrodeposition of multilayered nanostructures by a single-bath method

Methods of quartz microgravimetry (in solutions containing no copper ions) and stripping voltammetry (in copper-containing solutions) are used to study the process of anodic dissolution of thin deposits of pure Co and Ni and deposits of these metals with inclusion of copper in the potential region of copper deposition. It is shown that, under these conditions, Ni practically does not dissolve in either the sulfate or chloride-containing electrolytes, whereas Co dissolves in sulfate electrolytes at a rate that is dependent on the potential and increases with its shift into the positive region. Stability of ternary CoNiCu deposits is examined and it is demonstrated that additionally inserting Ni in the composition of a magnetic CoCu layer facilitates suppression of selective dissolution of Co.

Anodic behavior of gold in acid thiourea solutions: A cyclic voltammetry and quartz microgravimetry study

It is shown that at potentials E 100 μA cm−2) starts at E ≥ 0.65 V, with the primary process being the oxidation of thiourea, which gives rise a current peak at E ≃ 1.0 V. The thiourea oxidation at E ≥ 1.1 produces the appearance of catalytically active species, which drastically accelerate the gold dissolution process in the potential region extending from a steady-state value to 0.6 V, where the current efficiency for gold approaches 100% and a peak emerges at E ≃ 0.55 V. The peak’s height is commensurate with the value of the limiting diffusion current associated with the ligand supply. The species in question make no discernible impact on the thiourea oxidation process. Formamidine disulfide, which forms during the anodic oxidation of thiourea or which is added in solution on purpose, exerts no noticeable catalytic influence on the anodic gold dissolution. The catalytically active species is presumably the S2− ion, product of decomposition and deep oxidation of thiourea and formamidine disulfide. Indeed, adding sulfide ions in solution has a strong catalytic effect on the gold dissolution, whose character is identical to that of the effect exerted by products of anodic oxidation of thiourea at E ≥ 1.1 V μA cm−2.

Copper Corrosion in Acid Chloride Solutions: A Quartz Microgravimetry Study

Making use of the quartz microgravimetry method allows one to in situ obtain the m vs. t curves simultaneously with the Ecor vs. t curves (m is the weight of a dissolved or deposited substance, t a time period, Ecor a corrosion potential), which gives one a chance to determine the corrosion rate and its dependence on the concentration of copper ions and chloride ions in solution to within a good accuracy. The corrosion rate increases with increasing concentration of ions of divalent copper in solution, while an increase in the concentration of chloride ions does not lead to its change. The formation of a salt film of an intermediate compound of univalent copper during the copper dissolution process in solutions diluted with respect to chloride ions (0.1 M NaCl, 0.03 M CuCl2) is discovered experimentally. In the m vs. t curves, the formation of the film manifests itself in the form of an increase in the electrode weight, while the corrosion potential transients reflect but weakly the occurring complex surface conversions. Techniques for the identification of intermediate solid species are proposed. The coefficients of mass transfer with respect to ions of divalent copper are determined. Explanations for variations in the system's behavior following a decrease in the concentration of chloride ions in solution are offered.

Copper in Acid Chloride Solutions: Electrochemical Behavior by Quartz Microgravimetry and Voltammetry

The cathodic deposition of copper on a gold electrode and its subsequent anodic dissolution in an acid chloride solution, where two successive stages of a one-electron transfer are distinguishable because of the stability of chloride complexes of Cu(I), is studied by voltammetry and quartz microgravimetry. The formation of a film of an intermediate compound of Cu(I) during the deposition and dissolution of copper is revealed experimentally. Techniques for identifying the intermediate solid species are suggested. During a cathodic polarization, a film of intermediate compound CuCl forms at a reduced concentration of chloride ions in the Cu(II)/Cu(I) process, while during the anodic dissolution of the copper deposit formed during the cathodic polarization the intermediates appear in the Cu(0)/Cu(I) process, the concentration of chloride ions notwithstanding. The change in the electrochemical behavior of the system caused by a decrease in the concentration of chloride ions is explained.

Catalytic Activity of Thallium, Lead, and Bismuth Adatoms in the Gold Dissolution Reaction in Cyanide Solutions: A Comparative Characterization

Quartz microgravimetry is used to determine the ratio between coefficients of mass transfer (1 : 0.54 : 0.48), which characterizes relative values of rates of diffusion of hydroxy complexes of thallium, lead, and bismuth in alkaline solutions. The ratio is used when refining the condition under which on a renewable electrode in solutions containing these ions at the concentration c i the electrode coverage by relevant adatoms Θ i with increasing duration of contact of the electrode with solution reaches constant values: (c Tl t) = (0.54c Pb t) = (0.48c Bi t). Measured are i,t curves on a renewable gold electrode at E = const in solutions containing 0.1 M KCN, 0.1 M KOH, 0.01 M KAu(CN)2, and 8 × 10–6 M compounds of thallium or 1.5 × 10–5 M, lead, or 1.6 × 10–5 M, bismuth. Shown is that at (Θ, E) = const the currents of dissolution of gold in these solutions increase in the series Tl < Pb < Bi, which evidences an increase in this series of the catalytic activity of adatoms of these metals. Shown is that at Θ = const the catalytic action of adatoms of thallium and bismuth has an approximately additive character. The obtained data are analyzed with allowance made for the explanation offered earlier for the catalytic effect of adatoms on the anodic dissolution of gold based on the hypothesis about the shift of the potential of the free zero charge in the negative direction after substituting a metal atom for chemisorbed cyanide ions.

Underpotential Deposition of Te Monolayers on Au Surfaces from Perchloric Acid Solution Studied by Chronocoulometry and EQCM

We report a study of the underpotential deposition (UPD) of Te monolayers onto Au electrodes from perchloric acid solution using electrochemical quartz microgravimetry (EQCM) and chronocoulometry. We find that tellurium(IV) oxide (as TeO32-, TeO2 or HTeO2+) is adsorbed onto Au at potentials positive of the UPD region. EQCM experiments, in which an Au electrode poised at +0.7 V in pure HClO4 electrolyte was monitored as a function of time before and after the addition of TeO2, showed a slow adsorption of a submonolayer of TeO2. Energy-dispersive X-ray (EDX) measurements confirm the presence of a Te-containing species on the surface. Two distinct reductive UPD features at approximately +0.400 V and −0.100 V vs Ag|AgCl were observed by cyclic voltammetry. EQCM measurements indicate that there is a small, reproducible mass decrease accompanying the first UPD wave, consistent with the loss of H2O from the surface as an adsorbed layer of HTeO2+ is reduced to a submonolayer of Te atoms. Chronocoulometry indicates a charge density of 160 μC/cm2 for the first UPD wave, which, when taken together with the mass change data, is consistent with the four-electron reduction of adsorbed HTeO2+ to Te. In addition, analysis of the current−time data indicates that this process occurs by a two-dimensional instantaneous nucleation and growth mechanism, resulting in an ordered overlayer with a fractional coverage of ca. 0.41. The second UPD peak results in the formation of a dense monolayer by reduction of HTeO2+ from solution. This process also appears to occur by a direct four-electron reduction and exhibits simple Langmuir adsorption behavior as evidenced by exponentially decaying current−time transients. The saturation coverage is approximately 0.9.

From Cyclic Voltammetry to Scanning Electrochemical Microscopy: Modern Electroanalytical Methods to Study Organic Compounds, Materials, and Reactions

This review shows some recent developments in the use of electroanalytical methods in the context of organic electrochemistry. Several techniques (cyclic voltammetry, spectroelectrochemistry, electrochemical quartz microgravimetry, and scanning electrochemical microscopy) for elucidation of properties and reactivity of organic compounds and materials are discussed. Such techniques also allow the detailed analysis of electron transfer initiated chemical reactions. Advantages added by techniques not only recording current-potential-time relationships, but including spectral, mass, and spatial information are pointed out. Thus, structures of redox active or electron transfer generated species become accessible, properties of surface bound and deposited molecules can be determined, and lateral resolution for both, analysis of the chemical nature of electrode surfaces, and induction of reactions on electrodes is provided.