Oxygen desorption from polycrystalline palladium: Thermal desorption of O<Subscript>2</Subscript> from a chemisorbed layer of O<Subscript>ads</Subscript> in the course of the decomposition of PdO surface oxide and in the release of oxygen from the bulk of palladium

The desorption of oxygen from polycrystalline palladium (Pd(poly)) was studied using temperature-programmed desorption (TPD) at 500–1300 K and the amounts of oxygen absorbed by palladium (n) from 0.05 to 50 monolayers. It was found that the desorption of O₂ from Pd(poly), which occurred from a chemisorbed oxygen layer (O_ads), in the release of oxygen from a near-surface metal layer in the course of the decomposition of PdO surface oxide, and in the release of oxygen from the bulk of palladium (O_abs), was governed by repulsive interactions between O_ads atoms and the formation and decomposition of O_ads-Pd*-O_abs structures (Pd* is a surface palladium atom). At θ ≤ 0.5, the repulsive interactions between O_ads atoms (ɛ_aa = 10 kJ/mol) resulted in the desorption of O₂ from Pd(poly) at 650–950 K. At 0.5 ≤ n ≤ 1.0, the release of inserted oxygen from a near-surface palladium layer occurred during TPD in the course of the migration of O_abs atoms to the surface and the formation-decomposition of O_ads-Pd*-O_abs structures. As a result, the desorption of O₂ occurred in accordance with a first-order reaction with a thermal desorption (TD) peak at T _max ∼ 700 K. At 1.0 ≤ n ≤ 2.0, the decomposition of PdO surface oxide occurred at a constant surface cover-age with oxygen during TPD in the course of the formation-decomposition of O_ads-Pd*-O_abs structures. Because of this, the desorption of O₂ occurred in accordance with a zero-order reaction at low temperatures with a TD peak at T _max ∼ 675 K. At 1.0 ≤ n ≤ 50, oxygen atoms diffused from deep palladium layers in the course of TPD and arrived at the surface at high temperatures. As a result, O₂ was desorbed with a high-temperature TD peak at T > 750 K.     

DFT quantum-chemical calculations of nitrogen oxide chemisorption and reactivity on the Cu(100) surface

A DFT quantum-chemical study of NO adsorption and reactivity on the Cu₂₀ and Cu₁₆ metal clusters showed that only the molecular form of NO is stabilized on the copper surface. The heat of monomolecular adsorption was calculated to be ΔH _m = ?49.9 kJ/mol, while dissociative adsorption of NO is energetically unfavorable, ΔH _d = + 15.7 kJ/mol, and dissociation demands a very high activation energy, E _a = + 125.4 kJ/mol. Because of the absence of NO dissociation on the copper surface, the formation mechanism of the reduction products, N₂ and N₂O, is debatable since the surface reaction ultimately leads to N-O bond cleavage. As the reaction occurs with a very low activation energy, E _a = 7.3 kJ/mol, interpretation of the NO direct reduction mechanism is both an important and intriguing problem because the binding energy in the NO molecule is high (630 kJ/mol) and the experimental studies revealed only physically adsorbed forms on the copper surface. It was found that the formation mechanism of the N₂ and N₂O reduction products involves formation (on the copper surface) of the (O_adN-NO_ad) dimer intermediate that is chemisorbed via the oxygen atoms and characterized by a stable N-N bond (r _N-N ～1.3 Å). The N-N binding between the adsorbed NO molecules occurs through electron-accepting interaction between the oxygen atoms in NO and the metal atoms on the “defective” copper surface. The electronic structure of the (O_adN-NO_ad) surface dimer is characterized by excess electron density (ON-NO)^δ? and high reactivity in N-O_ad bond dissociation. The calculated activation energy of the destruction of the chemisorbed intermediate (O_adN-NO_ad) is very low (E _a = 5–10 kJ/mol), which shows that it is kinetically unstable against the instantaneous release of the N₂ and N₂O reduction products into the gas phase and cannot be identified by modern experimental methods of metal surface studies. At the same time, on the MgO surface and in the individual (Ph₃P)₂Pt(O₂N₂) complex, a stable (O_adN-NO_ad) dimer was revealed experimentally.     

Oxygen dissolution in polycrystalline palladium at O2 pressures of 0.1 to 100 Pa

Oxygen dissolution in polycrystalline palladium Pd(poly) at O₂ pressures ( $P_{O_2 } $ ) of 0.1 to 100 Pa and a temperature of 600 K has been investigated by temperature-programmed desorption. The dissolution process under these conditions includes O₂ chemisorption on the oxide film surface, the insertion of Oads atoms under the oxide layer, and their diffusion into the subsurface layers of palladium. During chemisorption, a structure ensuring that the O_ads coverage of the surface increases with increasing $P_{O_2 } $ forms on the surface of the oxide film. This is favorable for O_ads penetration through the oxide film and increases the amount of absorbed oxygen. The O_ads coverage of the surface calculated via the Langmuir equation at an O₂ desorption activation energy of E _des = 125 kJ/mol correlates with the number of absorbed oxygen monolayers (n). At n ≥ 1, oxygen absorption by Pd(poly) is due to the diffusion of O atoms in the palladium lattice. After the accumulation of 14–18 oxygen monolayers in the subsurface layers of palladium, oxygen absorption practically stops depending on $P_{O_2 } $ . Thus, the acceleration of oxygen dissolution in palladium is due to the formation of the surface oxide film and the increase in the O_ads coverage of this film, which facilitates the insertion of O_ads atoms into the subsurface layers of palladium.     

Interaction between oxygen and polycrystalline palladium at O<Subscript>2</Subscript> pressures of 10<Superscript>−6</Superscript>–10 Pa

The interaction between oxygen and polycrystalline palladium (Pd(poly)) at \(P_{O_2 } \) = 2.6 × 10^?6–10 Pa and T = 300–1300 K was studied by the thermal desorption (TD) method. The interaction between O₂ and Pd(poly) is governed by the O₂ pressure and the sample temperature. At low pressures of \(P_{O_2 } \) (≤1.3 × 10^?5 Pa), O₂ is chemisorbed dissociatively on the Pd(poly) surface. During chemisorption, the O_ads-surface bond energy and the O₂ sticking coefficient gradually decrease as the surface coverage θ increases. At \(P_{O_2 } \) ≥ 10^?2 Pa and T ≤ 500 K, after the saturation of the O_ads layer (θ ～ 0.5), O_ads atoms penetrate under the surface layer of the metal to form surface palladium oxide. At \(P_{O_2 } \) ≥ 1 Pa and T > 500 K, after the saturation of the surface oxide film 2 ML in thickness (n ～ 2), O_ads atoms penetrate into the oxide film and then into the subsurface palladium layer and diffuse deep into the metal bulk. As a result, the oxygen uptake at 700 K is n ～ 50. Upon heating, the surface oxides decompose, desorbing O₂, which gives rise to a low-temperature TD peak with T _max = 715 K. The release of oxygen inserted in the subsurface layers of palladium shows itself as a distinct high-temperature TD peak with T _max ≥ 750 K.     

Dissolution of oxygen in polycrystalline palladium at $${P_{{O_2}}}$$= 100 Pa and temperatures of 500 to 950 K

The dissolution of oxygen in polycrystalline palladium Pd(poly) at an O₂ pressure of 100 Pa and temperatures of 500–950 K has been investigated by temperature-programmed desorption. At 500 K, the process yields a surface palladium film that includes an oxide-like reconstructed structure on a rarefied metal surface layer. At this temperature, palladium sorbs ~2 monolayers (ML) of oxygen. At 600–800 K, palladium dissolves up to ~140 ML of oxygen as a result of O₂ chemisorption on the surface of the oxide film, penetration of O_ads atoms under the oxide film, and their diffusion into the metal bulk. The dependence of the amount of oxygen sorbed by Pd(poly) (n) on the time of exposure to an O₂ atmosphere is described by a nearparabolic function, n = at^b, indicating that oxygen atoms diffuse in the metal lattice. The activation energy of this diffusion, Е _dif, is ~83.5 kJ/mol. At high temperatures (800–950 K), palladium sorbs much less oxygen (≤10 ML). This is due to the complete decomposition of the surface oxide film, a process that markedly hampers the insertion of Oads atoms under the surface layer of the metal.     

Catalytic properties of copper chromite ferrites in water gas shift reaction and hydrogen oxidation

The catalytic properties of a series of copper chromite ferrite samples with the composition CuCr_2–xFe_xO₄ (where x = 0–2) and a spinel-type structure in reactions with reducing (water gas shift reaction, WGSR) and oxidizing (the oxidation of hydrogen) reaction atmospheres were studied. The samples were obtained by the thermal decomposition of mixed hydroxo compounds. The distribution of Cu²⁺ ions in the tetrahedral and octahedral crystallographic positions of spinel, which depends on the Cr³⁺/Fe³⁺ ratio, affects the apparent activation energy (E_a) in both of the reactions. In WGSR, E_a is ～33 kJ/mol for CuCr₂O₄, in which Cu²⁺ ions mainly occupy tetrahedral positions, whereas E_a ≈ 100 kJ/mol for CuFe₂O₄, in which Cu²⁺ ions mainly occupy octahedral positions. In the reaction of hydrogen oxidation, E_a is ～71 kJ/mol for CuCr₂O₄ or ～42 kJ/mol for CuFe₂O₄. The value of E_a for the mixed chromite ferrites changes with the replacement of chromium ions by iron ions and, hence, with a ratio between the amounts of copper ions in the tetrahedral and octahedral oxygen positions of spinel.     

Mechanisms of oxygen adsorption and desorption on polycrystalline palladium

The adsorption and desorption of oxygen on a polycrystalline palladium (Pd(poly)) surface (10-to 100-μm crystallites; ～32% (100), ～18% (111), ～34% (311), and ～15% (331)) at P _O2 ≤ 1.3 × 10^?5 Pa and T = 500–1300 K have been studied by TPD and mathematical modeling. The kinetics of O₂ adsorption and desorption on Pd(poly) are primarily governed by the formation and decomposition of oxygen adsorption structures on the (100) and (111) crystallite faces. The O₂ adsorption rate is constant at ? ≤ 0.15–0.25 owing to the formation of the p(2 × 2) structure with an O_ads-surface bonding energy of D(Pd-O) = 364 kJ/mol on the (100) and (111) faces. The adsorption rate decreases with increasing coverage at ? ≥ 0.15–0.25 because of the growth, on the (100) face, of the c(2 × 2) structure, in which D(Pd-O) is reduced to 324 kJ/mol by lateral interactions in the adsorption layer. A high-temperature (～800 K) O₂ desorption peak is observed for ? ≤ 0.25, which is due to O₂ desorption from a disordered adsorption layer according to a second-order rate law with an activation energy of E _des = 230 kJ/mol. A lower temperature (～700 K) O₂ desorption peak is observed for ? ≥ 0.25, which is due to O₂ released by the c(2 × 2) structure according to a first-order rate law with E _des = 150 kJ/mol. At ? ≥ 0.25, there are repulsive interactions between O_ads atoms on Pd(poly) (ε_aa = 5–10 kJ/mol).     

Experimental study of intermediates and wave phenomena in co oxidation on platinum metal (Pt,Pd) surfaces

The mechanism of catalytic CO oxidation on Pt(100) and Pd(110) single-crystal surfaces and on Pt and Pd sharp tip (～10³ Å) surfaces has been studied experimentally by temperature-programmed reaction, temperature desorption spectroscopy, field electron microscopy, and molecular beam techniques. Using the density functional theory the equilibrium states and stretching vibrations of oxygen atoms adsorbed on the Pt(100) surface have been calculated. The character of the mixed adsorption layer was established by high resolution electron energy loss spectroscopy—molecular adsorption (O_2ads, CO_ads) on Pt(100)-hex and dissociative adsorption (O_ads, CO_ads) on Pt(100)-(1×1). The origin of kinetic self-oscillations for the isothermal oxidation of CO in situ was studied in detail on the Pt and Pd tips by field electron microscopy. The initiating role of the reversible phase transition (hex) ? (1 × 1) of the Pt(100) nanoplane in the generation of regular chemical waves was established. The origination of self-oscillations and waves on the Pt(100) nanoplane was shown to be caused by the spontaneous periodical transition of the metal from the low-active state (hex) to the highly active catalytic state (1 × 1). A relationship between the reactivity of oxygen atoms (O_ads) and the concentration of CO_ads molecules was revealed for the Pd(110) surface. Studies using the isotope label ¹⁸O_ads demonstrated that the low-temperature formation of CO₂ at 150 K is a result of the reaction of CO with the highly reactive state of atomic oxygen (O_ads). The possibility of the low-temperature oxidation of CO via interaction with the so-called “hot” oxygen atoms (O_hot) appearing on the surface at the instant of dissociation of O_2ads molecules was studied by the molecular beam techniques.     

Oxidation of the polycrystalline gold foil surface and XPS study of oxygen states in oxide layers

Gold oxide films obtained on the surface of polycrystalline gold foil upon oxidation by oxygen activated by a high-frequency discharge have been studied by X-ray photoelectron spectroscopy. High-frequency O₂ activation affords oxide films more than 3–5 nm thick. As follows from Au4f spectra, the surface gold atoms are oxidized to the oxidation state +3. The O1s spectra have a composite shape and are decomposed into four components that characterize nonequivalent states of oxygen in the resulting oxide films. It is assumed that the two major oxygen states (E _b(O1s) = 529.0 and 530.0 eV) correspond to the oxygen atoms in two-and three-dimensional gold oxide Au₂O₃, respectively. The oxygen states characterized by the higher binding energies (E _b(O1s) = 531.8 and 535.2 eV) likely correspond to molecular oxygen in peroxide and superoxide groups, respectively.     

Adsorption properties of γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> as measured by gas chromatography

The adsorption properties of γ-Al₂O₃ were studied using gas chromatography. Isotherms of adsorption of n-alkanes (C₆–C₉), hex-1-ene, benzene, and isobutanol were measured within 70–100°C. The isosteric heats of adsorption and contributions to them from dispersion (Δq _dis) and specific (Δq _sp) interactions were determined for hex-1-ene, benzene, and isobutanol. Under the conditions covered, hex-1-ene molecules are adsorbed mainly on account of dispersion interactions. For the adsorption of benzene, Δq _dis is nearly twice as large as Δq _sp, while for the adsorption of isobutanol, Δq _sp is nearly twice as large as Δq _dis. At 100°C, isobutyl alcohol is chemisorbed.     

Molecular mechanism of propane oxidative dehydrogenation on surface oxygen radical sites of VO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/TiO<Subscript>2</Subscript> catalysts

Minimum energy pathways of propane oxidative dehydrogenation to propene and propanol on supported vanadium oxide catalyst VO _x /TiO₂ were studied by periodic discrete Fourier transform (DFT) using a surface oxygen radical as the active site. The propene formation pathway was shown to consist of two consecutive hydrogen abstraction steps. The first step includes C_β–H bond activation of propane followed by the formation of a surface hydroxyl group V–O _t H and a propyl radical n-C₃H₇. This step with the activation energy E* = 0.56 eV (54.1 kJ/mol) appears to be rate-determining. The second step involves the reaction of the bridging O _b oxygen atom with the methylene C–H bond of propyl radical n-C₃H₇ followed by the formation of a hydroxylated surface site HO _t –V⁴⁺–O _b H and propene. The initial steps of the C–H bond activation during propane conversion to propanol and propene by ODH on V⁵⁺–(O _t O _b )^? active sites are identical. The obtained results demonstrate that participation of surface oxygen radicals as the active sites of propane ODH makes it possible to explain relatively low activation energies observed for this reaction on the most active catalysts. The presence of very active radical species in low concentration seems to be the key factor for obtaining high selectivity.     

Theoretical study of V<Subscript>20</Subscript>O<Subscript>50</Subscript> oxovanadate cluster compounds with alkali metal atoms

The energies and structural and spectroscopic characteristics of model М _n V₂₀O₅₀ systems corresponding to compounds of the V₂₀O₅₀ oxovanadate cluster with alkali metal atoms (M = Li, K; n = 1–20) have been calculated by the density functional theory method (B3LYP). It has been demonstrated that, in the K _n V₂₀O₅₀ compounds, all the metal atoms are coordinated in the outer sphere to the edges of the hollow dodecahedral V₂₀O₅₀ cage to form three-center O_t?K?O_t bridges with terminal oxygen atoms. In the Li _n V₂₀O₅₀ compounds, the metal atoms can be coordinated both outside and inside the V₂₀O₅₀ cage. At n = 4, the most favorable isomer is endohedral Li₄O₄@V₂₀O₄₆ in the quintet state (S = 5), in which the four Li atoms are located in the inner cavity of the inverted O₄@V₂₀O₄₆ isomer of the oxovanadate cluster with four O atoms oriented to the cage center and form with them a corrugated eight-membered ring Li₄O₄. The decrease in energy caused by the formation of the endohedral isomer (4Li + V₂₀O₄₅₀ → Li₄O₄@V₂₀O₄₆) is estimated at ~377 kcal/mol. The exohedral isomer 4Li ? V₂₀O₅₀ (S = 5), in which the Li atoms are coordinated to the outside of the V₂₀O₅₀ cage, is ~23 kcal/mol less favorable. For the other members of the Li series with n from 4 to 20, the endohedral isomers with the inner Li₄O₄ ring remain preferable. At n > 4, the extra Li atoms fill the outer sphere of the cage, being coordinated to its edges to form three-center O_t?Li?O_t bridges with terminal oxygen atoms. The specific energy of formation of Li _n V₂₀O₅₀ (by the scheme nLi + V₂₀O₄₅₀ → Li₄O₄@V₂₀O₄₆Li_n-4) per Li atom monotonically decrease from ~98 (n = 2) to ~80 kcal/mol (n = 20). For K _n V₂₀O₅₀, these energies are ~20?25 kcal/mol lower than for the lithium analogues and decrease from ~80 (n = 2) to ~64 kcal/mol (n = 12). The atoms of both alkali metals in the M _n V₂₀O₅₀ systems have large positive effective charges (0.85e?0.92e for K and 0.65e?0.78e for Li), which also monotonically decrease with increasing n. The addition of each alkali metal atom is accompanied by its ionization (М → М⁺) along with the reduction of one of the neighboring pentavalent vanadium atoms to the tetravalent state (V^V → V^IV) and localization of the unpaired electron in its 3d shell. For all Li _n V₂₀O₅₀ complexes, the states with maximal multiplicity and parallel spins are the most preferable.     

IR spectra and structure of poly(vinylamide) complexes with hydrogen peroxide

The IR spectra of anhydrous thin films of hydrogen peroxide complexes with cyclic and aliphatic poly(N-vinylamides) have been studied. Splitting of a band due to stretching vibrations of C=O groups in the IR spectra of the poly(vinylcaprolactam) complex is accounted for by the resonance interaction of v _C=O vibrations of two monomer units linked by a hydrogen peroxide molecule. The formation of a N-H···O=C intramolecular hydrogen bond between neighboring polymer units is responsible for the observed low absorption of hydrogen peroxide by N-vinylamide polymers and copolymers. The energy E _H of hydrogen bonds formed between hydrogen peroxide and polymer chain fragments has been estimated by quantum-mechanical calculations. Depending on the complex structure, the value of E _H varies from 13 to 29 kJ/mol.     

Thermodynamic characteristics of protolytic equilibria in aqueous solutions of glycyl peptides

Protolytic equilibria in aqueous solutions of glycyl-DL-serine, glycyl-DL-threonine, and glycyl-DL-valine are investigated by means of potentiometry and calorimetry. Dissociation constants and heat effects of the above dipeptides are determined. Standard thermodynamic characteristics (pK°, Δ_disG°, Δ_disH°, Δ_disS°) of the investigated equilibria are calculated. The obtained results are compared to corresponding data on relative compounds.     

Dissociation energies of O–H bonds in alkylseleno- and alkyltelluro-substituted phenols

The O?H bond dissociation energy (D _O?H) has been determined for eight alkylseleno-substituted phenols, one alkyltelluro-substituted phenol, and one alkyltelluro-substituted pyridinol. D _O?H has been estimated by the intersecting-parabolas method from kinetic data using five reference compounds: α-tocopherol (D _O?H = 330.0 kJ/mol), 3,5-di-tert-butyl-4-methoxyphenol (D _O?H = 347.6 kJ/mol), 4-methylphenol (D _O?H = 361.6 kJ/mol), 2,6-di-tert-butyl-4-methylthiophenol (D _O?H = 336.3 kJ/mol), and 2,6-di-ter-tbutyl-4-methylphenol (D _O?H = 338.0 kJ/mol). The following D _O?H values (kJ/mol) have been obtained: 335.9 for 2,5,7,8-tetramethyl-2-phytyl-6-hydroxy-3,4-dihydro-2H-1-benzoselenopyran, 342.6 for 2-methyl-5-hydroxy-2,3-dihydrobenzoselenophene, 333.5 for 2,4,6,7-tetramethyl-5-hydroxy-2,3-dihydrobenzoselenophene, 339.4 for 2-tert-butyl-4-methoxy-6-octylselenophenol, 357.9 for dodecyl 3-(4-hydroxyphenyl) propyl selenide, 348.5 for dodecyl 3-(3,5-dimethyl-4-hydroxyphenyl)propyl selenide, 350.9 for dodecyl 3-(3-tert-butyl-4-hydroxyphenyl)propyl selenide, 338.0 for dodecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propyl selenide, 343.0 for 2,6-di-tert-butyl-4-(tellurobutyl-4′-phenoxy)phenol, and 338.8 for 6-octyltelluro-3-pyridinol. The stabilization energies of phenoxyl radicals containing R substituents (X = O, S, Se, Te) have been compared.     

Measuring the rate constant of the reaction between chlorine atoms and CHF<Subscript>2</Subscript>Br by Cl atom resonance fluorescence

The rate constant of the reaction between Cl atoms and CHF₂Br has been measured by chlorine atom resonance fluorescence in a flow reactor at temperatures of 295–368 K and a pressure of ~1.5 Torr. Lining the inner surface of the reactor with F-32L fluoroplastic makes the rate of the heterogeneous loss of chlorine atoms very low (k_het ≤ 5 s^–1). The rate constant of the reaction is given by the formula k = (4.23 ± 0.13) × 10^–12e^{(–15.56 ± 1.58)/RT} cm³ molecule^–1 s^–1 (with the activation energy in kJ/mol units). The possible role of this reaction in the extinguishing of fires producing high concentrations of chlorine atoms is discussed.     

Thermal stability of surface nitrogen–oxygen complexes and phase transitions in ZrO<Subscript>2</Subscript>

The IR spectra of surface compounds observed in the course of the temperature-programmed desorption (TPD) of NO_x and the TPD spectra are compared. The high-temperature peaks of desorption are related to the decomposition of surface nitrites and nitrates. The low-temperature peaks of NO_x desorption with maximums below 140°C are caused by the decomposition of surface nitrosyls. On the heating of surface nitrosyls, the following two reaction paths are possible: desorption at low temperatures and conversion into nitrates. The shape of the TPD spectra of NO depends on the phase composition of test samples. The transition of a tetragonal phase into a monoclinic one occurred upon the surface dehydroxylation of polycrystalline particles with the formation of particles with a tetragonal nucleus and a monoclinic crust. This transition is reversible. The cooling of a sample in a moist atmosphere leads to the transition of the monoclinic crust to the tetragonal phase.     

Phase equilibria in the Tl-TlCl-Te system and thermodynamic properties of the compound Tl<Subscript>5</Subscript>Te<Subscript>2</Subscript>Cl

The Tl-Te-Cl system was studied in the Tl-TlCl-Te composition region by differential thermal analysis, X-ray powder diffraction, and emf and microhardness measurements. A series of polythermal sections, an isothermal section at 400 K, and a projection of the liquidus surface of the phase diagram were constructed. The ternary compound Tl₅Te₂Cl characterized by a wide homogeneity region and incongruent melting by a syntectic reaction at 708 K was shown to exist. This compound was found to crystallize in tetragonal lattice (space group I4/mcm) with the parameters a = 8.921 Å, c = 12.692 Å, Z = 4. Wide phase separation regions were also found in the system, including a three-phase separation region in the Tl-TlCl-Tl₂Te subsystem. Regions of primary crystallization of phases, and the types and coordinates of in- and monovariant equilibria in the T-x-y diagram were determined. From emf measurement data, the standard thermodynamic functions of formation and the standard entropy were calculated for the compound Tl₅Te₂Cl, as follows: ?ΔG ₂₉₈ ⁰ = 355.9 ± 1.1 kJ/mol, ?ΔH ₂₉₈ ⁰ = 377.1 ± 5.0 kJ/mol, and S ₂₉₈ ⁰ = 474.1 ± 6.8 J/(mol K).     

Determination of Rutin in Drinks Using an Electrode Modified with Carbon Nanotubes-Prussian Blue

A new sensor was developed using a screen-printed carbon electrode modified with single-walled carbon nanotubes (SWCNTs) and Prussian blue (PB) coated with chitosan. The modified electrode allowed the oxidation and reduction of rutin at 0.25 and 0.096 V, respectively, with a ΔE of 0.154 V. Furthermore, the peak currents increase nearly 100% compared with the electrode without modification. The process was more reversible compared with the electrode modified with only SWCNTs or PB. Cyclic voltammetry was used to characterize the modified electrode surface. The quantification of rutin was more sensitive with adsorptive stripping voltammetry than with anodic stripping voltammetry. Adsorption potential, adsorption time and pH were optimized based on the oxidation of rutin: E_ads =–0.10 V, t_ads = 60 s, pH 3.0. The detection limit (3σ/b) was 0.01 μM and the relative standard derivation was 3%. The new sensor was used in the quantification of rutin in black tea, coffee and synthetic drink of tea with satisfactory results.