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Adsorption of methane, ethane and propane and their coadsorption with hydrogen on evaporated palladium thin films at 195 K and 298 K was investigated by means of surface potential change measurements, observation of gas phase composition and volumetric measurements. Adsorption at 195 K occurs without any significant decomposition of hydrocarbon admolecules, while at 298 K approximately 10% of the total deposit of ethane and propane can be decomposed. Propane admolecules strongly promote the incorporation of coadsorbed hydrogen adatoms into the bulk of palladium film at 195 K.

Hydrogen adsorption on thin iron films was studied through the application of surface potential measurements by means of a rapidly and continuously recording static capacitor system and by TDS experiments. Three electronegatively polarized states of the adsorbate were detected: (i) strongly bound β - S adatoms, (ii) weakly bound β - W atomic adspecies, and (iii) molecular deposit denoted α - E . Thermal disorder on the surface diminishes the average dipole moments and the depolarization effect within the β - S adspecies.

The kinetics of hydrogen interaction with thin cobalt films at 78 K have been studied by means of sticking probability and surface potential changes (ΔSP) measurements and by thermal desorption mass spectrometry (TDMS). Hydrogen was found to adsorb with a high initial sticking coefficient ( S 0 close to unity). The mechanism of hydrogen incorporation into the bulk of Co film has been analyzed. Three TDMS peaks were detected. The TDMS peak arising from hydrogen adsorbed at equilibrium pressure > 1×10 −6 Torr was attributed to the desorption of hydrogen species incorporated into the bulk of Co film. A detailed analysis of the isothermal desorption of a weakly adsorbed hydrogen adspecies has been performed.

A rapidly-recording, static-capacitor method was used to study surface potential changes that occur during ethylene adsorption on Ni, Pd, and Pt films at 298 K. A precise dosing system for the introduction of gases and a careful determination of the roughness factor allowed us to relate the surface potential to the concentration of the various adsorbed species. Using this information we propose a mechanism for ethylene selfhydrogenation. Ethylene admolecules adsorbed in the second layer react readily with hydrogen whereas those from the first layer do not. On platinum films, only the electropositively-polarised β + hydrogen adatoms are reactive with ethylene, but with Ni and Pd films only the electronegatively-polarised β − hydrogen adatoms are reactive.

The sticking probability S(θ) for hydrogen adsorption on thin iron films have been measured within the pressure interval of 10-10-10-1 Torr, over both the adsorption states β-S and β-W. The role of the precursor state and the mutual interaction is shown.

The kinetics of surface potential changes in palladium films was studied in order to investigate the possibility of determining surface areas of these films by means of adsorption of oxygen or hydrogen and by titration of preadsorbed oxygen with hydrogen or preadsorbed hydrogen with oxygen at 348–370 K. It was found that the incorporation of oxygen in the bulk of palladium films and the occurrence of unreactive forms of the adsorbate in the case of titration of preadsorbed hydrogen with oxygen as well as desorption of hydrogen during the evacuation of the apparatus complicate the problem to such an extent that the volumetric method alone is inadequate. This method can be used for the determination of the surface area of palladium films only when combined with a determination of the kinetics of surface potential changes or some other method which makes it possible to follow the behaviour of the adsorbate on the surface of the metal.

The nature of hydrogen adsorption on thin platinum films at 78, 195, 273 and 298 K has been studied by means of sticking probability measurements and thermal desorption mass spectrometry (TDMS). A high value of the initial sticking coefficient (S0 ≈ 0.95) was found at all temperatures. The behaviour of the sticking probability S as a function of hydrogen coverage θ has been analyzed. Three TDMS peaks of hydrogen were detected on Pt films when the adsorption was carried out at 195 K. The TDMS analysis carried out for hydrogen adsorbed at 78 K, revealed the existence of a molecular form of hydrogen deposit.

The kinetics and thermodynamics of hydrogen adsorption on thin cobalt films at 195, 273 and 298 K have been studied by means of sticking probability measurements, thermal desorption mass spectrometry (TDMS) and examination of adsorption isotherms. The dissociative adsorption occurs with a high initial sticking coefficient ( S 0 close to unity) at all temperatures. The behaviour of the sticking probability S as a function of hydrogen coverage θ has been analyzed. Two TDMS peaks were detected when hydrogen adsorption was carried out at 195 K. The isosteric heat of adsorption remains constant at 286 K up to θ ≈ 0.5 and then decreases indicating the arising of a new adsorbed state of hydrogen at θ > 0.5. A detailed analysis of the adsorption entropy for T ≈ 286 K has been performed.

It has been proved that hydrogen atoms desorb from the surface of a decomposing thin palladium hydride film. A thin gold film deposited and sintered in situ was used as a selective adsorbent for atomic hydrogen. The TDMS (thermal desorption mass spectrometry) technique was applied to detect the adsorption of hydrogen on gold and to determine the amount adsorbed.

Hydrogen adsorption on evaporated Co films has been studied by means of measurements of the surface potential changes that occur during this process, and analysis of the desorption spectrum of hydrogen. It has been observed that hydrogen adsorbed at 78 K on Co films exists in three forms with essentially different electrical properties: atomic, electronegatively polarized β− form; atomic, electropositively polarized β+ form and reversibly adsorbed, molecular, positively polarized α form. The β− form is not homogeneous from the point of view of the bond energy with the metal surface and consists of the states βs− and β− characterized by activation energy of desorption 10.0 and 18.8 kcal/mol H2 correspondingly. The Activation energy of desorption of the β+ form is low, i.e. 2.1 kcalmol H2.

Publisher Summary This chapter describes the adsorption of alkanes and their coadsorption with hydrogen on evaporated palladium thin films. Adsorption of methane, ethane, and propane and their coadsorption with hydrogen on evaporated palladium thin films at 195 K and 298 K is investigated by the means of surface potential change measurements, observation of gas phase composition, and volumetric measurements. Adsorption at 195 K occurs without any significant decomposition of hydrocarbon admolecules while at 298 K, approximately 10% of total deposit of ethane and propane can be decomposed. Propane admolecules promote incorporation of coadsorbed hydrogen adatoms into the bulk of palladium film at 195 K.

The measurements of surface potential (SP) have been carried out to distinguish between elementary steps of surface processes accompanying the formation of weakly bound oxygen state on thin Fe, Pd and Ti films at 78 K. This state appears under the oxygen pressure higher than 10−2 Pa, following the strong chemisorption of oxygen adatoms. Both adsorption and desorption phenomena have been carried out under isothermal conditions. It has been found that weakly bound (activation energy of desorption < 18 kJ/mol), positively polarized oxygen admolecules (δ+), are present on Fe, Pd and Ti surfaces at 78 K, being located on the top of strongly chemisorbed oxygen adatoms. The electrical nature of O2 ordering in the weakly bound oxygen layer has also been considered.

The surface layers were formed on titanium by plasma electrolytic oxidation (PEO) in the solutions which contain various amounts of Na2SiO3x5H2O, Na3PO4x12H2O and Ca(CH3COO)2xH2O. The layers were characterized using a scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) and an X-ray diffractometer (XRD). The titanium/oxide surface layer interface was analyzed by X-ray photoelectron spectroscopy (XPS). The adhesive strength of the oxide layers was evaluated by the scratch-test. The bioactivity of the surface was determined by soaking in a simulated body fluid (SBF) for 7 and 30 days. The corrosion resistance was determined by electrochemical methods after 13, 181, and 733 h exposure in SBF at a temperature of 37°C. The oxide layers obtained were rough and porous and enriched with Ca, P, Si, and Na and their properties depended on the concentration of the components of the electrolyte. The results of the electrochemical examinations, after a 13 h exposure in SBF, show that the surface modification by PEO improves the corrosion resistance of titanium and it is not degraded after a long-term exposure in SBF. The electrochemical impedance spectroscopy (EIS) results indicate that the surface layers have a complex structure. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2012.

Thin Fe films, evaporated on glass, appears to be a very useful catalytic material applied for "in situ" investigation of gas adsorption [1, 2] and multigas interactions [3, 4]. It is common practice for these films to be deposited at liquid nitrogen or room temperature, and then heated to higher reaction temperature. This annealing procedure changes the structure of the film. However, in spite of the wide applications, experimental investigation of Fe film structure during such annealing treatment is relatively scarce [5]. It is our aim to partially fill this gap by investigating the morphology and structure of thin Fe films evaporated onto a quartz substrate at 78 K followed by annealing within a wide temperature range. We have found that the temperature and duration of annealing play a crucial role in this process [6].

Correction for ‘Titania/chitosan–lignin nanocomposite as an efficient photocatalyst for the selective oxidation of benzyl alcohol under UV and visible light’ by Ayesha Khan et al., RSC Adv., 2021, 11, 34996–35010. DOI: 10.1039/D1RA06500A

A molecularly imprinted polymer (MIP) film based electrochemical sensor for selective determination of tyramine was devised, fabricated, and tested. Tyramine is generated in smoked and fermented food products. Therefore, it may serve as a marker of the rottenness of these products. Importantly, intake of large amounts of tyramine by patients treated with monoamine oxidase (MAO) inhibitors may lead to a “cheese effect”, namely, a dangerous hypertensive crisis. The limit of detection at S/N = 3 of the chemosensor, in both differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) determinations, with the use of the Fe(CN)64-/Fe(CN)63- redox probe, was 159 and 168 µM tyramine, respectively. The linear dynamic concentration range was 290 µM to 2.64 mM tyramine. The chemosensor was highly selective with respect to the glucose, urea, and creatinine interferences. Its DPV determined apparent imprinting factor was 5.6. Moreover, the mechanism of the “gate effect” in the operation of the polymer film-coated electrodes was unraveled.