Vol 55, No 3 (2019)

Adsorption of hydrogen in four types of activated carbons of different origin with specific micropore volumes ranging from 0.46 to 0.96 cm³/g is studied at temperatures of 303, 313, 323, and 333 K and pressures up to 20 MPa. The saturation adsorption of hydrogen vapors in the considered types of activated carbons is calculated at the hydrogen boiling point (20.38 K) and a pressure of 0.101 MPa using the Dubinin theory of volume filling of micropores (TVFM). The theoretical calculations show that the type FAS-2008 adsorbent, which is produced using liquid-phase furfural polymerization, has the highest adsorption capacity. Using the TVFM and taking into account linearity of the adsorption isosteres, we also estimate adsorption of hydrogen in the type AU3:5 slit-shaped microporous carbon adsorbent at a temperature of 303 K and pressures 10 and 20 MPa. The collected experimental data and theoretical calculations are compared to the data for 101 kPa and 20.38 K. The highest hydrogen adsorption, 7.9 wt %, at 20 MPa and 303 K is predicted for a model slit-shaped microporous graphene-based adsorbent, type AU3:5.

Spherical carbon adsorbents have been synthesized with introduction of mesoporous MCM-48; their adsorption activity towards toxic components of cigarette smoke including nicotine has been studied with the purpose of application as fillers for filters in smoking rooms. The structure-sorption properties of the surface, as well as the composition of the surface layer of the carbon material, have been examined by means of low-temperature adsorption/desorption of nitrogen, X-ray photoelectron and IR-spectroscopy, and pH- and conductometric titration. It has been demonstrated that upon carbonization and activation the surface layer of the synthesized carbon adsorbents contained protolytically active carboxyl (0.1; 0.35 mmol/g) and hydroxyl groups, as well as a wide range of other oxygen-containing groups. The synthesized material has demonstrated a narrow pore size distribution (5–9 nm), while micropores were virtually absent. It has been established that the spherical mesoporous activated carbon synthesized in the present study with having a developed specific surface area of 1680 m²/g and the sorption capacity towards nicotine of 9.2 mmol/g has demonstrated superior properties exceeding those of the commercially produced material. Total chemical regeneration of the adsorbents (up to five to seven cycles) has been achieved through extraction by organic solvents (chloroform or methanol) without subsequent thermal treatment. Interaction of gaseous products of cigarettes burning with the spherical carbon samples occurred throughout the whole volume and not only on the external surface. It has been demonstrated that the investigated adsorbents can be applied in both stationary smoking rooms and cabins equipped with autonomous ventilation.

Mineral adsorbents, such as talc, are materials that are abundant in nature and used as scavengers, binding agents, fillers, etc. Mechanical and physicochemical pretreatment creates new opportunities for the production of highly effective mineral materials with a wide range of destinations. The possibility of using various techniques to enhance the adsorption properties of dispersed talc, namely, enrichment and use in a mixture with another mineral, treatment with various reagents, and changing the temperature and acidity conditions, is demonstrated. Phenomena and trends having an effect on the adsorption ability of talc are considered. Surface modification of talc can significantly increase its technological capability of absorbing resinous components of wood pulp in the manufacture of paper. It is shown that the adsorption and structural characteristics of dispersed talc change significantly after modifying it with organic reagents. The best effect is achieved when pretreating talc with cationic surfactant N-cetylpyridinium chloride. The resulting adsorbent is characterized by a high value of rosin adsorption, reaching 200 mg/g, which is commensurate with the data on the absorption of rosin by talc pretreated with a Penta-416 industrial mixture. Substantial changes in the surface properties due to an increase in the temperature, a change in the acidity, and a shift in the hydrophilic-hydrophobic balance occur when using the accessible, affordable, and safe anionic surfactants. The highest value of adsorption of rosin (160–170 mg/g) is typical for samples of talc modified with sodium oleate and enriched with zinc oxide. The importance of pretreatment of talc with solutions of mineral acids and salts that promote settling of suspensions and the formation of a compact precipitate is shown.

The excess adsorption isotherms of cumene from solutions in n-octane in zeolite NaX have been measured at 303.15, 338.15 and 363.15 K using the conventional static method. The absolute (limiting) adsorption values of the pure components have been measured by the pycnometric method. The absolute adsorption isotherms for the system have been calculated using a non-fitting three parameter equation, based on the modified Dubinin–Radushkevich one. The detailed derivation of the formulas for these calculations is given. The absolute adsorption data are then used for estimation of average adsorbate density and other characteristics of the adsorbed phase.

The possibility of using a reduced form of graphene oxide (RGO) and unreduced form of graphene oxide (GO) as a potential basis to be used for “designing” supramolecular structures was illustrated by the example of three different types of particles. As it can form bonds of various nature, GO may be also used (being in the reduced form) as an electrically conducting component of a composite and (remaining in the non-conducting oxidized form) as an accumulator of any particles. The electrochemical behavior of the obtained composites was studied.

Zinc oxide (ZnO) is the most commonly and widely studied material in the field of nano science and technology due to its unique characteristics, such as wide band gap energy (3.37 eV), electrical and thermal stability, large exciton binding energy (60 meV), biocompatibility and biosafety. Copper is considered as an important dopant for ZnO due to their almost similar ionic radii which enhances the properties of ZnO. Thus, pure and copper-doped nanocrystalline ZnO particles were synthesized through sol–gel approach in the current study. The concentration of the dopant is varied from (0.1–0.3%) and the composition, structural and optical characterizations were performed by using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, UV-Vis optical absorption and photoluminescence (PL) spectrometer. The structural analysis confirmed that copper ions substitute Zn ions without altering their wurtzite structure and a crystallite size of 10–16 nm with high degree of crystallization. Morphological properties conducted using SEM confirmed copper doping strongly influenced the grain size and morphology of ZnO NPs. Moreover, the morphology variation is observed from spherical nanoparticles to nanorods with Cu (0.2%) doping into host matrix. The morphological variation may be attributed to strong influence of Cu ions on the growth rate of ZnO. PL measurement had been carried out at room temperature in which high intensity broad emission peaks were observed in visible region around 450–700 nm that indicates the superposition of green and yellow-orange emission bands. Currently, light-emitting diodes (LEDs) giving green light emission have been combined with broad-band visible phosphors to make white-light LEDs. Thus, green photo luminescent copper-doped ZnO nanoparticles from the current study is highly significant in the fabrication of white-light LEDs.

The process of aging of water-soluble formulation based on polyaniline with poly(2-acrylamido-2-methyl-1-propanesulfonic acid) complex was studied by controlling the value of pH, optical absorption spectra, the rheological properties of its solutions, and the specific conductivity of the films cast from the studied solutions. It was shown that solutions of water-soluble compositions based on polyaniline acquire stable characteristics after 6-week storage; these characteristics are retained for at least 6 months. They can be used for technological processes (inkjet printing, spin coating, dip-coating) for obtaining functional layers for optoelectronics.

The structure and properties of Ti–B–N, Ti–Cr–B–N and Ti–Si–B–C–N coatings, deposited by magnetron sputtering are investigated. Various approaches to increasing adhesion strength are considered: deposition of sublayers, application of a high bias voltage at the beginning of deposition, preliminary ion etching of a substrate, and implantation by high-energy ions at various stages of deposition. Scratch testing is used to evaluate coating adhesion.

Using stationary electrolysis, the effect of the structure and concentration of some organic acids on kinetic parameters of electrodeposition of nickel from sulfate electrolytes containing cyclic lactams, such as ε-caprolactam (CL) and N-methylpyrrolidone (MP), microstructure, mean grain size, and crystallite orientation has been studied. Integrated analysis of the data of polarization, adsorption, and spectral investigations has shown that enhancement of adsorption of amino acids in the presence of lactams leads not only to an increase in the polarization of the process, but also to significant changes of surface morphology. According to X-ray phase analysis and SEM data, the surface becomes smoother in the presence of amino acids, the grain size decreases, and a predominant orientation of crystallites appears in some cases. The formation of metal–polymer sharp-edged grains in the coatings prepared in the presence of CL and glycine has resulted in the formation of continuous smoothed layer and appearance of mirror shine of the deposits.

In this study, a set of multilayer hard nanocrystalline coatings of Al/AlN with 35, 55 and 75 bilayer were prepared by DC magnetron sputtering on AISI 52100 steel specimens at nitrogen fractions of 35 and 65% in the Ar + N₂ discharge. X-ray diffraction analysis indicates a polycrystalline structure of AlN + Al and AlN phases for 35% N₂ and 65% N₂ fraction, respectively. Nanoindentation tests showed hardness values from 11 to 19 GPa and elastic modulus of ~200 GPa almost independent of the bilayer number for both, 35% N₂ and 65% N₂. Tribological tests evaluated with a CSM pin-on-disk tribometer showed a reduction in the wear rate compared to AISI 52100 steel specimens. Multilayer coatings deposited at 35% N₂ fraction presented a lower friction coefficient than those coatings deposited at 65% N₂. The origin of such a decrease in the coefficient of friction was associated with the presence of the Al phase in the coatings deposited at 35% N₂. The wear mechanism for both 35 and 65% N₂ were different. For the first case, the wear is controlled by plastic flow and abrasive wear, while in the second case, is dominated by adhesive wear.

Anticorrosion performance of the sol–gel coatings was investigated for their applications to carbon steels. Cracking seemed to be a major problem in achieving the corrosion protection of the sol–gel coatings. It was found that some modifications from the original coating material such as the reduced particle size and structural change of the coating layer exerts a significant effect on the crack formation, which can be understood by the concept of critical thickness. Once corrosion occurred at the steel/coating interface, the cracking of the coating became accelerated as a result of oxide formation at the interface as it generates tensile stress on the sol–gel coating for the crack propagation. From the EIS analysis, it is demonstrated that the sol–gel coating would be not an ideal barrier for corrosion protection. Even though there was no crack on the coating, the charge transfer occurred through the film (frequency shift of time constant) with time, resulting in the corrosion at the steel/sol–gel coating interface with the crack propagation of the coating.

The corrosion resistance of reinforcing steels are of interest to the building and construction industry as it decides the durability of structures. These steels passivates under very high alkaline pore solution (leached solution from concrete). However, they corrode once they come in direct contact with chlorides ions (near sea coast and/or de-icing material) causing premature deterioration of the entire concrete structure. To protect steel bar from corrosion, they are alloyed with chromium (up to 0.50%) in steps to steel and their corrosion resistance behavior are compared with unalloyed rebar in chloride environment. In general, chromium addition in steel provides better corrosion protection through surface passivation than unalloyed one. However, in the present study, increase in chromium content in steel did not show a direct relationship to the corrosion protection of thermo mechanically treated (TMT) rebars. To ensure the corrosion protection of TMT rebars, the critical limit of chromium addition should be 0.3%. The corrosion resistance of the TMT with varying chromium content followed the following trends: TMT-0.5Cr > TMT-0.3Cr > TMT > TMT-0.1Cr.

The inhibition effect of expired Simvastan drug on Cu corrosion in 1 M HNO₃ at 25°C was investigated using potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS) and electrical frequency modulation (EFM) as well as weight loss (WL) measurements. Electrochemical studies data support that examined expired drug is an efficient inhibitor for mild steel corrosion. The adsorption of the examined drug obeys Langmuir’s adsorption isotherm. Polarization studies indicate that this inhibitor acts as a mixed type inhibition. The effect of temperature on corrosion inhibition has been studied and the thermodynamic activation and adsorption parameters were calculated and discussed. The protective film formed on the surface was confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The results collected from the studied techniques are in good agreement to confirm the ability of using expired Simvastan drug as corrosion inhibitor for Cu in acid media. The relationships between the inhibition efficiency (%IE) and some quantum chemical parameters have been discussed.

Here, by various electrochemical and analytical techniques, we have examined whether Eruca sativa aqueous extract can inhibit the corrosion of carbon steel in calcareous synthetic water. We detected differences in the morphology and phases of the films formed on the metallic surface under corrosion conditions. The electrochemical results suggest that, in the presence of E. sativa extract, the observed decrease in the corrosion current is associated with an increase in polarization resistance. EIS results reveal the presence of two time constants. The first one, at high frequency range (HF), is associated to the faradic process. The second one, at low frequency (LF), is related to the redox reaction occurring in the passive film. The highest inhibition efficiency, related to the large fraction of phenolic compounds present in the extract, can reach up to 95% with a dose of only 30 ppm.

Surface modifications of dental implants are of vital importance to enhance osseointegration and improve their corrosion resistance. This study characterized the surface properties of boron nitride (BN) coated titanium implants and their corrosion behaviors. Pretreated implant surfaces were coated successfully with BN by RF-magnetron sputtering system. Surface morphology and elemental composition of uncoated and BN-coated implant surfaces were examined by using X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) coupled with energy dispersive X-ray spectrometer (EDS). The corrosion tests were performed by use of artificial saliva. The tri-dimensional topography of the uncoated sandblasted, large-grit, acid-etched (SLA) implant surface showing sponge-like characteristics, revealed characteristic differences at micro level after BN-coating. It had more holes and peaks in addition to the sponge-like characteristics which further improved its surface microroughness. Boron-to-nitrogen ratio of the coated surface was obtained in the range of 0.8–1.6. The BN-coated SLA implant had no weight loss in the corrosion test. However, the surface characteristics of implants before coating had an impact on corrosion behavior of other implant types. The results demonstrated that titanium implants can be coated with BN successfully and this coating improves the surface properties of dental implants.

A double electric layer on carbon material has been studied for the first time in water in the temperature range from room temperature to 300°С. A decisive contribution of pseudocapacity, which is determined by the processes with surface groups, and the slowness of these processes has been stated from the dependence of current–voltage curves on temperature and the voltage sweep rate.