In recent years, research of metal oxide semiconductor-based sensors has focused on morphology modification of thin film structures. One of the promising materials that is being developed is SnO₂. In this research, nanostructured SnO₂ thin film was grown using the ultrasonic spray pyrolysis and chemical bath deposition methods with and without external magnet assistance (0.1 T). As precursor solution of the ultrasonic spray pyrolysis process, the SnCl₂·2H₂O is dissolved in distilled water, with pH varied by adding 37% HCl solution. The precursor solution for the chemical bath deposition process was SnCl₂·2H₂O, which is dissolved in urea solution with pH customized by adding the NaOH solution. All resulting nanostructured SnO₂ thin film samples were characterized by using X-ray diffraction and scanning electron microscopy techniques. The resulting morphologies of SnO₂, prepared by chemical bath deposition, using magnetic field, HMTA framework-assisted chemical bath deposition, and ultrasonic spray pyrolysis are spherical, cubic, and spherical, respectively. The sensor response pattern of nanostructured SnO₂ thin films, prepared by all tested methods, to 30 ppm CO, is similar in that the response increases with the increase of working temperature. The SnO₂ thin film prepared by ultrasonic spray pyrolysis method shows the greatest sensitivity value of 95.12%, with a response time of 216 seconds and a recovery time of 558 seconds, at working temperature of 300 degrees Celsius.
The objective of this work is to produce activated carbon from sugar beet molasses containing TiO₂ for CO₂ adsorption and reduction. Textural properties of activated carbons were obtained based on the adsorption-desorption isotherms of nitrogen at 77 K. The specific surface areas of activated carbons were calculated by the Brunauer-Emmett-Teller method. The volumes of micropores were obtained by density functional theory method. The adsorption isotherms of CO₂ were measured up to the pressure of 1 atm at a temperature of 40°C. The best activated carbon adsorbed 1.9 mmol/g of CO₂.
The aim of the investigations was a modification of DTO, a commercial activated carbon (AC), to improve CO₂ adsorption capacity. The adsorption of CO₂ up to 40 bar at 40°C temperature was investigated. The volumetric method was applied for CO₂ adsorption isotherm measurements. The starting material - DTO - was modified using chemical activation (KOH, ZnCl₂, K₂CO₃). The textural parameters of all the ACs were determined by nitrogen adsorption at the liquid nitrogen temperature of -196°C on Quadrasorb SI. Results showed that the AC modified with KOH had the highest S_{BET}, V_{tot}, V_{mic} values of 2063 m²/g, 1.13 cm³/g, and 0.67 cm³/g, respectively. ACs with a wider pore size distribution (from micropores to mesopores) were obtained. The maximum CO₂ adsorption was equal to 14.44 mmol/g for DTO/KOH - modified carbon whereas 8.07 mmol/g of CO₂ was adsorbed at DTO. The CO₂ adsorption capacities of the ACs were found to be closely correlated with the BET surface areas of the materials tested. The experimental data was fitted to the Freundlich, Langmuir, Sips and Toth equations to determine the model isotherm. The Sips model was found to be the best for fitting the adsorption of CO₂.
Aim of this research is to obtain effective, molasses based activated carbon, which would adsorb big amounts of CO₂. Molasses was mixed with KOH. Weight ratio of dry materials was 1:1 (AC1, AC3) and 1:2 (only AC2). Homogeneous mixture was obtained. Material was left for 3 h at 25°C. Drying lasted for 12 h at 200°C, and the material was grounded. The mixture was pyrolysed at 750°C, under constant flow (18 dm³/min) of nitrogen. The material was grounded again. Then, powder was washed with water, until filtrate was neutral, which took about 5 dm³ of water. AC3 was washed with 1 dm³ of water. After drying, materials were soaked in HCl (0.1 mol/dm³) for 19 h, and washed with water, until filtrate was neutral. CO₂ adsorption was performed under high pressure up to 40 atm, at 40°C. Specific surface area (according to the Brunauer-Emmett-Teller equation) was calculated for AC1, AC2 and AC3 and it is respectively 1985, 1967, and 2026 m²/g, micropore volume - 0.714, 0.707, and 0.728 cm³/g and it was between 75% and 89% of total pore volume. The excess uptake at 40 atm pressure was as follows: AC1 - 14.02 mmol/g, AC2 - 12.75 mmol/g, and AC3 - 15.79 mmol/g.
In this work gasochromic effect in TiO_{2} thin films doped with palladium and tantalum (without catalyst film) have been described. The results have shown that in nanocrystalline TiO_{2}:(Ta, Pd), with anatase structure, the film colorization effect in alcohol presence was observed. Both colorization and also bleaching effect were stable and thermally activated.
The concentration of helium in groundwater may be a good environmental tracer for groundwater dating in hydrogeology. In this work, we present a chromatographic method for simultaneous analysis of helium, neon, and argon in groundwater from a single groundwater sample. Proper use of environmental tracers for dating purposes requires the knowledge of the recharge temperature of the system and the excess air. Both parameters can be determined by measuring the concentration of argon and neon in groundwater. The lowest helium concentration in groundwater is 4.8×10¯⁸ cm³_{STP}/g_{H₂O} at sea level and temperature 10°C. In view of the deficiency of a suitable detector with a limit of detection for helium at the level of 4.8×10¯⁸ cm³_{STP}/g_{H₂O}, the application of the enrichment method is necessary. In this work, the cryogenic method of enrichment with activated charcoal at abated pressure conditions was applied. Helium, neon and argon are analyzed on two gas chromatographs equipped with capillary and packed columns (filled with molecular sieve 5A and activated charcoal) and three thermo-conductive detectors. The chromatographic method was applied to groundwater dating from Kraków and Żarnowiec aquifers. The levels of detection for measurement systems for the tested compounds are: 1.9×10¯⁸ cm³_{STP}/cm³ for neon, 3.1×10¯⁶ cm³_{STP}/cm³ for argon, and 1.2×10¯⁸ cm³_{STP}/cm³ for helium.
A mixture of antiferromagnetic Cu_{1.4}Mn_{1.6}O₄ and Cu_{0.5}Zn_{0.5}Mn₂O₄ or/and ZnMn₂O₄ spinels was prepared. Dealuminated HY zeolite and silica were doped by these Cu-Mn-Zn spinels. The materials were investigated by X-ray diffraction, the Fourier transform infrared spectroscopy and EPR spectroscopy. Additionally, all the samples were tested for their activity for isopropyl alcohol dehydration/dehydrogenation. Three EPR signals were observed for Cu-Mn-Zn/dealuminated HY and Cu-Mn-Zn/SiO₂ samples at 293 K. In contrast to the spectra recorded at 293 K, only one broad line attributed to Cu-Mn-Zn spinels was visible at 77 K. The EPR signal from pure Cu-Mn-Zn spinels consists only of a single broad line when recorded at 293 K, whereas at 77 K the line is narrower. For all samples subjected to evacuation at high vacuum up to 573 K, the Cu-Mn-Zn spinels were stable. The evacuation at 673 K resulted in a rapid lowering of the intensity of EPR spectrum.
The aim of this paper is to summarize the results of experiments carried out at our laboratory on the response of the work function of several thin films of transition metals and rare earth metals to interaction with molecular hydrogen. The main focus concerns the description of surface phenomena accompanying the reaction of hydride formation as a result of the adsorbate's incorporation into the bulk of the thin films. Work function changes Δ Φp caused by adsorption and reaction concern the surface, hence this experimental method is appropriate for solving the aforementioned problem. A differentiation is made between the work function changes ΔΦp due to creation of specific adsorption states characteristic of hydrides, and ΔΦp arising as a result of surface defects and protrusions induced in the course of the reaction. The topography of thin metal films and thin hydride films with defects and protrusions was illustrated by means of atomic force microscopy. For comparison, the paper discusses work function changes caused by H_2 interaction with thin films of metals which do not form hydrides (for example platinum), or when this interaction is performed under conditions excluding hydride formation for thermodynamic reasons. Almost complete diminishing of ΔΦp was observed, in spite of significant hydrogen uptake on some rare earth metals, caused by formation of the ordered H-Y-H surface phase.
Changes in bulk single grain YBCO superconductor at exposition to air were studied. The increase of the sample weight caused by reaction with air moisture was observed by weighing the samples over two months period. Thermal analyses and mass spectrometry of the exposed samples has shown evolution of water and oxygen during sample heating. Observation with scanning electron microscope confirmed the formation of some nanosize phases at the inner sample surfaces. XPS spectra done on the freshly cleaved and on the air exposed (001) surfaces confirmed changes in Ba and Cu bonds. Observed structural changes did not caused systematic changes in measured trapped field.
For the first time the thermal desorption of H_2, N_2, O_2 and CO_2 is presented for antimony sulfoiodide (SbSI) xerogel made up of large quantity nanowires. The desorption has been observed near ferroelectric phase transition established at T_{c}=293.0(2) K. The Sievert measurements have shown that the hydrogen uptake is linear function of H_2 pressure (when p < 1.1×10^5 Pa). The hydrogen storage density in SbSI gel amounted 1.24× 10^{-2} wt% (for p = 1.08×10^5 Pa at room temperature).
We study adsorption of the benzene molecule on the Si terminated (0001) surface of 4H-SiC by performing first principles calculations in the framework of density functional theory. We find out that chemical reaction leading to the chemisorption of benzene on the surface has endothermic character. The adsorbed benzene molecule is bounded to two surface Si atoms and it does not lose its integrity, however, it undergoes strong deformations and causes distortion of the substrate. We analyze also changes in the electronic structure caused by benzene adsorption.
Partial blocking of mesopores in the ordered MCM-41 silica by DC550 silicon oil was proposed as a preparation method of the material with controlled porosity and fixed pore size. The porosity of the samples with various content of DC550 was examined with the use of low temperature nitrogen sorption and positron annihilation lifetime spectroscopy. It was shown that the oil blocks the primary pores by forming the plugs near its entrances, but also partially locates in the interparticle spaces. The comparison of the results obtained from both investigation techniques was used to make the first attempt to obtain the calibration of ortho-positronium intensity, depending on pore volume. This is necessary to improve the utility of positron annihilation lifetime spectroscopy as a porosimetric technique. The need to take the migration of positronium to larger free volume into account is discussed.
We present the results of ab initio calculations of gas adsorption processes on graphene. Static density functional theory framework is used to obtain adsorption energies of several species on a Stone-Wales defected graphene monolayer. The Van der Waals interaction is taken into account by a semi-empirical correction. Sites closer to the defect are found to induce stronger adsorption compared to sites further away, where the graphene crystal structure is intact. The Car-Parrinello ab initio molecular dynamics simulations are performed at high temperatures. CH₃ is found to be stably physisorbed or chemisorbed at 300 K.
Relative work functions of vicinal surfaces to the (100) plane copper surface were determined from the Δ ϕ changes during adsorption of potassium. The initial value of the work function of the different planes was determined from its saturation value under the condition that it corresponds to the potassium overlayer of the same structure and density. It was found that the work function decreases linearly with step density for this step orientation.
PbTe and its solid solution (Pb,Cd)Te containing 2% of CdTe and PbTe grown by self-selecting vapour growth technique were investigated by inelastic X-ray scattering using synchrotron radiation. The ID28 beamline at ESRF with the incident photon energy of 17794 eV and the energy resolution of 3 meV was applied for that purpose. The measurements were performed at room temperature along [001]-type high symmetry direction in the Brillouin zone. In spite of a very low energy of phonon branches they can be determined by inelastic X-ray scattering with a high accuracy. The transversal acoustic phonon dispersion obtained by inelastic X-ray scattering corresponds well to those resulting from inelastic neutron scattering measurements and ab initio calculations. Apart from expected structures corresponding to the bulk phonons an additional scattering related to the crystal surface properties was observed in the inelastic X-ray scattering spectra. The analysis performed with the use of secondary ion mass spectroscopy technique demonstrated a presence of a thin oxide layer at sample surfaces.
The main common idea of two conference papers delivered at OMEE-2017 was to demonstrate an importance of the speciation level knowledge in modern adsorption materials science. In order to prove this, two groups of adsorptive materials were used: three samples of Mg-Al-CO₃ layered double hydroxides produced by different synthesis methods and ten samples of Fe-Ce oxide-based composites with various ratios of Fe-to-Ce. In both cases of studies, it was not possible to find direct correlation between adsorptive performances of the materials and their structural properties obtained by conventional characterisation techniques. However, anion adsorptive removals of each group of inorganic composites correlated with their structural properties studied on the level of speciation. It was shown that strong anion removal potential of Mg-Al-CO₃ layered double hydroxides was associated with richness in speciation of chemical elements (Mg, Al) and interlayer anions (CO₃²¯) as well as with generous hydration. Adsorptive performances of inorganic anion exchangers based on Fe-Ce hydrous oxides were explained by simulation extended X-ray absorption fine structures simulation. The best anion removers were found to be those Fe/Ce oxide-based composites whose Fe outer shells were formed from backscattering oscillations from both O and Fe atoms.
Ti/TiN multilayer films with a few multilayer periods and a total sub-μm thickness were deposited on AISI 304 stainless steel substrates by ion coating deposition technique. To investigate the effect of hydrogen treatment on the corrosion behavior of the multilayers, some of the samples were hydrogen treated after deposition of the first and/or the second Ti interlayer. ^{14}N(d,α_1) ^{12}C nuclear reaction and the Rutherford backscattering spectrometry were used to obtain the atomic composition profiles and thickness of Ti/TiN layers. Nuclear reaction analysis confirmed the presence of two separable TiN layers of comparable thickness on the surface and in depth of the two-period multilayers. These techniques were used to determine the thickness of individual Ti and TiN layers and revealed that the stoichiometry of TiN layers was approximately Ti:N=1:1. Hydrogen depth profile in the prepared samples was obtained by elastic recoil detection analysis. It was found that a remarkable volume of hydrogen was uptaken by the Ti layer in the hydrogen treated samples. The TiN (200) diffraction peak in the X-ray diffraction pattern was observed with different intensities depending on the sample preparation parameters. The corrosion behavior of the multilayers was studied by means of potentiodynamic polarization in 0.5 M NaCl solutions. It was found that the hydrogen treatment of Ti interlayer could potentially improve the corrosion properties of the Ti/TiN layers.
The constant adsorption energy surfaces for hydrogen adsorbed on Si- and C-terminated hexagonal 4H-SiC{0001} surfaces have been calculated within density functional theory framework. The two unreconstructed and one reconstructed √3 × √3 surfaces were taken into account. We show that on all surfaces there is a global energy minimum indicating the most favourable adsorption site corresponding to H atom adsorption on-top of the topmost substrate layer atom. In case of reconstructed surface, there is another small and shallow local minimum. Moreover, the diffusion barrier is much higher at reconstructed surface than at unreconstructed ones.
The sorption properties of Transcarpathian clinoptilolite towards Nd(III) and Gd(III) under dynamic condition have been studied. Nd(III) was sorbed with the best efficiency on the uncalcined clinoptilolite samples from the solutions at pH 6.5. Clinoptilolite samples that were previously calcined at 250°C exhibit the maximal sorption capacity towards Gd(III) from the solutions at pH 9.5. Nd(III) and Gd(III) sorption on clinoptilolite mechanisms are different: Nd(III) is sorbed according to the ion-exchange mechanism, and the sorption of Gd(III) is carried out mainly by means of the adsorption of soluble hydrolyzed forms of Gd(III) on the zeolite surface. The differences in sorption mechanisms of these lanthanides give an opportunity to separate Nd(III) and Gd(III) from the solutions at pH 9.5. The maximal sorption capacity of the clinoptilolite regarding Nd(III) and Gd(III) at the optimal conditions was found to be 1810 and 6500 μg/g. The best desorbent of Nd from the clinoptilolite is 7 M HNO₃ solution. The best desorbent of Gd is 1 M solution of KCl acidified to pH 2.6, which provides a 100% withdrawal of Gd from the zeolite matrix. Transcarpathian clinoptilolite is proposed as a sorbent for the preconcentration of trace amounts of Nd(III) and Gd(III) from aqueous solutions in a solid phase extraction mode.
Magnetic nanostructured materials have been found to be very efficient in wastewater decontamination. Among the various synthesis methods, co-precipitation is a rapid and cost-effective technique for the manufacturing of magnetic nanoparticles; moreover, using green chemistry for their stabilization with natural non-toxic capping agents in aqueous solution, such materials become potential candidates as nanocatalytic formulations for water remediation, topic which represents the aim of the present study. Thus, three types of environment-friendly magnetic fluids were synthesized using the chemical precipitation route, the resulted samples being further characterized by various analytical techniques, in order to assess their microstructural features. The results revealed excellent stability in suspension of all samples, the magnetite nanoparticles exhibiting sizes in the nanoscale range with a relatively spherical shape and suitable magnetic properties. Such nanoparticle based products could be the right choice for magnetic responsive and recyclable materials used in the degradation of emerging pollutants from wastewaters.
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