Beytullah Afsin

Abstract:

Abstract: X-ray powder diffraction (XRPD) analysis demonstrated that the main montmorillonite component of Unye bentonite was more effective in the Pb2+, Cu2+, Ni2+, Co2+, Zn2+, Al3+ and Fe3+ fixation processes in the interlayer space of the mineral than the nonclay fractions. All cation-exchanged bentonites experienced slight shifts in non-lattice bands whereas the features emerged at 3400 and 3200 cm−1 are unique to the newly inserted cations. The clay dehydration up to 150 °C and then the release of the water of the cation hydration shell in the temperature range of 150–300 °C were followed by dehydroxilation between 300 and 700 °C, after which no water remains in the bentonite structure. Additional features observed at elevated temperatures were assigned to the cation migration and the collapse of the clay framework. The surface areas of the Zn- and Fe-bentonites and those of the Pb-, Cu-, Ni-, Co- and Al-bentonites were found to be much higher and lower than that of raw bentonite, respectively, which were explained by the emergence of the micropores and medium mesopores in the interlayer spacings of the samples, respectively.

Abstract: Abstract The surface area of kaolinite-benzamide (K-Bz) 6.62 m2 g–1, which is noticeably lower than that of kaolinite-dimethyl sulphoxide (K-DMSO) 14.61 m2 g–1, the co-perturbation of the inner-surface hydroxyl features at 3697 and 3650 cm–1, and the increase of d(001) value by 7.44 Å are all related to the benzamide species inserted into the kaolinite structure through the replacement of the K-DMSO composites. Disappearance of the DMSO reflections and emergence of well-defined features at 6.04(2θ) and 11.16(2θ), 001 and 002 reflections with d values of 14.62 and 7.92 Å, respectively point out that the DMSO species were substituted efficiently by benzamide molecules. The thermal stability of the K-Bz derivative up to 300°C can be attributed to the slightly tilted aromatic ring keying into the gibbsitic sheets via the –NH2 groups.

Abstract: The penetration of the phenanthroline ligand into the interlayer space of the Cu-bentonite results in the formation of Cu(Phen)3-bentonite composite. The expansion of the d001 basal spacing of the Cu-Bent from 14.24 to 17.7 Å on intercalation and the colour change indicate the cation immobilized dimeric ligand species’ presence, which are thermally stable up to 315°C. The shift to higher frequency of the ring vibrations resulted from the π interactions is associated with the linkage of the tilted monomers to the smectite layers at elevated temperatures. The OH stretches and the bending peaks decrease in the intensity in parallel with an easy exchange between the water groups and the aromatic backboned ligands at room temperature.

Abstract: Acid activation increases the protonated species on a kaolinite surface at the expense of coordinately bound NH3 entities. The presence of NH4- ions on an activated sample is not proof of the presence of protonic acid centres alone since the added proton may have come from the residual water in the interlayer. Progressive dehydration of the surface results in a strong increase in chemisorbed NH3. However, the 'ring frequency' region of coordinately bound pyridine (Py) and of the pyridiniurn ion (Py+) indicates that the strong acid sites on activated kaolinite are of the Lewis type.

Abstract: Chemisorbed surface hydroxy-formate species on Pb(110), formed by reacting gaseous HCOOH with pre-adsorbed atomic oxygen, yields O(1s) and C(1s) photoelectron peaks at 531.3 and 288.3 eV, respectively. The three desorption features can be assigned as multilayer HCOOH at 190 K, a monolayer formic acid at 230 K and a metastable state (hydroxy-formate) at 300 K. Heating the overlayer in vacuum to 450 K results in removal of all surface hydroxyl although the higher temperature peak which corresponds to the recombination of surface protons with formate species remains stable. The formate species desorbs partially from the metal surface with extensive decomposition as shown by a large C(1s) residue at 285.0 eV.

Abstract: Non-dissociative adsorption of ammonia on a Cu(110) surface leads to the formation of two distinct entities between 80 and 298K. A single XP N(ls) peak at 401 eV and the VEEL spectra characterize the alpha ammonia species which is primarily physically coordinated to surface sites via diverse types of hydrogen bonds. The beta picture is clearly evident by the persistent R-xy mode at 410 cm(-1). Direct interaction between the 'monolayer' and most of the 'overlayer' NH3 groups reduces the Bronsted acidity of surface copper atoms. No N-H bond rupture occurs prior to the transformation of the beta pattern back into the form and an ammonia-free surface is regenerated eventually.

Abstract: A facile oxygen-induced chemisorptive replacement reaction occurs when a Bi(0001)-O overlayer is exposed to hydrogen chloride at 298K. The overlayer, which conforms to the stoichiometry BiOCl2, is stable in contrast to analogous chemistry observed earlier with a Pb(110) surface. Evidence for discrete localized states associated with Bi2+ or Bi3+ species is observed from shifts in the Bi(4f) binding energies while the charge distribution

Abstract: The activation of ammonia by oxygen at Cu(110) has been investigated by X-ray photoelectron and electron energy loss spectroscopies. The chemistry observed is dependent on the temperature, whether oxygen is preadsorbed and its surface coverage, or whether the oxygen is coadsorbed with ammonia. Amide species NH2(a) are formed only when adsorbed ammonia is exposed to dioxygen at low temperatures. With increasing temperature further step-wise dehydrogenation occurs to give imide NH(a) and nitrogen adatoms N(a). For an ammonia-rich dioxygen-ammonia mixture a facile reaction to form exclusively bent imide species occurs at 295 K with no evidence for chemisorbed oxygen being present until θNH approaches unity. A hot transient O−(s) species is implicated in the reaction mechanism. On the other hand for θoxygen → 1.0 the oxygen overlayer is relatively unreactive, imide formation being kinetically slow and limited in extent. Furthermore there is no evidence in the HREEL spectra for a loss peak characteristic of δnh although a νNH loss peak is present. This suggests a linear form of NH(a) in contrast to the bent form generated by coadsorption of ammonia and dioxygen. Two different oxygen species can exist at the copper surface: one that is highly reactive to ammonia and undergoes chemisorptive replacement, the other inactive. We suggest that the former is O−-like and associated with isolated oxygen atoms and the latter O2−-like and associated with multi-oxygen atom copper nuclei. High catalytic oxydehydrogenation activity can be maintained during the coadsorption of dioxygen and ammonia, provided the development of O2− species (oxide growth associated with surface reconstruction) is suppressed. The latter has been shown to occur even at low oxygen coverages (θ ≈ 0.1) the ammonia molecule acting as a sensitive and specific probe for the isolated O−-like species. The O−(s) species are therefore transients in the development of the chemisorbed oxygen overlayer and characterised by high chemical reactivity. Support for this model comes from recent scanning tunnelling microscope studies of the Al(111)-oxygen system of Ertl and coworkers [Phys. Rev. Lett. 68 (1992) 624] (ref. [1]).

Abstract: A combination of photoelectron and vibrational spectroscopies has established that a high energy formate species generated at a Pb(110)-surface is tilted with respect to the surface normal and decomposes spontaneously through H-bonding interactions with HCOOH(g) at 295 K.

Abstract: The coadsorption of dioxygen and ammonia results in a highly selective oxy-dehydrogenation reaction to form just chemisorbed imide NH(a) species at a Cu(110) surface at 298 K. The latter have been characterised by both core-level, N(1s), and vibrational (HREEL) spectroscopy. The role of a transient dioxygen precursor O2−(s) is discussed.