M. Baibarac, I. Baltog, L. Mihut, S. Pasuk, S. Lefrant
Carbon, Volume 51, January 2013, Pages 134-142
Polarized Raman scattering studies on stiff layered structure of surfactant intercalated with trilayer graphene were performed at different intensities and excitation wavelengths. The D and 2D Raman bands reach the highest and lowest intensity when the polarization of laser excitation light is oriented along and perpendicular on the edges. The 2D band discloses two lorentzian components, separated by ∼40 cm−1, which result from the action of interplanar forces, of Casimir nature. The value of ∼40 cm−1 is close to the energy value associated with E2g interplanar layer shear mode evidenced so far only by neutron spectrometry. A new result regards the opposite variation of the intensities of D and 2D bands with the increase of the wavelength of the excitation light. This originates in the different origin of the D and 2D bands; the former is dependent on disorder including also the graphene edges while the latter, results from in a double resonant mechanism combined with a Casimir effect. One demonstrates that the magnitude of Casimir force, which activates interlayer vibration modes, depends on the carrier density on the graphene sheets which can be varied both by the intensity and the wavelength of the excitation laser light.
Raman spectra at kexc = 457.9 nm of trilayer grapheme in different morphological forms:
(A)-dispersed with surfactant (SDS) in aqueous solution; (B)-intercalated in stiff layered structure of (top graphene layer view); (C&D - intercalated in stiff layered structure (graphene edge view). The red and blue spectra have been obtained under excitation light polarized along and perpendicular on the layers, inset C and D, respectively.
J. Choina, H. Kosslick, Ch. Fischer, G.-U. Flechsig, L. Frunza, A. Schulz
Applied Catalysis B: Environmental, Volume 129, 17 January 2013, Pages 589–598
Due to the growing importance of low concentrated pollution of surface, ground and drinking, the photocatalytic decomposition of ibuprofen down to low ppm concentrations over titania catalyst has been investigated in detail. The catalyst was characterized by XRD, TEM, diffuse reflection UV–Vis and nitrogen adsorption measurement. The photocatalytic abatement of ibuprofen was monitored by UV–Vis spectrometry, chromatographic by GC/MS, and HPLC coupled electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). Catalytic performance has been studied by varying the catalyst and substrate concentration as well as decreasing the catalyst-to-substrate mass ratio over a wide range. The photocatalytic treatment with titania catalyst leads to rapid mineralization of ibuprofen. Formation of intermediate reaction products has been investigated. It is proposed that intermediates in part form oligomeric species, which are responsible for catalyst poisoning. Additional, the influence of the pH value, oxygen supply and catalyst re-use have been checked.