In situ green synthesis of Ag nanoparticles on graphene oxide/TiO2 nanocomposite and their catalytic activity for the reduction of 4-nitrophenol,congo red and methylene blue

The Ag/RGO/TiO₂ nanocomposite was synthesized through an environmentally benign, simple, cost efficient, surfactant-free and green method using Euphorbia helioscopia L. leaf extract as a stabilizing and reducing agent. The E. helioscopia L. leaf extract was used for the reduction of Ag⁺ ions and GO to Ag NPs and RGO, respectively. The GO/TiO₂ and Ag/RGO/TiO₂ nanocomposites were characterized by FT-IR, UV–vis, TEM, XRD, SEM, EDS and ICP techniques. The Ag/RGO/TiO₂ nanocomposite was highly active for the reduction of 4-nitrophenol (4-NP), congo red (CR) and methylene blue (MB) in aqueous media at an ambient temperature. The Ag/RGO/TiO₂ nanocomposite was easily separated and recovered from the reaction mixture by centrifugation and reused for several cycles without any significant loss of catalytic activity.     

Characteristics of V2O5 supported on sulfated TiO2 for selective catalytic reduction of NO by NH3

V₂O₅ supported on sulfated TiO₂ catalyst was investigated by using Raman and infrared spectroscopies to examine the surface structure of vanadia and the hydroxyl groups of titania along with the sulfate species on the catalyst surface. The surface structure of vanadia plays a critical role, particularly for the reduction of NO by NH₃. The polymeric vanadate species on the catalyst surface is the active reaction site for this reaction system. The surface sulfate species enhanced the formation of the polymeric vanadate by reducing the available surface area of the catalyst. The formation of the polymeric vanadate species on the catalyst surface also depends on the number of hydroxyl groups on the support. Both the sulfate and the vanadate species strongly interacted with the hydroxyl groups on titania. The fewer the number of the hydroxyl sites on the catalyst surface became by increasing the calcination temperatures, the more the polymeric vanadate species formed. A model was proposed to elucidate the progressive alteration of the surface structure of vanadia by the amounts of V₂O₅ loadings and the sulfate species on the catalyst surface.     

Extending surface Raman spectroscopy to transition metals for practical applications IV. A study on corrosion inhibition of benzotriazole on bare Fe electrodes

The emphasis in the present study was placed on developing Raman spectroscopy into a versatile technique, which offers an opportunity for investigating the inhibition effect on the corrosion process of bare Fe surfaces. Several surface pretreatments have been developed to bare Fe electrodes in order to obtain a surface of optimal surface-enhanced Raman scattering (SERS). It has been shown that the surface enhancement factor (SEF) of a bare Fe electrode can reach about two to three orders, depending on the roughening procedure. Therefore, SERS can be extended successfully to study some Fe electrode systems of practical importance. Here we present a study on the film formation process and inhibition effect of benzotriazole (BTA) on Fe surfaces. The results show that BTA interacts with Fe surface through its two N atoms of the triazole ring and surface complex polymer of [Fe_n(BTA)_p]_m is formed, which may suppress the dissolution and oxidation of Fe effectively. In addition, the solution pH, the synergetic effect of I⁻ with BTA was revealed to have a significant influence on the inhibition efficiency.     

Raman scattering activities for partially-oriented systems: the case of a unique molecular symmetry axis perpendicular to the uniaxial direction

Raman scattering activities have been derived for the case where the system has uniaxial order imposed on it, but the molecular or factor group's axis of symmetry is perpendicular to the uniaxial direction. The symmetry axis has random ordering about the uniaxial direction around which orientation averaging is done. The expressions for the scattering activities in the molecular co-ordinate system are related to a fixed laboratory co-ordinate system. This is carried out for the three orthogonal orientations of the sample in right-angle and back-scattering geometries.     

Vanadium species in new catalysts for the selective oxidation of methane to formaldehyde: Activation of the catalytic sites

New vanadium oxide supported on mesoporous silica catalysts for the oxidation of methane to formaldehyde were investigated by infrared and Raman spectroscopies to identify and characterize the molecular structure of the most active and selective catalytic sites. In situ and operando experiments have been conducted in order to understand the redox and hydroxylation/dehydroxylation processes of the vanadium species. (SiO)₂VO(OH) species were identified in these catalysts in reaction conditions and shown to undergo a deprotonation at 580 °C under vacuum, leading to a site giving a photoluminescence band at 550 nm attributed to reverse radiative decay from the excited triplet state:

(V⁴⁺–O⁻)^*  (V⁵⁺O²⁻). An activation mechanism of vanadium monomeric species with electrophilic oxygen species is proposed.