Carbon Domains on MoS2/TiO2 System via Catalytic Acetylene Oligomerization: Synthesis, Structure, and Surface Properties

Abstract

Carbon domains have been obtained at the surface of a MoS2/TiO2 (Evonik, P25) system via oligomerization and cyclotrimerization reactions involved in the interaction of the photoactive material with acetylene. Firstly, MoS2 nanosheets have been synthesized at the surface of TiO2, via sulfidation of a molybdenum oxide precursor with H2S (bottom-up method). Secondly, the morphology and the structure, the optical and the vibrational properties of the obtained materials, for each step of the synthesis procedure, have been investigated by microscopy and spectroscopy methods. In particular, transmission electron microscopy images provide a simple tool to highlight the effectiveness of the sulfidation process, thus showing 1L, 2L, and stacked MoS2 nanosheets anchored to the surface of TiO2 nanoparticles. Lastly, in-situ FTIR spectroscopy investigation gives insights into the nature of the oligomerized species, showing that the formation of both polyenic and aromatic systems can be taken into account, being their formation promoted by both Ti and Mo catalytic sites. This finding gives an opportunity for the assembly of extended polyenic, polyaromatic, or mixed domains firmly attached at the surface of photoactive materials. The presented approach, somehow different from the carbon adding or doping processes of TiO2, is of potential interest for the advanced green chemistry and energy conversion/transport applications.

Few-Layer MoS2 Nanodomains Decorating TiO2 Nanoparticles: A Case Study for the Photodegradation of Carbamazepine

“…Concerning the spectrum of pure TiO 2 in the 750–350-cm −1 range (Figure 2, black curve), the bands at 144 cm −1 , 396 cm −1 , 514 cm −1 and 636 cm −1 are assigned, respectively, to the typical E g , B 1g , A 1g and E g Raman active modes, respectively, of the anatase phase, as well described in literature, while the shoulder at 608 cm −1 and the very small peak at 444 cm −1 (highlighted by asterisks) are ascribed to the A 1g and E g modes of the rutile phase [8,25,27]. …”

“…First of all, the main features are due to the typical adsorptions of CO on the different Ti sites of the TiO 2 surface. Specifically, the intense main peak centered at 2178 cm −1 can be explained with the building up of parallel CO oscillators interacting with five-fold coordinated Ti 5c 4+ sites located on flat (101) surfaces [48], while the one at 2155 cm −1 is explained with hydrogen interactions of CO with residual OH groups, even present after the thermal treatment [25,27,48]. It is noteworthy that, even if not reported in Figure 4, for the sake of simplicity, the previously discussed 2178-cm −1 band shifts to higher frequencies, when CO pressure is decreased, due to the changes of the lateral interactions between adjacent CO molecules on the surface of TiO 2 .…”

“…Moving to the sharp band at 2140 cm −1 , it is assigned to CO in a “liquid-like” state, caused by liquid nitrogen temperature and physically adsorbed as a multilayer surface [25,27], while the one at 2146 cm −1 is due to CO adsorbed on facelets of the rutile phase.…”

“…It has been proven that the treatment of a TiO 2 surface under H 2 S atmosphere can induce a modification of the titania electronic structure, causing a red shift of its absorption edge [25]. Some articles [26,27,28] suggest that MoS 2 /TiO 2 composites are good photocatalysts, thanks to the efficient charge-carrier separation [29]. Along with this line of thinking, H 2 S, S, CS 2 , etc., have been used to create hybrid heterojunctions.…”

Zinc Oxide Nanostructures: From Chestnut Husk-Like Structures to Hollow Nanocages, Synthesis and Structure

“…In the last years, many studies have been focused on both the synthesis [1] and the morphological-structural characterization of new functional materials to use in post-synthesis treatments (deposition on substrates, blending with polymers, building up of two-dimensional (2D)/three-dimensional (3D) lattices with control of the properties at nanoscopic level) [2][3][4][5]. As a matter of fact, nanocrystals represent a class of materials, with enhanced properties and innovative functionalities (i.e., electrical, electronic, optical, mechanical, thermal, magnetic, catalytic, photocatalytic, etc.)…”