Engineered TMDs and TMTHs 2D-materials for Gas Sensing and Photoelectrocatalytic applications

Nanomaterials represent a significant percentage of materials science research. Among them, bidimensional (2D) materials have gained ever increasing relevance; on this account, twenty years of research and technological development of 2D materials and their applications have now passed since the discovery of Graphene in 2004. This thesis work is focused on (i) the synthesis and characterization of innovative 2D materials (ii) their application as functional interfaces for gas sensing and photoelectrocatalysis (PEC) (iii) some technological aspects related to the measurement systems (i.e. the design of innovative gas sensing substrates and the setup and calibration of a photoelectrocatalysis test cell) The bidimensional materials studied in this work belong to the families of Transition Metal Dichalcogenides (2D-TMDs) and Transition Metal Trihalides (2D-TMTHs). Regarding 2D-TMDs, by means of a variety of synthesis techniques (mainly Liquid Phase Exfoliation – LPE and Hydro-Solvothermal Growth – SG), the synthesis of 2D-SnSe2 and 2D-In2Se3, plus a 2D-SnSe2/TiO2 heterostructure have been achieved; moreover, by exploiting their spontaneous tendency towards oxidation in environmental conditions, both amorphous/crystalline 2D layered heterostructures and bidimensional layered amorphous metal oxides (hereafter named LAMOS), have been synthesized, specifically obtaining 2D a-SnO2 from controlled annealing of 2D-SnSe2 and 2D a-In2O3/In2Se3 heterostructure from controlled annealing of 2D-In2Se3. Regarding 2D-TMTHs, for the first time 2D-CrCl3 has been exfoliated by means of LPE, a high yield, industrially scalable method. Three of the above-mentioned interfaces, more precisely 2D a-SnO2, 2D a-In2O3/In2Se3 and 2D-CrCl3 have been applied for the first time in gas sensing, achieving good performances in detecting reducing/oxidizing gases in dry/wet environments with good sensitivities, limits of detections (LOD) and long-term stabilities. The 2D-SnSe2/TiO2 heterostructure showed promising results as a photoelectrocatalyst for the Oxygen Evolution Reaction (OER). Moreover, the electronic structure of the heterojunction has been schematized and a hypothesis on the mechanism given to explain its PEC-OER capabilities. Some of the activities developed in this PhD work have been carried out in collaboration with other research groups, including the Department of Physical and Chemical Sciences of the University of L’Aquila, the Department of Chemistry of the University of Sassari and the Department of Industrial Engineering of the University of Padova. The gas sensor substrates design and manufacturing has been carried out in collaboration with Fondazione Bruno Kessler (FBK).