Executive Summary : | Chalcogenide perovskites (ABX₃, where A being a group II cation (such as Ca2+, Sr2+, or Ba2+), B as a group IV transition metal ion (eg., Ti4+, Zr4+, or Hf4+), and X a chalcogenide ion (S2– or Se2–) have earth abundant elemental composition `which make them low-cost material for catalyzing useful reactions such as photocatalytic splitting of water for Hydrogen and Oxygen generation. In addition, the high stability (to water/moisture), robust nature (especially BaZrS3 remains stable in water for hours), the high value of absorption coefficient (~105 cm-1), and suitable band gap of around 2 eV (~1.85 eVfor BaZrS3 and 2.05 eV for SrZrS3) and comparatively higher electrical conductivity than oxide perovskite make chalcogenide perovskites ideal candidates for photocatalysis. But in the literature, there are only very few recent reports on photocatalytic applications of these materials so far. While, these few reports are promising, their photocatalytic performance is yet to be at per with conventional photocatalytic materials. It is suggested that in most cases, the d-block transition metal ions (B cations) in these perovskites play a major role in catalysis. However, previous reports also show excess use of sulfur (chalcogen) precursor in the synthesis of chalcogenide perovskites. As a result, most of the B cations expected to be well-passivated and not available to bind the adsorbates for catalysis. In contrast, the big size or bulk crystals are well studied, but cannot provide much surface area and active sites for catalysis. Hence, the chalcogenide rich surface and fewer surfaces could be considered as one of the main factors behind their inferior performance. On reducing the size of the material to nanometer scale, surface to volume ratio increases tremendously. Further, the removal of excess chalcogen from the surface by nanocrystal surface engineering can make the material efficient in catalysis. Another important point to note is that the nanoparticles of chalcogenide perovskite exhibit a higher value of electron spin compared to the bulk, which affects the d-orbital electron fillings (increase in eg filling) of B cations, leading to a further increase in catalytic activity of these materials. Based on these points, this project is focused on the promising task of synthesizing colloidal nanocrystals of chalcogenide perovskites, their characterization, nanocrystal surface modification, photo-physical studies, and eventually applying them in photocatalytic reactions such as water splitting. Solution-processed thin film electrodes of these chalcogenide nanomaterials will be fabricated for other catalytic reactions. Moreover, doping or substitution at A and B sites alter the oxidation states of B cations which can further improve the catalytic properties. Different lanthanides (for example Eu2+, La3+) and transition metals (such as Mn2+) will be used as dopants to further fine-tune the photocatalytic properties. |