Colloidal synthesis and growth mechanism study of anisotropic multicomponent metal chalcogenide nanocrystals for energy applications
Creators: name: Kapuria, Nilotpal
Publisher: name: University of Limerick
Year: 2023
Subjects: classificationCode: 34
subject: Chemical sciences
subject: FOS: Chemical sciences

description: The thesis describes the novel colloidal approaches to synthesizing anisotropic multicomponent metal chalcogenide nanocrystals and their energy applications. The impact of ligands, precursors, temperature, time, and solvents on nanocrystal growth kinetics is thoroughly elucidated to achieve fine control over morphology, composition, and crystal phases. In addition, the mechanistic insights provided by a sequential aliquot study offer a deep understanding of the transformative chemistry of these NCs.Chapter 3 reports the synthesis of colloidal Cu-Bi-Zn-S nanorods (NRs) evolved from insitu generated Bi seeded Cu2-xS heterostructures. We find the seed transforms into Bi rich CuxBiySz (y&gt;x) phase and the stems transforms into CuxBiySz (x&gt;y) phase. The interface of the heterostructure alloys to form a ternary CuxBiySz polymorph as a transitional segment. The dissolution of the Bi rich seed and recrystallization of the Cu rich stem into the transitional segment, followed by the incorporation of Zn2+ to form the quaternary Cu-Bi-Zn-S composition. The present study also reveals the thermoelectric properties of the NRs. The NRs exhibit promising thermoelectric properties with very low thermal conductivity values of 0.45 W/mK and 0.65 W/mK at 775 K and 605 K, respectively, for Zn poor (n-type) and Zn rich NRs (p-type).The effect of an intermediate lamellar Cu-thiolate complex formation and it’s relative stability on hetero nucleation of Bi-(Cu2-xS)n heterostructures is demonstrated in chapter 4. The stability of the Cu-thiolate complex is regulated by varying denticity, concentration, and chain length of alkyl phosphonic acids. Modulation of Cu-thiolate stability controls the degree of heteronucleation of Cu2-xS on in-situ formed Bi seeds forming tunable numbers of Cu2-xS stems on Bi core. Further, the heterostructures are used as anode materials in K-ion battery where the importance of spatially separated multiple Cu2-xS stems on cycling performance is showcased. Chapter 5 reports the growth mechanism and synthetic controls for multinary NaBi1-xSbxSe2-ySy NCs synthesized using Se-alkahest chemistry. We reveal the effect of Sb and S substitution on the nanocrystal morphology and size. Furthermore, the thermoelectric properties of the Sb substituted NCs are studied where the NaBi0.75Sb0.25Se2-ySy NCs exhibit ultralow thermal conductivity of 0.25 W.m-1 .K-1 at 596 K with average thermal conductivity of 0.35 W.m-1K -1 between 358 to 596 K and ZTmax of 0.24.Chapter 6 demonstrates a solution-based phase control strategy for synthesizing layered transition metal disulfide nanosheets by modulating precursor reactivity. By tuning precursor-ligand chemistry, 2H, 1T', and 2H-1T' phases as polytypes are modulated in the layered nanosheets. The flexibility to selectively modify the reactivity of S and metal precursors allowed control over the proportion of a specific phase in the synthesized nanosheets. In addition, the formed nanosheets are deployed as electrocatalysts for the oxygen reduction reaction. Polytypic MoS2 displayed a high onset potential of 0.82 V (vs RHE) among all synthesized nanosheets. This work provides important insights into designing scalable solution-based pathways to engineering phases in polytypic transition metal disulfide nanocrystals.