Development of bimetallic nanocrystals for efficient photocatalytic applications

• Main Author: Zhang, Chu
• Other Authors: Xue Can
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering::Materials; Engineering::Nanotechnology
• Online Access: https://hdl.handle.net/10356/173230
• Institution: Nanyang Technological University

As the shortage of energy and environmental degradation, developing efficient photocatalysts to drive the solar-to-chemical conversion offers a promising solution to the current problems. With multifunctional properties, bimetallic nanocrystals (NCs) have gained increasing attention compared with their counterpart monometallic ones in the past few years, especially in the field of catalysis. To improve the photocatalytic performance, various bimetallic NCs have been deposited onto semiconductors as cocatalysts for constructing high-performance metal-semiconductor heterostructures (MSHs). It was reported that the structure, size, and composition of bimetallic NCs all have influence on the activity of MSHs. However, the study on bimetallic cocatalysts is still limited due to the availability of bimetallic NCs with desired structures and compositions. In the first work, we developed a facile ligand-assisted approach for the preparation of AuNi core-shell (c-AuNi) and Janus (j-AuNi) NCs with well-defined shape in the assistance of TPP and TOP, respectively. Comprehensive investigation on the structural transformation of bimetallic AuNi NCs demonstrated that the adding sequence as well as relative amount of phosphorus ligands are crucial in determining the final configuration of AuNi NCs. Accordingly, mechanisms elucidating the formation of the two distinct structures were proposed. In addition, this strategy can be generalized for the preparation of other bimetallic NCs with a successful example of core-shell Ag@Ni nanoparticles (NPs). Then as-synthesized AuNi NCs were deposited as cocatalysts on graphitic carbon nitride (GCN) for photocatalytic H2 generation. The results showed that the GCN decorated with either c-AuNi NCs or j-AuNi NCs exhibited higher activity than that of monometal deposited Au/GCN and Ni/GCN heterostructures, indicating the superiority of bimetallic cocatalysts. In particular, j-AuNi/GCN displays the best optimal H2 production activity at 36 mmol g-1 h-1, due to the synergistic enhancement of increased light absorption from the Au portion, resulting from the SPR effect, and efficient separation electrons from the Ni portion. In the second work, bimetallic CuPd NPs decorated mesoporous TiO2 nanomaterial, and CuRu NPs decorated 2D mesoporous TiO2 nanosheets (NSs), were synthesized by combined hydrothermal and sol-gel methods, respectively. The photocatalytic H2 production activity of CuPd/TiO2 and CuRu/TiO2 heterostructures was investigated from the aspects of metal precursors, loading weight of total metal, and the ratio of two metals. For CuPd/TiO2, it was found that the kinds of Cu2+ precursors have a big influence on the photocatalytic activity of H2 production. The CuPd/TiO2-Cl exhibited higher activity of 4.87 mmol g-1 h-1 in contrast with that of CuPd/TiO2-NO3 (4 mmol g-1 h-1) and CuPd/TiO2-acac (2.23 mmol g-1 h-1) prepared with CuCl2, Cu(NO3)2 and Cu(acac)2, respectively. As for CuRu/TiO2, both the kinds of Cu2+ precursors and the ratio of Cu to Ru play important role in the performance of H2 production. The results showed that Cu3Ru/TiO2-acac presented the highest activity at 5.2 mmol g-1 h-1 by using Cu(acac)2 as precursor with 3:1 metal ratio of Cu to Ru, and 2 at % total metal loading amounts. In summary, our work provides a novel insight on the synthesis of bimetallic NCs especially consisting of noble and transition metals, and the construction of high-efficiency MSHs with bimetallic cocatalysts for solar-driven H2 production.