Unraveling the Photocatalytic Behavior of Metal-Organic Frameworks: Structure-Performance Correlations

Abstract

With the increasing demand for energy consumption and the limitations of traditional carbon-based energy sources, the importance of renewable energy generation is undeniable. Among the various methods for generating and storing energy, green hydrogen production through photocatalytic water splitting has gained significant interest. However, despite numerous studies dedicated to finding the perfect material, achieving large-scale industrial applications is still a distant goal. Metal-Organic Frameworks (MOFs) have emerged as a particularly intriguing option due to their exceptional tunability and versatility. Nevertheless, there remains a substantial gap in our understanding of their performance and fundamental aspects. In this study, we focus on Ti-based MOFs, which have shown great promise owing to the redox properties of titanium. We introduce a novel Ti-oxo chain pyrene MOF called ACM- 1, which exhibits remarkable activity in both the hydrogen evolution reaction (HER) and organic transformations. This outstanding performance can be attributed to the high mobility of photogenerated electrons and the strong localization of holes within the material. To further enhance the photocatalytic activity of ACM-1, we employ defect engineering techniques, specifically fluorination of the metal-oxo units. The introduction of fluorine effectively reduces the band gap of the material, leading to improved light absorption capabilities and a significant boost in photocatalytic performance. Additionally, we synthesize a new MOF named ICGM-1, which shares isochemical characteristics with the well-studied MIL-125-NH2. Despite the identical NH2-bdc linker, ICGM-1 differs in terms of its Ti-sbu composition, providing a unique opportunity to investigate the influence of node geometry on photocatalytic activity. Our study reveals that the rod-type geometry is unfavorable due to lower electron charge mobility, highlighting the importance of node architecture in designing efficient photocatalysts. Finally, we report the synthesis of two new Zr-based MOFs, ACM-10 and ACM-11, based on the redox-active TTFT linker. Through Ti grafting, we demonstrate the potential of ACM-10 for HER, further expanding the range of viable MOF photocatalysts.

Date of Award	Aug 2023
Original language	English (US)
Awarding Institution	Physical Sciences and Engineering
Supervisor	Jorge Gascon (Supervisor)