When I entered the Faculty of Science at Kyoto University as a Bachelor student, I found that I was initially bored because I had no interest in the content of the lectures. After three years have passed without any remarkable memories about science and chemistry, I was assigned to Professor Kazuki Nakanishi’s laboratory. The first research topic given to me by Professor Nakanishi was a joint research theme on tungsten carbide with a company. However, I encountered a problem within the first few months. The company’s equipment broke down, and nothing could be done from my side. Hence, Professor Nakanishi advised me that I should pursue the research according to my own instincts. Since the theme of the joint research was about tungsten carbide and the main topic of the Nakanishi Group was the control of pore structures by sol-gel processing, I decided to try to prepare tungsten oxide with controlled pore structures via sol-gel processing. To realize this theme, I proposed the concept of a synthetic process using the polymerization of peroxotungstates. However, this theme was very difficult and even after several hundred trials, there was no positive data for my Bachelor thesis. Despite these results, it was this research theme that sparked my interest in chemistry because I learned how difficult and interesting it can be to create and realize a concept for a research theme, and the depth of natural phenomena that cannot be solved simply by repeated experiments.
After entering my Master’s program, I proposed a new topic involving hierarchically porous ceramics toward flow adsorbent and wrote a paper. This experience of writing a paper was a second turning point for me. I realized that by not only reading papers, but also by writing one’s own paper while performing experiments, I could build upon the background and values of other authors.
For example, in the field of hierarchically porous materials, the length scales for describing “hierarchical” structures are different depending on the background of the researcher. Members of the Nakanishi laboratory, who are specialists in sol-gel chemistry, find hierarchical relationships mainly in pores with dimensions of tens of nanometres and micrometres. On the other hand, some researchers in crystal engineering find hierarchically porous structures between micropores of less than two nanometres in size. Thus, when we shift the criteria of the hierarchy from the meso-/macroscopic scale to the molecular-level, there should be an opportunity to design spatial and architectural features of the materials by combining knowledge from both the crystal engineering and sol-gel processing domains. For example, meso/macroporous materials are known to inevitably contain defects. On the other hand, with the remarkable advances in the field of crystal engineering, some types of defects in microporous crystalline structures can be controlled through defect engineering processes. If the combination of these domains allow us to prepare materials with control of both architectural and spatial features across multiple-length scales from the molecular-level (including defects) toward the macroscopic scale, a milestone in the design of hierarchically structured materials would be achieved.
In my Doctoral program, starting from the above turning points and ideas, I have been working to establish this interdisciplinary concept through the creation of model materials with control of both architectural and spatial features by exploiting ideas from the fields of porous ceramics and porous crystals (including metal-organic frameworks). To date, this work has led to several publications (Y. Hara et. al, J. Mater. Chem. A, 2018, 6, 9041-9048; Angew. Chem. Int. Ed. 2019, 58, 19047-19053; J. Phys. Chem. C, 2021, 125, 1403-1413; Nanoscale, 2021, 13, 6341-6356; Mater. Adv. 2021, 2, 4235-4239), with others under preparation. I have now reached the last year of my PhD and am looking forward to new challenges and the opportunity to explore new ideas at the forefront of materials engineering.