Revealing the molecular structure of copper phosphonate groups anchored inside SBA-15 silica channels: Theoretical and experimental study

This is the authors' abstract. We don't add key points for this paper.

This study aims to thoroughly understand the local structure of copper phosphonate groups covalently attached via propyl arms to pores interior of SBA-15 mesoporous silica. The studied sample contains 20% of propyl-POO2Cu groups attached to the mesoporous silica matrix as host material. X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) at the copper K-edge were utilized to discern the valence state and geometric arrangement of copper sites within the pores. Various machine learning techniques, including principal component analysis, K-means clustering, and neural networks, were applied to theoretically calculated XANES spectra. This facilitated our quantitative analysis of the experimental spectrum and the extension of the EXAFS equation fit to the second shell. Additional molecular structure analysis was performed based on Raman scattering supported by numerical simulations. Nuclear magnetic resonance aided in analyzing the silicon and phosphorus environment. Results indicate that copper atoms are coordinated by two phosphonate groups, forming a pseudo-bi-trigonal pyramid with surrounding oxygen atoms. These results contribute to a better understanding of the physical properties of the studied nanocomposite material. This, in turn, makes it possible to optimize the molecular structure of materials to optimize their antimicrobial and photonic properties, making them useful in practice.