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Relative to conventional wet-chemical synthesis techniques, on-surface synthesis of organic networks in ultrahigh vacuum has few control parameters. The molecular deposition rate and substrate temperature are typically the only synthesis variables to be adjusted dynamically. Here we demonstrate that reducing conditions in the vacuum environment can be created and controlled without dedicated sources─relying only on backfilled hydrogen gas and ion gauge filaments─and can dramatically influence the Ullmann-like on-surface reaction used for synthesizing two-dimensional covalent organic frameworks (2D COFs). Using tribromo dimethylmethylene-bridged triphenylamine ((Br)DTPA) as monomer precursors, we find that atomic hydrogen (H) blocks aryl-aryl bond formation to such an extent that we suspect this reaction may be a factor in limiting the ultimate size of 2D COFs created through on-surface synthesis. Conversely, we show that control of the relative monomer and hydrogen fluxes can be used to produce large self-assembled islands of monomers, dimers, or macrocycle hexamers, which are of interest in their own right. On-surface synthesis of oligomers, from a single precursor, circumvents potential challenges with their protracted wet-chemical synthesis and with multiple deposition sources. Using scanning tunneling microscopy and spectroscopy (STM/STS), we show that changes in the electronic states through this oligomer sequence provide an insightful view of the 2D COF (synthesized in the absence of atomic hydrogen) as the end point in an evolution of electronic structures from the monomer.
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http://dx.doi.org/10.1021/acsnano.2c11463 | DOI Listing |
Nano Lett
December 2024
Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Fudan University, Shanghai 200438, China.
Creating densely functionalized supported materials without aggregation has been one of the ultimate goals for heterogeneous catalysts. Direct conversion of readily available bulk materials into highly dispersed supported materials could be highly beneficial for real applications. In this work, we invented an on-surface synthetic strategy for generating highly loaded and well-dispersed nickel nanoparticles on nickel oxide supports (Ni/NiO).
View Article and Find Full Text PDFJ Phys Chem Lett
December 2024
BNLMS, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
Metal-alkynyls, an emerging class of functional metal-organic materials, have attracted widespread attention due to their fascinating properties and multifaceted potential applications, such as luminescence, nonlinear optics, liquid crystals, and catalysis. Despite considerable effort toward their synthesis, precise construction of complex metal-alkynyl structures with a high selectivity remains a great challenge. The rise of on-surface chemistry not only offers a route to realizing controlled synthesis of low-dimensional (LD) metal-alkynyls but also provides an opportunity for their in-depth investigations with advanced surface characterization techniques such as scanning tunneling microscopy.
View Article and Find Full Text PDFJ Am Chem Soc
December 2024
Department of Applied Physics, Aalto University, Helsinki 02150, Finland.
Scanning probe microscopy (SPM) techniques have shown great potential in fabricating nanoscale structures endowed with exotic quantum properties achieved through various manipulations of atoms and molecules. However, precise control requires extensive domain knowledge, which is not necessarily transferable to new systems and cannot be readily extended to large-scale operations. Therefore, efficient and autonomous SPM techniques are needed to learn optimal strategies for new systems, in particular for the challenge of controlling chemical reactions and hence offering a route to precise atomic and molecular construction.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
December 2024
Department Smart Hybrid Materials Laboratory (SHMs), Department of Chemistry, Division of Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Kingdom of Saudi Arabia.
Ionic covalent organic framework (COF) nanosheets are becoming increasingly attractive as promising two-dimensional (2D) materials for proton transport due to their ionic functionality and tailor-made pores. However, most synthetic methods for nanosheets rely on surface-assisted methods or phase transformation often yielding nanosheets with low aspect ratios. In this study, we present a bottom-up approach utilizing an oil-oil-water triphase system to achieve the large-scale synthesis of ionic COF nanosheets.
View Article and Find Full Text PDFHeliyon
December 2024
National Centre of Excellence in Physical Chemistry, University of Peshawar, Peshawar, Pakistan.
Green methanol fuel synthesis by CO hydrogenation is regarded as one of the potential viable techniques for meeting future energy demands. Enhancing catalytic performance and process knowledge are crucial for the practicality of catalyzed CO conversion pathways. Here, co-precipitation was utilized to prepare Cu-Zn bimetallic catalysts based on silica gel.
View Article and Find Full Text PDFEnter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!