title: "Smart poisoning" of Co/SiO2catalysts by sulfidation for chirality-selective synthesis of (9,8) single-walled carbon nanotubes.
abstract: The chirality-selective synthesis of relatively large (diameter > 1 nm) single-walled carbon nanotubes (SWCNTs) is of great interest for a variety of practical applications, but only a few catalysts are available so far. Previous studies suggested that S (compounds) can enhance the chirality-selectivity of Co catalysts in SWCNT synthesis, however, the mechanism behind is not fully understood, and no tailorable methodology has yet been developed. Here, we demonstrate a facile approach to achieve the chirality-selective synthesis of SWCNTs by the sulfidation-based poisoning of silica-supported Co catalysts using a mixture of H2S and H2. The UV-vis-NIR, photoluminescence, and Raman spectroscopy results together show that the resulting SWCNTs have a narrow diameter distribution of around 1.2 nm, and (9,8) nanotubes have an abundance of ∼38% among the semiconducting species. More importantly, the carbon yield achieved by the sulfided catalyst (2.5 wt%) is similar to that of the nonsulfided one (2.7 wt%). The characterization of the catalysts by X-ray diffraction, X-ray photoelectron spectroscopy, X-ray fluorescence, and H2temperature-programmed reduction shows that the sulfidation leads to the formation of Co9S8nanoparticles. However, Co9S8nanoparticles are reduced back to regenerate metallic Co nanoparticles during the synthesis of SWCNTs, which maintain a high carbon yield. In this process, Co9S8nanoparticles seemingly intermediate the production of Co nanoparticles with narrow size distribution. Due to the fact that the poisoning step improves the quality of the end-product rather than hampering the growth process, we have coined the process developed as "smart poisoning". This study not only reveals the mechanism behind the beneficial role of S in the selective synthesis of relatively large SWCNTs but also presents a promising method to create chirality-selective catalysts with high activity for scalable synthesis.
authors.affiliation: Nanyang Technological University, School of Chemical and Biomedical Engineering, Singapore, 637459, Singapore.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yuan
authors.affiliation: Nanyang Technological University, School of Chemical and Biomedical Engineering, Singapore, 637459, Singapore and The University of Sydney, School of Chemical and Biomolecular Engineering, NSW, 2006, Australia. yuan.chen@sydney.edu.au.
authors.forename: H Enis
authors.initials: HE
authors.lastname: Karahan
authors.affiliation: Koç University, KUYTAM Surface Science and Technology Center, Rumelifeneri Yolu, Sarıyer, 34450, İstanbul, Turkey.
authors.forename: Cansu
authors.identifier: http://orcid.org/0000-0003-1023-4030
authors.initials: C
authors.lastname: Yıldırım
authors.affiliation: The University of Sydney, School of Chemical and Biomolecular Engineering, NSW, 2006, Australia. yuan.chen@sydney.edu.au.
authors.forename: Li
authors.initials: L
authors.lastname: Wei
authors.affiliation: Koç University, KUYTAM Surface Science and Technology Center, Rumelifeneri Yolu, Sarıyer, 34450, İstanbul, Turkey and Koç University, Chemistry Department, Rumelifeneri Yolu, Sarıyer, 34450, İstanbul, Turkey.
authors.forename: Özgür
authors.initials: Ö
authors.lastname: Birer
authors.affiliation: Nanyang Technological University, School of Chemical and Biomedical Engineering, Singapore, 637459, Singapore and The University of Sydney, School of Chemical and Biomolecular Engineering, NSW, 2006, Australia. yuan.chen@sydney.edu.au.
authors.forename: Shengli
authors.initials: S
authors.lastname: Zhai
authors.affiliation: Nanyang Technological University, School of Chemical and Biomedical Engineering, Singapore, 637459, Singapore.
authors.forename: Raymond
authors.initials: R
authors.lastname: Lau
authors.affiliation: The University of Sydney, School of Chemical and Biomolecular Engineering, NSW, 2006, Australia. yuan.chen@sydney.edu.au.
authors.forename: Yuan
authors.identifier: http://orcid.org/0000-0001-9059-3839
authors.initials: Y
authors.lastname: Chen