Chiral-Selective CoSO₄/SiO₂ Catalyst for (9,8) Single-Walled Carbon Nanotube Growth

Abstract

Electronic and optical properties of single-walled carbon nanotubes (SWCNTs) correlate with their chiral structures. Many applications need chirally pure SWCNTs that current synthesis methods cannot produce. Here, we show a sulfate-promoted CoSO(4)/SiO(2) catalyst, which selectively grows large-diameter (9,8) nanotubes at 1.17 nm with 51.7% abundance among semiconducting tubes and 33.5% over all tube species. After reduction in H(2) at 540 °C, the catalyst containing 1 wt % Co has a carbon yield of 3.8 wt %, in which more than 90% is SWCNT. As compared to other Co catalysts used for SWCNT growth, the CoSO(4)/SiO(2) catalyst is unique with a narrow Co reduction window under H(2) centered at 470 °C, which can be attributed to the reduction of highly dispersed CoSO(4). X-ray absorption spectroscopy (XAS) results suggested the formation of Co particles with an average size of 1.23 nm, which matches the diameter of (9,8) tubes. Density functional theory study indicated that the diameter of structurally stable pure Co particles is scattered, matching the most abundant chiral tubes, such as (6,5) and (9,8). Moreover, the formation of such large Co particles on the CoSO(4)/SiO(2) catalyst depends on sulfur in the catalyst. XAS results showed that sulfur content in the catalyst changes after catalyst reduction at different conditions, which correlates with the change in (n,m) selectivity observed. We proposed that the potential roles of sulfur could be limiting the aggregation of Co atoms and/or forming Co-S compounds, which enables the chiral selectivity toward (9,8) tubes. This work demonstrates that catalysts promoted with sulfur compounds have potentials to be further developed for chiral-selective growth of SWCNTs.

Sorting Semiconducting Single‐Walled Carbon Nanotubes by Water‐Soluble Polyfluorene Assisted Electrophoresis and Its Application in Field‐effect Transistors

“…[34] In Figure 2(a), it is observed that nine major semiconducting species exist in the SDS suspended SWNTs. They are (6, 5), (7,5), (7,6), (8,4), (8,6), (8,7), (9, 4), (9, 5) and (10, 2) which are marked with orange borders in Figure 2(c). While nine species can also be observed in Figure 2(b) which are semiconducting enriched fractions after AGE/w-PFO.…”

“…While nine species can also be observed in Figure 2(b) which are semiconducting enriched fractions after AGE/w-PFO. They are (7,5), (7,6), (8,4), (8,6), (8,7), (9, 4), (9, 5), (10,2), and (10, 3) which are marked with green dots of different darkness in Figure 2(c), according to calibrated PL peak intensity. In the graphene sheet map, Figure 2(c), the suspension preferences of pristine SWNTs and semiconducting enriched SWNTs by AGE/w-PFO are summarized.…”

“…[35] Therefore, each calibrated species abundance is obtained through dividing the experimental PL intensity (peak height above the baseline) by a theoretical intensity factor. [36] From the calculated abundance of relative species in Table1, we can find that AGE/w-PFO mainly selects for (7,6), (8,4), (8,6), (8,7), (9,4), (9,5), and (10,3).…”

“…The absorbance peaks in the 870-1600 nm, 500-870 nm and 440-670 nm range correspond to the first and second van Hove electronic transitions of semiconducting species ( 11 S E and S 22 E ) and first van Hove electronic transitions of metallic species ( M 11 E ), respectively. Metallic species such as (7, 7), (8,5), (9,9), (10, 7), (11,5), and (13,4) are detected and shown in the pristine HiP-CO SWNTs spectrum. For the semiconducting fraction extracted from the upper fraction after AGE/w-PFO, the peaks in the region of M 11 E decrease obviously which suggests the reduction of metallic species in semiconducting fraction.…”

“…Although some research has been done to directly synthesize chiral selective nanotubes, the purity and yield of s-SWNTs are not satisfied. [8,9] In order to gain pure and scalable s-SWNTs, separation of raw carbon nanotube materials is still an optimal choice until now.In the last decade, various techniques have been developed to separate semiconducting SWNTs, such as polymer wrapping, density gradient ultracentrifugation (DGU), sephacryl gel-based chromatography, agarose gel, two-phase separation, etc. [10][11][12][13][14][15][16][17][18][19][20][21] Each of these techniques is able to separate SWNTs into metallic and semiconducting species in different level of success.…”