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We report liquid-phase exfoliation (LPE) of bulk layered-structure semiconductor, MnIn 2 Se 4 , to nanoscale thick sheets by ultrasonication followed by sequential centrifugation at 2000, 5000, and 7500 rpm. The nanosheets exfoliated by LPE in isopropyl alcohol show an average thickness of 50, 40, and 14 nm, respectively. The smallest of these values corresponds approximately to ten 7-atom thick [Se–In–Se–Mn–Se–In–Se] layers that compose the bulk structure of MnIn 2 Se 4 . Both the bulk material and the exfoliated samples show photoluminescence, but the weak shoulder observed from the indirect band gap emission is obviously suppressed in the nanosheet samples as compared to the bulk sample. Similar to the bulk, the nanosheets isolated at 2000 and 5000 rpm exhibit spin-glass behavior with a freezing temperature of ∼3 K. In contrast, the nanosheets isolated at 7500 rpm do not exhibit any anomalies in their low-temperature magnetic behavior. These results demonstrate the possibility to extend the LPE technique to van-der-Waals materials with several-atom-thick layers.
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Effects of two wet exfoliation strategies on the yield and colloidal behavior of 2D hexagonal boron nitride nanosheets
Abstract We report the exfoliation process optimization, physicochemical characterizations, and comparative aggregation behavior of the inorganic 2D nanomaterial hexagonal Boron Nitride (h-BN) produced from two repetitive sonication-centrifugation processes with varying centrifugation speeds and recycle frequency: Continuous and Segmented protocols. Enhancing exfoliation efficiency and understanding aqueous stability are essential for sustainable design and environmental applications. Results showed that the Segmented protocol outperformed the Continuous protocol by having a six-fold increase in the exfoliated h-BN nanosheet yield by reusing the unexfoliated bulk h-BN and decreasing centrifugation speeds. Centrifugation speeds of 1880 and 950 rpm produced nanosheets of similar sizes due to the slight difference in the centrifugal force generated in both protocols. Moreover, nanosheets from both protocols had enhanced polarity due to the higher amounts of −OH bonds attached to the exposed edges of the nanosheets. However, the hydroxylation percentage of the nanosheets decreased with centrifugation speed. Both protocols produced h-BN nanosheets that were stable in DI water dispersion. The comparatively lower initial aggregation rate at all centrifugation speeds supported the fact that the Segmented protocol nanosheets were more stable than the Continuous ones. The Segmented protocol h-BN nanosheets showed better overall stability at lower speeds than the other centrifugation speeds. Segmented protocol nanosheets from 3750 rpm had the lowest aggregation rate than the other centrifugation speed. These findings assist in finding the balance between exfoliation protocol, environmental application, and implication of h-BN nanosheets.
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- PAR ID:
- 10572420
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Nano Express
- Volume:
- 6
- Issue:
- 1
- ISSN:
- 2632-959X
- Format(s):
- Medium: X Size: Article No. 015011
- Size(s):
- Article No. 015011
- Sponsoring Org:
- National Science Foundation
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