The Stability of UV-Defluorination-Driven Crosslinked Carbon Nanotubes: A Raman Study

Carbon nanotubes (CNTs) are often regarded as semi-rigid, all-carbon polymers. However, unlike conventional polymers that can form 3D networks such as hydrogels or elastomers through crosslinking in solution, CNTs have long been considered non-crosslinkable under mild conditions. This perception changed with our recent discovery of UV-defluorination-driven direct crosslinking of CNTs in solution. In this study, we further investigate the thermal stability of UV-defluorination-driven crosslinked CNTs, revealing that they are metastable and decompose more readily than either pristine or fluorinated CNTs under Raman laser irradiation. Using Raman spectroscopy under controlled laser power, we examined both single-walled and multi-walled fluorinated CNTs. The results demonstrate that UV-defluorinated CNTs exhibit reduced thermal stability compared to their pristine or untreated fluorinated counterparts. This instability is attributed to the strain on the intertube crosslinking bonds resulting from the curved carbon lattice of the linked CNTs. The metallic CNTs in the crosslinked CNT networks decompose and revert to their pristine state more readily than the semiconducting ones. The inherent instability of crosslinked CNTs leads to combustion at temperatures approximately 100 °C lower than those required for non-crosslinked fluorinated CNTs. This property positions crosslinked CNTs as promising candidates for applications where mechanically robust, lightweight materials are needed, along with feasible post-use removal options.

Optimized Electrode/Electrolyte Interface of MWCNT/SnO2 Composite through Gas-Solid Fluorination

The benefit of enriching solid-electrolyte interface with fluorine atoms through the use of fluorinated additives into the electrolyte composition has recently gained popularity for anode materials used in secondary lithium-ion batteries. Another strategy is to provide these fluorine atoms via surface fluorination of the electrode material, particularly for multiwalled carbon nanotube (MWCNT)/SnO₂-based composites where fluorination must act selectively on SnO₂. Our study presents two methods of surface fluorination applied on MWCNT/SnO₂, one using F₂(g) and the other XeF₂(s). These fluorinating agents are known for their different particle penetration depths. An ultrathin and very dense fluorinated layer achieved by the action of F₂(g) allows to form a very stable interface leading to gravimetric capacities of 789 mA h g^-1 after 50 cycles. A thin and porous fluorinated layer made by the action of XeF₂(s) favors the formation of a new Sn-based fluorinated phase, never reported in the literature, which also stabilizes capacities over 50 cycles. In any case, the value of adding fluorine atoms to the surface of the electrode material to improve cycle stability is demonstrated.

Low temperature preparation of highly fluorinated multiwalled carbon nanotubes activated by Fe3O4 to enhance microwave absorbing property

Conventional approaches to preparing highly fluorinated multiwalled carbon nanotubes (MWCNTs) always require a high temperature. This paper presents a catalytic approach to realizing the effective fluorination of MWNCTs at room temperature (RT). Fe₃O₄/MWCNTs composites with Fe₃O₄ loaded on MWCNTs were first prepared using the solvothermal method, followed by fluorination treatment at RT. The attachment of Fe₃O₄ changes the charge distribution and dramatically improves the fluorination activity of MWCNTs. Consequently, the fluorine content of fluorinated Fe₃O₄/MWCNTs (F-Fe₃O₄/MWCNTs) can reach up to 17.13 at% (almost six times that of the unloaded sample) only after fluorination at room temperature, which leads to an obvious decrease in permittivity. Besides, the partial fluorination of Fe₃O₄ brings about abnormally enhanced permeability due to strengthened exchange resonance. Benefiting from the lower permittivity and higher permeability, F-Fe₃O₄/CNTs composite exhibits increased impedance matching and thus an enhanced microwave absorption property with a minimal reflection loss of -45 dB at 2.61 mm when the filler content is 13 wt%. The efficient absorption bandwidth (<-10 dB) reaches 4.1 GHz when the thickness is 2.5 mm. This work illustrates a novel catalytic approach to preparing highly fluorinated MWCNTs as promising microwave absorbers, and the design concept can also be extended to the fluorination of other carbon materials.