(578e) Surface Modification of a Mxene with Silane Coupling Agents

MXenes are a family of hydrophilic, electrically conductive, 2D nanomaterials based on early transition metal carbides and carbonitrides with high aspect ratio and few atomic layer thickness [1]. The general formula of MXenes is M_n+1X_nT_x, where T represents a surface functional group such as OH, F, O or H [2]. The most well-known member of the MXene family is Ti₃C₂. From morphological point of view, MXenes are similar to graphene oxide, as their sheet thicknesses do not exceed 1 nm but their lateral dimensions can be as large as tens of microns [3]. Similar to other 2D materials, MXenes usually appear in the form of stacked sheets and their properties strongly depend on their morphology, stacked bundles versus individual sheets, and the kind of chemical species that exist between their layers. For practical uses, MXenes need to be intercalated. As there are weak interactions between MXene layers, intercalation of MXenes is possible via sonication. MXenes can form freestanding thin films. However, their mechanical properties are not high enough to be used in practical applications [4]. They can be modified with silane coupling agents, enabling them to incorporate into polymeric matrices. Silane coupling agents are chemicals capable of forming durable bonds between organic and inorganic materials. A silane coupling agent usually has a hydrolysable group like alkoxy in its structure, which changes to a silanol group after undergoing a hydrolysis reaction. In addition, it can bear an organo-functional group like amine, diamine, methacrylate, epoxy, vinyl, chloro, or phenyl [5]. A silanol group can react with hydroxyl groups available on the surface of an inorganic material, bonding the inorganic material to an organic one.

This paper presents a study of surface functionalization of Ti₃C₂T_x, the most studied MXene, with 3-(trimethoxysilyl) propyl methacrylate (MPS) and 3-aminopropyl (diethoxy) methylsilane (APDEMS). The surface functionalizations were carried out in both anhydrous and hydrous conditions, and advantages and disadvantages of each approach were investigated. The surface functionalizations were verified using characterization techniques including electrophoretic light scattering to measure zeta potential, contact angle goniometry, FTIR spectroscopy, UV-Vis spectroscopy, TGA, XRD, XPS and SEM. The APDEMS- and MPS-modified MXenes, respectively, showed surface charges of +32.77 and -17.98 mv versus -31 mv for the pure MXene. Surface modification reactions caused the disappearance of the hydroxyl group peak in the FTIR spectrum of the MXene and the appearance of new peaks attributed to the silane coupling agents. Water contact angle increased when the surface of the MXene was functionalized with the coupling agents. The UV-Vis spectrum of the MXene was changed due to the surface modification, and TGA results showed a weight loss peak around 370 ^oC, which is ascribed to the coupling agent decomposition. XRD showed that the surface modifications increase the gallery distance of the MXene sheets, and the extent of this increase depends on the type of the coupling agent used. Finally, XPS results verified the formation of covalent bonds between the MXene and the coupling agents. Due to their gained surface functional groups, the functionalized MXenes can participate in many grafting reactions to form in-situ nanocomposites.

References

1. Lei, J.-C., X. Zhang, and Z. Zhou, Recent advances in MXene: Preparation, properties, and applications. Frontiers of Physics, 2015. 10(3): p. 276-286.
2. Naguib, M., V.N. Mochalin, M.W. Barsoum, and Y. Gogotsi, 25th anniversary article: MXenes: a new family of two‐dimensional materials. Advanced Materials, 2014. 26(7): p. 992-1005.
3. Anasori, B., Y. Xie, M. Beidaghi, J. Lu, B.C. Hosler, L. Hultman, P.R. Kent, Y. Gogotsi, and M.W. Barsoum, Two-dimensional, ordered, double transition metals carbides (MXenes). ACS nano, 2015. 9(10): p. 9507-9516.
4. Ling, Z., C.E. Ren, M.-Q. Zhao, J. Yang, J.M. Giammarco, J. Qiu, M.W. Barsoum, and Y. Gogotsi, Flexible and conductive MXene films and nanocomposites with high capacitance. Proceedings of the National Academy of Sciences, 2014. 111(47): p. 16676-16681.
5. Padhiyar, S. and R. Desai, Silane Coupling Agent Work as Crosslinking Agent in Elastomer.