Interaction of polar and non-polar polyfluorenes with layers of 2D titanium carbide (MXene): 2DWorld beyond Graphene

Two-dimensional (2D) materials have garnered immense interest particularly after the discovery of unique physical properties of graphene. Recently, a family of 2D metal carbides and nitrides (MXenes) have been discovered and synthesized by selective etching the A element layers from ternary transition metal carbides and/or nitrides with a general formula of Mn+1AXn (M=early transition metal, Ti, V, Mo, etc., A=group XIII and XIV elements, X=C/N and n=1, 2 or 3). As a result, the MXene compositions are generally represented as Mn+1XnTx. After wet chemical etching, surface functional groups (Tx), such as F, O, and OH terminate MXene surface. 1 Despite its short history, MXenes have already shown a huge potential in a broad range of applications such as energy conversion and storage, water purification, catalysis, antibacterial agent, transparent conductive electrodes, electromagnetic shielding and others.2 Nanoscale design of Hybrid materials, with incorporation of conjugated polymers(CP) into MXene layers, is a promising way to further increase the applications of MXenes. The CP provide a unique set of properties, including, variable band gap, controlled exciton and charge transport, processability flexibility, transparence and if necessary water solubility, and the MXene exhibits metallic conductivity and mechanically strong support. Here, we study the interaction of CP with, Ti3C2Tx, using polyfluorene derivatives (PFO) (FIG 1) having the same conjugated backbone but different lateral chain from apolar to polar.3 Three PFO having no polar, with polar nitrogen, and with charged nitrogen functionality were synthesized via the Suzuki polycondensation reaction. The hybrid free standing flexible films were prepared by vacuum filtration of CP and MXene solutions after 24h stirring. Our results demonstrated that polar polymers with charged nitrogen ends tend to strongly interact with MXenes layers. When optimized composites were tested as pseudocapacitive electrodes, improved capacitance values and excellent capacitance retention were observed.