Flexible reduced graphene oxide (rGO) sheets are being considered for applications in portable electrical devices and flexible energy storage systems. However, the poor mechanical properties and electrical conductivities of rGO sheets are limiting factors for the development of such devices. Here we use MXene (M) nanosheets to functionalize graphene oxide platelets through Ti-O-C covalent bonding to obtain MrGO sheets. A MrGO sheet was crosslinked by a conjugated molecule (1-aminopyrene-disuccinimidyl suberate, AD). The incorporation of MXene nanosheets and AD molecules reduces the voids within the graphene sheet and improves the alignment of graphene platelets, resulting in much higher compactness and high toughness. In situ Raman spectroscopy and molecular dynamics simulations reveal the synergistic interfacial interaction mechanisms of Ti-O-C covalent bonding, sliding of MXene nanosheets, and π-π bridging. Furthermore, a supercapacitor based on our super-tough MXene-functionalized graphene sheets provides a combination of energy and power densities that are high for flexible supercapacitors.

Graphene and two-dimensional transition metal carbides and/or nitrides (MXenes) are important materials for making flexible energy storage devices because of their electrical and mechanical properties. It remains a challenge to assemble nanoplatelets of these materials at room temperature into in-plane isotropic, free-standing sheets. Using nanoconfined water-induced basal-plane alignment and covalent and π-π interplatelet bridging, we fabricated Ti ₃ C ₂ T _x MXene-bridged graphene sheets at room temperature with isotropic in-plane tensile strength of 1.87 gigapascals and moduli of 98.7 gigapascals. The in-plane room temperature electrical conductivity reached 1423 siemens per centimeter, and volumetric specific capacity reached 828 coulombs per cubic centimeter. This nanoconfined water-induced alignment likely provides an important approach for making other aligned macroscopic assemblies of two-dimensional nanoplatelets.

Assembling titanium carbide (Ti ₃ C ₂ T _x ) MXene nanosheets into macroscopic films presents challenges, including voids, low orientation degree, and weak interfacial interactions, which reduce mechanical performance. We demonstrate an ultrastrong macroscopic MXene film using liquid metal (LM) and bacterial cellulose (BC) to sequentially bridge MXene nanosheets (an LBM film), achieving a tensile strength of 908.4 megapascals. A layer-by-layer approach using repeated cycles of blade coating improves the orientation degree to 0.935 in the LBM film, while a LM with good deformability reduces voids into porosity of 5.4%. The interfacial interactions are enhanced by the hydrogen bonding from BC and the coordination bonding with LM, which improves the stress-transfer efficiency. Sequential bridging provides an avenue for assembling other two-dimensional nanosheets into high-performance materials.

Lignocellulosic materials were conventionally treated as wastes for disposal, but have now become very important in modern life due to their great roles in the supply of renewable resources. Recently, significant attention has been paid to the dissolution of cellulose, hemicellulose, and lignin, and the production of chemicals and fuels from these feedstocks. It has been demonstrated that lignocellulose has great potential from a sustainable economy perspective and this field has been developing rapidly. Thus, it is critical to review the recent progress in studies on the utilization of lignocellulosic materials. In particular, this work was designed to highlight recent computation-based studies on the chemistry of lignocellulosic materials, from the structural and energetic properties of individual lignocellulose components to their reaction mechanisms in various systems. Importantly, this review summarizes some major simulation studies on the utilization of cellulose, hemicellulose, and lignin via dissolution, catalytic conversion, and pyrolysis by using density functional theory, first-principles calculation, molecular dynamics simulation, and conductor-like screening models. It has been shown that the theoretical and computational investigations play a key role in the understanding of the efficient utilization of lignocellulose.