Design of Novel Carbon Nanothread-based Julian F.R.V. Silveira, Vinicius Millan, André R. Muniz* Departamento de Engenharia Química, Universidade Federal do Rio Grande do Sul *[email protected]

Abstract Carbon or nanothreads are a novel family of one-dimensional , recently synthesized by solid-state high-pressure reaction of crystalline , characterized by ultrathin filaments of sp3 carbon atoms with hydrogenated surfaces. They exhibit varied atomic configurations and a remarkable mechanical strength, as demonstrated in a series of experimental and computational studies. In this work, we use a combination of classical (MD) and Monte Carlo (MC) simulations and ab initio Density Functional Theory (DFT) Calculations to propose and evaluate the feasibility of the synthesis of novel two- and three-dimensional nanomaterials using the same approach, as well as to determine their physical properties and potential practical applications. Results show that a quite diverse family of highly-ordered nanoporous carbon materials can be obtained by distinct approaches, such as the covalent assembly of conventional nanothreads and the use of larger aromatic molecules in the process. These materials exhibit a high porosity with narrow pore size distributions, high specific surface area, low density and high flexibility, maintaining the intrinsic high mechanical strength of nanothreads. This set of physical properties enable their use as functional materials in a series of potential applications. We evaluated their mechanical strength (by MD simulations) aiming their application in reinforced , their adsorption capacity (by MC simulations) toward gas storage (for a series of gases of interest), and their use as ultrathin membranes for gas separation. In the latter case, we use MD simulations to demonstrate the possibility of finely controlling the characteristic pore diameters by application of uniaxial tensile strain on the material. The membranes can be strained to an extent that would provide optimal pore sizes to separate a desired gaseous mixture by molecular sieving mechanism, providing remarkable ideal and real selectivities for certain pair of gases as shown in MD simulations (equal or much superior to conventional materials). This computational analysis will certainly motivate future experimental studies toward realization of such promising materials, as well as the exploration of other possible technological applications for them beyond those of conventional nanoporous materials, considering their outstanding combination of properties.

Keywords Nanoporous materials, molecular simulation, molecular sieves, membranes, adsorption