1
Introduction
Deâen Jiang1, Shannon M. Mahurin2, and Sheng Dai2, 3
1 Department of Chemistry, University of California, Riverside, CA, USA
2 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
3 Department of Chemistry, University of Tennessee, Knoxville, TN, USA
Burning fossil fuels for electricity and transportation has led to steadily increasing CO2 levels in the atmosphere, as recorded in the Keeling curve [1], and, consequently, global warming. This concern has become a major driving force for a larger share of renewable energy in power generation and for electrifying transportation. However, coalâfired and natural gasâfired power plants have a long lifetime, which makes postâcombustion carbon capture necessary. In addition, preâcombustion carbon capture will be an important part of cleanâcoal technology. Removal of CO2 from natural gas is also important, especially given the shaleâgas boom. Moreover, direct air capture of CO2 has also been explored by many, since there is already a large amount of emitted CO2 in the air. Hence, carbon capture and storage (CCS) is important for mitigating global warming and climate change [2].
Novel materials hold the key to energyâefficient carbon capture. As a frontier research area, carbon capture has been a major driving force behind many materials technologies. This book aims to present an overview of the advances in materials research for carbon capture, beyond the commercial amineâbased solventâsorption technologies. Broadly speaking, carbonâcapture materials can be divided into two categories: sorbents and membranes. Common sorbents are highâsurfaceâarea porous materials, such as zeolites, metalâorganic frameworks (MOFs), covalentâorganic frameworks (COFs), and amorphous porous carbonaceous materials. Membranes are mainly of the polymeric type, while inorganic, carbonaceous, and mixedâmatrix membranes (MMMs) are being actively explored.
MOFs are promising largeâcapacity adsorbents for CO2 due to their great chemical tunability in controlling the pore size, pore shape and topology, metalâsite chemistry, and linker functional groups [3]. In Chapter 2, Ge and Ma present an overview of the MOF materials for carbon capture, focusing on the correlation between MOF structure and CO2 uptake and tabulating the bestâperforming MOFs; they also briefly discuss pure MOF membranes and MOFâcontaining mixedâmatrixâmembranes.
One weakness limiting the application of many MOFs in capturing CO2 from waterâvaporâsaturated flue gas is their sensitivity to moisture. Porous carbonaceous materials, on the other hand, are both chemically and thermally stable. They are usually made from pyrolysis of a carbonâatomâcontaining precursor that can be either a polymer or a small molecule [4]. At the highâtemperatureâtreatment end (âź900 °C or higher), the carbon content is high (>90 mol%), and the resulting materials are just called porous carbons. In Chapter 3, Zhang and Lu review the different approaches to make porous carbons, from the perspectives of templates and precursors, and their performances for carbon capture as adsorbents.
Ben, Qiu, and their workers have pioneered the design and synthesis of a different type of porous carbonaceous materials called porous aromatic frameworks (PAFs), which can be visualized by replacing all the CC bonds in the diamond with groups such as the biphenyl, leading to a material with a huge surface area of over 5000 m2 gâ1 [5]. PAFs have generated a lot of interest as a material platform for gas storage and separation. In Chapter 4, Ben and Qiu review PAFs for carbon capture and strategies for their further improvement.
Computational modeling and virtual screening are playing an increasingly important role in materials discovery for catalysts, batteries, thermoelectrics, and topological phases, to name a few. So carbon capture is not an exception. In Chapter 5, Jain, Babarao, and Thornton comprehensively review the computational methods, candidate materials, and criteria for virtual screening of materials as membranes and sorbents for carbon capture. Moreover, they show the physical insights that can be gained from computational modeling in understanding the many factors that come into play.
In Chapter 6, Jiang and workers further summarize the advances in using computational modeling to guide the development of ultrathin membranes based on 2D materials such as graphene for gas separations. Interlayerâspacing tuning exhibits great potential in control of molecular and ionic transport in 2D membranes [6â8]. The field of 2D membranes for gas separations was to a large extent initiated by the original proof of concept of oneâatomâthin membranes for gas separations by Jiang et al. [9]. In this chapter, they review the progress made both experimentally and computationally in this field since their original work in 2009, focusing on the computational aspects for guiding future experimental developments.
Polymeric membranes are commercially used for gas separations and water desalination [10]. Their performances are limited by a tradeâoff between selectivity and permeability called the Robeson upper bound [11]. In Chapter 7, Bara and Horne review the polymeric membranes for CO2 separation for different types of polymers; they also briefly touch upon facilitated transport and membrane contactors. In Chapter 8, Huang and Dai present an overview of carbonâbased membranes for CO2 separation.
Increasing materials complexity has been a key driver in recent advance...
