Ionic Liquids and Metal-Organic Frameworks as Advanced Environmental Materials for CO2 Capture

The industrial revolution during the twentieth century has caused a drastic increase in global warming. Carbon dioxide (CO2) gas is the main constituent of anthropogenic greenhouse gases (GHGs) which cause global warming. The concentration of CO2 in the atmosphere has reached 414.83 ppm. This high CO2 level in the atmosphere has far-ranging effects on health and the environment. CO2 traps heat and hence causes climate change. Respiratory diseases are also caused by a high level of CO2. Various approaches are under consideration to control the emission of CO2 into the atmosphere. Conventional methods for CO2 capture include physical adsorption, absorption, cryogenic distillation, and membrane gas separation. Novel material has been explored for carbon capture and storage (CCS). Ionic liquids (ILs) and metal-organic frameworks (MOFs) are some of these materials. ILs represent a class of materials consisting entirely of ions and are at a liquid state below 100 °C. ILs emerged as exciting materials for CO2 capture and conversion to valuable products because of their non-volatile nature, structure-tunability, and high CO2 adsorption capacity. Similarly, MOFs have gained tremendous attention from researchers in the field of CCS. MOFs are compounds having metal ions or clusters connected through organic ligands to form one-, two-, or three-dimensional structures. MOFs are porous materials with ultra-high porosity, low mass to volume ratio, high surface area, high thermal and chemical stability, and adjustable functionalities. This chapter starts with a brief introduction of existing carbon capture technologies and is followed by an introduction to ILs, their CO2 solubility, and selectivity. The transport properties of ILs and mixed solvents used for CO2 capture have also been discussed. Furthermore, a brief history of MOFs and criteria for MOFs selection for environmental applications have been described as well. MOFs' adsorption capacity and selectivity for CO2, and their physical, thermal, and chemical stability have also been presented. The applications of MOFs for wastewater treatment and CO2 capture have also been discussed.