Suitable pore designs and functionalities can render COFs as adsorbents for trapping hazardous metals, organic and bio-pollutants, and greenhouse gases. Due to their distinct features, COFs represent themselves as viable alternative materials to address these issues. Earth’s environment is under threat from the increasing disposal of hazardous ingredients such as heavy metals and poisonous organic and bio-organic chemicals. The most attractive feature of COFs is their framework structure with uniform and extended porous channels, attracting the interest of scientists in the purification/separation field. ( a) Illustration of COFs towards environmental applications and ( b) important classes of COFs and their pore geometry by binding different linkers. Among many important aspects, COFs offer pore post-functionalization due to their organic nature, for specific desirable applications such as gas storage, catalysis, electronic devices, electrode material for batteries, etc.įigure 1. Some of the important applications and various types of COFs are shown in Scheme 1 and Figure 1, respectively. Similarly, Thomas and co-workers reported triazine-based COFs prepared at 400 ☌, exhibiting excellent thermo-chemical stabilities. Banerjee and co-workers prepared β-ketoenamine COFs with exceptional stability at high temperatures and in extreme acidic and basic conditions. Later, imine-based COFs were reported to have superior chemical and solvent stability. These COFs, however, are prone to deformation in the presence of even trace amounts of humidity rendering them unsuitable in aqueous conditions. Yaghi and co-workers first reported COFs based on boroxine and boronate ester rings. Their pore geometry, size, and functionalities can be pre-determined by choosing building units from a large bank. Their synthesis involves reticular chemistry, which gives immense freedom of pre-design. Covalent organic frameworks (COFs) are a class of crystalline framework material synthesized from purely organic building blocks. Various amorphous materials such as hyper-cross-linked polymers (HCPs), porous organic polymers (POPs), conjugated microporous polymers (CMPs), and activated carbon and crystalline materials such as metal-organic frameworks (MOFs) and zeolites, have shown excellent preliminary separation performance. In recent years, adsorption- (entrapment) and membrane (size exclusion)-based purification have attracted immense research and industrial interest due to their low energy consumption as well as simple and environmentally friendly operation. Therefore, purification processes with low energy requirements may benefit the environment by saving energy on one hand and saving important capital costs on the other. Moreover, many industries waste a large amount of precious chemical compounds and organic solvents due to the lack of economical separation/purification materials. Industrial effluents also contain a large amount of chemical and bio-chemical hazardous ingredients polluting the already scarce freshwater resources.
These processes, however, operate at the expense of environmental deterioration by consuming an enormous amount of energy, further promoting global warming. Purification processes such as distillation, evaporation, concentration, and crystallization are important in basic research as well as playing an important role in industries.
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