One pot synthesis of crystalline covalent organic polymers with tunable pores for the removal of gold and toxic organic pollutants

Abstract

The construction of crystalline covalent organic framework from flexible building blocks, especially macrocyclic hosts, rare in literature. Further, tuning the number of pores and their sizes in the final covalent organic frameworks (COFs)/covalent organic polymers (COPs) is challenging and exciting. Recently, attempts have been made to synthesise the crystalline covalent organic framework starting from a macrocyclic crown ether host. However, the synthetic strategies involve multi-step organic reactions. Herein, we report the construction of a crystalline covalent organic framework/polymers from a single-step reaction. Further, this approach will allow us to pre-determine the pore sizes and their properties to attain the focused covalent organic frameworks (COFs)/covalent organic polymers (COPs) materials of specific surfaces and functions. Based on this approach, we have constructed two triphenylene-based crown ether COPs, COP-TPC6 and COP-TPC8, from dibenzo-18-crown-6 and dibenzo-24-crown-8, respectively. The obtained COPs displayed remarkable removal capacity toward gold (COP-TPC6 = 1157 mg/g and COP-TPC8 = 943 mg/g) with high selectivity over a wide pH range. Furthermore, the obtained COP-TPCs displayed good removal capacity towards a wide range of organic dyes like thiazine dye, triarylmethane dye and azo dye via supramolecular non-covalent interaction. COP-TPC6 displayed good removal capacity toward Neutral red (NR) (Qmax = 500 mg/g), Malachite green (MG) (Qmax = 364 mg/g) and Mordant orange (MoO) (Qmax = 193.8 mg/g). Similarly, COP-TPC8 displayed a removal capacity of Qmax of 307 mg/g for NR, 544 mg/g for MoO and 144.77 mg/g for MG. This work will help the scientific communities to fabricate adsorbents with combined physical and chemical features of triphenylene and crown ethers units.