Adsorption of dihydroxybenzene isomers over Schiff-based network-1-derived nitrogen-enriched carbon: Effective and favorable adsorption of hydroquinone

Abstract

Urbanization and modernization through intense industrial activity led to the disposal of harmful and non-biodegradable organic substances including dihydroxybenzene isomers such as hydroquinone, catechol, and resorcinol. A covalent-organic polymer Schiff-based network-1, SNW1 was synthesized, pyrolyzed, and subsequently carbonized again, after mixing with KOH, at 800 °C. The obtained carbon, prepared in two-step-carbonization (named as SNW1-2DC), was applied to the adsorption of dihydroxybenzene isomers; showed remarkable performance in hydroquinone adsorption with the maximum adsorption capacity (Q0) of 1060 mg/g at neutral conditions. This Q0 is 6.0 and 5.5 times that of activated carbon and the carbon obtained from the simple pyrolysis of SNW1, respectively; of note, this value represents the highest compared to any previously reported findings. Moreover, the regenerated adsorbent, with simple ethanol washing, performed well for up to 5 cycles. This material could be suggested as a promising adsorbent in hydroquinone removal from water. The adsorption mechanism, including hydrogen bonding, could be suggested. Interestingly, the performance of SNW1-2DC in the adsorptive removal of catechol and resorcinol was very low in comparison with that of hydroquinone. The relative adsorption performances of SNW1-2DC for dihydroxybenzene isomers could be explained with density functional theory calculation and thermodynamic parameters. The most favorable hydroquinone adsorption (among the three dihydroxybenzene isomers) over SNW1-2DC might be because of less endothermic adsorption and more effective H-boning interaction between hydroquinone and SNW1-2DC than that between catechol or resorcinol and the adsorbent.