Record-high adsorption capacity of metal-azolate framework-5 (MAF-5)-derived porous carbon for adsorptive removal of catechol from water

Removal of catechol, one of the priority pollutants, from water resources is important for our sustainability. In this work, the adsorptive elimination of catechol from water (with catechol in concentrations that are relevant to that of wastewater and surface waters) was carried out by using porous carbons that were prepared via pyrolysis (in two steps) of a metal-organic framework named MAF-5(Zn) with the composition of [Zn(2-ethylimidazole)2]). The obtained carbons were highly porous and doped with nitrogen (pyridinic, pyrrolic, and graphitic species) and oxygen (carboxylic, phenolic, and lactonic species) atoms. One carbon, named M5DC (800), illustrated the highest adsorption capacity for catechol, compared with any adsorbents reported so far (more than 2 times that of the second performing adsorbent). However, M5DC(800) was not very effective in the adsorption of other dihydroxybenzene isomers like resorcinol and hydroquinone. The favorable adsorption of catechol over M5DC(800) could be interpreted via adsorption under wide conditions, analysis with X-ray photoelectron spectroscopy, and calculations; the effective adsorption could be explained mainly with hydrogen bonding (especially, when catechol has intra H-bonding before the adsorption on the carbon) where catechol is H-donor to pyridinic and carboxylic sites of the carbon. M5DC(800) could be suggested as a useful adsorbent to remove catechol from water based on the huge adsorption capacity and ready reusability.