Tunning MIL-101(Cr) MOF polymorphism towards efficient adsorption and localized Fenton-like degradation of para-nitroaniline by Fe incorporation

The employment of metal–organic frameworks (MOFs) in the context of eliminating organic contaminants from water has garnered significant interest in contemporary research. This study investigated the impact of varying quantities of iron on the MIL-101(Cr) adsorbent. For the first time, a polymorphic Cr/Fe-MOF was utilized for the adsorption and localized Fenton-like degradation of p-nitroaniline (PNA). Importantly, the Fe centers exhibited a ternary role of (i) transforming MIL-101 into MIL-53lt morphology, (ii) boosting PNA adsorption on the MIL(Cr) material, and (iii) enabling the Fenton-like decomposition of the adsorbed PNA in reduced solution volume. Cr:Fe(50:50) exhibited the highest adsorption capacity of 378.9 mg/g, notwithstanding its smaller surface area (SBET = 8.9 m2/g). Overall, adsorption kinetics and isotherms correlated better with pseudo-second-order and Langmuir models, respectively. The adsorption mechanism was attributed to breathing effect, H-bonding and π-π interaction. Besides, PNA degradation kinetics stood at 0.21 min−1, and the reactive oxygen species were identified as •OH, •O2– and 1O2. During continuous removal of PNA, the Cr:Fe(50:50) MOF immobilized onto cotton met the environmental discharge standard (1 mg/L) up to 52 bed volumes (initial P = 10.0 mg/L at 1 mL/min). This study not only presents a superior polymorphic MOF adsorbent but also promotes the fabrication of localized Fenton-like catalysts for the removal of organic contaminants in wastewater.