Growing efforts have been focused on processing MOF particles into hydrogels. We propose a novel one-step method for the preparation of a novel 3D alginate based MOF hydrogel and use it for tetracycline removal. Rather than the formation of ZIF-67-alginate hydrogel (AM-M) using Co-alginate as the precursor, the Co²⁺ chelates with alginate and 2-methylimidazolate simultaneously and forms into a different MOF hydrogel (MA-M). The microstructure of the material turns from a smooth surface similar to the alginate hydrogel into a uniform particle-like one, indicating the AM-M has a polymer skeleton while the MA-M has a whole MOF structure. In tetracycline adsorption, the MA-M reaches equilibrium faster than AM-M. The maximum adsorption capacity of tetracycline adsorption on MA-M is 364.89 mg g⁻¹, which is higher than that of AM-M (302.32 mg g⁻¹). The MA-M has good regeneration properties after 10 cycles. The results pave a new way for the preparation of novel polymer based MOF hydrogels with great potential for water treatment.

Considerable attention has been paid to water treatment using nanomaterials. In this study, ethylene glycol (EG) is used to control the formation of α-FeOOH/reduced graphene oxide (RGO) hydrogels in a facile way. The EG-promoted α-FeOOH/RGO hydrogels exhibit higher moisture content, more porous structure, lower agglomeration, larger swelling, higher specific area, more defects in graphene sheets, stronger Fe–O–C bonds, and higher roughness than those without modification. More importantly and interestingly, we found for the first time that the α-FeOOH/RGO hydrogels could generate reactive oxygen species (ROS) without the addition of H₂O₂, and this property is also enhanced in EG-promoted hydrogels due to (i) the increase in defects in graphene sheets leading to enhanced oxygen reduction reaction (ORR) and (ii) the strengthening of Fe–O–C bonds relating to dual reaction centers with stronger generation of ˙OH. In tetracycline degradation from water, the increase in electron density disparity in the material and the promoted role of tetracycline as an electron donor are proved to be the main reasons for the enhanced tetracycline removal from aqueous solution. Results obtained through density functional theory (DFT) indicate that the electrons could be transferred from the N area in tetracycline to the Fe area in the material, based on which we found a special π–π interaction (between tetracycline and graphene) coupled with π–Fe interactions (between graphene and α-FeOOH) as an efficient pollutant removal method. Our findings provide a simple strategy for the structure improvement of environmental nanomaterials and enrich their mechanism studies.

Enhanced tetracycline removal through dual-reaction centers in Fe₃O₄@Fe/graphene aerogel prepared from an Fe-chelated-polymer.