Synthesis of reusable NH2-MIL-125(Ti)@polymer monolith as efficient adsorbents for dyes wastewater remediation

NH2-MIL-125(Ti) is a Ti-MOFs (MOFs: metal-organic frameworks) with high adsorption properties and is therefore widely used for wastewater purification. However, the powdered MOF material suffers from the dis-advantages of being difficult to separate and being potentially wasted due to easy agglomeration, which limits its application in practical applications. Here, a mesoporous Ti-MOF/polymer (PEG, PVA, and PAM) monolithic material was prepared by freeze casting in liquid nitrogen (-196 degrees C) as an adsorbent for wastewater remediation. The composites could be easily picked up with tweezers and used for recovery tests. Characterization results such as XRD, BET, FT-IR, and SEM proved the successful synthesis of Ti-MOF/polymer. Adsorption tests using 100 mg/ L methylene blue (MB) simulated wastewater showed that the Ti-MOF/PEG monolithic material had the best adsorption capacity. The order of adsorption was Ti-MOF@PEG10 (747.4 mg/g) > Ti-MOF@PVA10 (687.4 mg/ g) > Ti-MOF@PAM10 (633.7 mg/g) > NH2-MIL-125(Ti) (571.4 mg/g). The effects of polymer dosage, different pollutants (methylene blue, methyl orange, indigo, actual textile wastewater), pH, anions, and cations on the adsorption effect of Ti-MOF/polymer were also investigated. It was demonstrated that all the above pollutants were well adsorbed by this Ti-MOF/polymer in the pH range 3-9. The adsorption isotherms and kinetic data are fully consistent with the Langmuir and pseudo-secondary models. This suggests that the adsorption between the pollutant and the adsorbent is a chemical interaction. Thermodynamic studies indicate that the adsorption process is exothermic and spontaneous. This work provides the potential methods to fabricate Ti-MOF/polymer monolith to avoid the pollution from powdery adsorbents that could be practical applications.