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

Abstract

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 disadvantages 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 °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.