Adsorption of terephthalic acid and p-toluic acid from aqueous solution using metal organic frameworks: Effect of molecular properties of the adsorbates and structural characteristics of the adsorbents

ABSTRACT The adsorptive removal of terephthalic acid (TPA) and p-toluic acid (p-tol) by metal organic frameworks (MOF) of Cu-BTC, Fe-BTC, MIL-101(Cr) and MIL-53(Al) was investigated in this study. The influence of various factors including solution pH, contact time, and initial concentration of TPA and p-tol solutions on the adsorption behavior was evaluated. Different adsorption isotherms and kinetic models were used to fit experimental adsorption data. It was found that the Langmuir and Redlich-Peterson adsorption isotherms were adequate to represent the experimental data (R 2 > 0.97) and that the adsorption kinetics was well-represented by a pseudo-second-order kinetic model (R 2 > 0.98). The zeta potential of the four MOFs decreased with increasing pH confirming the importance of the electrostatic interactions between adsorbents and TPA (or p-tol) as well as the importance of physicochemical properties of the adsorbates and characteristics of the adsorbents. Highest adsorption capacity for TPA (non-polar) and p-tol (polar) were obtained over microporous Cu-BTC (1838.6 mg/g) and mesoporous MIL-53(Al) (1056.7 mg/g), respectively. Furthermore, adsorption studies using an industrial wastewater from a TPA production plant suggested that compared with the conventional adsorbents such as activated carbon and multiwall carbon nanotubes, MOFs (especially mesopore-types) can be used as promising adsorbents in the adsorptive removal of organic pollutants from wastewaters.