Removal of benzoic acid from industrial wastewater using metal organic frameworks: equilibrium,kinetic and thermodynamic study

In this work, the adsorption of benzoic acid (BA) over metal organic framework of chromium-benzenedicarboxylates (MIL-101) is reported for the first time. The influences of pH, contact time, initial concentration, and temperature of BA solution on the adsorption behavior were investigated. The Langmuir adsorption isotherm was adequate to represent the experimental data (R² > 0.99) and the adsorption kinetics was well-represented by a pseudo-second order kinetic model (R² > 0.96). The zeta potential of MIL-101 decreased with increasing pH confirming the importance of electrostatic interactions between MIL-101 and BA as well as the importance of the large pore volume (1.32 m³/g) and large surface area (2390 m²/g) of MIL-101 for adsorption interaction. The thermodynamics analysis indicated negative free energy, enthalpy, and entropy changes suggesting that the adsorption of BA on MIL-101 is spontaneous and exothermic. The adsorption capacity of BA adsorption over MIL-101 was compared with those for other conventional adsorbents. The maximum capacities of BA uptake on MIL-101, activate carbon, and multiwall carbon nanotubes were 769.2, 406.5, and 341.2 mg/g, respectively, suggesting the superiority of MIL-101 as an adsorbent. Adsorption of real wastewaters containing other organic compounds in addition to BA confirmed the versatility of MIL-101 as a suitable adsorbent in wastewater treatment compared with conventional adsorbents.