Evaluating Pb(II) adsorption capacity of aluminum terephthalate metal−organic framework

Abstract Aluminum terephthalate metal−organic framework (MIL-53(Al)) was synthesized via the hydrothermal method. The influence of the molar ratio between AlCl 3 and terephthalic acid (TA), reaction temperature, and material-treated temperature was investigated. The resulting MIL-53(Al) synthesized with the AlCl 3 /TA molar ratio of 1:0.5 and the reaction temperature ranging from 120 to 200 °C exhibits high crystallinity. The thermal treatment of as-synthesized MIL-53(Al) at 450 °C for 8 h unblocked the pores via the decomposition of unreacted TA molecules and enlarged the surface area of the material (from 11.4 m 2 g −1 to 121.9 m 2 g −1 ), while increasing Pb(II) removal efficiency. The Pb(II) adsorption on calcined MIL-53(Al) occurs favourably at low temperatures (<40 °C) and is exothermic. The adsorption is favourable according to the Langmuir isotherm, while moderately difficult according to the Freundlich isotherm. The adsorption capacity for Pb(II) calculated from the Langmuir model is 28.09 mg g −1 . The Pb(II) adsorption efficiency of the material increases significantly when pH increases from 2 to 6. The mechanism of the adsorption process is also discussed.