Optimization of praseodymium(III) recovery by Zn-BDC@graphene oxide composite using response surface methodology and speciation resolved adsorption mechanism

Recovery of rare earth elements (REEs) from industrial waste is a glorious channel for waste to resource transformation. Herein, Zn-BDC-graphene oxide composite (Zn-BDC@GO) was crafted via combining terephthalic acid ligand (BDC) coordinated to Zn2+ center (Zn-BDC) and graphene oxide (GO) to recover Pr(III) from aqueous solution. Recovery performance was optimized using response surface methodology (RSM). Speciation resolved adsorption mechanism was clarified via amalgamating Zn-BDC@GO and Pr(III) speciation, statistical thermodynamics, isotherms and kinetics, as well as multifarious spectroscopy. Result delivers, Zn-BDC@GO renders Pr(Ⅲ) recovery efficiency superior to either GO or Zn-BDC. The maximum mono layer adsorption capacity given by the Langmuir model is 436.68 mg·g− 1 at pH 6, dosage 500 mg·L− 1 and contact time 60 min. RSM clarifies the optimum Pr(III) recovery percent as 99.583% under pH 6.852, Zn-BDC@GO dosage 582.197 mg·L− 1 and contact time 54.017 min. Moreover, Zn-BDC@GO can effectively recover Pr(Ⅲ) from binary lanthanides Pr/Sm, Pr/Eu, Pr/Gd with high selectivity coefficient 24.74, 60.46, 122.77, respectively, exhibiting exceptional selectivity. Statistical thermodynamic functions including enthalpy, Gibbs free energy, entropy, etc., unveil that adsorption is exothermic, spontaneous and randomness increasing. Isotherm and kinetic fittings uniformly designates favorable chemisorption controlled by surface reaction. Speciation and versatile spectroscopy (FTIR, Raman, fluorescent, XPS) reveal that Pr(Ⅲ) is attached to COO, C-O-C, C-C and C = C mainly in the form of Pr3+ via electrostatic attraction and electron transfer to yield maximum adsorption at pH = 6. This work illuminates the adsorption behaviour and mechanism of Pr(Ⅲ) over Zn-BDC@GO, as to shed light on developing MOFs based materials for REEs recovery.