Novel Zr-based MOF with Ortho-hydroxyl group selectively traps germanium from aqueous media

Recovery of Ge(IV) from solution is of increasing interest. A novel metal–organic framework adsorbent (Ma-Zr-MOF) is synthesized using mucic acid. A series of characterizations prove the successful synthesis of Ma-Zr-MOF. The maximum adsorption capacity of germanium by Ma-Zr-MOF is 82.06 mg/g at 298 K and pH 6.0, which is better than some of the previously reported adsorbents. The adsorption of germanium ions by Ma-Zr-MOF is in accordance with the pseudo-second-order kinetics and Langmuir isothermal models, the adsorption type is single-layer chemical adsorption on a uniform surface. Thermodynamic calculations yield that the adsorption process is endothermic and spontaneous. Ma-Zr-MOF has good selectivity and anti-interference, and maintains repeatability after five adsorption and desorption cycles. Based on the experimental analysis and density functional theory (DFT) calculations, it is concluded that the Ortho-hydroxyl group played an important role in the adsorption of germanium and that the adsorption mechanism included chelation and ion exchange. In conclusion, Ma-Zr-MOF is proved to be a feasible material for the recovery of Ge(IV) from aqueous media.