Ultra-high capacity of lanthanum-doped UiO-66 for phosphate capture: Unusual doping of lanthanum by the reduction of coordination number

In this paper, a simple solvothermal reaction was developed to synthesize the novel lanthanum-doped UiO-66. Unlike the usual doping, the La-MOFs (La-BDC) can be generated in the process of doping. Meanwhile, the results of XRD, BET and SEM demonstrated that the La-BDC exhibited a great influence on the structure of UiO-66, such as the disappearance of the (2 0 0) crystal surface, the rapid reduction of specific surface area and the complete deformation of the micro-morphology. Compared with the synthesized La-BDC, the result of XPS confirmed that the coordination number between lanthanum and terephthalic reduced from seven-coordination to six-coordination in La-BDC after doping, which means that more adsorption sites were exposed and thus the adsorption of phosphate was enhanced. Indeed, La-UiO-66 was proved to have a greater adsorption capacity for phosphate. The maximum adsorption capacity was 348.43 mg g−1 for 0.2La-UiO-66. The results of FT-IR and XPS revealed that surface hydroxyl groups (Zr-OH and La-OH) played a significant role in the phosphate adsorption. Batch adsorption experiments showed that 0.2La-UiO-66 possessed the rapid adsorption equilibrium, marvelous anti-interference ability, and remarkable durability as well as excellent performance in the treatment of real wastewater. The as-synthesized La-UiO-66 not only provides a promising candidate for the control of eutrophication, but also develops a new strategy for design of high-performance adsorbents.