High-performance lanthanum-based metal-organic framework with ligand tuning of the microstructures for removal of fluoride from water.

Excess fluoride in water poses a threat to ecology and human health, which has attracted global attention. In this study, a series of lanthanum-based metal-organic frameworks (La-MOFs) were synthesized by varying the organic ligands (i.e., terephthalic acid (BDC), trimesic acid (BTC), biphenyl-4,4-dicarboxylic acid (BPDC), 2,5-dihydroxyterephthalic acid (BHTA), and 1,2,4,5-benzenetetracarboxylic acid (PMA)) to control the microscopic structure of the MOFs and subsequently apply them for the removal of fluoride in water. The maximum capture capacities of La-BTC, La-BPDC, La-BHTA, La-PMA, and La-BDC at 298 K are 105.2, 125.9, 145.5, 158.9, and 171.7 mg g-1, respectively. The adsorption capacity is greater than most reported adsorbents. The adsorption isotherms of La-MOFs for fluoride are well fit to the Langmuir isotherm model. In addition, the adsorption kinetics of La-BTC, La-BPDC, La-BHTA, La-PMA, and La-BDC follows the pseudo-second-order kinetic model, and the kinetic rate-limiting step of adsorption is chemical adsorption. Thermodynamics revealed that temperature is favorable for the adsorption of fluoride. Meanwhile, La-BTC, La-BPDC, La-BHTA, La-PMA, and La-BDC are suitable for the removal of fluoride in a relatively wide pH range (4.0-9.0). Simultaneously, from X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis, electrostatic attraction and ligand exchange are identified as the main action mechanisms for the adsorption of fluoride of La-MOFs. The prepared La-MOFs are used as efficient adsorbents for removal of fluoride in actual water, indicating that they have great potential in removing fluoride in real and complex environmental water. This work provides a new strategy for designing adsorbents with adjustable microstructure and expected function to effectively recover fluorosis in water.

Cerium-doped MIL-101-NH2(Fe) as superior adsorbent for simultaneous capture of phosphate and As(V) from Yangzonghai coastal spring water.

A series of novel cerium-doped MIL-101-NH2 materials were synthesized using the solvothermal method for the simultaneous efficient removal of phosphate and As(V). According to the characterization results, cerium was successfully loaded onto MIL-101-NH2 and that Ce-MOFs might be generated during the loading process, which modified the crystal structure of MIL-101-NH2 and resulted in MOFs with different microstructures. In single-uptake systems containing only phosphate or As(V), isothermal adsorption experiments showed that 1Ce-MIL-101-NH2 exhibited better adsorption properties of phosphate and As(V) than MIL-101-NH2. Furthermore, the uptake amounts of phosphate and As(V) reached 341.5 mg/g and 249 mg/g, respectively. Superior uptake amounts for binary phosphate (167.36 mg/g) and As(V) (87.55 mg/g) were achieved with 1Ce-MIL-101-NH2. Kinetic experiments revealed a higher uptake rate of phosphate than of As(V). FT-IR and XPS analyses showed that the main mechanism for the removal of phosphate and As(V) from water by 1Ce-MIL-101-NH2 was the formation of an Fe/CeOP inner complex through ligand complexation and electrostatic attraction. Furthermore, 1Ce-MIL-101-NH2 exhibited high selectivity and excellent efficiency in removing phosphate and As(V) in contaminated spring water in the presence of competing anions; this further confirms the application potential of the novel adsorbent.